Synaptic pharmacology of barbiturates and benzodiazepines

General anaesthetics and their effects on GABA(A) receptor desensitization

1. Intravenous anaesthetics, including propofol and thiopental have at least three distinct effects on GABA(A) receptor function. 2. Low concentrations of these drugs enhance the amplitude of currents evoked by sub-saturating concentrations of GABA whereas higher concentrations directly activate the receptor in the absence of GABA. 3. Propofol and some barbiturates also decrease the rate and extent of desensitization as indicated by a prolongation in the decay of currents evoked by saturating concentrations of GABA. 4. In contrast, sedative benzodiazepines that lack general anaesthetic properties do not directly activate the GABA(A) receptor. 5. In addition, benzodiazepines such as midazolam, have no effect on desensitization when examined in the presence of saturating concentrations of GABA. 6. Here, we discuss the effects of intravenous general anaesthetic on desensitization of the GABA(A) receptor.

Pentobarbital sodium inhibits the release of noradrenaline in the medial preoptic area in the rat

The effect of pentobarbital sodium (PB) on noradrenaline (NA) release in the medial preoptic area was studied in ovariectomized rats by a microdialysis method coupled to HPLC. Dialyzates were collected at 6-min intervals before and after the injection in freely moving rats. PB injected i.p. at a dose of 35 mg/kg caused a marked, approximately 40-50% decrease in NA release, which became evident 50 min after the injection and lasted for another 60 min during which the observation was performed. The results suggest that the anesthetic effect of barbiturates is related to the reduction in NA release in the brain.

Chronic L-lysine develops anti-pentylenetetrazol tolerance and reduces synaptic GABAergic sensitivity

L-Lysine 10 mmol/kg given to mice for 1 to 10 days significantly increased clonic and tonic seizure latencies caused by 60 mg/kg pentylenetetrazol (PTZ). On day 1 the clonic and tonic seizure latencies were increased from 160.4 +/- 26.3 and 828.6 +/- 230.8 s to 286.1 +/- 103.3 and 982.3 +/- 98.6 s, respectively. Both clonic and tonic seizure latencies increased steadily with additional L-lysine treatment without significant change in survival rate. On day 10, the anticonvulsant effect reached its highest level with a block of tonic seizures and a survival rate of 100% without tolerance developing. Acute L-lysine treatment significantly increased the mean clonic latency from 85.8 +/- 5.24 to 128.2 +/- 9.0 s and the mean tonic seizure latency from 287.2 +/- 58.7 to 313.5 +/- 42.2 s with 80 mg/kg PTZ. On the day 10 of treatment, the anticonvulsant effect of L-lysine was highest, with a significant increase of 155 and 184% in clonic and tonic latencies over the control, respectively. After 15- and 20-day treatment, clonic and tonic seizures latencies and survival rate decreased, suggesting development of tolerance. Brain membranes from tolerant mice showed decreased enhancement by gamma-aminobutyric acid of specific [3H]flunitrazepam binding from 210 +/- 8 to 169 +/- 5% with EC50 values of 4.1 +/- 1.4 and 7.8 +/- 1.5 microM, respectively. Scatchard analysis of [3H] flunitrazepam binding showed no significant change of apparent binding affinity (KD) or binding density (Bmax) after chronic L-lysine exposure. L-Lysine enhanced the specific [35S]tert-butyl bicyclophosphorothionate (TBPS) binding in brain membranes dose dependently.(ABSTRACT TRUNCATED AT 250 WORDS)

High-dose flunitrazepam anesthesia

Benzodiazepines have receptors in the nervous system as well as in the kidney, liver, skeletal and ileal muscle, lungs and the heart. Flunitrazepam is a benzodiazepine with pronounced hypnotic effects in the usual dosage. High dose flunitrazepam anesthesia is suggested for prolonged surgical procedures as an alternative to the well known high-dose opiate anesthesia. Its reversal using flumazenil can shorten the post-operative anesthetic effect.

Double-blind controlled trial of flumazenil in patients who underwent upper gastrointestinal endoscopy

The antisedative effect of flumazenil, a benzodiazepine antagonist, was studied in a double-blind placebo controlled trial in 61 patients who underwent upper gastrointestinal endoscopy and sedation with benzodiazepines. The efficacy of flumazenil in reversing the effect of both benzodiazepines, diazepam and midazolam, was significantly higher than placebo (p less than 0.0001). The effect of flumazenil was prompt and was clearly noticed at the first assessment, 5 min after its administration. In none of the patients was a relapse of the sedative effect of the benzodiazepines noticed. The administration of flumazenil was free of major side effects. Flumazenil administration permits an earlier discharge of patients following endoscopy. Its availability in the endoscopy suite may improve the outcome of serious but rare side effects related to benzodiazepines.

Hypothermia induced by baclofen, a possible index of GABAB receptor function in mice, is enhanced by antidepressant drugs and ECS

1 Intraperitoneal injection to mice of the gamma-aminobutyric acidB (GABAB) receptor agonist (+/-)-baclofen induces a dose-dependent decrease in rectal temperature. 2 Injection of (-)-baclofen intracerebroventricularly at doses that had no effect when given peripherally induced a marked hypothermia. (+)-Baclofen was without effect. 3 The decrease in rectal temperature induced by (-)-baclofen when injected intraperitoneally was highly correlated with an increase in sedation. 4 Repeated administration of amitriptyline (10 mg kg-1 daily for 14 days) resulted in mice displaying an enhanced temperature and sedation response to injection of (+/-)-baclofen (5 mg kg-1) 24 h after the last dose of antidepressant. 5 An enhanced hypothermic response was also seen following repeated administration of zimeldine, mianserin or desipramine (all 10 mg kg-1 daily for 14 days) or repeated electroconvulsive shock (ECS; 5 ECS over 10 days) 24 h after the last treatment. 6 A single administration of any of the antidepressant drugs or ECS or repeated administration of the anxiolytic drug flurazepam (20 mg kg-1 daily for 14 days) did not alter the baclofen-induced hypothermic response. 7 Administration of (+/-)-baclofen (5 mg kg-1) daily for 5 or 14 days attenuated the baclofen-induced hypothermic response. However, one pretreatment dose did not alter the response. 8 It has previously been reported that repeated baclofen administration decreases GABAB receptor number in the brain while repeated administration of antidepressant drugs and ECS increases the density of this receptor. The current data therefore suggest that baclofen-induced hypothermia may provide a simple index of GABAB receptor function in the brain and strengthens the evidence that GABAB receptor function is enhanced by antidepressant drugs and ECS.

Influence of meprobamate and phenobarbital upon local cerebral glucose utilization: parallelism with effects of the anxiolytic diazepam

The [1-14C]2-deoxyglucose technique was employed for an evaluation of the regional pattern of alteration of brain metabolism induced by the anxiolytics phenobarbital (which is described in small doses as anxiolytic agent) and meprobamate. Their effects were compared with those produced by the anxiolytic benzodiazepine diazepam which we have described in a previous study. In low doses, both meprobamate (30 mg/kg i.v.) and phenobarbital (5 mg/kg i.v.) elicited a regional pattern of changes similar to those seen with diazepam. Thus, the local cerebral glucose utilization (LCGU) of the mammillary nuclei, the lateral and ventral thalamic nuclei, the anterior thalamic nuclei and the geniculate nuclei was significantly decreased. A doubling of the dose (meprobamate 60 mg/kg i.v.; phenobarbital 10 mg/kg i.v.), however, resulted in a decrement in LCGU in virtually every brain region examined. Further, at this higher dose, phenobarbital significantly increased LCGU in the interpeduncular nucleus. These data demonstrate that both meprobamate and phenobarbital, in moderate doses induce selective alterations in LCGU in particular brain regions with the pattern of changes similar to that induced by diazepam. The structures affected may be of general importance for the expression of the anxiolytic actions of each of those classes of minor tranquilizers in clinical use.

Controlled trial of acupuncture for disabling breathlessness

In a randomised controlled trial, twelve matched pairs of patients with chronic obstructive pulmonary disease received traditional Chinese acupuncture or placebo acupuncture. After three weeks' treatment the traditional-acupuncture group showed significantly greater benefit in terms of subjective scores of breathlessness and six-minute walking distance. Objective measures of lung function were unchanged in either group. Whether these differences are mediated by endogenous opiate and/or peptide release remains speculative.

Endogenous benzodiazepine receptor agonist in human and mammalian plasma

Using ultra-filtration steps and HPLC-separation, a low molecular weight ligand of the benzodiazepine receptor was isolated from plasma of various mammalian species including man. The endogenous ligand acts on benzodiazepine receptors agonistically and apparently has a receptor affinity similar to Diazepam. The ligand is not identical with Diazepam as indicated by HPLC and UV-spectroscopy.

Drug-induced rhythmic burst activity of cerebellar neurons

The discharge of cerebellar neurons was investigated in the rabbit and the rat under the influence of pentobarbital, diazepam or medazepam. In the rabbit, these drugs are known to induce a rhythm ranging between 4 and 25 Hz in the red nucleus (RN) and the cerebellum (Cb). Purkinje cells (P cells) in the intermediate zone of the cerebellar cortex as well as neurons of the interposed nucleus (IPN) were found to discharge with burst patterns fully synchronized with the drug-induced RN rhythm. In contrast, P cells in the medial cerebellar zone responded to these drugs only with changes in their discharge rate. Since P cells of the intermediate longitudinal zone project to the RN mainly via the IPN, the present findings complement our previous results, indicating that the rhythmic electrical activity in the RN is initiated by the cerebellum. The three drugs had similar effects on the activity of cerebellar units in the rabbit and the rat. The investigation also shows that, in spite of the uniform morphological structure of the cerebellar cortex, P cells do not respond uniformly to a given drug: the diversity of findings published on the P cell response to barbiturates or benzodiazepine derivatives may be explained by differences in the recording sites.

Evidence for the involvement of brain GABA and serotonin systems in the anticonflict effects of chlordiazepoxide in rats

Using male hooded Lister rats the effects of GABAergic and serotonergic treatments alone and with chlordiazepoxide (CDP) were compared with the behavioral effects of CDP in a conditioned conflict procedure with three components; Reward, Time Out, and Conflict. CDP (2.5, 5.0, and 10.0 mg/kg ip) dose- relatedly increased punished and time out responding, but increased rewarded responding in an inversely dose-related manner. Punished responding was enhanced by chronic treatment to a rate which remained stable between 9 and 19 injections. The GABA transaminase inhibitor ethanolamine-O-sulfate (EOS), given chronically in drinking water (5.0 mg/ml), increased punished responding linearly to a high stable level after 2-3 weeks. Rewarded and time out responding were less substantially increased. CDP given with EOS dose- relatedly increased time out and punished responding substantially above the rates found with either treatment alone. The GABA antagonist picrotoxin blocked the increase in punished and time out responding found with EOS and CDP alone. The tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA; 100 mg/kg x 3) linearly increased punished responding for the first week of treatment. CDP with PCPA selectively and significantly increased punished responding above the rates for either treatment alone, but the increases were not as substantial as those with EOS + CDP. The serotonin reuptake inhibitor Wy 25093 reduced increases in time out and punished responding under CDP, and the precursor 5-hydroxytryptophan (5-HTP) counteracted increases in punished responding under PCPA but also substantially reduced rewarded responding. These results provide evidence that both increased GABA and decreased serotonin transmission are involved in the anticonflict effects of CDP, as EOS and PCPA both mimicked and potentiated effects of CDP, while picrotoxin, Wy 25093, and 5-HTP counteracted them.(ABSTRACT TRUNCATED AT 250 WORDS)

Flurazepam: effects on sodium and potassium currents in myelinated nerve fibres

The effect of flurazepam-HCl on single myelinated nerve fibres of the frog Rana esculenta was investigated. Flurazepam affected both Na and K currents: 0.25 mM of the drug decreased the peak Na inward current to about 50%. The initial increase and subsequent decay of the Na current was slowed down by a factor of 1.5 independent of membrane potential. The drug induced a slow phase in the recovery from Na inactivation and frequency dependence of the Na current block. The K current rose at a normal rate and was then inactivated to a sustained outward current. The time constant of block development (tau k) and the steady state block were potential-dependent. With 1 mM flurazepam, tau k decreased from 2.9 ms at E = 10 mV to 1.5 ms at E = 90 mV, and the steady state block increased from 65% at E = -20 mV to 81% at E = 90 mV. Recovery from the block proceeded faster at E = -70 mV (tau = 27 ms) than at E = -120 mV (tau = 89 ms). The effects of the drug on the K current were interpreted in terms of the reaction scheme proposed by Armstrong (J. Gen. Physiol. 54, 553; 1969).

Anticonvulsant activity of GABA uptake inhibitors and their prodrugs following central or systemic administration

The activity of compounds inhibiting neuronal or glial GABA uptake has been assessed following intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) administration in DBA/2 mice (sound-induced seizures) or Swiss S mice (pentylenetetrazol-induced seizures). Sound-induced seizures are suppressed by the i.c.v. injection of (+/-)-nipecotic acid, 3.2 mumol, or (+/-)-cis-4-hydroxynipecotic acid, 2 mumol, but not by i.p. injection of (+/-)-nipecotic acid, 3.2 mmol/kg or (+/-)-cis-4-hydroxynipecotic acid 4 mmol/kg. Pentylenetetrazol-induced seizures are not suppressed by i.c.v. injection of (+/-)-nipecotic acid 1-4 mumol, or (+/-)-cis-4-hydroxynipecotic acid, 2-4 mumol. THPO (4,5,6,7-tetrahydroisoxazolo[4.5-c]pyridin-3-ol), 1-5 mumol i.c.v. or 1-4 mmol/kg i.p., protects against sound-induced seizures. There is no protection against pentylenetetrazol seizures after i.c.v. THPO injection, but THPO, 2-8 mmol/kg i.p., is protective. Among prodrugs, (+/-)-nipecotic acid pivaloyloxymethyl ester protects against sound-induced seizures, when given i.c.v. (3.2 mumol) or i.p. (1.6-3.2 mmol/kg) and against pentylenetetrazol seizures when given i.p. (0.5-4 mmol/kg). (+/-)-cis-4-hydroxynipecotic acid methyl ester protects against sound-induced seizures when given i.p. (3.2 mmol/kg), but is only partially protective against pentylenetetrazol seizures, when given i.p. (4 mmol/kg). Some prodrugs induce myoclonus following either i.c.v. or i.p. administration.

Anticonvulsant action of excitatory amino acid antagonists

Compounds that antagonize neuronal excitation induced by dicarboxylic amino acids were tested in two animal models of epilepsy, namely sound-induced seizures in DBA/2 mice and threshold pentylenetetrazol seizures in Swiss mice. Sound-induced seizures could be prevented by intracerebroventricular injection of compounds that block excitation due to N-methyl-D-aspartic acid. The most potent such compound, 2-amino-7-phosphonoheptanoic acid, was anticonvulsant in both test systems when given either intraperitoneally or intracerebroventricularly. Specific antagonists of excitation that is caused by amino acids provide a new class of anticonvulsant agents.

Effect of pentobarbital on the noradrenaline release induced by drugs and field electrical stimulation from cerebral and femoral arteries of the cat

The present studies showed that field electrical stimulation, high potassium (K+), tyramine and ionophore X537A induced tritium release from cerebral and femoral arteries of cat prelabelled with [3H]noradrenaline. The secretion caused by K+ or field stimulation was CA2+-dependent and was antagonized by high concentrations of pentobarbital (10(-4) and 10(-3) M), whereas that induced by the rest of the drugs was unchanged in the same situations. The noradrenaline uptake by these arteries was reduced by pentobarbital (10(-3) M and 10(-4) M). These results suggest that this barbiturate interferes with Ca2+ entry to the adrenergic nerve endings, and therefore antagonizes the noradrenaline release by Ca2+-dependent processes (exocytosis).

Effects of phenytoin on pyramidal neurons of the rat hippocampus

The effects of phenytoin (35 micrograms/ml) on membrane properties and inhibitory postsynaptic potential (IPSPs) in CA1 and CA3 pyramidal neurons of the in vitro rat hippocampus were examined. No significant change was observed on input resistance or resting membrane potential. Action potential amplitude, overshoot, rate of rise and rate of decay were decreased. IPSP conductance increase and reversal potential, evoked in CA3 cells through mossy fiber stimulation and in CA1 cells through recurrent and Schaffer's collateral stimulation, were unaffected.

Flunitrazepam: a review of its pharmacological properties and therapeutic use

Flunitrazepam is a benzodiazepine derivative whose hypnotic effect predominates over the sedative, anxiolytic, muscle-relaxing and anticonvulsant effects characteristic of benzodiazepines. Thus, it is used as a night-time hypnotic and in anaesthesiology: due to the pronounced hypnotic effect it is not appropriate as a daytime sedative. As a hypnotic for insomnia its effect is usually characterised by a very fast onset of action and quiet sleep without interruptions. On the morning after a hypnotic dose some residual psychomotor impairment does occur, which is comparable to that with usual doses of nitrazepam or flurazepam, but clinically apparent 'hangover' occurs infrequently. There is no pronounced cumulative effect with chronic use. In anaesthesiology it has proven to be useful as a hypnotic on the night before operation, as an oral, intramuscular or intravenous premedication, in induction and as a supplement to other anaesthetics. Its sedative and amnesic properties can also be beneficial in intensive care patients. Much of the usefulness of flunitrazepam in anaesthesia relates to its synergistic effect with other anaesthetics, to its effective amnesic action and its acceptable effects on circulation and respiration. Possible drawbacks include a somewhat unusual course of induction (when used for this purpose) and an often prolonged recovery. Although the safe dosage range is wide with flunitrazepam, its effective application both as a hypnotic for insomnia and in anaesthesiology is dependent upon use of the optimal dosage, and adequate knowledge of its pharmacokinetic properties.

Effects of the bicyclic GABA agonist, THIP, on myoclonic and seizure responses in mice and baboons with reflex epilepsy

THIP, 4,5,6,7-tetra hydroisoxazolo[5,4-C]pyridine-3-ol, has been evaluated as an anticonvulsant in DBA/2 mice showing audiogenic seizures, and in baboons, Papio papio, with photosensitive epilepsy. No protection against seizures was seen after THIP, 1-4 mg/kg, intraperitoneally in mice. THIP, 8 mg/kg, reduced clonic and subsequent seizure responses at 1 h. It also reduced rectal temperature and impaired posture and spontaneous activity. In baboons THIP, 0.25-8 mg/kg, iv, failed to protect against photically induced myoclonic responses. Toxic signs after THIP, 8 mg/kg, included focal or generalised myoclonus. THIP is thus not effective against reflex epilepsy.

Receptors for the age of anxiety: pharmacology of the benzodiazepines

Investigation of the actions of the benzodiazepines has provided insights into the neurochemical mechanisms underlying anxiety, seizures, muscle relaxation, and sedation. Behavioral, electrophysical, pharmacological, and biochemical evidence indicates that the benzodiazepines exert their therapeutic effects by interacting with a high-affinity binding site (receptor) in the brain. The benzodiazepine receptor interacts with a receptor for gamma-aminobutyric acid, a major inhibitory neurotransmitter, and enhances its inhibitory effects. The benzodiazepine receptor may also interact with endogenous substances and several naturally occurring compounds, including the purines and nicotinamide, are candidates for this role. Both the purines and nicotinamide possess some benzodiazepine-like properties in vivo, although further work will be required to confirm their possible roles as endogenous benzodiazepines.

An in vivo method for testing putative GABA-like compounds

A technique is described that enables compounds with GABA-ergic properties to be rapidly identified in vivo. Electrical stimulation of the neostriatum in the conscious rat evoked a contralateral head-turn. Evidence is presented that this easily timed motor response involves, at least in part, GABA-ergic mechanisms in the globus pallidus. GABA drugs were injected through a cannula into the ipsilateral globus pallidus and their effects on head-turning observed. Known GABA agonists including muscimol slowed the head-turn, whereas the GABA antagonist picrotoxin facilitated it. A number of drugs such as baclofen, diazepam, and pentobarbitone which have been attributed with GABA-like properties behaved like GABA agonists in the head-turn model following either intrapallidal or intraperitoneal injection. Other drugs, e.g. tranquillizers, with no known GABA-like properties, did not effect the head-turn time.

Acute stress reduces the sensitivity of the vasculature to sympathetic control

Vascular smooth muscle from rabbits subjected to acute severe stress exhibits decreased sensitivity to sympathetic regulation. Stimulation of the sympathetic innervation of isolated vascular segments resulted in a similar subsensitivity as did exposure to norepinephrine (NE) but not histamine. Periodic contraction of these segments caused an increase in their maximum ability to contract independent of the constrictor procedure used. These results suggest that the increase in sympathetically mediated NE release that occurs in stress and some other pathological conditions may result in a blunting of neural control and possibly resistance to certain therapeutic agents.

Benzodiazepine binding after in vivo elevation of GABA

[3H]Diazepam binding was measured in rat cortical membranes. Acute and chronic amino-oxyacetic acid (AOAA) pretreatment greatly increased GABA levels, but did not alter diazepam binding. The GABA normally present was sufficient to maximally stimulate diazepam binding. In in vivo binding studies, acute and chronic AOAA treatment increased the amount of [3H]diazepam in the brain at the time of sacrifice, thus increasing both specific and nonspecific binding and leaving unchanged the fraction of drug specifically bound. Fluctuation of brain GABA may not affect benzodiazepine binding unless the normal concentration is greatly depressed.

Selective antagonism by benzodiazepines of neuronal responses to excitatory amino acids in the cerebral cortex

1 The recently discovered benzodiazepine receptor exists in high concentration in the cerebral cortex. We have, therefore, examined the effects of diazepam and chlordiazepoxide on cortical neurone responses to excitatory and inhibitory amino acids and acetylcholine, in the cortex of rats anaesthetized with urethane.2 Chlordiazepoxide applied by microiontophoresis reduced the responses to glutamate and aspartate but acetylcholine responses were unaffected on most cells even by much higher doses of benzodiazepine. gamma-Aminobutyric acid (GABA) and taurine responses were unaffected on most cells, but were reduced on 4 of 25 units. After intravenous diazepam, responses to GABA and taurine were reduced on 3 cells and unchanged on 11.3 On Purkinje cells in the cerebellum a number of cells (5 of 16) exhibited a substantial increase in responses to GABA and taurine following intravenous or iontophoretic application of benzodiazepines.4 It is suggested that the highly selective reduction of excitatory amino acid responses in the cerebral cortex may be of particular relevance to the behavioural effects of benzodiazepines.

Electroencephalographic and behavioral effects of a GABA agonist (muscimol) on photosensitive epilepsy in the baboon, papio papio

Muscimol, 0.25-1.0 mg/kg, i.v., was administered acutely to 4 adolescent baboons, Papio papio, that show photically induced epilepsy. On the EEG, slowing of background rhythms was associated with the appearance of spikes, polyspikes, and recurring symmetrical spike-wave complexes. These changes were maximal 0.5-2 hr after muscimol injection. Regular testing with intermittent light stimulation showed either no change from control responses or a more severe epileptiform EEG 0.1-3 hr after muscimol. Photically induced myoclonus was not modified by muscimol. Despite its GABA-abonist properties, muscimol is not an effective anticonvulsant.

GABA receptor-mediated modulation of 3H-diazepam binding in rat cortex

Three membrane preparations of rat cortex were used to examine the effects of GABA, bicuculline and bicucine on specific 3H-diazepam binding. In the crude synaptosomal fraction, GABA had no effect on either the maximal binding capacity (Bmax) or dissociation constant (KD) of 3H-diazepam binding. Bicuculline and bicucine both decreased binding affinity. This was antagonized by adding GABA. In the repeatedly washed membrane preparation, and in the washed, frozen and thawed preparation, GABA increased binding affinity and, at high concentrations, increased Bmax. Increased binding affinity was observed with as little as 10(-8) M GABA in the washed, frozen and thawed preparation. Bicuculline inhibited the effect of GABA on 3H-diazepam binding. It was found that about 3 X 10(-5) M GABA was present in the assay medium containing crude synaptosomal fraction. These results suggest endogenous GABA is present in, and influences the results of 3H-diazepam binding assays. Furthermore, it appears that GABA and bicuculline affect 3H-diazepam binding through their binding to the specific GABA binding site.

The effects of the combined administration of gamma-hydroxybutyrate and diazepam on sleep parameters in the rat

The actions of diazepam and gamma-hydroxybutyrate (GHB) were assessed on the sleep-wakefulness cycle of male Wistar rats. One and 2 mg/kg diazepam and 12.5 mg/kg GHB had no effects on the sleep variables. After 25 mg/kg GHB, slow wave sleep (SWS2) was significantly increased. Following the combined administration of non-effective doses of GHB and diazepam, significantly higher amounts of SWS2 at the expense of wakefulness were obtained. The injection of a subconvulsant dose of bicuculline (2.5 mg/kg) prior to treatments which significantly increased SWS2 prevented this effect to show up. It is suggested that the actions of GHB and diazepam on the sleep-awake cycle are related to the same neurotransmitter system.

Enhancement of GABA-mediated postsynaptic inhibition in cultured mammalian spinal cord neurons: a common mode of anticonvulsant action

Murine spinal cord neurons grown in dissociated cell culture were used to study the effects of barbiturate (phenobarbital, mephobarbital) and benzodiazepine (diazepam, chlordiazepoxide( anticonvulsants on amino acid responses. Both types of anticonvulsant augmented GABA-mediated postsynaptic inhibition without augmenting beta-alanine or glycine-mediated postsynaptic inhibition. Barbiturates, but not benzodiazepines, antagonized glutamate-mediated postsynaptic excitation. Augmentation of GABA-mediated inhibition by the anticonvulsants should contribute to their anticonvulsant action; antagonism of glutamate-mediated excitation by barbiturates should also contribute to their anticonvulsant action and could be at least in part responsible for their sedative actions.

Benzodiazepine receptor binding: the interactions of some non-benzodiazepine drugs with specific [3H] diazepam binding to rat brain synaptosomal membranes

The interaction of several non-benzodiazepine drugs with [3H] diazepam binding to benzodiazepine receptors in rat brain synaptosomal membranes was investigated. Baclofen, benzoctamine, hydroxyzine, chlorpromazine, haloperidol, imipramine, and amitriptyline displace specific [3H] diazepam binding, but the concentrations needed are too high to explain pharmacological effects of these drugs by an interaction with benzodiazepine receptors. The most potent non-benzodiazepine drug for inhibiting specific [3H] diazepam binding was methaqualone (IC50 value of 150 micrometer). It is suggested that interactions with benzodiazepine receptors may account for the anxiolytic and anticonvulsive side effects of this drug. The analeptic drug pentylenetetrazole interacts with benzodiazepine receptor binding with an IC50 value of about 1 mM, which is possibly too high to explain its convulsive properties by an antagonism at the benzodiazepine receptor.

Central actions of benzodiazepines: general introduction

After a brief review of the characteristic somatic and psychotropic effects of benzodiazepines evidence is presented which supports a specific facilitatory action of these drugs on GABA ergic synapses within the mammalian central nervous system. Benzodiazepines enhance presynaptic inhibition in the spinal cord and dorsal column nuclei as well as postsynaptic inhibition in dorsal column nuclei, hippocampus, hypothalamus, cerebral cortex, cerebellar cortex, which are all examples of recurrent and collateral inhibition mediated by GABA ergic intrinsic neurones. In addition, the compounds also enhance the inhibitory effect of GABA ergic long projection neurones in the substantia nigra and the lateral vestibular nucleus of Deiters. Several problems remain to be solved, such as the exact site at which benzodiazepines initiate their action (pre-synaptically at GABA ergic nerve endings or postsynaptically at the target cells) and the possible existence of endogenous ligands for the benzodiazepine receptor. Some suspected implications which studies on benzodiazepine binding sites could have for a deeper understanding of the mode of action of these drugs are discussed.