Effect of diazepam and pentobarbital on aminooxyacetic acid-induced accumulation on GABA

Effects of acute and subacute treatment with ergot drugs on the GABA system in specific brain regions

The effect of dihydroergotoxine and dihydroergotamine on Γ-aminobutyric acid (GABA) levels, the aminooxyacetic acid (AOAA)-induced accumulation of GABA, and the in vitro activity of L-glutamate decarboxylase (GAD) have been examined in various regions of rat brain. Dihydroergotoxine (1 mg kg−1) decreased the concentration of GABA and enhanced the AOAA-induced accumulation of GABA in the caudate nucleus and cingulate cortex. Dihydroergotoxine 10·0 mg kg−1 decreased the AOAA-induced accumulation of GABA in the substantia nigra. The repeated treatment with dihydroergotoxine, 0·05 mg kg−1 for eight days, also decreased the concentration of GABA in the cingulate cortex and diminished the AOAA-induced accumulation of GABA in the substantia nigra. The administration of 0·1 mg kg−1, but not higher doses; of dihydroergotamine, enhanced the AOAA-induced accumulation of GABA in the cingulate cortex. Dihydroergotamine (10·0 mg kg−1) decreased the concentration of GABA in the cingulate cortex and increased the AOAA-induced accumulation of GABA in the caudate nucleus. The activity of GAD in the cingulate cortex, but not in the caudate nucleus, was enhanced after a high dose of dihydroergotamine. Observed increases in the AOAA-induced accumulation of GABA indicate that dihydroergotoxine and dihydroergotamine in at least some brain areas cause an apparent increase in GABA syn-synthesis in vivo, which is presumably a compensatory phenomenon due to a diminished GABAergic transmission under the influence of these drugs.

Effect of depth electrode implantation with or without subsequent kindling on GABA turnover in various rat brain regions

Kindling is a chronic model of epilepsy characterized by a progressive increase in response to the same regularly applied electrical stimulus. The biological basis of the kindling phenomenon requires to be determined, but several studies indicate that impairment of GABAergic inhibition may be involved. In the present experiments, GABA turnover was determined in vivo by the GABA aminotransferase (GABA-T) inhibition method in 13 brain regions in three groups of rats: (1) a group which was kindled via electrical stimulation of intra-amygdala electrodes and was sacrificed 36 days after the last fully kindled seizure for neurochemical determinations; (2) a group of implanted but non-stimulated rats (sham control group) in which neurochemical measurements were done at the same time after electrode implantation as in the kindled group; and (3) a group of non-implanted, naive control rats. Regional GABA levels were determined after vehicle injection as well as 30 and 90 min after administration of aminooxyacetic acid (AOAA) at a dose which completely inhibits GABA-T. Compared to naive controls, prolonged electrode implantation in the amygdala induced a significant reduction of AOAA-induced GABA accumulation in amygdala, hippocampus, piriform cortex, olfactory bulb, frontal cortex, striatum, hypothalamus, tectum, and cerebellar cortex. In view of the GABA hypothesis of kindling, reduced GABA turnover in response to electrode implantation would suggest that the implantation per se exerts a pro-kindling effect, which was recently demonstrated in rats with intraamygdala electrodes. However, amygdala kindling itself appeared to antagonize the effect of electrode implantation in most regions. Thus, although, compared to naive controls, the predominant change in kindled rats was a decrease in GABA turnover, this decrease was less marked than in sham controls. In thalamus and brainstem kindling markedly increased GABA turnover above the levels determined in both naive and sham controls, possibly in response to impaired postsynaptic GABAergic function. The data indicate that both electrode implantation and kindling significantly alter regional GABA turnover, which might contribute to the pathophysiology of the kindling phenomenon. Furthermore, the data substantiate that the choice of adequate controls is critical in neurochemical and functional studies on the kindling phenomenon.

Neurochemical changes associated with the action of acute administration of diazepam in reversing the behavioral paradigm conditioned emotional response (CER)

Neurotransmitter turnover of biogenic monoamines (dopamine, norepinephrine, and serotonin) and amino acids (glutamate, aspartate, and gamma-aminobutyric acid) was evaluated in rats exposed to the conditioned emotional response (CER) paradigm in the absence (total suppression) or presence of acute 5 mg/kg i.p. diazepam (which reversed suppression and restored normal responding). Based on previous studies of CER, with controls for shock and stimulus histories, the results with respect to the anxiolytic could be divided into several categories: changes in turnover which are associated only with the CER behavior; changes associated only with the drug, diazepam; changes which augmented the effects of the behavior; or changes which were the reverse of those associated with the behavior. Due to the multitude and complexity of the results, not all observations have clear explanations at this time. However, for the CER behavior per se, it is apparent that a combination of neurotransmitters, including some implications about acetylcholine, act in concert to bring about the behavioral suppression. The action of diazepam is more complex, involving the full spectrum of neurotransmitters to bring about its direct and indirect effects.

Effects of acute barbiturate administration, tolerance and dependence on brain GABA system: comparison to alcohol and benzodiazepines

Central nervous system depressants, e.g., barbiturates, alcohol and benzodiazepines, have a wide spectrum of activity in humans and animals. Evidence accumulated suggests that some of the pharmacological actions exerted by these agents may be mediated through GABA system by mimicking GABAergic transmission. This review attempts to summarize the evidence available as to how the GABA system plays a part in the barbiturate actions and the development of tolerance to and physical dependence on barbiturates. The comparisons of the effects of alcohol, barbiturates and benzodiazepines at different steps of GABA synapse are also presented. Furthermore, the results which have been reported in the literature are inconsistent. This may be due to differences in: (a) animal models used; (b) brain regions used; (c) protocols (dose, duration, form and route of administration, etc.) used in treating animals and/or (d) techniques (pharmacological, biochemical, physiological, etc.) used.

Changes in GABA content and turnover in discrete regions of rat brain after systemic administration of caerulein

The effects of systemically injected caerulein, a cholecystokinin octapeptide analogue, on GABA content and turnover have been studied in various regions of rat brain. Caerulein decreased GABA levels in the nucleus accumbens, tuberculum olfactorium and substantia nigra and diminished GABA turnover rates in the striatum, nucleus accumbens and substantia nigra, as estimated from the rate of GABA accumulation after inhibition of GABA transaminase by aminooxyacetic acid (AOAA). These results indicate the effect of caerulein on the utilization of GABA in specific cerebral regions and suggest that the GABAergic system is involved in the mechanism of action of peripherally administered caerulein.

Reversal by apomorphine of the gabaculine-induced GABA accumulation in mouse cortex

To test the assumption that in the mice cortex the rate of accumulation of gamma-aminobutyric acid (GABA) after irreversible inhibition of 4-aminobutyrate: 2-oxoglutarate aminotransferase (EC 2.6.1.19; GABA-T) represents an index of GABA turnover, we examined whether the reversal of the gabaculine-induced accumulation of GABA elicited by apomorphine was due to a decrease in GABA turnover or to a modulation of the activity of the GABA-T inhibitor. Therefore, we simultaneously measured the action of apomorphine on gabaculine-induced accumulation of GABA and on GABA-T activity. In vitro, apomorphine (3 and 30 microM) did not alter the concentration-dependent inhibition of GABA-T by gabaculine. Ex vivo, apomorphine (2 x 0.5 mg/kg s.c.) markedly decreased (69%) gabaculine-induced (150 mg/kg i.p.) accumulation of GABA. This drug had no direct effect on GABA-T activity, but significantly reduced from 83 to 71% the inhibition of GABA-T by gabaculine. The linear correlation found between GABA levels and GABA-T activity allowed the quantification of the decrease in GABA turnover elicited by apomorphine. The results showed that apomorphine decreased significantly (P less than 0.001) the rate of GABA synthesis from 7.48 to 3.36 micromol GABA/g per h, if the partial reversal of gabaculine-induced inhibition of GABA-T is considered and 2.44 micromol/g per h if not. Apomorphine effect on GABA accumulation is mainly due to a decrease of the rate of GABA synthesis and to a lesser extent to a reversal of the inhibitory activity of gabaculine. Thus, inhibition of GABA-T by gabaculine is a sensitive and reliable method for the estimation of the rate of synthesis.

Use of inhibitors of gamma-aminobutyric acid (GABA) transaminase for the estimation of GABA turnover in various brain regions of rats: a reevaluation of aminooxyacetic acid

The technique of estimating gamma-aminobutyric acid (GABA) turnover by inhibiting its major degrading enzyme GABA-T (4-aminobutyrate:2-oxoglutarate aminotransferase; EC 2.6.1.19) and measuring GABA accumulation has been used repeatedly, but, at least in rats, its usefulness has been limited by several difficulties, including marked differences in the degree of GABA-T inhibition in different brain regions after systemic injection of GABA-T inhibitors. In an attempt to improve this type of approach for measuring GABA turnover, the time course of GABA-T inhibition and accumulation of GABA in 12 regions of rat brain has been studied after systemic administration of aminooxyacetic acid (AOAA), injected at various doses and with different routes of administration. A total and rapidly occurring inhibition of GABA-T in all regions was obtained with intraperitoneal injection of 100 mg/kg AOAA, whereas after lower doses, marked regional differences in the degree of GABA-T inhibition were found, thus leading to underestimation of GABA synthesis rates, e.g., in substantia nigra. The activity of the GABA-synthesizing enzyme GAD (L-glutamate-1-decarboxylase; EC 4.1.1.15) was not reduced significantly at any time after intraperitoneal injection of AOAA, except for a small decrease in olfactory bulbs. Even the highest dose of AOAA tested (100 mg/kg) was not associated with toxicity in rats, but induced motor impairment, which was obviously related to the marked GABA accumulation found with this dose. The increase in GABA concentrations induced with intraperitoneal injection of 100 mg/kg AOAA was rapid in onset, allowing one to estimate GABA turnover rates from the initial rate of GABA accumulation, i.e., during the first 30 min after AOAA injection. GABA turnover rates thus determined were correlated in a highly significant fashion with the GAD activities determined in brain regions, with highest turnover rates measured in substantia nigra, hypothalamus, olfactory bulb, and tectum. Pretreatment of rats with diazepam, 5 mg/kg i.p., 5-30 min prior to AOAA, reduced the AOAA-induced GABA accumulation in all 12 regions examined, most probably as a result of potentiation of postsynaptic GABA function. The data indicate that AOAA is a valuable tool for regional GABA turnover studies in rats, provided the GABA-T inhibitor is administered in sufficiently high doses to obtain complete inhibition of GABA degradation.

Inhibitory influence of dihydroergosine on the aggressiveness of rats and mice

Fifty mg/kg of ergot alkaloid dihydroergosine (DHESN) inhibited the mouse-killing behavior of isolated male rats, while 10 mg/kg did not. This effect of DHESN (50 mg/kg) lasted for 24 hr. When an additional injection of DHESN (50 mg/kg) was given to mouse-killer rats 6 days following the first, the mouse-killing behavior was again inhibited. The effect of the second drug injection also persisted for 24 hr and was accompanied by an increased concentration of 5-HT in the raphe nuclei and hypothalamus and by a decreased concentration of GABA in the olfactory bulbs. DHESN also inhibited aggressiveness in isolated mice. Two hr following the administration of 10 mg/kg DHESN the fighting was inhibited in 46% of pairs tested, while 50 mg/kg abolished it completely. The effect of 50 mg/kg lasted 24 hr. These results, showing the antiaggressive effects of DHESN, support our previous suggestion that DHESN might presumably be a new antidepressant, and suggest that besides the serotoninergic, the GABA-ergic system might also be involved in the modification of behavior induced by this drug.

Sex difference in the turnover of GABA in the rat substantia nigra

The turnover of GABA (estimated from the post-mortem accumulation of GABA), and the activity of glutamic acid decarboxylase and GABA transaminase, along with the saturation of both enzymes by cofactor pyridoxal phosphate, were studied in the substantia nigra of rats of both sexes. Although no sex differences were found in the in vitro measured characteristics of both enzymes involved in GABA metabolism, the turnover of GABA was greater in males. This finding is consistent with our previous reports showing the greater resistance of male rats to GABA-related convulsions.

Diazepam increases gamma-aminobutyric acid in human cerebrospinal fluid

In 11 neurological patients, levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) were determined in cerebrospinal fluid (CSF) before and 1, 3, 5, and 8 min after intravenous injection of diazepam (2 or 5 mg). GABA levels increased progressively after intravenous injection of 5 but not 2 mg of the benzodiazepine, the differences from preinjection values being significant at 3, 5, and 8 min. Furthermore, when relative CSF GABA alterations determined after injection of diazepam were compared to those determined in sequential CSF aliquots of 10 patients without diazepam injection, mean GABA increases after diazepam were significantly different from controls in all CSF fractions. The data suggest that, in addition to its well-known effects on postsynaptic GABA function, diazepam may exert effects on endogenous GABA concentrations and/or on GABA release in the human CNS as reflected by elevation of GABA levels in human CSF.

Effect of diazepam on brain neurotransmitters, plasma corticosterone, and the immune system of stressed rats

Rats were treated with injections of diazepam (1 or 10 mg/kg) and stressed by restraint lasting 3 hours. This was performed once or, in animals immunized with sheep erythrocytes, repeatedly for 4 consecutive days. After repeated stress and/or diazepam treatment, the levels of brain noradrenalin decreased in all treated groups. Although both treatments (stress and diazepam) diminished the 5-hydroxytryptamine (5-HT)/5-hydroxyindoleacetic acid (5-HIAA) ratio, treatment with either dose of diazepam prevented the stress-induced fall of this ratio. The activity of hypothalamic glutamate decarboxylase, the enzyme taking part in GABA synthesis, was affected neither by the acute nor by repeated stress and/or diazepam treatment. The levels of plasma corticosterone were enhanced in all stressed rats, with and without drug. This finding was in accordance with the enhanced weights of adrenal glands in repeatedly stressed rats. The tendency to a corticosterone rise after repeated treatment with diazepam, 10 mg/kg, coincided with the enhanced weights of adrenal glands in these animals. The plaque-forming cell (PFC) response was reduced in all stressed animals and in animals treated with diazepam, 10 mg/kg. Accordingly, high doses of diazepam given repeatedly to rats are immunosuppressive, achieving this effect presumably by an enhancement of glucocorticoid secretion. Neither the low nor the high doses of diazepam affect the stress-induced enhancement of hypothalamohypophysial-adrenal axis activity and consecutive immunosuppression.

Effects of chronic administration of phenobarbital in low doses on control of breathing in the cat

The ventilatory response to CO hypoxia (FICO = 0.0025), hypercapnia, and hypoxia was studied in a group of intact, conscious cats before and during chronic administration of phenobarbital (60 mg/day). It was found that the ventilatory response to hypercapnia or hypoxia was not significantly modified during phenobarbital administration. However, the ventilatory response to CO hypoxia was markedly blunted with phenobarbital: the initial ventilatory inhibition was still observed but the subsequent hyperventilation was delayed. Furthermore, the tachypnea was less intense and the decrease in tidal volume was smaller during CO hypoxia. In addition, the behavioral reactions which usually accompanied the tachypnea were attenuated and unconsciousness was often noted. These results indicate that the modifications caused by phenobarbital do not result from a general inhibition of the respiratory control network but rather from a selective inhibition of the structures rostral to the brain stem. As a consequence, the behavioral reactions and resulting respiratory activation were attenuated. Since the hypoxic tachypnea and behavioral reactions are observed only during central hypoxemia, it is concluded that arterial chemoreceptor afferents normally inhibit the supra-pontine structures which are otherwise stimulated by central hypoxemia.

Hypophysial GABA after ether stress, dexamethasone or inhibition of GABA catabolism

Ether stress (2 X 2 min within 15 min) and dexamethasone treatment (1 mg/kg IP; 1, 3 and 12 hours before sacrifice), the procedures supposed to increase the activity of glutamate decarboxylase (GAD) in the hypothalamus, fail to affect the concentration of GABA in the rat hypophysis. Five and/or ten minutes post-mortem an increased GABA level in the hypothalamus and cingulate cortex, and a decreased GABA concentration in the hypophysis was found. Three and four hours after the IP administration of 1-cycloserine (50 mg/kg) and 1-glutamic acid-gamma-hydrazide (160 mg/kg) respectively (both drugs are inhibitors of GABA catabolism) the concentration of GABA raised in all the regions examined. On the basis of studies in the whole gland it might be concluded that the concentration of GABA in the hypophysis depends more on GABA release from extrahypophysial tissue and GABA degradation in the hypophysis than on the extrahypophysial GABA synthesis. Also on the basis of post-mortem studies in the whole gland no indication for the appearance of GABA synthesis in hypophysis could be found.

Protective effects of diazepam and valproate on beta-vinyllactic acid-induced seizures

GABA level and the activity of L-glutamate-1-decarboxylase (GAD) (EC 4.1.1.15) were studied in brains of mice treated with beta-vinyllactic acid, a new, selective and pyridoxal phosphate-independent GAD inhibitor. Valproate and diazepam protected mice against convulsions caused by beta-vinyllactic acid although both anti-epileptic drugs antagonized neither the decrease in GABA concentrations nor the inhibition of GAD observed after treatment with beta-vinyllactic acid alone. Assuming that the anticonvulsant effect measured with both antiepileptics is GABA mediated, these results support the hypothesis of a postsynaptic enhancement of GABAergic transmission by diazepam and valproate.

Chronic ventilatory effects of diazepam and barbiturates in conscious cats

The chronic ventilatory effects of several hypnotics were investigated in six conscious cats recorded during control periods and during three consecutive days' administration of either diazepam (5 mg), pentobarbital (30 mg) or phenobarbital (60 mg). Ventilation was analyzed in terms of tidal volume (VT), breathing rate (BR) and minute ventilation (V = VT X BR). Minute ventilation was increased with diazepam owing to an increase in breathing rate in spite of a small decrease in tidal volume. With pentobarbital, minute ventilation was not changed because the decrease in breathing rate was compensated for by an increase in tidal volume. With phenobarbital, the results were more variable from one animal to another and on average, only tidal volume was increased. The animals were often excited following the administration of diazepam and sometimes drowsy with pentobarbital; with phenobarbital, behaviour varied among animals. Obviously, the present results cannot be extrapolated if different doses and perhaps different duration of drug administration are used. It is suggested that the ventilatory effects of the drugs cannot be explained only by a direct action on the brain stem respiratory network. Since the level of vigilance was altered by the various drugs, it is proposed that the ventilatory changes observed could be secondary to a supra-pontine action of the drugs which could modify both the level of alertness and respiratory activity.

The quinolines PK 8165 and PK 9084 possess benzodiazepine-like activity in vitro but not in vivo

The quinolines PK 8165 and PK 9084 bind to brain benzodiazepine receptors in vitro. However, unlike diazepam, these molecules do not reduce GABA turnover, possess anxiolytic properties, or displace [3H]flunitrazepam from benzodiazepine receptors in vivo. The pharmacological properties of PK 8165 and PK 9084 in vivo are thus unrelated to the benzodiazepine receptor.

Cortical GABA turnover during bicuculline seizures in rats

The rate of cortical gamma-aminobutyric acid (GABA) turnover was estimated by determining the rate of GABA accumulation following inhibition of GABA transaminase by gamma-vinyl-GABA (1.5 g/kg, i.v.) in paralysed, ventilated rats. During 1 h of bicuculline-induced seizures (1.2 mg/kg, i.v.) the rate of accumulation of cortical GABA level is approximately threefold greater than in the control group receiving gamma-vinyl-GABA alone, suggesting that the GABA shunt activity increases in parallel with the increase in overall cortical metabolic rate observed during bicuculline seizures. Pretreatment with gamma-vinyl-GABA did not affect the bicuculline-induced changes in other major cortical amino acids.

The influence of GABAergic drugs on PGO activity in the cat

The effects of drugs modifying GABAergic neurotransmission have been examined on ponto-geniculo-occipital (PGO) waves induced in the encéphale isolé cat by reserpine (PGOres), Ro4-1284 (PGO1284) or PCPA (PGOPCPA). The GABA agonists muscimol and THIP both caused large increases in density of PGOPCPA. The PGO1284 and PGOres were less affected although, of these, a larger increase in PGO1284 density was recorded. None of the increases could be reversed by subsequent injection of bicuculline. Chlordiazepoxide brought about large increases in PGOPCPA density but was ineffective in altering PGOres or PGO1284. The GABA transaminase inhibitor gamma-acetylenic GABA increased the density of all PGO waves but was not effective in the case of PGOPCPA. These results confirm a role for GABA in modulating PGO activity. The pathways involved in this GABA modulation are discussed.

Amino acids in the substantia nigra of rats with striatal lesions produced by kainic acid

In an attempt to estimate the pool size of glutamate and other amino acids in gamma-aminobutyric acid (GABA)-containing neurons, we determined the content of 12 amino acids in the bilateral substantia nigra of rats, in which unilateral striatal lesions had been made with kainic acid two weeks earlier. The assay of the amino acids (including glutamate, aspartate, glutamine, asparagine, glycine, and GABA) and ethanolamine was based on HPLC and fluorimetric detection after precolumn derivatization with omicron-phthaldialdehyde. The levels of all measured amino acids (except those of tyrosine, threonine, and ethanolamine) were decreased in the affected striatum, but only the levels of aspartate, taurine, and GABA were lowered in the ipsilateral substantia nigra. These results indicate that the pool size of the various amino acids in the striatonigral GABAergic pathway is small compared to their nigral content, and that in addition to GABA a significant fraction of aspartate and taurine may be confined to nerve terminals in the substantia nigra.

The effect of ethanol on GABAergic transmission

One of the many actions of ethanol involves the GABAergic system. The interaction of ethanol with GABAergic neurons is a complex one involving both presynaptic and postsynaptic sites. Through a presumed fluidization of membranes after a single dose of ethanol, the available in vitro evidence suggests that ethanol disrupts the normal functioning of the GABA-benzodiazepine-chloride ionophore complex in a complicated manner involving a sequential activation of different active sites leading to the facilitation of GABA transmission. This finding has been supported in vivo using electrophysiological techniques. Presynaptic GABAergic neurons may experience a reduced activity, especially at low doses of ethanol. After chronic ethanol treatment, GABAergic transmission may be reduced, especially during an ethanol withdrawal syndrome. Also, other changes in the GABA-benzodiazepine-chloride ionophore complex suggest GABA transmission is suppressed postsynaptically. Drugs which enhance the actions of GABA may be suitable inhibitors of the ethanol withdrawal syndrome. In particular a new class of drugs, the triazolopyridazines, may be promising compounds for treatment of withdrawal with a more specific mode of action and fewer side effects.

Effect of aminooxyacetic acid (AOAA) on GABA levels in some parts of the rat brain

The accumulation of GABA in the cerebellum and medulla oblongata-pons of rats has been studied after inhibition of GABA-T (EC 2.6.1.19) by different doses of AOAA. It was found that intraperitoneal (i.p.) injections of AOAA were, at least during the first hour after injection, much less effective than intravenous (i.v.) injections probably due to poor absorption i.p. After i.v. injection, AOAA caused a maximal accumulation of GABA in the cerebellum at a dose of 50 mg/kg. This maximal effect was virtually unchanged up to a dose of 150 mg/kg (the highest dose tested i.v.). If GAD (EC 4.1.1.15) was inhibited by 3-mercaptopropionic acid 30 min after AOAA (90 mg/kg i.v.) the GABA level was stable for at least another 30 min. The rate of GABA accumulation in the cerebellum during the first 15 min after AOAA (50-150 mg/kg i.v.) was 0.086 mumol/g/min and thereafter 0.034 mumol/g/min. It is concluded that AOAA in vivo in a wide dose range inhibits GABA-T almost 100% without affecting GAD to any great extent, and that the onset of action is rapid after i.v. but not after i.p. injection.

Synaptosomal uptake and release of dopamine in substantia nigra: effects of gamma-aminobutyric acid and substance P

Nigral tissue prepared as synaptosomes demonstrates both high and low affinity uptake of [3H]dopamine. Recently accumulated [3H]dopamine is releasable by 35 mN K+. Substance P increases both uptake and release of dopamine by nigral synaptosomes; gamma-aminobutyric acid (GABA) inhibits release with no effect on uptake at concentrations less than 10-(4) M. In the striatum, substance P inhibits both uptake and release of dopamine. The results support the existence of dopamine-containing terminals in substantia nigra tissue. The differences in response to substance P and GABA found between nigra and striatum may reflect structural differences in dopamine-containing processes in these areas, related to their proposed origin as dendtritic (substantia nigra) and axonal (striatal) terminal.

Benzodiazepines: potentiation of a GABA inhibitory response in the dorsal raphe nucleus

Based on evidence that the dorsal raphe nucleus (DR) has specific and independent receptors for 5HT, GABA and glycine (Gallager and Aghajanian, 1976; Wang and Aghajanian, 1977), alterations in the firing rate of DR neurons following the administration of benzodiazepines (BZ) were evaluated to determine whether they were the result of a direct interaction with 5HT receptors or due to interactions of these drugs with GABA and/or glycine. The effects of BZs after both direct and systemic application were tested in rats using microiotophoretic and single-cell recording techniques. Although the BZs did not alter the spontaneous firing rate of the DR, both the systemic and iontophoretic administration of these drugs were found to potentiate the inhibitory response produced by GABA. The data suggest that this potentiation is mediated postsynaptically. Since the effects of BZs on the spontaneous activity of the DR are only apparent following pretreatments with AOAA, it is speculated that these drugs may only have pronounced effects when GABAergic input is prominent.