Anti-addiction Drug Ibogaine Prolongs the Action Potential in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Ibogaine is a plant alkaloid used as anti-addiction drug in dozens of alternative medicine clinics worldwide. Recently, alarming reports of life-threatening cardiac arrhythmias and cases of sudden death associated with the ingestion of ibogaine have accumulated. Using whole-cell patch clamp recordings, we assessed the effects of ibogaine and its main metabolite noribogaine on action potentials in human ventricular-like cardiomyocytes derived from induced pluripotent stem cells. Therapeutic concentrations of ibogaine and its long-lived active metabolite noribogaine significantly retarded action potential repolarization in human cardiomyocytes. These findings represent the first experimental proof that ibogaine application entails a cardiac arrhythmia risk for humans. In addition, they explain the clinically observed delayed incidence of cardiac adverse events several days after ibogaine intake. We conclude that therapeutic concentrations of ibogaine retard action potential repolarization in the human heart. This may give rise to a prolongation of the QT interval in the electrocardiogram and cardiac arrhythmias.

Neuroprotective activity of 2-amino-1,3,4-thiadiazole derivative 4BrABT--an in vitro study

4BrABT (2-(4-Bromophenylamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole) is a compound known for its interesting in vitro anticancer profile. 4BrABT inhibited proliferation and motility of several cancer cell lines in concentrations which were not toxic to normal cells. A major problem associated with cancer chemotherapy, but also caused by environmental factors such as pesticides, is neurotoxicity. Therefore, the aim of the presented study was an in vitro evaluation of the neuroprotective activity of this compound. 4BrABT activity (1-100 μM) was tested in cultures of mouse neurons, rat astrocytes and rat oligodendrocytes. A possible protective action of the compound in different neurodegenerative models, as serum deprivation (SD), excitotoxicity (presence of 500 μM glutamate in culture medium), as well as cisplatin toxicity (astroglia--50 μM and oligodendroglia--100 μM) was investigated. Cell viability in the tested cultures was assessed with the use of LDH and MTT methods. Moreover, 4BrABT ability to prevent the cisplatin-induced apoptosis in astrocyte and oligodendrocyte cultures was analysed after Hoechst 33342 fluorostaining. The obtained results indicate that 4BrABT was not toxic to neurons, astrocytes and oligodendrocytes. Moreover, a decrease in the neuronal LDH level was observed, which may suggest the ability of 4BrABT to act as a trophic agent. Furthermore, the protective action of the studied compound was shown in neuronal cultures exposed to neurotoxic conditions (presence of glutamate and trophic stress) and in cisplatin-treated astrocytes and oligodendrocytes. The expression of anticancer and neuroprotective activity raises hopes for the potential use of 4BrABT as a safe anticancer drug, or neuroprotective agent in chemotherapy-associated neurotoxicity.

Zinc pre-treatment enhances NMDAR-mediated excitotoxicity in cultured cortical neurons from SOD1(G93A) mouse, a model of amyotrophic lateral sclerosis

Zn²+ is co-released at glutamatergic synapses throughout the central nervous system and acts as a neuromodulator for glutamatergic neurotransmission, as a key modulator of NMDA receptor functioning. Zn²+ is also implicated in the neurotoxicity associated with several models of acute brain injury and neurodegeneration. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons in the spinal cord and cortex. In this study, we have investigated the modulatory role exerted by Zn²+ in NMDA-mediated neurotoxicity in either near-pure or mixed cortical cultured neurons obtained from either mice over-expressing the G93A mutant form of Cu/Zn superoxide dismutase (SOD1) human gene, a gene linked to familial ALS, or wild type (WT) mice. To that aim, SOD1(G93A) or WT cultures were exposed to either NMDA by itself or to Zn²+ prior to a toxic challenge with NMDA, and neuronal loss evaluated 24 h later. While we failed to observe any significant difference between NMDA and Zn²+/NMDA-mediated toxicity in mixed SOD1(G93A) or WT cortical cultures, different vulnerability to these toxic paradigms was found in near-pure neuronal cultures. In the WT near-pure neuronal cultures, a brief exposure to sublethal concentrations of Zn²+-enhanced NMDA receptor-mediated cell death, an effect that was far more pronounced in the SOD1(G93A) cultures. This increased excitotoxicity in SOD1(G93A) near-pure neuronal cultures appears to be mediated by a significant increase in NMDA-dependent rises of intraneuronal Ca²+ levels as well as enhanced production of cytosolic reactive oxygen species, while the injurious process seems to be unrelated to activation of nNOS or ERK1/2 pathways. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Effects of perinatal exposure to bisphenol A on brain neurotransmitters in female rat offspring

Pregnant Sprague-Dawley (CD IGS) rats were orally administered doses of bisphenol A (BPA) at 4, 40, and 400 mg/kg, from gestation days 6 to postnatal day 20. Neurotransmitters such as dopamine (DA) and serotonin (5HT) were extracted from the brains of dams and female offspring, and measured using liquid chromatography. BPA at 400 mg/kg was toxic and dosed rats died. At 3 wk after birth, brain levels of 3,4-dihydroxyphenylacetic acid (DOPAC, a DA metabolite), homovanillic acid (HVA, a DA metabolite), 5HT, 5-hydroxyindoleacetic acid (5HIAA, a 5HT metabolite) in female offspring were increased and the HVA/DA ratio was high in some brain areas of BPA-treated groups as compared with controls. At the age of 6 wk, levels of choline (Ch) in BPA-treated groups at 4 and 40 mg/kg were higher than control in all of eight brain areas. No changes were observed in acetylcholine (ACh) contents. In 9-wk-old offspring, changes in monoamines and metabolites were scattered and not great. At 3 wk after delivery, levels of 5HIAA in some brain areas of dams treated with BPA were higher than in control dams. Dose dependent increases in HVA and the HVA/DA ratio of the occipital cortex, and in the HVA/DA ratio of the frontal cortex were observed. The turnover of DA and 5HT was accelerated in 3-wk-old offspring and dams. BPA possesses very weak estrogenic activity. Changes in cerebral neurotransmitters observed in offspring and dams in this study may have been related to the estrogenic activity of BPA. However, further investigation is needed to examine the contribution of hormonal activity to such neurotransmitter changes.

Early pathophysiological features in canine renal papillary necrosis induced by nefiracetam

To ascertain the early pathophysiological features in canine renal papillary necrosis (RPN) caused by the neurotransmission enhancer nefiracetam, male beagle dogs were orally administered nefiracetam at 300 mg/kg/day for 4 to 7 weeks in comparison with ibuprofen, a non-steroidal anti-inflammatory drug (NSAID), at 50 mg/kg/day for 5 weeks. During the dosing period, the animals were periodically subjected to laboratory tests, light-microscopic, immunohistochemical, and electron-microscopic examinations and/or cyclooxygenase (COX)-2 mRNA analysis. In laboratory tests, a decrease in urinary osmotic pressure and increases in urine volume and urinary lactate dehydrogenase (LDH) level were early biomarkers for detecting RPN. Light-microscopically, nefiracetam revealed epithelial swelling and degeneration in the papillary ducts in week 7, while ibuprofen displayed degeneration and necrosis in the papillary interstitium in week 5. In immunohistochemical staining with COX-2 antibody, nefiracetam elicited a positive reaction within interstitial cells around the affected epithelial cells in the papillary ducts (upper papilla) in week 7, and ibuprofen positively reacted within interstitial cells adjacent to the degenerative and/or necrotic lesions in week 5. Ultrastructurally, nefiracetam exhibited reductions of intracellular interdigitation and infoldings of epithelial cells in the papillary ducts, whereas ibuprofen showed no changes in the identical portions. Thus, the early morphological change in the papilla brought about by nefiracetam was quite different from that elicited by ibuprofen. By the renal papillary COX-2 mRNA expression analysis, nefiracetam exceedingly decreased its expression in week 4, but markedly increased it in week 7, suggesting an induction of COX-2 mRNA by renal papillary lesions. These results demonstrate that the epithelial cell in the papillary ducts is the primary target site for the onset of RPN evoked by nefiracetam.

Is chemical neurotransmission altered specifically during methylmercury-induced cerebellar dysfunction?

Methylmercury (MeHg) is an important environmental neurotoxicant that is present in seafood and affects the developing and mature nervous system. The neurotoxicity induced by MeHg is a concern, particularly for fish-eating populations and pregnant or nursing women. During MeHg-induced neurotoxicity, degeneration of the granule cell layer in the cerebellum occurs, which leads to deficits in motor function. I suggest that the action of MeHg on specific neurotransmitter receptors contributes to the selective vulnerability of granule cells. MeHg appears to stimulate M(3) muscarinic acetylcholine receptors and to inhibit GABA(A) receptor subtypes preferentially on cerebellar granule cells. This could lead to the loss of tonic inhibition of granule cells as a result of antagonism of GABA(A) receptors, and a M(3)-receptor-mediated increase in the intracellular concentration of Ca(2+) and block of a K(+)-dependent leak current. The net result would be increased spontaneous release of glutamate, which, coupled with a MeHg-induced impairment of glutamate uptake by astrocytes, could cause Ca(2+)-mediated cytotoxicity.

The toxicology of bioregulators as potential agents of bioterrorism

Bioregulators or modulators are biochemical compounds such as peptides, that occur naturally in organisms. Advances in biotechnology create the potential for the misuse of peptide bioregulators in offensive biological weapons programmes. Bioregulators are a new class of weapons that can damage the nervous system, alter mood, trigger psychological changes and kill. Over the last twenty years, neuroscience has produced an explosion of knowledge about receptor systems in the nerve cells that are of critical importance in receiving chemical transmitter substances released by other nerve cells. Bioregulators are closely related to substances normally found in the body that regulates normal biological processes. The potential military or terrorist use of bioregulators is similar to that of toxins. Together with increased research into toxins, the bioregulators have also been studied and synthesized. This paper presents a review of bioregulators that could be used in terrorist or other hostile activities.

Organic solvents and the dopaminergic system

Organic solvents pose a considerable health risk for humans. It is due to their ability to cross biological barriers and indisputable toxicity on the one hand, and the wealth of applications and large production and consumption volumes on the other. The primary target of the toxic action of organic solvents is the nervous system. In this paper, some literature data showing that dopaminergic neurons and their projections are particularly susceptible to the toxic solvent action are presented.

Comprehensive evaluation of canine renal papillary necrosis induced by nefiracetam, a neurotransmission enhancer

The effects of nefiracetam, a neurotransmission enhancer, on renal biochemistry and morphology with toxicokinetic disposition were investigated in both in vivo and in vitro systems. In the in vivo studies with rats, dogs, and monkeys, only the dog exhibited renal papillary necrosis. Namely, when beagle dogs were orally administered with 300 mg/kg/day of nefiracetam over 11 weeks, decreased urinary osmotic pressure was noted from week 5, followed by increases in urine volume and urinary lactate dehydrogenase from week 8. The first morphological change was necrosis of ductal epithelia in the papilla in week 8. In toxicokinetics after 3 weeks of repeated oral administration to dogs, nefiracetam showed somewhat high concentrations in serum and the renal papilla as compared with rats and monkeys. As for metabolites, although metabolite-18 (M-18) concentration in the renal papilla of dogs was between that in rats and monkeys, the concentration ratios of M-18 in the papilla to cortex and papilla to medulla were remarkably high. In the in vitro studies, while nefiracetam itself showed no effects on the synthesis of prostaglandin E2 and 6-keto-prostaglandin F1alpha, a stable metabolite of prostaglandin I2, in canine renal papillary slices, only M-18 among the metabolites clearly decreased both prostaglandin syntheses. The basal prostaglandin synthesis in canine renal papillary slices was extremely low relative to those in rats and monkeys. Taken together, certain factors such as basal prostaglandin synthesis, M-18 penetration into the renal papilla leading to an intrarenal gradient, and inhibitory potential of M-18 on prostaglandin synthesis were considered to be crucial for the occurrence of renal papillary necrosis in dogs.

[Glutamate--a transmitter in the tensionfield between toxin and trophine]

Glutamate is the most important excitatory transmitter in the central nervous system. A tremendous complexity in the actions of this excitatory transmitter was found and an equally great complexity in the molecular structures of the receptors activated by glutamate. The glutamate receptor system influences nearly all other neurotransmitter systems. Glutamate also plays a central role in important processes of the central nervous system like the long-term potentiation in the hippocampus and the central sensitization for pain stimuli in the spinal cord, which is predominantly mediated by NMDA-receptors. But there are actions of glutamate beyond its function as an excitatory transmitter. Glutamate also has a trophic influence on neurons--depending upon the developmental stage. The excitotoxicity of glutamate mediated by NMDA-receptors is the common ultimate mechanism of acute and chronic nerve cell death and plays an important role in many acute neurologic diseases. The modulation of the glutamate system for example by antagonist of the glutamate-receptors might be a possible way in therapy of many different diseases of the central nervous system.

Heterologous desensitization of beta-adrenoceptor signal transduction in vivo

The hemodynamic actions of pituitary adenylate cyclase-activating polypeptide (PACAP-27) rapidly diminish upon repeated i.v. injection in rats treated with the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME). We now report that the beta-adrenoceptor agonist isoproterenol (0.5 microg/kg, i.v.) produces pronounced hypotensive and vasodilator effects in anesthetized rats pretreated with L-NAME (100 micromol/kg, i.v.). However, the hypotensive and vasodilator actions of isoproterenol were markedly diminished in L-NAME-treated rats in which tachyphylaxis to PACAP was induced immediately prior to the injection of the beta-adrenoceptor agonist. This suggests that a reduction in tissue concentrations of nitric oxide-containing factors allows tachyphylaxis to PACAP-27-mediated vasodilation to occur in vivo and that this process leads to the heterologous desensitization of beta-adrenoceptor-mediated responses.

Bioenergetics and glutamate excitotoxicity

Bioenergetic defects and abnormalities in glutamate neurotransmission have both been proposed to play important roles in neurological diseases of varying chronology, etiology and pathology. Recent experimental evidence suggests an intimate relationship between these two systems. Metabolic inhibition predisposes neurons to glutamate-mediated "excitotoxic" damage. The exact mechanism of this increased susceptibility is yet to be defined, but may involve, singly or in combination, decreased voltage-dependent Mg2+ blockade of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor, abnormalities in cellular Ca2+ homeostasis, or elevated production of reactive oxygen species. It is believed that enhancement of excitotoxicity by impaired metabolism may be a ubiquitous mechanism of neuronal death in neurological disease. Further elucidation of the exact mechanism of this enhancement may lead to the discovery of new targets for therapeutic intervention.

Excitotoxicity and neurodegeneration in amyotrophic lateral sclerosis

The pathogenesis of sporadic amyotrophic lateral sclerosis (ALS) is unknown, but several observations suggest that glutamate could participate in selective motor neuron degeneration. Extracellular levels of glutamate are elevated in ALS. Synaptic concentrations of glutamate are regulated by high-affinity glutamate transport, and defects in glutamate transport have also been observed in ALS tissue. Three sodium-dependent glutamate transporters have now been identified: a neuronal transporter EAAC1, and two astroglial transporters GLT-1 and GLAST. The defect in glutamate transport in ALS appears to be relatively specific for the GLT-1 subtype. The role of chronic excess glutamate and glutamate transporter loss has been investigated in experimental paradigms, where it was found that excitotoxicity could account for selective motor neuron degeneration. These culture paradigms have demonstrated that motor neurons are sensitive to glutamate toxicity via non-NMDA receptors and that various agents (e.g., antioxidants, glutamate release inhibitors, non-NMDA receptor antagonists) can be neuroprotective. These experimental studies will provide a basis for understanding the primary and secondary role of glutamate in motor neuron death and will provide important insight into possible therapeutic interventions.

Nitric oxide mediates the sustained opening of NMDA receptor-gated ionic channels which follows transient excitotoxic exposure in hippocampal slices

In the rat hippocampal slice, a brief exposure to glutamate and glycine increased MK-801 binding to 246% of controls. Increased binding persisted 90 min after removal of those amino acids from the incubation medium. Posttreatment with the competitive substrate inhibitor of nitric oxide synthase, N omega-nitro-L-arginine or with hemoglobin, which binds NO extracellularly, inhibited this postexcitotoxic increase in MK-801 binding. L-Arginine reversed this inhibitory effect but D-arginine did not. The combination of tetrodotoxin and low Ca2+, which blocks transmitter release prevented the poststimulation increase in MK-801 binding, suggesting a presynaptic component. These findings suggest that the sustained opening of NMDA receptor-gated ionic channels seen after transient glutamate/glycine stimulation is mediated by NO.

Protection by prostaglandins from glutamate toxicity in cortical neurons

The growing evidence that glutamate may be an important agent mediating ischemic damage to neurons, led us to investigate the possible protective effects of pharmacological agents against glutamate in a model system of cortical neurons. In this study we examined, in particular, the cytoprotective effect of prostaglandins. Experiments were carried out in vitro by using rat cortical neurons in culture for 10 days. They were incubated for 3h with glutamate (10 microM) in the presence or absence of various pharmacological agents including prostaglandins (PGD2, PGE1, PGE2, PGF2 alpha, PGI2, 6-Keto-PGF1 alpha, carba-TXA2, carba-PGI2 and PGF2 alpha-methylester). Increase in lacticodehydrogenase (LDH) release into the culture medium has been measured as an index of cell injury. When neurons were incubated with glutamate they released LDH due to NMDA-receptor activation since D-L-2-amino-5-phosphonovaleric acid, a specific receptor antagonist, protected the cells. The protective activity of oxypurinol, amflutizole, superoxide dismutase, NG nitro-L-arginine and quinacrine, also suggests that xanthine oxidase activation, the generation of superoxide radical, and nitrix oxide, as well as phospholipase A2 stimulation are responsible for neuron injury (i.e. LDH release). All the tested prostaglandins, except PGF2 alpha-methylester, afforded significant protection at concentrations between 0.1 and 10 microM. The order of potency of the prostanoids was: PGF2 alpha = PGE2 > Carba-TXA2 > PGE1 > PGD2 > PGI2 = Carba-PGI2 > 6-Keto-PGF1 alpha. Additional experiments showed that prostaglandins did not compete for the NMDA binding site and that they did not inhibit free radical-related membrane damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitatory amino acid antagonists protect cochlear auditory neurons from excitotoxicity

Since ischemic damage in the brain is linked to glutamate excitotoxicity, the effects of an acute exposure to glutamate, alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) or N-methyl-D aspartate (NMDA) on the radial dendrites were compared with those occurring after a severe cochlear ischemia. Glutamate and AMPA, but not NMDA, produced a drastic swelling restricted to the radial dendrites below the inner hair cells (IHCs). At a concentration of 20 microM AMPA, a full electrophysiological recovery could be observed in some cochleas after washing the drug out. A prior perfusion of 6-7-dinitroquinoxaline-2,3-dione (DNQX, 50 microM) prevented the 25 microM AMPA-induced dendritic swelling. No protective effect of D-2-amino-5-phosphonopentanoate (D-AP5) could be observed. In the same way, ischemia (5-40 minutes) resulted in a clear swelling of the radial dendrites. While D-AP5 had no protective effects, 50 microM DNQX protected most of the radial dendrites from the ischemia-induced swelling, excepting those contacting the modiolar side of the IHCs. Finally, 50 microM DNQX + 50 microM D-AP5 resulted in a nearly complete protection of all the radial dendrites. Altogether, these results suggest that the acute swelling of radial dendrites primarily occurs via AMPA/kainate receptors. However, in radial dendrites contacting the inner hair cells on their modiolar side, NMDA receptors may be also involved.

Excitatory transmitter neurotoxicity

The major excitatory neurotransmitters in the mammalian CNS--glutamate (Glu) and acetylcholine (ACh)--have vitally important beneficial functions but also harbor treacherous neurotoxic potential which, as described in this review, can be expressed in several different ways.

Cysteine sulphinate and cysteate: mediators of cysteine toxicity in the neonatal rat brain?

Excitotoxic amino acids contain two acidic groups, but cysteine represents an exception to this rule. The hypothesis that cysteine toxicity is mediated by the oxidized and diacidic metabolites cysteine sulphinate and/or cysteate was tested in the present study. The issue was approached in three different ways. Firstly, the distribution of brain injury after subcutaneous administration of cysteine (1 mg/g) to 4-day-old rats was compared with that caused by cysteine sulphinate (3 mg/g). Secondly, the effects of excitatory amino acid receptor antagonists on cysteine and cysteine sulphinate toxicity were investigated. Thirdly, the cerebral concentrations of cysteine sulphinate were determined after cysteine administration and compared with those obtained after cysteine sulphinate injection. The cerebral cortex was the region most vulnerable to cysteine toxicity, followed by the hippocampus (especially the medial subicular neurons), amygdala, caudoputamen, cerebellum and septum. Pronounced extravasation of red blood cells was observed in lesioned areas. One day after cysteine administration, the injury was infarction-like and sharply demarcated. Cysteine sulphinate-induced damage resembled cysteine-induced lesions in some respects: the anterior cingulate and retrosplenial cortices, as well as medial subicular cells, were quite vulnerable. However, the differences prevailed. Cysteine sulphinate, but not cysteine, killed neurons of the superficial part of the tectum, the medial habenula, the ventromedial hypothalamus and the arcuate nucleus. Further, while cysteine toxicity was prominent in deep cortical layers, cysteine sulphinate preferentially damaged superficial cortical neurons. Cysteine toxicity was abolished by pretreatment with MK-801, a selective NMDA antagonist, but not by 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo(F)quinoxaline, a selective AMPA receptor blocker. In contrast, the considerably smaller lesion seen after cysteine sulphinate administration was only partially prevented by MK-801. Large (19-fold) increases in cortical cysteine sulphinate concentration were noted after injection of a toxic dose of cysteine. This corresponds to 90 nmol cysteine sulphinate/g protein. The cysteate concentration was not increased above the detection limit. Injection of a toxic dose of cysteine sulphinate elevated cysteine sulphinate concentration in the frontomedial cortex (a region consistently injured by cysteine sulphinate) almost three orders of magnitude more than that observed after cysteine administration. Taken together, these results strongly suggest that neither cysteine sulphinate nor cysteate alone mediate cysteine toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Protective effects of a vitamin B12 analog, methylcobalamin, against glutamate cytotoxicity in cultured cortical neurons

The effects of methylcobalamin, a vitamin B12 analog, on glutamate-induced neurotoxicity were examined using cultured rat cortical neurons. Cell viability was markedly reduced by a brief exposure to glutamate followed by incubation with glutamate-free medium for 1 h. Glutamate cytotoxicity was prevented when the cultures were maintained in methylcobalamin-containing medium. Glutamate cytotoxicity was also prevented by chronic exposure to S-adenosylmethionine, which is formed in the metabolic pathway of methylcobalamin. Chronic exposure to methylcobalamin and S-adenosylmethionine also inhibited the cytotoxicity induced by N-methyl-D-aspartate or sodium nitroprusside that releases nitric oxide. In cultures maintained in a standard medium, glutamate cytotoxicity was not affected by adding methylcobalamin to the glutamate-containing medium. In contrast, acute exposure to MK-801, a NMDA receptor antagonist, prevented glutamate cytotoxicity. These results indicate that chronic exposure to methylcobalamin protects cortical neurons against NMDA receptor-mediated glutamate cytotoxicity.

Ultrastructural evidence that mercuric chloride lowers the threshold for glutamate neurotoxicity in an organotypic culture of rat cerebellum

Separate exposure of organotypic cultures, derived from newborn rat cerebellum, to non-toxic concentration of either 100 microM glutamate (GLU) or 1 microM mercuric chloride (MC), for as long as 3 days, produced no distinct ultrastructural changes in neurons and glial cells. By contrast, simultaneous exposure to both agents resulted, as early as after 30 min, in microvacuolar degeneration of neurons and later on in postsynaptic abnormalities, typically accompanying excitotoxic lesions but not heavy metal-induced lesions. The results indicate that MC at low micromolar concentrations lowers the threshold for GLU neurotoxicity.

The inhibition of agonist- or depolarisation-evoked formation of inositol phosphate by excitatory amino acids in rat cerebral cortex is due to the neurotoxic action of this class of neurotransmitter and is mediated by sodium influx

Previous work has shown that excitatory amino acids inhibit agonist or depolarisation evoked formation of inositol phosphate in brain. In this paper, possible mechanisms by which this may be occurring have been investigated. The inhibition of carbachol-stimulated formation of inositol phosphate by kainic acid (KA) was abolished if the tissue was incubated in a sodium-free medium. The sodium channel activator, veratridine (10 microM) and the sodium ionophore, monensin (3 microM), also inhibited the response of inositol phosphate to carbachol; tetrodotoxin (300 nM) reversed the effect of veratridine but not monensin or KA. Incubation with cadmium (0.3 mM) or removal of extracellular calcium did not alter the effects of KA, monensin or veratridine. The effects of KA were significantly reduced with the Na+/K(+)-ATPase inhibitor, ouabain (10-100 microM). Inhibition by KA was still observed in tissue that had been prestimulated with KA and then washed to remove the agonist. Incorporation of [3H]inositol into inositol lipids was significantly reduced by KA, in the absence or presence of carbachol. It is suggested that the inhibition of the turnover of stimulated phosphoinositide, by excitatory amino acids, is related to the neurotoxic actions of these transmitters and is mediated by Na+ influx, with a consequent activation of Na+/K(+)-ATPase, depletion of cellular ATP and reduction in synthesis of inositol lipid.

Effect of neurotransmitter-selective drugs in mice selected for differential sensitivity to the hypothermic actions of ethanol

Mice selectively bred for resistance (HOT) and sensitivity (COLD) to the hypothermic effect of EtOH were tested for their hypothermic response to neurotransmitter-specific drugs and for the effect of such drugs on EtOH induced hypothermia (HT). The drugs administered were the opiate drugs morphine, levorphanol and U50488H, the dopamine agonists apomorphine, LY171535 and SKF38393, the dopamine antagonist chlorpromazine, the alpha adrenergic agonist St587, the cholinergic agonist nicotine and amphetamine, which increases the release of catecholamines. All of the drugs tested, with the exception of SKF38393 and amphetamine, induced a hypothermic response in HOT and COLD mice. SKF38393 had no effect on body temperature or HT produced by EtOH. Amphetamine caused HT at low doses and hyperthermia at high doses. COLD mice were more sensitive than HOT mice to the hypothermic effect of morphine and levorphanol, mu-opiate agonists, and U50488H, a relatively specific kappa agonist. All of the other drugs tested were approximately equally potent in HOT and COLD mice. These results suggest that the differential sensitivity of HOT and COLD mice to EtOH-induced HT may be partially mediated through genetic changes in opiate mechanisms.

Low calcium-induced release of glutamate results in autotoxicity of cerebellar granule cells

Primary cultures of cerebellar rat granule neurons were grown for 18-22 days in vitro in the absence of antibiotics. When the cultures were placed in a low calcium (no EGTA) balanced salt solution at room temperature, rapid cell death occurred usually within 30 min of placing cells in the buffer. Changes in the cells were evident within 10 min and included an apparent cellular granulation with a partial loss of cell body birefringence at 10 x magnification which was complete by 30 min. This rapid death was prevented by (1) replacing chloride in the buffer with acetate; (2) increasing the osmolarity of the buffer by 30% with sucrose; (3) the addition of the selective excitatory amino acid (EAA) antagonist, 2-amino-7-phosphonoheptanoic acid (APH, 200 microM) but not by the selective kainate-quisqualate antagonist, glutamylaminomethylsulfonic acid (GAMS, 400 microM); or (4) the addition of one of the following calcium channel antagonists, verapamil (400 microM) diltiazem (150 microM) or lanthanum (5 microM). Placing cells in low calcium buffer resulted in a 3.7- and 3.2-fold increase in the non-selective secretion of aspartate and glutamate (as well as other amino acids) over baseline secretion (same buffer except containing 2.5 mM calcium). This increase was partially prevented by verapamil, but not by APH or chloride deletion. Verapamil only partially prevented the efflux of glutamate in buffer containing 1 mM EGTA. These results indicate that placing cells in low calcium buffer results in neurotoxicity secondary to both the influx of chloride and water in conjunction with the efflux of amino acids, some of which stimulate an excitatory amino acid receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca2+ modulators as antidotes to imipramine and neurotransmitter toxicity

Flunarizine and nimodipine, Ca2+ modulators which exert antagonist effects against catecholamines and serotonin and have specific action on the brain, were used as antidotes to imipramine toxicity in the rat. Imipramine, a tricyclic antidepressant, inhibits synaptic reuptake of catecholamines and serotonin. Flunarizine administered concurrently with imipramine increased survival time significantly (p less than 0.04). After a lethal dose of imipramine (85 mg/kg) 5 out of 5 animals treated with flunarizine (2.37 +/- 1.21 mg/kg in divided doses) and 4 out of 5 animals treated with nimodipine (0.36 +/- 0.11 mg/kg) survived. The acute toxicity of imipramine might be related, in part, to drug-induced alteration in turnover of excitatory neurotransmitters which will induce intracellular Ca2+ accumulation and damage to vital organs. These toxic effects of endogenously produced neuroamines may be antagonized by nimodipine or flunarizine.