Determination of γ-Aminobutyric Acid in the Mouse Hypothalamus and Hippocampus Using Liquid Chromatography/Electrochemistry

Effect of piribedil, a D-2 dopaminergic agonist, on dopamine, amino acids, and free radicals in gerbil brain after cerebral ischemia

The excitatory amino acids (EAA) are involved in the pathogenesis of the cerebral ischemia. Moreover, several investigators have demonstrated that a considerable amount of dopamine (DA) is released in the striatum after ischemia reperfusion/insult (IRI). Recently, studies have demonstrated in vitro, that D-2 agonist, at the level of striatum and retina, may represent a powerful signal to inhibit release of excitatory amino acids implicated in cerebral ischemia. Therefore we have been incited to test, in vivo, the action of a D-2 agonist, piribedil, on gerbil brain after IRI. We have used the Stroke Index (SI); then to precise the mechanism of action, we have determined the levels of dopamine, EAA, and hydroxyl-free radicals (OH), in striatum, hippocampus, and hemisphere. Piribedil, administered at dose of 10 mg/kg, per os, 60 min before induction of transient cerebral ischemia in gerbils, presents a neuroprotective effect, as measured by SI and significantly reverses the increase of DA, EAA, and OH induced by IRI. The mechanism of action of piribedil could be related to its D-2 agonist property.

gamma-Aminobutyric acid, catecholamine and indoleamine determinations from the same brain region by high-performance liquid chromatography with electrochemical detection

A new procedure for the measurement of gamma-aminobutyric acid, norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid from the same brain region was developed. In general, two separate high-performance liquid chromatographic runs were performed, one for the gamma-aminobutyric acid determination and one for the determination of the monoamines. The electrochemical detection of gamma-aminobutyric acid was determined by a new procedure that utilized a small aliquot of the brain sample prepared for monoamine measurement. This assay was linear and parallel between 6 and 200 ng per 20-microliters injection with 5-aminovaleric acid utilized as an internal standard. Inter-assay variability averaged 5% throughout the assay with gamma-aminobutyric acid values in the gerbil hypothalamus of 344 micrograms/g. The catecholamine assay has been characterized previously and utilizes 3,4-dihydroxybenzylamine as an internal standard with less than 5% variability. Norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid levels in the gerbil hypothalamus averaged 2922, 729, 797 and 272 ng/g, respectively. This new protocol allows a wide range of neurochemicals to be determined and evaluated from the same brain region.

Acamprosate modulates synaptosomal GABA transmission in chronically alcoholised rats

Male Sprague-Dawley rats were pulmonary alcoholised for 30 days. Six were treated with acamprosate (400 mg/kg/day, PO) during alcoholisation. The control nonalcoholised group also received acamprosate (400 mg/kg/day, PO) during the 30 days. At the end of the experiment, brains areas (cortex, hippocampus, thalamus, striatum, and olfactory bulbs) were dissected for the study of synaptosomal 3H-GABA uptake. In another experiment, GABA levels were determined in the same areas using HPLC with electrochemical detection. Blood ethanol levels were also measured during alcoholisation. Acamprosate treatment did not modify blood ethanol levels. In cortex and olfactory bulbs, alcoholisation increased 3H-GABA uptake (Vmax) with an increase in the affinity (Km). 3H-GABA uptake was not affected by alcoholisation in other brain areas. In hippocampus and thalamus, acamprosate treatment enhanced 3H-GABA uptake (Vmax) only in alcoholised rats. Moreover, in thalamus, alcoholisation enhanced GABA levels. The effect of alcohol and acamprosate on GABA presynaptic events is discussed and it is concluded that the action of ethanol and acamprosate on GABA transport could be, in part, responsible for the modulation by acamprosate treatment of ethanol behaviour.

Glutamate accumulation and increased hydroxyl free radical formation in the abdominal aorta and heart of gerbil after ischemia/reperfusion insult

The concentration of glutamate as well as the hydroxylation of salicylate, as an index of hydroxyl free radical formation, has been determined in the abdominal aorta and heart of gerbils undergoing an ischemia/reperfusion insult (IRI) and compared to control sham-operated gerbils. The amount of glutamate and hydroxylated salicylate (dihydroxybenzoic acid, DHBA) was significantly increased in both the aorta and heart of IRI-treated gerbils as compared to the aorta and in the heart of sham-operated gerbils. Vitamin E (90 mg/kg at 24 and 1 h prior to an IRI) pretreatment prevented the increase of both glutamate and DHBA in both the aorta and heart of IRI-lesioned gerbils. The results suggest that increases in glutamate, perhaps due to the decreased activities of glutamine synthetase, are correlated with increased oxygen free radical formation during an ischemia/reperfusion insult to the heart.

Free radicals and neurotransmitters in gerbil brain. Influence of age and ischemia reperfusion insult

In gerbil brain, levels of hydroxyl radicals (OH.) and neurotransmitters such as glutamate, aspartate, GABA (gamma aminobutyric acid) are low at birth, reach a plateau and decrease with age. On the other hand, when gerbils are exposed to an ischemia reperfusion insult (IRI) the older animals have a higher stroke index and hydroxyl radical as well as glutamate and other neuromediators are concomitantly increased. This discrepancy is probably due to differences in the ability of old individuals to respond to oxidative stress. The still incompletely understood relationship between oxidative damage to proteins and accumulation of amino acids, which have an important role as neurotransmitters at physiologic concentrations, but may become neurotoxic at high concentrations, is discussed.

Effects of inhibition of GABA catabolism by aminooxyacetic acid on enkephalinergic neurons--immunocytochemical and ultrastructural study in the enkephalinergic hypothalamoseptal tract of the guinea-pig

The immunocytochemical and ultrastructural features within [Met]enkephalin neurons of the guinea-pig hypothalamoseptal tract were investigated under chronic inhibition of GABAergic catabolism. This was achieved by raising the brain GABA concentration with aminooxyacetic acid which inhibits GABA-transaminase, the enzyme responsible for the catabolism of GABA. Guinea-pigs were injected intraperitoneally with 10 or 20 mg/kg per day aminooxyacetic acid for two, four or eight days and killed 16 h post-dose. Repeated injections of aminooxyacetic acid produced a great increase in immunoreactivity for GABA in nerve endings surrounding enkephalinergic perikarya in the magnocellular dorsal nucleus of the guinea-pig. Extensive immunocytochemical studies stressed the increase and redistribution of the immunoreaction for [Met]enkephalin in the perikarya of the magnocellular dorsal nucleus under such GABAergic activation. Quantitative and statistical analyses showed that administration of aminooxyacetic acid for eight days significantly increased the intensity of labelling within stimulated perikarya (P less than 0.001). A concomitant accumulation of immunopositive large granules in the enkephalinergic boutons of the lateral septum was observed. In the same way, ultrastructural changes in enkephalinergic cell bodies were analysed and reflected disturbances in the biosynthetic and digestive activities of enkephalinergic perikarya. We postulate that chronic inhibition of the GABAergic catabolism leads to modification in the metabolism of enkephalinergic neurons and to an inhibitory action of GABA on the [Met]enkephalin release from nerve endings. This study give morphological support to the complex functional interactions between GABA and opioid peptide transmitter system.

Very rapid assay of gamma-aminobutyric acid in mouse brain regions within 3 minutes by high-performance liquid chromatography with electrochemical detection

For assay of gamma-aminobutyric acid (GABA) in brain tissue, a very rapid and simple chromatographic procedure using high-performance liquid chromatography (HPLC) with electrochemical detection (ECD) in combination with precolumn o-phthalaldehyde (OPA) derivatization is described. Perchloric acid extracts of the tissue were mixed with OPA/beta-mercaptoethanol solution and the mixture was injected onto the HPLC system. The present method permits GABA assay within less than 3 min in one chromatographic run. Up to 100 samples a working day can be analyzed in the present method. The present method has been applied to the measurement of GABA levels in discrete brain regions of mice treated with aminooxyacetic acid and isoniazid.