Ethyl beta-carboline carboxylate lowers seizure threshold and antagonizes flurazepam-induced sedation in rats

Therapeutic Potential of GABAergic Signaling in Myelin Plasticity and Repair

Oligodendrocytes (OLs) produce myelin to insulate axons. This accelerates action potential propagation, allowing nerve impulse information to synchronize within complex neuronal ensembles and promoting brain connectivity. Brain plasticity includes myelination, a process that starts early after birth and continues throughout life. Myelin repair, followed by injury or disease, requires new OLs differentiated from a population derived from oligodendrocyte precursor cells (OPCs) that continue to proliferate, migrate and differentiate to preserve and remodel myelin in the adult central nervous system. OPCs represent the largest proliferative neural cell population outside the adult neurogenic niches in the brain. OPCs receive synaptic inputs from glutamatergic and GABAergic neurons throughout neurodevelopment, a unique feature among glial cells. Neuron-glia communication through GABA signaling in OPCs has been shown to play a role in myelin plasticity and repair. In this review we will focus on the molecular and functional properties of GABA_A receptors (GABA_ARs) expressed by OPCs and their potential role in remyelination.

A batch and cloud point extraction kinetic spectrophotometric method for determining trace and ultra trace amounts of Benzodiazepine drugs (Clonazepam and Nitrazepam) in pure and pharmaceutical preparations

Utilizing the batch Diazotization coupling reaction and the cloud point extraction kinetic spectrophotometric method, trace and Ultra trace amounts from reducing Nitrazepam and Clonazepam were evaluated by way of using 2,5-dimethoxyaniline as a new Chromogenic reagent to give colored products (red) in acidic medium which have a maximum absorption at 500 and 502 nm, respectively. In the work, the analytical data of batch and cloud point for Nitrazepam and Clonazepam depended on initial rate and fixation time. This involved concentrations of (0,3-9), (0.05-1.2), (0.5-10) and (0.025-1) µg mL−1, as well as molar absorptivity of (3.8×104), (3.1×105) (3.39×104) and (3.47×105) L mol−1 cm−1. According to our results, Sandall’s sensitivity were (0.0074), (0.0009), (0.0092) and (0.0009) µg cm−2, while detection limits were (0.055) and (0.069) µg mL−1, (8.4) and (8.5) ng mL−1. In addition, the measurements enrichment factors were (33.33) and (50), while preconcentration factors were (8) and (9.9), respectively. The reaction of Nitrazepam and Clonazepam with 2,5-dimethoxyaniline were a pseudo first order according to kinetic studies. The proposed methods are not affected by existence of excipients so the methods can be applied successfully for determination of Nitrazepam and Clonazepam in pharmaceutical preparations.

Multistep Solvent-Free 3 m2 Footprint Pilot Miniplant for the Synthesis of Annual Half-Ton Rufinamide Precursor

The development of a pilot-scale synthesis of the rufinamide precursor in flow chemistry is reported. Complex steps such as Taylor-flow, segmented flow, and high-temperature processing at high pressure (high-p,T) are successfully combined, overcoming the mixing and heat transfer issues of the scale-up. The cascaded multistep process operates essentially solvent-free in just 3 m² giving a productivity of 47 g/h (>400 kg/year), which increases by a factor of 7 the lab-scale productivity previously reported as a scale-up proof-of-concept. This publication also includes an economic study of the feasible implementation of this technology for a possible manufacturer, as well as an outline on business development strategies of how to implement such a disruptive technology.

Dopamine reuptake transporter (DAT) "inverse agonism"--a novel hypothesis to explain the enigmatic pharmacology of cocaine

The long held view is cocaine's pharmacological effects are mediated by monoamine reuptake inhibition. However, drugs with rapid brain penetration like sibutramine, bupropion, mazindol and tesofensine, which are equal to or more potent than cocaine as dopamine reuptake inhibitors, produce no discernable subjective effects such as drug "highs" or euphoria in drug-experienced human volunteers. Moreover they are dysphoric and aversive when given at high doses. In vivo experiments in animals demonstrate that cocaine's monoaminergic pharmacology is profoundly different from that of other prescribed monoamine reuptake inhibitors, with the exception of methylphenidate. These findings led us to conclude that the highly unusual stimulant profile of cocaine and related compounds, eg methylphenidate, is not mediated by monoamine reuptake inhibition alone. We describe the experimental findings which suggest cocaine serves as a negative allosteric modulator to alter the function of the dopamine reuptake transporter (DAT) and reverse its direction of transport. This results in a firing-dependent, retro-transport of dopamine into the synaptic cleft. The proposed mechanism of cocaine is, therefore, different from other small molecule negative allostereric modulators of the monoamine reuptake transporters, eg SoRI-6238, which merely reduce the rate of inward transport. Because the physiological role of DAT is to remove dopamine from the synapse and the action of cocaine is the opposite of this, we have postulated that cocaine's effect is analogous to an inverse agonist. If this hypothesis is validated then cocaine is the prototypical compound that exemplifies a new class of monoaminergic drugs; DAT "inverse agonists". This article is part of the Special Issue entitled 'CNS Stimulants'.

Little evidence of a role for the α1GABAA subunit-containing receptor in a rhesus monkey model of alcohol drinking

BACKGROUND

Alcohol potentiates GABAergic neurotransmission via action at the GABAA receptor. α1 subunit-containing GABAA receptors have been implicated as mediators, in part, of the behavioral and abuse-related effects of alcohol in rodents.

METHODS

We systematically investigated the effects of 1 α1-preferring benzodiazepine agonist, zolpidem, and 2 antagonists, β-carboline-3-carboxylate-tert-butyl ester (βCCT) and 3-propoxy-β-carboline hydrochloride (3-PBC), on oral self-administration of alcohol (2% w/v) or sucrose solution and observable behavior in rhesus macaques. We compared these effects to those of the nonselective benzodiazepine agonist triazolam, antagonist flumazenil, and inverse agonist β-carboline carboxylate (βCCE).

RESULTS

Alcohol and sucrose solutions maintained reliable baseline drinking behavior across the study. The α1-preferring compounds did not affect intake, number of sipper extensions, or blood alcohol levels (BALs) at any of the doses tested. Zolpidem, βCCT, and 3-PBC increased latency to first sipper extension in animals self-administering alcohol, but not sucrose, solution. Triazolam exerted biphasic effects on alcohol-drinking behavior, increasing intake at low doses but decreasing BAL and increasing latency at higher doses. At doses higher than those effective in alcohol-drinking animals, triazolam increased sucrose intake and latency. Flumazenil nonsystematically increased number of extensions for alcohol but decreased BAL, with no effects on sucrose drinking. βCCE decreased sipper extensions for alcohol and increased latency for first sucrose sipper extension, but full dose-effect relationships could not be determined due to seizures at higher doses.

CONCLUSIONS

Alcohol-drinking animals appeared more sensitive to the effects of GABAergic compounds on drinking behavior. However, these results do not support a strong contribution of α1GABAA receptors to the reinforcing effects of alcohol in primates.

Antidepressant-like effect of harmane and other beta-carbolines in the mouse forced swim test

The purpose of the present study was to determine the effects of harmane, norharmane and harmine on the immobility time in the mouse forced swim test (FST) - an animal model of depression. After 30 min of the beta-carbolines injections, mice were placed individually in a vertical glass cylinder (height, 25 cm; diameter, 12 cm) containing water about 15 cm deep at 22+/-1 degrees C and forced to swim. Treatment of animals with harmane (5-15 mg/kg, i.p.), norharmane (2.5-10 mg/kg, i.p.) and harmine (5-15 mg/kg, i.p.) reduced dose-dependently the time of immobility. Their antidepressant-like effects were not affected by pretreatment with reserpine at the dose of 5 mg/kg, i.p., 18 h before the test, which did not modify the immobility time. Conversely, when flumazenil (5 mg/kg, i.p.) was administered 30 min before the test, it was able to antagonize completely the antidepressant-like effects of harmane, norharmane and harmine. It was concluded that harmane, norharmane and harmine reduce the immobility time in this test, suggesting an antidepressant-like effect, via an inverse-agonistic mechanism located in the benzodiazepine receptors.

Development of subtype selective GABAA modulators

Drugs modulating gamma-aminobutyric acid (GABA) transmission via the benzodiazepine (BZ) site on the gamma-aminobutyric acid type A (GABAA) receptor have been in widespread use for more than 40 years to treat anxiety, epilepsy, and sleep disorders. These drugs have been shown to be safe, well tolerated, and effective although the mechanism by they produce a myriad of pharmacologic effects remains elusive. In recent years it has been discovered that, although the GABAA receptor is widely distributed in the brain, the substructure and composition of the receptor differs from between brain regions. Termed "GABAA receptor subtypes" their discovery leads to speculation that different subtypes may mediate specific effects of BZs such as anxiety or sedation. The phenotypic analysis of transgenic knock-in and knock-out mice in which particular GABAA receptors were rendered insensitive to the effects of BZ while others were unaffected confirmed this speculation. Subsequently, subtype-specific GABAA ligands were developed that, for example, retained the anxiolytic effects of BZs but were devoid of their sedative effects. Therefore, it may be possible to develop effective anxiolytic compounds that have a much reduced side-effect profile compared with existing drugs.

Benzodiazepines and anterior pituitary function

Benzodiazepines (BDZ) are one of the most prescribed classes of drugs because of their marked anxiolytic, anticonvulsant, muscle relaxant and hypnotic effects. The pharmacological actions of BDZ depend on the activation of 2 specific receptors. The central BDZ receptor, present in several areas of the central nervous system (CNS), is a component of the GABA-A receptor, the activation of which increases GABAergic neurotransmission and is followed by remarkable neuroendocrine effects. The peripheral benzodiazepine receptors (PBR), structurally and functionally different from the GABA-A receptor, have been shown in peripheral tissues but also in the CNS, in both neurones and glial cells, and in the pituitary gland. BDZ receptors bind to a family of natural peptides called endozepines, firstly isolated from neurons and glial cells in the brain and then in several peripheral tissues as well. Endozepines modulate several central and peripheral biological activities, including some neuroendocrine functions and synthetic BDZ are likely to mimic them, at least partially. BZD, especially alprazolam (AL), possess a clear inhibitory influence on the activity of the HPA axis in both animals and humans. This effect seems to be mediated at the hypothalamic and/or suprahypothalamic level via suppression of CRH. The strong negative influence of AL on hypothalamicpituitary-adrenal (HPA) axis agrees with its peculiar efficacy in the treatment of panic disorders and depression. BZD have also been shown to increase GH secretion via mechanisms mediated at the hypothalamic or supra-hypothalamic level, though a pituitary action cannot be ruled out. Besides the impact on HPA and somatotrope function, BDZ also significantly affect the secretion of other pituitary hormones, such as gonadotropins and PRL, probably acting through GABAergic mediation in the hypothalamus and/or in the pituitary gland. In all, BDZ are likely to represent a useful tool to investigate GABAergic activity and clarify its role in the neuroendocrine control of anterior pituitary function; their usefulness probably overrides what had been supposed before.

Unexpected absence of correlation between the genetic mechanisms regulating beta-carboline-induced seizures and anxiety manifested in an elevated plus-maze test

Among the ligands of the benzodiazepine site, one can mention the benzodiazepines as agonists and some beta-carbolines (e.g. methyl-beta-carboline-3-carboxylate, abbreviated hereafter beta-CCM) as inverse agonists. Most benzodiazepines and beta-carbolines act on processes involved in memory, anxiety, and convulsions with opposite physiological effects. Since these molecules have influences on both anxiety and convulsions, we predicted that there would exist a genetic correlation between anxiety evaluated in an elevated plus-maze and susceptibility to beta-CCM-induced seizures. Using inbred strains of mice, the genetic correlation was estimated with the Hegmann and Possidente model. An absence of genetic correlation was found, showing that the mechanisms responsible for basal anxiety measured with the elevated plus-maze test and those leading to susceptibility to beta-CCM-induced seizures do not share the same genetic pathways.

Benzodiazepines in perspective (II): The GABAA-Benzodiazepine Receptor Ligands

A huge number of natural and synthetic compounds modulate the function of the γ-aminobutyric acid type A receptor (GABAA-R) by interacting with several allosteric binding sites which may differ in the various GABAA-R subtypes. The benzodiazepine receptor (BDZ-R) is the most intensively studied allosteric site. It is the first allosteric modulatory site on a neurotransmitter receptor that has been found to mediate two opposite functions: facilitation and depression of GABAA-R function. The effects of BDZ-R ligands on behavior range from agonistic (anxiolytic, anticonvulsant, myore-laxant/ataxic and hypno-sedative effects) to inverse-agonistic (anxiety and panic, hypervigilance and convulsions). Of particular interest for the future are BDZ-R partial agonists, as they lack several of the undesired properties of classic full agonists. Furthermore the GABAA-R system shows a high plasticity. This polymorphism raises the possibility that ligands selective for distinct subtypes of BDZ-R may emerge as useful drugs. In both cases the possibility exists of achieving very subtle manipulations of GABAA-R function by using allosteric modulators.

The octadecaneuropeptide ODN induces anxiety in rodents: possible involvement of a shorter biologically active fragment

The octadecaneuropeptide ODN has been originally characterized as an endogenous ligand of central-type benzodiazepine receptors, on its ability to displace the anxiogenic compound beta-[3H]carboline-3-carboxylate methyl ester from its binding sites. The aim of the present study was to investigate the anxiogenic effects of intracerebroventricular administration of ODN in mice and rats. At doses ranging from 10 to 100 ng, ODN increased in mice the latency to explore a white compartment when the animals were placed in a black one. ODN also reduced the first stay duration in the white compartment. These effects were antagonized by diazepam (0.075 mg/kg, s.c.) as well as flumazenil (1 mg/kg, s.c.), indicating that ODN acts as an inverse agonist on central-type benzodiazepine receptors. In rats, ODN reduced the latency to enter a black compartment when the animals were placed in the white one. In the plus-maze elevated test, ODN reduced, in both mice and rats, the number of entries and the time spent in the open arm. In mice, ODN (100 ng) increased the thigmotaxis index, i.e. the distance traveled in the peripheral zone of the open field. Time-course studies revealed that a significant effect of ODN (100 ng) in the black/white compartment test was only observed 40 min after the injection and lasted between 3 and 6 h. The effect of a 1000-ng dose of ODN appeared more tardily than that of a 10-ng dose. In addition, a 1000-ng dose of ODN occluded the early effect of a 100-ng dose on the white compartment first stay duration. The COOH-terminal octapeptide of ODN was more rapidly effective than ODN in the black/white compartment test, suggesting that the anxiogenic effect of the peptide requires the formation of biologically active proteolytic fragment.

Effects of benzodiazepine receptor inverse agonists on locomotor activity and exploration in mice

This study investigates the effects of benzodiazepine receptor inverse agonists on the locomotor and exploratory behaviour of mice when tested in a familiar environment. The weak partial inverse agonist Ro 15-3505 (0.3, 1, 3 mg/kg i.p.) significantly increased locomotion and hole-dipping in habituated mice. However, the more efficacious partial inverse agonists Ro 15-4513 (0.3, 1, 3 mg/kg i.p.) and Ro 19-4603 (0.03, 0.1, 0.3 mg/kg i.p.) had no effect on these parameters. The benzodiazepine receptor antagonist flumazenil (3, 10, 20 mg/kg i.p.) also increased locomotion and hole-dipping in habituated mice, although like Ro 15-3505, these effects were of short duration occurring largely in the first 15 min following injection. Opposite effects were obtained with the partial benzodiazepine agonist Ro 17-1812 (1, 3, 10 mg/kg i.p.) which produced a longer-lasting significant decrease in hole-dipping behaviour in habituated mice without altering locomotion. Finally, in contrast to its effects in habituated animals, Ro 15-3505 (0.3, 1, 3 mg/kg i.p.) did not modify either locomotion or exploration in mice which were tested in a novel environment, showing that the effects of the inverse agonist were state-dependent. This demonstration that, under certain conditions, the weak benzodiazepine receptor inverse agonist Ro 15-3505 and the antagonist flumazenil, produce behavioural activation is in accordance with the work of others suggesting that these classes of compound may increase arousal and may therefore be of some value in treatment of memory disorders.

Chemical models of epilepsy with some reference to their applicability in the development of anticonvulsants

This paper reviews chemical models of epilepsy and their relevance in the identification and characterization of anticonvulsants. For each convulsant we discuss possible modes of administration, clinical type(s) of seizures induced, proposed mechanism(s) of epileptogenesis and, where available, responsiveness of the induced seizures to anticonvulsants. The following compounds are reviewed: pentylenetetrazol, bicuculline, penicillin, picrotoxin, beta-carbolines, 3-mercaptopropionic acid, hydrazides, allylglycine; the glycine antagonist strychnine; gamma-hydroxybutyrate; excitatory amino acids (glutamate, aspartate, N-methyl-D-aspartate, quisqualate, kainate, quinolinic acid); monosubstituted guanidino compounds, metals (alumina, cobalt, zinc, iron); neuropeptides (opioid peptides, corticotropin releasing factor, somatostatin, vasopressin); cholinergic agents (acetylcholine, acetylcholinesterase inhibitors, pilocarpine); tetanus toxin; flurothyl; folates; homocysteine and colchicine. Although there are a multitude of chemical models of epilepsy, only a limited number are applied in the routine screening of potential anticonvulsants. Some chemical models have a predictive value with regard to the clinical profile of efficacy of the tested anticonvulsants. Some chemical models may contribute to a better understanding of possible mechanisms of epileptogenesis.

Chronic treatment with a benzodiazepine agonist in vivo increases the actions of the benzodiazepine partial inverse agonist, FG7142, on the hippocampal slice in vitro

We have shown previously that chronic treatment of mice with a benzodiazepine agonist, flurazepam, increased the pharmacological actions of the partial inverse agonist, FG7142. We have investigated the neurophysiological basis for this using extracellular recordings of evoked field potentials in area CA1 of isolated hippocampal slices. The slices were prepared 48 h after the end of the chronic in vivo treatment, a time when no evidence of residual benzodiazepine agonist activity was found in the CNS. During perfusion with standard Ringer solution, no significant differences were seen between the field potentials in slices from flurazepam-treated mice and those from control animals. When FG7142 was added to the perfusion medium there was an increase in the secondary discharges that followed the initial population spikes, and an increase in paired pulse potentiation. These increases were significantly greater in slices from flurazepam-treated mice, compared with controls. The results show that the effects of the partial inverse agonist, FG7142, on an isolated neuronal preparation, were increased by chronic administration of a benzodiazepine agonist in vivo. This effect is suggested to be due to a decrease in GABAergic inhibition.

Effects of chlordiazepoxide and beta-carboline 3-carboxylic acid ethyl ester on non-suppressed and minimally-suppressed responding in the squirrel monkey

Lever-pressing of squirrel monkeys was maintained under a multiple fixed-interval (FI) 5-min schedule of food presentation. In one component, responding was suppressed to various degrees by the presentation of electric shock following each 30th response. When responding was either substantially or minimally suppressed, intermediate doses of chlordiazepoxide (CDAP, 1-30 mg/kg) increased both suppressed and non-suppressed responding. Beta-carboline 3-carboxylic acid ethyl ester (beta-CCE, 0.1-3 mg/kg) had little effect at low to intermediate doses (0.1-0.3 mg/kg) and decreased both minimally-suppressed and non-suppressed responding to a comparable extent at higher doses. Repeated daily dosing with beta-CCE (up to 10 mg/kg) resulted in rapid tolerance to its rate-decreasing effects. As agonists do not typically exhibit rapid tolerance for anxiolytic efficacy, the current results suggest that some behavioral effects of inverse agonists may not be strictly opposite those of benzodiazepines.

The role of neuronal calcium channels in dependence on ethanol and other sedatives/hypnotics

This review discusses the importance of neuronal calcium currents in dependence on ethanol, barbiturates, benzodiazepines and opiates. The main sections describe the actions of ethanol on control of intracellular calcium and on calcium and calcium-dependent conductance mechanisms. In particular, the effects of both acute and chronic ethanol treatment on dihydropyridine-sensitive, voltage-dependent, calcium channels are described. The later sections cover the effects of barbiturates, benzodiazepines and opiates on these systems. The conclusions suggest that dihydropyridine calcium channel antagonists may offer a new therapeutic approach to the treatment of ethanol and opiate dependence.

Anxiogenic effects of a benzodiazepine receptor partial inverse agonist, RO 19-4603, in a light/dark choice situation

In a light/dark choice procedure, the imidazothienodiazepinone RO 19-4603, given alone, induced a dose-dependent decrease in the time spent by mice in the lit box as well in the number of transitions between the two boxes. These data confirm the anxiogenic intrinsic properties of inverse agonists of the benzodiazepine receptor. Since RO 19-4603 also reversed the anxiolytic effects of ethanol and exhibited proconvulsant properties, it is suggested that the antagonistic action of this drug against ethanol could be due to an additive rather than an interactive process.

The GABA-benzodiazepine interaction fifteen years later

The main steps are presented that led to our current understanding of the interaction between benzodiazepine receptor ligands and the GABAA receptor. The benzodiazepine receptor is a modulatory site located on the GABAA receptor-chloride channel complex that has the unique property of being able to mediate positive as well as negative modulation of the chloride channel gating by the GABAA receptor. Some critical issues concerning the structure of the receptor-channel complex remain to be clarified. Research on the benzodiazepine-GABA interaction has led to novel concepts of drug action and receptor function and provides the basis for a whole spectrum of potential drugs with therapeutic utility.

GABAergic and dopaminergic transmission in the rat cerebral cortex: effect of stress, anxiolytic and anxiogenic drugs

Benzodiazepines produce their pharmacological effects by regulating the interaction of GABA with its recognition site on the GABAA receptor complex. In fact, the anxiolytic effect of benzodiazepines may be considered the consequence of the activation of the GABAA receptors induced by these drugs. On the contrary, beta-carboline derivatives which bind with high affinity to benzodiazepine recognition sites modulate the GABAergic transmission in a manner opposite to that of benzodiazepines. Thus, these compounds reduce the function of the GABA-coupled chloride channel and produce pharmacological effects (anxiogenic, proconvulsant and convulsant) opposite to those of benzodiazepines. Taken together, these data strongly indicate that the GABAA receptor complex plays a major role in the pharmacology, neurochemistry and physiopathology of stress and anxiety. This conclusion is further supported by the finding that the function of the GABAA/benzodiazepine receptor complex may be modified by the emotional state of the animals before sacrifice. Accordingly, using an unstressed animal model, the 'handling-habituated' rats, it has been demonstrated that stress, like anxiogenic drugs, decreases the function of GABAA receptor complex, an effect mimicked by the in vivo administration of different inhibitors of GABAergic transmission and antagonized by anxiolytic benzodiazepines. Moreover, a long-lasting down regulation of GABAergic synapses can be obtained after repeated administration of anxiogenic, proconvulsant and convulsant negative modulators of GABAergic transmission. The latter finding further suggests that GABAergic synapses undergo rapid and persistent plastic changes when the GABAergic transmission is persistently inhibited. Finally, the evidence that the activity of mesocortical dopaminergic pathways is altered in opposite manner by drugs that either inhibit or enhance the GABAergic transmission indicates that GABA has a functional role in regulation of dopaminergic neurons in the rat cerebral cortex. Altogether these results suggest that cortical GABAergic and dopaminergic transmission play a major role in the pharmacology, neurochemistry and pathology of the emotional states and fear.

Effects of GABAA receptor ligands on noradrenaline concentration and beta-adrenoceptor binding in mouse cerebral cortex

The present experiments investigated changes in beta-adrenoceptor binding and noradrenaline stores in mouse cerebral cortex after single treatments with drugs which bind to the GABAA receptor but which attenuate the actions of GABA. Neither the GABA antagonist, securinine, nor the picrotoxin/Cl- channel ligand, picrotoxin, affected noradrenaline levels or beta-adrenoceptor binding. However, both the benzodiazepine inverse agonist, DMCM, and pentylenetetrazole increased noradrenaline levels 24 h after injection. Only pentylenetetrazol modified beta-adrenoceptor binding: there was a significant increase in receptor number 4 days after injection, but a significant decrease after 7 days. The anxiogenic, proconvulsant drug, yohimbine, was without effect. The changes induced by DMCM and pentylenetetrazole do not seem to be related to the behavioural effects of these drugs or to their affinity for binding to benzodiazepine receptors. The possibility that these compounds have actions in addition to those at the GABAA receptor is discussed.

Barbiturates and the GABAA receptor complex

The GABA synapse plays an important role in the pharmacologic effects of barbiturates and the mechanisms involved in barbiturate tolerance and dependence. A synopsis of the effects which have been reported to date is found in Tables 1 and 2. Although the acute changes in neurotransmitter uptake and release are nonselective, a lag in the ability of the GABA synapse to compensate for discontinuation of barbiturate exposure may be important in the symptoms of withdrawal. Barbiturates cause changes in the properties of many receptors, but manipulations of the GABAA receptor in vivo correlate with changes in the therapeutic and toxicologic responses to barbiturates, indicating that the GABAA receptor complex plays a pivotal role in the effects of barbiturates. Experiments done in several laboratories show that barbiturate tolerance and dependence cause subtle changes in the properties of the GABAA receptor complex. These observations suggest that decreased GABA-stimulated chloride channel activity and reduced ability to modulate it may be important in causing barbiturate tolerance and the symptoms observed in withdrawal. Selection of drug-resistant rodent strains suggests that there may be genetic factors involved in drug tolerance and dependence. The complexity of the responses of the GABA synapse to both acute and prolonged exposure to barbiturates indicates that it is a valuable model for understanding how the central nervous system responds to drugs and the mechanisms involved in drug addiction.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

Antagonism of methoxyflurane-induced anesthesia in rats by benzodiazepine inverse agonists

Injection of the partial benzodiazepine inverse agonist Ro15-4513 (1-32 mg/kg i.p.) or nonconvulsant i.v. doses of the full benzodiazepine inverse agonist beta-CCE immediately following cessation of exposure of rats to an anesthetic concentration of methoxyflurane significantly antagonized the duration of methoxyflurane anesthesia as measured by recovery of the righting reflex and/or pain sensitivity. This antagonism was inhibited by the benzodiazepine antagonist Ro15-1788 at doses which alone did not alter the duration of methoxyflurane anesthesia. In addition, high-dose Ro15-4513 pretreatment (32 mg/kg) antagonized the induction and duration of methoxyflurane anesthesia but was unable to prevent methoxyflurane anesthesia or affect the induction or duration of anesthesia induced by the dissociative anesthetic ketamine (100 mg/kg). These findings indicate that methoxyflurane anesthesia can be selectively antagonized by the inverse agonistic action of Ro15-4513 and beta-CCE.

Inhibition of sleep and benzodiazepine receptor binding by a beta-carboline derivative

The effects of systemic injections of beta-carboline-3-carboxylate-t-butyl ester (beta-CCtB) were investigated with regard to normally occurring sleep and several measures of benzodiazepine receptor occupancy in rats. A dose of 30 mg/kg of beta-CCtB was found to have a long time-course of action as measured by an in vivo assay for benzodiazepine binding, with an 84% depletion of [3H]diazepam binding at one hour after the intraperitoneal injection. This dose of beta-CCtB was shown to delay sleep onset, decrease non-REM and total sleep in the first two hours after the injection, and to delay the appearance of REM sleep after the sleep onset. The dose- and time-dependence of the effects on sleep approximated the dose- and time-dependence of inhibitory effects of an IP injection of beta-CCtB on in vitro measures of benzodiazepine receptor affinity and number.

Opposite effects of diazepam and beta-CCE on immobility and straw-climbing behavior of rats in a modified forced-swim test

The present study was undertaken to examine how two ligands of the benzodiazepine receptor, which possess anxiolytic or anxiogenic actions, affect both the duration of immobility and the incidence of straw-climbing behavior in rats in a modified forced-swim test. Rats were injected IP with either vehicle, diazepam (0.5, 1, 5 mg/kg), or beta-carboline-3-carboxylic acid ethyl ester (beta-CCE; 0.5, 1, 2, 5 mg/kg), or a combination of diazepam at 1 mg/kg and beta-CCE at 2 mg/kg. In addition, Ro 15-1788 (1 mg/kg), a specific benzodiazepine antagonist, was injected IP 20 min after diazepam injection and immediately after beta-CCE injection, respectively. In the first 5-min period of the forced-swim test, diazepam at 5 mg/kg prolonged the duration of immobility, whereas beta-CCE at 1, 2 and 5 mg/kg reduced its duration. Immediately after the first 5-min test period, 4 straws were suspended above the surface of the water, and the number of straw-climbing attempts and the duration of immobility were measured for a subsequent 5-min test period. Straw-suspension elicited straw-climbing behavior in forced swimming rats, resulting in a shortening of the duration of immobility in this period. All doses of diazepam inhibited straw-climbing attempts and prolonged the duration of immobility in a dose-dependent manner. beta-CCE at 1 or 2 mg/kg enhanced straw-climbing attempts, but did not significantly affect the duration of immobility. Furthermore, the combined administration of diazepam and beta-CCE antagonized the respective drug effects on the duration of immobility and the number of straw-climbing attempts.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a single or repeated administration of the benzodiazepine inverse agonist FG7142 on behaviour and cortical adrenoceptor binding in the rat

We have reported previously an increase in the number of beta-adrenoceptors in mouse cerebral cortex 7 days after kindling of seizures by repeated once-daily administration of the benzodiazepine receptor inverse agonist, FG7142. In subsequent experiments, an even larger increase in beta-adrenoceptor number was found 7 days after a single injection of this compound. The present experiments investigated whether FG7142-induced changes in adrenoceptor binding are also found in the rat and whether the effects of a single and repeated injections of this drug differ quantitatively. In view of the anxiogenic effects of FG7142, we have also tested for parallel changes in behaviours associated with anxiety and exploration. Nine days after a single injection of FG7142, the number of beta-adrenoceptors in the cerebral cortex was greater than that found after repeated administration of this compound; this difference was statistically significant. There was no difference in beta-adrenoceptor binding to tissues from chronically FG7142-treated and vehicle-injected animals and there were no changes in alpha 2-adrenoceptor binding or noradrenaline levels after either a single or repeated FG7142 treatment. Neither single nor repeated FG7142 treatment modified spontaneous behaviour in either the elevated plus-maze test of anxiety or the holeboard test of exploration. The behavioural effects of yohimbine and clenbuterol in these tests were also unaffected by FG7142. We discuss the possibility that the difference in the effects of a single and repeated administration of FG7142 on beta-adrenoceptor binding is related to the expression of kindled seizures.

Benzodiazepines in the treatment of alcoholism

This chapter comprises three sections that cover the main aspects of benzodiazepines and alcohol: (1) the basic pharmacology of benzodiazepines; (2) use of benzodiazepines in the treatment of withdrawal; and (3) the use of benzodiazepines in treating alcoholics. The basic studies suggest that a major site of action of alcohol may be the GABA/benzodiazepine receptor complex and that compensatory alterations in this complex may underly withdrawal. In the section on alcohol withdrawal, interactions between the GABA/benzodiazepine receptor complex, sympathetic nervous system, and hypothalamic-pituitary-adrenal axis are discussed. Use of benzodiazepines in the treatment of the alcohol withdrawal syndrome are reviewed, including the possibility that the benzodiazepines may prevent withdrawal-induced "kindling." Lastly, we review indications for, and efficacy of, benzodiazepines in long-term treatment of patients with alcoholism. Benzodiazepines are not indicated for the treatment of alcoholism. Furthermore, they have very few indications in alcoholics and their dependency-producing potency has to be appreciated when they are used in patients with alcoholism.

Behavioral effects of benzodiazepine antagonists in chlordiazepoxide tolerant and non-tolerant rats

Rats were trained to respond under 3-min fixed-interval schedules of food presentation, and effects of the benzodiazepine-receptor ligands, flumazenil, 2-(4-methoxy-phenyl)-pyrazolo[4,3-c]quinolin-3(5H)-one (CGS 9895), 3-carbo-t-butoxy-beta-carboline (beta-CCtB), and beta-carboline-3-carboxylic acid ethyl ester (beta-CCE) were assessed before and after the induction of tolerance to chlordiazepoxide. Before daily administration of chlordiazepoxide, none of the antagonists produced appreciable effects on rates of responding up to doses of 32.0 mg/kg i.p. beta-CCE was the only antagonist studied at a higher dose (100.0 mg/kg i.p.), which decreased response rates. After 23 days of daily chlordiazepoxide administration (oral doses started at 10 and increased to 100 mg/kg/day by the 17th day), dose-effect curves for chlordiazepoxide were shifted to the right by about one-half log unit. Subjects were also more sensitive to the flumazenil, CGS 9895, and beta-CCtB, however, since these drugs produced only small effects in non-tolerant subjects, precise estimates of the degree of the shift in dose-effect curves could not be estimated. However, there were differences in the changes in the dose-effect curves induced by chlordiazepoxide tolerance. These results suggest differences in mechanism of action of antagonists in tolerant and non-tolerant subjects, and further that the sensitivity that is induced to antagonists in tolerant subjects is not conferred equally to all drugs having benzodiazepine antagonist activity.

Steroid modulation of the GABA/benzodiazepine receptor-linked chloride ionophore

Recent findings suggest that steroids with sedative-hypnotic properties interact specifically with the gamma-aminobutyric acidA/benzodiazepine receptor-chloride ionophore complex (GBRC). They show positive heterotropic cooperativity by allosterically enhancing the binding of GABA agonists and the clinically useful benzodiazepines (BZs) to their respective recognition sites. These steroids have stringent structural requirements for activity at the GBRC, with the essential requirements for high potency being a 3 alpha-hydroxyl group and a 5 alpha-reduced A-ring. Some of these steroids are naturally occurring metabolites of progesterone and deoxycorticosterone and have nanomolar potencies as potentiators of chloride channel conductance. These 3 alpha-hydroxylated, 5 alpha-reduced steroids do not act through any known sites on the GBRC. Thus, the exact site and mechanism of action remain to be determined. Together with the observation that physiological levels of these metabolites are sufficient to influence the function of the GBRC, the evidence clearly suggests a role for these steroids in the normal regulation of brain excitability by potentiating the postsynaptic effects of gamma-aminobutyric acid (GABA). Pharmacological studies of the GBRC-active steroids show that they possess anxiolytic and anticonvulsant activities. The potential therapeutic application of these steroids in the treatment of mood disorders and catamenial exacerbation of seizures associated with the menstrual cycle is discussed. Collectively, the evidence from the studies of these steroids imply that another mechanism by which the endocrine system influences brain function has been identified. Its characterization will provide important insight into how steroids modulate brain excitability under normal and pathophysiological states.

Discriminative stimulus properties of CGS 9896: interactions within the GABA/benzodiazepine receptor complex

Male rats were trained to discriminate the stimulus effects of CGS 9896 (30.0 mg/kg) from its vehicle. Once trained, discriminative performance was observed to be dose-responsive in the 3.75-30.0 mg/kg range and analysis of the dose-response curve generated an ED50 of 6.44 mg/kg. Generalization testing with chlordiazepoxide and pentobarbital produced CGS 9896-appropriate responding, whereas administration of the GABA agonists SL 75 102 resulted in 75% (intermediate) generalization to the CGS 9896 discriminative stimulus. Although full antagonism of the CGS 9896 cue was obtained following administration of Ro15-1788 and pentylenetetrazole, the inverse agonist DMCM failed to provide complete antagonism. These results suggest that the discriminative properties of CGS 9896 are consistent with its activity as a benzodiazepine receptor agonist.

Neuropharmacology of several beta-carboline derivatives and their 9-acetylated esters. In vivo versus in vitro studies in the rabbit

The effects of 3-methoxycarbonyl- (beta-CCM, Ia), 3-ethoxycarbonyl- (beta-CCE, Ic), 3-propoxycarbonyl- (PrCC, Ie), 3-N-methylcarboxamido- (FG-7142, Ig) beta-carboline and 2-acetyl-3-methoxycarbonyl-1,2-dihydro-beta-carboline (IIa) as well as of their corresponding 9-acetyl derivatives (Ib, Id, If, Ih and IIb) have been studied in rabbits. In addition, the effects of 6,7-dimethoxy-4-ethyl-3-methoxycarbonyl-beta-carboline (DMCM) have also been studied. In in vitro studies, these drugs compete with 3H-diazepam to benzodiazepine (BDZ) receptor in membrane preparations from brain cortex. The values of IC50 are in the nanomolar range without significant differences between the acetyl derivatives and their congeners only compound If shows a 10-fold decrease of the binding capacity in respect to its congener Ie. In the presence of 10(-5) M GABA, a decrease in the binding capacity for DMCM, Ia, Ic and Ig and an increase for If are observed. In vivo studies show that DMCM, Ia, Ib, IIa and IIb elicit three dose-dependent stages of electrocortical changes (trains of slow waves, trains of spike-and-wave complexes and "grand-mal" seizures). Compounds Ic, Id and Ig elicit only the first two stages. Compound Ih elicits only the first stage. While compound Ie does not affect the EEG pattern, its 9-acetyl derivative If induces changes (cortical spindles and disruption of the hippocampal theta waves) characteristic of agonist ligands of BDZ receptor. These findings confirm that the efficacy of compounds DMCM, Ia, Ic, Id, Ig and Ih as inverse agonists of BDZ receptor in the EEG paradigm parallels the reduction of their apparent binding affinity in the presence of GABA. The 9-acetylated compounds may be more inverse agonist in vivo than predicted from the in vitro findings, due to hydrolysis in the plasma.

Electrophysiology of benzodiazepine receptor ligands: multiple mechanisms and sites of action

Electrophysiology of BZR ligands has been reviewed from different points of view. A great effort was made to critically discuss the arguments for and against the temporarily leading hypothesis of the mechanism of action of BZR ligands, the GABA hypothesis. As has been discussed at length in the present article, an impressive body of electrophysiological and biochemical evidence suggests an enhancement of GABAergic inhibition in CNS as a mechanism of action of BZR agonists. Biochemical data even indicate a physical coupling between GABA recognition sites and BZR which, together with the effector site build-up by Cl- channels, form a supramolecular GABAA/BZR complex. By binding to a specific site on this complex, BZR agonists allosterically increase and BZR inverse agonists decrease the gating of GABA-linked Cl- channels, whereas BZR antagonists bind to the same site without an appreciable intrinsic activity and block the binding and action of both agonists as well as inverse agonists. While this model is supported by many electrophysiological experiments performed with BZR ligands in higher nanomolar and lower micromolar concentrations, it does not explain much controversial data from animal behavior and, more importantly, is not in line with electrophysiological effects obtained with low nanomolar BZ concentrations. The latter actions of BZR ligands in brain slices occur within a concentration range compatible with concentrations of BZ observed in CSF fluid, which would be expected to be found in the biophase (receptor level) during anxiolytic therapy in man. Enhanced K+ conductance seems to be a suitable candidate for this effect of BZR ligands. This direct action on neuronal membrane properties may underlie the many electrophysiological observations with extremely low systemic doses of BZR ligands in vivo which demonstrated a depressant effect on spontaneous neuronal firing in various CNS regions. Skeletomuscular spasticity and epilepsy are two neurological disorders, where both the enhanced GABAergic inhibition and increased K+ conductance may contribute to the therapeutic effect of BZR agonists, since electrophysiological and behavioral studies strongly support GABA-dependent as well as GABA-independent action of BZR ligands elicited by low to intermediate doses of BZ necessary to evoke anticonvulsant and muscle relaxant effects. Somewhat higher doses of BZR ligands, inducing sedation and sleep, lead perhaps to the only pharmacologically relevant CNS concentrations (ca. 1 microM) which might be due entirely to increased GABAergic inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of brain function by S-135, a benzodiazepine receptor inverse agonist

1. S-135, 2-(5-methylthien-3-yl)-2,5-dihydro-3H-pyrazolo[4,3-c]quinoline-3- one, bind binds to benzodiazepine receptors with a high affinity and shows pharmacological actions opposite to those of conventional benzodiazepine drugs. 2. S-135 induced no convulsion in mice by itself, but selectively potentiated the effect of subconvulsive dose of pentylenetetrazole. 3. S-135 potentiated rat crossed extensor reflex and Ro 15-1788 completely antagonized this potentiation. 4. S-135 antagonized pentobarbital-induced anesthesia, tetrabenazine-induced ptosis and reserpine-induced hypoactivity and shortened immobilization time in the despair test in mice, indicating that this compound possesses antidepressive properties. 5. S-135 antagonized amnesia in mice and rats in passive avoidance tasks. 6. Glucose utilization in brain areas relating to memory and arousal functions was enhanced following S-135 treatment. 7. These results indicate that S-135 can be a useful drug for activating depressed brain function.