Decrease In Glutamate Decarboxylase Research Articles

Biochemical and Enzymatic Analyses to Understand the Accumulation of γ-Aminobutyric Acid in Wheat Grown under Flooding Stress

Flooding induces low-oxygen stress, which reduces plant growth. The activity of the γ-aminobutyric acid (GABA) shunt is crucial for plant stress adaptation, in which it acts by changing cytosolic pH, limiting reactive oxygen species production, regulating nitrogen metabolism, and bypassing steps in the tricarboxylic acid cycle. GABA accumulates under osmotic stress as well as flooding stress. To clarify the dynamic roles of GABA accumulation in wheat under flooding stress, biochemical and enzymatic analyses were performed using a plant-derived smoke solution (PDSS), which rescued wheat growth from flooding stress. Alcohol dehydrogenase abundance increased under flooding stress; however, under the same conditions, pyruvic acid content increased only following PDSS application. Glutamic acid content increased under flooding stress, but decreased following the application of PDSS after 2 days of flooding. Glutamate decarboxylase abundance and GABA content increased under flooding stress, and further increased after 1 day of application of PDSS. Succinyl semialdehyde dehydrogenase accumulated after 2 days of flooding. These results suggest that flooding stress increases GABA content along with the increase and decrease of glutamate decarboxylase and succinyl semialdehyde dehydrogenase, respectively. Additionally, PDSS increased GABA content along with the increase of glutamate decarboxylase abundance at the initial stage of application.

A Sensitive Period of Mice Inhibitory System to Neonatal GABA Enhancement by Vigabatrin is Brain Region Dependent

Neurodevelopmental disorders, such as schizophrenia and autism, have been associated with disturbances of the GABAergic system in the brain. We examined immediate and long-lasting influences of exposure to the GABA-potentiating drug vigabatrin (GVG) on the GABAergic system in the hippocampus and cerebral cortex, before and during the developmental switch in GABA function (postnatal days P1-7 and P4-14). GVG induced a transient elevation of GABA levels. A feedback response to GABA enhancement was evident by a short-term decrease in glutamate decarboxylase (GAD) 65 and 67 levels. However, the number of GAD65/67-immunoreactive (IR) cells was greater in 2-week-old GVG-treated mice. A long-term increase in GAD65 and GAD67 levels was dependent on brain region and treatment period. Vesicular GABA transporter was insensitive to GVG. The overall effect of GVG on the Cl(-) co-transporters NKCC1 and KCC2 was an enhancement of their synthesis, which was dependent on the treatment period and brain region studied. In addition, a short-term increase was followed by a long-term decrease in KCC2 oligomerization in the cell membrane of P4-14 hippocampi and cerebral cortices. Analysis of the Ca(2+) binding proteins expressed in subpopulations of GABAergic cells, parvalbumin and calbindin, showed region-specific effects of GVG during P4-14 on parvalbumin-IR cell density. Moreover, calbindin levels were elevated in GVG mice compared to controls during this period. Cumulatively, these results suggest a particular susceptibility of the hippocampus to GVG when exposed during days P4-14. In conclusion, our studies have identified modifications of key components in the inhibitory system during a critical developmental period. These findings provide novel insights into the deleterious consequences observed in children following prenatal and neonatal exposure to GABA-potentiating drugs.

GABA Receptor Activation in the Lumbosacral Spinal Cord Decreases Detrusor Overactivity in Spinal Cord Injured Rats

We investigated the effects of intrathecal application of gamma-aminobutyric acid A and B receptor agonists on detrusor overactivity in spinal cord injured rats. Adult female Sprague-Dawley rats were used. At 4 weeks after Th9-10 spinal cord transection awake cystometry and recordings of external urethral sphincter electromyogram were performed to examine the effect of intrathecal application of the gamma-aminobutyric acid A and B agonists muscimol and baclofen or the gamma-aminobutyric acid A and B antagonists bicuculline and saclofen (Tocris Cookson, Ellisville, Missouri), respectively, at the level of the L6-S1 spinal cord. The expression of glutamate decarboxylase 67 mRNA in the L6-S1 spinal cord and dorsal root ganglia was also assessed. Muscimol and baclofen produced a dose dependent inhibition of the number (51% to 73% decrease) and amplitude (35% to 93% decrease) of nonvoiding bladder contractions and a decrease in micturition pressure. The effects of muscimol and baclofen were antagonized by bicuculline and saclofen, respectively. Bursting activity of external urethral sphincter electromyogram was inhibited, corresponding to the inhibition of bladder activity by muscimol and baclofen. Glutamate decarboxylase 67 mRNA levels in the spinal cord and dorsal root ganglia were decreased after spinal cord transection (55% and 84%, respectively). These results indicate that gamma-aminobutyric acid A and B receptor activation in the spinal cord inhibits detrusor overactivity. The decrease in glutamate decarboxylase 67 mRNA suggests hypofunction of GABAergic inhibitory mechanisms in the spinal cord. Therefore, stimulation of spinal GABAergic mechanisms could be effective for the treatment of detrusor overactivity after spinal cord injury.

Distribution of glutamate decarboxylase65 immunoreactive puncta on pyramidal and nonpyramidal neurons in hippocampus of schizophrenic brain.

Recent studies have reported an increase in GABAA receptor binding activity in several key corticolimbic regions, including the hippocampal formation, of postmortem schizophrenic brain. Because this change has been postulated to represent a compensatory upregulation of this receptor, the current report has sought to determine whether a decrease of glutamate decarboxylase (GAD), the enzyme responsible for the synthesis of GABA, may also be present in the hippocampus of schizophrenic subjects. A standard immunoperoxidase technique, together with a computer-assisted microscopic analysis, has been employed to evaluate the distribution of the 65 kDalton isoform of GAD (GAD65) in 12 normal controls and 13 schizophrenic subjects matched for age and postmortem interval (PMI). The results show no significant difference in the density of GAD65-immunoreactive (-IR) puncta in contact with pyramidal neurons (PN), nonpyramidal neurons (NP), or neuropil (NPL) in sectors CA1-4 and their various sub-laminae. When the data were considered in relation to neuroleptic exposure, a significant positive correlation between the density of GAD65-IR puncta and drug dose was found on both PNs (r = 0.814, P = 0.002; r = 0.777, P = 0.005, respectively) and NPs (r = 0.673, P = 0.023; r = 0.672, P = 0.024, respectively) in sectors CA4 and CA3. A similar result was found in the stratum oriens of CA3 (r = 0.704, P = 0.016) and CA2 (r = 0.774, P = 0.009). In each instance, two neuroleptic free schizophrenics showed the lowest density of GAD65-IR puncta. There was no significant relationship between the density of GAD65-IR puncta with either age or PMI. Taken together with previous data showing an upregulation of GABAA receptor activity in sectors CA3 and CA2, particularly the stratum oriens, this study provides further evidence in support of the hypothesis that an intrinsic defect of GABAergic activity may occur in the hippocampal formation of schizophrenic patients and show dose-related increases in relation to neuroleptic exposure.

Effect of AF64A on the cholinergic systems of the retina and optic tectum of goldfish.

AF64A, a presumed selective cholinergic neurotoxin has been used to study the effect on cholinergic systems of the goldfish retina and optic tectum. Toxin injection in the vitreum and in the optic tectum caused a selective decrease of choline acetyltransferase activity in both areas, while no significant decrease of glutamate decarboxylase and D-3H aspartate uptake were observed at different times after the injections. The effect was particularly dramatic in the retina of long term-injected animals, where choline acetyltransferase dropped to practically zero level. The ultrastructural analysis showed selective degeneration of some neurons in the amacrine and ganglion cell layer of the retina as well as of synaptic terminals and neuronal cell bodies in the optic tectum. The results favour a selective cholinotoxicity of AF64A in fish nerve tissue at doses substantially higher than those found to have additional unselective effects in mammals.

Cholinergic, GABAergic and excitatory amino acidic neurotransmission in the goldfish vagal lobe.

Some neurotransmitter systems operating in the goldfish vagal lobe, an hypertrophied gustatory center, have been studied by means of experimental (kainic acid injection and vagal rhizotomy), neurochemical and ultrastructural methods. The use of the neurotoxin, kainic acid, revealed the existence of cholinergic and GABAergic neurons in the vagal lobe. The results of histochemical observations and biochemical assays performed after rhizotomy of sensory and motor vagal roots, suggest that the motor neurons of the vagal motor layer are cholinergic. The same experiments also indicate that the primary gustatory afferents distributing to the sensory layer of the vagal lobe are, at least in part, cholinergic. By contrast, no decrease of excitatory amino acid uptake was demonstrated following the experimental lesions. GABA is likely to play an important role in the goldfish vagal lobe, particularly in the sensory layer, where the highest level of its synthetic enzyme, glutamate decarboxylase, is recorded. The significant decrease of glutamate decarboxylase in the sensory layer after vagal rhizotomy suggests that either GABAergic primary afferents reach the vagal lobe, or that deafferentation results in a decreased GABA synthesis in intrinsic GABAergic neurons.

Cholinergic and GABAergic forebrain projections to the habenula and nucleus interpeduncularis: Surgical and kainic acid lesions

The forebrain cholinergic and GABAergic projections to the habenula and nucleus interpeduncularis have been investigated by means of surgical and kainic acid lesions. Bilateral transection of the stria medullaris caused a 50% decrease of choline acetyltransferase in both the habenula and nucleus interpeduncularis, and a 65% decrease of glutamate decarboxylase in the habenula. Electrolytic lesions of the posterior septum (nucleus triangularis septi and nucleus septo-fimbrialis) accounted for at least 30–40% decrease of the cholinergic parameter in the habenula and nucleus interoeduncularis. Moreover, the choline acetyltransferase decrease in the habenula appeared restricted to the medial part of the nucleus. Kainic acid injections causing very large neuronal destruction in the nucleus of the diagonal band of Broca, and more than 70% decrease of choline acetyltransferase in the dorsal hippocampus, did not affect the cholinergic parameter in either the medial or lateral habenula or nucleus interpeduncularis. Kainic acid injections in the nucleus entopeduncularis resulted in a 40% decrease of glutamate decarboxylase in the habenula. Kainic acid injections in the nucleus of the diagonal band were accompanied by a 40% decrease of glutamate decarboxylase in the medial subdivision only. The present study points at the nuclei of the posterior septum as the source of a major cholinergic projection to the habenula and nucleus interpeduncularis, and reveals a previously unsuspected GABAergic input from the nucleus of the diagonal band to the medial habenula.

Glutamate uptake, glutamate decarboxylase and choline acetyltransferase in subcortical areas after sensorimotor cortical ablations in the cat

High affinity glutamate uptake (HAGU), glutamate decarboxylase (GAD) and choline acetyltransferase (CAT) activities were measured from subcortical nuclei in the cat brain after ipsilateral ablation of the sensorimotor cortex. Results showed a drop in HAGU in all the structures assayed except the subthalamic nucleus. These changes in HAGU are generally accompanied by a decrease in GAD while CAT is unaffected. However, in the red nucleus the drop in HAGU is concomitant to an increase in GAD and CAT. In the subthalamic nucleus HAGU and CAT are increased while GAD is decreased. These results are consistent with the concept that most corticofugal fibres to subcortical structures use glutamate as their neurotransmitter. Results concerning GAD suggest that GABAergic subcortical neurons are under a cortical influence. This influence seems to be weak on cholinergic neurons.

Decrease of glutamate decarboxylase (GAD)-immunoreactive nerve terminals in the substantia nigra after kainic acid lesion of the striatum.

Antiserum sheep 3 against rat brain glutamate decarboxylase (GAD) was employed for the immunohistochemical localization of GAD-immunoreactive nerve terminals in the substantia nigra (SN). To test whether the antiserum specifically localized GAD-containing axon terminals, the effect of kainic acid-induced striatal lesions on the reactive nerve endings in the SN was investigated. Seven days after the injection of 1 microgram kainic acid into the striatum, a 65% decrease in GAD-enzyme activity occurred in the ipsilateral SN. On immunohistochemical examination there was correspondingly a marked reduction of GAD-positive terminals. The parallel decrease in biochemical and immunohistochemical GAD activity indicates that antiserum sheep 3 can be used as a specific immunohistochemical probed for GAD-containing elements.

Dissociation between the presynaptic dopamine-sensitive adenylate cyclase and [ 3H]spiperone binding sites in rat substantia nigra

[3H]Spiperone binding sites and the dopamine-sensitive adenylate cyclase were measured in rat substantia nigra (s. nigra) 7 or 14 days after various lesions. Hemisections, which resulted in a 66% decline in tyrosine hydroxylase and cyclic nucleotide phosphodiesterase and a 73% decrease in glutamate decarboxylase, led to a 50% decrease in [3H]spiperone binding and to the almost complete disappearance of the dopamine-sensitive adenylate cyclase from the s. nigra on the lesioned side. 6-Hydroxydopamine injection into the s. nigra, which depleted tyrosine hydroxylase activity within the s. nigra by 85%, while leaving phosphodiesterase unaffected, resulted in a 40% decrease in [3H]spiperone binding but no change in the dopamine-sensitive adenylate cyclase. Intrastriatal injections of kainic acid did not alter tyrosine hydroxylase activity in the s. nigra, but decreased both glutamate decarboxylase (54%) and phosphodiesterase (68%); [3H]spiperone binding was unaffected by this lesion while the dopamine-sensitive adenylate cyclase was greatly reduced (50-75%). These results suggest that within the s. nigra the dopamine receptor binding sites as defined using [3H]spiperone are located on dopamine neurones while the dopamine-sensitive adenylate cyclase is located presynaptically on striatonigral nerve terminals.

CHANGES IN THE GABA SYSTEM IN EXPERIMENTAL ALLERGIC ENCEPHALOMYELITIS‐INDUCED PARALYSIS

Abstract— The content of γ‐aminobutyric acid (GABA), but not glutamate, and the uptake of [3H]GABA by synaptosomes was reduced in the lumbar cord of guinea pigs during experimental allergic encephalomyelitis (EAE)‐induced hind limb paralysis. The decrease in glutamate decarboxylase (GAD) activity in the dorsal and ventral parts of the cord was confined to the lumbar region, and appeared before the onset of motor dysfunction. No change in activity was found in the thoracic cord, motor cortex, cerebellum or striatum. GAD activity remained unchanged in animals which were EAE‐sensitized but did not develop the clinical symptoms. Choline acetyltransferase activity did not change in the cord during paralysis.