Safety and efficacy of magnesium-rich artificial cerebrospinal fluid for subarachnoid hemorrhage

Objectives

This study aimed to investigate the efficacy of using a newly formulated magnesium-rich artificial cerebrospinal fluid (MACSF) as an alternative to normal saline (NS) for intraoperative irrigation during aneurysm clipping in improving the prognosis of patients with Aneurysmal subarachnoid hemorrhage (aSAH).

Methods

Patients with aSAH who underwent intraoperative irrigation with MACSF or NS during the clipping in the First Affiliated Hospital of Xi 'an Jiaotong University from March 2019 to March 2022 were selected as MACSF group and NS group, respectively. The primary prognostic indicators were the incidence of favorable outcomes (mRS 0-2). The secondary outcome measures included cerebral vasospasm (CVS), mortality, total hospital stay, and intensive care unit (ICU) stay. Safety was evaluated based on the occurrence rates of hypermagnesemia, meningitis, and hydrocephalus.

Results

Overall, 34 and 37 patients were enrolled in the MACSF and NS groups, respectively. At 90 days after aSAH onset, the proportion of favorable prognosis in the MACSF group was significantly higher than that in the NS group (p = 0.035). The incidence of CVS within 14 days after surgery was significantly lower in the MACSF group than that in the NS group (p = 0.026). The mortality rate in the MACSF group was significantly lower than in the NS group (p = 0.048). The median lengths of hospital stay (p = 0.008) and ICU stay (p = 0.018) were significantly shorter in the MACSF group than in the NS group. No significant differences were observed in safety measures.

Conclusion

Using MACSF as an irrigation fluid for aneurysm clipping can significantly improve the 90-day prognosis of patients with aSAH, which may be related to the reduced incidence of CVS.

Clinical trial registration

https://www.clinicaltrials.gov, identifier NCT04358445.

Deciphering the impact of cerebrospinal fluid on stem cell fate as a new mechanism to enhance clinical therapy development

Neural stem cells (NSCs) hold a very significant promise as candidates for cell therapy due to their robust neuroprotective and regenerative properties. Preclinical studies using NSCs have shown enough encouraging results to perform deeper investigations into more potential clinical applications. Nevertheless, our knowledge regarding neurogenesis and its underlying mechanisms remains incomplete. To understand them better, it seems necessary to characterize all components of neural stem cell niche and discover their role in physiology and pathology. Using NSCs in vivo brings challenges including limited cell survival and still inadequate integration within host tissue. Identifying overlooked factors that might influence these outcomes becomes pivotal. In this review, we take a deeper examination of the influence of a fundamental element that is present in the brain, the cerebrospinal fluid (CSF), which still remains relatively unexplored. Its role in neurogenesis could be instrumental to help find novel therapeutic solutions for neurological disorders, eventually advancing our knowledge on central nervous system (CNS) regeneration and repair.

Neuroprotective Effects of Artificial Cerebrospinal Fluid: Analysis of Brainstem Auditory-Evoked Potential Monitoring During Microvascular Decompression in 117 Consecutive Patients

BACKGROUND AND OBJECTIVES

To study the efficacy of irrigation with artificial cerebrospinal fluid (aCSF) for protection of cranial nerves during surgery; the time required for recovery of brainstem auditory-evoked potentials (BAEPs) that would reflect cochlear function was analyzed in comparison with that for saline irrigation.

METHODS

This retrospective study included 117 consecutive patients (95 women, mean age 51.5 ± 11.4 year) who underwent microvascular decompression for hemifacial spasm. During surgery, BAEPs were monitored to avoid damage to the auditory pathways. When a delayed latency of >1 ms or a decrease in amplitude of >50% was detected in BAEP wave V, surgical maneuvers were halted, and the operative field was irrigated with saline or aCSF. Saline was used for irrigation in 58 patients and aCSF in the other 59. The time required for BAEP recovery at the first halt in each patient was analyzed, and the results were compared between the groups.

RESULTS

Surgical procedures were interrupted because of BAEP latency delays or decreases in amplitude in 51 of the patients in the saline group and 54 in the aCSF group. In both groups, the latencies and amplitudes recovered significantly with time and both recovered earlier after aCSF irrigation than after saline irrigation. Hearing outcome was not significantly different between 2 groups.

CONCLUSION

aCSF is effective for protection of cochlear nerve and promotes recovery from transient dysfunction during surgery. The protective effect may be attributed to multiple factors including conditioned pH, electrolyte composition, glucose, and microelements, such as magnesium and phosphate.

Solid-Contact Ion-Selective Electrodes for Histamine Determination

Solid-contact ion-selective electrodes for histamine (HA) determination were fabricated and studied. Gold wire (0.5 mm diameter) was coated with poly(3,4-ethlenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) as a solid conductive layer. The polyvinyl chloride matrix embedded with 5,10,15,20-tetraphenyl(porphyrinato)iron(iii) chloride as an ionophore, 2-nitrophenyloctyl ether as a plasticizer and potassium tetrakis(p-chlorophenyl) borate as an ion exchanger was used to cover the PEDOT:PSS layer as a selective membrane. The characteristics of the HA electrodes were also investigated. The detection limit of 8.58 × 10-6 M, the fast response time of less than 5 s, the good reproducibility, the long-term stability and the selectivity in the presence of common interferences in biological fluids were satisfactory. The electrode also performed stably in the pH range of 7-8 and the temperature range of 35-41 °C. Additionally, the recovery rate of 99.7% in artificial cerebrospinal fluid showed the potential for the electrode to be used in biological applications.

Preparation and characterisation of silica-based nanoparticles for cisplatin release on cancer brain cells

In the present work, the preparation, characterisation, and efficiency of two different silica nanostructures as release vehicles of Cisplatin are reported. The 1-hexadeciltrimethyl-ammonium bromide templating agent was used to obtain mesoporous silica nanoparticles which were later loaded with Cisplatin. While sol-gel silica was very fast prepared using an excess of acetic acid during the hydrolysis-condensation reactions of tetraethylorthosilicate and at the same time the Cisplatin was added. Several physicochemical techniques including spectroscopies, electronic microscopy, X-ray diffraction, N2 adsorption-desorption were used to characterise the silica nanostructures. An in vitro Cisplatin release test was carried out using artificial cerebrospinal fluid. Finally, the toxicity of all silica nanostructures was tested using the C6 cancer cell line. The spectroscopic results showed the suitable stabilisation of Cisplatin into the two different silica nanostructures. A large surface area was obtained for the mesoporous silica nanoparticles, while low areas were obtained in the silica nanoparticles. Cisplatin was released faster from mesoporous silica channels than from inside of aggregates nanoparticles silica. Cisplatin alone, as well as, cisplatin released from both silica nanostructures exerted a toxic effect on cancer cells. In contrast, both silica structures without the drug did not exert any toxic effect.

Effects of a new magnesium-rich artificial cerebrospinal fluid on contractile 5-hydroxytryptamine and endothelin receptors in rat cerebral arteries

Objectives Cerebral vasospasm after subarachnoid haemorrhage (SAH) is associated with cerebrovascular contractile receptor upregulation resulted from haemolysis in the subarachnoid space. This study developed a new magnesium-rich artificial cerebrospinal fluid (MACSF) formula and investigated its effects on receptor-mediated contraction in rat basilar arteries. Methods Clear and haemorrhagic cerebrospinal fluid (CSF) were collected from patients with hydrocephalus or SAH. MACSF was freshly prepared using clinical intravenous injections. Rat basilar arteries were segmented and incubated with clear CSF, haemorrhagic CSF or MACSF. The contractile responses were studied by myograph. The messenger ribonucleic acid (mRNA) and protein expression of 5-hydroxytryptamine 1B (5-HT_1B), endothelin subtype B (ET_B) and endothelin subtype A (ET_A) receptors were evaluated by real-time polymerase chain reaction (PCR) and Western blot analyses. Results Haemorrhagic CSF exposure shifted the contractile curves induced by 5-hydroxytryptamine (5-HT), sarafotoxins 6c (S6c) and endothelin-1 (ET-1) leftward with increased maximal contraction values. Furthermore, mRNA and protein expression were markedly elevated for 5-HT_1B, ET_B and ET_A receptors on arteries exposed to haemorrhagic CSF. However, the contractile responses to 5-HT, S6c or ET-1 and expression of 5-HT_1B, ET_B and ET_A receptors in rat cerebral arteries exposed to MACSF remained unaffected compared to those exposed to clear CSF. Besides, unlike normal saline which can inactive in-vitro vessels, MACSF can maintain their physiological activity. Conclusion Haemorrhagic CSF induces upregulation of 5-HT_1B, ET_B and ET_A receptors in rat cerebral arteries. However, MACSF can maintain in-vitro rat basilar arteries in good physiological activity and normal expression of contractile 5-HT and ET receptors.

The Effect of Irrigation Solutions on Recurrence of Chronic Subdural Hematoma: A Consecutive Cohort Study of 234 Patients

Chronic subdural hematomas (CSDHs) occur often in elderly persons and can occur with mild head trauma. With burr-hole irrigation as standard treatment, symptoms usually improve and can be cured, and outcomes are good, but postoperative recurrences are a common problem. This study investigated the effectiveness and recurrence rates when using artificial cerebrospinal fluid (ACF) instead of normal saline (NS) as an irrigation solution for burr-hole irrigation in patients with CSDH. This prospective study included 234 consecutive patients who underwent initial surgical treatment by burr-hole irrigation for a CSDH between April 2008 and June 2015. The irrigation solution used was changed from NS to ACF in June 2011. Factors examined with regard to recurrence included age, sex, unilateral or bilateral surgery, computed tomography (CT) findings, antiplatelet or anticoagulant drug use, past history, and irrigation solution (NS or ACF). These were analyzed by univariate and multivariate analyses. Univariate analyses (chi-square test) with a significance level <5% showed that recurrence rates were significantly lower in the ACF group than in the NS group (P = 0.003). Multivariate analysis (multiple logistic regression analysis) showed that the risk of recurrence was reduced 3.14-fold in the ACF group compared to the NS group (odds ratio, 3.143; 95% confidence interval, 0.1504–0.6733; P = 0.0028). None of the other factors were significantly different. In burr-hole irrigation for CSDH, the use of ACF instead of NS as an irrigation solution significantly reduces recurrence rates.

The effects of benzofury (5-APB) on the dopamine transporter and 5-HT2-dependent vasoconstriction in the rat

5-APB, commonly marketed as 'benzofury' is a new psychoactive substance and erstwhile 'legal high' which has been implicated in 10 recent drug-related deaths in the UK. This drug was available on the internet and in 'head shops' and was one of the most commonly sold legal highs up until its recent UK temporary ban (UK Home Office). Despite its prominence, very little is known about its pharmacology. This study was undertaken to examine the pharmacology of 5-APB in vitro. We hypothesised that 5-APB would activate the dopamine and 5-HT systems which may underlie its putative stimulant and hallucinogenic effects. Autoradiographic studies showed that 5-APB displaced both [(125)I] RTI-121 and [(3)H] ketanserin from rat brain tissue suggesting affinity at the dopamine transporter and 5-HT2 receptor sites respectively. Voltammetric studies in rat accumbens brain slices revealed that 5-APB slowed dopamine reuptake, and at high concentrations caused reverse transport of dopamine. 5-APB also caused vasoconstriction of rat aorta, an effect antagonised by the 5-HT2A receptor antagonist ketanserin, and caused contraction of rat stomach fundus, which was reversed by the 5-HT2B receptor antagonist RS-127445. These data show that 5-APB interacts with the dopamine transporter and is an agonist at the 5-HT2A and 5-HT2B receptors in the rat. Thus 5-APB's pharmacology is consistent with it having both stimulant and hallucinogenic properties. In addition, 5-APB's activity at the 5-HT2B receptor may cause cardiotoxicity.

Ischemia-induced depolarizations and associated hemodynamic responses in incomplete global forebrain ischemia in rats

Spontaneous depolarizations around the core are a consistent feature of focal cerebral ischemia, but the associated regional hemodynamic changes are heterogeneous. We determined how the features of depolarizations relate to subsequent cerebral blood flow (CBF) changes in global forebrain ischemia. Forebrain ischemia was produced in halothane-anesthetized rats (n=13) by common carotid artery occlusion and hypovolemic hypotension. Mean arterial blood pressure (MABP) was monitored via a femoral catheter. Specific illuminations allowed the capture of image sequences through a cranial window to visualize: changes in membrane potential (voltage-sensitive dye method); CBF (laser speckle contrast imaging); cerebral blood volume (intrinsic optical signal, IOS at 540-550nm); and hemoglobin deoxygenation (IOS at 620-640nm). A depolarization occurred (n=9) when CBF fell below 43.4±5% of control (41±4mmHg MABP), and propagated with a distinct wave front at a rate of 2.8mm/min. Depolarizations were either persistent (n=4), intermediate (n=3) or short, transient depolarization (n=2). Persistent and intermediate depolarizations were associated with sustained hypoperfusion (-11.7±5.1%) and transient hypoperfusion (-17.4±5.2, relative to CBF before depolarization). Short, transient depolarizations did not generate clear CBF responses. Depolarizations during incomplete global ischemia occurred at the lower limit of CBF autoregulation, propagated similar to spreading depolarization (SD), and the hemodynamic responses indicated inverse neurovascular coupling. Similar to SDs associated with focal stroke, the propagating event can be persistent or transient.

Vasopressin indirectly excites dorsal raphe serotonin neurons through activation of the vasopressin1A receptor

The neuropeptide vasopressin (AVP; arginine-vasopressin) is produced in a handful of brain nuclei located in the hypothalamus and extended amygdala and is released both peripherally as a hormone and within the central nervous system as a neurotransmitter. Central projections have been associated with a number of functions including regulation of physiological homeostasis, control of circadian rhythms, and modulation of social behavior. The AVP neurons located in the bed nucleus of the stria terminalis and medial amygdala (i.e., extended amygdala) in particular have been associated with affiliative social behavior in multiple species. It was recently demonstrated that in the mouse AVP projections emanating from extended amygdala neurons innervate a number of forebrain and midbrain brain regions including the dorsal raphe nucleus (DR), the site of origin of most forebrain-projecting serotonin neurons. Based on the presence of AVP fibers in the DR, we hypothesized that AVP would alter the physiology of serotonin neurons via AVP 1A receptor (V1AR) activation. Using whole-cell electrophysiology techniques, we found that AVP increased the frequency and amplitude of excitatory post-synaptic currents (EPSCs) in serotonin neurons of male mice. The indirect stimulation of serotonin neurons was AMPA/kainate receptor dependent and blocked by the sodium channel blocker tetrodotoxin, suggesting an effect of AVP on glutamate neurons. Further, the increase in EPSC frequency induced by AVP was blocked by selective V1AR antagonists. Our data suggest that AVP had an excitatory influence on serotonin neurons. This work highlights a new target (i.e., V1AR) for manipulating serotonin neuron excitability. In light of our data, we propose that some of the diverse effects of AVP on physiology and behavior, including social behavior, may be due to activation of the DR serotonin system.

Glial activation and post-synaptic neurotoxicity: the key events in Streptozotocin (ICV) induced memory impairment in rats

In the present study the role of glial activation and post synaptic toxicity in ICV Streptozotocin (STZ) induced memory impaired rats was explored. In experiment set up 1: Memory deficit was found in Morris water maze test on 14-16 days after STZ (ICV; 3mg/Kg) administration. STZ causes increased expression of GFAP, CD11b and TNF-α indicating glial activation and neuroinflammation. STZ also significantly increased the level of ROS, nitrite, Ca(2+) and reduced the mitochondrial activity in synaptosomal preparation illustrating free radical generation and excitotoxicity. Increased expression and activity of Caspase-3 was also observed in STZ treated rat which specify apoptotic cell death in hippocampus and cortex. STZ treatment showed decrease expression of post synaptic markers CaMKIIα and PSD-95, while, expression of pre synaptic markers (synaptophysin and SNAP-25) remains unaltered indicating selective post synaptic neurotoxicity. Oral treatment with Memantine (10mg/kg) and Ibuprofen (50 mg/kg) daily for 13 days attenuated STZ induced glial activation, apoptotic cell death and post synaptic neurotoxicity in rat brain. Further, in experiment set up 2: where memory function was not affected i.e. 7-9 days after STZ treatment. The level of GFAP, CD11b, TNF-α, ROS and nitrite levels were increased. On the other hand, apoptotic marker, synaptic markers, mitochondrial activity and Ca(2+) levels remained unaffected. Collective data indicates that neuroinflammatory process and oxidative stress occurs earlier to apoptosis and does not affect memory function. Present study clearly suggests that glial activation and post synaptic neurotoxicity are the key factors in STZ induced memory impairment and neuronal cell death.

Involvement of dorsal hippocampus glutamatergic and nitrergic neurotransmission in autonomic responses evoked by acute restraint stress in rats

The dorsal hippocampus (DH) is a structure of the limbic system that is involved in emotional, learning and memory processes. There is evidence indicating that the DH modulates cardiovascular correlates of behavioral responses to stressful stimuli. Acute restraint stress (RS) is an unavoidable stress situation that evokes marked and sustained autonomic changes, which are characterized by elevated blood pressure (BP), intense heart rate (HR) increase and a decrease in cutaneous temperature. In the present study, we investigated the involvement of an N-methyl-D-aspartate (NMDA) glutamate receptor/nitric oxide (NO) pathway of the DH in the modulation of autonomic (arterial BP, HR and tail skin temperature) responses evoked by RS in rats. Bilateral microinjection of the NMDA receptor antagonist AP-7 (10 nmol/500 nL) into the DH attenuated RS-evoked autonomic responses. Moreover, RS evoked an increase in the content of NO₂/NO₃ in the DH, which are products of the spontaneous oxidation of NO under physiological conditions that can provide an indirect measurement of NO production. Bilateral microinjection of N-propyl-L-arginine (0.1 nmol/500 nL; N-propyl, a neuronal NO synthase (nNOS) inhibitor) or carboxy-PTIO (2 nmol/500 nL; c-PTIO, an NO scavenger) into the DH also attenuated autonomic responses evoked by RS. Therefore, our findings suggest that a glutamatergic system present in the DH is involved in the autonomic modulation during RS, acting via NMDA receptors and nNOS activation. Furthermore, the present results suggest that NMDA receptor/nNO activation has a facilitatory influence on RS-evoked autonomic responses.

The cholinergic agonist carbachol increases the frequency of spontaneous GABAergic synaptic currents in dorsal raphe serotonergic neurons in the mouse

Dorsal raphe nucleus (DRN) serotonin (5-HT) neurons play an important role in feeding, mood control and stress responses. One important feature of their activity across the sleep-wake cycle is their reduced firing during rapid-eye-movement (REM) sleep which stands in stark contrast to the wake/REM-on discharge pattern of brainstem cholinergic neurons. A prominent model of REM sleep control posits a reciprocal interaction between these cell groups. 5-HT inhibits cholinergic neurons, and activation of nicotinic receptors can excite DRN 5-HT neurons but the cholinergic effect on inhibitory inputs is incompletely understood. Here, in vitro, in DRN brain slices prepared from GAD67-GFP knock-in mice, a brief (3 min) bath application of carbachol (50 μM) increased the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) in GFP-negative, putative 5-HT neurons but did not affect miniature (tetrodotoxin-insensitive) IPSCs. Carbachol had no direct postsynaptic effect. Thus, carbachol likely increases the activity of local GABAergic neurons which synapse on 5-HT neurons. Removal of dorsal regions of the slice including the ventrolateral periaqueductal gray (vlPAG) region where GABAergic neurons projecting to the DRN have been identified, abolished the effect of carbachol on sIPSCs whereas the removal of ventral regions containing the oral region of the pontine reticular nucleus (PnO) did not. In addition, carbachol directly excited GFP-positive, GABAergic vlPAG neurons. Antagonism of both muscarinic and nicotinic receptors completely abolished the effects of carbachol. We suggest cholinergic neurons inhibit DRN 5-HT neurons when acetylcholine levels are lower i.e. during quiet wakefulness and the beginning of REM sleep periods, in part via excitation of muscarinic and nicotinic receptors located on local vlPAG and DRN GABAergic neurons. Higher firing rates or burst firing of cholinergic neurons associated with attentive wakefulness or phasic REM sleep periods leads to excitation of 5-HT neurons via the activation of nicotinic receptors located postsynaptically and presynaptically on excitatory afferents.

Dopaminergic enhancement of excitatory synaptic transmission in layer II entorhinal neurons is dependent on D₁-like receptor-mediated signaling

The modulatory neurotransmitter dopamine induces concentration-dependent changes in synaptic transmission in the entorhinal cortex, in which high concentrations of dopamine suppress evoked excitatory postsynaptic potentials (EPSPs) and lower concentrations induce an acute synaptic facilitation. Whole-cell current-clamp recordings were used to investigate the dopaminergic facilitation of synaptic responses in layer II neurons of the rat lateral entorhinal cortex. A constant bath application of 1 μM dopamine resulted in a consistent facilitation of EPSPs evoked in layer II fan cells by layer I stimulation; the size of the facilitation was more variable in pyramidal neurons, and synaptic responses in a small group of multiform neurons were not modulated by dopamine. Isolated inhibitory synaptic responses were not affected by dopamine, and the facilitation of EPSPs was not associated with a change in paired-pulse facilitation ratio. Voltage-clamp recordings of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) glutamate receptor-mediated excitatory postsynaptic currents (EPSCs) were facilitated by dopamine, but N-methyl-D-aspartate receptor-mediated currents were not. Bath application of the dopamine D₁-like receptor blocker SCH23390 (50 μM), but not the D₂-like receptor blocker sulpiride (50 μM), prevented the facilitation, indicating that it is dependent upon D₁-like receptor activation. Dopamine D₁ receptors lead to activation of protein kinase A (PKA), and including the PKA inhibitor H-89 or KT 5720 in the recording pipette solution prevented the facilitation of EPSCs. PKA-dependent phosphorylation of inhibitor 1 or the dopamine- and cAMP-regulated protein phosphatase (DARPP-32) can lead to a facilitation of AMPA receptor responses by inhibiting the activity of protein phosphatase 1 (PP1) that reduces dephosphorylation of AMPA receptors, and we found here that inhibition of PP1 occluded the facilitatory effect of dopamine. The dopamine-induced facilitation of AMPA receptor-mediated synaptic responses in layer II neurons of the lateral entorhinal cortex is therefore likely mediated via a D₁ receptor-dependent increase in PKA activity and a resulting inhibition in PP1-dependent dephosphorylation of AMPA receptors.

Novel anticonvulsive effects of progesterone in a mouse model of hippocampal electrical kindling

Progesterone is a known anticonvulsant, with its inhibitory effects generally attributed to its secondary metabolite, 5α,3α-tetrahydroprogesterone (THP), and THP's enhancement of GABAA receptor activity. Accumulating evidence, however, suggests that progesterone may have non-genomic actions independent of the GABAA receptor. In this study, we explored THP/GABAA-independent anticonvulsive actions of progesterone in a mouse model of hippocampal kindling and in mouse entorhinal slices in vitro. Specifically, we examined the effects of progesterone in kindled mice with or without pretreatments with finasteride, a 5α-reductase inhibitor known to block the metabolism of progesterone to THP. In addition, we examined the effects of progesterone on entorhinal epileptiform potentials in the presence of a GABAA receptor antagonist picrotoxin and finasteride. Adult male mice were kindled via a daily stimulation protocol. Electroencephalographic (EEG) discharges were recorded from the hippocampus or cortex to assess "focal" or "generalized" seizure activity. Kindled mice were treated with intra-peritoneal injections of progesterone (10, 35, 100 and 160mg/kg) with or without finasteride pretreatment (50 or 100mg/kg), THP (1, 3.5, 10 and 30mg/kg), midazolam (2mg/kg) and carbamazepine (50mg/kg). Entorhinal cortical slices were prepared from naïve young mice, and repetitive epileptiform potentials were induced by 4-aminopyridine (100μM), picrotoxin (100μM) and finasteride (1μM). Pretreatment with finasteride did not abolish the anticonvulsant effects of progesterone. In finasteride-pretreated mice, progesterone at 100 and 160mg/kg decreased cortical but not hippocampal afterdischarges (ADs). Carbamazepine mimicked the effects of progesterone with finasteride pretreatments in decreasing cortical discharges and motor seizures, whereas midazolam produced effects similar to progesterone alone or THP in decreasing hippocampal ADs and motor seizures. In brain slices, progesterone at 1μM inhibited entorhinal epileptiform potentials in the presence of picrotoxin and finasteride. We suggest that progesterone may have THP/GABAA-dependent and independent anticonvulsive actions in the hippocampal-kindled mouse model.

Neonatal tissue injury reduces the intrinsic excitability of adult mouse superficial dorsal horn neurons

Tissue damage during the neonatal period evokes long-lasting changes in nociceptive processing within the adult spinal cord which contribute to persistent alterations in pain sensitivity. However, it remains unclear if the observed modifications in neuronal activity within the mature superficial dorsal horn (SDH) following early injury reflect shifts in the intrinsic membrane properties of these cells. Therefore, the present study was undertaken to identify the effects of neonatal surgical injury on the intrinsic excitability of both GABAergic and presumed glutamatergic neurons within lamina II of the adult SDH using in vitro patch clamp recordings from spinal cord slices prepared from glutamic acid decarboxylase-green fluorescent protein (Gad-GFP) mice. The results demonstrate that hindpaw surgical incision at postnatal day (P) 3 altered the passive membrane properties of both Gad-GFP and adjacent, non-GFP neurons in the mature SDH, as evidenced by decreased membrane resistance and more negative resting potentials in comparison to naïve littermate controls. This was accompanied by a reduction in the prevalence of spontaneous activity within the GABAergic population. Both Gad-GFP and non-GFP neurons displayed a significant elevation in rheobase and decreased instantaneous firing frequency after incision, suggesting that early tissue damage lowers the intrinsic membrane excitability of adult SDH neurons. Isolation of inward-rectifying K(+) (K(ir)) currents revealed that neonatal incision significantly increased K(ir) conductance near physiological membrane potentials in GABAergic, but not glutamatergic, lamina II neurons. Overall, these findings suggest that neonatal tissue injury causes a long-term dampening of intrinsic firing across the general population of lamina II interneurons, but the underlying ionic mechanisms may be cell-type specific.

Inflammation enhances Y1 receptor signaling, neuropeptide Y-mediated inhibition of hyperalgesia, and substance P release from primary afferent neurons

Neuropeptide Y (NPY) is present in the superficial laminae of the dorsal horn and inhibits spinal nociceptive processing, but the mechanisms underlying its anti-hyperalgesic actions are unclear. We hypothesized that NPY acts at neuropeptide Y1 receptors in the dorsal horn to decrease nociception by inhibiting substance P (SP) release, and that these effects are enhanced by inflammation. To evaluate SP release, we used microdialysis and neurokinin 1 receptor (NK1R) internalization in rat. NPY decreased capsaicin-evoked SP-like immunoreactivity in the microdialysate of the dorsal horn. NPY also decreased non-noxious stimulus (paw brush)-evoked NK1R internalization (as well as mechanical hyperalgesia and mechanical and cold allodynia) after intraplantar injection of carrageenan. Similarly, in rat spinal cord slices with dorsal root attached, [Leu(31), Pro(34)]-NPY inhibited dorsal root stimulus-evoked NK1R internalization. In rat dorsal root ganglion neurons, Y1 receptors colocalized extensively with calcitonin gene-related peptide (CGRP). In dorsal horn neurons, Y1 receptors were extensively expressed and this may have masked the detection of terminal co-localization with CGRP or SP. To determine whether the pain inhibitory actions of Y1 receptors are enhanced by inflammation, we administered [Leu(31), Pro(34)]-NPY after intraplantar injection of complete Freund's adjuvant (CFA) in rat. We found that [Leu(31), Pro(34)]-NPY reduced paw clamp-induced NK1R internalization in CFA rats but not uninjured controls. To determine the contribution of increased Y1 receptor-G protein coupling, we measured [(35)S]GTPγS binding simulated by [Leu(31), Pro(34)]-NPY in mouse dorsal horn. CFA inflammation increased the affinity of Y1 receptor G-protein coupling. We conclude that Y1 receptors contribute to the anti-hyperalgesic effects of NPY by mediating the inhibition of SP release, and that Y1 receptor signaling in the dorsal horn is enhanced during inflammatory nociception.

Nicotinamide pre-treatment ameliorates NAD(H) hyperoxidation and improves neuronal function after severe hypoxia

Prolonged hypoxia leads to irreversible loss of neuronal function and metabolic impairment of nicotinamide adenine dinucleotide recycling (between NAD(+) and NADH) immediately after reoxygenation, resulting in NADH hyperoxidation. We test whether the addition of nicotinamide (to enhance NAD(+) levels) or PARP-1 inhibition (to prevent consumption of NAD(+)) can be effective in improving either loss of neuronal function or hyperoxidation following severe hypoxic injury in hippocampal slices. After severe, prolonged hypoxia (maintained for 3min after spreading depression) there was hyperoxidation of NADH following reoxygenation, an increased soluble NAD(+)/NADH ratio, loss of neuronal field excitatory post-synaptic potential (fEPSP) and decreased ATP content. Nicotinamide incubation (5mM) 2h prior to hypoxia significantly increased total NAD(H) content, improved neuronal recovery, enhanced ATP content, and prevented NADH hyperoxidation. The nicotinamide-induced increase in total soluble NAD(H) was more significant in the cytosolic compartment than within mitochondria. Prolonged incubation with PJ-34 (>1h) led to enhanced baseline NADH fluorescence prior to hypoxia, as well as improved neuronal recovery, NADH hyperoxidation and ATP content on recovery from severe hypoxia and reoxygenation. In this acute model of severe neuronal dysfunction prolonged incubation with either nicotinamide or PJ-34 prior to hypoxia improved recovery of neuronal function, enhanced NADH reduction and ATP content, but neither treatment restored function when administered during or after prolonged hypoxia and reoxygenation.

Genetic deficiency of β2-containing nicotinic receptors attenuates brain injury in ischemic stroke

One of the major consequences of stroke is brain injury caused by glutamate-mediated excitotoxicity. Glutamate-mediated excitatory activities are partially driven by β2-containing nicotinic acetylcholine receptors (β2-nAChRs). In examining the role of β2-nAChRs in cerebral ischemic injury, excitotoxicity and stroke outcome, we found that deficiency of β2-nAChRs attenuated brain infarction and neurological deficit at 24 and 72 h after transient middle cerebral artery occlusion (MCAO). Genetic deletion of β2-nAChRs associated with reduced terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL(+)) and cleaved caspase-3(+) cells after MCAO, together with a reduction of extracellular glutamate and oxygen-glucose deprivation-induced increase of excitatory inputs in cortical neurons. Pharmacologic pretreatment with a selective β2-nAChRs antagonist reduced brain infarction, neurological deficit, and MCAO-induced glutamate release. These findings suggest that deficiency of β2-nAChRs, also achievable by pharmacological blockade, can decrease brain infarction and improve the neurological status in ischemic stroke. The improved outcome is associated with reduced extracellular glutamate level and lower excitatory inputs into ischemic neurons, suggesting a reduction of glutamate-mediated excitotoxicity in the mechanisms of neuroprotection.

Synaptic plasticity in glutamatergic and GABAergic neurotransmission following chronic memantine treatment in an in vitro model of limbic epileptogenesis

Chronic N-methyl-D-aspartate receptor (NMDAR) blockade with high affinity competitive and uncompetitive antagonists can lead to seizure exacerbation, presumably due to an imbalance in glutamatergic and GABAergic transmission. Acute administration of the moderate affinity NMDAR antagonist memantine in vivo has been associated with pro- and anticonvulsive properties. Chronic treatment with memantine can exacerbate seizures. Therefore, we hypothesized that chronic memantine treatment would increase glutamatergic and decrease GABAergic transmission, similar to high affinity competitive and uncompetitive antagonists. To test this hypothesis, organotypic hippocampal slice culture were treated for 17-21 days with memantine and then subjected to electrophysiological recordings. Whole-cell recordings from dentate granule cells revealed that chronic memantine treatment slightly, but significantly increased sEPSC frequency, mEPSC amplitude and mEPSC charge transfer, consistent with minimally increased glutamatergic transmission. Chronic memantine treatment also increased both sIPSC and mIPSC frequency and amplitude, suggestive of increased GABAergic transmission. Results suggest that a simple imbalance between glutamatergic and GABAergic neurotransmission may not underlie memantine's ictogenic properties. That said, glutamatergic and GABAergic transmission were assayed independently of one another in the current study. More complex interactions between glutamatergic and GABAergic transmission may prevail under conditions of intact circuitry.

Social isolation stress reduces hippocampal long-term potentiation: effect of animal strain and involvement of glucocorticoid receptors

BACKGROUND

Depressive patients show cognitive impairments that are strongly associated with cortisol levels and hippocampus functioning that interact via unknown mechanisms. In addition, a relation between depression and hippocampal synaptic plasticity was described.

METHODS

In the first experiment, strain-dependent effects of 72-h social isolation on long-term potentiation (LTP) in the CA1 area of the in vitro hippocampus, was determined. Extracellular field excitatory postsynaptic potentials were recorded and a brief high-frequency stimulation (100 Hz, 1s) was applied and recording resumed after the high frequency stimulation (HFS) for 30 min to determine the effect of HFS. In the second experiment we investigated the effect of 72 h of corticosterone treatment and the involvement of glucocorticoid receptors (GRs) in the effect of 72 h of social isolation on LTP in the CA1 area of hippocampus, in vitro.

RESULTS

Genetic background has a major effect on the level of hippocampal LTP impairment in mice following social isolation. Data showed that the potentiation levels in socially housed (SH) A/J mice were significantly higher than the SH C57BL/6J mice (224.88 ± 16.65, 131.56 ± 6.25% of the baseline values, t(9)=2.648, p=0.026). However, both strains showed depressed induction of potentiation when reared in an isolated environment for 72 h, and no significant difference was recorded between the two (112.88 ± 16.65%, and 117.91 ± 3.23% of the baseline values, respectively, t(10)=0.618, p=0.551). Social isolation increased corticosterone levels significantly and chronic corticosterone infusion in SH phenocopied the LTP impairments observed in socially isolated mice. Infusion of the GR antagonist RU38486 rescued the LTP-impairments following social isolation.

CONCLUSIONS

These findings support the notion that increased levels of stress hormone act via the GR on hippocampal functioning and that, in this way, the cognitive deficits in mood disorders may be restored.

Neurosteroids modulate epileptiform activity and associated high-frequency oscillations in the piriform cortex

Allotetrahydrodeoxycorticosterone (THDOC) belongs to a class of pregnane neurosteroidal compounds that enhance brain inhibition by interacting directly with GABAA signaling, mainly through an increase in tonic inhibitory current. Here, we addressed the role of THDOC in the modulation of interictal- and ictal-like activity and associated high-frequency oscillations (HFOs, 80-500 Hz; ripples: 80-200 Hz, fast ripples: 250-500 Hz) recorded in vitro in the rat piriform cortex, a highly excitable brain structure that is implicated in seizure generation and maintenance. We found that THDOC: (i) increased the duration of interictal discharges in the anterior piriform cortex while decreasing ictal discharge duration in both anterior and posterior piriform cortices; (ii) reduced the occurrence of HFOs associated to both interictal and ictal discharges; and (iii) prolonged the duration of 4-aminopyridine-induced, glutamatergic independent synchronous field potentials that are known to mainly result from the activation of GABAA receptors. Our results indicate that THDOC can modulate epileptiform synchronization in the piriform cortex presumably by potentiating GABAA receptor-mediated signaling. This evidence supports the view that neurosteroids regulate neuronal excitability and thus control the occurrence of seizures.

Brain and peripheral pharmacokinetics of levodopa in the cynomolgus monkey following administration of opicapone, a third generation nitrocatechol COMT inhibitor

OBJECTIVE

The present study aimed at evaluating the effect of opicapone, a third generation nitrocatechol catechol-O-methyltransferase (COMT) inhibitor, on the systemic and central bioavailability of 3,4-dihydroxy-l-phenylalanine (levodopa) and related metabolites in the cynomolgus monkey.

METHODS

Four monkeys, implanted with guiding cannulas for microdialysis probes, in the substantia nigra, dorsal striatum and prefrontal cortex, were randomized in two groups that received, in a crossover design, vehicle or 100 mg/kg opicapone for 14 days. Twenty-three hours after last administration of vehicle or opicapone, animals were challenged with levodopa/benserazide (12/3 mg/kg). Extracellular dialysate and blood samples were collected over 360 min (at 30 min intervals) for the assays of catecholamine and COMT activity.

RESULTS

Opicapone increased levodopa systemic exposure by 2-fold not changing Cmax values and reduced both 3-O-methyldopa (3-OMD) exposure and Cmax values by 5-fold. These changes were accompanied by ∼76-84% reduction in erythrocyte COMT activity. In dorsal striatum and substantia nigra, opicapone increased levodopa exposure by 1.7- and 1.4-fold, respectively, reducing 3-OMD exposure by 5- and 7-fold respectively. DOPAC exposure was increased by 4-fold in the substantia nigra. In the prefrontal cortex, opicapone increased levodopa exposure and reduced 3-OMD levels by 2.3- and 2.4-fold, respectively.

CONCLUSIONS

Opicapone behaved as long-acting COMT inhibitor that markedly increased systemic and central levodopa bioavailability. Opicapone is a strong candidate to fill the unmet need for COMT inhibitors that lead to more sustained levodopa levels in Parkinson's disease patients.

Heat shock protein 70 protects against seizure-induced neuronal cell death in the hippocampus following experimental status epilepticus via inhibition of nuclear factor-κB activation-induced nitric oxide synthase II expression

Status epilepticus induces subcellular changes that may eventually lead to neuronal cell death in the hippocampus. Based on an animal model of status epilepticus, our laboratory showed previously that sustained hippocampal seizure activity activates nuclear factor-κB (NF-κB) and upregulates nitric oxide synthase (NOS) II gene expression, leading to apoptotic neuronal cell death in the hippocampus. The present study examined the potential modulatory role of heat shock protein 70 (HSP70) on NF-κB signaling in the hippocampus following experimental status epilepticus. In Sprague-Dawley rats, kainic acid (KA) was microinjected unilaterally into the hippocampal CA3 subfield to induce prolonged bilateral seizure activity. Expression of HSP70 was elevated as early as 1h after the elicitation of sustained seizure activity, followed by a progressive elevation that peaked at 24h. Pretreatment with an antisense oligonucleotide against hsp70 decreased the HSP70 expression, and significantly augmented IκB kinase (IKK) activity and phosphorylation of IκBα, alongside enhanced nuclear translocation and DNA binding activity of NF-κB in the hippocampal CA3 neurons and glial cells. These cellular events were followed by enhanced upregulation of NOS II and peroxynitrite expression 3h after sustained seizure activity that led to an increase of caspase-3 and DNA fragmentation in the hippocampal CA3 neurons 7days after experimental status epilepticus. We concluded that HSP70 protects against apoptotic cell death induced by NF-κB activation and NOS II-peroxynitrite signaling cascade in the hippocampal CA3 and glial cells following experimental status epilepticus via suppression of IKK activity and deactivation of IκBα.

Glycogen synthase kinase-3 reduces acetylcholine level in striatum via disturbing cellular distribution of choline acetyltransferase in cholinergic interneurons in rats

Cholinergic interneurons, which provide the main source of acetylcholine (ACh) in the striatum, control the striatal local circuits and deeply involve in the pathogenesis of neurodegenerative diseases. Glycogen synthase kinase-3 (GSK-3) is a crucial kinase with diverse fundamental functions and accepted that deregulation of GSK-3 activity also plays important roles in diverse neurodegenerative diseases. However, up to now, there is no direct proof indicating whether GSK-3 activation is responsible for cholinergic dysfunction. In the present study, with combined intracerebroventricular injection of Wortmannin and GF-109203X, we activated GSK-3 and demonstrated the increased phosphorylation level of microtubule-associated protein tau and neurofilaments (NFs) in the rat striatum. The activated GSK-3 consequently decreased ACh level in the striatum as a result of the reduction of choline acetyltransferase (ChAT) activity. The alteration of ChAT activity was due to impaired ChAT distribution rather than its expression. Furthermore, we proved that cellular ChAT distribution was dependent on low phosphorylation level of NFs. Nevertheless, the cholinergic dysfunction in the striatum failed to induce significant neuronal number reduction. In summary, our data demonstrates the link between GSK-3 activation and cholinergic dysfunction in the striatum and provided beneficial evidence for the pathogenesis study of relevant neurodegenerative diseases.

Synaptic deficits in layer 5 neurons precede overt structural decay in 5xFAD mice

Synaptic decay and neurodegeneration are hallmarks of Alzheimer's disease that are thought to precede dementia. Recently, we have reported that the first signs of neuritic dystrophy in a new transgenic mouse model of familial Alzheimer's disease (FAD) called the "5xFAD" are axonal dystrophy followed by loss of spines on basal dendrites. The 5xFAD mouse has profound loss of layer 5 neurons by 12months, and these initial structural insults appear between 4 and 6months of age. Here, we test, for the first time, if synaptic failure of layer 5 neurons in the 5xFAD mouse precedes these structural changes. We used longitudinal, in vivo two-photon fluorescence imaging of bigenic 5xFAD/YFP mice to assess the overall structural stability of layer 5 neurons in young mice (age less than 14weeks). We found these neurons to be structurally and morphologically sound. In parallel, we used in vitro, whole-cell patch clamp electrophysiology of layer 5 pyramidal neurons, from mice aged 8-12weeks, to reveal significant pre- and postsynaptic defects in these cells. Thus our data suggest that layer 5 neurons in the 5xFAD mouse model have synaptic deficits at an early time point, before any overt structural dystrophy, and that such synaptic failure, with co-temporal biochemical changes, may be an early step in neuronal loss.

Sleep-wake and diurnal modulation of nitric oxide in the perifornical-lateral hypothalamic area: real-time detection in freely behaving rats

Nitric oxide (NO) has been implicated in the regulation of sleep. The perifornical-lateral hypothalamic area (PF-LHA) is a key wake-promoting region and contains neurons that are active during behavioral or cortical activation. Recently, we found higher levels of NO metabolites (NOx), an indirect measure of NO levels, in the PF-LHA during prolonged waking (SD). However, NO is highly reactive and diffuses rapidly and the NOx assay is not sensitive enough to detect rapid-changes in NO levels across spontaneous sleep-waking states. We used a novel Nafion®-modified Platinum (NF-PT) electrode for real-time detection of NO levels in the PF-LHA across sleep-wake cycles, dark-light phases, and during SD. Sprague-Dawley male rats were surgically prepared for chronic sleep-wake recording and implantation of NF-PT electrode into the PF-LHA. Electroencephalogram (EEG), electromyogram (EMG), and electrochemical current generated by NF-PT electrode were continuously acquired for 5-7days including one day with 3h of SD. In the PF-LHA, NO levels exhibited a waking>rapid eye movement (REM)>non-rapid eye movement (nonREM) sleep pattern (0.56±0.03μM>0.47±0.02μM>0.42±0.02μM; p<0.01). NO levels were also higher during the dark- as compared to the light-phase (0.53±0.03μM vs. 0.44±0.02μM; p<0.01). NO levels increased during 3h of SD as compared to undisturbed control (0.58±0.04μM vs. 0.47±0.01μM; p<0.05). The findings indicate that in the PF-LHA, NO is produced during behavioral or cortical activation. Since elevated levels of NO inhibits most of the PF-LHA neurons that are active during cortical activation, these findings support a hypothesis that NO produced in conjunction with the activation of PF-LHA neurons during waking/SD, inhibits the same neuronal population to promote sleep.

Effects of prolyl-hydroxylase inhibition and chronic intermittent hypoxia on synaptic transmission and plasticity in the rat CA1 and dentate gyrus

Chronic intermittent hypoxia (CIH) is an underlying component of obstructive sleep apnoea and has been shown to have deleterious and damaging effects on central neurons and to impair synaptic plasticity in the CA1 region of the rat hippocampus. CIH has previously been shown to impair synaptic plasticity and working memory. CIH is a potent inducer of hypoxia inducible factor (HIF), a key regulator in a cell's adaptation to hypoxia that plays an important role in the fate of neurons during ischemia. Levels of HIF-1α are regulated by the activity of a group of enzymes called HIF-prolyl 4-hydroxylases (PHDs) and these have become potential pharmacological targets for preconditioning against ischemia. However little is known about the effects of prolyl hydroxylase inhibition and CIH on synaptic transmission and plasticity in sub-regions of the hippocampus. Male Wistar rats were treated for 7-days with either saline, CIH or PHD inhibition (dimethyloxaloylglycine, DMOG; 50mg/kg, i.p.). At the end of treatment all three groups showed no change in synaptic excitability using paired pulse paradigms. However long-term potentiation (LTP) was impaired in the CA1 region of the hippocampus in both CIH and DMOG treated animals. LTP induced in the dentate gyrus was not significantly affected by either CIH or DMOG treatment. We also investigated the effect of 7-day CIH and DMOG treatment on the recovery of synaptic transmission following an acute 30min hypoxic insult. CIH treated animals showed an improved rate of recovery of synaptic transmission following re-oxygenation in both the CA1 and the dentate gyrus. These results suggest that LTP induction in the CA1 region is more sensitive to both CIH and DMOG treatments than the dentate gyrus.

Selective potentiation of (α4)3(β2)2 nicotinic acetylcholine receptors augments amplitudes of prefrontal acetylcholine- and nicotine-evoked glutamatergic transients in rats

Prefrontal glutamate release evoked through activation of α4β2* nicotinic acetylcholine receptors (nAChRs) situated on thalamic glutamatergic afferents mediates cue detection processes and thus contributes to attentional performance. However, little is known about the respective contributions of the high sensitivity and low sensitivity (LS) stoichiometries of the α4β2 nAChR, (α4)2(β2)3 and (α4)3(β2)2, to these processes. In the present study we employed glutamate-sensitive microelectrodes and the (α4)3(β2)2-selective positive allosteric modulator (PAM) NS9283 to investigate the importance of the LS α4β2 nAChR for glutamate release in the rat medial prefrontal cortex (mPFC). Firstly, the signaling evoked by physiologically relevant ACh concentrations through the (α4)3(β2)2 nAChR in HEK293 cells was potentiated by NS9283, consistent with the classification of NS9283 as a PAM. In urethane-anesthetized rats, intra-prefrontal pressure ejections of NS9283 evoked glutamatergic transients. Importantly, this glutamate release was attenuated by removal of cholinergic projections to the recording area. This finding indicates that the effects of NS9283 depend on endogenous ACh, again consistent with effects of a PAM. We then conducted microdialysis to demonstrate the presence of extracellular ACh in urethane-anesthetized control rats. While detectable, those levels were significantly lower than in awake rats. Finally, the amplitudes of glutamatergic transients evoked by local pressure ejections of a low concentration of nicotine were significantly augmented following systemic administration of NS9283 (3.0mg/kg). In conclusion, our results indicate that a LS α4β2 nAChR PAM such as NS9283 may enhance the cholinergic modulation of glutamatergic neurotransmission in the cortex, thereby perhaps alleviating the attentional impairments common to a range of brain disorders.

A novel liquid chromatography/tandem mass spectrometry method for the quantification of glycine as biomarker in brain microdialysis and cerebrospinal fluid samples within 5min

Glycine is an important amino acid neurotransmitter in the central nervous system (CNS) and a useful biomarker to indicate biological activity of drugs such as glycine reuptake inhibitors (GRI) in the brain. Here, we report how a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method for the fast and reliable analysis of glycine in brain microdialysates and cerebrospinal fluid (CSF) samples has been established. Additionally, we compare this method with the conventional approach of high performance liquid chromatography (HPLC) coupled to fluorescence detection (FD). The present LC-MS/MS method did not require any derivatisation step. Fifteen microliters of sample were injected for analysis. Glycine was detected by a triple quadrupole mass spectrometer in the positive electrospray ionisation (ESI) mode. The total running time was 5min. The limit of quantitation (LOQ) was determined as 100nM, while linearity was given in the range from 100nM to 100μM. In order to demonstrate the feasibility of the LC-MS/MS method, we measured glycine levels in striatal in vivo microdialysates and CSF of rats after administration of the commercially available glycine transporter 1 (GlyT1) inhibitor LY 2365109 (10mg/kg, p.o.). LY 2365109 produced 2-fold and 3-fold elevated glycine concentrations from 1.52μM to 3.6μM in striatal microdialysates and from 10.38μM to 36μM in CSF, respectively. In conclusion, we established a fast and reliable LC-MS/MS method, which can be used for the quantification of glycine in brain microdialysis and CSF samples in biomarker studies.

Adolescent chronic mild stress alters hippocampal CB1 receptor-mediated excitatory neurotransmission and plasticity

Endocannabinoids (eCBs) are involved in the stress response and alterations in eCB signaling may contribute to the etiology of mood disorders. Exposure to chronic mild stress (CMS), a model of depression, produces downregulation of the cannabinoid 1 (CB1) receptor in the hippocampus of male rats. However, it is unknown how this stress-induced change in CB1 levels affects eCB-mediated neurotransmission. In vitro, field potential recordings from CMS-exposed (21-days) rats were performed to assess the effects of stress on eCB-regulated glutamatergic neurotransmission in/on hippocampal area CA1. We observed that application of the CB1 agonist, WIN 55,212-5 (1 μM), in stress animals resulted in a ∼135% increase in excitatory neurotransmission, whereas CB1 activation in non-stress animals leads to a ∼30% decrease. However, during blockade of GABA(A) neurotransmission with picrotoxin, CB1 activation yielded a ∼35% decrease in stress animals. These findings indicate that CMS does not directly affect glutamatergic neurotransmission. Rather, CMS sensitizes CB1 function on GABAergic terminals, leading to less inhibition and an increase in excitatory neurotransmission. This finding is reinforced in that induction of weak long-term-potentiation (LTP) is enhanced in CMS-exposed animals compared to controls and this enhancement is CB1-dependent. Lastly, we observed that the LTP-blocking property of WIN 55,212-5 shifts from being glutamate-dependent in non-stress animals to being GABA-dependent in stress animals. These results effectively demonstrate that CMS significantly alters hippocampal eCB-mediated neurotransmission and synaptic plasticity.

Chronic ceftriaxone treatment rescues hippocampal memory deficit in AQP4 knockout mice via activation of GLT-1

Aquaporin-4 (AQP4) is the predominant water channel protein in the mammalian brain, and is mainly expressed in astrocytes. Besides its important role in water transport across the blood-brain barrier, our present study demonstrated that AQP4 deficiency impaired hippocampal long-term potentiation (LTP) and hippocampus-dependent memory formation, accompanied by the increase in extracellular glutamate concentration and N-methyl-d-aspartate (NMDA) receptor-mediated currents in hippocampal dentate gyrus (DG) region. The impairment of LTP and memory formation of AQP4 knockout (KO) mice was mediated by the downregulation of glutamate transporter-1 (GLT-1) expression/function, since it can be rescued by β-lactam antibiotic ceftriaxone (Cef), a potent GLT-1 stimulator. These results suggest that AQP4 functions as the modulator of synaptic plasticity and memory, and chronic Cef treatment rescues hippocampal memory deficit induced by AQP4 knockout.

Phosphodiesterase 10A controls D1-mediated facilitation of GABA release from striato-nigral projections under normal and dopamine-depleted conditions

In the present study, we found that PDE10A inhibitor papaverine, alone or in combination with the D1 receptor agonist SKF38393, did not change spontaneous IPSCs (sIPSCs) frequency or amplitude in the substantia nigra pars reticulata (SNpr). An increase in frequency, but not in amplitude, of sIPSCs was only observed when SKF38393 and PDE10A inhibitors were associated to perfusion with higher extracellular K(+). On the other hand, the amplitude of evoked IPSCs (eIPSCs) of the striato-nigral projection to SNpr, was increased in response to co-administration of SKF38393 and papaverine in normal extracellular potassium. Of note, both an increase in sIPSCs frequency and eIPSC amplitude could be obtained either by a robust stimulation of adenylyl cyclase (AC) with forskolin (10 μM) or by a lower dose of forskolin (1 μM) associated to PDE inhibition. We next investigated the effects produced by dopamine (DA) depletion in the striatum. Under this condition, SKF38393 alone increased either sIPSCs frequency and eIPSC amplitude. In addition, in the striatum of DA-depleted mice we found reduced PDE10A levels and higher cAMP-dependent phosphorylation in response to D1 receptor stimulation. In accordance with these biochemical data, perfusion with papaverine had no effect on the SKF38393-induced changes of IPSCs in slices of DA-depleted mice. These findings reveal a dynamic interplay between PDE10A activity, level of neuronal network depolarization and degree of dopaminergic tone in the ability of D1 receptors to facilitate the GABAergic transmission to SNpr neurons from the direct nigro-striatal pathway. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

Contribution of CA3 and CA1 pyramidal neurons to the tonic α7 nAChR-dependent glutamatergic input to CA1 pyramidal neurons

The Schaffer collaterals are among the major glutamatergic inputs to CA1 pyramidal neurons, the primary output of the hippocampus, which also receive sparse recurrent inputs from pyramidal neurons in the CA1 field. Although tonically active α7 nicotinic acetylcholine receptors (nAChRs) have been shown to sustain spontaneous glutamate transmission to CA1 pyramidal neurons in hippocampal slices under resting conditions, it remains to be determined whether these receptors are those expressed by CA3 or CA1 pyramidal neurons. This study was designed to test the hypothesis that the CA3 field of the hippocampus is a significant source of α7 nAChR-sustained glutamatergic transmission to CA1 pyramidal neurons. To this end, spontaneous excitatory postsynaptic currents (EPSCs) were recorded from CA1 and CA3 pyramidal neurons in intact rat hippocampal slices as well as from CA1 pyramidal neurons in CA3-ablated slices under various experimental conditions. Surgical removal of the CA3 region from the slices reduced by 20% the frequency of spontaneous EPSCs recorded from CA1 pyramidal neurons. This finding is in agreement with the concept that the CA3 field contributes significantly to the maintenance of spontaneous glutamatergic synaptic activity in CA1 pyramidal neurons. In addition, the α7 nAChR antagonist methyllycaconitine (MLA, 10nM) reduced the frequency of spontaneous EPSCs recorded from CA1 pyramidal neurons by 30% in intact slices and 12% in CA3-ablated slices. Taken together, these results demonstrate that tonically active α7 nAChRs in CA3 pyramidal neurons and/or in the Mossy fibers that innervate the CA3 pyramidal neurons do in fact contribute to the maintenance of glutamatergic synaptic activity in CA1 pyramidal neurons of hippocampal slices under resting conditions.

Independent of 5-HT1A receptors, neurons in the paraventricular hypothalamus mediate ACTH responses from MDMA

Acute and chronic complications from the substituted amphetamine 3,4-methylenedioxymethamphetamine (MDMA) are linked to activation of the hypothalamic-pituitary-adrenal (HPA) axis. How MDMA activates the HPA axis is not known. HPA responses to stress are known to be mediated through the paraventricular (PVH) hypothalamus and to involve serotonin-1a (5-HT1A) receptors. We sought to determine if the PVH and 5-HT1A receptors were also involved in mediating HPA responses to MDMA. Rats were pretreated with either saline or a 5-HT1A antagonist, WAY-100635 (WAY), followed by a systemic dose of MDMA (7.5mg/kg i.v.). Animals pretreated with WAY had significantly lower plasma ACTH concentrations after MDMA. To determine if neurons in the PVH were involved, and if their involvement was mediated by 5-HT1A receptors, rats implanted with guide cannulas targeting the PVH were microinjected with the GABAA receptor agonist muscimol, aCSF, or WAY followed by MDMA. Compared to aCSF, microinjections of muscimol significantly attenuated the MDMA-induced rise in plasma ACTH (126 vs. 588pg/ml, P=<0.01). WAY had no effect. Our data demonstrates that neurons in the PVH, independent of 5-HT1A receptors, mediate ACTH responses to MDMA.

2-Guanidine-4-methylquinazoline acts as a novel competitive antagonist of A type γ-aminobutyric acid receptors

The pentameric A type γ-aminobutyric acid receptors (GABAARs) are the major inhibitory neurotransmitter receptors in the nervous system and have long been considered as important pharmaceutical targets for the treatment of multiple neurological or psychological disorders. Here, we show that 2-guanidine-4-methylquinazoline (GMQ), a recently identified acid-sensing ion channel (ASIC) modulator, strongly and preferentially inhibits GABAAR among the major neurotransmitter-gated ion channels in cultured rat hippocampal neurons. GMQ inhibited GABA (1 μM)-induced currents in a competitive manner, with an IC50 (0.39±0.05 μM) comparable to that of bicuculline. Schild analysis revealed a slope of 1.04±0.06 for GMQ on α1β2 GABAARs expressed in HEK293T cells. Single-channel analysis showed that GMQ decreased open probability of GABAARs without affecting conductance. Moreover, GMQ inhibited GABAergic neurotransmission in hippocampal neurons, while having no significant effect on the basal field excitatory postsynaptic potentials (fEPSPs) and the intrinsic excitability of neurons. Using site-directed mutagenesis, we further demonstrated that mutations at Glu155 of β2 subunit and Phe64 of α1 subunit, both located inside the GABA binding pocket, profoundly decreased the sensitivity of the receptor to both GABA and GMQ. Interestingly, these mutations did not significantly affect the inhibition by amiloride, a diuretic structurally similar to GMQ and a known GABAAR inhibitor. We conclude that GMQ represents a novel chemical structure that acts, possibly, by competing with GABA binding to GABAARs. It is anticipated that GMQ and its analogs will facilitate the development of new chemical probes for GABAARs.

Patterned high-frequency stimulation induces a form of long-term depression dependent on GABAA and mACh receptors in the hippocampus

Certain patterns of neural activity can induce N-methyl-D-aspartic acid receptor (NMDAR)-dependent synaptic plasticity, one of the important foundations of memory. Here, we report that a patterned high-frequency stimulation (PHS) induces rat hippocampal long-term depression (LTD) in an NMDAR-independent manner that requires coactivation of GABA(A)Rs and muscarinic acetylcholine receptors (mAChRs), and endocytosis of AMPARs. Thus, we disclose that a patterned high-frequency stimulation triggers GABAAR and mAChR-dependent LTD in the hippocampus.

Intracerebroventricular administration of ouabain, a Na/K-ATPase inhibitor, activates mTOR signal pathways and protein translation in the rat frontal cortex

Intracerebroventricular (ICV) injection of ouabain, a specific Na/K-ATPase inhibitor, induces behavioral changes in rats in a putative animal model of mania. The binding of ouabain to Na/K-ATPase affects signaling molecules in vitro, including ERK1/2 and Akt, which promote protein translation. We have also reported that ERK1/2 and Akt in the brain are involved in the ouabain-induced hyperactivity of rats. In this study, rats were given an ICV injection of ouabain, and then their frontal cortices were examined to determine the effects of ouabain on the mTOR/p70S6K/S6 signaling pathway and protein translation, which are important in modifications of neural circuits and behavior. Rats showed ouabain-induced hyperactivity up to 8h following injection, and increased phosphorylation levels of mTOR, p70S6K, S6, eIF4B, and 4E-BP at 1, 2, 4, and 8h following ouabain injection. Immunohistochemical analyses revealed that increased p-S6 immunoreactivity in the cytoplasm of neurons by ouabain was evident in the prefrontal, cingulate, and orbital cortex. These findings suggested increased translation initiation in response to ouabain. The rate of protein synthesis was measured as the amount of [(3)H]-leucine incorporation in the cell-free extracts of frontal cortical tissues, and showed a significant increase at 8h after ouabain injection. These results suggest that ICV injection of ouabain induced activation of the protein translation initiation pathway regulated by ERK1/2 and Akt, and prolonged hyperactivity in rats. In conclusion, protein translation pathway could play an important role in ouabain-induced hyperactivity in a rodent model of mania.

Hydrogen sulfide attenuates neurodegeneration and neurovascular dysfunction induced by intracerebral-administered homocysteine in mice

High levels of homocysteine (Hcy), known as hyperhomocysteinemia are associated with neurovascular diseases. H2S, a metabolite of Hcy, has potent anti-oxidant and anti-inflammatory activities; however, the effect of H2S has not been explored in Hcy (IC)-induced neurodegeneration and neurovascular dysfunction in mice. Therefore, the present study was designed to explore the neuroprotective role of H2S on Hcy-induced neurodegeneration and neurovascular dysfunction. To test this hypothesis we employed wild-type (WT) males ages 8-10 weeks, WT+artificial cerebrospinal fluid (aCSF), WT+Hcy (0.5 μmol/μl) intracerebral injection (IC, one time only prior to NaHS treatment), WT+Hcy+NaHS (sodium hydrogen sulfide, precursor of H2S, 30 μmol/kg, body weight). NaHS was injected i.p. once daily for the period of 7 days after the Hcy (IC) injection. Hcy treatment significantly increased malondialdehyde, nitrite level, acetylcholinestrase activity, tumor necrosis factor-alpha, interleukin-1 beta, glial fibrillary acidic protein, inducible nitric oxide synthase, endothelial nitric oxide synthase and decreased glutathione level indicating oxidative-nitrosative stress and neuroinflammation as compared to control and aCSF-treated groups. Further, increased expression of neuron-specific enolase, S100B and decreased expression of (post-synaptic density-95, synaptosome-associated protein-97) synaptic protein indicated neurodegeneration. Brain sections of Hcy-treated mice showed damage in the cortical area and periventricular cells. Terminal deoxynucleotidyl transferase-mediated, dUTP nick-end labeling-positive cells and Fluro Jade-C staining indicated apoptosis and neurodegeneration. The increased expression of matrix metalloproteinase (MMP) MMP9, MMP2 and decreased expression of tissue inhibitor of metalloproteinase (TIMP) TIMP-1, TIMP-2, tight junction proteins (zonula occulden 1) in Hcy-treated group indicate neurovascular remodeling. Interestingly, NaHS treatment significantly attenuated Hcy-induced oxidative stress, memory deficit, neurodegeneration, neuroinflammation and cerebrovascular remodeling. The results indicate that H2S is effective in providing protection against neurodegeneration and neurovascular dysfunction.

Phoenixin: a novel peptide in rodent sensory ganglia

Phoenixin-14 amide, herein referred to as phoenixin, is a newly identified peptide from the rat brain. Using a previously characterized rabbit polyclonal antiserum against phoenixin, enzyme-immunoassay detected a high level (>4.5 ng/g tissue) of phoenixin-immunoreactivity (irPNX) in the rat spinal cords. Immunohistochemical studies revealed irPNX in networks of cell processes in the superficial dorsal horn, spinal trigeminal tract and nucleus of the solitary tract; and in a population of dorsal root, trigeminal and nodose ganglion cells. The pattern of distribution of irPNX in the superficial layers of the dorsal horn was similar to that of substance P immunoreactivity (irSP). Double-labeling the dorsal root ganglion sections showed that irPNX and irSP express in different populations of ganglion cells. In awake mice, intrathecal injection of phoenixin (1 or 5 μg) did not significantly affect the tail-flick latency as compared to that in animals injected with artificial cerebrospinal fluid (aCSF). Intrathecal administration of phoenixin (0.5, 1.25 or 2.5 μg) significantly reduced the number of writhes elicited by intraperitoneal injection of acetic acid (0.6%, 0.3 ml/30 g) as compared to that in mice injected with aCSF. While not affecting the tail-flick latency, phoenixin antiserum (1:100) injected intrathecally 10 min prior to the intraperitoneal injection of acetic acid significantly increased the number of writhes as compared to mice pre-treated with normal rabbit serum. Intrathecal injection of non-amidated phoenixin (2.5 μg) did not significantly alter the number of writhes evoked by acetic acid. Our result shows that phoenixin is expressed in sensory neurons of the dorsal root, nodose and trigeminal ganglia, the amidated peptide is bioactive, and exogenously administered phoenixin may preferentially suppress visceral as opposed to thermal pain.

Maternal mobile phone exposure adversely affects the electrophysiological properties of Purkinje neurons in rat offspring

Electromagnetic field (EMF) radiations emitted from mobile phones may cause structural damage to neurons. With the increased usage of mobile phones worldwide, concerns about their possible effects on the nervous system are rising. In the present study, we aimed to elucidate the possible effects of prenatal EMF exposure on the cerebellum of offspring Wistar rats. Rats in the EMF group were exposed to 900-MHz pulse-EMF irradiation for 6h per day during all gestation period. Ten offspring per each group were evaluated for behavioral and electrophysiological evaluations. Cerebellum-related behavioral dysfunctions were analyzed using motor learning and cerebellum-dependent functional tasks (Accelerated Rotarod, Hanging and Open field tests). Whole-cell patch clamp recordings were used for electrophysiological evaluations. The results of the present study failed to show any behavioral abnormalities in rats exposed to chronic EMF radiation. However, whole-cell patch clamp recordings revealed decreased neuronal excitability of Purkinje cells in rats exposed to EMF. The most prominent changes included afterhyperpolarization amplitude, spike frequency, half width and first spike latency. In conclusion, the results of the present study show that prenatal EMF exposure results in altered electrophysiological properties of Purkinje neurons. However, these changes may not be severe enough to alter the cerebellum-dependent functional tasks.

Interleukin-1β alters the sensitivity of cannabinoid CB1 receptors controlling glutamate transmission in the striatum

Proinflammatory cytokines such as tumor necrosis factor-α and interleukin-1β (IL1β) regulate both excitatory and inhibitory synaptic transmission in the central nervous system. The interaction between IL1β and endocannabinoid system (ECS) is also emerging, based on the evidence that IL1β effects on striatal spontaneous excitatory and inhibitory postsynaptic currents are regulated by transient receptor potential vanilloid 1 (TRPV1) channels, members of the ECS. Furthermore, IL1β has also been shown to control the sensitivity of cannabinoid CB1 receptors controlling GABA transmission (CB1Rs(GABA)) in the striatum. To better detail the synaptic action of IL1β, and to clarify its complex interaction with the ECS, here we investigated the possible interplay between IL1β and CB1Rs controlling glutamate transmission (CB1Rs(glu)), other critical elements of the ECS. Our results show that the sensitivity of CB1Rs(glu) is fully blocked in the presence of IL1β in corticostriatal brain slices, and that the protein kinase C/TRPV1 pathway is involved in this effect. IL1β failed to modulate the sensitivity of glutamate synapses to the stimulation of GABAB receptors. We also provided evidence that IL1β-CB1Rs(GABA) but not IL1β-CB1Rs(glu) interaction is under the control of the brain-derived neurotrophic factor (BDNF)/trkB signaling and of lipid raft composition, because BDNF gene partial deletion, pharmacological blockade of trkB and membrane cholesterol removal with methyl-β-cyclodextrin all blocked IL1β-mediated inhibition of CB1Rs(GABA) but left unaltered the sensitivity of CB1Rs(glu) to this cytokine. Our results provide further evidence that synaptic transmission and the ECS are regulated by IL1β in the striatum.

Presynaptic TRPV1 vanilloid receptor function is age- but not CB1 cannabinoid receptor-dependent in the rodent forebrain

Neocortical and striatal TRPV1 (vanilloid or capsaicin) receptors (TRPV1Rs) are excitatory ligand-gated ion channels, and are implicated in psychiatric disorders. However, the purported presynaptic neuromodulator role of TRPV1Rs in glutamatergic, serotonergic or dopaminergic terminals of the rodent forebrain remains little understood. With the help of patch-clamp electrophysiology and neurochemical approaches, we mapped the age-dependence of presynaptic TRPV1R function, and furthermore, we aimed at exploring whether the presence of CB1 cannabinoid receptors (CB1Rs) influences the function of the TRPV1Rs, as both receptor types share endogenous ligands. We found that the major factor which affects presynaptic TRPV1R function is age: by post-natal day 13, the amplitude of capsaicin-induced release of dopamine and glutamate is halved in the rat striatum, and two weeks later, capsaicin already loses its effect. However, TRPV1R receptor function is not enhanced by chemical or genetic ablation of the CB1Rs in dopaminergic, glutamatergic and serotonergic terminals of the mouse brain. Altogether, our data indicate a possible neurodevelopmental role for presynaptic TRPV1Rs in the rodent brain, but we found no cross-talk between TRPV1Rs and CB1Rs in the same nerve terminal.

Histamine up-regulates astrocytic glutamate transporter 1 and protects neurons against ischemic injury

Astrocytic glutamate transporter 1 (GLT-1) is responsible for the majority of extracellular glutamate clearance and is essential for preventing excitotoxicity in the brain. Up-regulation of GLT-1 shows benefit effect on ischemia-induced neuronal damage. In present study, we examined the effect of histamine, a neurotransmitter or neuromodulator, on GLT-1 expression and function. In acute hippocampal slices, histamine selectively increased GLT-1 expression independent of neuronal activities. Similar up-regulation of GLT-1 was also observed after histamine treatment in pure cultured astrocytes, which was abolished by H1 receptor antagonist or PKC inhibitor. Cell surface biotinylation and whole-cell patch recordings of glutamate transporter current confirmed the up-regulation of functional GLT-1 following histamine exposure. Histamine treatment decreased the extracellular glutamate content and alleviated neuronal cell death induced by exogenous glutamate challenge. Moreover, we found a significant neuroprotective effect of histamine in brain slices after oxygen-glucose deprivation (OGD). In addition, histidine, the precursor of histamine, also showed neuroprotection against ischemic injury, which was accompanied by reversion of declined expression of GLT-1 in adult rats subjected to middle cerebral artery occlusion (MCAO). These neuroprotective effects of histamine/histidine were blocked by GLT-1 specific inhibitor dihydrokainate or H1 receptor antagonist. In summary, our results suggest that histamine up-regulates GLT-1 expression and function via astrocytic H1 receptors, thus resulting in neuroprotection against excitotoxicity and ischemic injury.

Thalamocortical relationships and network synchronization in a new genetic model "in mirror" for absence epilepsy

Electroencephalographic generalized spike and wave discharges (SWD), the hallmark of human absence seizures, are generated in thalamocortical networks. However, the potential alterations in these networks in terms of the efficacy of the reciprocal synaptic activities between the cortex and the thalamus are not known in this pathology. Here, the efficacy of these reciprocal connections is assessed in vitro in thalamocortical slices obtained from BS/Orl mice, which is a new genetic model of absence epilepsy. These mice show spontaneous SWD, and their features can be compared to that of BR/Orl mice, which are free of SWD. In addition, since gap junctions may modulate the efficacy of these connections, their implications in pharmacologically-induced epileptiform discharges were studied in the same slices. The thalamus and neocortex were independently stimulated and the electrically-evoked responses in both structures were recorded from the same slice. The synaptic efficacy of thalamocortical and corticothalamic connections were assessed by measuring the dynamic range of synaptic field potential changes in response to increasing stimulation strengths. The connection efficacy was weaker in epileptic mice however, this decrease in efficacy was more pronounced in thalamocortical afferents, thus introducing an imbalance in the reciprocal connections between the cortex and thalamus. However, short-term facilitation of the thalamocortical responses were increased in epileptic mice compared to non-epileptic animals. These features may favor occurrence of rhythmical activities in thalamocortical networks. In addition, carbenoxolone (a gap junction blocker) decreased the cumulative duration of 4-aminopyridine-induced ictal-like activities, with a slower time course in epileptic mice. However, the 4-aminopyridine-induced GABA-dependent negative potentials, which appeared to trigger the ictal-like activities, remained. Our results show that the balance of the reciprocal connections between the thalamus and cortex is altered in favor of the corticothalamic connections in epileptic mice, and suggest that gap junctions mediate a stronger cortical synchronization in this strain.

Kinin-B2 receptor exerted neuroprotection after diisopropylfluorophosphate-induced neuronal damage

The kinin-B2 receptor (B2BKR) activated by its endogenous ligand bradykinin participates in various metabolic processes including the control of arterial pressure and inflammation. Recently, functions for this receptor in brain development and protection against glutamate-provoked excitotoxicity have been proposed. Here, we report neuroprotective properties for bradykinin against organophosphate poisoning using acute hippocampal slices as an in vitro model. Following slice perfusion for 10min with diisopropylfluorophosphate (DFP) to initiate the noxious stimulus, responses of pyramidal neurons upon an electric impulse were reduced to less than 30% of control amplitudes. Effects on synaptic-elicited population spikes were reverted when preparations had been exposed to bradykinin 30min after challenging with DFP. Accordingly, bradykinin-induced population spike recovery was abolished by HOE-140, a B2BKR antagonist. However, the kinin-B1 receptor (B1BKR) agonist Lys-des-Arg(9)-bradykinin, inducing the phosphorylation of mitogen-activated protein kinase (MEK/MAPK) and cell death, abolished bradykinin-mediated neuroprotection, an effect, which was reverted by the ERK inhibitor PD98059. In agreement with pivotal B1BKR functions in this process, antagonism of endogenous B1BKR activity alone was enough for restoring population spike activity. On the other hand pralidoxime, an oxime, reactivating acetylcholinesterase (AChE) after organophosphate poisoning, induced population spike recovery after DFP exposure in the presence of bradykinin and Lys-des-Arg(9)-bradykinin. Lys-des-Arg(9)-bradykinin did not revert protection exerted by pralidoxime, however when instead bradykinin and Ly-des-Arg(9)-bradykinin were superfused together, recovery of population spikes diminished. These findings again confirm the neuroprotective feature of bradykinin, which is, diminished by its endogenous metabolites, stimulating the B1BKR, providing a novel understanding of the physiological roles of these receptors.

Opposite long-term synaptic effects of 17β-estradiol and 5α-dihydrotestosterone and localization of their receptors in the medial vestibular nucleus of rats

In brainstem slices of male rats, we examined in single neurons of the medial vestibular nucleus (MVN) the effect of exogenous administration of estrogenic (17β-estradiol, E2) and androgenic (5α-dihydrotestosterone, DHT) steroids on the synaptic response to vestibular afferent stimulation. By whole cell patch clamp recordings we showed that E2 induced synaptic long-term potentiation (LTP) that was cancelled by the subsequent administration of DHT. Conversely, DHT induced synaptic long-term depression (LTD) that was partially reversed by E2. The electrophysiological findings were supported by immunohistochemical analysis showing the presence of estrogen (ER: α and β) and androgen receptors (AR) in the MVN neurons. We found that a large number of neurons were immunoreactive for ERα, ERβ, and AR and most of them co-localized ERβ and AR. We also showed the presence of P450-aromatase (ARO) in the MVN neurons, clearly proving that E2 can be locally synthesized in the MVN. On the whole, these results demonstrate a role of estrogenic and androgenic signals in modulating vestibular synaptic plasticity and suggest that the enhancement or depression of vestibular synaptic response may depend on the local conversion of T into E2 or DHT.

Rodent brain slice model for the study of white matter injury

OBJECTIVE

Cerebral white matter (WM) injury is common after cardiac surgery in neonates and young infants who have brain immaturity and genetic abnormalities. To understand better the mechanisms associated with WM injury, we tested the adequacy of a novel ex vivo brain slice model, with a particular focus on how the maturational stage modulates the injury.

METHODS

To replicate conditions of cardiopulmonary bypass, we transferred living brain slices to a closed chamber perfused by artificial cerebrospinal fluid under controlled temperature and oxygenation. Oxygen-glucose deprivation (OGD) simulated circulatory arrest. The effects of maturation were investigated in 7- and 21-day-old mice (P7, P21) that are equivalent in maturation stage to the human fetus and young adult.

RESULTS

There were no morphologic changes in axons after 60 minutes of OGD at 15°C in both P7 WM and P21 WM. Higher temperature and longer duration of OGD were associated with significantly greater WM axonal damage, suggesting that the model replicates the injury seen after hypothermic circulatory arrest. The axonal damage at P7 was significantly less than at P21, demonstrating that immature axons are more resistant than mature axons. Conversely, a significant increase in caspase3(+) oligodendrocytes in P7 mice was identified relative to P21, indicating that oligodendrocytes in immature WM are more vulnerable than oligodendrocytes in mature WM.

CONCLUSIONS

Neuroprotective strategies for immature WM may need to focus on reducing oligodendrocyte injury. The brain slice model will be helpful in understanding the effects of cardiac surgery on the immature brain and the brain with genetic abnormalities.

Analysis of peptides secreted from cultured mouse brain tissue

Peptides represent a major class of cell-cell signaling molecules. Most peptidomic studies have focused on peptides present in brain or other tissues. For a peptide to function in intercellular signaling, it must be secreted. The present study was undertaken to identify the major peptides secreted from mouse brain slices that were cultured in oxygenated buffer for 3-4h. Approximately 75% of the peptides identified in extracts of cultured slices matched the previously reported peptide content of heat-inactivated mouse brain tissue, whereas only 2% matched the peptide content of unheated brain tissue; the latter showed a large number of postmortem changes. As found with extracts of heat-inactivated mouse brain, the extracts of cultured brain slices represented secretory pathway peptides as well as peptides derived from intracellular proteins such as those present in the cytosol and mitochondria. A subset of the peptides detected in the extracts of the cultured slices was detected in the culture media. The vast majority of secreted peptides arose from intracellular proteins and not secretory pathway proteins. The peptide RVD-hemopressin, a CB1 cannabinoid receptor agonist, was detected in culture media, which is consistent with a role for RVD-hemopressin as a non-classical neuropeptide. Taken together with previous studies, the present results show that short-term culture of mouse brain slices is an appropriate system to study peptide secretion, especially the non-conventional pathway(s) by which peptides produced from intracellular proteins are secreted. This article is part of a Special Issue entitled: An Updated Secretome.

Reduced social interaction, behavioural flexibility and BDNF signalling in the BTBR T+ tf/J strain, a mouse model of autism

Autism is a neurodevelopmental disorder characterized by social and communication impairments and repetitive behaviours. The inbred BTBR T+ tf/J (BTBR) strain, a putative mouse model of autism, exhibits lower social interactions, higher repetitive self-grooming levels and unusual pattern of vocalizations as compared to C57BL/6J strain. First aim of the present study was to evaluate at adolescence (postnatal days 30-35) male BTBR and C57BL/6J performances in two different tasks involving either investigation of social cues (same strain partners) or non social ones (inanimate objects). In the social interaction test, BTBR mice showed a reduction of investigation of the social partner, due to a selective reduction of head sniffing, associated with a decrease in ultrasonic vocalizations. By contrast, no strain differences were detected in object investigations. Second aim of the study was to evaluate adult male BTBR and C57BL/6J performances in a fear conditioning task. Strain differences were evident during contextual retest: these strain differences primarily suggested a lack of behavioural flexibility in BTBR mice (i.e., realizing the occurrence of changes in the experimental paradigm). Subsequent electrophysiological analysis in hippocampal slices from adult BTBR and C57BL/6J mice revealed a significant reduction of Brain Derived Neurotrophic Factor (BDNF)-induced potentiation of synaptic transmission in BTBR mice. BDNF and tyrosine kinase B (TrkB) protein levels measured in the hippocampal region were also lower in BTBR as compared to C57BL/6J mice. These data confirm the presence of low levels of direct interaction with social stimuli in BTBR mice at adolescence, in the absence of any strain difference as for investigation of physical objects. At adulthood in BTBR mice clear signs of behavioural inflexibility were evident whereas both biochemical and electrophysiological data point to decreased BDNF signalling (likely due to a reduction in TrkB levels) in the hippocampus of this mouse strain.