Biomedical subjects

M K Ticku

Publications and source records attributed to M K Ticku.

At least 91 records · Page 5Linked to original sources

PubMed1989

Chronic ethanol treatment selectively increases the binding of inverse agonists for benzodiazepine binding sites in cultured spinal cord neurons.

The effect of chronic ethanol treatment, and its withdrawal on the binding of ligands to the benzodiazepine binding sites of gamma-aminobutyric acid (GABA) receptor complex, was investigated in C57BL/6J mice spinal cord cultured neurons. Chronic ethanol (50 mM) treatment increased the specific binding of inverse agonists of the benzodiazepine binding sites, without affecting the binding of agonist or antagonist to this site. Thus, chronic ethanol exposure of the neurons increased the binding of [3H] Ro 15-4513 [ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5-alpha][1,4]benzodiazepine-3-carboxylate] and methyl-1-beta carboline-3-carboxylate [( 3H]beta-CCM), but not the binding of [3H]flunitrazepam or [3H]Ro 15-1788 [ethyl-8-fluro-5-6-dihydro-5-methyl-6-OxO-4H-imidazo[1,5-alpha][1, 4] benzodiazepine-3-carboxylate]. This increase was due to an increase in the number of binding sites for Ro 15-4513 and beta-CCM, and not due to a change in receptor affinity. The increase was observed as early as after a 12-hr exposure of the neurons with ethanol, and remained elevated at 24-hr withdrawal, returning to control values at 48-hr withdrawal. These results further strengthen the notion that Ro 15-4513 and related inverse agonists binding site on the GABA-benzodiazepine receptor complex may be involved in ethanol-s behavioral, biochemical and pharmacological effects which are mediated via GABAA receptor system. The significance of the enhanced binding sites for Ro 15-4513 and beta-CCM in the actions of ethanol, tolerance and withdrawal is discussed.

Alcoholism↗

PubMed1988

Chronic ethanol administration increases the binding of the benzodiazepine inverse agonist and alcohol antagonist [3H]RO15-4513 in rat brain.

Chronic ethanol treatment which produced intoxication and physical dependence in rats, produced an increase in the specific binding of ethanol antagonist [3H]RO15-4513 in rat brain cerebral cortex and cerebellum, but not in hippocampus and striatum. The increase in both the regions was due to an increase in the number (Bmax) of receptor sites. These results suggest that the RO15-4513 binding sites on the oligomeric GABA receptor complex are altered following chronic ethanol administration, and support the notion of a unique role of RO15-4513 as an ethanol antagonist.

Acoustic Stimulation↗

PubMed1988

Developmental aspects of benzodiazepine receptors and GABA-gated chloride channels in primary cultures of spinal cord neurons.

The developmental aspects of gamma-aminobutyric acid (GABA)-benzodiazepine receptor ionophore complex in mouse cultured spinal cord neurons was investigated in vitro. We examined benzodiazepine binding, GABA enhancement of benzodiazepine binding and GABA activation of chloride channels to intact cultured neurons during the development (days 1-14). Specific benzodiazepine binding increased with time from day 3 (Bmax = 546 fmol/mg protein) to day 14 (Bmax = 1746 fmol/mg protein). There was no significant difference in the affinity (Kd) of [3H]flunitrazepam for its receptor sites from day 3 to 14. Specific binding of [3H]flunitrazepam to the intact cells was also increased in the presence of GABA during all stages of development. The EC50 value of the GABA concentration (14-16 microM) required to enhance [3H]flunitrazepam binding did not change from day 3 to 14. GABA receptor-activated chloride channels, studied by 36Cl-influx was also observed at all ages in culture, and indicated an early development (as early as day 3) of these GABA-gated channels. These studies indicate that GABA-benzodiazepine-ionophore complex develop early in cultured spinal cord neurons, and these neurons provide an ideal system to study GABAergic events.

Animals↗

PubMed1988

CNS depressants accelerate the dissociation of 35S-TBPS binding and GABA enhances their displacing potencies.

The specific binding of 35S-t-butylbicyclophosphorothionate (TBPS) was studied in synaptosomal membranes of rat cerebral cortex. The displacing potencies of eleven CNS depressants and three convulsants were determined in the presence of 1 microM GABA and 10 nM R 5135. GABA enhanced the displacing potencies of depressants of most diverse chemical structures: diaryltriazine (LY 81067), pyrazolopyridine (etazolate), cinnamide, glutarimide, 2,3-benzodiazepine (tofizopam) and alcohol derivatives, barbiturates, (+)etomidate, methaqualone and meprobamate. In contrast, the IC50 values of convulsants (picrotoxinin, pentetrazol and the barbiturate enantiomer S(+) MPPB) were not significantly affected. The depressants accelerated either basal or GABA-augmented dissociation of 35-TBPS mainly by increasing the contribution of its rapid first phase.

Animals↗

PubMed1988

Interactions of pentobarbital and phenobarbital with GABAergic drugs against chemoconvulsants in rats.

Pentobarbital and phenobarbital exhibited anticonvulsant effects against picrotoxin (10 mg/kg, IP) as well as against strychnine (4 mg/kg, IP). Pentobarbital was also effective against bicuculline whereas only hypnotic doses of phenobarbital provided some protection against bicuculline- (8 mg/kg, IP) induced convulsions. Diazepam as well as THIP, but not baclofen, were also effective against all the three chemoconvulsants. Baclofen or subeffective doses of diazepam or THIP, when combined with subeffective dose of pentobarbital exhibited anticonvulsant activity against all the chemoconvulsants studied. On the other hand, a combination of subeffective doses of these agents with subeffective doses of phenobarbital provided protection only against picrotoxin and strychnine. These observations indicate that pentobarbital is quite effective against convulsions caused by agents acting at picrotoxin site, GABAA receptor or glycine receptor whereas phenobarbital is effective only against agents acting at picrotoxin site and glycine receptor, and is very weak anticonvulsant against agents causing blockade of GABAA receptors. Furthermore, activation of GABAA receptors or benzodiazepine receptors also provide protection against agents acting at GABAergic system or glycine receptors. On the contrary, activation of only GABAB receptors is inadequate to provide the protective effect. However, the activation of GABAA as well as GABAB receptors facilitate the anticonvulsant effect of both the barbiturates. Furthermore, pentobarbital, but not phenobarbital, facilitates the anticonvulsant effect of benzodiazepines against chemoconvulsants acting at GABAergic site or glycine receptors.

Animals↗

PubMed1988

Molecular interactions of ethanol with GABAergic system and potential of RO15-4513 as an ethanol antagonist.

The behavioral and biochemical effects of ethanol in man and animals have been investigated for a long time. A role of catecholamines in the central stimulatory action and during withdrawal has been envisaged, but more recent observations have revealed the involvement of inhibitory synaptic transmitter, GABA, in the actions of ethanol. Ethanol-induced motor incoordination, hypnosedation, antianxiety, and anticonvulsant actions are reported to be GABA-mediated. Involvement of the GABA system has been implicated in ethanol withdrawal-induced seizures in animals. More direct evidences using Cl- influx studies in synaptoneurosomes and spinal neuronal culture studies confirm such a mode of action of ethanol, probably influencing the chloride channel modulation at the GABA-benzodiazepine receptor ionophore complex. RO15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-Oxo-4H-imidazo [1,5-alpha], [1,4] benzodiazepine-3-carboxylate), a novel imidazobenzodiazepine, an analogue of the classical benzodiazepine antagonist is reported to possess alcohol antagonistic properties. RO15-4513 reverses both the behavioral and biochemical effects of ethanol, including the action of GABA-induced Cl- fluxes. But its potential clinical application may be restricted due to its inverse agonistic property. The present review focuses on the GABA-linked behavioral and biochemical actions of ethanol and discusses the potential of RO15-4513 as an alcohol antagonist.

Animals↗

PubMed1988

Ethanol potentiation of GABAergic transmission in cultured spinal cord neurons involves gamma-aminobutyric acidA-gated chloride channels.

The interaction of ethanol with gamma-aminobutyric acid (GABA)-mediated 36-Cl-influx and its modulation by various drugs was investigated in C57 mice spinal cord cultured neurons. Ethanol (5-100 mM) potentiated the effect of GABA on 36Cl-influx; whereas at concentrations greater than or equal to 50 mM ethanol activated Cl- channels directly. The effect of ethanol was specific for GABAA receptor-gated Cl- channels, as ethanol did not potentiate glycine-induced 36Cl-influx in the same neurons. Both the enhancing and direct effects of ethanol on 36Cl-influx were blocked by GABA antagonists like bicuculline, picrotoxinin and inverse agonists of the benzodiazepine site like the imidazodiazepine R015-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5 alpha], [1,4]benzodiazepine-3-carboxylate) and N-methyl-beta-carboline-3-carboxamide (FG-7142). Ethanol potentiating effect of GABA-induced 36Cl-influx was also reversed by methyl-6,7-dimethyl-4-ethyl-beta-carboline-3-carboxylate. The effects of the inverse agonists were blocked by the benzodiazepine receptor antagonist R015-1788. Both R015-4513 and FG-7142 reversed direct and GABA potentiating effects of ethanol effect at concentrations lower than those that exhibit inverse agonistic activity in the 36Cl-influx assay in cultured neurons. These results suggest that ethanol facilitation of GABAAergic transmission involves GABA receptor-gated Cl- channels and that this interaction may be responsible for some of the pharmacological effects of ethanol.

Animals↗

PubMed1987

GABAergic supersensitivity within the pars reticulata of the rat substantia nigra following chronic haloperidol administration.

These studies were performed to evaluate the effects of chronic haloperidol administration on the responsiveness of the pars reticulata neurons of the substantia nigra (SNR) to microiontophoretically applied gamma-aminobutyric acid (GABA) and glycine. Rats were administered haloperidol in their feed (CHAL treatment) for 30 days in increasing concentrations. All experiments were conducted two days after termination of the CHAL treatment. GABA receptor binding and neuronal responsiveness to GABA were significantly increased within the SNR following CHAL treatment. The mean EC50 value for GABA was significantly decreased for SNR neurons in CHAL-treated rats, but there was no change in the EC50 for glycine. Specific [3H]GABA binding (4 nM) was elevated by more than 50% within the SNR. Scatchard analysis of [3H]muscimol binding data revealed that the binding capacities (Bmax) of both high and low affinity GABA binding sites within the SNR were significantly increased without a change in the apparent dissociation constants (Kd) of either site. Although no regional difference in responsiveness to GABA was detected within the SNR of CHAL-treated rats, the spontaneous activity of neurons located within the rostral two-thirds of the nucleus was reduced; however, there was no change in spontaneous activity of neurons located within the caudal one-third. These data provide direct physiological evidence to support the conclusion that the increase in GABA binding within the SNR following CHAL treatment reflects a neuronal supersensitivity to GABA.

Animals↗

PubMed1987

Benzodiazepine and beta-carboline modulation of GABA-stimulated 36Cl-influx in cultured spinal cord neurons.

GABAA agonists stimulate 36Cl-influx in spinal cord cultured neurons in a concentration-dependent manner. This effect of GABAA receptor stimulation is enhanced by benzodiazepines like clonazepam, diazepam and flurazepam and attenuated by (+)bicuculline and picrotoxinin. The beta-carbolines, methyl-6, 7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) and propyl-beta-carboline-3-carboxylate (beta-CCPr) exhibited opposite effects, with DMCM attenuating, while beta-CCPr potentiating GABA's effect. These results are consistent with the behavioral and electrophysiological effect of benzodiazepines and beta-carbolines with GABA receptor complex.

Animals↗

PubMed1987

Central cardiovascular effects of baclofen in spontaneously hypertensive rats.

This study was conducted to investigate the effects of centrally administered baclofen on blood pressure and heart rate in conscious spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Administration of baclofen (1.0 microgram/kg) into the lateral cerebral ventricle (icv) produced an increase in mean arterial pressure (MAP) in both SHR and WKY rats. The increase in MAP was significantly lower in SHR (13 +/- 3 mmHg) when compared with WKY (27 +/- 5 mmHg). The changes in heart rate (HR) were variable, from no change to a very small increase and did not differ significantly between SHR and WKY rats. The ability of baclofen to interfere with baroreceptor reflexes was also tested in separate experiments. In SHR, icv injection of baclofen (1.0 microgram/kg) significantly suppressed the pressor response and bradycardia evoked by phenylephrine 3.0 micrograms/kg iv, whereas in WKY, the pressor and HR responses to similar injections of phenylephrine were not affected by icv baclofen. Similarly, baclofen treatment modified hypotensive response and reflex tachycardia induced by nitroprusside (10.0 micrograms/kg) iv in SHR but not in WKY rats. Administration of sympathetic ganglionic blocker hexamethonium (HEX; 25 mg/kg) iv produced an equivalent decrease in MAP between SHR and WKY following icv injection of baclofen (1.0 microgram/kg). These results suggest that the effects of baclofen on the baroreceptor reflexes in SHR may not be mediated by a change in peripheral sympathetic tone.

Animals↗

PubMed1987

Baclofen induces catatonia in rats.

Baclofen (10 and 20 mg/kg, i.p.) induced catatonia in rats within 10 min of its administration and the effect lasted for 3 hr. Muscimol (100 ng i.c.v. or 1 mg/kg, i.p.) as well as GABA (5 micrograms i.c.v.) potentiated the effect without producing any effect per se. Bicuculline, bromocriptine and scopolamine failed to modify the catatonia induced by baclofen, thereby ruling out the involvement of GABAA receptors, dopaminergic and cholinergic mechanisms. However, GABAB receptor antagonists, such as homotaurine and delta-amino-n-valeric acid, reversed the catatonia induced by baclofen in rats. Since baclofen is known to bind to a subpopulation of GABA receptors (bicuculline-insensitive) and baclofen-induced catatonia was susceptible to reversal by homotaurine and delta-amino-n-valeric acid, it is suggested that this effect could be mediated through GABAB receptors.

Animals↗

PubMed1987

A dietary haloperidol regimen for inducing dopamine receptor supersensitivity in rats.

The induction of dopaminergic supersensitivity in rats by the administration of haloperidol in their diet for 30 days (CHAL) in three increasing concentrations (7-15 mg/kg/day) was compared to that induced by single daily subcutaneous injections (SCHAL, 0.7 mg/kg) on the basis of biochemical (radioimmunoassay of serum haloperidol levels, 3H-spiroperidol binding) or behavioral (apomorphine stereotypy, spontaneous locomotor activity) parameters. The two modes of administration produced equivalent blood levels of haloperidol by day 30. At 48 hours post treatment: spontaneous locomotor activity and stereotyped behavior were significantly increased in both groups of haloperidol-treated rats, stereotyped behavior was significantly greater in CHAL- vs. SCHAL-treated rats at 8 days post treatment and specific 3H-spiroperidol binding was increased 64% and 236% within the striatum and GP, respectively, of CHAL-treated vs. control rats. Scatchard analysis of 3H-spiroperidol binding isotherms revealed a significant increase in the Bmax of high affinity binding sites [KD approximately 55 pM] within the striatum of both CHAL- and SCHAL-treated rats at 48 hours post treatment. A second, lower affinity site was resolved within the SCHAL-treated group which was not detected within striatal homogenates of CHAL-treated or control rats.

Administration, Oral↗

PubMed1987

Characteristics of flunitrazepam binding to intact primary cultured spinal cord neurons and its modulation by GABAergic drugs.

The interaction of [3H]flunitrazepam and its modulation by various drugs was studied in intact primary cultured spinal cord neurons. In the intact cells, the [3H]-flunitrazepam binding was rapid and saturable. The benzodiazepine binding sites exhibited high affinity and saturability, with an apparent KD of 6.1 +/- 1.6 nM and Bmax of 822 +/- 194 fmol/mg protein. The association and dissociation of [3H]flunitrazepam binding exhibited monoexponential kinetics. Specifically bound [3H]flunitrazepam was displaced in a concentration-dependent manner by benzodiazepines like flunitrazepam, clonazepam, diazepam, Ro 15-1788, and beta-carbolines like methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3'-carboxylate. Specific [3H]flunitrazepam binding to intact cells was enhanced in a concentration-dependent manner by gamma-aminobutyric acid (GABA) agonists and drugs which facilitate GABAergic transmission like etazolate, (+)-etomidate, and pentobarbital. The enhancing effect of GABA agonists was antagonized by bicuculline and picrotoxinin. These results suggest that the intact cultured spinal cord neurons exhibit the properties of benzodiazepine GABA receptor-ionophore complex. Since these cells can also be studied in parallel for characterizing GABA-induced 36Cl-influx, they provide an ideal in vitro assay preparation to study GABA synaptic pharmacology.

Animals↗

PubMed1987

Behavioral and functional studies indicate a role for GABAAergic transmission in the actions of ethanol.

Ethanol interacts allosterically with the picrotoxin binding sites on the oligomeric GABA receptor complex in vitro. Chronic ethanol treatment does not alter the binding properties of [35S]t-butyl-bicyclophosphorothioate or [3H]flunitrazepam to brain membranes. In behavioral studies, ethanol prevents convulsions induced by bicuculline, picrotoxin and maximal electroshock seizures. Further, subprotective dose of ethanol in combination with other facilitators of GABAergic transmission, provide protection against these convulsions. Finally, ethanol potentiates the effect of GABA on 36Cl-influx in cultured spinal cord neurons. These studies indicate a role for GABAAergic transmission in the actions of ethanol.

Animals↗

PubMed1986

Anticonvulsant profile of drugs which facilitate GABAergic transmission on convulsions mediated by a GABAergic mechanism.

The effects of selected modulators of GABAergic transmission, either alone or in combination, were tested for their potency on the seizure pattern and mortality induced by convulsant drugs in rat. Pentobarbital and diazepam were effective against both tonic and clonic seizure components induced by bicuculline and picrotoxin. The anticonvulsant profile of ethanol closely resembled that of pentobarbital. Pentobarbital, diazepam and ethanol did not modify seizures induced by strychnine. In contrast, progabide, a central gamma-aminobutyric acid (GABA) receptor agonist, caused significant protection only against convulsions induced by strychnine and its lethality, but did not protect against seizures induced by bicuculline or picrotoxin. Data on interaction of drugs with subprotective doses of these agents clearly demonstrated potentiation of the anticonvulsant actions of these modulators. Thus, seizures induced by bicuculline were more sensitive to the inhibition by pentobarbital in combination with diazepam or ethanol, while pentobarbital with progabide was equally effective against convulsions induced by GABA antagonists. Diazepam, in combination with progabide, blocked only convulsions induced by picrotoxin. Ethanol, in combination with either pentobarbital or with diazepam, was effective against all the three convulsant drugs. These results are consistent with the concept that drugs which facilitate GABAergic transmission are effective against seizures related to an impairment of GABA transmission. Further, the present data indicate that tonic seizures are more susceptible to the actions of drugs than the clonic component. Smaller doses of these drugs, alone or in combination, modified the seizure patterns and mortality, whereas at larger doses, the possible involvement of a nonspecific depressant action cannot be ruled out.

Animals↗

PubMed1986

Effect of chronic treatment of ethanol on benzodiazepine and picrotoxin sites on the GABA receptor complex in regions of the brain of the rat.

Ethanol has been shown to enhance gamma-aminobutyric acid (GABA)ergic transmission. In this study an examination was made of the effect of chronic treatment with ethanol and its withdrawal at 24 h on the binding of [3H]flunitrazepam and [35S]t-butylbicyclophosphorothionate (TBPS) to brain regions in rat. Rats were rendered tolerant to, and dependent on, ethanol by an intragastric intubation method. The affinity (KD) or the binding capacity (Bmax) of [3H]flunitrazepam or [35S]TBPS was not altered by chronic treatment with ethanol or during withdrawal from ethanol. Neither the enhancing effect of GABA on the binding of [3H]flunitrazepam nor its inhibitory effect on the binding of [35S]TBPS were affected by chronic treatment with ethanol or its withdrawal at 24 h. These results suggest that the sensitivity of benzodiazepine and picrotoxin sites on the oligomeric GABA receptor complex is not affected during tolerance to, or withdrawal from ethanol. It is suggested that the effects of ethanol on GABAergic transmission may be produced at the level of coupled chloride ion channels.

Animals↗

PubMed1986

Comparison of anticonvulsant effect of pentobarbital and phenobarbital against seizures induced by maximal electroshock and picrotoxin in rats.

Pentobarbital and phenobarbital exhibited anticonvulsant effect against maximal electroshock (MES) and picrotoxin-induced seizures in rats. Bicuculline, a GABAA receptor antagonist, reversed the anticonvulsant effect of pentobarbital, but not of phenobarbital, at a dose having no effect per se. Although picrotoxin (2 mg/kg, IP) potentiated MES seizures, it did not reverse the anticonvulsant effect due to either pentobarbital or phenobarbital. GABAB receptor antagonists such as delta-amino-n-valeric acid and homotaurine failed to modify the anticonvulsant effect due to pentobarbital or phenobarbital. Furthermore, GABAA agonist muscimol but not baclofen, a GABAB receptor agonist, exhibited the anticonvulsant effect against MES-induced seizures. However, baclofen when combined with sub-effective dose of pentobarbital or phenobarbital offered protection against MES seizures. Pentobarbital and phenobarbital were effective in almost equivalent doses against MES, as well as against picrotoxin-induced seizures. These observations indicated that pentobarbital exhibits anticonvulsant effect against MES seizures through the involvement of GABAA receptors, and activation of GABAB receptors alone does not seem to play any significant role in MES seizures and in the anticonvulsant effect of pentobarbital. However, activation of GABAB receptor does potentiate the facilitatory effect of barbiturates on GABAAergic transmission and in their anti-MES effect. Moreover, these results also suggest that the anticonvulsant effect of barbiturates against MES-seizures may involve other mechanisms in addition to GABAAergic transmission.

Amino Acids↗

PubMed1986

Ethanol enhances GABA-induced 36Cl-influx in primary spinal cord cultured neurons.

Ethanol has a pharmacological profile similar to other centrally acting drugs, which facilitate GABAergic transmission. GABA is known to produce its effects by increasing the conductance to Cl- ions. In this study, we have examined the effect of ethanol on GABA-induced 36Cl-influx in primary spinal cord cultured neurons. GABA produces a concentration-dependent, and saturable effect on 36Cl-influx in these neurons. Ethanol potentiates the effect of GABA on 36Cl-influx in these neurons. GABA (20 microM) increased the 36Cl-influx by 75% over the basal value, and in the presence of 50 mM ethanol, the observed increase was 142%. Eadie-Hoffstee analysis of the saturation curves indicated that ethanol decreases the Km value of GABA (10.6 microM to 4.2 microM), and also increases the Vmax. Besides potentiating the effect of GABA, ethanol also appears to have a direct effect in the absence of added GABA. These results suggest that ethanol enhances GABA-induced 36Cl-influx and indicate a role of GABAergic system in the actions of ethanol. These results also support the behavioral and electrophysiological studies, which have implicated GABA systems in the actions of ethanol. The potential mechanism(s) and the role of direct effect of ethanol is not clear at this time, but is currently being investigated.

Animals↗