The distribution of several amino acids in specific ganglia and nerve bundles of the lobster

Changes in the content of glutamate and GABA in the cerebellar vermis and hemispheres of the Purkinje cell degeneration (pcd) mutant

The contents of glutamate and GABA, as well as aspartate, glycine, and alanine, were examined in the cerebellar vermis and hemispheres of normal and Purkinje cell degeneration (pcd) mutant mice at 6, 9, and 12 months of age. Relative to normal values, the content of glutamate was approximately 50% lower in the vermis for the 3 age groups. In the hemispheres, the content of glutamate was also lower than control values and showed a progressive loss from 30 to 47% with age. On the other hand, in the case of GABA in the vermis, the level was 39% lower in the pcd mutant at 6 months of age but no different from control values at 12 months. However, relative to data for normal mice, the content of GABA in the hemispheres was consistently lower (20%) for all age groups. The level of aspartate was approximately 60% lower in the cerebellar vermis and 45 to 55% lower in the hemispheres of the mutant with respect to control data for all three age groups. Likewise, alanine showed a reduced content in the hemispheres (36-46%) and vermis (24%) in the mutant relative to normal values at 6, 9, and 12 months of age. On the other hand, the level of glycine was 43-64% higher in the vermis and 77-100% greater in the hemispheres of the mutant than in the control group. The higher values for glycine were observed at the two oldest ages. In conclusions, the data are consistent with the idea that glutamate and GABA are present in high concentrations in granule and Purkinje cells, respectively, and provide additional support for a transmitter function for both amino acids in the cerebellum.

Monoamine, amino acid and cholinergic interactions in slices of rat cerebral cortex

Interactions of monoamine, amino acid and cholinergic transmitter systems were studied in slices of rat cerebral cortex using a superfusion procedure and measuring release of endogenous dopamine (DA), norepinephrine (NE), serotonin (5-HT), GABA, glutamate (GLU) and aspartate (ASP). Depolarizing concentrations of K+ were used to induce a Ca2+-dependent, Mg2+-inhibited release of the monoamines and amino acids. Submaximal release of the monoamines and amino acids was observed at 35 mM K+, which permitted studies of possible excitatory or inhibitory actions of the added agents. The 35 mM K+-stimulated, Ca2+-dependent release of GABA was inhibited 40, 30 and 25% by 100 microM NE, DA and 5-HT, respectively. The release of GLU was potentiated by NE and reduced by DA. Both DA and 5-HT inhibited the release of ASP. The Ca2+-dependent, K+-stimulated release of endogenous NE, DA and 5-HT was not altered by 100 microM GABA, GLU or ASP. However, 100 microM GLU did enhance the stimulated release of GABA. The cholinergic agonist, carbachol, enhanced the stimulated release of NE, 5-HT and GLU 10, 60 and 40%, respectively. On the other hand, carbachol attenuated the release of DA and GABA approximately 20%. One interpretation of the data is that the amino acid transmitter pathways in slices of the cerebral cortex of the rat can be controlled by monoaminergic and cholinergic systems while the monoamine afferents appear to have a cholinergic regulation but not a major direct amino acid transmitter influence.

Comparison of the effects of a convulsant barbiturate on the release of endogenous and radiolabeled amino acids from slices of mouse hippocampus

The convulsant barbiturate 5-(2-cyclohexylidene-ethyl)-5-ethyl barbituric acid (CHEB) stimulates the spontaneous release of endogenous and radiolabeled acetylcholine (ACh) from mouse hippocampal slices in vitro. In order to determine if the ability of CHEB to release ACh was unique to this neurotransmitter, we have studied the action of this drug in vitro on the release of both radiolabeled and endogenous putative neurotransmitter and non-transmitter amino acids in the hippocampus. Although CHEB stimulated the spontaneous release of both [3H]gamma-n-aminobutyric acid (GABA) and endogenous GABA, CHEB had different effects on the spontaneous release of radiolabeled and endogenous L-glutamate and L-aspartate: L-[3H]glutamate release was inhibited by CHEB, but endogenous L-glutamate release was unaffected by CHEB, but endogenous L-aspartate release was stimulated. The spontaneous release of the amino acids L-alanine and glycine (not thought to be neurotransmitters in the hippocampus) was not affected by CHEB. The results of this study indicate that CHEB does not always stimulate the release of all putative neurotransmitters. The ability of this drug to release ACh, GABA, and L-aspartate may be the result of some specific interaction of CHEB with nerves using these neurotransmitters in the hippocampus. In addition, the results suggest some problems that may be encountered when radiolabeled substances are used to study neurotransmitter release.

Distribution of glycine, GABA, aspartate and glutamate in the rat spinal cord

Glycine, GABA, aspartate and glutamate are putative neurotransmitters in the mammalian spinal cord. The distribution of these amino acids was determined in the rat spinal cord. Transversely, the highest levels of glycine, aspartate and glutamate were in the intermediate and ventral gray; whereas, the highest levels of GABA were in the dorsal gray. Longitudinally, the highest levels of GABA and aspartate were in the thoracic and lumbar segments; whereas, the highest levels of glycine and glutamate were in the cervical and thoracic segments, respectively. In general, the distribution of these amino acids is similar to that reported for the cat, dog and human.

In vitro release of endogenous amino acids from granule cell-, stellate cell-, and climbing fiber-deficient cerebella

The K+-stimulated, Ca2+-dependent release of glutamate, aspartate, gamma-aminobutyric acid (GABA), alanine, taurine, and glycine was measured in slices of cerebella obtained from control, and granule cell-, granule cell plus stellate cell-, or climbing fiber-deficient cerebella of the rat. The 55 mM-K+-stimulated release of glutamate and GABA was 10-fold greater in the presence of Ca2+ than in its absence. The stimulated release of aspartate was 4-fold higher when Ca2+ was present in the bathing media, while the value for alanine was twice as high as the amount obtained in the absence of Ca2+. There was no stimulated release of either taurine or glycine from the cerebellar slices. Increasing the Mg2+ concentration to 16 mM inhibited the K+-stimulated, Ca2+-dependent release of glutamate, GABA, aspartate, and alanine 85% or more. The K+-stimulated, Ca2+ dependent release of glutamate, aspartate, and alanine from x-irradiated cerebella deficient in granule cells was reduced to 50-57% of control value. Additional x-irradiation treatment, which further reduced the cerebellar granule cell population and also prevented the acquisition of stellate cells, decreased the release of glutamate by 77%, aspartate by 66%, alanine by 91%, and, in addition, decreased the release of GABA by 55%. The K+-stimulated, Ca2+-dependent release of glutamate, aspartate, GABA, and alanine was not changed in climbing fiber-deficient cerebella obtained from 3-acetylpyridine-treated rats. The data support a transmitter role for GABA and glutamate in the cerebellum, but do not support a similar function for either taurine or glycine. The data also suggest that alanine and aspartate may be co-released along with glutamate from granule cells.

Levels of glutamate, aspartate, GABA, and taurine in different regions of the cerebellum after x-irradiation-induced neuronal loss

The levels of glutamate (Glu), aspartate (Asp), gamma-amino-n-butyric acid (GABA), and taurine (Tau) were determined in the cortex, molecular layer, and deep nuclei of cerebella of adult rats exposed to X-irradiation at 12-15 days following birth (to prevent the acquisition of late-forming granule cells; 12-15x group) and 8-15 days following birth (to prevent the acquisition of granule and stellate cells; 8-15x group). Also, the levels of the four amino acids were measured in the crude synaptosomal fraction (P2) isolated from the whole cerebella of the control, 12-15x, and 8-15x groups. The level of Glu was significantly decreased by (1) 6-20% in the cerebellar cortex; (2) 15-20% in the molecular layer; and (3) 25-50% in the P2 fraction of the X-irradiated groups relative to control values. The content of Glu in the deep nuclei was not changed by X-irradiation treatment. Regional levels of Asp were unchanged by X-irradiation, while its level in P2 decreased by 15-30% after treatment. The levels of GABA and Tau in the molecular layer, deep nuclei, or P2 were not changed in the experimental groups. However, there was a 15% increase in the levels of GABA and Tau in the cerebellar cortex of the 8-15x group relative to control values. The data support the proposed role of glutamate as the excitatory transmitter released from the cerebellar granule cells but are inconclusive regarding a transmitter role for either Tau or GABA from cerebellar stellate cells.

A highly specific and sensitive determination of gamma-aminobutyric acid by gas chromatography mass spectrometry

A procedure for the identification and quantification of picomole quantities of gamma-aminobutyric acid in tissue samples is given. This procedure combines the chemical specificity of dinitrophenylation with that of gas chromatography mass spectrometry to eliminate the interferences encountered with other direct derivatization procedures. Only a limited number of dinitrophenyl amino acid ethyl esters and some fatty ethyl esters are detected in the solution used for analysis. Identification is based on retention time and on the relative abundances of the three major ion fragments of the gamma-aminobutyric acid derivative. Quantitation is accomplished using isotope dilution techniques with [2H2]gamma-aminobutyric acid as an internal standard. The procedure has been successfully applied to samples of human cerebrospinal fluid and to extracts of ganglia from the mollusc, Aplysia californica.

Neurochemical correlates of behavior: levels of amino acids in four areas of the brain of the rat during drug-induced behavioral excitation

The levels of GABA, aspartate, glutamate, glycine and alanine were determined in 4 specific brain areas (telencephalon, diencephalon-mesencephalon cerebellum and pons-medulla oblongata) of rats killed during a period of drug-induced behavioral excitation. Behavioral excitation was obtained in adult, male Wistar rats working on a Sidman shock-avoidance schedule following administration of 2 mg/kg tetrabenazine (TBZ) 18 hr after iproniazid (50 mg/kg) pretreatment. When compared to trained animals (working on the avoidance schedule but receiving no drugs), the excited rats had increased levels of GABA in the telencephalon and diencephalon-mesencephalon, decreased levels of aspartate in all 4 brain areas, and a lower content of glycine in the pons-medulla region. The changes in the levels of aspartate in all areas of the brain, GABA in the diencephalon-mesencephalon, and glycine in the pons-medulla were significantly correlated (p less than 0.01) with the degree of excitation. It was observed that avoidance training alone produced increases in the levels of four amino acids: aspartate in telencephalon and cerebellum, GABA in cerebellum, and glycine and glutamate in the pons-medulla. The injection of iproniazid alone or iproniazid followed by TBZ into naive animals had little effect on the levels of the five amino acids. The data are discussed in terms of aspartate and GABA interacting as neurotransmitters with cholinergic and catecholaminergic and/or serotonergic neurons to produced the behavioral excitation.

Content of amino acids in axons from the CNS of the lobster

The contents of alanine, proline, glycine, GABA, glutamate, and aspartate were measured in four bundles of axons (designated areas A through D) from the circumesophageal connective of the lobster (Homarus americanus). The contents of these amino acids were also determined in individual axons within specific bundles and in the external sheath covering the circumesophageal connective. Within the nerve bundles the levels of aspartate were highest of the amino acids measured, ranging from 1.95 +/- 0.12 mumol/mg protein in area C to 7.55 +/- 0.54 mumol/mg protein in area B. On the other hand, GABA had the lowest value in the four bundles; its highest level was found in area C (0.083 +/- 0.006 mu mol/mg protein) and the lowest in area B (none detected). The content of glycine ranged from 1.63 +/- 0.14 (area C) to 2.52 +/- 0.32 mumol/mg protein in area A; that for glutamate ranged from 0.390 +/- 0.019 (area C) to 1.01 +/- 1.03 (area B). The contents of alanine and proline changed relatively little from bundle-to-bundle. The content of aspartate was the highest of any of the amino acids assayed in individual axons (with diameters in the range of 40 to 65 mu) dissected from areas B and C. Glycine had the next highest content followed in order by glutamate, proline, and alanine. GABA was not detected in these axons. With the exception of GABA (which could not be detected), aspartate had the lowest level (0.066 +/- 0.017) and glycine had the highest level (2.00 +/- 0.498 mumol/mg protein) in the external sheath covering the the circumesophageal connective.