Mechanisms of the initial treatment phenomenon to diazepam in the rat

Tolerance to the anticonflict effects of diazepam: importance of methodological considerations

The present study examines the effects of chronic diazepam treatment on conflict behavior in rats using the Geller-Seifter paradigm. A dose-response function for the effects of diazepam (DZ) on punished and unpunished responding was determined (0.0, 0.63, 1.25, 2.5, and 5.0 mg/kg DZ intraperitoneally) using five independent groups. The test doses of DZ produced an inverted U-shaped function where punished responding increased as a function of dose up to 2.5 mg/kg and then decreased at 5.0 mg/kg. All groups were then treated with 2 x 5 mg/kg DZ per day for 5 days. When the dose-response function was redetermined at 36 h post-chronic treatment, it was found that the function had shifted to the right, indicating tolerance. Because of the inverted U-shaped nature of the original function, tolerance was manifested as a decrease in responding on the ascending portion of the function and as an increase in responding on the dose (5 mg/kg) representing the descending side of the inverted U.

Initial subsensitivity to anxiolytic treatments on conflict behavior in rats: parametric studies across drug classes

In conflict paradigms, benzodiazepines (BZs) often exhibit maximal anticonflict effects only after three to four BZ exposures (anxiolytic initial subsensitivity; AIS). The present experiments examined 1) whether AIS occurs with non-BZ anxiolytics and 2) whether prior exposure to non-BZs prevents the occurrence of BZ AIS. Female rats were trained to stable responding levels on a repeated-measures punished drinking paradigm. In Experiment 1, dose-response curves for the effects of the BZs chlordiazepoxide and diazepam, the barbiturates (BBs) pentobarbital and amobarbital, and the non-BZ, non-BB agent carbamazepine were determined in five groups of rats (one group/drug); dose-response curves were determined on two occasions for each drug. There was an AIS with both BZs, with the anticonflict effect being significantly greater for dose-response determination #2. There was no AIS with the BBs (robust and dose-dependent increases in punished responding on both determinations) or with carbamazepine (weak anticonflict effect on both determinations). In Experiment 2, the rats from Experiment 1 received a single-dose challenge with chlordiazepoxide (10 mg/kg). This challenge resulted in a robust anticonflict effect in subjects with a history of repeated BZ treatment; in contrast, subjects with a history of repeated BB or carbamazepine treatment exhibited smaller anticonflict responses. These data suggest that 1) the AIS does not occur with non-BZ anxiolytics and 2) the BZ AIS cannot be prevented by repeated exposure to non-BZs.

Cellular and learned tolerances to chlordiazepoxide hypothermia and ataxia

Four groups of rats received chlordiazepoxide (CDP): a) intermittently, experiencing hypothermia and rotarod performance (RR) deficit after test doses (contingency); b) chronically, experiencing hypothermia and RR deficit after test doses; c) intermittently, RR preceding test doses and with protection against hypothermia afforded by exposure to heat lamps (nonexperienced, noncontingency); and d) chronically, RR preceding test doses and with protection against hypothermia. After 36 days of chronic CDP (groups 2 and 4) or vehicle (groups 1 and 3), all groups experienced RR and body temperature (BT) drug deficits after test doses of CDP at the postwithdrawal test. Group 1 but not group 3 was tolerant to peak hypothermia of the drug. Both chronic groups (2 and 4) showed marked tolerance to hypothermia. At the postwithdrawal test, after discontinuing chronic CDP or vehicle for 9 days, only groups 2 and 4 lost drug tolerance to hypothermia. After extinction training (daily testing of RR and BT after injecting vehicle over 9 days), group 2 but not group 4 was again less sensitive to CDP-induced hypothermia at the postextinction test. Regarding CDP-induced RR ataxia, group 1 was more tolerant than group 3 at the postchronic test, while group 4 but not group 2 also showed tolerance to ataxia. At the postwithdrawal test, only group 4 lost tolerance to peak RR ataxic effects of CDP. At the postextinction test, only group 1 lost tolerance for ataxia relative to postchronic test results.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic anxiolytic treatment effects on conflict behavior in the rat

The present studies examined the effects of chronic posttest treatment with the antipanic agent alprazolam (ALP) or the traditional anxiolytic agents chlordiazepoxide (CDP) and phenobarbital (PhB) on conflict behavior. In daily ten-minute sessions, water-deprived rats were trained to drink from a tube which was occasionally electrified (0.25 or 0.5 mA). Electrification was signalled by a tone. Chronic ALP (10 mg/kg/day), CDP (40 mg/kg/day), PhB (80 mg/kg/day) or vehicle were injected IP after conflict testing (in some experiments again 12-16 hours later) for a minimum of 6 weeks. Chronic ALP (but not CDP or PhB) resulted in a time-dependent increase in punished responding, with a latency to onset of 3-4 weeks; this effect was not antagonized by the benzodiazepine antagonist Ro15-1788. These data support the hypothesis that conflict paradigms may serve as animal models for the study of antipanic agents. Moreover, these data suggest that not all anxiolytics will exhibit antipanic efficacy.

The natural history of tolerance to the benzodiazepines

Dependence on benzodiazepines following continued use is by now a well-documented clinical phenomenon. Benzodiazepines differ in their dependence potential. The present studies were aimed at examining the possibility that differential rates of tolerance development might account for differences in dependence risk. Four studies are reported. The first three studies concerned normal subjects. The development of tolerance over a fifteen day period was demonstrated for three different benzodiazepines (ketazolam, lorazepam and triazolam) using two paradigms. Tolerance in terms of a reduction in effectiveness of a repeated given dose was most notable for the benzodiazepine with a medium elimination half-life (lorazepam) for physiological, behavioural and subjective measures. In the case of the drug with the longest elimination half-life (ketazolam) reduction in effectiveness could only be assumed to be occurring if account was taken of the steady increase in plasma concentrations of active metabolites. For this drug it seemed that the physiological measures were those most likely to demonstrate the development of tolerance. Although triazolam showed few significant drug effects on this paradigm (testing being 12 hours after ingestion of this short half-life benzodiazepine), tolerance was seen to develop on some subjective measures. Using an alternative method of testing tolerance, assessing responses to a diazepam challenge dose, a high degree of tolerance on two-thirds of the measures was observed in subjects when pretreated with the benzodiazepine with the most marked accumulation of active metabolites (ketazolam). The other two drugs also led to tolerance development on a range of measures; this was more marked for lorazepam than triazolam. Blunting of the growth hormone response to diazepam was the most sensitive and reliable method of detecting tolerance to the benzodiazepines. Symptoms on discontinuation of the two weeks' intake of the benzodiazepines were marked for all the drugs but unrelated to either the tolerance induced or the elimination half-life of the particular drug. A further clinical study revealed that tolerance persisted in a group of long-term benzodiazepine users for between four months and two years following complete abstinence from the drug. These patients appeared to be less affected by diazepam in terms of its commonly observed subjective effects, regardless of their original medication. These ex-long-term users of benzodiazepines were, however, more likely to manifest two specific types of effects--immediate 'symptom' reduction and exacerbation of 'withdrawal symptoms' over the subsequent week.(ABSTRACT TRUNCATED AT 400 WORDS)

Diazepam-ethanol interaction: initial treatment and combined treatment effects

Water-deprived female Sprague-Dawley rats were trained in a conditioned suppression of drinking paradigm. Experiment 1 assessed the effects of prior experience with ethanol on the initial treatment deficit of diazepam (1A) and the influence of prior experience with diazepam on the initial treatment effects of ethanol (1B). In Experiment 1A, half the animals received three daily doses of ethanol, while the other half received vehicle for 3 days. All rats then received vehicle followed by 3 days of ethanol treatment. No significant effect of prior experience with ethanol was observed on the diazepam initial treatment deficit. In Experiment 1B, half the animals received vehicle followed by three daily doses of diazepam, while the other half received vehicle. All subjects then received vehicle followed by 3 days of ethanol treatment. No significant effect of prior experience with diazepam was noted on ethanol's initial treatment effects. Experiment 2 assessed the effects of diazepam (0, 1, 2, and 4 mg/kg) and ethanol (0, 0.5, 1 and 2 g/kg) alone and in combination in the conflict test. Diazepam, administered alone, resulted in an antipunishment effect. Ethanol alone did not produce an antipunishment effect. The combination of the two drugs generally decreased both punished and unpunished responding. Further, the CNS depressant effects of these drugs appear to be additive. The qualitative effects of these two drugs are different enough to disallow generalization to each other in a conflict test.