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Biomedical subjects

K G Lloyd

Publications and source records attributed to K G Lloyd.

At least 91 records · Page 5Linked to original sources
PubMed1980

Kinetics of L-DOPA metabolism in the caudate nucleus of cats with ventrotegmental lesions.

Sixteen days after a unilateral lesion of the ventromedial tegmentum (VMT) of the midbrain, adult cats received an intravenous dose of L-DOPA (20 mg/kg), and the caudate nucleus from each hemisphere was removed at various time intervals thereafter. In the caudate nucleus contralateral, to the VMT lesions, DA levels reached 200% of control values within 15 min, and maintained this elevation for at least 2 hours. DA levels in the caudate nucleus ipsilateral to the VMT lesion were much lower than contralateral values; however, they were much higher than those of non-DOPA treated animals with comparable lesions. DA levels in the caudate nucleus of the lesioned hemisphere were directly related to the remaining DOPA decarboxylase activity. The striatal serotonin concentrations were unchanged after L-DOPA, but an increase in 5-hydroxyindoleacetic acid levels was observed. From these results, we conclude that, (i) in cats with nigrostriatal tract lesions after low doses of L-DOPA comparable to those given to patients with Parkinson's disease, the bulk of the newly formed DA in the caudate nucleus is contained in nigrostriatal neurons, and (ii) there exists an inverse relationship between the ability of the caudate to synthesize DA and the severity of the nigrostriatal tract lesion.

Animals↗
PubMed1980

Biphasic effects of direct, but not indirect, GABA mimetics and antagonists on haloperidol-induced catalepsy.

At very low doses the GABA agonists SL 76002 and muscimol diminish haloperidol-induced catalepsy. At somewhat higher doses these compounds potentiate catalepsy. Biphasic effects on DA-receptor mediated functions have previously been noted with bicuculline and picrotoxinin. In contrast, manipulation of GABA levels by enzyme inhibition induced only a monophasic effect on dopamine-mediated behaviour. The potentiation of GABA levels by enzyme inhibition induced only a monophasic effect on dopamine-mediated behaviour. The potentiation of haloperidol-induced catalepsy by GABA mimetics is also observed with dipropylacetate, delta-aminovaleric acid and gamma-acetylenic GABA. This GABA-mimetic potentiation of catakepsy was blocked by the coadministration of bicuculline. These results confirm and extend the hypothesis that GABA-neurons influence DA neuron function. Furthermore they suggest that more than one group of GABA receptors influence directly and/or indirectly DA neuronal function, with different resultant effects.

Allylglycine↗
PubMed1980

New anticonvulsants: Schiff bases of gamma-aminobutyric acid and gamma-aminobutyramide.

Schiff bases of gamma-aminobutyric acid (gammaAbu) and gamma-aminobutyramide (gammaAbuNH2) were prepared and tested for anticonvulsant and gammaAbu mimetic activity. 4-[[(4-Chlorophenyl)(5-fluoro-2-hydroxyphenyl)methylene]amino]butanoic acid monosodium salt (4) and 4-[[(4-chlorophenyl)(5-fluoro-2-hydroxyphenyl)methylene]amino]butanamide (5) blocked bicuculline-induced lethality and convulsions and displaced [3H]gammaAbu from its membrane binding sites. In the rat dorsal root sensory ganglion, compound 4 exhibited gammaAbu agonist properties. Compounds 4 and 5 are thus anticonvulsants and directly acting gammaAbu mimetics.

Animals↗
PubMed1979

[3H]GABA binding in brains from Huntington's chorea patients: altered regulation by phospholipids?

Binding sites for tritum-labeled gamma-aminobutyric acid (GABA) in cerebellar cortex of Huntington's chorea patients have an increased affinity but unaltered maximum capacity as compared to binding sites in tissue from control patients. A similar binding pattern is produced in control membranes by treatment with Triton X-100, phospholipase C, or glycerophosphoethanolamine. Thus, it is likely that phospholipids or their metabolites regulate the accessibility of the GABA binding site and that this regulation is abnormal in Huntington's chorea.

Cerebellar Cortex↗
PubMed1979

An analysis of [3H]gamma-aminobutyric acid (GABA) binding in the human brain.

The binding of [3H]GABA to membranes prepared from human brains obtained post morten was examined. This binding was independent of patient sex, age (16--80 years), postmortem interval (4--33 h) or storage time when frozen (0-64 months). In preparations from cerebellar cortex various compounds displaced [3H]GABA binding with the following order of potency: muscimol greater than 3-aminopropanesulfonic acid greater than GABA greater than imidazoleacet acid greater than delta-amino-n-valeric acid greater than 3-hydroxyGABA greater than bicuculline. Other compounds active 'in vitro' included strychnine, homocarnosine and some (e.g. clozapine, thioridazine, pimozide) but not all (chlorpromazine, haloperiodol) neuroleptics. Compounds inactive 'in vitro' included aminooxyacetic acid, baclofen, picrotoxin, anticholinergics, metrazole, anticonvulsants and naloxone. Triton X-100 augmented the [3H]GABA binding (25 nM) by about 10--20-fold in most brain regions. [3H]GABA binding (IC50) was altered in Huntington's chorea and Reye's syndrome, but not in schizophrenics (4-neuroleptic-treated patients) or sudden infant death syndrome. The data presented strongly support the proposal that the measurement of [3H]GABA binding in postmortem human brain offers a reflection of the state of the physiologically relevant GABA receptor.

Adolescent↗
PubMed1979

Familial fatal Parkinsonism with alveolar hypoventilation and mental depression.

The clinical, pathological, and neurochemical characteristics of a newly recognized inherited neurological disorder are reported. Lethargy and mental depression are early symptoms, followed by mild parkinsonism and progressive weight loss. Failure of automatic respiratory control develops and may result in sudden death. Advanced degeneration of the substantia nigra, cell loss and gliosis of the basal ganglia, and focal gliosis in the medulla are seen on pathological study. Degeneration of the nigrostriatal dopaminergic system is evidenced by low levels of tyrosine hydroxylase, dopamine, homovanillic acid, and L-dopa decarboxylase in postmortem brain samples. Taurine concentrations in fasting plasma and CSF are somewhat depressed; brain contents of taurine are within normal limits.

Brain↗
PubMed1979

Sodium-independent, high-affinity binding of [3H]gamma-aminobutyric acid in human neurological disorders.

With respect to [3H]GABA-binding in material prepared from human post-mortem brain, the following observations have been made: (1) The [3H]GABA binding site in the cerebellum has the pharmacological characteristics of the physiological GABA-receptor observed in other species. Together with the post-mortem stability exhibited for [3H]GABA-binding, this provides an approach for determining the functional state of the GABA-receptor in various disease states; (2) In Parkinson's disease [3H]GABA-binding in the substantia nigra is significantly decreased whereas that in the putamen and caudate nucleus is unaltered. The former finding likely indicates that GABA binding sites (receptors) occur on nigral dopaminergic cell bodies and/or dendrites. The latter finding may signify that relatively few of the striatal [3H]GABA binding sites occur on dopaminergic nerve terminals in the human caudate or putamen; (3) In Huntington's disease [3H]GABA binding was decreased in the caudate nucleus and putamen, in parallel wih the massive cell loss and gliosis observed in this condition. Membranes prepared from cerebellar tissue of these patients possessed an increased affinity for [3H]GABA-binding; (4) Pre-treatment of cerebellar membranes from control brains with Triton-X-100 (0.02%) or phospholipase-C (0.001 units) results in kinetic changes very similar to those observed in Huntington's brains. In contrast, such treatment was virtually without effect on the IC50 or KD for [3H]GABA on cerebellar membranes prepared from Huntington's brains; (5) These results imply that a phospholipid, possibly related to phosphoglycerolethanolamine, is altered in the membrranes of Huntington's patients and that this phospholipid normally has a role in controlling accessibility to the GABA-receptor.

Binding, Competitive↗
PubMed1978

Differential blockade of bicuculline convulsions by neuroleptics.

Haloperidol, pimozide, sulpiride and metoclopramide blocked bicuculline-induced convulsions in mice. Chlorpromazine and thioridazine exhibited this effect at low doses whereas at higher doses (e.g. 1 mg/kg i.p. chlorpromazine) this activity was no longer apparent. A dose of phenoxybenzamine which was inactive alone (7.5 mg/kg i.p.) completely blocked the anti-bicuculline effect of sulpiride and antagonized that of haloperidol. These data are interpreted as indicating that intact noradrenergic systems are necessary for the anti-bicuculline effect of the neuroleptics.

Animals↗