Ischemia in the dorsal hippocampus is associated with acute extracellular release of dopamine and norepinephrine

The Locus Coeruleus Noradrenaline System in Delirium

Delirium is a brain state involving severe brain dysfunction affecting cognitive and attentional capacities. Our opinion statement review aims to elucidate the relationship between abnormal arousal and locus coeruleus (LC) activity in cognitive dysfunction and inattention in delirium states. We propose (1) that enhanced noradrenaline release caused by altered arousal in hyperactive delirium states leads to increased noradrenergic transmission within the LC and subcortical and cortical brain regions including the prefrontal cortex and hippocampus, thus affecting how attention and cognition function. In hypoactive delirium states, however, we are presuming (2) that less arousal will cause the release of noradrenaline to diminish in the LC, followed by reduced noradrenergic transmission in cortical and subcortical brain areas concentrated within the prefrontal cortex and hippocampus, leading to deficient attention and cognitive processing. Studies addressing the measurement of noradrenaline and its derivatives in biomaterial probes regarding delirium are also covered in this article. In conclusion, the LC-NA system plays a crucial role in generating delirium. Yet there have been no large-scale studies investigating biomarkers of noradrenaline to help us draw conclusions for improving delirium's diagnosis, treatment, and prognosis, and to better understand its pathogenesis.

Glycation Increases the Risk of Microbial Traversal through an Endothelial Model of the Human Blood-Brain Barrier after Use of Anesthetics

The function of the human blood–brain barrier (BBB), consisting mainly of the basement membrane and microvascular endothelial cells, is to protect the brain and regulate its metabolism. Dysfunction of the BBB can lead to increased permeability, which can be linked with several pathologies, including meningitis, sepsis, and postoperative delirium. Advanced glycation end products (AGE) are non-enzymatic, posttranslational modifications of proteins, which can affect their function. Increased AGE levels are strongly associated with ageing and degenerative diseases including diabetes. Several studies demonstrated that the formation of AGE interfere with the function of the BBB and may change its permeability for soluble compounds. However, it is still unclear whether AGE can facilitate microbial traversal through the BBB and how small compounds including anesthetics modulate this process. Therefore, we developed a cellular model, which allows for the convenient testing of different factors and compounds with a direct correlation to bacterial traversal through the BBB. Our results demonstrate that both glycation and anesthetics interfere with the function of the BBB and promote microbial traversal. Importantly, we also show that the essential nutrient and antioxidant ascorbic acid, commonly known as vitamin C, can reduce the microbial traversal through the BBB and partly reverse the effects of AGE.

Relationship Between Serum Norepinephrine Levels at ICU Admission and the Risk of ICU-Acquired Delirium: Secondary Analysis of the Melatonin Evaluation of Lowered Inflammation of ICU Trial

Supplemental Digital Content is available in the text.

Abnormal secretion of catecholamines is well known to cause delirium. In particular, disturbances of catecholamine balance can cause ICU-acquired delirium. The aim of this study was to evaluate the association between the serum levels of catecholamines and the risk of occurrence of ICU-acquired delirium separately in patients who had/had not received exogenous catecholamines before ICU admission.

Do stress markers and anesthetic technique predict delirium in the elderly?

BACKGROUND

Postoperative delirium (PD) is a prevalent complication of elderly surgical patients, which predisposes to worsened cognitive recovery and dementia. Risk of PD has been associated with increasing magnitude of the hypothalamic-pituitary-adrenal stress response (serum cortisol, epinephrine and norepinephrine) to surgery. Anesthetics suppress this response; however, some (total intravenous anesthesia, TIVA) more than others (anesthetic gases). Prior comparisons of anesthetics have been equivocal but have not included stress markers. We hypothesized that TIVA would decrease serum stress markers and the incidence of PD.

METHODS

We performed a prospective cohort study of 76 elderly major surgical patients. Patients received TIVA or sevoflurane gas, and blood was drawn for serum markers pre-, intra-, and postoperatively. PD was assessed with the Confusion Assessment Method. We compared stress markers and PD between patients who received TIVA versus sevoflurane, and then modeled PD including stress and anesthetic.

RESULTS

The group that received TIVA during surgery demonstrated lower levels of all stress markers compared to the gas group, but no difference in PD. However, across groups, the postoperative norepinephrine level was much higher in patients who developed PD. Other markers and other times had no effect.

CONCLUSION

The development of PD depends more on postoperative stress than intraoperative stress or anesthetic.

Neuropathogenesis of delirium: review of current etiologic theories and common pathways

Delirium is a neurobehavioral syndrome caused by dysregulation of neuronal activity secondary to systemic disturbances. Over time, a number of theories have been proposed in an attempt to explain the processes leading to the development of delirium. Each proposed theory has focused on a specific mechanism or pathologic process (e.g., dopamine excess or acetylcholine deficiency theories), observational and experiential evidence (e.g., sleep deprivation, aging), or empirical data (e.g., specific pharmacologic agents' association with postoperative delirium, intraoperative hypoxia). This article represents a review of published literature and summarizes the top seven proposed theories and their interrelation. This review includes the "neuroinflammatory," "neuronal aging," "oxidative stress," "neurotransmitter deficiency," "neuroendocrine," "diurnal dysregulation," and "network disconnectivity" hypotheses. Most of these theories are complementary, rather than competing, with many areas of intersection and reciprocal influence. The literature suggests that many factors or mechanisms included in these theories lead to a final common outcome associated with an alteration in neurotransmitter synthesis, function, and/or availability that mediates the complex behavioral and cognitive changes observed in delirium. In general, the most commonly described neurotransmitter changes associated with delirium include deficiencies in acetylcholine and/or melatonin availability; excess in dopamine, norepinephrine, and/or glutamate release; and variable alterations (e.g., either a decreased or increased activity, depending on delirium presentation and cause) in serotonin, histamine, and/or γ-aminobutyric acid. In the end, it is unlikely that any one of these theories is fully capable of explaining the etiology or phenomenologic manifestations of delirium but rather that two or more of these, if not all, act together to lead to the biochemical derangement and, ultimately, to the complex cognitive and behavioral changes characteristic of delirium.

The importance of systemic response in the pathobiology of blast-induced neurotrauma

Due to complex injurious environment where multiple blast effects interact with the body parallel, blast-induced neurotrauma is a unique clinical entity induced by systemic, local, and cerebral responses. Activation of autonomous nervous system; sudden pressure increase in vital organs such as lungs and liver; and activation of neuroendocrine-immune system are among the most important mechanisms that contribute significantly to molecular changes and cascading injury mechanisms in the brain. It has been hypothesized that vagally mediated cerebral effects play a vital role in the early response to blast: this assumption has been supported by experiments where bilateral vagotomy mitigated bradycardia, hypotension, and apnea, and also prevented excessive metabolic alterations in the brain of animals exposed to blast. Clinical experience suggests specific blast-body-nervous system interactions such as (1) direct interaction with the head either through direct passage of the blast wave through the skull or by causing acceleration and/or rotation of the head; and (2) via hydraulic interaction, when the blast overpressure compresses the abdomen and chest, and transfers its kinetic energy to the body's fluid phase, initiating oscillating waves that traverse the body and reach the brain. Accumulating evidence suggests that inflammation plays important role in the pathogenesis of long-term neurological deficits due to blast. These include memory decline, motor function and balance impairments, and behavioral alterations, among others. Experiments using rigid body- or head protection in animals subjected to blast showed that head protection failed to prevent inflammation in the brain or reduce neurological deficits, whereas body protection was successful in alleviating the blast-induced functional and morphological impairments in the brain.

Progressive multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system, which starts in the majority of patients with a relapsing/remitting MS (RRMS) course , which after several years of disease duration converts into a progressive disease. Since anti-inflammatory therapies and immune modulation exert a beneficial effect at the relapsing/remitting stage of the disease, but not in the progressive stage, the question was raised whether inflammation drives tissue damage in progressive MS at all. We show here that also in progressive MS, inflammation is the driving force for brain injury and that the discrepancy between inflammation-driven tissue injury and response to immunomodulatory therapies can be explained by different pathomechanisms acting in RRMS and progressive MS.

Effects of the noradrenergic system in rat white matter exposed to oxygen-glucose deprivation in vitro

Norepinephrine (NE) is released in excess into the extracellular space during oxygen-glucose deprivation (OGD) in brain, increasing neuronal metabolism and aggravating glutamate excitoxicity. We used isolated rat optic nerve and spinal cord dorsal columns to determine whether the noradrenergic system influences axonal damage in white matter. Tissue was studied electrophysiologically by recording the compound action potential (CAP) before and after exposure to 60 min of OGD at 36 degrees C. Depleting catecholamine stores with reserpine was protective and improved CAP recovery after 1 h of reperfusion from 17% (control) to 35%. Adding NE during OGD decreased CAP recovery to 8%, and adding NE to reserpine during OGD eliminated the protective effect of the latter. Selective inhibitors of Na(+)-dependent norepinephrine transport desipramine and nisoxetine improved recovery to 58% and 44%, respectively. alpha2 adrenergic receptor agonists UK14,304 and medetomidine improved CAP recovery to 41% and 46% after 1 h of OGD. Curiously, alpha2 antagonists alone were also highly protective (e.g., atipamezole: 86% CAP recovery), at concentrations that did not affect baseline excitability. The protective effect of alpha2 receptor modulation was corroborated by imaging fluorescent Ca(2+) and Na(+) indicators within axons during OGD. Both agonists and antagonists significantly reduced axonal Ca(2+) and Na(+) accumulation in injured axons. These data suggest that the noradrenergic system plays an active role in the pathophysiology of axonal ischemia and that alpha2 receptor modulation may be useful against white matter injury.

Pathoetiological model of delirium: a comprehensive understanding of the neurobiology of delirium and an evidence-based approach to prevention and treatment

Delirium is the most common complication found in the general hospital setting. Yet, we know relatively little about its actual pathophysiology. This article contains a summary of what we know to date and how different proposed intrinsic and external factors may work together or by themselves to elicit the cascade of neurochemical events that leads to the development delirium. Given how devastating delirium can be, it is imperative that we better understand the causes and underlying pathophysiology. Elaborating a pathoetiology-based cohesive model to better grasp the basic mechanisms that mediate this syndrome will serve clinicians well in aspiring to find ways to correct these cascades, instituting rational treatment modalities, and developing effective preventive techniques.

Effect of mivazerol, a alpha-agonist, on striatal norepinephrine concentration during transient forebrain ischemia in rats

BACKGROUND

We have previously reported that mivazerol, a alpha(2)-agonist, possibly provides neuroprotection against transient forebrain ischemia in rats. This study was designed to investigate the ability of mivazerol to attenuate ischemia-induced increase in striatal norepinephrine concentration after transient forebrain ischemia in rats.

METHODS

Male Sprague-Dawley rats, anesthetized with halothane, were assigned to one of three groups (n=10 each); control (C, normal saline 1 ml/kg), mivazerol 20 microg/kg (M20), and 40 microg/kg (M40) groups. Monitored variables included temporal muscle temperature (maintained at 37.5+/-0.1 degrees C), electroencephalogram, systolic/diastolic blood pressure, heart rate, arterial blood gases, and blood glucose concentrations. Thirty minutes after subcutaneous drug administration, forebrain ischemia was induced with hemorrhagic hypotension (systolic arterial pressure: 40-50 mmHg) and bilateral carotid artery occlusion for 10 min, and then the brain was reperfused. Norepinephrine concentration in the interstitial fluids in the striatum was analyzed using in vivo microdialysis in combination with high-performance liquid chromatography.

RESULTS

Ischemia resulted in a prompt increase in norepinephrine concentrations in the striatum in all groups. However, there were no significant differences in norepinephrine concentrations in the striatum between the three groups at any period.

CONCLUSIONS

Our results indicate that mivazerol did not attenuate ischemia-induced increase in striatal norepinephrine concentration. This suggests that the possible neuroprotective property of mivazerol is not related to inhibition of norepinephrine release in the brain.

Mechanisms of Brain Injury after Global Cerebral Ischemia

Cerebral ischemia results in a rapid depletion of energy stores that triggers a complex cascade of cellular events such as cellular depolarization and Ca2+ influx, resulting in excitotoxic cell death. The critical determinant of severity of brain injury is the duration and severity of the ischemic insult and early restoration of CBF. Induced therapeutic hypothermia following CA is the only strategy that has demonstrated improvement in outcomes in prospective, randomized clinical trials. Although pharmacologic neuro-protection has been disappointing thus far in a variety of experimental animal models, further research efforts are directed at using some agents that demonstrate marginal or moderate efficacy in combination with hypothermia. Although the signal transduction pathways and intracellular molecular events during cerebral ischemia and reperfusion are complex, potential therapeutic neuroprotective strategies hold promise for the future.

Neuroprotective effect of mivazerol, an alpha 2-agonist, after transient forebrain ischemia in rats

BACKGROUND

We examined whether mivazerol, an alpha2-agonist, had neuroprotective effects after transient forebrain ischemia in rats.

METHODS

Male Sprague-Dawley rats, anesthetized with halothane, were assigned to one of four groups (n=10 each): control (C, normal saline) and mivazerol 10 microg/kg (M10), 20 microg/kg (M20) and 40 microg/kg (M40) groups. Thirty minutes after drug administration, forebrain ischemia was induced with hemorrhagic hypotension and bilateral carotid artery occlusion for 10 min, and then the brain was reperfused. The neurologic outcome was evaluated 24 h, 48 h and 7 days after ischemia, followed by histologic evaluation.

RESULTS

The survival rate during 7 days was significantly lower in group M40 than in groups M10 and M20 (P<0.05). The neurologic outcome was significantly better in groups M10 and M20 than in group M40 7 days after ischemia (P<0.05). The number of intact neurons in hippocampal CA1 was significantly greater in group M20 than in the other groups (P<0.05). Neuronal injury in the neocortex was significantly less in group M20 than in groups C and M40 (P<0.05).

CONCLUSIONS

Our results suggest that mivazerol, up to 20 microg/kg, provides neuroprotective effects, whereas 40 microg/kg may exaggerate neuronal injury after transient forebrain ischemia in rats.

Implication of ionotropic glutamate receptors in the release of noradrenaline in hippocampal CA1 and CA3 subregions under oxygen and glucose deprivation

A strong linkage between adrenergic and glutamatergic systems exists in the CNS but it is still unclear whether the excessive release of noradrenaline under ischemic conditions is modulated by excitatory amino acids. We studied the effect of selective glutamate receptor antagonists on the release of [3H]noradrenaline evoked by glucose and oxygen deprivation in hippocampal CA1, CA3 and dentate gyrus subregions. The release of glutamate, aspartate and GABA was measured by HPLC. Omission of oxygen and glucose increased the release of [3H]noradrenaline as well as the release of amino acids. Maximum effect on noradrenaline release was observed in CA1 region. The relative increase of the release after 30 min energy deprivation (R(2)) versus the basal release under normal conditions (R(1)), i.e. the R(2)/R(1) ratio was 7.1+/-1.0, 3.87+/-0.4 and 3.26+/-0.27 for CA1, CA3 and dentate gyrus, respectively. The [3H]noradrenaline outflow in response to glucose and oxygen deprivation was abolished at low temperature, but not by Ca(2+) removal, suggesting a cytoplasmic release process. In CA1 and CA3 [3H]noradrenaline release was significantly attenuated by MK-801, an NMDA receptor antagonist. The AMPA receptor antagonist GYKI-53784 had no effect in CA3, but partly reduced noradrenaline release in CA1. Our results suggest that ionotropic glutamate receptors seem to be implicated in the massive cytoplasmic release of noradrenaline in CA1 what may contribute to its selective vulnerability.

The Effect of Sevoflurane and Propofol on Cerebral Neurotransmitter Concentrations During Cerebral Ischemia in Rats

Sevoflurane and propofol are neuroprotective possibly by attenuating central or peripheral catecholamines. We evaluated the effect of these anesthetics on circulating catecholamines and brain neurotransmitters during ischemia in rats. Forty male Sprague-Dawley rats were randomly assigned to one of the following treatment groups: fentanyl and N(2)O/O(2) (control), 2.0% sevoflurane, 0.8-1.2 mg x kg(-1) x min(-1) of propofol, and sham-operated rats with fentanyl and N(2)O/O(2). Ischemia (30 min) was produced by unilateral common carotid artery occlusion plus hemorrhagic hypotension to a mean arterial blood pressure of 32 +/- 2 mm Hg. Pericranial temperature, arterial blood gases, and pH value were maintained constant. Cerebral catecholamine and glutamate concentrations, sampled by microdialysis, and plasma catecholamine concentrations were analyzed using high-pressure liquid chromatography. During ischemia, circulating catecholamines were almost completely suppressed by propofol but only modestly decreased with sevoflurane. Sevoflurane and propofol suppressed brain norepinephrine concentration increases by 75% and 58%, respectively, compared with controls. Intra-ischemia cerebral glutamate concentration was decreased by 60% with both sevoflurane and propofol. These results question a role of circulating catecholamines as a common mechanism for cerebral protection during sevoflurane and propofol. A role of brain tissue catecholamines in mediating ischemic injury is consistent with our results.

IMPLICATIONS

During incomplete cerebral ischemia, the neuroprotective anesthetics sevoflurane and propofol suppressed cerebral increases in norepinephrine and glutamate concentrations. In contrast, propofol, but not sevoflurane, suppressed the ischemia-induced increase in circulating catecholamines to baseline levels. The results question a role for plasma catecholamines in cerebral ischemic injury.

Mechanisms of ischemic brain damage

Neurologic complications from cerebral ischemia occur frequently following cardiac arrest, as well as in the perioperative period in cardiac surgery. The cellular and molecular mechanisms of cerebral ischemia are complex. This article discusses several important cell death and salvage pathways that are important in experimental cerebral ischemia that may be critical to outcome in clinical brain injury.

Potent sigma 1-receptor ligand 4-phenyl-1-(4-phenylbutyl) piperidine provides ischemic neuroprotection without altering dopamine accumulation in vivo in rats

The in vivo signaling of ischemic neuroprotection provided by sigma-receptor ligands remains unclear. Catecholamines have been implicated in the propagation of ischemic neuronal injury, and previous in vitro studies suggest that sigma ligands modulate dopaminergic neurotransmission. In this study, we tested the hypothesis that the potent sigma(1)-receptor ligand 4-phenyl-1-(4-phenylbutyl) piperidine (PPBP) attenuates the increase of extracellular dopamine in ischemic striatum. Under controlled physiological conditions, a microdialysis probe was implanted in right caudoputamen (CP) complex of adult male Wistar rats. Rats were subjected to 2 h of transient middle cerebral artery occlusion (MCAO) by the intraluminal suture technique. In a blinded, randomized fashion, rats were divided into five treatment groups: Group 1 (n = 8; saline-saline) continuous i.v. infusion of saline vehicle 30 min before MCAO followed by saline at reperfusion until the end of the experiment; Group 2 (n = 8; PPBP-PPBP) i.v. PPBP 30 min before MCAO followed by 1 micromol x kg(-1) x h(-1) of PPBP; Group 3 (n = 8; saline-PPBP) i.v. saline before MCAO followed by PPBP; Group 4 (n = 4) surgical shams (saline-saline); and Group 5 (n = 4) surgical shams (PPBP-PPBP). Infarction volume at 22 h of reperfusion in the CP complex (percentage of ipsilateral structure) was significantly attenuated in rats treated with PPBP-PPBP (27.3% +/- 9.1%) and saline-PPBP (27.8% +/- 12.7%) compared with saline-saline (59.3% +/- 7.3%) treatment. There was a three- to fourfold increase in dopamine concentrations in the microdialysates within 40 min of the onset of MCAO. Dopamine and its metabolites dihydroxy phenylacetic acid and homovallinic acid levels were similar among the three groups subjected to MCAO. Therefore, PPBP provides significant ischemic neuroprotection in the CP complex without altering the acute accumulation of dopamine in vivo during transient focal ischemia in the rat.

Glial cell line-derived neurotrophic factor modulates ischemia-induced tyrosine hydroxylase expression in rat hippocampus

Recently, we have reported that glial cell line-derived neurotrophic factor (GDNF), which supports the survival of dopaminergic neurons, prevents delayed neuronal death in the hippocampal CA1 region induced by transient forebrain ischemia. In the present study, we examined the role of GDNF in the expression of tyrosine hydroxylase (TH) mRNA induced by transient forebrain ischemia in rats. The expression of TH mRNA was increased in a time-dependent manner, with a significant increase in 24 h to 7 days, in the hippocampus after induction of transient forebrain ischemia, as determined using the reverse transcription and polymerase chain reaction method. Although it has been suggested that the increase of dopamine beta-hydroxylase mRNA expression correlates with the activation of noradrenergic neurons, no increase of dopamine beta-hydroxylase mRNA in the hippocampus was observed in our system. Western blot analysis revealed that TH protein, but not dopamine beta-hydroxylase protein, was produced in a time-dependent manner in the hippocampus during the ischemia. Interestingly, the induction level of TH mRNA was reduced by intrahippocampal microinjection of GDNF (1.0 microg), and this local GDNF treatment also reduced the increase of TH-like immunohistochemistry-positive terminals in the hippocampus. In contrast, local GDNF treatment of normal rats increased the TH mRNA expression at 6-12 h. These findings suggest that GDNF protects against neuronal degeneration including delayed neuronal death in the hippocampal CA1 region by modulating the expression levels of TH mRNA and protein.

Antioxidant LY231617 enhances electrophysiologic recovery after global cerebral ischemia in dogs

OBJECTIVE

The potent antioxidant LY231617 (2,6-bis(1,1-dimethylethyl)-4-[[(1-ethyl)amino]methyl]phenol hydrochloride) is cytoprotective in models of focal and global cerebral ischemia. We tested the hypothesis that administration of LY231617, before the insult, would improve recovery of cerebral electrical activity and metabolic function after transient global cerebral ischemia by improving cerebral blood flow (CBF) during the reperfusion period.

DESIGN

Randomized, controlled, prospective study.

SETTING

Research laboratory at a university teaching hospital.

SUBJECTS

Twenty-four male beagle dogs.

INTERVENTIONS

All experiments were performed under pentobarbital anesthesia and controlled conditions of normoxia, normocarbia, and normothermia. Twelve control dogs received 20 mL/kg saline (vehicle) bolus into the right atrium and 0.01 mL/kg/min i.v., beginning 20 mins before 13 mins of global cerebral ischemia (by aortic occlusion). The dogs in the drug-treated group received LY231617 as a 10-mg/kg bolus 20 mins before ischemia and 5 mg/kg/hr throughout reperfusion (n = 12). CBF was measured using radiolabeled microspheres.

MEASUREMENTS AND MAIN RESULTS

Total CBF, cerebral oxygen consumption, and somatosensory evoked potentials (SEP) were measured during 240 mins of reperfusion. CBF was similar in both vehicle- and LY231617-treated animals at baseline and throughout the experimental period. In all animals, SEP became isoelectric between 60 and 100 secs after cross-clamping of the ascending aorta. SEP amplitude recovery was significantly higher in drug-treated animals compared with controls (73%+/-15% vs. 39%+/-14% [mean+/-SEM] from baseline at 120 mins [p<.05] and 86%+/-12% vs. 49%+/-14% from baseline at 240 mins [p< .05]).

CONCLUSIONS

LY231617 improves recovery of cerebral electrical function after complete transient global ischemia via mechanisms unrelated to cerebral circulatory effects.

Effects of norepinephrine on NMDA-induced neurotoxicity in cerebellar granular cell culture of rat pups

In this study, norepinephrine was tested in 0.1, 1, 10, 25 and 50 microM doses in 100 microM NMDA toxicity on cerebellar granular cell culture of rats. NMDA in 100 microM concentration induced cell death significantly with respect to controls. Death cell population was 1.08 +/- 0.44% in control and 22.15 +/- 2.46% in 100 microM NMDA (P < 0.0001). None of the norepinephrine concentrations administrated 15 min prior to NMDA was able to reduce death cell scores to control levels. Results were 8.75 +/- 0.83% in 0.1 microM, 7.0 +/- 1.01% in 1 microM, 17.25 +/- 1.31% in 10 microM, 35.5 +/- 1.38% in 25 microM and 17.9 +/- 1.72% in 50 microM norepinephrine plus 100 microM NMDA administrated groups (P < 0.0001 for all with respect to control). Labetalol, as an alpha and beta blocker in 0.5 microM concentration which was given 15 min prior to norepinephrine was able to block the effects of it. In comparison with 100 microM NMDA administered group, only low doses of norepinephrine reduced the death cell scores significantly (for 0.1 and 1 microM norepinephrine plus NMDA groups; P < 0.0001). For 10 and 50 microM norepinephrine plus NMDA groups, death cell scores were found statistically insignificant from the NMDA-administered group (P > 0.05 for both) while for the 25 microM norepinephrine plus NMDA group, the death cell score was found to be statistically increased (P < 0.0001).

Characteristics of the NMDA receptor modulating hypoxia/hypoglycaemia-induced rat striatal dopamine release in vitro

We investigated the functional characteristics of the NMDA receptor that modulates hypoxia/hypoglycaemia-induced striatal dopamine release. Dopamine release was detected by fast cyclic voltammetry in rat neostriatal slices. Four variables were measured: T(on) -- time from initiation of hypoxia/hypoglycaemia to the onset of dopamine release, Tpk -- time from onset to maximum, deltaDA/delta(t) -- rate of dopamine release and DAmax -- maximum extracellular dopamine concentration. In controls, T(on) = 164.9 +/- 1.7 s, Tpk = 20.9 +/- 0.9 s, deltaDA/delta(t) = 5.31 +/- 0.44 microM/s and DAmax = 79.1 +/- 2.5 microM (means +/- S.E.M., n = 203). Cis-4-(phosphonomethyl)piperidine-2-carboxylic acid (CGS 19755, 20 microM) lengthened, while N-methyl-D-aspartate (NMDA) (100 microM) shortened T(on). (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,1 0-imine hydrogen maleate (MK 801, 1 and 10 microM) and dextromethorphan (10 and 100 microM) increased Tpk and decreased DAmax. Neither glycine (100 microM), 7-chlorokynurenic acid (50 microM) nor 5-nitro-6,7-dichloro-1,4-dihydroquinoxaline-2,3-dione (ACEA 1021, 100 microM) had any effect although 7-chlorokynurenic acid blocked the effect of NMDA. Increasing [Mg2+] from 1.3 to 3.7 mM, increased Tpk and decreased deltaDA/delta(t). Dithiothreitol (1 mM) accelerated T(on) while 5.5-dithio-bis-(2-nitrobenzoic acid) (1 mM) delayed T(on). Neither drug affected Tpk, DAmax or deltaDA/delta(t). Neither spermidine (100 microM) nor arcaine (100 microM) affected T(on), Tpk or deltaDA/delta(t) although arcaine decreased DAmax. In conclusion, hypoxia/hypoglycaemia-induced dopamine release was influenced by an NMDA receptor although modulation of the glycine recognition site of the receptor was ineffective, as were agents acting at polyamine modulatory zones. These findings highlight differences between recombinant and native NMDA receptors and suggest caution in extrapolating molecular biology to functional studies.

Sodium channel blockade unmasks two temporally distinct mechanisms of striatal dopamine release during hypoxia/hypoglycaemia in vitro

Massive striatal dopamine release during cerebral ischaemia has been implicated in the resulting neuronal damage. Sodium influx is an early event in the biochemical cascade during ischaemia and blockade of sodium channels may increase resistance to ischaemia by reducing energy demand involved in compensation for sodium and potassium fluxes. In this study, we have determined the effects of opening and blockade of voltage-gated sodium channels on hypoxia/hypoglycaemia-induced dopamine release. Slices of rat caudate nucleus were maintained in a slice chamber superfused by an oxygenated artificial cerebrospinal fluid containing 4 mM glucose. Ischaemia (hypoxia/hypoglycaemia) was mimicked by a switch to a deoxygenated artificial cerebrospinal fluid containing 2 mM glucose and dopamine release was measured using fast cyclic voltammetry. In drug-free (control) slices, there was a 2-3 min delay after the onset of hypoxia/hypoglycaemia followed by a rapid dopamine release event which was associated with anoxic depolarization. In slices treated with the Na+ channel opener, veratridine (1 microM), the time to onset of dopamine release was shortened (101 +/- 20 s, compared with 171 +/- 8 s in controls, P < 0.05). Conversely, phenytoin (100 microM), lignocaine (200 microM) and the highly selective sodium channel blocker, tetrodotoxin (1 microM) markedly delayed and slowed dopamine release vs paired controls. In the majority of cases, dopamine release was biphasic after sodium channel blockade: a slow phase preceded a more rapid dopamine release event. The latter was associated with anoxic depolarization. Neither the fast nor the slow release events were affected by pretreatment with the selective dopamine uptake blocker GBR 12935 (0.2 microM), suggesting that uptake carrier reversal did not contribute to these events. In conclusion, sodium channel antagonism delays and slows hypoxia/hypoglycaemia-induced dopamine release in vitro. Furthermore, sodium channel blockade delays anoxic depolarization and its associated neurotransmitter release, revealing an earlier dopamine release event that does not result from reversal of the uptake carrier.

Effect of cerebral ischemia on dopamine receptors and uptake sites in the gerbil hippocampus

Dopamine D1 and D2 receptors and uptake sites were studied in the gerbil hippocampus, parietal cortex and thalamus 1 h to 7 days after 10 min of cerebral ischemia using the occlusion of bilateral common carotid arteries. [3H]SCH23390 ([N-methyl-3H]R[+]-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-7-ol-be nzazepine) and [3H]mazindol were used as markers of dopamine D1 receptors and uptake sites, respectively. [3H]Nemonapride was used to label dopamine D2 receptors. No obvious alteration in [3H]SCH23390 and [3H]mazindol binding was found in the hippocampus up to 48 h after ischemia. These bindings showed a significant reduction in the hippocampus after 7 days of recirculation. In contrast, [3H]nemonapride binding was unaffected in the hippocampus during the recirculation periods. The parietal cortex and thalamus also exhibited no significant changes in [3H]SCH23390, [3H]nemonapride and [3H]mazindol binding after ischemia. MAP2 (microtubule-associated protein 2) immunoreactivity was unchanged in all regions up to 48 h after ischemia. Thereafter, a marked loss of MAP2-immunoreactive neurons was observed in the hippocampal CA1 and CA3 neurons 7 days after recirculation. These findings were consistent with histological observations with cresyl violet staining. Our results demonstrate that dopamine D1 receptors and dopamine uptake sites in the hippocampus are susceptible to cerebral ischemia, whereas dopamine D2 receptors in this region are particularly resistant. Furthermore, these findings suggest that dopamine transmission may not be major factor in producing ischemic hippocampal damage.

Is chlormethiazole neuroprotective in experimental global cerebral ischemia? A microdialysis and behavioral study

Chlormethiazole, an anticonvulsive agent, has been shown to have a possible neuroprotective effect against cerebral ischemia. In addition, chlormethiazole inhibits methamphetamine-induced release of dopamine, protecting against this neurotransmitter's neurotoxicity. The aim of this work was to ascertain whether, in experimental cerebral ischemia, chlormethiazole administration attenuated the ischemia-induced rise of the extracellular concentration of aminergic neurotransmitters and whether it reduces ischemia-induced deficits in memory and learning. Histology for assessment of ischemic damage was a so included. The four-vessel occlusion rat model was used to induce global cerebral ischemia. Aminergic neurotransmitters and their metabolites in the striatal extracellular fluid obtained by microdialysis were assayed by high-performance liquid chromatography-electrochemical detection. The drug was administered either IP (50 mg/kg-1) or directly through the dialysis probe (30 microM) 80 min before ischemia. For the behavioral test and histology, the drug was given IP (100 mg/kg-1) 1 h postischemia. The results obtained did not demonstrate any statistically significant evidence that chlormethiazole has an effect on the ischemia-induced rise in extracellular dopamine and serotonin levels. There was also no variation in metabolite levels. Behavioral measures (learning, recall) were not changed appreciably by the treatment. We observed no significant cell protection in the hippocampus (CA1, CA1), striatum, and entorhinal cortex in animals treated with chlormethiazole. We conclude that, under our experimental conditions, chlormethiazole has little or no effect on the neurochemical, neurobehavioral, and histological consequences of global cerebral ischemia.

Involvement of N- and P/Q- but not L- or T-type voltage-gated calcium channels in ischaemia-induced striatal dopamine release in vitro

Calcium influx and transmitter efflux are central events in the neuropathological cascade that occurs during and following cerebral ischaemia. This study explored the role of voltage-gated calcium channels (VGCCs) in ischaemia-induced striatal dopamine (DA) release in vitro. Slices (350 microm thickness) of rat neostriatum were superfused (400 ml/h) with an artificial cerebrospinal fluid (aCSF) at 34 degrees C and subjected to episodes of 'ischaemia' by reduction of the glucose concentration from 4 to 2 mM and gassing with 95% N2/5% CO2. DA release was monitored with fast cyclic voltammetry at implanted carbon fibre microelectrodes. The time to onset, time to peak, rate and magnitude of DA release were measured. Non-selective blockade of VGCCs with a high concentration of Ni2+ (2.5 mM), markedly delayed (P < 0.01) and slowed (P < 0.05) DA release but preferential blockade of T-type VGCCs with a lower concentration (200 microM) had no effect. DA release was also unaffected by selective antagonism of L-type VGCCs with nimodipine and nicardipine (10 microM each). Selective blockade of N-type VGCCs with omega-conotoxin GVIA (100 nM) delayed DA release (P < 0.05) but did not affect its rate or magnitude. Blockade of P- and possibly Q-type VGCCs with omega-agatoxin IVA (up to 200 nM) both delayed (P < 0.05) and slowed (P < 0.05) DA release. Preferential blockade of P- type VGCCs with neomycin (500 microM) also delayed (P < 0.05) and slowed (P < 0.05) DA release. These findings suggest that N-, P- and possibly Q- but not L- or T-type VGCCs mediate ischaemia-induced DA release. Although it is not possible to say, on the basis of these results, that the effects are directly upon the dopamine terminals, these calcium channels nevertheless constitute promising targets for therapeutic intervention.

Effect of prenatal malnutrition on release of monoamines from hippocampal slices

The effect of prenatal protein malnutrition on release of monoamine neurotransmitters, their precursors and metabolites, from hippocampal slices was investigated in 15, 30, 90 and 220 days old male rats. The release of dopamine and its metabolites, tryptophan, and 5-hydroxyindoleacetic acid from hippocampal slices of malnourished rats was greater than release from control slices at all ages studied. Malnutrition also significantly increased the release of normetanephrine but only in the 220 day age group. Potassium-induced depolarization increased release of tyrosine, normetanephrine and 5-hydroxyindoleacetic acid less from slices of malnourished than from control rats. The release of norepinephrine, normetanephrine, serotonin and 5-hydroxyindoleacetic acid increased significantly with age while the release of tyrosine, 3,4-dihydroxyphenylacetic acid and homovanillic acid decreased significantly with age. Age was also significantly associated with the effectiveness of potassium-induced depolarization in increasing release of tyrosine, norepinephrine, normetanephrine, tryptophan, serotonin and 5-hydroxyindoleacetic acid.

The role of L-type voltage dependent calcium channels in stimulated [3H]norepinephrine release from canine hippocampal slices following global cerebral ischemia and reperfusion

The hippocampus is among those brain regions which are selectively vulnerable to ischemic damage. Hippocampal damage due to transient cerebral ischemia is mainly of the delayed, non-necrotic type which may arise after disruption or activation of specific cellular systems, including transmitter release through excitatory amino acid receptors. We investigated the contribution of L-type voltage dependent calcium channels (VDCCs) to glycine (GLY) potentiated N-methyl-D-aspartate (NMDA) receptor- and potassium-stimulated [3H]norepinephrine (NE) release in a canine model of global cerebral ischemia and reperfusion. Tissue was collected from four experimental groups: non-arrested controls (NA), global cerebral ischemia induced by 10 minute cardiac arrest (CA), and CA followed by 30 min or 24 hours reperfusion after restoration of spontaneous circulation. Brain slices prepared from all groups accumulated approximately equivalent amounts of [3H]NE. The sensitivity of [3H]NE release to stimulation by NMDA/GLY or elevated potassium was unchanged after ischemia and reperfusion. About 30% of release stimulated by the addition of 20 mM potassium was inhibited by the NMDA receptor-operated channel antagonist MK801 in all groups except CA in which only 4% of release was inhibited by MK801. The ability of 1 microM nitrendipine (NTP) to block stimulated release indicated that the contribution of the L-type VDCC to potassium or NMDA/GLY-stimulated release was significant only in NA and 24 hour reperfused animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of D1 dopamine receptor mechanism in ischemia-induced impairment of CA1 presynaptic fiber spikes in rat hippocampal slices

The effect of dopamine (DA) receptor agonists and antagonists on hypoxia/hypoglycemia (ischemia)-induced decrease in CA1 presynaptic fiber spikes elicited by the stimulation of Schaffer collateral were investigated using hippocampal slices. Treatment with D1 dopamine receptor antagonist, SCH23390 produced a concentration-dependent attenuation of the ischemia-induced decrease of presynaptic potentials. The magnitude of recovery of the CA1 presynaptic potential in SCH233390-treated slices at 10 and 100 microM was 28 and 54%, respectively. Whereas, treatment with D1 dopamine receptor agonist, SKF38393 exacerbated the ischemia-induced decrease in the CA1 presynaptic potential. The decrease of CA1 presynaptic potential by ischemia was affected by neither D2 dopamine receptor agonist, bromocriptin and quinpirole nor D2 dopamine receptor antagonist, sulpiride. The neuroprotective effect of SCH23390 was completely blocked by cotreatment with SKF38393. The present results demonstrated that the blockade of D1 dopamine receptor function played a neuroprotective role in ischemic damage, suggesting a facilitatory role of D1 dopamine receptor-operated function in ischemia-induced neuronal deficits.

The alpha 2 adrenergic agonist, dexmedetomidine, selectively attenuates ischemia-induced increases in striatal norepinephrine concentrations

This study was designed to evaluate the ability of a selective alpha 2 adrenergic agonist (dexmedetomidine) to attenuate ischemia-induced increases in striatal norepinephrine, 3 methoxy-4-hydroxyphenethyleneglycol (MHPG), dopamine, and 5-hydroxyindoleacetic acid (5-HIAA). Following the induction of anesthesia with halothane and oxygen, microdialysis catheters were stereotactically inserted into the striatum of 9 New Zealand white rabbits. Monitored variables included epidural temperature, arterial blood gases and pH, mean arterial pressure, blood glucose concentrations and the electroencephalogram. Following collection of baseline samples of dialysate, animals were randomized to receive a continuous infusion of saline (n = 4) or dexmedetomidine (n = 5). Cerebral ischemia was produced by the inflation of a neck tourniquet and induction of deliberate hypotension. Dialysate collection continued during the ischemic period and for the ensuing 140 min of reperfusion. All dialysate was frozen at -80 degrees C prior to its analysis by liquid chromatography for catecholamine content. There were no significant differences between the two groups for temperature, arterial blood gases, or mean arterial pressure. Blood glucose concentrations increased in the dexmedetomidine group. The electroencephalogram became isoelectric within 30 s of tourniquet inflation in all animals. Analysis of the norepinephrine and MHPG levels revealed significantly lower values for the dexmedetomidine-treated group during and following the ischemic period. There were no differences between groups for extracellular dopamine or 5-HIAA concentrations. These results suggest that the alpha 2 agonist dexmedetomidine can selectively attenuate ischemia-induced increases in striatal norepinephrine concentrations.

Sustained increase in adrenergic activity in gerbil striatum following transient ischemia

We investigated the changes in striatal monoaminergic functions, focusing on the release and metabolism, in a cerebral ischemic model induced by a 5-min bilateral occlusion of the carotid arteries (BOCA) and reperfusion in anesthetized gerbils. In the microdialysis study, the striatal extracellular level of dopamine (DA) markedly increased (144-fold) immediately after BOCA. Although norepinephrine (NE) and 5-hydroxytryptamine (5-HT) could not be detected in the dialysates throughout the baseline period, they increased to detectable levels after BOCA. On the contrary, the tissue contents of NE and 5-HT decreased or tended to decrease up to 4 hr following reperfusion. Striatal DA contents did not show any changes in the early period after ischemia-reperfusion and slightly increased at 4 hr or later. Tissue contents of 3-methoxytyramine (3-MT), a metabolite of DA by catechol-O-methyltransferase (COMT), increased 0 and 5 min after reperfusion. Normethanephrine (NMN), which is a metabolite of NE by COMT, also increased not only 5 min after but also up to 4 hr after ischemia-reperfusion, indicating a sustained increase in NE release. These results suggested that the neuronal activity of NE, which is supposed to exert a protective effect on ischemic damage, was enhanced for a longer period than that of DA after transient ischemia.

Enzyme properties of monoamine oxidase in the frontal cortex and liver of the gerbil (Meriones unguiculatus)

1. Enzyme properties of monoamine oxidase (MAO) in the frontal cortex and liver of the gerbil were investigated using 5-hydroxytryptamine (5-HT), benzylamine (Bz) and tyramine (Tyr) as substrates. 2. The Km values of MAO towards the three substrates were almost similar to the values in other species. The Vmax value of MAO towards Bz was much lower than the value towards 5-HT. 3. In the inhibition studies with selective MAO-A and MAO-B inhibitors, clorgyline and deprenyl, deamination of 5-HT, Bz and Tyr in both tissues was induced by MAO-A alone, MAO-B alone and both forms of the enzyme, respectively, indicating the same substrate specificity as that in rats. 4. The apparent proportion of MAO-A to MAO-B activities in the gerbil liver was approximately 6:4, whereas MAO-A in the frontal cortex of the gerbil was exclusively predominant, consistent with the previous data in the golden hamster which belongs to the same family as the gerbil.

Dopamine release from canine striatum following global cerebral ischemia/reperfusion

The elevation of extracellular dopamine (DA) levels in the striatum of experimental animals subjected to ischemic insult has been well documented. The contribution of excessive DA to neuronal damage can be inferred from the ability of DA antagonists, as well as selective destruction of dopaminergic tracts, to confer neuroprotection in models of ischemia. In the current study, we report an enhanced releasability of preloaded [3H]DA in response to either elevated potassium or N-methyl-D-aspartate (NMDA) from striatal slices of beagles that had experienced 10 min of ischemia induced by cardiac arrest. The elevation in sensitivity to potassium stimulation was transient, approaching control levels after 30 min of reperfusion. In contrast, release stimulated by NMDA was elevated immediately after cardiac arrest and remained elevated for as long as 24 h of reperfusion. Release stimulated by NMDA was enhanced by glycine (Gly) and inhibited by MK801, consistent with mediation through the NMDA receptor/channel complex. The increased sensitivity of DA release, coupled with the high levels of excitatory amino acids (EAAs), including glutamate (Glu), aspartate (Asp) and Gly in ischemic brain, probably contribute to the extensive neuronal cell damage.

Hydrogen peroxide production by monoamine oxidase during ischemia-reperfusion in the rat brain

Monoamine oxidase (MAO) as a source of hydrogen peroxide (H2O2) was evaluated during ischemia-reperfusion in vivo in the rat brain. H2O2 production was assessed with and without inhibition of MAO during and after 15 min of ischemia. Metabolism of H2O2 by catalase during ischemia and reperfusion was measured in forebrain homogenates using aminotriazole (ATZ), an irreversible H2O2-dependent inhibitor of catalase. Catecholamine and glutathione concentrations in forebrain were measured with and without MAO inhibitors. During ischemia, forebrain blood flow was reduced to 8% of baseline and H2O2 production decreased as measured at the microperoxisome. During reperfusion, a rapid increase in H2O2 generation occurred within 5 min as measured by a threefold increase in oxidized glutathione (GSSG). The H2O2-dependent rates of ATZ inactivation of catalase between control and ischemia-reperfusion were similar, indicating that H2O2 was more available to glutathione peroxidase than to catalase in this model. MAO inhibitors eliminated the biochemical indications of increased H2O2 production and increased the catecholamine concentrations. Mortality was 67% at 48 h after ischemia-reperfusion, and there was no improvement in survival after inhibition of MAO. We conclude that MAO is an important source of H2O2 generation early in brain reperfusion, but inhibition of the enzyme does not improve survival in this model despite ablating H2O2 production.

Effect of local cyanide perfusion on rat striatal extracellular dopamine and its metabolites as studied by in vivo brain microdialysis

To investigate in vivo effects of energy failure on functions of dopaminergic neurons, we administered 0 (control), 0.2, 1 or 2 mM sodium cyanide (NaCN) dissolved in Ringer's solution for 60 min into the rat striatum through a brain microdialysis membrane. During NaCN perfusion, a transient and concentration-dependent increase in dopamine (DA) levels in the dialysate was observed. The maximum DA level during 2 mM NaCN perfusion was found to be 63-fold higher than the control levels. Leves of 3,4-dihydroxyphenylacetic acid and homovanillic acid were continuously lowered during and after NaCN perfusion. These data suggest that suppression of ATP production by NaCN induces an abrupt and remarkable increase in dopamine release from the nerve terminal in the striatum.