Neurotransmitters In Rat Brain Research Articles

In vivo determination of the monoamine neurotransmitters in rat brain by liquid chromatography with a thioctic acid/iridium oxide–palladium modified electrode

The fabrication and application of a electrochemical detector (ED) with the thioctic acid (TA)/iridium oxide (IrO2)–palladium (Pd) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) at the TA/IrO2–Pd CME were investigated by differential pulse voltammetry (DPV). It was found that the CME could be permselective to DA cations and exile the AA anions, which could be used to determine the monoamine neurotransmitters and avoid the interference of AA in LC. In liquid chromatography with electrochemical detection (LC–ED), DA, norepinephrine (NE), 5-hydroxytryptamine (5-HT), epinephrine (E) and 3,4-dihydroxyphenylactic acid (DOPAC) were determined at the CME. The linear ranges of five analytes were over three orders magnitude and the limits of detection were 0.05 pmol for DA, 0.05 pmol for NE, 0.05 pmol for E, 0.10 pmol for 5-HT and 1.00 pmol for DOPAC. The application of this method coupled with microdialysis sampling for the in vivo determination of the monoamines in rat brain was also investigated.

In vivo monitoring of the monoamine neurotransmitters in rat brain using microdialysis sampling with liquid chromatography electrochemical detection

The fabrication and application of a novel electrochemical detector (ED) with the new ion-exchange polymer-overoxidized polypyrrole (OPPy) film chemically modified electrode (CME) for liquid chromatography (LC) are described. The electrochemical behavior of dopamine (DA) and ascorbate (AA) at the OPPy CME is investigated by cyclic voltammetry (CV). It is found that the CME can permselective dopamine cations and exile the ascorbate anions, which could be used to determine the monoamine neurotransmitters and avoid the interference of ascorbate in liquid chromatography. The thickness of the OPPy film has an important effect on the sensitivity and selectivity for dopamine with respect to ascorbate. In liquid chromatography with electrochemical detection (LC-ED), DA, norephinephrine (NE), 5-hydroxytryptamine (5-HT), epinephrine (E) and 3,4-dihydroxyphenylacetic acid (DOPAC) have good and stable current responses at the CME. The linear ranges of five analytes are over three orders of magnitude and the limits of detection are 0.05 pmol for DA, 0.05 pmol for NE, 0.05 pmol E, 0.1 pmol for 5-HT and 1.0 pmol for DOPAC. The applications of this method coupled with microdialysis sampling for the in vivo determination of the monoamine neurotransmitters in the different areas of rat brain is satisfactory.

The N-Methyl-[formula omitted]-aspartate Neurotransmitter Receptor Is a Mammalian Brain Target for the Dinoflagellate Pfiesteria piscicida Toxin

Blooms of Pfiesteria piscicida, a dinoflagellate in eastern U.S. coastal rivers, are believed to secrete toxins that kill fish and produce short-term memory loss in humans. Only one or two of Pfiesteria's multiple stages secrete the toxin, and only under certain environmental conditions. Thus, neither the presence of Pfiesteria nor fish kill alone can be indicative of toxin presence. The objective of this study was to identify the mammalian molecular brain target for the toxin that is associated with decrements in memory. Seven rat brain neurotransmitter receptors were selected to study because of their reported roles in cognitive function: receptors for nicotine, muscarine, AMPA/kainate, N-methyl-d-aspartate (NMDA), γ-aminobutyric acid, and dopamine 1 and 2. The effects of 17 environmental and laboratory samples on radioactive ligand binding to these receptors were studied. Of the seven receptors, binding only to the NMDA receptor was inhibited by only the two Pfiesteria-containing waters (identified by PCR) that also killed fish, and not by any of the other 15 samples tested. It is suggested that inhibition of NMDA-receptor binding is the cause of memory loss in exposed humans. Thus, it could be a useful biomarker for the toxin's presence in rivers for decisions on closures and for identification of the fractions containing the toxin during its purification. Knowledge of the toxin's molecular target, and how it affects its function, also leads to suggestions for therapeutics to use in animal models.

Are Neuropeptides FF and SF Neurotransmitters in the Rat?

We have compared the affinities and anti-opioid activities of the different peptides putatively produced by the rat NPFF precursor, NPAFLFQPQRF-NH2 (NPA-NPFF) and EFWSLAAPQRF-NH2 (EFW-NPSF), with those already identified in nervous tissue, FLFQPQRF-NH2 (NPFF) and SLAAPQRF-NH2 (NPSF). NPFF and NPA-NPFF exhibit a high affinity (0.34 and 0.14 nM, respectively) for [125I]1DMe binding sites of the rat spinal cord. In contrast, EFW-NPSF displays an affinity 13 times higher than NPSF (1.99 and 9.5 nM, respectively). In rat dorsal raphe neurones, EFW-NPSF, NPFF, and NPA-NPFF maximally reduce the inhibitory effect of nociceptin on the [Ca2+]i transients triggered by depolarization by 39, 31, and 58%, respectively. NPSF is inactive in the same test. We conclude that NPA-NPFF and EFW-NPSF are likely to be the physiologically active neurotransmitters in rat brain.

Effect of estradiol and tamoxifen on brain membranes: investigation by infrared and fluorescence spectroscopy

Nongenomic effects of steroids on rat brain neurotransmitter transporters and receptors have been reported in several laboratories. In the present study, we have investigated possible membrane effects of 17α- and 17β-estradiol, as well as tamoxifen, by studying their interactions with synthetic phospholipid membranes using Fourier transform infrared spectroscopy. We have also used the fluidity of rat striatal and frontal cortex membranes, as determined by fluorescence depolarization of the probe 1,6-diphenyl-1,3,5-hexatriene (DPH), to probe the effects of these drugs on membranes. Our results show that tamoxifen induces conformational disorder along the acyl chains of deuterated dimirystoylphosphatidylcholine and decreases the gel to liquid-crystalline phase transition temperature by approximately 10°C. Similar effects, although less pronounced, were observed with 17β-estradiol, whereas 17α-estradiol had no significant effect. The DPH fluorescence anisotropy of striatum and frontal cortex membranes was decreased in vitro with 17β-estradiol or tamoxifen and also with 17α-estradiol, but to a lesser extent. These results suggest a stereospecific estradiol effect on membranes and that the effects of these compounds are not related to their activity on estrogen receptors. These observations support a different mechanism of action of steroids that could be implicated in their neuroprotective activity.

Effect of cassava on motor co-ordination and neurotransmitter level in the albino frat

The root of Cassava, a tropical plant, is consumed in the tropics and has been attributed as the cause for various tropical neuropathies. This study aims to discover the neurotoxic effects of chronic cassava consumption of Indian origin and the effect of malnutrition. The assessment is based on the motor co-ordination and brain neurotransmitters in rats. Cassava consumption reduced the motor co-ordination, but the changes in neurotransmitter levels due to cassava consumption (except for 5HT in corpus striatum) was identical with malnutrition-induced changes, indicating that the toxicity of chronic cassava consumption (of Indian origin) is mainly due to the associated protein calorie malnutrition (PCM).

Effects of the Immunostimulant, Levamisole, on Opiate Withdrawal and Levels of Endogenous Opiate Alkaloids and Monoamine Neurotransmitters in Rat Brain

This report presents evidence that the immunostimulant drug levamisole, (−)-(S)-2,3,5,6-tetrahydro-6-phenylimidazo[2,1-b] thiazole monohydrochloride, produced a significant elevation of endogeneous morphine and codeine levels in brain regions and peripheral organs and attenuated the effects of naltrexone-induced withdrawal in morphine-addicted rats. Levamisole also significantly altered the metabolism of norepinephrine, dopamine, and serotonin in specific brain regions. These results suggest that levamisole’s attenuation of opiate withdrawal may be related to its ability to increase endogeneous opiate alkaloid levels and/or to alter central monoaminergic function. Levamisole does not have significant affinity for opiate receptors. These results raise the intriguing possibility that agents such as levamisole, which elevate the levels of the endogenous opiate alkaloids, might be useful for treating narcotic withdrawal. The mechanism for the immunostimulatory properties of agents such as levamisole and muramyl dipeptide (MDP) have not been established. We suggest that the ability of MDP and levamisole to increase endogenous opiate alkaloids may be related to their immunostimulatory properties.

Rat brain neurotransmitter turnover rates altered during withdrawal from chronic cocaine administration

This experiment utilized neurotransmitter turnover rates to assess the effects of withdrawal from cocaine on the brain. A triad-littermate design was used to evaluate the importance of response dependency on the effects of withdrawal from chronic cocaine administration upon brain biogenic monoamine and amino acid putative neurotransmitter turnover rates. Each member of a triad was exposed to one of three conditions. Cocaine infusions (0.33 mg/inf) were used to engender and maintain lever pressing by one rat under an FR 2 schedule, while the second and third rats received simultaneous infusions of either cocaine or saline, respectively. After a minimum of 15 days exposure to the three treatment conditions and 24 h after the start of the last drug session, the triads were pulse labeled with [ 14C]glucose, [ 3H]tyrosine and [ 3H]tryptophan and killed 60 or 90 min later by total immersion in liquid nitrogen. The frozen brains were removed and dissected at −20° C into 22 areas. The content and specific radioactivities for dopamine (DA), noradrenaline (NA), serotonin (5-HT), aspartate (Asp), glutamate (Glu), glycine (Gly) and γ-aminobutyric acid (GABA) were determined in each brain region using high pressure liquid chromatography with electrochemical (biogenic monoamines) or fluorescence (amino acids) detection followed by liquid scintillation spectrometry. Turnover rates (TOR) were calculated and compared across treatment conditions. The significant decreases in TOR resulting from chronic cocaine exposure included 5-HT in the frontal cortex, DA in the cingulate cortex, entorhinal-subicular and motor-somatosensory cortices and NA in the inferior colliculus. Significant increases in TOR were also observed which included 5-HT in the preoptic-diagonal band region, DA in the hippocampus and NA in the pyriform and temporal-auditory cortices, the dentate gyrus and brainstem. GABA TOR was also increased in the preoptic-diagonal band region, dentate gyrus and brainstem of both groups receiving cocaine as was Glu TOR in the pyriform cortex and cerebellum. In addition, changes were seen in the rats under the ratio schedule of cocaine self-administration that were not seen in rats receiving yoked-cocaine infusions that included increased TOR of 5-HT in the pyriform cortex, NA in the caudate-putamen and GABA in the pyriform and motor-somatosensory cortices. Decreased 5-HT TO was seen in the motor-somatosensory cortex and dentate gyrus in the rats that had self-administered cocaine compared to the yoked-cocaine infused group. Perhaps the most interesting changes were those seen in the yoked-cocaine group that were reversed in the rats whose responding was maintained by cocaine. These included reversals of changes in GABA TO in the temporal-auditory cortices, caudate-putamen, ventral tegmental area and in DA, NA and GABA TO in the substantia nigra. In general, these data indicate that withdrawal from chronic exposure to cocaine produces changes in brain neuronal activity which may represent rebound increases that could be an indication of an acute withdrawal responses. These data indicate that DA, NA, 5-HT and GABA releasing neurons in selected brain regions are part of these processes. In addition, the effects on some brain neuronal systems may depend on the context under which the drug is presented.

Effects of prazosin on the dopaminergic neurotransmission in rat brain

Effects of systemic and local administration of prazosin, an α 1-adrenoceptor antagonist, on dopaminergic neurotransmission in the caudate putamen and nucleus accumbens were characterized in microdialysis experiments. Prazosin (10 mg/kg s.c.) resulted in blood pressure reduction, however, did not alter dopamine release in the two examined brain areas. In contrast, local administration of prazosin (10 μM) via the microdialysis probe resulted in a clear attenuation of dopamine output, indicating that tonically activated α 1-adrenoceptors stimulate dopamine release in the caudate putamen as well as in the nucleus accumbens. The relevance of this finding for antipsychotics exhibiting antagonism at α 1-adrenoceptors is discussed.

Heterogeneous subregional binding patterns of 3H-WIN 35,428 and 3H-GBR 12,935 are differentially regulated by chronic cocaine self- administration

We examined the influence of chronic cocaine exposure, in an unlimited access self-administration paradigm, on density of the dopamine transporter (3H-WIN 35,428 and 3H-GBR 12,935 binding) and concentration of monoamine (dopamine, serotonin, noradrenaline and metabolites) neurotransmitters in rat brain. In normal rodent striatum 3H-WIN 35,428 and 3H-GBR 12,935 binding to the dopamine transporter, although generally similar, showed different subregional rostrocaudal and mediolateral gradients, suggesting that the two ligands might bind to different subtypes or states of the dopamine transporter. Following chronic, unlimited access cocaine self-administration, binding of 3H-WIN 35,428 was significantly elevated in whole nucleus accumbens (+69%, p < 0.001) and striatum (+65%, p < 0.001) on the last day of cocaine exposure ("on-cocaine group"); whereas in the 3 week withdrawn animals ("cocaine-withdrawn group"), levels were either normal (striatum) or reduced (-30%, p < 0.05, nucleus accumbens). Although similar changes in 3H-GBR 12,935 binding were observed, this dopamine transporter ligand showed a smaller and highly subregionally dependent increase in binding in striatal subdivision of the on-cocaine group, but a more marked binding reduction in the cocaine-withdrawn animals. As compared with the controls, mean dopamine levels were reduced in striatum (-15%, p < 0.05) of the on-cocaine group and in nucleus accumbens (-40%, p < 0.05) of the cocaine-withdrawn group. These data provide additional support to the hypothesis that some of the long-term effects of cocaine exposure (drug craving, depression) could be consequent to reduced nucleus accumbens dopamine function. Our data also suggest that dopamine transporter concentration, and perhaps function, might undergo up- or downregulation, either as a direct effect of cocaine, or indirectly as part of a homeostatic response to altered synaptic dopamine levels, and therefore might participate in the neuronal events underlying cocaine-induced behavioral changes.

Separation and quantitation of the amino acid neurotransmitters in rat brain by capillary electrophoresis

Capillary electrophoresis (CE) has been used to separate the CBI derivatives of the neurotransmitters γ-yaminobutyric acid, glycine. glutamate. aspartate. norepinephrine and dopamine from 18 other amino acids present in the rat brain. The procedure, which requires an injection volume of < 10 nl, gave detection limits of 24–40 fmol using UV detection at 420 nm. Efficiencies for the derivatized amino acids varied from 344,000 to 444,000 theoretical plates. The method was applied successfully to the quantitation of the amino acid neurotransmitters and several other amino acids in a rat brain homogenate.

Chronic exposure to morphine and naltrexone induces changes in catecholaminergic neurotransmission in rat brain without altering μ-opioid receptor sensitivity

In order to investigate the role of μ-opioid receptor regulation in catecholaminergic neurotransmission during morphine tolerance/dependence and supersensitivity, we measured changes in number and functional properties of two distinct types of μ receptors in the brain of rats chronically treated with morphine and naltrexone. In membranes of striatum and cortex of morphine treated rats the binding of μ ligand [ 3H]DAMGO was unaltered, whereas an increase in μ binding sites was found in these brain regions of naltrexone treated rats. The ability of the μ agonist DAMGO to inhibit the dopamine D-1 receptor stimulated cAMP production in striatal slices and the electrically evoked release of [ 3H]noradrenaline from cortical slices was unaffected in both experimental groups. The major changes found were an increased D-1 receptor stimulated cAMP production and an enhanced release of nonadrenaline in morphine treated rats and a decreased D-1 receptor stimulated cAMP production in naltrexone treated rats. These data support the hypothesis that tolerance and supersensitivity to morphine and other μ-opioids may be caused by up- and down-regulated neuronal second messenger systems linked to μ-opioid receptors, rather than by changes in the sensitivity of the μ-opioid receptor itself.

Opioid receptor-mediated inhibition of evoked catecholamine release from cultured neurons of rat ventral mesencephalon and locus coeruleus

The effects of selective opioid agonists on the evoked release of [ 3H]dopamine and [ 3H]noradrenaline were studied in cultured dopaminergic neurons of the ventral mesencephalon (containing the substantia nigra and ventral tegmental area) and in cultured neurons of the noradrenergic locus coeruleus, respectively. The cultures were prepared from embroyonic day 15 rat brains. After 9 days in culture, the calcium-dependent release of [ 3H]dopamine from dopaminergic substantia nigra/ventral tegmental aera neurons induced by 23 mM k + appeared to be inhibited exclusively by activation of κ-opioid receptors, as [ 3H]dopamine release was inhibited selectively by the κ- agonists U69,593 and dynorphin-(1–13) (EC 50 8 and 5 nM, respectively), and this inhibitory effect was antagonized by the κ-selective antagonist nor-binaltorphine (K i 0.07 nM). In contrast, cultured noradrenergic locus coeruleus neurons appeared to contain release-inhibitory μ-opioid receptors only, as evoked [ 3H]noradrenaline release was inhibited selectively by the μ agonist [D-Ala 2, MePhe 4, Gly-ol 5]enkephalin (EC 50 45 nM), a response that was antagonized by the preferential μ antagonist naloxone (K i = 0.7 nM). The δ-opioid receptor agonist [D-Ser 2(O-butyl), Leu 5]enkephaly-Thr 6 did not affect catecholamine release. Dopamine release from cultured ventral mesencephalic neurons, induced by 100 μM N-Methyl-D-Aspartate (NMDA), also appeared to be subject to κ receptor-mediated inhibition, whereas NMDA-induced noradrenaline release from cultured locus coeruleus neurons was under the inhibitor control of μ receptors. It is therefore concluded that in rat brain neurotransmitter release from dopaminergic and noradrenergic neurons, originating from the substantia nigra/vental tegmental area and the locus coeruleus, is liable to inhibition by homogenous populations of κ- and μ-opioid receptors, respectively, independent of the input of non-opioid neurons from distict nuclei.

Effects of methamphetamine and ethanol on learning and brain neurotransmitters in rats

The interactions of methamphetamine (MAMP) and ethanol (EtOH) on multiple active/passive avoidance performance and neurotransmitters in different brain regions were examined. After the acquisition schedules, rats were retrained under the influence of MAMP (2 mg/kg/day, IP), EtOH (2 g/kg/day, IP), and in combination over 20 days in rats ( n = 6 per group). As a function of progress of drug treatment, MAMP-EtOH mixtures disrupt the learned avoidance performance and produced severe impairment of discriminative behavior caused by enhancement of excitability induced by MAMP when compared with MAMP only. At withdrawal, MAMP-EtOH-induced impairments of performance significantly persisted, whereas MAMP-only-induced impairments slightly recovered. At the eleventh day of drug withdrawal, MAMP-only-induced alterations of neurotransmitter levels at different regions were alleviated by EtOH, but these did not return to normal levels. These data provide support for the direct antagonistic and indirect additive interactions following constant daily treatment with a combination of MAMP and EtOH. EtOH may be an important factor in MAMP abuse to MAMP-induced psychosis or neurotoxicity.

Tandospirone and its metabolite, 1-(2-pyrimidinyl)-piperazine—II. Effects of acute administration of 1-PP and long-term adminstration of tandospirone on noradrenergic neurotransmission

1-(2-Pyrimidinyl)-piperazine (1-PP) is a common metabolite of the antidepressant/anxiolytic 5-HT 1A agonists, tandospirone (SM-3997), gepirone, buspirone and ipsapirone. The present electrophysiological studies were undertaken to characterize in vivo the effect of 1-PP on noradrenergic (NE) neurotransmission in rat brain. At small doses, 1-PP (ED 50 = 80 μg/kg, i.v.) reversed the depressant effect of the α 2-adrenoceptor agonist, clonidine (20 μg/kg, i.v.) on the firing activity of NE neurones of the locus coeruleus. After long-term treatment with tandospirone (10 mg/kg/day, s.c. × 14 days), the responsiveness of these NE neurones to intravenous administration of clonidine was decreased but their mean firing frequency remained within the control range. The effect of 1-PP on the postsynaptic α 2-adrenoceptor of pyramidal neurones in the hippocampus was investigated: intravenous administration of 1-PP (2–8 mg/kg, i.v.) reduced the effect of microiontophoretically-applied NE on CA 3 pyramidal neurones of the dorsal hippocampus, without affecting their responsiveness to GABA and 5-HT. The effect of the electrical stimulation of NE neurones of the locus coeruleus in reducing firing activity of pyramidal neurones, which is mediated by postsynaptic α 1-adrenoceptors, was increased by 47% after acute administration of 1-PP (4 mg/kg, i.v.) presumably as a result of blockade of terminal α 2-autoreceptors. The effectiveness of these stimulations remained unchanged after long-term treatment with tandospirone. Furthermore, the decrease in the effectiveness of stimulation of the locus coeruleus, obtained by increasing the frequency from 1 to 5 Hz, a phenomenon due to an increased activation of terminal α 2-adrenergic autoreceptors by endogenous NE, remained unaltered after long-term treatment with tandospirone. In addition to the initial depressant effect, stimulation of the locus coeruleus induces a late activation of these neurones which is mediated by a β-adrenoceptor. The degree of activation induced by stimulation of the locus coeruleus was similar in controls and in long-term tandospirone-treated rats. It is concluded that 1-PP acts as an antagonist at somatodendritic and terminal α 2-adrenergic autoreceptors, as well as at postsynaptic α 2-adrenoceptors, in the central nervous system of the rat. However, the levels of 1-PP attained after long-term administration of tandospirone were not sufficient to modify NE neurotransmission.

A method for immunofluorescent demonstration of three coexisting neurotransmitters in rat brain and spinal cord, using the fluorophores fluorescein, lissamine rhodamine, and 7-amino-4-methylcoumarin-3-acetic acid.

Coexistence of neurotransmitters within single nerve fibers or terminals can be convincingly demonstrated by the use of multicolor immunofluorescence. The present study examined whether three-color immunocytochemical localization of coexisting neurotransmitters can be performed using the blue fluorophore AMCA. Spectrofluorometric examination of secondary antibodies conjugated with AMCA, fluorescein, and lissamine rhodamine showed that the peaks of excitation and emission were well separated and that dots of AMCA-conjugated IgG dried on slides were not visible when viewed using microscope filters for rhodamine and fluorescein. These findings suggest that AMCA might be suitable for three-color immunofluorescence. The usefulness of AMCA for triple labeling was tested directly by staining sections of rat brainstem and spinal cord for serotonin (5HT), substance P (SP), and either enkephalin (ENK) or prepro-thyrotropin-releasing hormone 160-169 (ppT), a marker peptide for thyrotropin-releasing hormone. Triple labeling for 5HT, SP, and ppT was observed in both brainstem and spinal cord but was only very rarely observed for 5HT,SP, and ENK. No evidence was found for artifactual triple labeling, although false negatives appeared to be possible in some circumstances. We conclude that AMCA can be combined with fluorescein and lissamine rhodamine for three-color immunofluorescent studies of coexisting neurotransmitters. In addition, the coexistence of 5HT with ENK appears to be much less common than the coexistence of 5HT with either SP or ppT.

Age-related alteration in excitatory amino acid neurotransmission in rat brain

The excitatory amino acids as neurotransmitters in the neocortex, hippocampus, striatum, thalamus, amygdala, nucleus basalis of Meynert and cerebellum from rats aged 4 months, 12 months and 24 months have been examined by measuring sodium-dependent high affinity uptake of D-[ 3H]-aspartate into preparations containing synaptosomes. Calcium-dependent K +-stimulated release of endogenous glutamate from the nucleus basalis was also measured. The hippocampus and cerebellum failed to show significant age-related changes in uptake of D-[ 3H]-aspartate. D-[ 3H]-aspartate uptake decreased significantly in the neocortex (29%), striatum (29%), nucleus basalis (26%), amygdala (19%) and thalamus (16%) in the middle-aged rats as compared to the young rats, but the changes were not progressive with age. The release of glutamate from the nucleus basalis was unaltered during the aging process.

Studies of the in vitro effect of methylmercury chloride on rat brain neurotransmitter enzymes.

The in vitro effect of methylmercury (MM) on the enzymatic activities of brain cell specific marker enzymes, choline acetyltransferase (CAT), glutamic acid decarboxylase (GAD), 2',3'-cyclic nucleotide phosphohydrolase (CNP), glutamine synthetase (GS) and enolase was examined. The results demonstrate that at 100 microM MM, GS activity was not affected whereas a small decrease in the activity of both GAD (20%) and enolase (10%) was observed. CNP and CAT activity appeared to be more sensitive toward MM with 100 microM MM producing inhibition of 50% and 30%, respectively. The addition of sulfhydryl protecting reagents such as DTT or sodium thioglycolate can restore the enzyme activities to normal control levels despite prior exposure of the enzymes to MM.

Effect of ischemia on hydroxylase cofactor (tetrahydrobiopterin) and monoamine neurotransmitters in rat brain.

Hydroxylase cofactor, monoamine neurotransmitters and their metabolites were measured in ischemic rat brain produced by four-vessel occlusion for 30 and 60 min periods. Slight reduction of hydroxylase cofactor activity was observed in the ischemic cortex after 60 min. Dopamine increased in the brainstem, and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, increased throughout the brain. Decrease in norepinephrine was observed in the whole brain. Decrease in serotonin and increase in 5-hydroxyindoleacetic acid, a metabolite of serotonin, was observed in the ischemic cerebral cortex. The present study has revealed that there appears to be no significant relationship between hydroxylase cofactor activity and monoamine levels in the ischemic brain. Thus, the hydroxylase cofactor does not play a main role in regulating monoamine synthesis in the acute phase of brain ischemia.

Beta-N-Oxalylamino-L-alanine: action on high-affinity transport of neurotransmitters in rat brain and spinal cord synaptosomes.

beta-N-Oxalylamino-L-alanine (BOAA) is a dicarboxylic diamino acid present in Lathyrus sativus (chickling pea). Excessive oral intake of this legume in remote areas of the world causes humans and animals to develop a type of spastic paraparesis known as lathyrism. BOAA is one of several neuroactive glutamate analogs reported to stimulate excitatory receptors and, in high concentrations, cause neuronal vacuolation and necrosis. The present study investigates the action of BOAA in vitro on CNS high-affinity transport systems for glutamate, gamma-aminobutyric acid (GABA), aspartate, glycine, and choline and in the activity of glutamate decarboxylase (GAD), the rate-limiting enzyme in the decarboxylation of glutamate to GABA. Crude synaptosomal fractions (P2) from rat brain and spinal cord were used for all studies. [3H]Aspartate transport in brain and spinal cord synaptosomes was reduced as a function of BOAA concentration, with reductions to 40 and 30% of control values, respectively, after 15-min preincubation with 1 mM BOAA. Under similar conditions, transport of [3H]glutamate was reduced to 74% (brain) and 60% (spinal cord) of control values. High-affinity transport of [3H]GABA, [3H]glycine, and [3H]choline, and the enzyme activity of GAD, were unaffected by 1 mM BOAA. While these data are consistent with the excitotoxic (convulsant) activity of BOAA, their relationship to the pathogenesis of lathyrism is unknown.