A novel modulatory binding site for zinc on the GABAA receptor complex in cultured rat neurones.
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1. The properties of gamma-aminobutyric acidA (GABAA) receptor-ion channel complexes and the interaction with the transition metal zinc, were studied on rat sympathetic and cerebellar neurones in dissociated culture using patch clamp recording techniques. 2. The antagonism of GABA-induced membrane currents by zinc on sympathetic neurones was subject to developmental influence. Using embryonic sympathetic neurones acutely cultured for 24-72 h, GABA responses were more depressed by zinc when compared to responses evoked on adult neurones cultured for the same period. For neurones developing in vivo, the percentage inhibition of GABA responses produced by zinc in embryonic neurones was estimated to decline by 50% after 48.2 days following birth. 3. Embryonic sympathetic neurones maintained in culture for prolonged periods (40-50 days in vitro, DIV) became less sensitive to zinc when compared to neurones cultured for shorter periods (10-20 DIV). The decrease in the zinc inhibition for neurones maintained in vitro proceeded at an apparent rate of 0.55% per day. 4. Activation of the GABA receptor by muscimol (0.2-2 microM) was also antagonized by zinc (50-100 microM). 5. Lowering the pH of the perfusing Krebs solution did not affect the inhibition of GABA responses by zinc on sympathetic neurones. 6. Modulation of the GABAA receptor by some benzodiazepines, a barbiturate, a steroid based on pregnanolone, or antagonists bicuculline and picrotoxinin, did not interfere with the antagonism exerted by zinc on sympathetic neurones. A novel binding site for zinc on the GABAA receptor is proposed. 7. Analysis of the GABA-activated current noise on sympathetic neurones revealed two kinetic components to the power spectra requiring a double Lorentzian fit. The time constant describing the fast component (tau 2, 2.1 ms) was unaffected by zinc, whereas the slow component time constant (tau 1, 21.7 ms) was slightly reduced to 17.1 ms. 8. The apparent single-channel conductance for GABA-activated ion channels was determined from the power spectra (gamma s = 22.7 pS) and also from the relationship between the mean GABA-induced inward current and the variance of the current (gamma v = 24 pS). Zinc (25-100 microM) did not affect the single-channel conductance. 9. Single GABA-activated ion channels were recorded from outside-out patches taken from the soma of large cerebellar neurones. Single GABA channels were capable of activation to multiple current amplitudes which were assessed into the following conductance levels: 8, 18, 23, 29 and 34 pS.(ABSTRACT TRUNCATED AT 400 WORDS) (+info)
Drug-induced changes in brain acetylcholine.
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In rats, drug-induced depression of the central nervous system has been shown generally to be associated with an elevation in level of total acetylcholine in the brain. This generalization held true for a wide variety of depressant drugs with one notable exception: the subacute administration of reserpine, with which there was an increase in cerebral acetylcholine after the first dose, but a return to normal levels after subsequent doses, despite continued depression of the animals. Reduction in the level of total acetylcholine in the brain followed the administration of certain convulsants (pentylenetetrazole and 3,5-dimethylbutylethylbarbiturate); but no change was seen after the administration of several mildly exciting agents. The notable exceptions to this generalization were atropine and scopolamine, which significantly lowered brain acetylcholine in doses producing mild excitation in only some of the animals and no gross manifestations in the rest. (+info)
The use of ethamivan in the treatment of barbiturate poisoning.
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Ethamivan was used as a respiratory analeptic in the treatment of nine cases of severe barbiturate poisoning. Initial intravenous injections of 100 to 150 mg. of ethamivan increased the depth of respirations within a minute. Prolonged respiratory stimulation was achieved by a continuous intravenous infusion of 500 to 3000 mg. of ethamivan per litre of fluid. If hypotension occurred, an intravenous drip of noradrenaline was used; fluid overloading was avoided by adjusting the concentrations of drugs given, so that no more than a total of 125 c.c. of fluid per hour was administered. The chief side effect of overdosage of ethamivan was muscular twitching. This did not prove to be a problem and was of some value in determining the amount of drug given. The nine patients survived. It was concluded that ethamivan is a useful agent in the treatment of barbiturate poisoning. (+info)
KORSAKOFF'S SYNDROME ASSOCIATED WITH ADRENAL VIRILISM.
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Korsakoff's syndrome of obscure etiology was observed in a 34-year-old single woman with an 11-year history of hirsutism and mood swings, and previous hospitalizations for mania three years ago and depression 11 years ago.Recently the virilism had intensified with increased muscularity and coarsening of facial features. The 24-hour urinary 17-ketosteroids ranged between 14.4 mg. and 21.5 mg. and were suppressed by dexamethasone. The 17-hydroxycorticosteroid excretion was normal. These and other findings suggested a diagnosis of adrenal virilism due to adrenocortical hyperplasia. In the absence of other discernible causes it appeared that the adrenal pathology was responsible for the Korsakoff's syndrome. Both conditions responded well to glucocorticoid therapy although low doses were necessary to avoid mania.It is speculated that the encephalopathy was due to an associated adrenal insufficiency. Although hypoadrenalism is accepted as a complication of only the infant form of adrenal virilism, it is noteworthy that this patient had pathological pigmentation of her skin. (+info)
INDUCED PROTECTION OF ADRENAL CORTEX AGAINST 7,12-DIMETHYLBENZ(ALPHA)ANTHRACENE. INFLUENCE OF ETHIONINE. INDUCTION OF MENADIONE REDUCTASE. INCORPORATION OF THYMIDINE-H3.
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7,12-Dimethylbenz[a]anthracene (7,12-DMBA) exerts adrenocorticolytic effects which set it apart from all other polynuclear aromatic hydrocarbons and aromatic amines which have been investigated. Adrenal damage by this compound appears to be due to its steric and electronic properties together with its unusually high solubility in lipides. Many compounds given prior to 7,12-DMBA induced protection of adrenal. The most efficient inducers of protection are flat condensed aromatics possessing 4 or 5 rings; very small doses of these compounds were required to induce protection. Other compounds devoid of these properties induced protection but large or repeated doses were necessary. All inducers of protection had to be given prior to 7,12-DMBA to prevent adrenal necrosis; when given simultaneously with, or later than, this compound adrenal apoplexy resulted. Protective aromatics and 7,12-DMBA as well induced synthesis of menadione reductase in liver. 3-Methylcholanthrene (3-MC) induced this enzyme in many normal organs including liver, lung, adrenal, and in mammary cancer as well. dl-Ethionine under appropriate conditions of time and dosage eliminated the adrenal protection induced by aromatics and also delayed the induction of menadione reductase while depressing the amount of this enzyme which was synthesized. 7,12-DMBA caused a greatly reduced incorporation of tritium from thymidine-H(3) into washed acid-insoluble residue of adrenal. 3-MC given in advance mitigated the drastic effect of 7,12-DMBA on DNA synthesis and increased considerably the amount of tritium which was incorporated. The specific damage to adrenal by 7,12-DMBA is a direct effect on cells. Protection of adrenal is a secondary effect which requires induction of protein synthesis and it results in improvement in synthesis of DNA. (+info)
SOME PHARMACOLOGICAL PROPERTIES OF THIOPROPERAZINE AND THEIR MODIFICATION BY ANTI-PARKINSONIAN DRUGS.
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The pharmacological properties of a phenothiazine derivative thioproperazine have been compared with those of chlorpromazine, and the modifications by some anti-Parkinsonian drugs of its actions on the central nervous system have been studied. Thioproperazine was less potent than chlorpromazine in lowering blood pressure and antagonizing adrenaline in the cat, in depressing respiratory rate in the rabbit, in producing hypothermia and analgesia and in reducing the minimum anaesthetic dose of hexobarbitone in mice, and in protecting rats from convulsions induced by tryptamine. It was roughly equipotent to chlorpromazine in reducing locomotor activity of mice. Thioproperazine was more potent than chlorpromazine in protecting grouped mice from the acute toxicity of dexamphetamine, in preventing the acute behavioural disturbances produced by dexamphetamine in the rat, in producing a state of experimental catatonia in the rat and in preventing the emetic action of apomorphine in the dog. Hyoscine, benztropine or promethazine greatly reduced the ability of thioproperazine to prevent behavioural changes due to dexamphetamine in the rat and also abolished symptoms of experimental catatonia produced by thioproperazine. In contrast, the antiapomorphine activity of thioproperazine in the dog was not reduced to any extent by hyoscine or benztropine. (+info)
EFFECTS OF ETHAMIVAN IN PATIENTS WITH CHRONIC RESPIRATORY DISEASE.
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Nineteen patients suffering from chronic respiratory disease were evaluated before, during and after ethamivan administration by serial measurement of arterial pH, pCO(2), plasma ethamivan levels and alveolar ventilation. Ethamivan was administered intravenously as a single injection of 50 mg. in five patients; as an injection of 25 mg./kg. in five patients; as an intravenous injection of (a) 50 mg. over 15 minutes and (b) 150 mg. over 15 minutes in five patients; and finally as an oral dose of 300 to 500 mg. in five patients.Plasma levels of ethamivan became unmeasurable within 15 minutes of receiving the largest dose. Alveolar ventilation increased only in patients receiving the highest intravenous dose, and no significant changes in blood gases were elicited in any patient. (+info)
SOME ACTIONS OF CENTRALLY ACTIVE AND OTHER DRUGS ON THE TRANSMISSION OF SINGLE NERVE IMPULSES THROUGH THE ISOLATED SUPERIOR CERVICAL GANGLION PREPARATION OF THE RABBIT.
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The effect of some centrally-active and other drugs on the transmission of single nerve impulses through the isolated superior cervical ganglion preparation of the rabbit has been studied by recording both preganglionic and postganglionic action potentials. Block of conduction in the axon could be distinguished from block of the synaptic mechanism. The drugs did not appear to exert any one characteristic form of blocking action. A continuous spectrum of drug action linked an agent such as meprobamate which acted predominantly on the synapse to benactyzine which acted mainly by blocking axonal conduction. The drugs have been divided into three groups. Group I: hexamethonium, meprobamate, paraldehyde, amylobarbitone, methylpentynol and azacyclonal; these acted relatively selectively at the ganglion. Group II: N714C (the cis-isomer of chlorprothixene), prochlorperazine, methylpentynol carbamate, pipradrol, promethazine, perphenazine and procaine; the action of these drugs on the ganglion could be accounted for entirely in terms of their axonal depressant action. Group III: chlorprothixene, promazine, N720 (dihydrochlorprothixene), chlorpromazine, hydroxyzine and benactyzine; these drugs also blocked axonal conduction but in addition they appeared to exert a "facilitating" action at the ganglionic synapse. The actions of adrenaline, adrenochrome, iproniazid, ergotoxine, mescaline and lysergic acid diethylamide on transmission were also studied. The implications of the modifications of ganglionic transmission produced by these drugs is discussed. (+info)