Associative control of tolerance to the sedative and hypothermic effects of chlordiazepoxide

Acquisition and extinction of conditioned nicotine analgesic tolerance

These studies demonstrated the acquisition and extinction of conditioned tolerance to the analgesic effect of nicotine in rats. In Experiment 1, distinctive environmental cues were either paired or unpaired with nicotine. Following acquisition, the paired group was more tolerant to nicotine than the unpaired and saline groups. Conditioned tolerance was extinguished in the paired group after placebo sessions in the distinctive environment. Experiment 2 examined whether the distinctive environment functioned as a CS or as an occasion setter for injection cues. After acquisition, exposure to the distinctive environment, with or without placebo injections, resulted in extinction. This demonstrates that the distinctive environment served as a CS, not as an occasion setter for injection cues.

Measuring the emergence of tobacco dependence: the contribution of negative reinforcement models

This review of negative reinforcement models of drug dependence is part of a series that takes the position that a complete understanding of current concepts of dependence will facilitate the development of reliable and valid measures of the emergence of tobacco dependence. Other reviews within the series consider models that emphasize positive reinforcement and social learning/cognitive models. This review summarizes negative reinforcement in general and then presents four current negative reinforcement models that emphasize withdrawal, classical conditioning, self-medication and opponent-processes. For each model, the paper outlines central aspects of dependence, conceptualization of dependence development and influences that the model might have on current and future measures of dependence. Understanding how drug dependence develops will be an important part of future successful tobacco dependence measurement, prevention and treatment strategies.

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)

Tolerance to anticonvulsant effects of the partial benzodiazepine receptor agonist abecarnil in kindled rats involves learning

The effects of chronic treatment with the beta-carboline, abecarnil, a novel partial and/or subtype-specific agonist at central benzodiazepine receptors, were studied on fully kindled amygdaloid seizures in rats. Two different experimental protocols were used to differentiate between "pharmacologic tolerance', i.e. tolerance as a function of drug exposure, and "contingent tolerance, i.e. tolerance contingent upon the repeated occurrence of the criterion effect, i.e. the anticonvulsant effect. When kindled seizures were repeatedly initiated during chronic treatment of rats with abecarnil (5 mg/kg i.p. three times daily), marked tolerance developed to its anticonvulsant effect, although plasma levels of abecarnil even increased during the 2 weeks of treatment. When the same treatment protocol was used, but seizures were initiated only at the start and end of the treatment period, almost no tolerance to the anticonvulsant effect of abecarnil was measured, indicating an important role of learning processes for the development of tolerance. In contrast to the differences in anticonvulsant tolerance between the two protocols, the motor impairment induced by abecarnil was similarly attenuated during chronic treatment according to both protocols. The data indicate that, because of the response contingency in abecarnil tolerance, development of tolerance to anticonvulsant effects of this compound depends critically on seizure frequency during drug administration, while adverse effects of this compound are reduced independently of seizure frequency.

Cellular and learned tolerances for pentobarbital hypothermia

The development of behavioral tolerance to pentobarbital-induced hypothermia, as separable from cellular and metabolic tolerance, was established. Pentobarbital (PB) was administered to 4 groups of rats, 2 groups of which received intermittent (INT) IP PB treatment. One of these groups, INT/EXP, experienced the hypothermic (measured as rectal body temperature) drug effect after PB injection. The other group, INT/NONEXP, was monitored for body temperature functions (room temperature) before receiving PB (vehicle administration) and then prevented from experiencing PB-induced hypothermia by maintenance of body temperature with a towel wrap restraint and a heating lamp. The INT/EXP group also received equivalent exposure to this towel wrap after vehicle administration. Two other groups received chronic PB treatment (IP and in ground chow), one with experience for hypothermia after injections (CHR/EXP) and one prevented from experiencing the hypothermia (CHR/NONEXP). These groups also received equivalent exposure to the body temperature (at room temperature) testing and towel wrap restraint, EXP rats after vehicle injections and NONEXP after drug injections. A postchronic test of all groups compared the extent of PB hypothermia to prechronic test effects to assess the degree of tolerance. The INT/EXP group demonstrated behavioral tolerance for PB-induced hypothermia, as contrasted with the INT/NONEXP group which demonstrated little or no tolerance. Prominent tolerance was noted in both chronic groups for PB hypothermia, without a significant difference between them. After the postchronic test, chronic treatment was discontinued for 9 days (withdrawal) followed by 9 days of extinction training (vehicle behavioral testing). The two intermittent groups demonstrated no change in the hypothermic drug response during the postwithdrawal and postextinction drug tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Situational specificity of tolerance to effects of phencyclidine on responding of rats under fixed-ratio and spaced-responding schedules

Responding of rats (n = 5) was maintained under DRL (lever) and Time-Delay (nose-key) schedules of food presentation in different experimental chambers during two separate daily sessions. Tolerance that developed to rate-decreasing effects of phencyclidine for nose-key pressing under the Time-Delay schedule did not extend to effects of phencyclidine on lever pressing under the DRL schedule. In a second experiment, both lever and nose-key pressing of rats were maintained under individual and multiple fixed-ratio schedules. One group of animals (n = 5) experienced both the individual and the multiple schedules in the same experimental chamber and another group (n = 5) experienced the individual and the multiple schedules in different experimental chambers. Tolerance that developed to behavioral effects of phencyclidine during the individual schedule did not extend to responding on even the same manipulandum under the multiple schedule in a different experimental chamber. In contrast, tolerance that developed to behavioral effects of phencyclidine during the individual schedule did extend to responding on even the different manipulandum under the multiple schedule in the same experimental chamber. Thus, tolerance that developed in the environment that was coincident with the pharmacologic actions of phencyclidine did not extend to similar operants in a different environmental condition, but did extend even to a different operant and schedule context in the same environmental condition.

The history of benzodiazepine dependence: a review of animal studies

This article provides a historical review of the animal literature relating to the development of tolerance to the behavioral effects of benzodiazepines, and the incidence of biochemical and behavioral changes that result from termination of benzodiazepine treatment (spontaneous withdrawal responses). It charts the slow emergence of a pertinent animal literature and highlights conclusions that were prevalent in 1963 (at the introduction of diazepam), 1973 (at the introduction of lorazepam), 1980 and the present day. For 25 years the animal literature has lagged behind the clinical literature, but recent studies into the neurochemical mechanisms of benzodiazepine dependence and possible treatments for withdrawal responses suggest that, at last, animal experiments may be about to make a substantial contribution.

Modulation of tolerance to the GABAA agonist THIP by environmental cues

The present experiment assessed the extent to which environmental stimulation could influence tolerance to the sedative and catatonic effects of the GABAA agonist, 4,5,6,7-tetrahydroisoxozolo(5,4-c)pyridin-3-ol (THIP), through associative learning processes. A conditioning paradigm was used, with THIP as unconditioned stimulus and environmental cues as conditioned stimulus. One group of mice received 15 mg/kg THIP in the testing environment; the second group was exposed to THIP in the colony room, while a third group received only saline. On a tolerance testing session, all mice received 15 mg/kg THIP in the testing environment. Results show that mice previously given THIP in the testing environment display a greater tolerance than mice receiving the drug in the alternative environment. Subsequently, a placebo was given to all mice in the testing environment to assess the influence of environmental cues alone; mice previously given THIP in the testing environment exhibited an enhancement of motility. The results agree with an associative model of tolerance which predicts that environmental cues associated with drug exposure elicit a conditioned compensatory response that cancels the unconditioned effect of the drug.

Conditioned stimulus control of morphine hyperthermia

Classical conditioning of morphine hyperthermia was examined using an explicit conditioned stimulus (CS) paired with intravenous (IV) morphine administration. Rats were implanted with a jugular vein cannula and a biotelemetry device for monitoring body temperature. The animals were housed 24 h/day in the chambers in which all testing occurred. The CS was a 15-min light/noise stimulus. The unconditioned stimulus (US) was an infusion of morphine (5 mg/kg). Rats were assigned to either the Paired group, which received morphine with the CS, or the Unpaired group, which received explicitly unpaired presentations of the CS and US. The CS-morphine pairings resulted in development of a conditioned hyperthermic response in the Paired group evoked by the CS in the absence of morphine. The development of morphine hyperthermia was more rapid in the Paired group in the presence of the CS than in its absence in the same group and more rapid in the Paired group than in the Unpaired group during the CS. These results clearly show that learning affects the response to morphine administered repeatedly. In contrast to previous studies, conditioned hyperthermia was elicited within 15 min by a discrete CS in a situation where the response was not confounded by handling or the stress of injection.

Continuous slow release of low levels of diazepam produces tolerance to its depressant and anxiolytic effects on the startle reflex

Development of tolerance to the depressant effects of diazepam on the acoustic startle reflex and to the blockade of fear-potentiated startle, a measure of fear or anxiety in rodents, was evaluated after chronic administration via continuous release from implanted diazepam-filled silastic capsules or daily intraperitoneal (i.p.) injections. After continuous exposure to diazepam via capsule implants, complete tolerance occurred to the depressant effects of diazepam on startle and partial tolerance occurred to the antifear effects. In contrast, no tolerance was observed after daily i.p. injection with comparable amounts of diazepam (5 mg/kg) although tolerance could be produced by daily i.p. injections of a much higher dose of diazepam (20 mg/kg). These data suggest that tolerance to at least some behavioral effects may be much easier to produce with continuous rather than intermittent occupation of benzodiazepine receptors.

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)

Investigation of the development of tolerance to the actions of zolpidem and midazolam

It is well established that tolerance can develop very rapidly to the behaviour-suppressing effects of benzodiazepines. In previous studies, however, the depressant action of zolpidem, a novel hypnotic acting at the benzodiazepine receptor, on operant behaviour in rats was maintained after many injections. An experiment was carried out, therefore, to compare the effects of acute and chronic administration of zolpidem and midazolam. Rats were trained to press a lever in standard operant test chambers to obtain 45 mg food pellets on an FR 10 schedule. Dose-response curves were then established, before, immediately after and 4 weeks after the daily administration of midazolam (3.0 mg/kg s.c.) or zolpidem (1.0 mg/kg) for 10 days. In confirmation of previous work, marked tolerance developed to the response-rate-decreasing effect of midazolam, the dose-response curve being shifted to the right by a factor of 6 and also flattened. No significant dissipation of this tolerance occurred during a period of 4-6 weeks. In contrast, repeated administration of zolpidem produced only a small degree of tolerance, the dose-response curve being shifted by a factor of two. There was little evidence for cross tolerance between the two drugs, zolpidem-treated rats being sensitive to a dose of midazolam and midazolam-treated rats sensitive to a dose of zolpidem. Although the explanation for the development of tolerance to midazolam is unknown, these results suggest that the mechanisms of action of midazolam and zolpidem in reducing response rates are different.

Analysis of the role of behavioural factors in the development of tolerance to the benzodiazepine midazolam

Two experiments were conducted on the acute and chronic effects of the short-acting benzodiazepine midazolam on fixed ratio schedule-maintained operant responding in rats. Acute administration of midazolam produced suppression of responding in large doses but elevation of responding in small doses. Following intermittent (every third day) chronic treatment tolerance developed rapidly to the rate-suppressant effects of large doses of midazolam but did not develop to the rate-elevating effects of small doses, even after chronic treatment with large doses of the drug. Thus, when tolerance was measured in terms of shifts in dose-effect curves, it was manifested as a non-parallel shift in the curve after chronic treatment. Since tolerance developed to the effects of large but not small doses, the observed tolerance could not be attributed to changes in disposition of the drug. The development of tolerance did not depend on whether the drug was given before or after behavioural testing. These findings contrast with data reported in behavioural studies with other sedative-hypnotics (ethanol, barbiturates). Animals tolerant to midazolam showed no cross-tolerance to ethanol, a drug for which there is reliable evidence indicating that behavioural factors play a role in acquisition of tolerance. Tolerance to midazolam cannot therefore be explained in terms of learned strategies acquired as a result of drug-induced loss of rewarding stimuli. This conclusion contrasts with recent suggestions (File, 1985; File and Pellow, 1985) that tolerance to benzodiazepines may be mediated by instrumental conditioning processes.