Evidence of a role for GABA in benzodiazepine effects on food preference in rats

Neonatal administration of a GABA-T inhibitor alters central GABAA receptor mechanisms and alcohol drinking in adult rats

Long-term effects of chronic treatment with a GABA-T (GABA-transaminase) inhibitor, ethanolamine O-sulphate (EOS) (200 mg/kg/day for the postnatal days 3-21) on the binding parameters of GABAA receptors, hypothalamic monoamines and subsequent behavior were studied in Wistar rats. At the age of 1 month, EOS-treated rats showed reduced activity in the open-field and, at the age of 4 months, their voluntary alcohol consumption was increased. No changes were seen in Porsolt's swim test or in the plus-maze test. Weight gain was significantly retarded in EOS-treated rats. Maximal stimulation of [3H] flunitrazepam binding by GABA was decreased in the cerebral cortex and the EC50-value for the GABA stimulation increased in the hippocampus in the EOS rats at the age of 4 months. EOS treatment did not alter the cerebellar diazepam sensitive and insensitive binding components of the imidazobenzodiazepine [3H]Ro 15-4513. No changes were observed in the hypothalamic monoamine concentrations. The results are in agreement with the idea that GABA-T inhibitor treatment permanently alters GABAA mechanisms. Moreover, altering the CNS GABA level during development increases adult alcohol intake in rat.

Behavioral effects of GABA agonists in relation to anxiety and benzodiazepine action

A considerable body of biochemical and neurophysiological evidence implicates GABA in anxiety and in benzodiazepine action. The present article surveys the behavioral effects of GABA agonists and their interactions with drugs acting at the benzodiazepine receptor in animal anxiety paradigms. Certain GABA agonists, notably valproate, simulate many behavioral actions of benzodiazepines. Moreover, several behavioral studies of the interaction of GABA agonists with benzodiazepines support the hypothesis of a benzodiazepine receptor complex with one or more GABA, benzodiazepine and probably other binding sites. However, there are also a number of anomalous findings of GABA agonist action alone and in combination with benzodiazepines. It is argued that these paradoxical results can better be accounted for in terms of the receptor complex and the distribution of the drugs, rather than by suggesting that the anxiolytic actions of benzodiazepines are not mediated by GABA systems. The potential clinical usefulness of GABA agonists in anxiety is commented upon.

Chlordiazepoxide-induced selection of saccharin-flavoured food in the food-deprived rat

Following a period of food-deprivation, adult male rats were given a choice between three sources of food in a 15 min test. All three consisted of a mash of powdered food and water; saccharin and quinine were added to two of them, respectively. Chlordiazepoxide (5 and 10 mg/kg, IP) significantly reduced the latency to begin eating, and also increased the overall level of food consumption. Its hyperphagic effect was due to a selective increase in ingestion of the saccharin-flavoured food, and was not due to a general increase in food consumption across all three food sources. Analysis of the micro-structure of feeding indicated that the increase in food intake depended upon an increase in the duration of individual bouts. Other feeding parameters were not significantly affected by chlordiazepoxide. These data suggest the CDP treatments affect feeding behaviour selectively, both in relation to the taste characteristics of the food, and also with regard to alterations in the micro-structure of the feeding responses.

Neurotransmitters, anxiety and benzodiazepines: a behavioral review

The possible involvement of serotonin, GABA and opioid peptides in anxiety and in the mechanism of action of benzodiazepine tranquilizers have recently been the subjects of intensive biochemical, neurophysiological and behavioral research. The present review examines the behavioral evidence, viewing anxiety and benzodiazepine action as far as possible separately. Four behavioral paradigms of experimental anxiety or "conflict behaviors" are described and assessed for soundness with some practical considerations. The functional significance and pharmacology of benzodiazepine receptors are discussed, and the cases for a number of putative endogenous ligands are examined. Conflict behavior is attenuated by drugs which reduce functional serotonin activity and enhanced by serotonin agonists, but there is little evidence to implicate serotonin in benzodiazepine action. GABA antagonists both intensify conflict and reduce benzodiazepine effects, but evidence of the reverse effects with GABA agonists is more equivocal. The interpretation of behavioral effects of opiate agonists and antagonists and their interactions with benzodiazepines is hindered by their actions on motivational systems other than anxiety, and evidence for an important role of opioid peptides is only suggestive. Some promising lines for future research are indicated.

Effects of chlordiazepoxide and sodium valproate in two tests of spatial behaviour

The effects of chlordiazepoxide (CDP) and sodium valproate (VPA) were studied in rats trained to asymptotic performance on two tests of spatial behaviour, the 8-arm radial maze and the 8-choice arena. The task in the 8-arm maze was to locate a single food pellet at the end of each arm. Both CDP and VPA caused an increase in errors, an increase in performance time, and the utilization of a non-spatial response strategy. The task in the 8-choice arena was to locate a single water bottle from an octagonal array of eight otherwise empty bottles. For one group the goal bottle remained in the same place from trial to trial; for a second group the position of the goal bottle was cued by a black card over the nozzle; for the third group the goal bottle was uncued and moved randomly from trial to trial. VPA had no effect on performance, but CDP impaired performance in all three groups. These patterns of effects suggest that VPA may specifically disrupt working memory, but that the impairment of spatial performance by CDP probably results from a non-specific perceptual or attentional deficit.

GABA and the behavioral effects of anxiolytic drugs

Much recent research has shown that benzodiazepine binding sites in the central nervous system are associated with GABA receptors. It is therefore possible that the pharmacological and therapeutic effects of benzodiazepines and drugs with similar profiles are mediated through GABAergic mechanisms. In this paper the evidence is considered for a possible involvement of GABA in the behavioral effects of anxiolytic drugs. There are a number of reports that the behavioral actions of anxiolytics can be antagonised by GABA antagonists such as bicuculline or picrotoxin but there are many contradictory findings and these drugs are difficult to use effectively in behavioral studies. In general, GABA agonists do not exert anxiolytic-like behavioral effects after systemic injection but intracerebral administration of muscimol has been shown to produce benzodiazepine-like actions. Although a number of questions remain unanswered, current evidence does not provide strong support for a role for GABA in the behavioral effects of anxiolytic drugs.

Behavioural pharmacology of food, water and salt intake in relation to drug actions at benzodiazepine receptors

Drugs which are agonists at benzodiazepine receptors produce many interesting behavioural effects, and amongst these are the stimulation of food, water and salt intake. This review examines the evidence for benzodiazepine effects on these forms of ingestion, and makes tentative proposals about their modes of action. The recent advent of putative benzodiazepine antagonists and inverse agonists provides important new pharmacological tools for the analysis of factors which control ingestion. Preliminary data on examples of such drugs are considered. Anorectic effects of inverse agonists are described. It is clear, though, that the categorization of a drug in one test situation may not apply to another. For example, the compound Ro15-1788 appears as a specific antagonist in one test, a partial agonist in another, and apparently lacks effect in a third. We are not yet sufficiently forward in our understanding of drug actions at benzodiazepine receptors, and their interactions with particular test circumstances, to predict and account for divergent effects of this kind.

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

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

Chlordiazepoxide-induced hyperphagia in rats: lack of effect of GABA agonists and antagonists

Because of the evidence that benzodiazepine binding sites are associated with GABA receptors in the central nervous system, it has been suggested that the behavioural effects of benzodiazepines may be mediated by GABAergic mechanisms. In order to investigate this hypothesis in relation to the hyperphagia produced by benzodiazepines, the effects of chlordiazepoxide were compared with those of the GABA agonists progabide and muscimol and the GABA antagonists picrotoxin and bicuculline. In rats adapted to a 22 h/day food deprivation schedule chlordiazepoxide produced a dose-related increase in food intake. Neither progabide nor muscimol produced a similar effect after IP injection, nor did these drugs potentiate the effects of a dose of chlordiazepoxide. Picrotoxin and bicuculline, each given at a sub-convulsant dose, did not affect quantities of food consumed and also did not antagonise the effect of chlordiazepoxide. These results provide no evidence for the hypothesis that chlordiazepoxide-induced hyperphagia in rats is mediated by GABAergic mechanisms.

Minireview. Benzodiazepine-opiate antagonist interactions in relation to feeding and drinking behavior

Benzodiazepines reliably produce overconsumption of food and fluids. Opiate antagonists, naloxone and naltrexone, block the benzodiazepine-induced hyperphagia and hyperdipsia at low doses. Hence, activation of endogenous opioid mechanisms may be closely involved in the benzodiazepine facilitatory effects on ingestional behavior. Evidence is reviewed that opiate antagonists diminish feeding and drinking responses, and may enhance satiety processes in feeding and drinking, in addition to selectively diminishing the palatability of attractive foods and fluids. It is proposed that a single mechanism of action of the opiate antagonists would be sufficient to account for both effects on feeding and drinking. Biochemical data confirm that acute benzodiazepine treatment in vivo is associated with a naloxone-reversible release of striatal enkephalin. It is possible therefore that there is a close association between the behavioral and biochemical data, which both show that acute benzodiazepine effects are reversed by opiate antagonists. The implied relationship between benzodiazepine and endogenous opioid mechanisms may be relevant to the question of concurrent opiate-benzodiazepine abuse.

GABA and endorphin mechanisms in relation to the effects of benzodiazepines on feeding and drinking

Behavioural actions of benzodiazepines have a number of significant characteristics. Anxiolytic effects are demonstrable both clinically and experimentally; in addition, there is excellent evidence for a reinforcing effect of these compounds, and a direct involvement in ingestional responses. This review focusses on the effects of benzodiazepines on the latter feeding and drinking responses. A necessary mediator of benzodiazepine action in the central nervous system appears to be the facilitation of inhibitory GABAergic neurotransmission. It follows, therefore, that behavioural consequences of benzodiazepine action may depend crucially on enhanced GABAergic activity in the brain. Evidence for some involvement of GABAergic mechanisms in the control of feeding and drinking responses is reviewed. Only a few data are so far available to link benzodiazepines effects on ingestional behaviour directly to GABAergic transmission. A major current theme in the psychopharmacology of feeding and drinking behaviour is the possible involvement of endogenous opioid peptides. There is a strong suggestion in the experimental data that there are links between benzodiazepine and endorphinergic mechanisms in relation to ingestional responses. A promising future line of approach appears to be a delineation of benzodiazepine-GABA-endorphin interrelations in the control of food and water consumption.

The effects of chronic diazepam treatment on body weight and food intake in rats

A series of experiments are reported in all of which the effects of chronic (14-18 days) diazepam treatment on body weight were evaluated under various conditions, and one experiment in which weight gain and daily food intake were monitored simultaneously. The effect of diazepam treatment on body weight was compared to that of vehicle treatment in the following groups: (1) young adult females, (2) pregnant females, (3) shock treated young males (4) nonshocked young males. The effect of diazepam treatment on prenatally diazepam exposed and nonexposed males and females was investigated at seven months of age. Food intake was also measured during chronic diazepam and vehicle treatment. The findings show consistent and reliable differences between diazepam and vehicle treatment. Diazepam treated animals eat less in the long run and gain less weight than vehicle treated controls. Prenatal exposure to diazepam enhances the effect of diazepam treatment in adulthood.

Effects of THIP on chronic anxiety

The effects of THIP, a GABA agonist, were examined in patients with anxiety disorders. Eight patients were prescribed THIP (5-20 mg) to be taken three times a day for 2 weeks in a single-blind study, with placebo conditions preceding and following the active drug period. Anxiety ratings significantly decreased on several measures during active drug treatment and increased again with placebo administration. However, the anxiolytic effects of THIP appeared to be weak and occurred at, or close to dose levels which induced sedation and undesirable side effects. As with other GABA agonists and GABA-mimetic drugs, side effects included giddiness, depersonalization, poor concentration, and transitory delirious states, suggesting that excessive stimulation of the GABAergic system may disrupt normal brain functioning.

Effects of chronic chlordiazepoxide treatment on novel and familiar food preference in rats

Chlordiazepoxide (CDP) given acutely has been found to have dose-related effects in rats given food preference tests. Low doses selectively increase consumption of familiar food, while high doses increase novel food consumption. The present study examined the effects of three doses of CDP given chronically. All doses (2.5, 5.0 and 10.0 mg/kg) selectively increased novel food eating. There was some evidence for a selective retardation of eating rate for familiar food and an enhanced taste preference for sweet food in CDP-treated rats. However, the overall results suggest that increased consumption of novel food represents an antineophobic action of CDP, which is potentiated by chronic treatment over a low to medium dose range.