Glutamic Acid Decar Research Articles

Gabaergic nerve terminals decrease in the substantia nigra following hemitransections of the striatonigral and pallidonigral pathways

Glutamic acid decar☐ylase (GAD), the enzyme that synthesizes the neurotransmitter, GABA, was immunocytochemically localized in axon terminals as well as in small and medium-sized neurons of the rat substantia nigra. The pattern formed by GAD-containing axon terminals with the dendrites and somata of neurons in the substantia nigra was altered following ipsilateral hemitransections of the striatonigral and pallidonigral pathways. A marked reduction of GAD-positive terminals occurred throughout this brain region, but the ventral fifth of the pars reticulata showed a nearly normal pattern of GAD-positive axon terminals. The results of this investigation are consistent with results from biochemical studies which have indicated that the striatonigral and/or pallidonigral pathways are GABAergic. In addition, these results suggest that the residual GABAergic terminals remaining after hemitransection are derived from intrinsic neurons of the substantia nigra.

Effect of discrete kainic acid-induced lesions of corpus caudatus and globus pallidus on glutamic acid decar☐ylase of rat substantia nigra

Locally applied kainic acid was used in order to destroy pallidal perikarya without damaging axons en passage, in an effort to clarify the role of the globus pallidus as a source of nigral GABAergic terminals. Rats were microinjected unilaterally with kainic acid in the globus pallidus, head, body and tail of the caudate and were sacrificed 7 days later. The forebrain of each rat was examined histologically in order to establish the extent of the lesion and nigral glutamate decar☐ylase (GAD) was assayed as a marker of GABAergic terminals. Kainic acid produced in the globus pallidus loss of neuronal perikarya and reactive gliosis. Large multipolar neurons of the globus pallidus were characteristically absent on the lesioned-side. Lesions of the pallidum resulted in a non-significant (5.5%) reduction of nigral GAD. Kainate lesions restricted to the head of the caudate resulted in a significant (19%) drop of nigral GAD, while lesions of the caudate body provided the largest reductions of nigral GAD (53%). Lesions of the caudate tail were without effect. The results indicate that nigral GAD arises mostly from the body and, in part, also from the head of the caudate but not from the globus pallidus or from the tail of the caudate.

Neurotoxic action of capsaicin on spinal substance P neurons

The effect of capsaicin injections into neenatal rats on the ultrastructure of the neonatal dorsal horn and on some biochemical and behavioral parameters in the adult were examined. Electron microscopic observations revealed degeneration and glial engulfment of boutons and umyelinated axons in the dorsal horn 2 and 6 h after neonatal subcuntaneous capsaicin injections. Capsaicin treatment had no effect on the activities of glutamic acid decar☐ylase and choline acetytransferase in the dorsal horn. Results of substance P measurements in the CNS showed no effect of capsicin administration on straital, hypothalamic or nigral substance P content, whereas substance P levels in the dorsal horn of teh spinal cord were reduced by half. The density of [ 3Hnaloxone binding sites in the dorsal horn was significantly reduced, while the affinity was not affected. Capsaicin-treated animals showed significantly increased latencies to respond to a noxious thermal stimulus in both tail-flick and hot- plate tests. The results are discussed in relation to the current concepts of the involvement of substance P and opiate systems in nociception and the potential use of neonatal capsaicin as a selective neurotoxin for the education of the spinal mechanisms of pain.

Neurotransmitter-related enzymes in senile dementia of the alzheimer type

Choline acetyltransferase (ChAT), acetylcholinesterase (AChE) and glutamic acid decar☐ylase (GAD) activities were measured in 20 brain regions from autopsied control and senile dementia of the Alzheimer type (SDAT) cases. Large, widespread reductions in the activities of ChAT and AChE were found in tissues from SDAT cases, while GAD activities were reduced in 3 of the 20 regions investigated. AChE activity in cerebrospinal fluid from SDAT cases was similar to that found in samples from non-demented patients.

Alteration in tyrosine hydroxylase, glutamic acid decar☐ylase and choline acetyltransferase in basal ganglia following herpes simplex virus inoculation in rat neostriatum

Alteration in tyrosine hydroxylase, glutamic acid decar☐ylase and choline acetyltransferase in basal ganglia following herpes simplex virus inoculation in rat neostriatum

Dendro axonic transmission. I. Evidence from receptor binding of dopaminergic and cholinergic agents

Spiroperidol binding in the substantia nigra and QNB and a-bungarotoxin ( a-Btx) binding in the neostriatum were measured in rats with lesions designed to produce selective alterations in pre- and postsynaptic neuronal processes. The objective was to determine whether presynaptic receptor sites may exist for dendritically released transmitters. Spiroperidol was used to measure dopaminergic receptor sites while QNB and a-Btx were used to measure muscarinic and nicotinic cholinergic receptor sites, respectively. The binding results were correlated with measurements on the individual striata of tyrosine hydroxylase (as an index of the integrity of nigrostriatal dopaminergic neurons) and of glutamic acid decar☐ylase (as an index of the integrity of striatal interneurons and descending striatonigral pathways). The results indicate that muscarinic receptor sites in the striatum are on neuronal perikarya or dendrites but nicotinic receptor sites are on afferent dopaminergic and corticostriatal neurons; in the substantia nigra spiroperidol binding is on afferent striatonigral neurons. The results, together with available biochemical and morphological data, are used to support the hypothesis that communication at many CNS synapses may involve a neurotransmitter dialog rather than a monolog. If true, this will affect interpretations of many pharmacological, behavioral and physiological experiments.

Substance P: Depletion in the dorsal horn of rat spinal cord after section of the peripheral processes of primary sensory neurons

The substance P content, glutamic acid decar☐ylase and choline acetyltransferase activities and the level of [ 3H]diprenorphine binding were measured in various regions of the lumbar spinal cord of rats after unilateral section of the sciatic nerve or after dorsal rhizotomy. Sciatic nerve section produced a 75–80% depletion of substance P in the dorsal horn but did not change the substance P content of the ventral horn. The onset of substance P depletion occurred within 7 days and was maintained for 2 months. The substance P content of the dorsal root ganglia and both the peripheral and central branches of primary sensory neurons was also reduced after sciatic nerve section. Glutamic acid decar☐ylase and choline acetyltransferase activity were unchanged; however, a small decrease in opiate receptor binding occurred 1 month after nerve section. Dorsal rhizotomy produced an 80% depletion of substance P in the dorsal horn. In addition, the substance P content of the ventral horn was significantly reduced. Glutamic acid decar☐ylase activity in the dorsal horn was unaffected by dorsal rhizotomy whereas opiate receptor binding was reduced by 40%. From these studies it appears that peripheral nerve injury results in the degeneration of primary sensory neurons which contain and release substance P as neurotransmitter.

Uptake of γ-aminobutyric acid and glutamic acid decar☐ylase activity in chick embryo neuroretinas in monolayer cultures

Uptake of γ-aminobutyric acid and glutamic acid decar☐ylase activity in chick embryo neuroretinas in monolayer cultures

The localization of acetylcholinesterase in the corpus striatum and substantia nigra of the rat following kainic acid lesion of the corpus striatum: A biochemical and histochemical study

The distribution of acetylcholinesterase in the corpus striatum and substantia nigra was examined with the use of kainic acid lesions of the corpus striatum and pharmacohistochemical experiments. Histochemically identified acetylcholinesterase-containing neurons in the striatum were among those which were destroyed by kainic acid. Complementary biochemical studies demonstrated that approximately 50% of the total acetylcholinesterase activity in the striatum was localized in these acetylcholinesterase-containing neurons. Intrastriatal injections of kainic acid produced a substantial decrease in the activity of the glutamic acid decar☐ylase in the substantia nigra, thus demonstrating that neurons contributing to the striato- and/or pallidonigral pathways had been lesioned. However, nigral acetylcholinesterase activity was not significantly reduced by the striatal kainic acid injections. Furthermore, stereotaxic injections of colchicine along the course of the striatonigral projection failed to produce an accumulation of acetylcholinesterase in these fibers proximal to the injection. In contrast, injections of colchicine into the nigrostriatal projection led to a proximal accumulation of acetylcholinesterase in the fibers of this system, thus confirming the presence of acetylcholinesterase in the ascending dopaminergic neurons. It is concluded that the striato- and pallidonigral projections in the rat do not contain significant levels of acetylcholinesterase. Furthermore, acetylcholinesterase-containing neurons in the striatum appear to be interneurons rather than the source of striatal efferents. It is suggested that some of these acetylcholinesterase-containing neurons may be striatal cholinergic interneurons.

Anterior striatal projections to the globus pallidus, entopeduncular nucleus and substantia nigra in the rat: The GABA connection

The projections of the head of the striatum of the rat were studied by autoradiography and horseradish peroxidase (HRP) histochemistry. After injections of [ 3H]-leucine into the head of the striatum, accumulations of autoradiographic grains were observed over the neuropil of the globus pallidus (GP), entopeduncular nucleus (EP) and substantia nigra, pars reticulata (SNR). The striatal projections to GP and EP were confirmed using HRP histochemistry. Injections of HRP into GP resulted in the appearance of reactive perikarya which were localized mainly in the central core region of the striatum. HRP injections into EP also produced labeled cells in the striatum but those were found in different regions of the striatum in different animals. It was not possible to discern topograhical relationships. Striatal hemitransections just anterior to GP significantly decreased glutamic acid decar☐ylase (GAD) activities in GP and EP, but did not have significant effects on the activity of this enzyme in the whole SN. Identical results were obtained with electrolytic lesions of the head of the striatum when the lesions did not encroach upon GP. Stereotaxic injections of kainic acid into the same region of the striatum significantly decreased GAD activities in GP, EP and SN. However, histological examination of the kainic acid lesions showed involvement of the GP and more caudal striatal regions. This may account for the significantly greater decrease in GAD in the GP and SN after these lesions than after the two other lesioning procedures. These results suggest that the projections from anterior striatum to GP and EP are GABA-containing systems. In contrast, although the same region of the striatum can be shown anatomically to project to the SN, this does not appear to be GABAergic. Rather, these findings are consistent with the view that the major source of the massive GABAergic innervation of the SN originates in the GP or in the caudal striatum immediately anterior, dorsal or lateral to the GP.

The use of kainic acid in the localization of enzymes in the substantia nigra

The selective destruction of neuronal perikarya via intracerebral injections of kainic acid was used to elucidate the cellular location of four neurotransmitter-related enzymes in the substantia nigra (SN). Two weeks after intranigral injections of kainic acid, dopamine-sensitive adenylate cyclase, glutamic acid decar☐ylase (GAD), choline acetyltransferase (CAT) and acetylcholinesterase (AChE) were measured in the SN. Histological examination of the SN, and a reduction of striatal tyrosine hydroxylase (TH) activity by 94%, confirmed the extensive loss of neuronal cell bodies in the SN. Dopamine stimulation of adenylate cyclase was not reduced in the lesioned SN, supporting the view that dendritically-released dopamine can regulate cyclic AMP synthesis in afferent terminals to these dendrites. Nigral GAD activity was significantly reduced by the lesions, suggesting that there are GAD-containing perikarya in the SN. CAT activity was not affected by the kainic injections, indicating the absence of cholinergic perikarya in the SN. Nigral AChE activity was significantly decreased after kainic injections, thus confirming the presence of AChE within the nigral perikarya. The results suggest that dopamine-sensitive adenylate cyclase and CAT are located within afferents to the SN, while GAD and AChE are found, to some extent at least, in neuronal soma of the SN. The differential effects of kainic acid on these enzymes suggest that this compound may be a useful neurochemical tool with which to determine the cellular distribution of enzyme systems in the central nervous system.

Tissue culture analysis of neurogenesis: Myelination and synapse formation are retarded by serum deprivation

Explants from newborn mouse cerebellum were cultured in nutrient media containing either adequate (30%) or low (15% or 7.5%) serum content. By light microscopic observation, delayed and inhibited myelination was detected in cultures fed with low serum media (experimental cultures). Specific activities of two enzymes related to myelin synthesis, 2′,3′-cyclic nucleotide-3′-phosphohydrolase and 3-hydroxy-3-methylglutaryl coenzyme A reductase, were also reduced in experimental cultures. Morphometric analysis of electron micrographs showed that the size of presynaptic endings and total area occupied by synapses in experimental cultures were substantially reduced, while synaptic density per unit area increased. Reflecting the results of synaptic underdevelopment, the levels of two neurotransmitter enzymes, choline acetyltransferase and glutamic acid decar☐ylase, were also decreased in experimental cultures.

Glutamic acid decar☐ylase and choline acetyltransferase in human foetal brain

Glutamic acid decar☐ylase and choline acetyltransferase in human foetal brain

Striatal lesions with kainic acid: neurochemical characteristics

Stereotaxic injection of 2.5 μg of kainic acid, a rigid analogue of glutamate, into the rat striatum caused a 70% reduction in the striatum of the cholinergic parameters, choline acetyltransferase, acetylcholine and synaptosomal uptake of choline and a similar reduction in the GABAergic parameters, glutamic acid decar☐ylase, γ-aminobutyric acid (GABA) and synaptosomal uptake of GABA. In contrast, the striatal content of dopamine and the synaptosomal uptake of dopamine were unchanged, and the activity of tyrosine hydroxylase was significantly increased. Significant changes in the activity of neurotransmitter synthesizing enzymes were demonstrable within 6 h after injection of 2.5 μg of kainic acid and maximal effects occurred at 48 h; the activities of choline acetyltransferase and glutamic acid decar☐ylase remained depressed up to 21 days after injection. The kinetic characteristics of striatal tyrosine hydroxylase were altered 48 h after injection with a two-fold increase in the V max for tyrosine and a three-fold reduction in K m for the pteridine cofactor. In contrast to the effects of kainic acid, the injection of copper sulfate, a non-specific toxin, caused a proportionate reduction in the dopaminergic as well as the cholinergic and GABAergic presynaptic markers. The kainate lesion caused an 85% decrement in the activity of dopamine-sensitive adenylate cyclase, a 40% reduction in the specific binding of [ 3H]quinuclidinyl benzilate and a 195% increase in the specific binding of [ 3H]GABA in the striatum. The morphology of the kainate injected striatum was markedly altered with nearly a complete loss of intrinsic neurons, increased number of glial cells but intact internal capsule fibers. Intracerebral injection of nanomolar quantities of kainic acid appears to cause degeneration of neurons with cell bodies near the injection site while sparing axons terminating in or passing through the region.

On GABA function and physiology in the pineal gland

Pineal gamma-aminobutyric acid (GABA) content and glutamic acid decar☐ylase (GAD) activity were found not to be influenced by environmental light, catecholamines, sympathetic innervation, or input via the pineal stalk. The observation that GAD activity did not disappear after pineal stalk section, ganglionectomy, or 48 h of organ culture leads us to suggest that GAD activity is not located in nerve processes entering the pineal gland. Treatment in organ culture with an inhibitor of protein synthesis did not greatly influence the slow rate of decrease of GAD activity. This finding is consistent with the conclusion that GAD turnover is slow. Treatment of denervated glands or glands containing functional sympathetic nerve structures with GABA, amino-oxyacetic acid (AOAA) or bicuculline in organ culture did not alter unstimulated levels, or significantly block the adrenergic stimulation of the activity of pineal serotonin N-acetyl transferase (NAT). It is clear from our studies that GABA does not influence or modulate the adrenergic regulation of pineal NAT activity, and that GABA content and synthesis are not regulated by an adrenergic mechanism. The role of GABA in the pineal gland remains to be discovered.

Distribution of glutamic acid decar☐ylase in certain rhombencephalic and thalamic nuclei of the rat

Distribution of glutamic acid decar☐ylase in certain rhombencephalic and thalamic nuclei of the rat

Neurochemical aspects of the ontogenesis of gabanergic neurons in the rat brain

Examination of various biochemical characteristics of the GABAnergic nervous system in the rat brain was made between 15 days of gestation and adulthood. At birth, the concentration of GABA in whole brain and most regions is approximately 50% of adult levels, whereas the medulla-pons has achieved adult levels by this time. Compared to GABA levels, there is a marked lag in the development of the activity of glutamic acid decar☐ylase in all areas studied; however, the activity of the enzyme increases in a linear fashion from birth to adulthood. The development of the uptake of GABA into particulate fractions prepared from whole brain and regions differs markedly from that of GABA and glutamic acid decar☐ylase, with uptake near adult levels by birth, peaking considerably above that of the adult between one to two weeks after birth and then declining toward adult activity by 4 weeks after birth. Examination of the kinetics of GABA uptake into resuspended P 2 fractions demonstrates that the developmental changes in the uptake reflects differences in the V max whereas theK t remains constant. Studies on the development of the apparent postsynaptic receptor for GABA reveals that in all regions binding is approximately 25% of adult up to 8 days after birth, at which time it increases dramatically, approximating adult levels by 4 weeks after birth. The rise in the density of the apparent postsynaptic GABA receptor after 8 days postpartum correlates best with the increase in the activity of glutamic acid decar☐ylase, a presynaptic marker.

Evidence for the local synthesis of a transmitter enzyme (glutamic acid decar☐ylase) in crayfish peripheral nerve

The activities of three enzymes of neurotransmitter metabolism (choline acetyl-transferase, CAT; acetylcholinesterase, AChE; and glutamic acid decarboxylase, GAD) were studied in normal, transected, and organ cultured crayfish nerves. CAT (to a lesses extent AChE) was dramatically decreased in activity when the nerve was cut proximal to the nerve cell bodies. GAD activity was unaffected by such procedures. In organ cultured nerve, where both motor and sensory axons degenerated, the CAT and AChE activities were virtually absent, whereas GAD activity remained close to normal levels. Inhibition of protein synthesis in cultured nerve caused the GAD activity to decrease rapidly. In view of these data, and the well documented fact that motor axons survive axotomy whereas sensory axons do not, a hypothesis that GAD is synthesized in the peripheral nerve is presented.

Quantitative localization of tyrosine hydroxylase, dopamine-β-hydroxylase, phenolethanolamine-N-methyl transferase, and glutamic acid decar☐ylase in spinal cord

Sensitive radiometric assays for tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), phenylethanolamine-N-methyl transferase (PNMT), and glutamic acid decarboxylase (GAD) have been combined with microdissection techniques for quantitative localization of these synthetic enzymes in rabbit spinal cord. TH was present uniformly in gray and white matter. DBH was higher in the lateral horns than in the other gray matter areas, and was not detectable in white matter. PNMT was detectable in gray but not white matter, and was considerably lower in activity than the other catecholamine synthetic enzymes. GAD was higher in the dorsal horns at the cervical and lumbar levels than in other gray matter areas and relatively low in white matter. GAD activity was considerably higher than the catecholamine synthetic enzyme activities. The quantitative localizations are consistent with the qualitative immunohistochemical enzymes maps and distributions of the related putative neurotransmitters.

Brain glutamic acid decar☐ylase and open field activity in ten inbred strains of mice

Brain glutamic acid decar☐ylase and open field activity in ten inbred strains of mice