Diazepam-induced NaCl solution intake: independence from renal factors

Benzodiazepine effects on licking responses for sodium chloride solutions in water-deprived male rats

The aim of this study was to investigate, for the first time, the effects of a centrally active benzodiazepine receptor agonist, midazolam maleate, on the microstructure of licking responses for a range of sodium chloride (NaCl) solutions in mildly water-deprived male rats. Doses of midazolam were chosen (0.3-3.0 mg/kg. i.p.) which have been characterised in studies of licking responses for several different kinds of nutrients. NaCl concentrations (0.075 M-0.45 M) were chosen to cover a range of taste preferences and acceptability. A brief-contact testing session was employed to focus on the initial determinants of licking responses (i.e. taste palatability), and to minimise any contribution of post-ingestional effects. The results indicate the midazolam significantly increased the total number of licks recorded across all salt concentrations, but that it had no effect on the number of bouts of licking. Instead, midazolam specifically enhanced the mean duration of licking bouts, an effect that was most evident at the weaker but more acceptable NaCl concentrations (0.075 M and 0.15 M). In addition, midazolam diminished the intrabout rate of licking across all salt concentrations. These results confirm that benzodiazepines can exert a specific pattern of effects on the microstructure of licking for salt solutions. They are discussed in terms of the oropharyngeal stimulation controlling intake and the palatability or "liking" hypothesis for the effects of benzodiazepines on taste stimuli, and indicate that the hypothesis is applicable to salt solution ingestive behaviour.

Sedation and need-free salt intake in rats treated with clonidine

The effect of intraperitoneal injection of clonidine (9-72 microg/kg) on need-free 1.5% NaCl intake and on performance (defined as percent of a complete trial) in the rotarod test, was studied in normovolemic adult male rats. Clonidine (18 and 36 microg/kg) inhibited the 1.5% NaCl intake in a 2-h test at doses that did not alter the performance in the rotarod test. The dose of 36 microg/kg did not inhibit 10% sucrose intake. Only the highest dose (72 microg/kg) of clonidine inhibited the 1.5% NaCl intake and the performance in the rotarod test, and produced signs of sedation. Sedation was determined either by change in posture (immobility or lack of postural tonus) of the animals during the ingestive test or by their performance in the rotarod test. The results suggest that sedation is not a determinant effect on the inhibition of 1.5% NaCl intake induced by clonidine.

Schedule-induced polydipsic consumption of hypertonic NaCl solutions: effects of chlordiazepoxide

Rats were exposed to daily, 3-h sessions of schedule-induced polydipsia (SIP) in which either water, hypertonic NaCl solution (1.5% or 2.2%), or concurrent water and 1.5% NaCl were available. Each condition was in effect for several, consecutive weeks. Presession subcutaneous injections of chlordiazepoxide (CDZP) produced dose-related increases in the polydipsic ingestion of both NaCl solutions but had smaller and less certain effects on water consumption. Under the concurrent-fluid presentation condition, CDZP primarily increased NaCl solution consumption. Conditions generating SIP may function to attenuate what might be viewed as the punishing effects of ingesting highly hypertonic NaCl solutions, thereby permitting the chronic self-administration of large, daily amounts. Like many benzodiazepines, CDZP can attenuate the effects of punishment and thereby also increase NaCl solution ingestion. The two sources of punishment attenuation may be additive, with both differentially effecting greater increases in hypertonic NaCl ingestion, compared to water, when both fluids are presented concurrently.

Effects of ethanol, caffeine, and clorazepate on hypertonic NaCl solution intake in rats

Previous reports indicate that several anxiolytics enhance the intake of hypertonic saline in rehydrating rats. This experiment was conducted to determine the effects of repeated (5 sessions) injection (i.p.) of ethanol (0.4 or 0.8 g/kg), caffeine (20 or 40 mg/kg) or clorazepate (3 mg/kg) on the ingestion of hypertonic saline (1.8%) in water-deprived rats. Saline intake increased with the acute administration of both clorazepate and ethanol (two doses), but it decreased with caffeine (two doses). It seems that the increase or decrease of hypertonic saline ingestion following acute drug administration continues to correlate well with anxiolytic or anxiogenic actions. However, following repeated administration of caffeine and ethanol, the effects on saline intake were not maintained in a reliable manner.

Anxiolytic effect of caffeine and caffeine-clonazepam interaction: evaluation by NaCl solution intake

The administration of drugs with anxiolytic action to rehydrating rats augments the intake of 1.5% NaCl solution. In order to clarify the status of caffeine as an anxiolytic agent and its possible interaction with a benzodiazepine having high potency and efficacy in this regard, caffeine (0.78-100 mg/kg) alone and caffeine (0.78-50 mg/kg) plus clonazepam (0.05 or 0.50 mg/kg) injections (IP) were administered to rehydrating rats prior to 1-hr sessions during which they drank 1.5% NaCl solution. When given alone, caffeine, within a particular dose range, and clonazepam at both doses, augmented NaCl solution intake, but when administered in combination, caffeine antagonized the effects of clonazepam.

Selective reduction by serotonergic agents of hypertonic saline consumption in rats: evidence for possible 5-HT1C receptor mediation

Previously, it has been shown that, in small doses, putative 5-HT1A receptor agonists selectively increase ingestion of hypertonic saline without affecting either water or isotonic saline intake. Evidence was obtained in the present series of experiments for selective reduction in hypertonic saline following the administration of a variety of serotonergic directly- and indirectly-acting agonists. Water, isotonic saline (0.9%), or hypertonic saline (1.8%) were made available to separate groups of water-deprived rats. The results indicated some selectivity with the 5-HT-uptake inhibitor and releaser d-fenfluramine and the 5-HT uptake inhibitor fluoxetine, and with the 5-HT agonists mCPP [1-3-chlorophenyl)piperazine] and MK 212 [6-chloro-2-(1-piperazinyl)pyrazine]. In each case, hypertonic intake was significantly suppressed. Distinct from these compounds were TFMPP [1-(3-(trifluoromethyl)phenyl)piperazine], RU 24969 [5-methoxy-3-(1,2,3,6-tetrahydropyridinyl)1H-indole], and quipazine. This second group either reduced fluid intake indiscriminately or reduced water and isotonic saline drinking. Selective reduction in the intake of hypertonic saline did not occur. Finally, peripheral-administration of 5-HT or the 5-HT1B agonist CGS 12066B [7-trifluoromethyl-4(4-methyl-1-piperazinyl-pyrolo) (1,2-a) 1:2 maleate], had no significant effect on fluid intake in any fluid condition. The results are discussed in terms of a possible serotonergic mechanism which may underlie inhibition of hypertonic salt drinking, and which involves mediation through a subtype of the 5-HT1 receptor.

The role of central- and peripheral-type benzodiazepine receptors in anxiolytic-agent augmentation of NaCl solution intake: effects of clonazepam and Ro 5-4864

Two 1,4 benzodiazepines bind preferentially to the central- and peripheral-type benzodiazepine receptor in the brain, clonazepam and Ro 5-4864, respectively. They were administered to rats to determine if the relation between known anxiolytic action and efficacy in augmenting NaCl solution ingestion in rehydrating rats would remain the case for these prototypic agents. Clonazepam (0.062-32.0 mg/kg, PO) was highly potent and efficacious and increased 1.5% NaCl solution intake in a dose-related fashion. Water intake could also be increased, but to a relatively minor degree. Ro 5-4864 (4-8 mg/kg, IP) did not affect 1.5% NaCl solution ingestion, nor did this dose range suppress the augmenting effect of clonazepam (0.5-2.0 mg/kg, PO) on the solution intake. Since clonazepam does, and Ro 5-4864 does not, possess punishment-attenuation properties in other tests, drug augmentation of NaCl solution ingestion by rehydrating rats continues to correlate well with known anxiolytic action.

Specific effect of putative 5-HT1A agonists, 8-OH-DPAT and gepirone, to increase hypertonic saline consumption in the rat: evidence against a general hyperdipsic action

Previous reports indicate that 5-HT1A agonists, in addition to benzodiazepines, increase the consumption of hypertonic saline in rehydrating rats. Experiment 1 investigated the effects of 8-OH-DPAT (10-100 micrograms/kg) and gepirone (0.1-3.0 mg/kg) on consumption of water and of saline over a range of concentrations (0.45%-2.8%) in a 30 min drinking test. The two 5-HT1A agonists dose-dependently increased ingestion of two hypertonic salt solutions, but produced little or no increase in the drinking of water, hypotonic or isotonic saline. Experiment 2 demonstrated that 8-OH-DPAT and gepirone did not enhance water consumption in animals given a water preload, or markedly increase drinking quinine-adulterated water. Taken together, the results indicate a selective dose-related effect of the two drugs to increase hypertonic saline drinking; they did not have a general hyperdipsic effect across all salt and water conditions, and they did not increase intake simply because of a low baseline level of consumption. Hence, 5-HT1A agonist act much more selectively than benzodiazepines in their effects on drinking responses.

Benzodiazepines and putative 5-HT1A agonists increase hypertonic saline consumption in rehydrating rats

Male rats were adapted to a 22 hr water-deprivation schedule, and to a 30 min test of hypertonic (1.8 or 2.7%) NaCl solution ingestion. A novel benzodiazepine, Ro23-0364, recently reported to have anxiolytic activity in rats and squirrel monkeys but to have limited potential to produce unwanted side effects, produced significant dose-related increases in hypertonic saline ingestion. Midazolam, a benzodiazepine full agonist, increased salt intake but the effect was offset at higher doses by the induction of sedation. Three putative 5-HT1A agonists, proposed as nonbenzodiazepine-related anxiolytics, were also tested: the highly selective 8-OH-DPAT, gepirone and ipsapirone (TVX Q 7821). In each case, occasions when hypertonic saline consumption was significantly increased were detected. At 300 micrograms/kg of 8-OH-DPAT and 10 mg/kg of gepirone, the appearance of a pronounced flattened body posture effectively interfered with drinking responses. It appears possible that a behavioural action shared by benzodiazepines and 5-HT1A agonists may be responsible for the increased hypertonic saline ingestion.

Characteristics of reserpine-induced suppression of NaCl solution intake in rats

Effects of single and repeated administration of reserpine on time-limited drinking of a hypertonic (1.5% w/w) NaCl solution were investigated in rats to assess whether this drug possesses anxiolytic action. Rats adapted to a 23-hr water-deprivation schedule with a free-feeding regimen were allowed a daily 1-hr water rehydration session. In the single-administration experiment, reserpine (0.1, 0.2 and 0.4 mg/kg, IP) was administered to rats at 15 min or 23 hr before a drinking session, where the fluid available was 1.5% NaCl solution. Drug was administered every 7th day. In the repeated-administration experiment, reserpine (0.1 mg/kg/day) was injected daily for 10 days 15 min before each drinking session. The fluid available was water on the first 9 days and NaCl solution on the 10th day. Reserpine suppressed NaCl solution intake when it was singly administered at 15 min before the rehydration, whereas no significant change in the fluid intake occurred when it was administered 23 hr before drinking, even though rats showed ptosis in response to 0.2 and 0.4 mg/kg doses. Tolerance developed to the suppressing effect of repeated administration of reserpine on fluid intake, although ptosis and sedation continued and body weights decreased. Tolerance was almost complete after 11 days. The results suggest that reserpine does not have an anxiolytic effect.

Novel benzodiazepine receptor ligands stimulate intake of hypertonic NaCl solution in rehydrating rats

Experiments were conducted to determine the degree of generality of previous findings that anxiolytics increased the ingestion of hypertonic saline in rehydrating rats. Further, potential differential effects amongst recently described benzodiazepine receptor partial agonists were explored. Finally, the hypothesis that benzodiazepine receptor partial inverse agonists would decrease the ingestion of hypertonic NaCl solution was tested. Results indicated that full agonists (midazolam, ZK 93423, zopiclone) produced substantial dose-related increases in hypertonic saline consumption. The putative 5-HT1A agonist, buspirone, produced only a dose-dependent decrease in saline intake. Partial agonists fell into two distinct categories: ZK 91296, CL 218,872 and two novel benzodiazepines, Ro16-6028 and Ro17-1812, also increased saline ingestion. In contrast, two pyrazoloquinolines, CGS 9896 and CGS 9895, had no significant effect on intake. Two compounds, CGS 8216 and FG 7142, described as benzodiazepine partial inverse agonists, did not significantly affect consumption of the hypertonic saline.

Differential effects of benzodiazepine receptor ligands on isotonic saline and water consumption in water-deprived rats

Water-deprived male rats were adapted to a 30 min test of water or saline drinking in a single-bottle acceptance test. The potent benzodiazepine agonist, clonazepam, produced significant increases in both water and saline consumption. Increases in the consumption of both were also obtained with the non-benzodiazepine agonist, zopiclone (a cyclopyrrolone), but not with the pyrazoloquinoline agonist, CGS 9896. Hence, some, but not all, benzodiazepine receptor agonists enhance drinking responses. The benzodiazepine receptor antagonists, Ro15-1788 and CGS 8216, had no significant effect on the intake of either isotonic saline or water. In contrast, the beta-carboline FG 7142, which has been described as an inverse agonist acting at benzodiazepine receptors, reduced both saline and water drinking at 10 and 20 mg/kg. Although the baseline level of saline drinking was considerably higher than that of water, there was no general indication that any drug effect on consumption interacted with the type of fluid in the drinking test. However, in the case of agonist-induced increases in consumption, peak effects occurred at different doses; they were lower for saline- than for water-drinking.

Partial agonists acting at benzodiazepine receptors can be differentiated in tests of ingestional behaviour

Several categories of compounds active at benzodiazepine receptors (BZR) in the brain have been distinguished: agonists, antagonists and the novel category of inverse agonist. In terms of their effects on ingestional responses (e.g., food, saline and water consumption), agonists increase levels of intake, inverse agonists reduce intake in some, if not all, tests, while antagonists block the effects of both agonists and inverse agonists. Attention is currently focussed upon a range of compounds which fall between full agonists and antagonists. These partial agonists are of particular interest since they act more selectively than full agonists, retaining effects in animal models of anxiolytic and anticonvulsant activity, for example, while largely lacking behaviourally-depressant effects. Recent data indicate that tests of ingestional behaviour distinguish between various BZR partial agonists. The benzodiazepines Ro23-0364, Ro16-6028 and Ro17-1812, as well as the beta-carboline ZK 91296, enhanced ingestional responses. The pyrazoloquinolines, CGS 9895 and CGS 9896, did not, but antagonized agonist-induced increases in ingestion.

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.

Animal models for the study of anti-anxiety agents: a review

Animal models for the study of anxiolytic agents are reviewed and evaluated according to pharmacological and behavioral criteria. Although there are important exceptions, in general, most early animal models have not provided a reliable basis for identifying compounds with potential anxiolytic action, or for delineating the mechanisms of anxiolytic drug action. The possibility that phylogenetically 'prepared' forms of defensive learning might serve as a basis for the study of anxiolytic agents is introduced.

A microgram dose of diazepam produces specific inhibition of ambulation in the rat

There is considerable consistency in the experimental literature showing that non-sedating doses of benzodiazepines can enhance the consumption of food, water and salt solutions. It is of great interest, therefore, that in a previous report low dose treatments with diazepam were found to significantly suppress the level of consumption of a palatable 0.005 M sodium saccharin solution in nondeprived male rats. The present study was designed to elucidate the behavioral characteristics of the inhibitory action of low dose diazepam treatments. Food consumption and general activity measures were chosen for analysis to examine the possibilities that low dose diazepam treatments might suppress ingestive behavior in a general way, or that the treatments might affect nonconsummatory responses including components of spontaneous motor activity. The results of two experiments succeeded in locating a highly specific inhibitory effect produced by 100 micrograms/kg diazepam. First, food consumption was not inhibited. Instead, 1.0 mg/kg diazepam produced significant elevations in food intake in both food-deprived and nondeprived animals. Second, vertical activity (rearing) and fine body movements were unaffected over the dose-range 0.1-3.0 mg/kg diazepam. Hence, low dose treatments with diazepam did not produce a generalised nonspecific behavioral depression. However, 100 micrograms/mg diazepam significantly inhibited coarse activity (measured automatically) and the corresponding ambulation measure (recorded by direct observation). The effect was present throughout a 1 hr test period and did not interact with the declining baseline level of activity. The results therefore confirm the presence of low dose diazepam-induced behavioral inhibition in quite a different context from the saccharin solution consumption study.(ABSTRACT TRUNCATED AT 250 WORDS)

Midazolam-induced increase in NaCl solution ingestion: differential effect of the benzodiazepine antagonists Ro 15-1788 and CGS 8216

After adaptation to a 23-hr water deprivation regimen, under which rats were allowed a daily 1-hr water rehydration session, they were injected (SC) with 1 or 2 drugs presession and given 1.5% NaCl solution to drink in place of water. Midazolam (0.5-1.0 mg/kg) increased the intake of 1.5% NaCl solution as did Ro 15-1788 (2.5-10.0 mg/kg). This confirmed a previously noted agonist effect of midazolam and partial agonist action of Ro 15-1788. When injected in combination with midazolam, Ro 15-1788 (2.5-10.0 mg/kg) antagonized the effect of midazolam. CGS 8216 (2.5-20.0 mg/kg) revealed no partial agonist action on the NaCl solution ingestion procedure nor did it block the effect of midazolam.

Chlordiazepoxide injection elevates the NaCl solution acceptance-rejection function

Injection (SC) of chlordiazepoxide (2-8 mg/kg) increased the intake of NaCl solution (0.5-3.0% NaCl) as well as water in water-deprived rats when these fluids were made available singly during daily 1-hr rehydration periods. The marked enhancement of this drug effect when NaCl solution was the available fluid does not appear to be due to the induction of a sodium appetite or the mimicking of an increase in water deprivation. The exaggeration of the drug effect when an NaCl solution is the drinking fluid, as opposed to water, may be useful as a sensitive index of action for punishment-attenuating (anxiolytic) drugs.