PubMed Health⌕ Search

Biomedical subjects

M K Ticku

Publications and source records attributed to M K Ticku.

At least 73 records · Page 4Linked to original sources
PubMed1990

Are GABAB receptors involved in the pharmacological effects of ethanol?

The interaction of ethanol with GABAB-receptor system and the selectivity of phaclofen for GABA-receptor subtypes were investigated by employing an in vitro model of 36Cl-influx assay in mammalian cultured neurons and also in vivo models of picrotoxin- and NMDA-induced convulsions in rats. Ethanol (20 mM), without having any effect per se, potentiated the effect of GABA on 36Cl-influx, whereas at concentration 50 mM, ethanol activated Cl(-)-channels directly in mice spinal cord cultured neurons. In contrast, (-)baclofen (100 microM) did not modify the effects of GABA or ethanol on 36Cl-influx. Similarly, phaclofen (500 microM), as well as pertussis toxin (140 ng/ml, overnight incubation) did not modify these effects. Interestingly, phaclofen (200 micrograms i.c.v.) reversed the anticonvulsant effect of ethanol, but not that of pentobarbital or diazepam or progabide, against picrotoxin-induced convulsions in rats. However, phaclofen failed to modify the anticonvulsant effect of ethanol against NMDA-induced convulsions. These observations indicate that phaclofen is devoid of GABAA-receptor blockade property, and the anticonvulsant effect of ethanol against picrotoxin may be mediated through the activation of both GABA-receptor subtypes.

Animals↗
PubMed1990

Chronic benzodiazepine antagonist treatment and its withdrawal upregulates components of GABA-benzodiazepine receptor ionophore complex in cerebral cortex of rat.

Effect of chronic administration of benzodiazepine (BZ) receptor antagonist Ro 15-1788 (flumazenil) (4 mg/kg once daily for 14 days) treatment and its withdrawal on locomotor activity, body temperature, and the binding pattern of receptor ligands that bind to GABA-BZ receptor ionophore complex in different regions of the brain of the rat was studied. Ro 15-1788 (x 14 d) increased the specific binding of [3H]ethyl-8-fluoro-5-6-dihydro-5-methyl-6-oxo-4H- imidazo[1,5 alpha][1,4]benzodiazepine-3-carboxylate [( 3H]Ro 15-1788), [3H]ethyl-8-azido-5-6-dihydro-5-methyl-6-oxo-4H- imidazo[1,5 alpha][1,4]benzodiazepine-3-carboxylate [( 3H]Ro 15-4513), [3H]flunitrazepam, and [35S]t-butylbicyclophosphorothionate [( 35S]TBPS) in cerebral cortex, and this increase in binding remained upregulated during the drug withdrawal at 24 h. The binding of [3H]Ro 15-1788 was also found significantly increased in the hippocampus, but not in cerebellum and striatum. The chronic Ro 15-1788 treatment did not alter the specific binding of [3H]GABA. Rosenthal analysis of the saturation isotherms indicated that the observed upregulation in the binding pattern of [3H]Ro 15-1788 and [3H]Ro 15-4513 in the cerebral cortex was due to an increase in the binding capacity (Bmax). The receptor affinity (Kd) was not changed. The withdrawal of Ro 15-1788 following its chronic administration also enhanced locomotor activity. However, no apparent change in body temperature was observed either due to chronic treatment or withdrawal. These data indicate that chronic Ro 15-1788 treatment and its withdrawal may produce an upregulation of subunits which bind the positive (benzodiazepines), negative (inverse agonist), and neutral (antagonist) ligands of benzodiazepine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1990

GABAB receptor activation inhibits Ca2(+)-activated 86Rb-efflux in cultured spinal cord neurons via G-protein mechanism.

86Rb-efflux assay in primary cultured spinal cord neurons was developed to study the effect of GABAB receptor activation on Ca2(+)-activated K(+)-channels. Depolarization of the cultured cells with 100 mM KCl increased the 86Rb-efflux significantly. This efflux was blocked partly by quinine sulfate, tetraethylammonium, and La3+, indicating the involvement of Ca2(+)-activated K(+)-channels. Both (-)-baclofen and GABA inhibited the Ca2(+)-activated 86Rb-efflux. This inhibition seems to be mediated through GABAB receptor activation as it was blocked by GABAB antagonist phaclofen, but not by bicuculline. Moreover, pertussis toxin blocked the ability of (-)-baclofen to inhibit the Ca2(+)-activated 86Rb-efflux, showing that GABAB receptor activation involves G-protein mechanism. Further, forskolin and phorbol ester also attenuated the action of (-)-baclofen. This suggests that the GABAB receptors are negatively coupled to adenylate cyclase. These results show that the action of GABAB receptors involved G-proteins and adenylate cyclase. This assay may provide an ideal model to study GABAB receptor pharmacology.

Adenylate Cyclase Toxin↗
PubMed1990

Comparison of anticonvulsant effect of ethanol against NMDA-, kainic acid- and picrotoxin-induced convulsions in rats.

The anticonvulsant effect of ethanol against N-methyl-D-aspartic acid-(NMDA), kainic acid-, and picrotoxin-induced convulsions was studied in rats. Ethanol (2 g/kg, ip) offered protection against these agents, and it was most effective against picrotoxin and least effective against kainic acid. MK801, NMDA receptor antagonist, also provided protection against these agents. However, it was most effective against NMDA and least effective against kainic acid. Ineffective doses of MK801 (0.1 mg/kg, ip) and ethanol (0.5 g/kg, ip), when administered concurrently, had a facilitatory anticonvulsant effect, thereby providing protection against mortality following severe convulsions induced by NMDA or picrotoxin, but not against kainic acid. The protective effect of ethanol against NMDA- and kainic acid-induced neurotoxicity, in contrast to picrotoxin-induced toxicity, was not reversed by imidazodiazepine, Ro 15-4513, an ethanol antagonist. Furthermore, Ro 15-4513 did not produce any proconvulsant effect with NMDA or kainic acid. These findings suggested that the anticonvulsant actions of ethanol may be attributed to its ability to antagonize NMDA-mediated excitatory responses and facilitate the GABAergic transmission.

Animals↗
PubMed1990

Role of N-methyl-D-aspartate (NMDA) receptors in experimental catalepsy in rats.

N-methyl-D-aspartic acid (NMDA; 40 mg/kg, i.p.) did not elicit catalepsy, but it potentiated the cataleptic effect of haloperidol and GABAB receptor agonist, baclofen. MK-801 (0.2 mg/kg, i.p.), NMDA-receptor antagonist, reversed haloperidol- but not baclofen-induced catalepsy. MK-801 also potentiated the anticataleptic effect of scopolamine and bromocriptine against haloperidol-induced catalepsy. Dihydropyridine (DHP) calcium-channel antagonists such as nimodipine and nitrendipine (10 mg/kg, i.p.), reversed the anticataleptic effect of MK-801, and potentiated the cataleptic effect of haloperidol, as well as baclofen. These observations indicate the involvement of NMDA receptors in catalepsy, and suggest a potential clinical implication of NMDA-receptor antagonists in Parkinson's disease.

Animals↗
PubMed1990

Alcohol and GABA-benzodiazepine receptor function.

gamma-Aminobutyric acid (GABA)A is a major inhibitory neurotransmitter in the mammalian CNS. GABAA ergic synapse is also an important site of action for a variety of centrally acting drugs, including benzodiazepines and barbiturates. Several lines of electrophysiological, behavioral, and biochemical studies implicate GABAA ergic synapse in the actions of alcohol. In electrophysiological studies, alcohol has been reported to enhance GABA-mediated responses in cortical neurons, spinal cord and substantia nigra, albeit, negative results have also been reported. In behavioral studies, GABAmimetics enhance alcohol's effects on motor coordination, while GABA antagonists have the opposite effect. In drug-combination studies, subeffective doses of alcohol, in combination with subeffective doses of other GABAmimetics, potentiate each other's effect in several seizure models. In functional studies, alcohol has been reported to potentiate GABA receptor-mediated 36Cl-flux in microsacs, neurosynaptosomes, and cultured spinal cord neurons at pharmacologically relevant concentrations. The potentiating effect of alcohol is blocked by GABA antagonists and the inverse agonists of the benzodiazepine receptor site. Taken together, these studies indicate that some of the central effects of alcohol are mediated via facilitation of GABAAergic transmission.

Alcoholism↗
PubMed1990

Functional coupling of presynaptic GABAB receptors with voltage-gated Ca2+ channel: regulation by protein kinases A and C in cultured spinal cord neurons.

Depolarization-induced 86Rb efflux, an index of K+ efflux, was developed by using mammalian cultured spinal cord neurons to study the effect of gamma aminobutyric acid (GABAB) receptor activation on Ca2(+)-activated K(+)-channels. The Ca2(+)-activated 86Rb efflux was obtained by using two methods. The first method utilized depolarizing concentrations of KCl (100 mM) to study the voltage-gated Ca2+ channel activation, whereas in the second method, calcium ionophore A23187 was used to get the voltage-independent Ca2(+)-activated 86Rb efflux. The GABAB receptor agonist baclofen inhibited the efflux induced by depolarization but not by A23187, whereas tricyclic antidepressant desipramine inhibited the efflux induced by both depolarization and A23187. These results suggest that the GABAB receptor activation inhibits 86Rb efflux by inhibiting the voltage-gated Ca2+ channels. Moreover, forskolin and the analogs of cAMP antagonized the action of baclofen, suggesting that the GABAB receptors are negatively coupled to adenylate cyclase. Furthermore, protein kinase C activators antagonized this action of baclofen, while the antagonists of protein kinase C reversed their action on baclofen. In addition, the inactive forskolin, 1,9-dideoxyl forskolin, and the inactive phorbol analog, phorbol 12,13-didecanoate, did not influence the action of baclofen. Thus, it is suggested that the GABAB receptor activation inhibited the voltage-gated Ca2+ influx and that this action is under modulatory control by kinases A and C.

Adenylyl Cyclases↗
PubMed1990

gamma-Aminobutyric acidA receptor desensitization in mice spinal cord cultured neurons: lack of involvement of protein kinases A and C.

Desensitization of the gamma-aminobutyric acidA (GABAA) receptor was studied in cultured mammalian spinal cord neurons, using a GABA-induced 36Cl-influx assay. GABAA receptor agonists such as GABA and muscimol produced desensitization of GABAA receptor-gated Cl- channels. The ability of GABA to induce desensitization was time and concentration dependent and reversible. Involvement of protein kinase A in the desensitization phenomenon was studied by using activators of adenylate cyclase (forskolin analogs) and membrane-permeant analogs of cyclic AMP (8-bromo-cAMP and dibutyryl-cAMP). Both active forskolin and the inactive forskolin analog 1,9-dideoxyforskolin decreased GABA-induced 36Cl- influx alone, as well as when preincubated in conjunction with GABA. The effect of forskolin analogs appears to be nonspecific and unrelated to generation of cyclic AMP. GABA-induced 36Cl- influx was also inhibited directly by 8-bromo-cAMP, dibutyryl-cAMP, and cAMP. Furthermore, the protein kinase A inhibitor H-8 did not reverse the effect of cAMP analogs on the inhibition of GABA-induced 36Cl- influx. Taken together, these results suggest that cAMP analogs inhibit GABA-induced 36Cl- influx by acting via an extracellular site. The inability of the active phorbol ester to modify GABA-induced desensitization rules out the involvement of protein kinase C in the GABA receptor desensitization. These results suggest that protein kinases A and C are not involved in GABAA receptor desensitization in mouse spinal cord cultured neurons.

Animals↗
PubMed1989

Chronic haloperidol administration increases GABA binding and enhances neuronal responsiveness to iontophoresed GABA in rat globus pallidus.

Experiments were conducted to assess the effects of chronic haloperidol (CHAL) administration on gamma-aminobutyric acid (GABA) receptor binding within the rat globus pallidus (GP) and on the responsiveness of individual pallidal neurons to microiontophoretically applied GABA and glycine. Rats were administered haloperidol in their food for 30 days in increasing concentrations and the experiments were conducted 2 days after termination of the haloperidol treatment. GABA receptor binding and neuronal responsiveness to GABA were significantly increased within the GP following CHAL treatment. The mean EC50 value for GABA was significantly decreased in the CHAL-treated rats, but there was no change in the EC50 for glycine. Scatchard analysis of [3H]muscimol binding demonstrated a single high-affinity binding site (Kd = 5 nM) within both control and CHAL-treated rats. The binding capacity (Bmax) of this high-affinity site was significantly increased in CHAL-treated rats without any change in the dissociation constant (Kd) for this site. These results suggest that CHAL administration may lead to a decrease in GABA release by striatopallidal efferents. The results of this study, combined with those of our previous study on SNR neurons, have demonstrated that blockade of striatally mediated dopamine (DA) neurotransmission leads to similar changes in GABAergic mechanisms at the level of the GP and SNR and suggest that DA regulation of the striatopallidal and striatonigral GABAergic pathways need not be differentially organized as has previously been postulated.

Action Potentials↗
PubMed1989

Chronic ethanol treatment alters the behavioral effects of Ro 15-4513, a partially negative ligand for benzodiazepine binding sites.

Pentylenetetrazol (PTZ)-induced convulsion were studied in control, chronic ethanol-maintained, and ethanol-withdrawal rats. The convulsive doses of PTZ varied among the different groups of rats. Ethanol-maintained rats required higher doses of PTZ to produce convulsions, compared to control and ethanol-withdrawal rats. The partially negative ligands for benzodiazepine binding sites, Ro 15-4513 (2 mg/kg, i.p.) and FG 7142 (20 mg/kg, i.p.) produced proconvulsant effect in saline (control) and ethanol-withdrawal rats as they potentiated the effect of subconvulsive dose of PTZ. A higher dose of Ro 15-4513 (4 mg/kg, i.p.), but not FG 7142 (up to 80 mg/kg, i.p.), also produced proconvulsant effect in ethanol-maintained rats. Furthermore, Ro 15-4513 (5, 10 mg/kg, i.p.), but not FG 7142 (up to 80 mg/kg, i.p.), produced clonic-tonic seizures of short duration in ethanol-withdrawal rats. These effects of Ro 15-4513 and FG 7142 were reversed by diazepam (2 mg/kg, i.p.), as well as by the GABA-neutral Ro 15-1788 (10 mg/kg, i.p.), thereby, indicating the involvement of central benzodiazepine receptors in the action of Ro 15-4513 and FG 7142. These observations suggest that chronic ethanol treatment selectively alters the receptor sensitivity to Ro 15-4513, an ethanol antagonist and partially negative ligand for BZ sites, and this observation supports the notion that ethanol effects are more susceptible to reversal by the imidazobenzodiazepine as compared to other negative ligand for BZ binding sites.

Animals↗
PubMed1989

The pharmacological properties of GABA receptor-coupled chloride channels using 36Cl-influx in cultured spinal cord neurons.

gamma-Aminobutyric acid (GABA) synaptic pharmacology was studied in cultured mouse spinal cord using various biochemical techniques. The intact cultures were used to study GABA uptake, benzodiazepine (BZ) binding and GABA-stimulated 36Cl-influx, all under similar physiological conditions. The cultures appear to contain a population of GABAergic neurons, since there was evidence of neuronal active transport of [3H]GABA by these cells. There also was a significant population of neuronal BZ receptors based on the finding of clonazepam-displaceable [3H]flunitrazepam (FLU) binding. In addition, the presence of GABA receptors coupled to the BZ receptors was shown by the enhancement of FLU binding by GABA (10-100 microM). GABAA and glycine-coupled Cl- channels were also demonstrated using 36Cl-influx. GABA-induced 36Cl-influx was specific for GABAA agonists, since GABAB receptor agonist, baclofen and other excitatory neurotransmitters did not alter the 36Cl-influx. Both GABA (Km = 9.1 microM) and muscimol (Km = 2.0 microM) produced concentration-dependent increases in 36Cl-influx in the cultures. The GABA-stimulated Cl-influx was blocked by the GABAA receptor antagonist (+)bicuculline (IC50 = 4.5 microM) and by the Cl- channel antagonist picrotoxinin (IC50 = 25 microM). These results indicate that spinal cord cultures are a useful model for comparing the binding characteristics of the GABA receptor complex to the activation of the coupled Cl- channels using the 36Cl-influx assay.

Animals↗
PubMed1989

Ethanol and the benzodiazepine-GABA receptor-ionophore complex.

Ethanol has a pharmacological profile similar to that of classes of drugs like benzodiazepines and barbiturates, which enhance GABAergic transmission in the mammalian CNS. Several lines of behavioral, electrophysiological and biochemical studies suggest that ethanol may bring about most of its effects by enhancing GABAergic transmission. Recently, ethanol at relevant pharmacological concentrations has been shown to enhance GABA-induced 36Cl-fluxes in cultured spinal cord neurons, synaptoneurosomes and microsacs. These enhancing effects of ethanol were blocked by GABA antagonists. Ro15-4513, an azido analogue of classical BZ antagonist Ro15-1788, reversed most of the behavioral effects of ethanol and other effects involving 36Cl-flux studies. The studies summarized below indicate that most of the pharmacological effects of ethanol can be related to its effects on GABAergic transmission.

Affinity Labels↗
PubMed1989

GABAB receptor activation inhibits Ca2+-activated potassium channels in synaptosomes: involvement of G-proteins.

86Rb-efflux assay from preloaded synaptosomes of rat cerebral cortex was developed to study the effect of GABAB receptor agonist baclofen on Ca2+-activated K+-channels. Depolarization (100 mM K) of 86Rb-loaded synaptosomes in physiological buffer increased Ca2+-activated 86Rb-efflux by 400%. The 86Rb-efflux was blocked by quinine sulphate, tetraethylammonium and La3+ indicating the involvement of Ca2+-activated K+-channels. (-)Baclofen inhibited Ca2+-activated 86Rb-efflux in a stereospecific manner. The inhibitory effect of (-)baclofen was mediated by GABAB receptor activation, since it was blocked by GABAB antagonist phaclofen, but not by bicuculline. Further, pertussis toxin also blocked the ability of baclofen or depolarizing action to affect Ca2+-activated K+-channels. These results suggest that baclofen inhibits Ca2+-activated K+-channels in synaptosomes and these channels are regulated by G-proteins. This assay may provide an ideal in vitro model to study GABAB receptor pharmacology.

Animals↗
PubMed1989

Interaction between GABAergic anticonvulsants and the NMDA receptor antagonist MK 801 against MES- and picrotoxin-induced convulsions in rats.

The interaction between GABAergic (barbiturates, diazepam, ethanol) and other (phenytoin) anticonvulsants and the N-methyl-D-aspartate (NMDA) receptor antagonist MK 801 in protecting rats against maximal electroshock (MES)- and picrotoxin-induced (10 mg/kg) convulsions was studied. MK 801 (0.1 to 5 mg/kg) showed anticonvulsant responses against MES-induced convulsions in a dose dependent manner, higher doses showing severe muscle relaxation, motor incoordination, and anticonvulsant action. It also produced stereotypic head movement, circling behavior, and affected locomotion. When subanticonvulsant dose (1 mg/kg) of MK 801 was simultaneously administered with subprotective doses of GABAergic anticonvulsants, it significantly potentiated the effects of barbiturates, as compared to other agents. At 1 mg/kg, MK 801 did not offer protection against tonic convulsions though protected (100%) the animals from mortality due to picrotoxin-induced convulsions. It potentiated the effect of a subprotective dose (5 mg/kg) of pentobarbital, but not of diazepam, against tonic convulsions. However, no mortality was observed in either group. The antiglutamate action of barbiturates, particularly that of pentobarbital, may contribute to the observed potentiating response between pentobarbital and MK 801.

Animals↗
PubMed1989

RO15-4513 but not FG-7142 reverses anticonvulsant effects of ethanol against bicuculline- and picrotoxin-induced convulsions in rats.

The reversal of anticonvulsant effect of ethanol against chemoconvulsions by RO15-4513 was investigated in rats as this novel imidazobenzodiazepine (ethyl-8 azido-5, 6-dihydro-5-methyl-6-Oxo-4H-imidazo [1,5a] [1,4] benzodiazepine-3-carboxylate) is reported to antagonize the acute behavioral and biochemical effects of ethanol in animals. Reversal of ethanol effects on onset of myoclonic jerks, tonic extensor phase, mortality time and percent protection against mortality were compared with not only other anticonvulsant pentobarbital but also with another inverse agonist FG-7142. Pretreatment with RO15-4513 (4 mg/kg) reversed the protective effect of ethanol against bicuculline-induced tonic extensor phase and mortality (87%). This response was sensitive to reversal by RO15-1788 (10 mg/kg). However, onset of myoclonic jerks and duration of clonus were not significantly altered. It also reversed the effect against picrotoxin but the reversal against mortality was up to 50%. As compared to ethanol, RO15-4513 reversed partially the protective effect of pentobarbital against bicuculline- and picrotoxin-induced convulsions. FG-7142 failed to reverse the protective effect of ethanol and pentobarbital against bicuculline-induced tonic extensor phase although it reversed the effect against onset and mortality. It had no effect on the protective effect against picrotoxin-induced convulsions. Both RO15-4513 and FG-7142 possessed proconvulsant effects against bicuculline but not against picrotoxin. These observations suggest that RO15-4513 has a more preferential action against ethanol effects as compared to the other inverse agonist.

Affinity Labels↗
PubMed1989

Binding pattern of [35S]t-butylbicyclophosphorothionate is not altered following electroconvulsive shock treatment in rats.

Single or repeated electroconvulsive shock (ECS) treatment-induced changes in [35S]t-butylbicyclophosphorothionate [( 35S]TBPS) binding patterns in specific regions, i.e., cerebral cortex, cerebellum, hippocampus, and striatum of rat brain were investigated. Specific [35S]TBPS binding in these brain regions was not altered following a single or repeated administration of ECS, nor was the inhibition of [35S]TBPS binding to GABA affected. These observations tend to suggest that the picrotoxin-site on the GABA receptor complex may not be directly involved in electroconvulsive shock.

Animals↗
PubMed1989

Benzodiazepine and beta-carboline interactions with GABAA receptor-gated chloride channels in mammalian cultured spinal cord neurons.

The interaction of benzodiazepine (BZ) and beta carbolines with GABAA receptor-gated chloride channels using 36Cl influx biochemical functional assay in mammalian spinal cord cultured neurons was investigated. BZ-receptor agonists such as flunitrazepam, diazepam, clonazepam and flurazepam enhanced the effect of submaximal concentrations of GABA (10 microM)-stimulated 36Cl influx. The rank order of potencies was flunitrazepam greater than clonazepam greater than diazepam greater than flurazepam. In contrast, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), ethyl-beta-carboline-3-carboxylate (beta-CCE), N-methyl-beta-carboline-3-carboxamide (FG 7142) and ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5 alpha][1,4]-benzodiazepine-3-carboxylate (Ro 15-4513) inhibited GABA-stimulated 36Cl influx. The rank order of inhibitory potencies for the inverse agonists was DMCM greater than beta-CCE greater than Ro 15-4513 greater than FG 7142. Although lower concentrations of Ro 15-1788 antagonized the enhancement of BZ agonists like diazepam and the inhibition of inverse agonists like DMCM on GABA-stimulated 36Cl influx without exhibiting any effect per se, higher concentrations of Ro 15-1788 (greater than or equal to 10(-6) M) enhanced GABA-stimulated 36Cl influx. These observations indicate that flunitrazepam, diazepam, clonazepam and flurazepam are agonists; DMCM, beta-CCE, Ro 15-4513 and FG 7142 are inverse agonists, whereas Ro 15-1788 is antagonist at lower concentrations and partial agonist at higher concentrations at the BZ receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗