Search Results - (Author, Cooperation:J. D. Wood)

2015-12-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

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Anisotropy ; Boron/*chemistry ; Fullerenes/*chemistry ; Silver/chemistry ; Vacuum

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: Synaptosomes and synaptoneurosomes were prepared from rat cerebral cortex. Comparison of the amino acid levels in the two types of organelles and of the effects of gabaculine thereon indicated that the neurosome portion of synaptoneurosomes constituted the major influencing component of the organelles. Administration to rats of inhibitors of γ-aminobutyric acid (GABA) degradation, such as gabaculine and L-cycloserine, resulted in elevated GABA levels in synaptoneurosomes and a decrease in muscimol-stimulated C1 uptake by the organelles. Addition of gabaculine directly to the incubation medium for the uptake assay had no effect on the C1 transport. In contrast, administration to rats of isonicotinic acid hydrazide, an inhibitor of GABA synthesis, decreased the GABA level in synaptoneurosomes and increased the muscimol-stimulated Cl− uptake by the organelles. Although the evidence is not unequivocal, it does support the concept of GABA released from nerve endings being taken up by the postsynaptic cell, from where it exerts a regulatory influence on the functioning of the GABA receptor/ion channel complex.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: Previous work by the authors had indicated that synaptosome-enriched preparations from the cerebral cortex of the rat contained a high-, a medium-, and a low-affinity uptake system for γ-aminobutyric acid (GABA). The present study demonstrated that this phenomenon also prevailed in synaptosomes from rat diencephalon, mesencephalon, and cerebellum, although the Fmax values for the high-and medium-affinity systems in the cerebellum were very low relative to those of the other regions. When a different type of preparation containing nerve endings (glomeruli) was obtained from the cerebellum, it possessed a Vmax value for the high-affinity system that was more similar to that for the corresponding system in synaptosomes from the other brain regions. In contrast to the above situation, synaptosomes from rat olfactory bulb lacked the low-affinity uptake system, as did synaptosomes from dog olfactory bulb. The aspartate/glutamate uptake systems, as measured with D-aspartate, provided a regional pattern quite different from those of GABA uptake. Only two uptake systems, a high-and a low-affinity system, were observed in all regions tested. All three GABA uptake systems were present in cortical synaptosomes from the mouse, hamster, and guinea pig, and all three systems were sodium dependent, energy dependent, temperature sensitive, and totally inhibited by nipecotic acid.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: The kinetic constants Km and Vmax for the uptake of γ-aminobutyric acid (GABA) by various preparations from rat cerebral cortex were determined by means of Eadie-Hofstee plots and computer analysis. The Km values were much greater in 0.1-mm slices than in synaptosomal preparations, and the Km value increased further with the thickness of the slices. The apparent high Km values in slices were probably due to depletion of the GABA concentration in the extracellular fluid as the exogenous GABA ran the gauntlet of competing uptake sites on its way to sites deep within the slice, thereby bringing about a requirement for higher GABA concentrations in the incubation medium in order to maintain the internal GABA levels at the “Km level.” Evidence was obtained for three GABA uptake systems with Km values (in synaptosomes) of 1.1 μM, 43 μM, and 3.9 mM, respectively. In contrast, only two uptake systems for d-aspartate were detected, with km values of 1.8 μM and 1.8 mM, respectively. The implications of the findings in the study with respect to previous data in the literature are discussed.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: Using tritium-labelled 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) its tissue distribution and metabolism were investigated in adult mice and 4-day-old chicks after systemic administration of the drug. It was found not to be significantly metabolized in the brain since metabolites of THPO corresponding to only approximately 8% of the parent compound could be detected 30 min after administration of the drug intramuscularly in mice. In the liver, however, THPO was found to be metabolized to a considerable extent. In chicks THPO metabolites were found in the brain but they accounted for 〈 35% of the radioactivity. The brain concentration of THPO in mice and chicks corresponded to respectively 10 and 50% of the dose injected intramuscularly and the tissue level was essentially constant for at least 3 h after injection. Following systemic administration of THPO to mice and chicks the contents of aspartate, glutamate, glutamine, and γ-aminobutyric acid (GABA) in whole brain and in synaptosomes was determined. It was found that only GABA contents were affected being increased in synaptosomes from mice and decreased in whole brain in chicks. Doses of THPO. which in chicks but not in mice led to brain levels that were sufficient to inhibit glial GABA uptake, were found to protect chicks but not mice against isonicotinic acid hydrazide-induced seizures. The findings are compatible with the notion that THPO exerts its anticonvulsant activity by inhibition of astrocytic GABA uptake. Key Words: 4,5,6.7-Tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO)—Anticonvulsant—γ-Aminobutyric acid—Mice—Chicks—THPO metabolism. Schousboe A. et al. Tissue distribution, metabolism, anticonvulsant efficacy, and effect on brain amino acid levels of the glia-selective 7-aminobutyric acid transport inhibitor 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol in mice and chicks. J. Neurochem. 47, 758–763 (1986).

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: Intramuscular administration of methionine to mice resulted in changes in the levels of aspartate, glutamate, glutamine, and γ-aminobutyrate in both nerve endings (synaptosomes) and “non-nerve-ending” tissue in the brain. However, the amino acid changes in the two locations differed considerably, not only in the time to onset of the changes, but also in the direction of the changes and in their duration. The results provide additional support for a glutamate-glutamine cycle between neurons and glia, and suggest that the decreases in amino acid levels in the nerve endings are due to an insufficient supply of glutamine from glia or other cellular structures, possibly compounded by an impairment in the uptake of glutamine into the nerve terminals. The primary cause of the glutamine deficiency is unknown because methionine did not affect the enzymes of glutamate and glutamine metabolism. Treatment of mice with methionine also resulted in an anticonvulsant action, but no correlation was observed between the latter phenomenon and the glutamate content of nerve endings.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: The potassium-stimulated release of γ-aminobutyric acid (GABA) from synaptosomes was determined in preparations from control rats and from rats treated with a convulsant agent [isonicotinic acid hydrazide (INH)] and an anticonvulsant agent (gabaculine). INH treatment brought about a significant decrease in Ca2+-dependent release of GABA with no effect on Ca2+-independent release, whereas gabaculine caused an increase in Ca2+-independent release with no effect on Ca2+-dependent release of GABA. Thus, the anticonvulsant action of gabaculine was not a simple reversal of the effects of INH on GABA release. The results indicate that there are at least two pools of GABA in nerve endings and support the hypothesis that exogenous GABA is taken up first into a pool that supplies GABA for Ca2+-independent release and then is transferred to a second pool (Ca2+-dependent releasable), where it mixes with newly synthesized GABA.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: The amino acid content of synaptosomes was determined in six regions of rat brain, and in all regions the five predominant amino acids were glutamate, glutamine, aspartate, taurine, and GABA (γ-aminobutyrate). However, the proportions of the individual amino acids varied considerably from one region to another, the GABA content being particularly high and the taurine content low in synaptosomes from the diencephalon and mesencephalon. Administration of isonicotinic acid hydrazide to rats lowered the synaptosomal GABA level by similar amounts in all brain regions, but the administration of gabaculine resulted in a particularly long-acting elevation in GABA levels in the nerve endings of the diencephalon and mesencephalon. The possibility is raised that the high GABA levels in the nerve terminals of the diencephalon may be involved in the gabaculine-induced lowering of the body temperature of the rats. A constancy in the amount of the synaptosomal pool of “aspartate + glutamate + glutamine + GABA” was observed despite large changes in the relative amounts of the four amino acids brought about by gabaculine.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: The intramuscular administration of L-cycloserine, gabaculine, and aminooxyacetic acid caused significant, time-dependent increases in the γ-aminobutyric acid (GABA) content of both whole brain and synaptosomalenriched preparations obtained from the tissue, a linear relationship being observed between the two parameters. In contrast, the administration of hydrazine resulted in a large increase in whole brain GABA level, with little change in the synaptosomal GABA content. The key factor in these different responses appeared to be the degree of inhibition of glutamic acid decarboxylase by the drugs. Pretreatment of mice with the GABA-elevating agents resulted in a delay in the onset of seizures, which was related directly to the increase in synaptosomal GABA content. Although the seizures were delayed, they occurred while the GABA content of nerve endings (synaptosomes) was above that in preparations from untreated animals. The decrease in GABA content at the onset of seizures, expressed as a percentage of the level at the time of injection of the convulsant agent, was, however, reasonably constant. A hypothesis to explain these results is proposed.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract— The GABA-elevating agents, aminooxyacetic acid, hydrazine, and hydroxylamine, all possessed anticonvulsant properties, although to a widely varying degree. Aminooxyacetic acid was the most efficacious in delaying drug-induced seizures in mice whereas hydroxylamine brought about only a slight delay in the onset of seizures. The anticonvulsant action was observed against various convulsant agents regardless of whether the convulsant mechanism might involve a deranged GABA metabolism (allylglycine, isonicotinic acid hydrazide, hydrazine), an interference with GABA function (picrotoxin) or some other mechanism (pentylenetetrazol). The anticonvulsant action was not related in a simple manner to either GABA levels or glutamic acid decarboxylase (GAD) activities but the anomalous situation whereby seizures occurred when the GABA content of brain was above normal could be resolved on the basis of an expression which included changes in both GABA levels and GAD activity. The possibility was proposed that the anticonvulsant action of aminooxyacetic acid involved two separate mechanisms.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

(1) Animals were exposed to hypoxic environments either by supplying them with breathing mixtures low in oxygen or by exposing them in a decompression chamber to simulated altitude. Both methods of producing hypoxia brought about significant increases in brain GABA levels.(2) Elevated GABA levels occurred in all species tested (mouse, hamster, rat, guinea pig, and rabbit) and reached maximal concentration 60 min after the initiation of breathing the hypoxic mixtures. Extension of the exposure beyond 60 min brought about a gradual decline in GABA level from the maximal value reached.(3) A linear relation was found between the oxygen content of the gas mixture and the elevation of GABA level. For guinea pigs, at least, the critical oxygen content required to prevent elevation of GABA level was 8.1 per cent.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract— The susceptibility of chicks to convulsions induced by hyperbaric oxygen increased with age during the first few weeks of life. The sensitivity of the levels of cerebral GABA to change by oxygen at high pressure (OHP) also increased with age. There was correlation between the rate of decrease in concentration of cerebral GABA and the time to onset of OHP seizures. The anti-convulsant action of intraperitoneally administered GABA was greater in 6-9-day-old chicks than in 21-23-day-old chicks, consistent with decreasing permeability of the blood-brain barrier to the amino acid with increasing age.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract: Di-n-propylacetate (DPA), aminooxyacetic acid (AOAA), and gabaculine were administered alone or in combination to Swiss mice. Six hours after administration of the drugs the anticonvulsant action (against isonicotinic acid hydrazide-induced seizures) of AOAA and DPA combined was less than that of AOAA alone. The cause of this phenomenon appeared to be an interaction between DPA and AOAA with respect to inhibition of GABA-T activity, resulting in a long-term diminished inhibition by AOAA, which in turn led to a lessening of the AOAA-induced elevation in the GABA content of nerve endings (synaptosomes). An excellent correlation was observed between the delay in onset of seizures and the elevation of synaptosomal GABA content.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Data have been presented indicating that in chicks the time lag in the onset of seizures after the administration of hydrazides was not caused by a slow penetration of the convulsant agents into the brain. A correlation was evident between the rate of decrease in concentration of cerebral GABA and the susceptibility of chicks to hydrazide-induced seizures. Earlier studies precluding a role for GABA in hydrazide-induced convulsions were re-examined.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

—The stability of the GABA content of synaptosomal-enriched fractions was evaluated by two approaches. Firstly, the addition of 10−3m-aminooxyacetic acid to the homogenizing medium totally inhibited the GABA-degrading enzyme in the fractions but did not affect the GABA levels. This indicated that GABA was not being metabolized during the normal preparation of the synaptosomal-enriched fraction. Secondly, when synaptosomal-enriched fractions were re-fractionated by discontinuous density gradient centrifugation, the GABA contents of the fractions before and after the second fractionation were very similar provided they were expressed on a per mg protein basis. It was therefore concluded that the GABA content of the organelles was not subject to change during the fractionation procedures. On the basis of these findings and others it was suggested that the synaptosomal-enriched fraction could be used as a model to evaluate drug-induced changes in GABA levels in nerve endings. In vivo experimentation indicated that the convulsant agents hydrazine, isonicotinic acid hydrazide and aminooxyacetic acid brought about similar decreases in the GABA content of the synaptosomal-enriched fractions prepared from tissue at the onset of seizures despite the fact that no correlation was observed between seizure activity and whole brain GABA levels.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

—The effect of intramuscularly administered INH on brain levels of GABA in chicks was dependent on the amount injected. A subconvulsant dose of INH (1·1 mmol/kg) produced a slow steady decline in the level of GABA, whereas a convulsant dose (2·19 mmol/kg) brought about a sequential fall and rise in GABA level. This sequence of events reflected changes in the relative activities of GAD and GABA-T brought about by the hydrazide. The administration of pyridoxine together with the INH (2·19 mmol/kg) prevented the onset of seizures and lessened the effect of the INH on GABA levels and GAD activity but not on GABA-T activity. The possibility that a deranged GABA metabolism is responsible for hydrazide-induced seizures is discussed.

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Abstract— The administration of different hydrazides to chicks (20-23 days post-hatching) in amounts giving similar latent periods before the onset of seizures produced (i) similar rates of decrease in content of cerebral GABA, (ii) considerable but dissimilar inhibitions of cerebral GAD activity, (iii) slight inhibitions of cerebral GABA-T activity. The results support the view that low GABA levels were involved in. the etiology of the seizures but seemed to rule out the possibility that a reduced turnover of GABA was responsible for the occurrence of the convulsions.

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