Differential alteration of dopamine, acetylcholine, and glutamate release during anoxia and/or 3,4-diaminopyridine treatment

The Association of Cerebral Oxygen Desaturation with Postoperative Cognitive Dysfunction in Older Patients: A Review

Postoperative cognitive dysfunction (POCD) is a neurological complication associated with surgery and anesthesia that is commonly observed in older patients, and it can significantly affect patient prognosis and survival. Therefore, predicting and preventing POCD is important. Regional cerebral oxygen saturation (rSO2) reflects cerebral perfusion and oxygenation, and decreased intraoperative cerebral oxygen saturation has been reported to increase the risk of POCD. In this review, we elucidated the important relationship between the decline in rSO2 and risk of POCD in older patients. We also emphasized the importance of monitoring rSO2 during surgery to predict and prevent adverse perioperative cognitive outcomes. The findings reveal that incorporating intraoperative rSO2 monitoring into clinical practice has potential benefits, such as protecting cognitive function, reducing perioperative adverse outcomes, and ultimately improving the overall quality of life of older adults.

K channel blockage with 3,4-diaminopyridine potentiates the effect of L-DOPA on dopamine release in striatal slices prepared from 6-OHDA pre-treated rats

Although L-DOPA revolutionized in the treatment of Parkinson's disease, most patients developed motor complications after several years of treatment. Adjunctive therapy to L-DOPA with drugs related to dopaminergic signaling may reduce its dose without decreasing the therapeutic efficiency and thus ameliorates its adverse effects. It has been shown that 3,4-diaminopyridine (3,4-DAP), a K channel blocker, increased dopamine release from striatal slices by increasing neuronal firing in striatal dopaminergic terminals. The current study investigates whether 3,4-DAP may enhance L-DOPA-induced dopamine (DA) release from striatal slices by increasing neuronal firing in striatal dopaminergic terminals. The effects of L-DOPA and 3,4-DAP on spontaneous DA and DOPAC release were tested in vitro, on acute rat striatal slices prepared from non-treated and 6-hydroxydopamine-pre-treated rats. DA and DOPAC levels were determined by HPLC methods. When 3,4-diaminopyridine was combined with L-DOPA, the observed effect was considerably greater than the increases induced by L-DOPA or 3,4-DAP alone in normoxic and neurodegenerative conditions produced by FeSO4 and 6-hydroxydopamine. Furthermore, L-DOPA plus 3,4-DAP also ameliorated DOPAC levels in neurodegenerative conditions. These data indicate that 3,4 DAP plus L-DOPA activates striatal dopaminergic terminals by increasing the DA release and, thus, could be considered as a promising finding in treatment of acute and chronic injury in dopaminergic neurons.

Nafion-Radical Hybrid Films on Carbon Nanotube Transistors for Monitoring Antipsychotic Drug Effects on Stimulated Dopamine Release

We developed floating electrode-based carbon nanotube biosensors for the monitoring of antipsychotic drug effects on the dopamine release from PC12 cells under potassium stimulation. Here, carbon nanotube field-effect transistors with floating electrodes were functionalized with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS^•) radicals by Nafion films. This method allows us to build selective biosensors for dopamine detection with a detection limit down to 10 nM even in the presence of other neurotransmitters such as glutamate and acetylcholine, resulting from the selective interaction between ABTS^• radicals and dopamine. The sensors were also utilized to monitor the real-time release of dopamine from PC12 cells upon the stimulation of high-concentrated potassium solutions. Significantly, the antipsychotic effects of pimozide on the dopamine release from potassium-stimulated PC12 cells could also be evaluated in a concentration-dependent manner by using the sensors. The quantitative and real-time evaluation capability of our strategy should provide a versatile tool for many biomedical studies and applications.

Partial and No Recovery from Delirium in Older Hospitalized Adults: Frequency and Baseline Risk Factors

OBJECTIVES

To determine the frequency and baseline risk factors for partial and no recovery from delirium in older hospitalized adults.

DESIGN

Cohort study with assessment of recovery status approximately 1 and 3 months after enrollment.

SETTING

University-affiliated, primary, acute-care hospital.

PARTICIPANTS

Medical or surgical inpatients aged 65 and older with delirium (N = 278).

MEASUREMENTS

The Mini-Mental State Examination (MMSE), Confusion Assessment Method (CAM), Delirium Index (DI), and activities of daily living (ADLs) were completed at enrollment and each follow-up. Primary outcome categories were full recovery (absence of CAM core symptoms of delirium), partial recovery (presence of ≥1 CAM core symptoms but not meeting criteria for delirium), no recovery (met CAM criteria for delirium), or death. Secondary outcomes were changes in MMSE, DI, and ADL scores between the baseline and last assessment. Potential risk factors included many clinical and laboratory variables.

RESULTS

In participants with dementia, frequencies of full, partial, and no recovery and death at first follow-up were 6.3%, 11.3%, 74.6%, and 7.7%, respectively; in participants without dementia, frequencies were 14.3%, 17%, 50.9%, and 17.9%, respectively. In participants with dementia, frequencies at the second follow-up were 7.9%, 15.1%, 57.6%, and 19.4%, respectively; in participants without dementia, frequencies were 19.2%, 20.2%, 31.7%, and 28.8%, respectively. Frequencies were similar in participants with prevalent and incident delirium and in medical and surgical participants. The DI, MMSE, and ADL scores of many participants with partial and no recovery improved. Independent baseline risk factors for delirium persistence were chart diagnosis of dementia (odds ratio (OR) = 2.51, 95% confidence interval (CI) =1.38, 4.56), presence of any malignancy (OR = 5.79, 95% CI = 1.51, 22.19), and greater severity of delirium (OR =9.39, 95% CI = 3.95, 22.35).

CONCLUSION

Delirium in many older hospitalized adults appears to be much more protracted than previously thought, especially in those with dementia, although delirium symptoms, cognition, and function improved in many participants with partial and no recovery. It may be important to monitor the longer-term course of delirium in older hospitalized adults and develop strategies to ensure full recovery.

Frequency, risk factors, and prognosis of prolonged delirium in elderly patients after hip fracture surgery

BACKGROUND

Delirium in elderly patients after hip fracture surgery is believed to be a transient event, although it frequently lasts for more than 4 weeks.

QUESTIONS/PURPOSES

We determined the incidence, risk factors, morbidity, and mortality of prolonged delirium in elderly patients after hip fracture surgery.

PATIENTS AND METHODS

We evaluated 232 elderly patients (older than 65 years) (232 hips) who underwent hip fracture surgery for the development and duration of delirium and categorized them into three groups; nondelirium group, transient (≤ 4 weeks) delirium group, and prolonged (> 4 weeks) delirium group. Patients underwent a global geriatric evaluation, which included postoperative complications, mortality, and functional and mental status evaluations. The three groups were compared with respect to these variables.

RESULTS

Seventy patients (30.2%) had delirium develop, and among these, 14 (20%) had prolonged delirium with a total incidence of 6%. Multivariate analysis showed preinjury dementia was a risk factor of prolonged delirium. At the final followup, five (62.5%) of the eight patients who were ambulatory outdoors in the prolonged delirium group became housebound, whereas only 18 (16.4%) of the 110 patients who were ambulatory outdoors in the nondelirium group became housebound. Survival at 40 months was 81.0% (95% confidence interval, 72.6%-89.3%) in the nondelirium group and 63.6% (95% confidence interval, 35.2%-92.1%) in the prolonged delirium group.

CONCLUSIONS

Prolonged delirium was found to be associated with a poor functional outcome and increased mortality.

LEVEL OF EVIDENCE

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Persistent delirium in older hospital patients

PURPOSE OF REVIEW

There are two contradictory views on the prognosis of delirium in older hospital patients. On one hand, the Diagnostic and Statistical Manual, 4th Text Revision (DSM-IV-TR), describes delirium as a transient cognitive disorder, the majority of affected individuals having a full recovery. On the other hand, longitudinal studies of delirium in this population report that the outcomes are poor. This review proposes to reconcile these two contradictory views.

RECENT FINDINGS

In older hospital patients, delirium appears to persist in 44.7% of patients at discharge and in 32.8, 25.6 and 21% of patients at 1, 3 and 6 months, respectively. The outcomes (cognition, function, nursing home placement, mortality) of patients with persistent delirium are consistently worse than the outcomes of patients who recover from delirium.

SUMMARY

The majority of older hospital patients with delirium may recover but the persistence of delirium in a substantial minority of patients may account, in large part, for the poor outcomes of delirium in this population. This proposal has potentially important implications for clinical practice and research.

Persistent delirium in older hospital patients: a systematic review of frequency and prognosis

BACKGROUND

one explanation for the poor prognosis of delirium among older hospital patients may be that many of these patients do not recover from delirium. We sought to determine the frequency and prognosis of persistent delirium (PerD) in older hospital patients by systematically reviewing original research on this topic.

METHODS

MEDLINE, EMBASE, PsycINFO and the Cochrane Database of Systematic Reviews were searched for potentially relevant articles. The bibliographies of relevant articles were searched for additional references. Eighteen reports (involving 1,322 patients with delirium) met the following seven inclusion criteria: original research published in English or French, prospective study design, study population of at least 20 hospital patients, patients aged 50 years or more, follow-up of at least 1 week, acceptable definition of delirium at enrollment and included at least one assessment for PerD at discharge or later. The methods of each study were assessed according to the six criteria for prognostic studies described by the Evidence-Based Medicine Working Group. Information about the sample origin and size, age, proportion with dementia, criteria for delirium, timing of follow-up assessments, criteria for PerD, proportion with PerD and prognosis of PerD was systematically abstracted from each report, tabulated and combined using standard meta-analysis techniques.

RESULTS

the combined proportions with PerD at discharge, 1, 3 and 6 months were 44.7% (95% CI 26.8%, 63.7%), 32.8% (95% CI 18.4%, 47.2%), 25.6% (95% CI 7.9%, 43.4%) and 21% (95% CI 1.4%, 40.6%), respectively. The outcomes (mortality, nursing home placement, function, cognition) of patients with PerD were consistently worse than the outcomes of patients who had recovered from delirium.

CONCLUSION

PerD in older hospital patients is frequent, appears to be associated with adverse outcomes and may account for the poor prognosis of delirium in this population. These findings have potentially important implications for clinical practice and research.

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.

Acetylcholine esterase activity and behavioral response in hypoxia induced neonatal rats: effect of glucose, oxygen and epinephrine supplementation

Brain damage due to an episode of hypoxia remains a major problem in infants causing deficit in motor and sensory function. Hypoxia leads to neuronal functional failure, cerebral palsy and neuro-developmental delay with characteristic biochemical and molecular alterations resulting in permanent or transitory neurological sequelae or even death. During neonatal hypoxia, traditional resuscitation practices include the routine administration of 100% oxygen, epinephrine and glucose. In the present study, we assessed the changes in the cholinergic system by measuring the acetylcholinesterase (AChE) activity and the behavioral responses shown by hypoxia induced neonatal rats and hypoxic rats supplemented with glucose, oxygen and epinephrine using elevated plus-maze and open-field test. The acetylcholine esterase enzyme activity showed a significant decrease in cerebral cortex, whereas it increased significantly in the muscle of experimental rats when compared to control. Hypoxic rats supplemented with glucose, glucose and oxygen showed a reversal to the control status. Behavioral studies were carried out in experimental rats with elevated plus-maze test and open-field test. Hypolocomotion and anxiogenic behavioral responses were observed in all experimental rats when compared to control, hypoxic rats supplemented with glucose, glucose and oxygen. Thus, our results suggest that brain damage due to hypoxia, oxygen and epinephrine supplementation in the neonatal rats cause acetylcholine-neuromuscular-defect leading to hypolocomotion and anxiogenic behavioral response. Glucose and glucose with oxygen supplementation to hypoxic neonates protect the brain damage for a better functional status in the later life.

Visual hallucinations in consultation-liaison neuropsychiatry

BACKGROUND

In consultation-liaison settings, neuropsychiatrists are commonly asked to assess patients with hallucinatory syndromes and to differentiate 'functional' from 'organic' psychotic presentations.

METHODS

The occurrence and management of visual hallucinations (VH) in healthy individuals, lesion states, neurodegenerative disorders, intoxication/withdrawal states and delirium are reviewed.

RESULTS

The presence of VH has been shown to predict a secondary rather than primary psychotic illness and an understanding of the neurobiology of the visual system - including how and where underlying neurotransmitter systems interact in visual processing and how perturbations can result in VH - allows for appropriate clinical assessment and management.

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.

Hypoxia-induced secretion of serotonin from intact pulmonary neuroepithelial bodies in neonatal rabbit

We examined the effects of hypoxia on the release of serotonin (5-HT) from intact neuroepithelial body cells (NEB), presumed airway chemoreceptors, in rabbit lung slices, using amperometry with carbon fibre microelectrodes. Under normoxia (P(O2) ~155 mmHg; 1 mmHg approximately 133 Pa), most NEB cells did not exhibit detectable secretory activity; however, hypoxia elicited a dose-dependent (P(O2) range 95-18 mmHg), tetrodotoxin (TTX)-sensitive stimulation of spike-like exocytotic events, indicative of vesicular amine release. High extracellular K(+) (50 mM) induced a secretory response similar to that elicited by severe hypoxia. Exocytosis was stimulated in normoxic NEB cells after exposure to tetraethylammonium (20 mM) or 4-aminopyridine (2 mM). Hypoxia-induced secretion was abolished by the non-specific Ca(2+) channel blocker Cd(2+) (100 microM). Secretion was also largely inhibited by the L-type Ca(2+) channel blocker nifedipine (2 microM), but not by the N-type Ca(2+) channel blocker omega-conotoxin GVIA (1 microM). The 5-HT(3) receptor blocker ICS 205 930 also inhibited secretion from NEB cells under hypoxia. These results suggest that hypoxia stimulates 5-HT secretion from intact NEBs via inhibition of K(+) channels, augmentation of Na(+)-dependent action potentials and calcium entry through L-type Ca(2+) channels, as well as by positive feedback activation of 5-HT(3) autoreceptors.

Differential alteration of catecholamine release during chemical hypoxia is correlated with cell toxicity and is blocked by protein kinase C inhibitors in PC12 cells

Release of neurotransmitters, including dopamine and glutamate, has been implicated in hypoxia/ischemia-induced alterations in neuronal function and in subsequent tissue damage. Although extensive studies have been done on the mechanism underlying the changes in glutamate release, few have examined the mechanism that is responsible for the changes in catecholamines. Rat pheochromocytoma-12 (PC12) cells synthesize, store, and release catecholamines including DA and NE. Therefore, we used HPLC and ED to evaluate extracellular DA and NE concentrations in a medium during chemical hypoxia in PC12 cells. Chemical hypoxia produced by KCN induced differential release of DA and NE. Under normal glucose conditions, KCN induced release of NE, but not DA. Under glucose-free conditions, KCN-induced release of DA was elevated transiently, whereas the release of NE increased progressively. Under parallel conditions, KCN biphasically elevated the level of cytosolic free calcium ([CA(2+)](i)) in glucose-free DMEM, peaking at 95 +/- 18 nM at 1,107 +/- 151 s, followed by a new plateau level at 249 +/- 24 nM sustained from 4,243 +/- 466 to 5,263 +/- 440 s. Cell toxicity, as measured by LDH release, was increased significantly by KCN in glucose-free DMEM but was diminished in the presence of glucose, and was correlated with DA release by chemical hypoxia. The protein kinase C (PKC) inhibitor GO6976 or staurosporine inhibited KCN-induced LDH release as well as the release of NE and DA. Taken together, selective activation of DA but not NE was correlated with the LDH release by chemical hypoxia, and was diminished with GO6976 or staurosporine. These results suggest that selective activation of PKC isoforms is involved in the chemical hypoxia-induced DA release, which may lead to neuronal cell toxicity.

Release of dopamine and norepinephrine by hypoxia from PC-12 cells

We examined the effects of hypoxia on the release of dopamine (DA) and norepinephrine (NE) from rat pheochromocytoma 12 (PC-12) cells and assessed the involvement of Ca2+ and protein kinases in stimulus-secretion coupling. Catecholamine release was monitored by microvoltammetry using a carbon fiber electrode as well as by HPLC coupled with electrochemical detection (ECD). Microvoltammetric analysis showed that hypoxia-induced catecholamine secretion (PO2 of medium approximately 40 mmHg) occurred within 1 min after the onset of the stimulus and reached a plateau between 10 and 15 min. HPLC-ECD analysis revealed that, at any level of PO2, the release of NE was greater than the release of DA. In contrast, in response to K+ (80 mM), DA release was approximately 11-fold greater than NE release. The magnitude of hypoxia-induced NE and DA releases depended on the passage, source, and culture conditions of the PC-12 cells. Omission of extracellular Ca2+ or addition of voltage-gated Ca2+ channel blockers attenuated hypoxia-induced release of both DA and NE to a similar extent. Protein kinase inhibitors, staurosporine (200 nM) and bisindolylmaleimide I (2 microM), on the other hand, attenuated hypoxia-induced NE release more than DA release. However, protein kinase inhibitors had no significant effect on K+-induced NE and DA releases. These results demonstrate that hypoxia releases catecholamines from PC-12 cells and that, for a given change in PO2, NE release is greater than DA release. It is suggested that protein kinases are involved in the enhanced release of NE during hypoxia.

Post-hypoxic recovery of acetylcholine release: different sensitivity of guinea pig neocortical and striatal slices

The release of endogenous acetylcholine (ACh) was measured in superfused guinea-pig cortical and striatal slices, kept at rest or electrically stimulated at different frequencies, before and during severe hypoxic conditions as well as after reoxygenation. In the cortex the basal release was unchanged by 30-60 min of hypoxia while it was inhibited in the striatum. The release evoked by short-term (2 min) stimulation at 0.5 Hz was moderately reduced (to 76%) by 30 min hypoxia in the cortex and in the striatum, but fully recovered after reoxygenation. The release evoked by continuous stimulation (from 5 to 10 to 20 Hz) was strongly inhibited (to 12-30%) in both areas after 30 min of hypoxia. After 30 min of reoxygenation, the recovery was complete in the cortex (mainly provided with cholinergic axons), but it was incomplete in the striatum (rich in cholinergic interneurones). The extent of the recovery in the latter area (i) was inversely related to stimulation frequency, (ii) did not depend on the depletion of neurotransmitter stores, because ACh tissue levels were fully restored by reoxygenation, and (iii) was consistently facilitated by excitatory aminoacid antagonists, slightly improved by the adenosine agonist R-phenylisopropyladenosine and unaffected by reducing the concentrations of radical species with catalase and superoxide dismutase or N omega-nitro-L-arginine. These results emphasize (i) the different vulnerability of the cortical and striatal cholinergic structures, (ii) the high sensitivity of the striatal interneurones to the frequency of stimulation during the posthypoxic recovery, and (iii) the relevant role played by endogenous glutamate on activity-dependent neurosecretory failure.

Glutamate efflux from rat brain slices and cultures: a comparison of the depolarizing agents potassium, 4-aminopyridine, and veratrine

The major excitatory amino acid neurotransmitter in the mammalian brain is glutamate (GLU). GLU release from nerve terminals is both calcium-dependent and -independent, yet these mechanisms of release are not fully understood. Potassium, 4-aminopyridine (4-AP) and veratrine are commonly used depolarizing agents that were studied for their ability to stimulate GLU efflux from brain slices. These agents produced significant regional variations in GLU efflux from rat brain slices. Potassium was the most potent of the three secretogogues tested. 4-AP produced a significant GLU efflux only in the cerebellum. Veratrine produced consistent stimulation of GLU efflux from all brain regions tested. Potassium was the only depolarizing agent tested that stimulated GLU release from primary astroglial cultures of rat cerebral cortex. All three agents also demonstrated an ability to inhibit GLU reuptake in brain slice preparations. This data suggest that both GLU release and uptake are modulated in a regionally selective manner, and that commonly used depolarizing agents affect not only calcium-dependent neuronal release, but also uptake and glial responses.

Regulatory Interactions Among Axon Terminals Affecting the Release of Different Transmitters from Rat Striatal Slices Under Hypoxic and Hypoglycemic Conditions

An in vitro model of ischemia was utilized to study the effects of both oxygen and glucose depletion on transmitter release from rat striatal slices. The spontaneous and stimulation-evoked releases of tritiated dopamine, gamma-aminobutyric acid, glutamate, and acetylcholine were measured. Hypoxia increased the evoked release of glutamate and dopamine without effect on the resting release. In contrast, hypoglycemia itself increased the resting release of dopamine. Hypoxia in combination with hypoglycemia provoked a massive release of glutamate, dopamine, and gamma-aminobutyric acid. The effect on acetylcholine release was less pronounced. Ca2+ withdrawal partly reduced the effect of hypoxia combined with hypoglycemia on dopamine release and application of tetrodotoxin (1 microM) abolished it. MK-801 (3 microM), an N-methyl-D-aspartate receptor antagonist, attenuated the effect of hypoxia and hypoglycemia on [3H]dopamine release. omega-Conotoxin (0.1 microM) had a similar effect on stimulation-evoked release under a hypoxic condition. The D2 receptor antagonist sulpiride (100 microM) failed to enhance the release of [3H]acetylcholine in hypoxia combined with hypoglycemia. It was suggested that in response to hypoxia combined with hypoglycemia there is a massive release of glutamate due to the increased firing rate which in turn releases dopamine from the axon terminals through stimulation of presynaptic N-methyl-D-aspartate receptors. Dopaminergic inhibitory control on ACh release seems not to be operative under conditions of hypoxia combined with hypoglycemia.

Simultaneous measurement of oxygen and dopamine: coupling of oxygen consumption and neurotransmission

Fast-scan cyclic voltammetry was used to simultaneously measure increases in dopamine concentration and decreases in O2 concentration evoked by brief electrical stimulation (two pulses at 10 Hz) in slices of rat caudate nucleus. Dopamine concentration began increasing immediately after the first pulse and reached a maximum within 200 ms of stimulation. The O2 concentration began to decrease 300-700 ms after onset of stimulus. Responses for both dopamine and O2 were dependent on external Ca2+ and were Cd2+ and tetrodotoxin sensitive. Only the O2 response was sensitive to CN- (0.15 mM). At short times after exposure to 50 microM ouabain, electrically stimulated dopamine overflow was increased by 150% and electrically stimulated changes in O2 concentration were unaffected. Maximum dopamine concentration was increased 28% by sulpiride (2 microM), 78% by L-DOPA (60 microM), 105% by nomifensine (10 microM) and unaffected by nialamide (10 microM). Maximum decrease in O2 concentration was increased by 25% by sulpiride and unaffected by nialamide, L-DOPA, or nomifensine. The decreases in O2 concentration are indicative of increased O2 consumption and are a measure of oxidative energy production evoked by electrical stimulation. The increase in dopamine is due to the release of dopamine balanced by uptake and serves as an indication of neurotransmitter activity. The results indicate that increases in oxidative energy production following electrical stimulation are dependent on external Ca2+ entry through Cd(2+)-sensitive channels. Possible mechanisms for this coupling are discussed.

Ca(2+)-independent release of glutamate during in vitro anoxia in isolated nerve terminals

The effects of in vitro anoxia on the release of glutamate in isolated nerve terminals were studied. The extra-synaptosomal concentration of glutamate ([Glu]ext) under aerobic conditions was 2.3 microM and increased to 4.9 microM after 10 min of anoxia. However, when synaptosomes were incubated in the presence of lactate plus pyruvate instead of glucose, to prevent anaerobic glycolysis, anoxia induced an eightfold increase in the [Glu]ext. The accumulation of glutamate in the external medium during anoxia was Ca2+ independent and insensitive to a significant reduction of the Ca(2+)-dependent release of the amino acid. These results indicate that a Ca(2+)-independent efflux of cytoplasmic glutamate occurs during in vitro anoxia in isolated nerve terminals.

Cerebral ischemia: changes in brain choline, acetylcholine, and other monoamines as related to energy metabolism

The relationship of cerebral neurotransmitters acetylcholine (ACh), noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5HT) to the energy state of the brain was examined in mice at various times following complete ischemia produced by decapitation, in gerbils submitted to transient global ischemia (10 min bilateral carotid artery occlusion, 5 or 30 min recirculation), and in rats 24 hr after irreversible microembolism. Ischemia caused significant reductions in brain monoamine concentrations. The alterations in NA, DA, and 5HT levels persisted during recirculation and were unrelated to energy restoration. They were accompanied by an increase in the concentrations of related metabolites, suggesting that synthesis was unable to compensate for the release of the transmitters at early post-ischemic time periods. As described for the catecholamines and 5HT, ischemia resulted in a significant decrease in ACh level, but recirculation was associated with a rapid increase in ACh concentration. Impaired synthesis and/or increased release of ACh can be responsible for the decrease in ACh concentration during ischemia. Early post-ischemic elevation of ACh may be related to the large increase in brain choline brought about by ischemia.

Cytosolic free calcium concentrations in synaptosomes during histotoxic hypoxia

Altered cytosolic free calcium concentrations ([Ca2+]i) accompany impaired brain metabolism and may mediate subsequent effects on brain function and cell death. The current experiments examined whether hypoxia-induced elevations in [Ca2+]i are from external or internal sources. In the absence of external calcium, neither KCl depolarization, histotoxic hypoxia (KCN), nor the combination changed [Ca2+]i. However, with external CaCl2 concentrations as small as 13 microM, KCl depolarization increased [Ca2+]i instantaneously while hypoxia gradually raised [Ca2+]i. The combination of KCN and KCl was additive. Increasing external calcium concentrations up to 2.6 mM exaggerated the effects of K+ and KCN on [Ca2+]i, but raising medium calcium to 5.2 mM did not further augment the rise. Diminishing the sodium in the media, which alters the activity and perhaps the direction of the Na/Ca exchanger, reduced the increase in [Ca2+]i due to hypoxia, but enhanced the KCl response. The changes in ATP following K+ depolarization, KCN or their combination in the presence of physiological calcium concentrations did not parallel alterations in [Ca2+]i, which suggests that diminished activity of the calcium dependent ATPase does not underlie the elevation in [Ca2+]i. Valinomycin, an ionophore which reduces the mitochondrial membrane potential, elevated [Ca2+]i and the effects were additive with K+ depolarization in a calcium dependent manner that paralleled the effects of hypoxia. Together these results suggest that hypoxia-induced elevations of synaptosomal [Ca2+]i are due to an inability of the synaptosome to buffer entering calcium.

Hypoxia-induced neurotransmitter deficits in neonatal rats are partially corrected by exogenous GM1 ganglioside

Exposure of 7-day-old rats to 7% oxygen/balance nitrogen for 2 h results in selective changes of cholinergic, serotonergic, and dopaminergic neuronal markers in the frontal cortex, hippocampus, and striatum when evaluated 3 weeks after the insult. There is also about a 15% deficiency in brain weight. Treatment with GM1 ganglioside, 50 mg/kg i.p., for 2 days before and for 3 weeks after the hypoxic insult partially corrects the neurodevelopmental abnormalities including the deficiency in brain weight. We conclude that GM1 ganglioside might have therapeutic potential for treating suspected neonatal hypoxia.

3,4-Diaminopyridine-induced noradrenaline release from CNS tissue as a model for action potential-evoked transmitter release: effects of phorbol ester

We used rabbit hippocampus slices preincubated with [3H]noradrenaline (NA) and applied short pulses of 3,4-diaminopyridine (3,4-DAP) during superfusion to investigate the mechanism underlying the 3H overflow evoked by 3,4-DAP and the effects of the protein kinase C (PKC) activator, 4 beta-phorbol 12,13-dibutyrate (PDB), in this model. The 3H overflow evoked by 200 microM 3,4-DAP (about 4-5% of tissue-tritium) was largely Ca2+-dependent, tetrodotoxin-sensitive and markedly reduced by clonidine, but it was enhanced by yohimbine. We also demonstrated that the response could be inhibited via presynaptic adenosine (A1-) and opioid (kappa-) receptors. PDB (1 microM) markedly increased the 3,4-DAP-evoked 3H overflow, its effect being almost unchanged following activation of presynaptic alpha 2-, A1- or kappa-receptors. Inhibitors of PKC (polymyxin B, staurosporine) almost abolished the 3,4-DAP-evoked 3H overflow and antagonized the effects of PDB. It is concluded that application of 3,4-DAP (200 microM for 2 min) to brain slices leads to depolarization of the neuronal membrane, Na+ current-carried action potentials, Ca2+ influx and the exocytotic release of NA, which in many aspects resembles the release evoked by electrical field stimulation. The findings with phorbol ester further support the involvement of PKC in transmitter release. Activation of PKC apparently does not directly interfere with signal transduction mechanisms of presynaptic inhibitory receptors on noradrenergic nerve terminals.

Cytosolic-free calcium and neurotransmitter release with decreased availability of glucose or oxygen

Exposing brain slices to reduced oxygen tensions or impairing their ability to utilize oxygen with KCN decreases acetylcholine (ACh) but increases dopamine (DA) and glutamate in the medium at the end of a release incubation. To determine if these changes are due to alterations in the presynaptic terminals, release from isolated nerve endings (i.e. synaptosomes) was determined during histotoxic hypoxia (KCN). KCN reduced potassium-stimulated synaptosomal ACh release and increased dopamine and glutamate release. Since several lines of evidence suggest that altered calcium homeostasis underlies these changes in release, the effects of reducing medium calcium concentrations from 2.3 to 0.1-mM were determined. In low calcium medium, KCN still increased dopamine and glutamate release, but had no effect on ACh release. Hypoxia increased cytosolic-free calcium in both the normal and low calcium medium, although the elevation was less in the low calcium medium. Thus, the effects of histotoxic hypoxia on cytosolic free calcium concentration paralleled those on glutamate and dopamine release. Reducing the glucose concentration of the medium also increased cytosolic-free calcium. The data are consistent with the hypothesis that hypoxia and hypoglycemia increase cytosolic-free calcium, which stimulates the release of dopamine and glutamate, whose excessive release may lead to subsequent cellular damage postsynaptically.

Phosphatidylinositol metabolism during in vitro hypoxia

The effects of in vitro histotoxic hypoxia (0.5 mM KCN) on potassium-stimulated phosphatidylinositol turnover were determined. In rat cortical slices that were prelabeled with [2-3H]inositol, depolarization with 60 mM KCl increased [2-3H]inositol monophosphate and [2-3H]inositol bisphosphate accumulation in a Ca2+-dependent manner. At early times (10 s and 1 min), histotoxic hypoxia enhanced potassium-stimulated [2-3H]inositol monophosphate and inositol bisphosphate accumulation. Under basal conditions, hypoxia did not alter the accumulation of [2-3H]inositol phosphates. These results are consistent with the following hypothesis. The hypoxic-induced increase in cytosolic free calcium that we reported previously may lead to the early stimulation of inositol phosphates formation during hypoxia through activation of phospholipase C. The impairment of inositol phosphates formation during more prolonged hypoxia may be due to negative feedback regulation of the phosphatidylinositol cascade by protein kinase C or to a reduction in ATP levels.

Effects of in vitro hypoxia on depolarization-stimulated accumulation of inositol phosphates in synaptosomes

The effects of potassium and in vitro histotoxic hypoxia (i.e. KCN) on phosphatidylinositol turnover in rat cortical synaptosomes were determined. [2-3H] Inositol prelabelled rat synaptosomes were prepared from cerebral cortex slices that had been incubated with [2-3H] inositol. Depolarization with 60 mM KCl increased [2-3H] inositol phosphates in a time dependent manner. Depolarization with 60 mM KCl increased [2-3H] inositol trisphosphate transiently at 5 s. K+ induced rapid formation of [2-3H]-inositol bisphosphate and maintained an elevated level for at least 5 min. K+ stimulated gradual formation of [2-3H] inositol monophosphate with time. One minute of hypoxia enhanced potassium-stimulated [2-3H] inositol bisphosphate formation. However, 30 min of hypoxia impaired potassium-stimulated accumulation of [2-3H] inositol phosphates. The effects of histotoxic hypoxia were all dependent upon calcium in the medium and on K+-depolarization. Thus, hypoxia altered the K+-induced accumulation of inositol phosphates in prelabelled synaptosomes in a time dependent, biphasic manner that was calcium dependent.

Selective damage in striatum and hippocampus with in vitro anoxia

An in vitro model of anoxia-induced brain damage was utilized to help elucidate the biochemical basis of cell damage due to reduced oxygen availability. Previous studies suggest that anoxia-induced damage may vary presynaptically, post-synaptically or in the cell body. Thus, the consequences of an anoxic treatment incubation were examined with hippocampal slices, which contain cholinergic nerve terminals but not cell bodies, and with slices from whole striatum or its subregions, which contain both cholinergic cell bodies and nerve terminals. Slices were preincubated with either oxygen or nitrogen (treatment incubation) and the persistent effects of this treatment on [14C]acetylcholine and 14CO2 production from [U-14C]glucose were assessed in a subsequent incubation under optimal conditions (test incubation). An anoxic treatment incubation reduced the subsequent test incubation production of CO2 about 40% in the hippocampus and striatum. The anoxic treatment incubation diminished ACh production by 46% in the striatum, but only minimally affected that in the hippocampus. Anoxic treatment incubations of synaptosomes did not alter test-incubation ACh synthesis or CO2 production. Omission of calcium from the anoxic treatment incubation increased striatal ACh synthesis by 88% and CO2 production in both regions. These results suggest that anoxia produces persistent changes in postsynaptic processes or cell bodies (in this model cholinergic ones) that differ from those in nerve terminals and that calcium is important in the production of these deficits.