Anticonvulsant action of diazepam: increase of cortical postsynaptic inhibition

Anticonvulsant activity and acute neurotoxic profile of Achyranthes aspera Linn

ETHNOPHARMACOLOGICAL RELEVANCE

Root powder of Achyranthes aspera Linn. (A. aspera) belongs to family Amaranthaceae is used in Indian traditional medicine for the management of epilepsy and its efficacy is widely acclaimed among the different rural communities.

AIM OF THE STUDY

The present study was aimed to establish the possible anticonvulsant effect of A. aspera methanolic root extract using acute anticonvulsant models and to evaluate the acute toxicity and neurotoxic potential A. aspera extract.

MATERIAL AND METHODS

A. aspera methanolic extract was standardized with respect to betaine using HPTLC. The maximal electroshock (MES), pentylenetetrazol (PTZ), picrotoxin and bicuculline induced seizure models were used to evaluate the anticonvulsant potential of standardized A. aspera root extract. The GABA content in cortex and hippocampus of extract treated mice was evaluated using HPLC. Moreover, the animals were also evaluated for acute toxicity study and neurotoxicity test.

RESULTS

A significant enhancement in the seizure threshold was observed by A. aspera extract (5 and 10mg/kg) treated mice in PTZ, picrotoxin and bicuculline models as compared to saline treated mice respectively, whereas the extract failed to show protection in MES induced seizures. Moreover, A. aspera treatment (5 and 10mg/kg) significantly enhances the GABA levels in hippocampus and cortex as compared to saline treated group. A. aspera root extract was devoid of any sign of acute toxicity as well as neurotoxicity.

CONCLUSIONS

A. aspera root extract exhibits significant anticonvulsant effect by facilitation of GABAergic neurotransmission in the brain.

Behavioral effects induced by antitumor cleronade diterpenes from Casearia sylvestris and in silico interactions with neuron receptors

ETHNOPHARMACOLOGICAL RELEVANCE

Casearia sylvestris is a medicinal plant traditionally used to treat snakebites, wounds, inflammation and gastric ulcers and scientific supports for have demonstrated its antitumor, antihyperlipidemic and antiparasitic properties.

AIM OF THE STUDY

To assess the effects of a fraction with casearins (FC) on adult mice using classical experimental models of animal behavior and theoretical calculations to verify the interaction of Casearin X (Cas X) with neuron receptors.

MATERIALS AND METHODS

Animals divided in 6 groups (n=9/group) were intraperitoneally treated with vehicle (DMSO 4%), FC (2.5, 5, 10 and 25mg/kg/day) and diazepam (2mg/kg) for 7 days. Thirty minutes after the last dose of treatment, acute toxicity and behavioral experiments were performed.

RESULTS

The highest dose of FC (25mg/kg/day) caused diarrhea, weight loss and death of one animal. Elevated plus maze test showed that lower doses [2.5mg/kg/day (36.4±5.1s) and 5mg/kg/day (43.9±6.2s)] increased the time spent in open arms (TSOA). Open field test revealed reduction in the number of crossings (54.9%, 51.1%, 48% and 67.7% for 2.5, 5, 10 and 25mg/kg/day, respectively) in all doses of FC studied and decrease of rearings at 25mg/kg/day (p<0.05). Computational calculations showed that the inhibition constant (Ki) for the Cas X-D₁ complex is up to 1000-fold more favourable than the Cas X-GABA_A complex. All ∆G° values obtained for Cas X-D₁ complexes were more negative than those seen with Cas X-GABA_A complexes.

CONCLUSIONS

Findings indicate a probable anxiolytic action of the FC since it reduces the number of crossings and rearings and prolonged the time spent in open arms, without sedative and myorelaxant effects, probably due to the interaction of Cas X with dopaminergic system.

Effects of GABA and anxiolytics on the single unit discharge of suprachiasmatic neurons in rat hypothalamic slices

The effects of gamma-aminobutyric acid (GABA), muscimol, baclofen and the anxiolytics; diazepam (DZP), flurazepam (FZP) and zopiclone on single-unit neural activities in the suprachiasmatic nucleus (SCN) were investigated using the rat hypothalamic slice preparation. Exposure of the slice to GABA 10(-4) M produced inhibitory responses in 65% of the 49 SCN neurons examined. The threshold concentration of GABA ranged from 10(-6) to 10(-4) M. Neurons responsive to GABA were not found to be restricted to a subdivision of the SCN, but were diffusely distributed throughout the nucleus. DZP, FZP and zopiclone produced responses similar to those of GABA. The inhibitory effects of GABA (10(-5) M) were potentiated by coadministration of DZP (10(-5) M). Muscimol and baclofen (10(-7) M to 10(-4) M) also inhibited SCN neuronal activity in a dose-dependent manner. Bicuculline (10(-5) M-10(-4) M) scarcely affected the baclofen-induced inhibition (1/6) but strongly antagonized the effects of muscimol (6/6), GABA (6/8) and DZP (4/5). These results suggest that the receptors mediating the inhibitory effects of GABA and anxiolytics within the SCN may be GABAA and/or GABAB or GABA-BDZ receptor complex, respectively.

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)

Diazepam action on gamma-aminobutyric acid-activated chloride currents in internally perfused frog sensory neurons

The Cl- current (ICl) in gamma-aminobutyric acid (GABA)-sensitive frog sensory neuron was separated from other Na+, Ca2+, and K+ currents using a suction pipette technique which allows internal perfusion under a single-electrode voltage clamp. Diazepam (DZP) itself evoked no response but facilitated the dose- and time-dependently GABA-induced ICl without changing the GABA equilibrium potential (EGABA) at concentrations ranging widely, from 3 X 10(-9) to 10(-4) M. In the presence of DZP, the GABA dose-response curve shifted to the left without changing the maximum current, indicating that DZP modifies the interaction between GABA and its receptor rather than affecting directly the channel activation step. The enhancement of the GABA-induced ICl by DZP depended neither on the membrane voltage nor on the inward or outward direction of the ICl. DZP also potentiated the ICl elicited by GABA agonists such as beta-alanine, taurine, homotaurine, 5-aminovaleric acid, l-GABOB, d-GABOB, glycine, and muscimol. The GABA response enhanced by pentobarbital (PB) was further enhanced by adding DZP, indicating that DZP and PB do not act in the same way. Ro5-3663, a diazepam analogue, enhanced the GABA-induced ICl only in a narrow range of the concentrations but inhibited the current at concentrations higher than 2 X 10(-6) M.

Amygdala kindled seizure stage is related to altered benzodiazepine binding site density

Benzodiazepine receptor binding was examined in rats at 3 stages of amygdaloid kindling (i.e., initial afterdischarge, Stage 3 and Stage 5) immediately or 24 hr after seizure. 3H-diazepam binding site density (Bmax) was significantly increased 24 hr after Stage 3 and Stage 5 kindled seizures in the hippocampus but not in the amygdala. There were no significant differences in the dissociation constants (KD) between kindled and control rats at any time point examined for either brain region. These results demonstrate that changes in benzodiazepine binding are observed with partial kindled seizures (i.e., Stage 3), indicating that generalized seizures are not prerequisite to increased benzodiazepine receptor site density.

Autoradiography of benzodiazepine receptor binding in the central nervous system of the normal C57BL6J mouse

[3H]flunitrazepam has been used as a photoaffinity label for the specific, clonazepam-displaceable 1,4-benzodiazepine binding sites in sections of normal C57BL6J mouse brain and spinal cord. Binding was visualized by light microscope autoradiography and quantified by a simple microdensitometric procedure. Specific flunitrazepam binding was seen to be highest in the colliculi, cerebral cortex, hippocampal formation, interpeduncular nucleus, mamillary body, hypothalamus, olfactory tubercle, and in the molecular layer and deep nuclei of the cerebellum. The distribution of specific flunitrazepam binding sites in mouse brain and spinal cord is discussed in terms of the known actions of the benzodiazepines.

Rectal diazepam: a clinical and EEG study after a single dose in children

EEG monitoring was performed on a group of ten children, aged 3 days to 13 years, during admission to the Paediatric Clinic at the University of Bologna for seizures. Diazepam was injected by rectal route as an anticonvulsant, using a dose of 0.5-1 mg/kg in the first nine children, whereas an intravenous bolus was administered to the last child. The main aim of this study was to document the time taken for the drug to reach the brain and to modify the electrical activity. We observed significant EEG changes between 1 and 9.30 min and, in particular, the appearance of fast activity over one or both hemispheres after rectal diazepam. The EEG results confirm the clinical efficacy of rectal diazepam.

Interactions between amino acid neurotransmitters and flurazepam in the neocortex of unanesthetized rats

The effects induced by the benzodiazepine flurazepam (FLU) upon neuronal responses to glutamic acid (GLUT), gamma-aminobutyric acid (GABA), and glycine (GLY) were studied in the cortex of unanesthetized rats using single-unit extracellular recordings in conjunction with iontophoretic techniques. The application of FLU (5-20 nA) did not affect excitatory responses to GLUT, but the spontaneous firing rate was depressed by equivalent doses of this benzodiazepine. A selective increase of GABA, but not of GLY-induced responses was seen when either low currents (5-10 nA) of FLU or GLUT driving currents were used to study the neuronal responses of the inhibitory amino acids upon steady neuronal firing. Our data demonstrate that in unanesthetized animals FLU does not affect GLUT-induced effects while it selectively increases GABA-mediated inhibition.

Chemical structure and biological activity of the diazepines

Since the introduction of chlordiazepoxide and diazepam many diazepines have been developed. Use of these drugs is increasing and considerable knowledge has accumulated about their mechanisms of action. The structural and pharmacological properties of these drugs are surveyed briefly.

Some pharmacological studies on the spastic mouse

1 Full-wave rectification and integration of the EMG signal recorded from the hamstring muscles of the spastic mouse was used to evaluate the actions of a variety of drugs on the muscle rigidity of these mutants, animals in which no histological lesion has yet been found. 2 Profound and long-lasting muscle relaxant responses were consistently observed upon the injection of diazepam (2 mg/kg, i.p.) and flunitrazepam (2 mg/kg, i.p.). Such responses were always greater than those obtained upon injection of 40% (v/v) propylene glycol (10 ml/kg) alone, the vehicle for the benzodiazepines. 3 The muscle relaxant action of a low dose (0.25 mg/kg i.p.) of the benzodiazepine Roll-6896 was not shared by the same dose of its enantiomer Roll-6893. 4 Profound and long-lasting muscle relaxation was caused by sodium valproate (696 mg/kg, i.p.). Consistent muscle relaxant responses were also observed upon the injection of pentobarbitone (30 mg/kg, i.p.), but not phenobarbitone (30 mg/kg, i.p.). 5 Other drugs that had little or no detectable effect on the muscle rigidity of the spastic mouse included diphenylhydantoin (30 mg/kg, i.p.) and bromocriptine (10 mg/kg, s.c.) while, in some animals, benztropine (2 mg/kg, i.p.) and baclofen (10 mg/kg, i.p.) increased muscle rigidity. 6 The development of full muscle relaxant responses to flunitrazepam (2 mg/kg, i.p.) and to sodium valproate (696 mg/kg, i.p.) was shown to depend upon mild warming of the animals with radiant heat, a procedure which can increase muscle spindle afferent input to the spinal cord. 7 The results suggest a hyperactivity of stretch reflexes in the spastic mouse, ameliorated selectively by those drugs that enhance the GABA-mediated presynaptic inhibition of such pathways.

Benzodiazepines and central inhibitory mechanisms

The effect of diazepam was evaluated on spontaneous activity and drug- and electrically-elicited inhibitions of neuronal activity. Doses of diazepam which did not change spontaneous firing rates markedly enhanced GABA-mediated inhibitions in rat cerebellum in situ and in tissue cultures of rat hypothalamus. The effects of diazepam were readily reversible, and could be antagonized by picrotoxin; no effect on glycine or norepinephrine-induced inhibition was seen. It is concluded that actions of diazepam are mediated, at least in part, by a specific increase in GABA-mediated inhibition in the central nervous system.

The GABA postsynaptic membrane receptor-ionophore complex. Site of action of convulsant and anticonvulsant drugs

The function of the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), has been implicated in the mode of action of many drugs which excite or depress the central nervous system. Many convulsant agents appear to block GABA action whereas anticonvulsants enhance GABA action. Some of these drug effects involve altered GABA-mediated synaptic transmission at the level of GABA biosynthesis, release from nerve endings, uptake into cells, and metabolic degradation. A greater number of agents of diverse classes appear to affect GABA action at the postsynaptic membrane, as determined from both electrophysiological and biochemical studies. The recently developed in vitro radioactive receptor binding assays have led to a wealth of new information about GABA action and its alteration by drugs. GABA inhibitory transmission involves the regulation, by GABA binding to its receptor site, of chloride ion channels. In this GABA receptor-ionophore system, other drug receptor sites, one for benzodiazepines and one for barbiturates/picrotoxinin (and related agents) appear to form a multicomponent complex. In this complex, the drugs binding to any of the three receptor categories are visualized to have an effect on GABA-associated chloride channel regulation. Available evidence suggests that the complex mediates many of the actions of numerous excitatory and depressant drugs showing a variety of pharmacological effects.

Pharmacology of GABA-mediated inhibition of spinal cord neurons in vivo and in primary dissociated cell culture

In this paper it is shown that the postsynaptic GABA-receptor chloride ion channel complex is composed of several functional subunits. There are probably at least two stereospecific locations on the receptor for GABA-binding and both must be occupied to obtain an increase in chloride conductance. The interaction between these sites is uncertain but there could be either positive cooperativity between the sites or only a requirement that both sites are occupied without occupation of either site affecting the affinity for GABA of the other site. There is a chloride conductance channel coupled to the GABA receptor which opens for an average of 20 msec and has an average conductance of 18 pS. The GABA-coupled chloride channel may or may not have the same composition as the glycine coupled chloride channel. In addition to the GABA-recognition site and the chloride ion channel, GABA-receptors must have additional binding sites or modulator sites where drugs can bind to modify GABA activation of the GABA receptor. The convulsant PICRO binds to a site which is independent of the GABA site and PICRO reduces GABA responses. Barbiturates and benzodiazepines augment GABA-responses without reducing GABA-binding and thus they must bind to a modulator site independent of the GABA recognition site. Whether or not this is the same site as the PICRO binding site is uncertain. Thus, the GABA-receptor-chloride ion channel complex is composed of at least: 1) two GABA-binding sites; 2) a chloride ion channel; 3) a convulsant binding site (PICRO-binding site) and 4) an anticonvulsant binding site. This organization serves several obvious purposes. First, since two GABA-molecules are required to activate GABA-coupled chloride ion channels, the dose-response relationship for GABA is sigmoidal and steep. Thus minor shifts in GABA affinity will produce large alterations in GABA-responses and the GABA receptor can be easily modulated. Second, since the receptors has binding sites for convulsant and anticonvulsant compounds which decrease and increase GABA-responses, GABAergic inhibition can easily be modulated.

Handling-induced seizures and rotational behavior in th Mongolian gerbil

The aim of this report was to examine the relationship between sensory-induced seizures, cerebral laterality (as measured by rotation) and nigrostriatal asymmetry in Mongolian gerbils. Seizure resistant gerbils made proportionally more spontaneous turns to be preferred direction than sensitive animals. Three prototypical antiepileptic drugs strongly elicited rotational behavior (carbamazepine (10-20 mg/kg), diazepam (16 mg/kg) and pentobarbital (40 mg/kg)) and two others (phenobarbital 20-40 mg/kg) and ethosuximide (500 mg/kg)) also appeared to potentiate rotation; only diphenylhydantoin and trimethadione were effective. Two dopaminergic agonists, amphetamine (4 mg/kg) and apomorphine (16 mg/kg) enhanced rotation at anticonvulsant doses while the dopaminergic antagonist haloperidol reduced rotational behavior at a dose (1 mg/kg) which exacerbate seizure severity. Finally, surgical induction of nigrostriatal asymmetry by means of unilateral electrolytic striatal lesions reduced seizure severity; sham and bilateral striatal lesions had no significant effects on seizures. These results suggest that seizure activity and rotational behavior are inversely related and, furthermore, that the link between these two behaviors may be the asymmetry between nigrostriatal dopaminergic systems.

Effects of diazepam on hippocampal excitability in the rat: action in the dentate area

Acute and chronic experiments were performed on rats to examine the effects of diazepam (Valium) on recurrent inhibition in the monosynaptic perforant path-dentate synapse of the dentate area of the dorsal hippocampus. Evidence was obtained which indicated that diazepam facilitated a presumably GABA mediated post synaptic recurrent inhibition in both acute and chronic preparations at 1 and 2 mg/kg doses (IP). Acute studies also revealed that diazepam prolonged recurrent inhibition, possibly by lengthening the IPSP. An effect of the drug on cholinergically mediated positive feedback from the septum could not be ruled out, however. Taken together, this study extends the evidence that diazepam acts centrally on GABA mediated inhibition in the limbic system. Furthermore, the limbic action of diazepam revealed here suggests a mechanism for the anticonvulsant properties of diazepam in epilepsy involving subcortical (limbic) circuitry.

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.

Water soluble benzodiazepines with agonistic and antagonistic actions on GABA-induced inhibition in cultured hypothalamus

The interaction of two benzodiazepine compounds, flurazepam (a sedative and RO 5-3663 (a convulsant), with amino acid depressions of spontaneous neuronal activity in hypothalamic tissue cultures has been examined. Flurazepam selectively potentiated, GABA-induced inhibition, while RO 5-3663 selectively reduced GABA-induced inhibtion. These results are interpreted as supporting the presence of two types of benzodiazepine binding sites in the brain which would modulate endogenous GABA-mediated inhibition and behavior.

Interaction of diazepam with synaptic transmission in the in vitro rat hippocampus

Diazepam (5 x 10(-8) - 10(-6) M) was found to augment recurrent inhibition of pyramidal neuron firing in a dose-dependent manner in rat hippocampal slices. To determine possible loci of this effect, diazepam was locally administered by pressure ejection from a micropipette, while recording action potentials from single inhibitory ("basket") interneurons. Diazepam induced reversible and reliable increases in interneuron firing in response to stimulation of Schaffer collateral and commissural afferents. Taken together with previous electrophysiological reports, these data suggest that benzodiazepines may augment central inhibition by increasing either the excitability of inhibitory interneurons, or by increasing the strength of excitatory afferents to these cells.

Relation between extracellular potassium concentration and neuronal activities in cat thalamus (VPL) during projection of cortical epileptiform discharge

Neuronal and potassium activities (ak) were measured in the nucleus ventro-posterolateralis thalami (VPL) during propagated epileptiform activity from the somatosensory cortex of cats. Seizures were induced by repetitive electrical stimulation of the cortical surface or by topical application of penicillin. The recruitment of VPL into a seizure resulted in large increases of ak to levels of up to 11.6 mmoles/l, accompanied by increased in neuronal discharge rate to 300/sec. Sometimes the rise in ak preceded active participation of a given thalamo-cortical relay (TCR) neuron in the seizure. After reaching a peak level, ak and neuronal discharge rate slowly declined during an ictal episode. After cessation of seizures all TCR neurons were inhibited, while ak fell to subnormal levels. The duration of these postictal depressions increased with the amplitude of preceding increases and subsequent undershoots in ak and could last up to 120 sec. During decay and undershoot in ak, relay capability of TCR neurons was reduced. Also the probability that action potentials elicited in intracortical endings of TCR cells would antidromically invade their cell bodies was decreased. The duration of these periods varied with the amplitude of undershoot in ak. Seizure threshold was increased during undershoots. These observations are consistent with a long-lasting postictal hyperpolarization of neuronal membranes. The hyperpolarization may be caused by the action of an electrogenic pump, which is probably involved in termination of seizure discharge.

Inosine may be an endogenous ligand for benzodiazepine receptors on cultured spinal neurons

Mouse spinal neurons grown in tissue culture were used to study the membrane effects of the benzodiazepine flurazepam and the naturally occurring purine nucleoside inosine, which competes for benzodiazepine receptor sites in the central nervous system. Application of inosine elicited two types of transmitter-like membrane effects: a rapidly desensitizing excitatory response and a nondesensitizing inhibitory response. Flurazepam produced a similar excitatory response which showed cross-desensitization with the purine excitation. Flurazepam also blocked the inhibitory inosine response. The results provide electrophysiological evidence that an endogenous purine can activate two different conductances on spinal neurons and that flurazepam can activate one of the conductances and antagonize the other.

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.

Effect of anticonvulsants on spiking activity induced by cortical freezing in cats

In an attempt to know whether the existing anticonvulsants act on epileptogenic focus, the effect on SA induced by freezing of the visual cortex was examined in gallamine-immobilized cats. The SA was localized in the neighbor or ipsilateral cortex of the freezing area; little epileptiform activity was produced in the contralateral anterior cortex, and ipsilateral thalamus and hippocampus. Spike frequency and its amplitude were stable over 8 hr. Diazepam suppressed SA and decreased spike frequency and its amplitude. Dipropylacetate and acetazolamide also suppressed SA. On the other hand, phenobarbital, carbamazepine, and a high dose of phenytoin enhanced SA and increased the spike frequency. Low doses of phenytoin and trimethadione were without effect in this aspect. Taurine suppressed SA and changed the spikes to wave-like forms. The EEG arousal response was depressed with phenobarbital, carbamazepine, diazepam, and a high dose of phenytoin, but not with the other drugs examined. From these results, it is suggested that diazepam, dipropylacetate, acetazolamide, and taurine depress the epileptogenic focus activity itself without relation to the activating system.

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.