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M K Ticku

Publications and source records attributed to M K Ticku.

At least 55 records · Page 3Linked to original sources
PubMed1993

Ethanol- and diazepam-withdrawal hyperlocomotion is not due to 5-HT3 receptor stimulation.

The effect of 5-HT3 receptor antagonists such as ondansetron, ICS 205-930, MDL 72222, metoclopramide, and zacopride was investigated on the ethanol as well as diazepam withdrawal phenomena in the present study. There was a significant increase in locomotor activity in the ethanol- as well as diazepam-withdrawn rats. The treatment of rats with 5-HT3 receptor antagonists during withdrawal phase did not modify the effect. The ethanol-withdrawn rats were more sensitive to pentylenetetrazole (PTZ)-induced convulsions as compared to control animals. 5-HT3 receptor antagonists did not attenuate the increased sensitivity of ethanol-withdrawn rats to PTZ. These observations indicated that 5-HT3 receptor antagonists are ineffective in attenuating hyperlocomotor activity following abrupt termination of chronic administration of ethanol or diazepam, and increased sensitivity to PTZ in the ethanol-withdrawn rats.

Animals↗
PubMed1993

Antibodies specific for GABAA receptor alpha subunits reveal that chronic alcohol treatment down-regulates alpha-subunit expression in rat brain regions.

Chronic administration of ethanol results in the development of tolerance and dependence. The molecular mechanism underlying these behavioral actions of ethanol is poorly understood. Several lines of evidence have suggested that some of the pharmacological actions of ethanol are mediated via a potentiation of GABAergic transmission. Chronic ethanol administration results in a reduction in the GABAA receptor-mediated 36Cl- uptake in cortical synaptoneurosomes and primary cultured neurons. We and others have shown that it also results in a 40-50% reduction in GABAA receptor alpha-subunit mRNA levels in the rat cerebral cortex. In the present study, we investigated the expression of alpha 1, alpha 2, and alpha 3 subunits of the GABAA receptor in the cerebral cortex and the alpha 1 subunit in the cerebellum by immunoblotting using polyclonal antibodies raised against alpha 1-, alpha 2-, and alpha 3-subunit polypeptides following chronic ethanol treatment. These results reveal that chronic ethanol administration to rats results in a 61 +/- 4% reduction in level of the GABAA receptor alpha 1 subunit (51 kDa), 47 +/- 8% reduction in level of the alpha 2 subunit (53 kDa), and 30 +/- 7% reduction in level of the alpha 3 subunit (59 kDa) in the cerebral cortex and a 56 +/- 5% reduction in content of the alpha 1 subunit in the cerebellum. In summary, this ethanol-induced reduction in content of the GABAA receptor alpha subunits may underlie alterations in the GABAA receptor function and could be related to cellular adaptation to the functional disturbance caused by ethanol.

Alcoholism↗
PubMed1993

Alcohol: effects on GABAA receptor function and gene expression.

Chronic ethanol treatment increased the binding of [3H]Ro15-4513 in cerebral cortex and cerebellum of rats and produced a reduction in the alpha 1, alpha 2, alpha 5 GABAA receptor subunits mRNAs in the cerebral cortex and alpha 1 subunit mRNA in the cerebellum, and an increase in alpha 6 subunit mRNA in the cerebellum. An increase in the alpha 6 subunit mRNA which selectively encodes Ro15-4513 binding in the cerebellum is consistant with an increase in the photolabelling of [3H]Ro15-4513 to the 55 KDa band in the cerebellum of chronic ethanol treated rats. Using polyclonal antibodies, we have confirmed that chronic ethanol treatment decreased alpha 1 subunit (51 KDa), alpha 2 subunit (53 KDa) and alpha 3 subunit (59 KDa) in cerebral cortex. These results suggest that chronic ethanol treatment produces a decrease in the expression of GABAA receptor subunit which may underlie a molecular basis for ethanol tolerance.

Alcoholism↗
PubMed1992

Effects of 5-HT receptor antagonists on seizure susceptibility and locomotor activity in DBA/2 mice.

The effect of antagonists of serotonin (5-HT) receptor subtypes and alpha 2-adrenoceptors was investigated on audiogenic seizures and locomotor activity in DBA/2 mice. 5HT1c receptor antagonists (mianserin and cyproheptadine), 5-HT3 receptor antagonist (zacopride) and 5-HT4 receptor antagonist (ICS 205-930) increased the latency of audiogenic seizures and decreased the severity of convulsions in young (20-27 days old) DBA/2 mice. However, the effect of these antagonists varied in older (30-37 days old) mice. Ketanserin, 5-HT2 receptor antagonist, was devoid of any activity on audiogenic seizures. Yohimbine (0.5 mg/kg, i.p.), an alpha 2-adrenoceptor antagonist, increased the severity of audiogenic seizures, and the anti-convulsant effect of 5-HT receptor subtypes antagonists became more pronounced in the presence of yohimbine. 5-HT3 and 5-HT4 receptor antagonists produced hypolocomotor activity in young mice whereas 5-HT1c and 5-HT2 receptor antagonists were devoid of any effect on locomotor activity. Yohimbine did not induce any effect on locomotor activity but the mice exhibited more pronounced hypolocomotor activity following the administration of 5-HT3, 5-HT4 and 5HT1c receptor antagonists in the presence of yohimbine. However, the results varied with these agents in the older mice. These observations implicate a role of 5-HT1c, 5-HT3, 5-HT4 and alpha 2-adrenoceptors in audiogenic seizures in young DBA/2 mice, and 5-HT3 and 5-HT4 receptors in locomotor activity in these mice. Furthermore, these results also suggest an interaction between 5-HT receptors and alpha 2-adrenoceptors, and differential development patterns of various 5-HT receptor subtypes in the CNS.

Acoustic Stimulation↗
PubMed1992

Aging related alterations in GABAA receptor subunit mRNA levels in Fischer rats.

The influence of aging on the binding of ligands to picrotoxin binding sites as well as steady state levels of mRNA for various alpha subunits of gamma-aminobutyric acid (GABA) receptor complex was investigated in male Fischer F-344 rats. In aged rats, the binding of [35S]t-butyl-bicyclophosphorothionate (TBPS) was significantly reduced. This decrease in TBPS binding derived from a reduced density of binding sites, rather than from affinity changes, in both cerebral cortex and cerebellum. In aged rats, alpha 1 mRNA level decreased approximately 70% between age 6 months and 24 months in the cerebral cortex (P less than 0.005). In contrast, alpha 1 mRNA remained unchanged in the cerebellum of old rats. The association of a decrease in picrotoxin binding sites in the cerebral cortex with a decline in alpha 1 mRNA level in the cerebral cortex and in alpha 2 mRNA level in the cerebellum is indicated. alpha 6 mRNA level increased with age in the cerebellum. These findings indicate a selective age related modulation in the stoichiometry of GABAA receptor in aging.

Aging↗
PubMed1992

Chronic GABA exposure down-regulates GABA-benzodiazepine receptor-ionophore complex in cultured cerebral cortical neurons.

Cerebral cortical cultured neurons were characterized for GABA-benzodiazepine (BZ) receptor complex, and the effect of chronic exposure of cortical neurons to GABA on GABA-BZ receptor system was investigated. In the intact cells, the [3H]flunitrazepam binding was rapid and saturable, with an apparent Kd of 4.2 +/- 1.5 nM and Bmax of 776 +/- 54 fmol/mg protein. Specifically bound [3H]flunitrazepam was displaced in a concentration-dependent manner by various BZ receptor ligands such as Ro15-1788, DMCM, Ro15-4513, clonazepam, alprazolam, diazepam and zolpidem, and enhanced by GABA, muscimol and pentobarbital. GABA induced enhancement of 36Cl-influx in a concentration-dependent manner (EC50 = 9 +/- 2 microM). Chronic exposure of the cultured neurons to GABA resulted in a reduced [3H]flunitrazepam, [3H]GABA, [3H]Ro15-1788, [3H]Ro15-4513 and [35S]TBPS binding, a reduced enhancement of [3H]flunitrazepam binding by GABA, and a reduced GABA-induced 36Cl-influx susceptible to reversal by concomitant exposure of the cultures to R 5135, a GABAA-receptor antagonist. These findings indicate that cerebral cortical cultured neurons provide an ideal model to study GABA-BZ receptor complex using binding and 36Cl-influx assays, and chronic exposure of cortical cultures to GABA leads to a down-regulation of GABA-BZ receptor system. It is a GABAA receptor-mediated slow process.

Animals↗
PubMed1992

Chronic ethanol administration alters gamma-aminobutyric acidA receptor gene expression.

Chronic ethanol (alcohol) administration has been associated with alterations in the binding and function of the gamma-aminobutyric acid (GABAA) receptor. To evaluate the mechanism underlying these changes, we measured the steady state levels of the mRNAs for the alpha 1, alpha 2, alpha 3, alpha 5, and alpha 6 subunits of the GABAA receptor after chronic ethanol administration to rats and ethanol withdrawal for 24 hr. The results indicated that chronic ethanol administration resulted in a 61% decline in the level of the GABAA receptor alpha 1 subunit mRNAs [3.8 and 4.3 kilobases (kb)] in the cerebral cortex in rats. The levels of the alpha 2 subunit mRNAs (6 and 3 kb) and the alpha 5 subunit mRNA (2.8 kb) were also reduced, by 61, 45, and 51%, respectively, whereas there was no change in the level of the alpha 3 subunit mRNA (3 kb). Furthermore, the ethanol-induced decrease in receptor mRNA levels persisted for 24 hr, after withdrawal of ethanol and returned to control values at 36 hr of withdrawal. alpha 1 mRNA levels in cerebellum also decreased by 28%. The level of the alpha 6 subunit mRNA, which selectively encodes Ro15-4513 binding sites, was found to be increased by approximately 76% in the cerebellum. Also, the photoaffinity labeling studies using [3H]Ro15-4513 indicated an increase in the levels of various protein components of the GABAA receptor, in the cerebellum and the cerebral cortex (e.g., 50- and 55-kDa proteins in the cerebellum and 41- and 50-kDa proteins in the cortex), after chronic ethanol treatment. The increase in alpha 6 mRNA in the cerebellum might be related to the increased labeling of the 55-kDa (approximately 56-kDa) protein and partially responsible for the increased binding, as reported previously by us. Because the alpha 6 subunit is not expressed in cortex, involvement of an as yet unknown subunit in this region cannot be ruled out. The effect of chronic ethanol treatment appears to be specific for GABAA receptor subunit mRNAs, because the same treatment did not alter the levels of glyceraldehyde-3-dehydrogenase mRNA or poly(A)+ RNA. In summary, these data indicate that chronic ethanol treatment results in an alteration in the regulation of expression of GABAA receptor subunit-encoding mRNAs, which could be due to alterations in transcription or mRNA stability.

Affinity Labels↗
PubMed1991

Aging reduces the mRNA of alpha 1 GABAA receptor subunit in rat cerebral cortex.

The effect of aging on the binding of ligands to the GABA, benzodiazepine and picrotoxin binding sites as well as alpha subunit mRNA level of GABAA receptor was investigated in cerebral cortex of male Fischer F-344 rats. In aged (730- to 770-day-old) rats, the binding of [35S]t-butylbicyclophosphorothionate (TBPS) was significantly reduced. Also, alpha 1 mRNA level was markedly decreased (86% suppression). In contrast, alpha 1 mRNA remained unchanged in cerebellum. These findings indicate a selective age-related structural change in GABAA receptor in rat cerebral cortex.

Aging↗
PubMed1991

Tricyclic antidepressants inhibit Ca(2+)-activated K(+)-efflux in cultured spinal cord neurons.

The effect of tricyclic antidepressants and monoamine oxidase inhibotors on the Ca(2+)-activated K(+)-efflux was studied using 86Rb-efflux assay in primary cultured mouse spinal cord neurons. Depolarization of the cultured cells with 100 mM KCl increased the 86Rb-efflux significantly in Ca(2+)-containing buffer, but not in Ca(2+)-free buffer. All the antidepressants examined, except the monoamine oxidase inhibitors, inhibited the 86Rb-efflux. Desipramine exhibited additivity with tetraethyl ammonium (TEA) and quinine sulfate (QSO4), but not with GABAB receptor agonist baclofen. The inhibitory action of antidepressants was not mediated through the GABAB receptors, since GABAB receptor antagonist, phaclofen, was unable to antagonize this effect. The ability of tricyclic antidepressants to inhibit calcium ionophore (A 23187)-induced 86Rb-efflux suggests that these drugs do not act at the level of voltage-gated Ca(2+)-channels. Furthermore, this effect does not seem to involve the G-proteins, adenylate cyclase, or protein kinase C systems, since pertussis toxin (PTX) and the activators of adenylate cyclase and protein kinase C did not reverse the effect of tricyclics on 86Rb-efflux. Taken together, these results suggest that antidepressants inhibit Ca(2+)-activated K(+)-channels at a stage subsequent to the voltage-gated Ca(2+)-channels.

Adenylate Cyclase Toxin↗
PubMed1991

Pharmacological effects of Withania somnifera root extract on GABAA receptor complex.

A methanolic extract of W. somnifera root inhibited the specific binding of [3H]GABA and [35S]TBPS, and enhanced the binding of [3H]flunitrazepam to their putative receptor sites. The extract (5 micrograms) inhibited [3H]GABA binding by 20 +/- 6 per cent whereas a concentration of 1 mg of the extract produced 100 per cent inhibition. The extract (5-100 micrograms) produced 20 +/- 4 to 91 +/- 16 per cent enhancement of [3H]flunitrazepam binding. In functional studies using 36Cl-influx assay in mammalian spinal cord neurons, W. somnifera root extract increased 36Cl-influx in the absence of GABA. This effect on 36Cl-influx was blocked by bicuculline and picrotoxin; and enhanced by diazepam. These results suggest that the W. somnifera extract contains an ingredient which has a GABA-mimetic activity.

Animals↗
PubMed1991

A functional assay to measure postsynaptic gamma-aminobutyric acidB responses in cultured spinal cord neurons: heterologous regulation of the same K+ channel.

The stimulation of postsynaptic gamma-aminobutyric acid (GABA)B receptors leads to slow inhibitory postsynaptic potentials due to the influx of K(+)-ions. This was studied biochemically, in vitro in mammalian cultured spinal cord neurons by using 86Rb as a substitute for K+. (-)-Baclofen, a GABAB receptor agonist, produced a concentration-dependent increase in the 86Rb-influx. This effect was stereospecific and blocked by GABAB receptor antagonists like CGP 35 348 (3-aminopropyl-diethoxymethyl-phosphonic acid) and phaclofen. Apart from the GABAB receptors, both adenosine via adenosine1 receptors and 5-hydroxytryptamine (5-HT) via 5-HT1 alpha agonists also increased the 86Rb-influx. These agonists failed to show any additivity between them when they were combined in their maximal concentration. In addition, their effect was antagonized specifically by their respective antagonists without influencing the others. These findings suggest the presence of GABAB, adenosine1 and 5-HT1 alpha receptors in the cultured spinal cord neurons, which exhibit a heterologous regulation of the same K(+)-channel. The effect of these agonists were antagonized by phorbol 12,13-didecanoate, an activator of protein kinase C, and pretreatment with pertussis toxin. This suggests that these agonists by acting on their own receptors converge on the same K(+)-channel through the Gi/Go proteins. In summary, we have developed a biochemical functional assay for studying and characterizing GABAB synaptic pharmacology in vitro, using spinal cord neurons.

Animals↗