The fate of “dark” neurons produced by transient focal cerebral ischemia in a non-necrotic and non-excitotoxic environment: Neurobiological aspects

The effect of Brucella abortus on glial activation and cell death in adult male rat's hippocampus

A zoonotic disease called brucellosis can cause flu-like symptoms and heart inflammation. The bacteria responsible for this disease can also enter the brain, causing a condition called neurobrucellosis that can result in long-term neurological problems. In this study, researchers aimed to determine the changes in the hippocampal cells of rats infected with Brucella. For the study, 24 adult male albino rats were inoculated with 1 × 106 CFU Brucella abortus 544. The rats were then deeply anesthetized, and their hippocampus samples were taken for stereological, histological, and molecular studies. The results showed that the infected rats had increased microgliosis and astrogliosis. Furthermore, a high level of caspase-3 in their hippocampal tissue indicated their susceptibility to apoptosis. Additionally, there was a decrease in expression of Ki67, which further supported this. Sholl's analysis confirmed a significant failure in glial morphology. The study demonstrated that the pathogen has the ability to destroy the hippocampus and potentially affect its normal physiology. However, more research is needed to clarify various aspects of neurobrucellosis.

Short-term hyperoxia-induced functional and morphological changes in rat hippocampus

Excess oxygen (O2) levels may have a stimulating effect, but in the long term, and at high concentrations of O2, it is harmful to the nervous system. The hippocampus is very sensitive to pathophysiological changes and altered O2 concentrations can interfere with hippocampus-dependent learning and memory functions. In this study, we investigated the hyperoxia-induced changes in the rat hippocampus to evaluate the short-term effect of mild and severe hyperoxia. Wistar male rats were randomly divided into control (21% O2), mild hyperoxia (30% O2), and severe hyperoxia groups (100% O2). The O2 exposure lasted for 60 min. Multi-channel silicon probes were used to study network oscillations and firing properties of hippocampal putative inhibitory and excitatory neurons. Neural damage was assessed using the Gallyas silver impregnation method. Mild hyperoxia (30% O2) led to the formation of moderate numbers of silver-impregnated "dark" neurons in the hippocampus. On the other hand, exposure to 100% O2 was associated with a significant increase in the number of "dark" neurons located mostly in the hilus. The peak frequency of the delta oscillation decreased significantly in both mild and severe hyperoxia in urethane anesthetized rats. Compared to normoxia, the firing activity of pyramidal neurons under hyperoxia increased while it was more heterogeneous in putative interneurons in the cornu ammonis area 1 (CA1) and area 3 (CA3). These results indicate that short-term hyperoxia can change the firing properties of hippocampal neurons and network oscillations and damage neurons. Therefore, the use of elevated O2 concentration inhalation in hospitals (i.e., COVID treatment and surgery) and in various non-medical scenarios (i.e., airplane emergency O2 masks, fire-fighters, and high altitude trekkers) must be used with extreme caution.

Omega-3 fatty acids prevent nicotine withdrawal-induced impairment of learning and memory via affecting oxidative status, inflammatory response, cholinergic activity, BDNF and amyloid-B in rat hippocampal tissues

In the present study, the main objective was to reveal whether treatment by Omega-3 fatty acids could prevent the adverse effects of adolescent nicotine withdrawal on spatial and avoidance memory in male rats. For this purpose, Morris water maze and passive avoidance tests were performed on male Wistar rats and the hippocampal levels of oxidative stress markers, inflammatory indices, brain-derived neurotrophic factor, nitrite, amyloid-B and acetylcholinesterase (AChE) were measured. Moreover, density of dark neurons were assessed in CA1 and CA3 regions. Results showed that adolescent nicotine exposure followed by a period of drug cessation exacerbates the behavioral indices of learning and memory through affecting a variety of biochemical markers within the hippocampal tissues. These changes lead to elevation of oxidative and inflammatory markers, reduction of neurotrophic capacity and increased AChE activity in hippocampal tissues. In addition, it was observed that co-administration of nicotine with Omega-3 fatty acids significantly prevents nicotine withdrawal-induced adverse effects through restoration of the mentioned biochemical disturbances. Therefore, we suggest administration of Omega-3 fatty acids as a safe, inexpensive and effective therapeutic strategy for prevention of memory dysfunctions associated with nicotine abstinence during adolescence.

Loss of cholinergic receptor muscarinic 1 impairs cortical mitochondrial structure and function: implications in Alzheimer's disease

Introduction: Cholinergic Receptor Muscarinic 1 (CHRM1) is a G protein-coupled acetylcholine (ACh) receptor predominantly expressed in the cerebral cortex. In a retrospective postmortem brain tissues-based study, we demonstrated that severely (≥50% decrease) reduced CHRM1 proteins in the temporal cortex of Alzheimer's patients significantly correlated with poor patient outcomes. The G protein-mediated CHRM1 signal transduction cannot sufficiently explain the mechanistic link between cortical CHRM1 loss and the appearance of hallmark Alzheimer's pathophysiologies, particularly mitochondrial structural and functional abnormalities. Therefore, the objective of this study was to analyze the molecular, ultrastructural, and functional properties of cortical mitochondria using CHRM1 knockout (Chrm1-/-) and wild-type mice to identify mitochondrial abnormalities. Methods: Isolated and enriched cortical mitochondrial fractions derived from wild-type and Chrm1-/- mice were assessed for respiratory deficits (oxygen consumption) following the addition of different substrates. The supramolecular assembly of mitochondrial oxidative phosphorylation (OXPHOS)-associated protein complexes (complex I-V) and cortical mitochondrial ultrastructure were investigated by blue native polyacrylamide gel electrophoresis and transmission electron microscopy (TEM), respectively. A cocktail of antibodies, specific to Ndufb8, Sdhb, Uqcrc2, Mtco1, and Atp5a proteins representing different subunits of complexes I-V, respectively was used to characterize different OXPHOS-associated protein complexes. Results: Loss of Chrm1 led to a significant reduction in cortical mitochondrial respiration (oxygen consumption) concomitantly associated with reduced oligomerization of ATP synthase (complex V) and supramolecular assembly of complexes I-IV (Respirasome). Overexpression of Chrm1 in transformed cells (lacking native Chrm1) significantly increased complex V oligomerization and respirasome assembly leading to enhanced respiration. TEM analysis revealed that Chrm1 loss led to mitochondrial ultrastructural defects and alteration in the tinctorial properties of cortical neurons causing a significant increase in the abundance of dark cortical neurons (Chrm1-/- 85% versus wild-type 2%). Discussion: Our findings indicate a hitherto unknown effect of Chrm1 deletion in cortical neurons affecting mitochondrial function by altering multiple interdependent factors including ATP synthase oligomerization, respirasome assembly, and mitochondrial ultrastructure. The appearance of dark neurons in Chrm1-/- cortices implies potentially enhanced glutamatergic signaling in pyramidal neurons under Chrm1 loss condition. The findings provide novel mechanistic insights into Chrm1 loss with the appearance of mitochondrial pathophysiological deficits in Alzheimer's disease.

The Relationship between p53-Positive Neurons and Dark Neurons in the Hippocampus of Rats after Surgical Interventions on the Nasal Septum

The study evaluates the dependence of p53 protein expression on the appearance of dark neurons (DNs) in the hippocampus in rats during experimental modeling of septoplasty. Septoplasty simulation was carried out on 15 sexually mature male Wistar rats. We studied histological sections of the hippocampus stained with Nissl toluidine blue and antibodies to the p53 protein. In the CA1 subfield, the number of p53-positive neurons significantly increased on the 2nd, 4th (p < 0.001) and 6th days (p < 0.05). In the dynamics, the peak of the growth of p53 protein expression in the cytoplasm of CA1 and CA2 neurons fell on the 2-4th day after the operation, and on the 6th day the number of these neurons decreased (p < 0.001). In the cytoplasm of CA3 neurons in all periods after surgery, an increase in the expression of the p53 protein as compared to the control group was noted. In the CA1 pyramidal layer, the number of DNs decreased on the 6th day (p < 0.001). In CA2, after 2 days, a minimum of DNs as compared with the 4th day (p < 0.001) was noted. In CA3, on the 4th day, there was a peak in DNs as compared with the rest of the days (p < 0.001). A positive strong association was found in all periods of assessment and in all subfields of the hippocampus between an increase in the number of dark and p53-positive neurons. The appearance of dark and p53-positive neurons in the hippocampal formation in rats after simulating septoplasty are typical responses of nervous tissue to stress. It is obvious that the expression of the p53 protein is associated with the basophilia of the cytoplasm of neurons, their morpho-functional state. Presumably, the p53 protein can trigger not only the activation of damaged neurons in the hippocampus but also play a neuroprotective role. Upcoming studies should determine the role of the p53 protein in the further fate of damaged neurons in the pyramidal layer and differentiate the mechanisms of its expression.

Motoneuron deafferentation and gliosis occur in association with neuromuscular regressive changes during ageing in mice

BACKGROUND

The cellular mechanisms underlying the age-associated loss of muscle mass and function (sarcopenia) are poorly understood, hampering the development of effective treatment strategies. Here, we performed a detailed characterization of age-related pathophysiological changes in the mouse neuromuscular system.

METHODS

Young, adult, middle-aged, and old (1, 4, 14, and 24-30 months old, respectively) C57BL/6J mice were used. Motor behavioural and electrophysiological tests and histological and immunocytochemical procedures were carried out to simultaneously analyse structural, molecular, and functional age-related changes in distinct cellular components of the neuromuscular system.

RESULTS

Ageing was not accompanied by a significant loss of spinal motoneurons (MNs), although a proportion (~15%) of them in old mice exhibited an abnormally dark appearance. Dark MNs were also observed in adult (~9%) and young (~4%) animals, suggesting that during ageing, some MNs undergo early deleterious changes, which may not lead to MN death. Old MNs were depleted of cholinergic and glutamatergic inputs (~40% and ~45%, respectively, P < 0.01), suggestive of age-associated alterations in MN excitability. Prominent microgliosis and astrogliosis [~93% (P < 0.001) and ~100% (P < 0.0001) increase vs. adults, respectively] were found in old spinal cords, with increased density of pro-inflammatory M1 microglia and A1 astroglia (25-fold and 4-fold increase, respectively, P < 0.0001). Ageing resulted in significant reductions in the nerve conduction velocity and the compound muscle action potential amplitude (~30%, P < 0.05, vs. adults) in old distal plantar muscles. Compared with adult muscles, old muscles exhibited significantly higher numbers of both denervated and polyinnervated neuromuscular junctions, changes in fibre type composition, higher proportion of fibres showing central nuclei and lipofuscin aggregates, depletion of satellite cells, and augmented expression of different molecules related to development, plasticity, and maintenance of neuromuscular junctions, including calcitonin gene-related peptide, growth associated protein 43, agrin, fibroblast growth factor binding protein 1, and transforming growth factor-β1. Overall, these alterations occurred at varying degrees in all the muscles analysed, with no correlation between the age-related changes observed and myofiber type composition or muscle topography.

CONCLUSIONS

Our data provide a global view of age-associated neuromuscular changes in a mouse model of ageing and help to advance understanding of contributing pathways leading to development of sarcopenia.

Loss of Immunohistochemical Reactivity in Association With Handling-Induced Dark Neurons in Mouse Brains

The handling-induced dark neuron is a histological artifact observed in brain samples handled before fixation with aldehydes. To explore associations between dark neurons and immunohistochemical alterations in mouse brains, we examined protein products encoded by Cav3 (neuronal perikarya/neurites), Rbbp4 (neuronal nuclei), Gfap (astroglia), and Aif1 (microglia) genes in adjacent tissue sections. Here, dark neurons were incidental findings from our prior project, studying the effects of age and high-fat diet on metabolic homeostasis in male C57BL/6N mice. Available were brains from 4 study groups: middle-aged/control diet, middle-aged/high-fat diet, old/control diet, and old/high-fat diet. Young/control diet mice were used as baseline. The hemibrains were immersion-fixed with paraformaldehyde and paraffin-embedded. In the hippocampal formation, we found negative correlations between dark neuron hyperbasophilia and immunoreactivity for CAV3, RBBP4, and glial fibrillary acidic protein (GFAP) using quantitative image analysis. There was no significant difference in dark neuron hyperbasophilia or immunoreactivity for any protein examined among all groups. In contrast, in the hippocampal fimbria, old age seemed to be associated with higher immunoreactivity for GFAP and allograft inflammatory factor-1. Our findings suggest that loss of immunohistochemical reactivity for CAV3, RBBP4, and GFAP in the hippocampal formation is an artifact associated with the occurrence of dark neurons. The unawareness of dark neurons may lead to misinterpretation of immunohistochemical reactivity alterations.

Neuroprotective activation of astrocytes by methylmercury exposure in the inferior colliculus

Methylmercury (MeHg) is well known to induce auditory disorders such as dysarthria. When we performed a global analysis on the brains of mice exposed to MeHg by magnetic resonance imaging, an increase in the T1 signal in the inferior colliculus (IC), which is localized in the auditory pathway, was observed. Therefore, the purpose of this study is to examine the pathophysiology and auditory dysfunction induced by MeHg, focusing on the IC. Measurement of the auditory brainstem response revealed increases in latency and decreases in threshold in the IC of mice exposed to MeHg for 4 weeks compared with vehicle mice. Incoordination in MeHg-exposed mice was noted after 6 weeks of exposure, indicating that IC dysfunction occurs earlier than incoordination. There was no change in the number of neurons or microglial activity, while the expression of glial fibrillary acidic protein, a marker for astrocytic activity, was elevated in the IC of MeHg-exposed mice after 4 weeks of exposure, indicating that astrogliosis occurs in the IC. Suppression of astrogliosis by treatment with fluorocitrate exacerbated the latency and threshold in the IC evaluated by the auditory brainstem response. Therefore, astrocytes in the IC are considered to play a protective role in the auditory pathway. Astrocytes exposed to MeHg increased the expression of brain-derived neurotrophic factor in the IC, suggesting that astrocytic brain-derived neurotrophic factor is a potent protectant in the IC. This study showed that astrogliosis in the IC could be an adaptive response to MeHg toxicity. The overall toxicity of MeHg might be determined on the basis of the balance between MeHg-mediated injury to neurons and protective responses from astrocytes.

The anticonvulsant effect of a polysaccharide-rich extract from Genipa americana leaves is mediated by GABA receptor

BACKGROUND

This study aimed to chemically characterize a polysaccharide-rich extract (PRE) obtained from Genipa americana leaves and evaluate its neuroprotective effect in the brain morphology and oxidative markers using mice behavioral models.

METHODS

Dry powder (5 g) of G. americana leaves were submitted to depigmentation in methanol. PRE was obtained by extraction in NaOH and precipitation with absolute ethanol and characterized by infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H and ¹³C NMR). Swiss mice (25-35 g) received saline (0.9% NaCl) or PRE (1-27 mg/kg) by intraperitoneal (i.p.) route, 30 min before evaluation in behavioral models (open field, elevated plus maze, sleeping time, tail suspension, forced swimming, seizures induced by pentylenetetrazole-PTZ). Animal's brain were dissected and analyzed for histological alterations and oxidative stress.

RESULTS

FTIR spectrum showed bands around 3417 cm^-1 and 2928 cm^-1, relative to the vibrational stretching of OH and CH, respectively. ¹H NMR spectrum revealed signals at δ 3.85 (methoxyl groups) and δ 2.4 (acetyl) ppm. ¹³C NMR spectrum revealed signals at δ 108.0 and δ 61.5 ppm, corresponding to C1 and C5 of α-L-arabinofuranosyl residues. PRE presented central inhibitory effect, increasing the latency for PTZ-induced seizures by 63% (9 mg/kg) and 55% (27 mg/kg), and the latency to death by 73% (9 mg/kg) and 72% (27 mg/kg). Both effects were reversed by the association with flumazenil.

CONCLUSIONS

PRE, containing a heteropolysaccharide, presents antioxidant and anticonvulsant effect in the model of PTZ-induced seizures via gamma-aminobutyric acid (GABA), decreasing the number of hippocampal black neurons.

Effects of GSM and UMTS mobile telephony signals on neuron degeneration and blood-brain barrier permeation in the rat brain

Blood-brain barrier (BBB) permeation and neuron degeneration were assessed in the rat brain following exposure to mobile communication radiofrequency (RF) signals (GSM-1800 and UMTS-1950). Two protocols were used: (i) single 2 h exposure, with rats sacrificed immediately, and 1 h, 1, 7, or 50 days later, and (ii) repeated exposures (2 h/day, 5 days/week, for 4 weeks) with the effects assessed immediately and 50 days after the end of exposure. The rats' heads were exposed at brain-averaged specific absorption rates (BASAR) of 0.026, 0.26, 2.6, and 13 W/kg. No adverse impact in terms of BBB leakage or neuron degeneration was observed after single exposures or immediately after the end of repeated exposure, with the exception of a transient BBB leakage (UMTS, 0.26 W/kg). Fifty days after repeated exposure, the occurrence of degenerating neurons was unchanged on average. However, a significant increased albumin leakage was detected with both RF signals at 13 W/kg. In this work, the strongest, delayed effect was induced by GSM-1800 at 13 W/kg. Considering that 13 W/kg BASAR in the rat head is equivalent to 4 times as much in the human head, deleterious effects may occur following repeated human brain exposure above 50 W/kg.

In vivo detection of hyperacute neuronal compaction and recovery by MRI following electric trauma in rats

PURPOSE

To verify the following phenomenon in vivo using quantitative magnetic resonance imaging (MRI). Neuronal compression may occur following brain injuries in the cortex and hippocampus. As well being characterized by previous histological studies in rats, the majority of these neurons undergo hyperacute recovery rather than apoptotic death.

MATERIALS AND METHODS

Twenty male Wistar rats were assigned into injured or sham-injured groups (n = 10). The injured group underwent an electric trauma model to provoke compacted neuron formation. A T1 map was acquired prior to the injury and 10 T1 maps were acquired consecutively over a period of 2.5 hours after the injury, using a 3.0T scanner. Voxelwise statistical analyses were performed between timepoints. To enable comparison with the histological appearance of the compacted neurons, silver staining was performed on a sham-injured rat and five injured rats, 10, 40, 90, 150, and 300 minutes after the injury.

RESULTS

A significant (corrected P < 0.05) increase in average T1 from the preinjury (895.24 msec) to the first postinjury timepoint (T1  = 951.37 msec) was followed by a significant (corrected P < 0.05) decrease (return) up to the last postinjury timepoint (T1  = 913.16 msec) in the voxels of the cortex and hippocampus. No significant (corrected P < 0.05) change in T1 was found in the sham-injured group.

CONCLUSION

The spatial and temporal linkages between the MRI T1 changes and the histological findings suggest that neuronal compaction and recovery is associated with T1 alterations. MRI therefore offers the possibility of in vivo investigations of neuronal compaction and recovery. J. MAGN. RESON. IMAGING 2016;44:814-822.

Increased Expression of Osteopontin in the Degenerating Striatum of Rats Treated with Mitochondrial Toxin 3-Nitropropionic Acid: A Light and Electron Microscopy Study

The mycotoxin 3-nitropropionic acid (3NP) is an irreversible inhibitor that induces neuronal damage by inhibiting mitochondrial complex II. Neurodegeneration induced by 3NP, which is preferentially induced in the striatum, is caused by an excess influx and accumulation of calcium in mitochondria. Osteopontin (OPN) is a glycosylated phosphoprotein and plays a role in the regulation of calcium precipitation in the injured brain. The present study was designed to examine whether induction of OPN protein is implicated in the pathogenesis of 3NP-induced striatal neurodegeneration. We observed overlapping regional expression of OPN, the neurodegeneration marker Fluoro-Jade B, and the microglial marker ionized calcium-binding adaptor molecule 1 (Iba1) in the 3NP-lesioned striatum. OPN expression was closely associated with the mitochondrial marker NADH dehydrogenase (ubiquinone) flavoprotein 2 in the damaged striatum. In addition, immunoelectron microscopy demonstrated that OPN protein was specifically localized to the inner membrane and matrix of the mitochondria in degenerating striatal neurons, and cell fragments containing OPN-labeled mitochondria were also present within activated brain macrophages. Thus, our study revealed that OPN expression is associated with mitochondrial dysfunction produced by 3NP-induced alteration of mitochondrial calcium homeostasis, suggesting that OPN is involved in the pathogenesis of striatal degeneration by 3NP administration.

Sleep deprivation does not affect neuronal susceptibility to mild traumatic brain injury in the rat

Mild and moderate traumatic brain injuries (TBIs) (and concussion) occur frequently as a result of falls, automobile accidents, and sporting activities, and are a major cause of acute and chronic disability. Fatigue and excessive sleepiness are associated with increased risk of accidents, but it is unknown whether prior sleep debt also affects the pathophysiological outcome of concussive injury. Using the "dark neuron" (DN) as a marker of reversible neuronal damage, we tested the hypothesis that acute (48 hours) total sleep deprivation (TSD) and chronic sleep restriction (CSR; 10 days, 6-hour sleep/day) affect DN formation following mild TBI in the rat. TSD and CSR were administered using a walking wheel apparatus. Mild TBI was administered under anesthesia using a weight-drop impact model, and the acute neuronal response was observed without recovery. DNs were detected using standard bright-field microscopy with toluidine blue stain following appropriate tissue fixation. DN density was low under home cage and sleep deprivation control conditions (respective median DN densities, 0.14% and 0.22% of neurons), and this was unaffected by TSD alone (0.1%). Mild TBI caused significantly higher DN densities (0.76%), and this was unchanged by preexisting acute or chronic sleep debt (TSD, 0.23%; CSR, 0.7%). Thus, although sleep debt may be predicted to increase the incidence of concussive injury, the present data suggest that sleep debt does not exacerbate the resulting neuronal damage.

Hypoxia/ischemia a key player in early post stroke seizures: modulation by opioidergic and nitrergic systems

Stroke is a leading cause of death, disability, and socioeconomic loss worldwide. All attempts at pharmacological reduction of the complications of stroke (e.g. post-stroke seizure, and brain׳s vulnerability to hypoxic/ischemic injury) have failed. Endogenous opioids and nitric oxide (NO) overproduction has been documented in brain hypoxia/ischemia (H/I), which can exert pro-convulsive effects. In this study, we aimed to examine the possible involvement of opioidergic and nitrergic pathways in the pathogenesis of post-stroke seizure. H/I was induced by right common carotid ligation and sham-operated mice served as controls. We demonstrated that right common carotid ligation decreases the threshold for clonic seizures induced by pentylenetetrazole (PTZ), a GABA antagonist. Furthermore, pro-convulsive effect of H/I following right common carotid ligation was blocked by naltrexone (NTX) (3mg/kg), NG-Nitro-l-arginine methyl ester (l-NAME) (10mg/kg), and aminoguanidine (AG) (100mg/kg) administration (P<0.001). Interestingly, co-administration of non-effective doses of NTX and l-NAME (1 and 0.5mg/kg, respectively) reverses epileptogenesis of H/I (P<0.001). In the same way, co-administration of non-effective doses of NTX and AG (1 and 5mg/kg, respectively), reverses epileptogenesis of H/I (P<0.001). Indeed, the histological studies performed on mice exposed to H/I confirmed our previous data. These findings suggest hyper-susceptibility to PTZ induced seizure following H/I is mediated by interaction of opioidergic, and iNOS/NO pathways. Therefore, our results identify new pharmacological targets and provide the rationale for a novel strategy to promote recovery after stroke and possibly other brain injuries.

Blast TBI Models, Neuropathology, and Implications for Seizure Risk

Traumatic brain injury (TBI) due to explosive blast exposure is a leading combat casualty. It is also implicated as a key contributor to war related mental health diseases. A clinically important consequence of all types of TBI is a high risk for development of seizures and epilepsy. Seizures have been reported in patients who have suffered blast injuries in the Global War on Terror but the exact prevalence is unknown. The occurrence of seizures supports the contention that explosive blast leads to both cellular and structural brain pathology. Unfortunately, the exact mechanism by which explosions cause brain injury is unclear, which complicates development of meaningful therapies and mitigation strategies. To help improve understanding, detailed neuropathological analysis is needed. For this, histopathological techniques are extremely valuable and indispensable. In the following we will review the pathological results, including those from immunohistochemical and special staining approaches, from recent preclinical explosive blast studies.

Transcriptomic analyses of neurotoxic effects in mouse brain after intermittent neonatal administration of thimerosal

Thimerosal is a vaccine antimicrobial preservative which has long been suspected an iatrogenic factor possibly contributing to neurodevelopmental disorders including autism. The association between infant vaccine thimerosal exposure and autism remains an open question. Although thimerosal has been removed from mandatory childhood vaccines in the United States, thimerosal-preserved vaccines are still widely used outside of the United States especially in developing countries. Notably, thimerosal-containing vaccines are being given to the newborns within the first 12-24 h after birth in some countries. To examine the possible neurotoxic effects of early neonatal exposure to a higher level of thimerosal, FVB mice were subcutaneously injected with thimerosal-mercury at a dose which is 20× higher than that used for regular Chinese infant immunization during the first 4 months of life. Thimerosal-treated mice exhibited neural development delay, social interaction deficiency, and inclination of depression. Apparent neuropathological changes were also observed in adult mice neonatally treated with thimerosal. High-throughput RNA sequencing of autistic-behaved mice brains revealed the alternation of a number of canonical pathways involving neuronal development, neuronal synaptic function, and the dysregulation of endocrine system. Intriguingly, the elevation of anterior pituitary secreting hormones occurred exclusively in male but not in female thimerosal-treated mice, demonstrating for the first time the gender bias of thimerosal-mercury toxicity with regard to endocrine system. Our results indicate that higher dose of neonatal thimerosal-mercury (20× higher than that used in human) is capable of inducing long-lasting substantial dysregulation of neurodevelopment, synaptic function, and endocrine system, which could be the causal involvements of autistic-like behavior in mice.

Neuronal hypoxia induces Hsp40-mediated nuclear import of type 3 deiodinase as an adaptive mechanism to reduce cellular metabolism

In neurons, the type 3 deiodinase (D3) inactivates thyroid hormone and reduces oxygen consumption, thus creating a state of cell-specific hypothyroidism. Here we show that hypoxia leads to nuclear import of D3 in neurons, without which thyroid hormone signaling and metabolism cannot be reduced. After unilateral hypoxia in the rat brain, D3 protein level is increased predominantly in the nucleus of the neurons in the pyramidal and granular ipsilateral layers, as well as in the hilus of the dentate gyrus of the hippocampal formation. In hippocampal neurons in culture as well as in a human neuroblastoma cell line (SK-N-AS), a 24 h hypoxia period redirects active D3 from the endoplasmic reticulum to the nucleus via the cochaperone Hsp40 pathway. Preventing nuclear D3 import by Hsp40 knockdown resulted an almost doubling in the thyroid hormone-dependent glycolytic rate and quadrupling the transcription of thyroid hormone target gene ENPP2. In contrast, Hsp40 overexpression increased nuclear import of D3 and minimized thyroid hormone effects in cell metabolism. In conclusion, ischemia/hypoxia induces an Hsp40-mediated translocation of D3 to the nucleus, facilitating thyroid hormone inactivation proximal to the thyroid hormone receptors. This adaptation decreases thyroid hormone signaling and may function to reduce ischemia-induced hypoxic brain damage.

Assessment of CA1 injury after global ischemia using supervised 2D analyses of nuclear pyknosis

Selective neuronal vulnerability is a common theme in both acute and chronic diseases affecting the nervous system. This phenomenon is particularly conspicuous after global cerebral ischemia wherein CA1 pyramidal neurons undergo delayed death while surrounding hippocampal regions are relatively spared. While injury in this model can be easily demonstrated using either histological or immunological stains, current methods used to assess the cellular injury present in these biological images lack the precision required to adequately compare treatment effects. To address this shortcoming, we devised a supervised work-flow that can be used to quantify ischemia-induced nuclear condensation using microscopic images. And while we demonstrate the utility of this technique using models of ischemic brain injury, the approach can be readily applied to other paradigms in which programmed cell death is a major component.

A cytoplasmic gel network capable of mediating the conversion of chemical energy to mechanical work in diverse cell processes: a speculation

Enigmatic morphological features of the formation and fate of "dark" (hyper-basophilic, hyper-argyrophilic and hyper-electrondense) neurons suggest that the mechanical work causing their dramatic shrinkage (whole-cell ultrastructural compaction) is done by a previously "unknown" ultrastructural component residing in the spaces between their "known" (i.e. visible in the conventional transmission electron microscopy) ultrastructural constituents. Embedment-free section electron microscopy revealed in these spaces the existence of a continuous network of gel microdomains, which is embedded in a continuous network of fluid-filled lacunae. We gathered experimental facts suggesting that this gel network is capable of a volume-reducing phase-transition (an established physico-chemical phenomenon), which could be the motor of the whole-cell ultrastructural compaction. The present paper revisits our relevant observations and speculates how such a continuous whole-cell gel network can do both whole-cell and compartmentalized mechanical work.

The effect of repetitive spreading depression on neuronal damage in juvenile rat brain

Spreading depression (SD) is pronounced depolarization of neurons and glia that travels slowly across brain tissue followed by massive redistribution of ions between intra- and extracellular compartments. There is a relationship between SD and some neurological disorders. In the present study the effects of repetitive SD on neuronal damage in cortical and subcortical regions of juvenile rat brain were investigated. The animals were anesthetized and the electrodes as well as cannula were implanted over the brain. SD-like event was induced by KCl injection. The brains were removed after 2 or 4 weeks after induction of 2 or 4 SD-like waves (with interval of 1 week), respectively. Normal saline was injected instead of KCl in sham group. For stereological study, paraffin-embedded brains were cut in 5 microm sections. The sections were stained with Toluidine Blue to measure the volume-weighted mean volume of normal neurons and the numerical density of dark neurons. The volume-weighted mean volume of normal neurons in the granular layer of the dentate gyrus and layer V of the temporal cortex in SD group were significantly decreased after four repetitive SD. Furthermore, densities of dark neurons in the granular layer of the dentate gyrus (after 2 weeks), the caudate-putamen, and layer V of the temporal cortex (after 4 weeks) were significantly increased in SD group. Repetitive cortical SD in juvenile rats may cause neuronal damage in cortical and subcortical areas of the brain. This may important in pathophysiology of SD-related neurological disorders.

Increased blood-brain barrier permeability in mammalian brain 7 days after exposure to the radiation from a GSM-900 mobile phone

Microwaves were for the first time produced by humans in 1886 when radio waves were broadcasted and received. Until then microwaves had only existed as a part of the cosmic background radiation since the birth of universe. By the following utilization of microwaves in telegraph communication, radars, television and above all, in the modern mobile phone technology, mankind is today exposed to microwaves at a level up to 10(20) times the original background radiation since the birth of universe. Our group has earlier shown that the electromagnetic radiation emitted by mobile phones alters the permeability of the blood-brain barrier (BBB), resulting in albumin extravasation immediately and 14 days after 2h of exposure. In the background section of this report, we present a thorough review of the literature on the demonstrated effects (or lack of effects) of microwave exposure upon the BBB. Furthermore, we have continued our own studies by investigating the effects of GSM mobile phone radiation upon the blood-brain barrier permeability of rats 7 days after one occasion of 2h of exposure. Forty-eight rats were exposed in TEM-cells for 2h at non-thermal specific absorption rates (SARs) of 0mW/kg, 0.12mW/kg, 1.2mW/kg, 12mW/kg and 120mW/kg. Albumin extravasation over the BBB, neuronal albumin uptake and neuronal damage were assessed. Albumin extravasation was enhanced in the mobile phone exposed rats as compared to sham controls after this 7-day recovery period (Fisher's exact probability test, p=0.04 and Kruskal-Wallis, p=0.012), at the SAR-value of 12mW/kg (Mann-Whitney, p=0.007) and with a trend of increased albumin extravasation also at the SAR-values of 0.12mW/kg and 120mW/kg. There was a low, but significant correlation between the exposure level (SAR-value) and occurrence of focal albumin extravasation (r(s)=0.33; p=0.04). The present findings are in agreement with our earlier studies where we have seen increased BBB permeability immediately and 14 days after exposure. We here discuss the present findings as well as the previous results of altered BBB permeability from our and other laboratories.

Pharmacologic analysis of the mechanism of dark neuron production in cerebral cortex

Dark neurons have plagued the interpretation of brain tissue sections, experimentally and clinically. Seen only when perturbed but living tissue is fixed in aldehydes, their mechanism of production is unknown. Since dark neurons are seen in cortical biopsies, experimental ischemia, hypoglycemia, and epilepsy, we surmised that glutamate release and neuronal transmembrane ion fluxes could be the perturbation leading to dark neuron formation while the fixation process is underway. Accordingly, we excised biopsies of rat cortex to simulate neurosurgical production of dark neurons. To ascertain the role of glutamate, blockade of N-methyl-D-aspartate (NMDA) and non-NMDA receptors was done prior to formaldehyde fixation. To assess the role of transmembrane sodium ion (and implicitly, water) fluxes, tetraethylammonium (TEA) was used. Blockade of NMDA receptors with MK-801 and non-NMDA receptors with the quinoxalinediones (CNQX and NBQX) abolished dark neuron formation. More delayed exposure of the tissue to the antagonist, CNQX, by admixing it with the fixative directly, allowed for some production of dark neurons. Aminophosphonoheptanoate (APH), perhaps due to its polarity, and TEA, did not prevent dark neurons, which were abundant in control formaldehyde fixed material unexposed to either receptor or ion channel antagonists. The results demonstrate a role for the pharmacologic subtypes of glutamate receptors in the pathogenetic mechanism of dark neuron formation. Our results are consistent with the appearance of dark neurons in biopsy where the cerebral cortex has been undercut, and rendered locally ischemic and hypoglycemic, as well as in epilepsy, hypoglycemia, and ischemia, all of which lead to glutamate release. Rather than a pressure-derived mechanical origin, we suggest that depolarization, glutamate release or receptor activation are more likely mechanisms of dark neuron production.

The mode of death of epilepsy-induced "dark" neurons is neither necrosis nor apoptosis: an electron-microscopic study

Morphological aspects of the formation and fate of neurons that underwent dramatic ultrastructural compaction ("dark" neurons) induced by 4-aminopyridine epilepsy were compared in an excitotoxic and a neighboring normal-looking area of the rat brain cortex. In the excitotoxic area, the later the ultrastructural compaction began after the outset of epilepsy, the higher the degree of mitochondrial swelling and ribosomal sequestration were; a low proportion of the affected neurons recovered in 1 day; the others were removed from the tissue through a necrotic-like sequence of ultrastructural changes (swelling of the cell, gradual disintegration of the intracellular organelles and dispersion of their remnants into the surroundings through large gaps in the plasma and nuclear membranes). In the normal-looking area, the ultrastructural elements in the freshly-formed "dark" neurons were apparently normal; most of them recovered in 1 day; the others were removed from the tissue through an apoptotic-like sequence of ultrastructural changes (the formation of membrane-bound, electrondense, compact cytoplasmic protrusions, and their braking up into membrane-bound, electrondense, compact fragments, which were swallowed by phagocytotic cells). Since these ultrastructural features differ fundamentally from those characteristic of necrosis, it seems logical that, in stark contrast with the prevailing conception, the cause of death of the epilepsy-induced "dark" neurons in the normal-looking cortical area cannot be necrosis. An apoptotic origin can also be precluded by virtue of the absence of its characteristics. As regards the excitotoxic environment, it is assumed that pathobiochemical processes in it superimpose a necrotic-like removal process on already dead "dark" neurons.