Lesions of the inferior olive increase glutamic acid decar☐ylase activity in the deep cerebellar nuclei of the rat

Inferior olive-climbing fiber lesions were made by administering 3-acetylpyridine to 16-day-old rats. This treatment produced multiple motor abnormalities which gradually improved over the subsequent 28 days. A significant increase in glutamic acid decar☐ylase (GAD) activity was found in the deep cerebellar nuclei 24 h after treatment. This elevation increased with time, reaching 134% of control values 28 days after treatment. GAD activity in the cerebellar vermis also increased but did so more slowly and to a lesser degree than in the deep nuclei, reaching 114% of control values 28 days after treatment. The results suggest the operation of different mechanisms in producing the increased GAD activity in the different areas.     

Specific cerebrovascular localization of glutamate decar☐ylase activity

Glutamate decar☐ylase (GAD) activity and GABA levels, determined with a [³H]muscimol radioreceptor assay, were found to be significantly higher in cerebral blood vessels from the piaarachnoid membrane as compared to extracranial vessels (aorta, mesenteric and femoral arteries, and vena cava). A cerebrovascular localization for GABA and GAD is consistent with earlier studies suggesting that an indigenous GABA system is involved in cerebral vascular function.     

Glutamic acid decar☐ylase and enkephalin immunoreactive axon terminals in the rat neostriatum synapse with striatonigral neurons

Synaptic interactions between striatal projection neurons and axon terminals containing immunoreactive glutamic acid decar☐ylase (GAD) or Leu-enkephalin were examined in the rat neostriatum using a combined method of horseradish peroxidase retrograde transport from the substantia nigra and immunohistochemistry at the electron microscopic level. Results showed that numerous immunoreactive GAD and enkephalin boutons formed synapses with the cell bodies and dendrites of medium-sized striatonigral neurons. These findings demonstrate that within the neostriatum GABA and enkephalin directly influence caudate output pathways.     

Glutamic acid decar☐ylase (GAD) activity in the rat substantia nigra after discrete bilateral kainic acid-inducedlesions of the caudate-putamen and globus pallidus: correlation with locomotor activity

Bilateral injections of kainic acid into the head (both anterior and posterior postions) of the caudate nucleus, the body of the caudate and the globus pallidus showed that the descending GABAergic innervation to the substantia nigra originates predominantly from the body of the caudate nucleus. Locomotor activity was enhanced following the lesions but thwere was no correlation with the severity of nigral GAD depletion.     

Glutamic acid decar☐ylase activity decreases in mouse neocortex after lesions of the basal forebrain

Glutamic acid decar☐ylase (GAD) activity was measured in the cerebral cortex of animals after acute and chronic lesions to basal forebrain cholinergic nuclei. Such lesions were shown to result in an extensive depletion of cholinergic markers in parietal cerebral cortex. A statistically significant 30% decrease in GAD activity was first detected at 6 weeks postlesion and was still measurable 8 months after the lesion. These results suggest that cholinergic inputs to cortex indirectly or directly influence GABAergic transmission in cortex.     

Role of serotonin in the apomorphine-induced increase of adrenomedullary ornithine decar☐ylase activity

The role of serotonin in the regulation of adrenomedullary ornithine decar☐ylase (ODC) activity has been explored in rats after systemic administration of p-chlorophenylalanine (PCPA) and intraventricular 5,6-dihydroxytryptamine (DHT) or in animals with electrolytic lesions of the medial and dorsal raphe nuclei. None of the treatments produced any alteration in endogenous ODC activity. However, all except lesion of the dorsal raphe nucleus significantly potentiated the induction of adrenomedullary ODC produced by apomorphine (APM) administration. It is suggested that serotonergic fibers originating partly in the medial raphe nucleus exert a tonic inhibitory action over the APM-induced increase in adrenomedullary ODC activity.     

Kinetically different, multiple forms of glutamate decar☐ylase in rat brain

Four molecular forms of rat-brain glutamate decar☐ylase were resolved by hydrophobic interaction chromatography on phenyl-Sepharose and affinity chromatography on ATP-agarose. SDS-polyacrylamide gel electrophoresis of purified enzyme and immunoblots of SDS gels indicated a subunit molecular weight of approximately 60, 000 for each form of the enzyme, and cross-linking with dimethyl suberimidate prior to electrophoresis indicated that each form has dimeric subunit structure. Immunoblots of non-denaturing gels showed differing electrophoretic mobilities among the forms. The kinetic properties of the 4 enzyme forms were found to be significantly different. The K_m for glutamate ranged from 0.17 ± 0.05 to 1.18 ± 0.08mM, and there was a greater than two-fold range in their rates of inactivation by glutamate and GABA in the absence of pyridoxal 5′-phosphate. In subcellular fractionation experiments the forms with greater electrophoretic mobility were recovered in the synaptosomal fraction, and the form with the lowest electrophoretic mobility was the most abundant in the postmicrosomal supernatant. Calcium-dependent binding of glutamate decar☐ylase in crude enzyme preparations to phospolipid vesicles was observed, but none of the purified enzyme forms showed an appreciable degree of binding to the vesicles.     

Immunocytochemistry of glutamate decar☐ylase in the deafferented habenula

The visualization of opiate binding sites within the hippocampus of the rat has been achieved by means of an in vitro autoradiography. In line with the concept of multiple opiate receptors, different opioid agonists revealed a particular distribution pattern. Whereas the selective δ-receptor agonist [³H]d-Ala², d-Leu⁵-enkephalin specifically labelled binding sites in the CA₂ area, [³H]etorphine grains displayed a uniform dense distribution throughout the pyramidal cell layers from CA₁ to CA₄.     

Ornithine decar☐ylase activity in dorsal root ganglia of regenerating frog sciatic nerve

Ornithine decar☐ylase (ODC) activity was studied in dorsal root ganglia (DRG) of regenerating frog sciatic nerve. There was a significant increase in activity two days after a crush lesion of the nerve 2.5 cm distal to the DRG. The increase reached a maximum after 7 days, then declined but remained above control levels for at least 9 days. An endoneural injection of vinblastine, a potent inhibitor of retrograde and orthograde axonal transport, between the DRG and the crush inhibited the increase in ODC. In contrast, injections of vinblastine into undamaged nerves failed to affect ODC. The increase in ODC and also the regenerative properties of the nerve could be prevented by daily i.p. injections of α-difluoromethyl ornithine. We suggest that a signal is formed at the site of injury in the sciatic nerve. This signal is conveyed to the DRG by retrograde axonal transport where it initiates the events leading to an increase in ODC. This increase appears to be necessary for the regeneration of sensory fibers in the frog sciatic nerve.     

The development of glutamic acid decar☐ylase in the visual cortex and the dorsal lateral geniculate nucleus of the rat

The activity of the enzyme glutamic acid decar☐ylase was measured in the visual cortex and the dorsal lateral geniculate nucleus of the rat at several postnatal ages. The results suggest that the developmental pattern of glutamic acid decar☐ylase is reflected in the morphology of the neurons which presumably contain the enzyme.     

Aromatic l-amino acid decar☐ylase immunohistochemistry in the suprachiasmatic nucleus of the sheep Comparison with tyrosine hydroxylase immunohistochemistry

Using antisera against tyrosine hydroxylase (TH) and aromatic l-amino acid decar☐ylase (AADC), we have demonstrated the presence of numerous AADC immunoreactive neurons and few TH immunoreactive neurons, Homogeneously distributed throughout the suprachiasmatic nucleus. Similar results have been described in other species. These observations show that this nucleus is able to synthesize trace amines (such as phenylethylamine or tyramine) in addition to dopamine. It is hypothesized that these trace amines are possibly involved in the integration of day length variation in sheep, a species whose reproduction is closely related to photoperiod.     

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.     

The effects ofN-methyl-d-aspartate and kainate lesions of the rat striatum on striatal ornithine decar☐ylase activity and polyamine levels

The intrastriatal injection ofN-methyl-d-aspartate (NMDA) (250 nmol) produced a delayed and marked increase in striatal ornithine decar☐ylase (ODC) activity and putrescine levels which peaked 6–15 h following the injection of NMDA. Striatal ODC activity subsequently returned to normal values while putrescine levels remained significantly elevated for up to 4 days following the lesion. NMDA produced an early and progressive decline in striatal spermine and spermidine levels, preceding the increase in ODC activity, with a maximum effect 2 h following injection. Spermidine levels returned to normal 6 h post-NMDA infusion, and subsequently increased to above normal levels 36 h and 4 days after the infusion of NMDA. This late increase in striatal spermidine levels paralleled an increase in the binding of the glial cell/macrophage marker [³H]PK 11195. Spermine levels tended to return to normal values 6 h after the injection of NMDA but may be further depressed at later intervals (15 h to 4 days). The intrastriatal injection of saline also resulted in a delayed increase in striatal ODC activity and putrescine levels, but these changes were minor compared to those produced by NMDA. Intrastriatal saline injection provoked no consistent change in striatal spermine or spermidine levels. The changes in polyamine metabolism produced by the instriatal injection of kainic acid (4 nmol) were only analysed at 6 and 15 h following injection but were qualitatively similar to those produced by NMDA although perhaps following a slightly more delayed time-course. Neurotoxic lesions of the striatum thus provoke changes in ODC activity and increased levels of putrescine that follow closely the time-course of similar events in the ischaemic brain. The initial early changes in spermine and spermidine levels induced by NMDA could perhaps alter the functioning of the NMDA receptor itself via its polyamine-sensitive modulatory site and contribute to a feed-forward activation of NMDA receptors and prolonged NMDA receptor-mediated toxicity.     

Evidence for the coexistence of glutamate decar☐ylase and Met-enkephalin immunoreactivities in axon terminals of rat ventral pallidum

Evidence for the coexistence of glutamate decarboxylase (GAD) and Met-enkephalin (Met-Enk) in axon terminals of ventral pallidum was demonstrated by colocalization of anti-GAD and anti-Met-Enk immunoreactivities in alternate adjacent 1 micron serial sections. Conventional electron microscopy of immunostained ventral pallidum confirmed that the immunoreactive structures were boutons which made predominantly symmetrical synapses on ventral pallidal cell bodies and dendrites.     

Time course of the reduction of GABA terminals in a model of focal epilepsy: a glutamic acid decar☐ylase immunocytochemical study

Immunocytochemical localization of glutamic acid decar☐ylase (GAD), the synthesizing enzyme for the neurotransmitter γ-aminobutyric acid (GABA), has been used to study the time course of the decrease in putative GABAergic synaptic terminals that occurs in an alumina gel-induced model of focal epilepsy. Monkeys were studied at progressive intervals following unilateral application of alumina gel to sensorimotor cerebral cortex, and were categorized into 3 different experimental groups depending upon their clinical status. These groups respectively exhibited: (1) no abnormal bioelectrical (EEG and ECoG) activity; (2) abnormal bioelectrical activity, but no clinical seizures; and (3) both abnormal bioelectrical activity and clinical seizures. Normal and sham-operated monkeys were also studied. The amounts of GAD-positive terminal-like structures were determined on control and experimental sides of motor cortex (layer V) of all specimens with an image analysis system. This quantitative study revealed that monkeys from the 3 experimental groups showed reductions of GAD-positive terminals on the experimental cortical side, with greater losses occurring at progressively longer times following alumina gel implants. Statistical tests showed that there were no significant cortical side differences for the normal and sham groups, but that cortical side variations were significantly different for each of the 3 experimental groups. Conventional electron microscopy of an early experimental stage revealed degenerating axon terminals in layer V of motor cortex, as well as phagocytosis of degenerating material and astrogliosis. Similar findings were obtained from a chronically epileptic specimen, except that degenerating terminals were observed less often and fibrous astrocytic scarring was more prevalent, especially surrounding the somata of pyramidal neurons. The main conclusion drawn from the results of this investigation is that significant decreases of GAD-positive terminals occur prior to the onset of clinical seizures, and this is consistent with a causal role for a loss of GABAergic innervation in the development of seizure activity in this primate model of focal epilepsy.     

Different charge forms of aromatic-l-amino-acid decar☐ylase

The isoelectric points (pI) of aromatic-l-amino-acid decar☐ylase (AADC) from two species, rat and cow, were determined by chromatofocusing. The enzyme from both rat brain and adrenal has a pI of 5.5, while the bovine adrenal enzyme has a different pI of 5.0. Thus, the variation of isoelectric point for AADC is limited to species differences but not tissue differences.     

Adrenomedullary ornithine decar☐ylase activity: Its use in biochemical mapping of the origins of the splanchnic nerve in the rat

The activity of ornithine decar☐ylase in the adrenal medulla of the rat can be induced transsynaptically by the repeated administration of apomorphine. Unilateral section of one to four ventral spinal cord roots from T4 to T12 partially prevents this effect. Interruption of the intercostal nerves (T7–T13), with preservation of the autonomic innervation of the adrenal medulla, does not produce any alteration in the response of the medullary ODC to APO in the operated side as compared to the intact side. Dorsal root section at T7–T10 leads to a small reduction, while section at T2–T4 has no effect at all. Thus, selective surgical interruption of spinal cord roots indicates that the bulk of splanchnic fibers mediating the transsynaptic induction of adrenomedullary ornithine decar☐ylase course in the ventral roots between T7 and T10. Dorsal rhizotomy demonstrates a modulatory role in this induction of afferent information to sympathoadrenal preganglionic neurons involved in innervation of the chromaffin cells.