Pavlovian control of cross-tolerance between pentobarbital and ethanol

Pavlovian Conditioning: A Functional Perspective

From a functional perspective, Pavlovian conditioning involves learning about conditioned stimuli (CSs) that have a pre-existing relation to an unconditioned stimulus (US) rather than learning about arbitrary or neutral CSs. In addition, the most important product of learning involves changes in how the organism responds to the US, not in how it responds to the CS, because the US is the more biologically relevant stimulus. These concepts are illustrated using examples from a variety of behavioral and physiological situations including caloric intake and digestion, breast feeding, poison-avoidance learning, eyeblink conditioning, sexual conditioning, fear conditioning, aggression, and drug tolerance and sensitization.

Opioid-NMDA receptor interactions may clarify conditioned (associative) components of opioid analgesic tolerance

Recent evidence suggests that acute administration of opioid analgesic drugs (such as morphine or heroin) produces delayed hyperalgesia. This hyperalgesic response is likely to result from hyperactivation of NMDA receptors triggered by stimulation of opioid receptors and may mediate acute tolerance. In support of this hypothesis, blockade of NMDA receptors attenuates opioid-induced delayed hyperalgesia and prolongs the duration of antinociceptive activity of morphine. Furthermore, the NMDA receptor-induced hyperalgesia is likely an unconditioned response to opioid receptor stimulation that becomes spatiotemporally associated with environmental cues accompanying repeated opioid exposure. This hypothesis conforms to the traditional Pavlovian requirement for conditioned and unconditioned responses to be qualitatively similar. In support of the role of NMDA receptor hyperactivation in morphine tolerance, NMDA receptor antagonists have been shown to block development of analgesic tolerance induced by repeated exposures to morphine. The view of the conditioned nature of opioid tolerance may be significantly extended by assuming that upon repeated drug administration an early-onset effect of a drug may become a predictive stimulus for a later-onset effect and, consequentially, it may become empowered to elicit the later-onset effect itself. Such 'intra-drug' conditioning hypothesis is well in line with the current experimental evidence but further studies will be needed to verify it directly.

Absence of tolerance to the aversive stimulus properties of ethanol following oral ethanol self-administration

Depending on the situation, ethanol can serve as a reinforcer in one paradigm and an aversive stimulus in another. The relationships between the two stimuli are not clear, particularly the behavioural adaptation following chronic ethanol exposure. We report on two experiments using an oral-self administration (OSA) paradigm and a conditioned taste aversion (CTA) paradigm. Male Wistar rats were exposed to ethanol using either the OSA or the CTA paradigm, and the consequences were examined in the same groups of rats by performing the other corresponding experiment. Thus, sensitisation or tolerance to the respective stimulus properties of ethanol would be detectable. For OSA experiments, rats were presented, under a free-choice setting, tap water and an ascending series of ethanol concentrations (2-10%) for up to 4 days per concentration. The amounts of ethanol and water consumed in 23-h sessions were measured. For CTA, a two-bottle procedure was employed. Distinctively flavoured solutions (saccharin or saline) were paired with IP injections of either ethanol (1.5 g/kg) or saline (1 ml/kg). Tests for aversion were made after two pairings, when both solutions were presented simultaneously for 10 min. At low concentrations of ethanol, drinking solution consumption was high, decreasing gradually with increasing concentrations; however, daily intake of orally self-administered ethanol remained stable. No significant differences could be established between the two groups tested. Ethanol preference [EtOH/EtOH + H2O] was attenuated in rats experienced with the CTA procedure before the OSA experiment. Injections of ethanol produced marked CTAs, even in rats that had consumed ethanol in the OSA experiment. The absence of tolerance to the aversive stimulus effects suggests that this stimulus property may not play a significant role in the consumption of ethanol.

Conditioned tolerance to the anorectic and corticosterone-elevating effects of nicotine

We have shown that tolerance to the behavioral effects of nicotine is partially dependent on conditioned environmental cues that predict drug delivery. The present research extends this finding to physiological effects of nicotine by assessing both the appetite-suppressing and adrenocortical-activating effects of nicotine, as measured by plasma corticosterone (CORT). In the first study, male rats on a 22-h food deprivation schedule were injected daily with 0.33 or 0.66 mg/kg (free base) of nicotine bitartrate or saline in a distinctive environment and tested for milk intake. Nicotine initially suppressed milk intake and tolerance developed over 10 days. Changing cues associated with drug administration partially reversed tolerance since injection of nicotine in a new environment reduced milk intake of tolerant animals. Similarly, animals who repeatedly received nicotine in one environment exhibited CORT levels lower than rats injected for the first time, and this tolerance also was partially reversed when administration occurred in the new environment. The second experiment indicated that the increased CORT of Experiment 1 was not a stress response associated with injecting animals in a different environment. These results indicate that tolerance to both behavioral and neuroendocrine effects of nicotine is influenced by conditioning.

Development of tolerance to kava in mice

1. The development of tolerance to the aqueous extract of kava, and to the lipid soluble extract (kava resin) was tested in mice. 2. Tolerance to the unknown pharmacologically active ingredient(s) developed very rapidly, given parenterally, in the aqueous extract. A minimally effective daily dose (50 mg/kg) of the aqueous extract for 3 days was sufficient to produce tolerance to a test dose of 150 mg/kg, which is close to the ED50. As tolerance was evident at the first test period it can be assumed to be physiological tolerance. 3. Kava resin decreased spontaneous motility and caused a loss of muscle control. A minimally effective daily dose of kava resin (100 mg/kg) did not produce tolerance to the above effects of a weekly test dose of kava resin (166 mg/kg) within 7 weeks. In a further experiment the dose was raised to 150 mg/kg twice daily and this schedule caused partial tolerance to occur within 3 weeks, but very little further tolerance developed over the ensuing 2-week period. 4. To try to induce learned (behaviourally acquired) tolerance a dose of 166 mg/kg kava resin was injected daily and animals were tested each day while under the influence of the drug. However, even under these conditions, there was no tolerance evident within 3 weeks, when the experiment was terminated. 5. It appears difficult to induce the development of physiological or learned tolerance to kava resin in mice.

Isodirectional conditioning effects of d-amphetamine and pentobarbital on schedule-controlled operant behavior in pigeons

Pigeons were trained to peck a key on a multi FR30-FI3' schedule. Presession injections of d-amphetamine (2 mg/kg) and pentobarbital (7.5 mg/kg, 10 mg/kg) were paired with presentation of a red light on the ceiling of the operant chamber. After the five pairings separated by two saline sessions in which a white light was lit, the red light was presented without drug injection. The red light came to cause an isodirectional (drug-like) effect on operant behavior. When the red light was paired with drug injections and operant behavior was prevented from occurring, the light did not acquire isodirectional conditioned effect. Thus, responding in the presence of the drug effect is necessary to establish the conditioning.

Environment-dependent effects of ethanol on DOPAC and HVA in various brain regions of ethanol-tolerant rats

The development of tolerance to the behavioral and biochemical effects of ethanol was studied. Rats were made tolerant to ethanol by the administration of daily ethanol injections (3 g/kg, IP) for 7 and 28 days. Tolerance developed both to the behavioral (hypothermic, sedative) and biochemical (accumulation of dopamine metabolites in various brain areas) actions of ethanol. However, it was found that this tolerance to both the behavioral and biochemical effects of ethanol was no longer present when previously ethanol-tolerant animals were moved from their home environment and given a challenge dose of ethanol (2.5 g/kg; IP) in a new, unfamiliar environment. Our findings confirm that ethanol tolerance cannot be explained on the basis of a singular neurochemical event. The development of ethanol tolerance is due to a complex interaction between environmental, learning, and biochemical factors.

Learning alcohol tolerance: the contribution of response expectancies

This paper reviews research on tolerance developed by task practice under alcohol, and concludes that tolerance in such a situation is influenced by the environmental consequence of drug-compensatory performance. Analysis of the evidence proposes that a learned association between the response and its consequence results in a response expectancy. When the consequence of drug-compensatory performance is more valuable, more tolerance is displayed. Support for this learning analysis is provided by some recent alcohol research indicating that response expectancies affecting tolerance can also be acquired by mental rehearsal of performance and its outcome under drug. Further, these response expectancies may be acquired during the course of a single drug dose, and may alter the display of acute tolerance to alcohol. Additional theoretical predictions are discussed, and the possible social and clinical relevance of the evidence is considered.

The contribution of environmental cues to cross-tolerance between ethanol and pentobarbital

The contribution of Pavlovian conditioning of environmental cues has been studied in relation to tolerance to ethanol-induced hypothermia and cross-tolerance to pentobarbital. Two groups of 12 male Sprague-Dawley rats were exposed every other day to a distinctive set of environmental cues paired with an IP injection of either ethanol 2.5 g/kg or an equivalent volume of isotonic saline. On alternating non-drug days, both groups received saline in the animal room. When they were tested for tolerance to the hypothermic effect of ethanol 2.5 g/kg and cross-tolerance to pentobarbital 25 mg/kg in each environment, tolerance and cross-tolerance in the ethanol-treated group were significantly more pronounced in the ethanol-paired environment than in the saline-paired environment. This indicates the importance of a conditional factor in tolerance and cross-tolerance in this paradigm. Determination of blood levels of ethanol and pentobarbital at various times after injection indicated that conditioned tolerance and cross-tolerance can be explained in part by dispositional factors.

Nicotine tolerance: an analysis of the time course of its development and loss in the rat

The time course of the development and loss of tolerance to nicotine was measured in female rats that were injected subcutaneously (SC), twice daily with 1.6 mg/kg nicotine. Tolerance to nicotine-induced decreases in locomotor activity and body temperature were observed. Tolerance to the effects of nicotine on both of these measures developed rapidly, with maximal changes occurring within 2-4 days after initiation of treatment. The binding of L-[3H]-nicotine was measured in six brain regions. Chronic nicotine treatment resulted in increases in binding in most brain regions. The increase in binding correlated significantly with the development of tolerance. Rats that had been injected chronically with nicotine did not lose their tolerance throughout a 7-day post-treatment test period. Control levels of binding were regained in all of the brain regions except cortex by 7 days after nicotine treatment was stopped. These findings indicate that changes in receptor binding may relate to the development of tolerance but the retention of tolerance is clearly not related to the number of brain nicotinic receptors, unless nicotine-induced decreases in body temperature and locomotor activity are controlled by cortical [3H]-nicotine binding sites.

Conditioned activity and the interaction of amphetamine experience with morphine's activity effects

This experiment assessed the transfer effect of Pavlovian conditioning with d-amphetamine sulfate (1 mg/kg) on morphine's activity effects. Prior experience with amphetamine resulted in higher levels of activity when challenged with morphine (10 and 20 mg/kg). This interactive effect of amphetamine, however, was present only in those animals who had experienced amphetamine paired with the activity test situation. Animals who had received equivalent doses of amphetamine unpaired with the testing environment did not differ from drug-naive control animals. Analysis of predrug activity levels revealed a conditioned activity response in paired animals compared to the controls. These findings suggest that the response interaction between drug conditioned responses and drug unconditioned responses is an important determinant of cross-drug effects between drugs of different pharmacological classes.

Influence of ambient temperature on the development and maintenance of tolerance to ethanol-induced hypothermia

The development of tolerance to the hypothermic effect of ethanol was examined during chronic ethanol treatment (5 g/kg PO daily) at various ambient temperatures (Ta). Tolerance to the hypothermic effect of ethanol, monitored at five-day intervals for 25 days, developed rapidly when ethanol treatment was carried out at 4 degrees C. On the other hand, rats receiving ethanol treatment at a Ta of 36 degrees C, at which they did not experience hypothermia, acquired tolerance more slowly, but achieved the same level of tolerance as other groups after 25 days of treatment. This cannot be accounted for by the repeated testing at 21 degrees C at five-day intervals, since it was also observed under a non-repeated testing condition. Once tolerance to the hypothermic effect of ethanol was acquired, termination of ethanol treatment resulted in the loss of tolerance, but mere prevention of the hypothermic effect of ethanol did not. These results suggest that tolerance still developed even though the organisms did not experience hypothermia during ethanol treatment. Therefore there appears to be a component of tolerance, that depends upon a direct cellular action of the drug, as distinct from the physiological consequences of that action. However, variation in the degree of physiological disturbance (hypothermia) during drug exposure can modulate the rate of development of this tolerance.

Sodium pentobarbital-induced cross-tolerance to ethanol is learned in the rat

Initially, rats were trained to walk on a treadmill to avoid footshock. Subsequently, rats given additional practice while pentobarbital-intoxicated became cross-tolerant to ethanol. However, rats given equivalent doses of pentobarbital after practice did not become cross-tolerant, nor did saline-vehicle controls. These results challenge the theories of cross-tolerance which are based exclusively upon cellular adaptations to pharmacological stimulation of drug-responsive neurons. That all of the cross-tolerance measured was attributable to the intoxicated practice suggests that this observed cross-tolerance was mediated by some form of learning.

Learned and pharmacologically-induced tolerance to ethanol and cross-tolerance to morphine and clonidine

The development of tolerance to the inhibitory effect of ethanol on the tail-flick reflex was studied in the spinal rat. This preparation was used in order to avoid uncontrolled learning effects. Tolerance due to intoxicated practice (learned tolerance) and tolerance due to mere ethanol exposure (pharmacologically-induced tolerance) were studied in separate experiments. It was found that that learned tolerance to ethanol also caused tolerance to morphine and clonidine, whereas pharmacologically-induced tolerance did not have the same effect. The results challenge the concept of "behaviorally augmented tolerance" and suggest that learned and pharmacologically-induced tolerance involve different basal mechanisms in the CNS.

Conditioned compensatory response to alcohol placebo in humans

An autonomic response opposite in direction to the effect of alcohol (i.e., a conditioned compensatory response) was found in normal social drinkers given alcohol placebo. Seven males received placebo in a distinctive drinking room after receiving vodka and tonic in two sessions in the same room; seven more males received distilled water in three sessions in that room. The response to placebo, consisting of decreased pulse transit time and finger skin temperature, was antagonistic to alcohol. The results support the application of the classical conditioning model of alcoholism to humans.

Learned tolerance to ethanol in a spinal reflex separated from supraspinal control

We have recently reported that ethanol-induced inhibition of the tail flick reflex in intact and spinal rats is diminished during an eight day period if the animals are tested daily under the influence of ethanol. Ethanol only, or testing before ethanol administration, is not followed by tolerance. In the present study we used the tail flick testing of spinal rats to investigate the effect on tolerance development of repetitively triggering the tail flick reflex during intoxication, and of just placing the intoxicated animals in the test apparatus. We also investigated if damage to the tail tissue, due to repetitive prolonged test exposure, would facilitate the reflex and thereby reduce the inhibitory effect of ethanol. The results indicated that triggering of the reflex in the presence of ethanol was necessary for the tolerance to develop. Facilitation of the tail flick reflex, due to damage of the tail tissue, was not revealed. Thus the tolerance observed seems to be caused by an adaption to ethanol learned by structures involved in the tail flick reflex.

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

Pavlovian control of tolerance to the sedative and hypothermic effects of chlordiazepoxide (CDP) was demonstrated in two experiments. In Experiment I, drug-experienced rats were repeatedly treated with CDP (30 mg/kg) in one environment (CS+); on alternate days, they were given saline injections in a different environment (CS-). Duration of sleeping and inactivity were used as measures of sedation. A comparable conditioning procedure was used in Experiment II, but tolerance to the hypothermic effect of CDP was the dependent measure. During tolerance testing, rats from both Experiments I and II were given CDP in one of three environments, CS+, CS-, or a novel environment (CSnov). In Experiment I, rats were equally tolerant in all three test environments when duration of sleep was assessed. However, when inactivity was used as the measure of tolerance, rats showed tolerance in CS+ and CS-, and significantly less tolerance in CSnov. Drug-naive controls showed similar nontolerant responses to CDP in all environments, thus ruling out the possibility that the effect of sedation was mediated nonassociatively. In Experiment II, drug-experienced rats showed tolerance to CDP-induced hypothermia in CS+ and CS- but less tolerance in CSnov. A compensatory hyperthermia was observed when these rats were given saline in CS+. There was some evidence for a generalization gradient in the conditional control of tolerance in both experiments.

Features of environment-dependent tolerance to ethanol

Mice given multiple injections of ethanol in a standardized environment develop environment-dependent tolerance to the hypnotic and hypothermic effects of ethanol. These animals also demonstrate environment-dependent cross-tolerance to the hypnotic and hypothermic effects of pentobarbital. Examination of the levels of ethanol in the brain and blood at various times after injection of a test dose of ethanol, as well as the examination of the rate of disappearance of ethanol from the blood, indicated that environment-dependent tolerance could be explained by dispositional factors. On the other hand, mice rendered tolerant to ethanol by a liquid diet technique demonstrate tolerance that is not environment-dependent, and there is no alteration in ethanol levels in different environments for animals fed the liquid diet. When the animals in either paradigm are tested by injecting ethanol directly into the brain, tolerance is observed that is not dependent on the environment. Tolerance produced by these two different paradigms is apparently due to different adaptive strategies used by the animal. Environment-dependent tolerance is partially related to the ability of the animal to change the disposition of ethanol, while environment-independent tolerance may be entirely due to other factors, such as changes in neuronal sensitivity to ethanol.

Learning and cross drug effects: thermic effects of pentobarbital and amphetamine

The effects of environmental cues explicitly paired or unpaired with pentobarbital on the thermic effects of pentobarbital and amphetamine were investigated. Rats received 19 injections of pentobarbital in a distinctive environment and were subsequently tested for the thermic effects of pentobarbital and amphetamine in the distinctive environment, another environment previously associated only with saline, or in the colony room not previously associated with injections. Rats tested in the context of the environmental cues previously associated with pentobarbital were tolerant to the hypothermic effect of pentobarbital, but rats tested in the environment previously associated only with saline or in the colony room were not tolerant. Pentobarbital-experienced rats administered amphetamine in the context of the usual pentobarbital cues exhibited an exaggerated hyperthermic reaction compared to previously drug-naive rats administered amphetamine. Pentobarbital-experienced rats injected with amphetamine in the homeroom exhibited a smaller hyperthermic response than previously drug-naive rats administered amphetamine in the home room. These results demonstrate that an animal's response to a drug can be affected by cues paired and unpaired with drug administration.

Learned tolerance to ethanol in the spinal cord

Learning has been claimed to be of major importance in the development of tolerance to ethanol. In the present study we investigated the influence of learning on tolerance to ethanol-induced inhibition of a spinal reflex (tail-flick response) in intact and spinal rats. On day 1 and 9, groups of rats were injected with either ethanol 2.5 g/kg IP or saline 30 min prior to tail-flick testing. On days 2-8 the groups were treated differently in order to reveal the importance of the drug alone, the test alone and the combination of the two on development of tolerance. On day 10, the rats rendered tolerant in the home room were transferred to a new test room to be tested. Both in intact and spinal rats development of tolerance was observed only if the animals were repetitively tested while intoxicated. Tolerance acquired in the home room was not attenuated by transfer to a new environment. Results in the spinal rats suggested that adaptive mechanisms leading to tolerance may also be located in the spinal cord. The tolerance observed may be regarded as learned from practice while intoxicated.

A conditioning model of alcohol tolerance

Tolerance to several effects of ethanol can be learned in a classical conditioning paradigm. In the conditioning model of tolerance, a response compensatory in nature to the effect of ethanol develops in association with the cues that signal the presence of ethanol. Tolerance produced by this procedure (environment-dependent tolerance) differs in several respects from tolerance produced in a paradigm in which learning would not be expected to play a significant role (environment-independent tolerance). Depletion of norepinephrine in the brain blocks the development of both types of tolerance, whereas depletion of serotonin enhances the rate of development of environment-dependent tolerance, but inhibits the development of environment-independent tolerance. Cued alterations in the volume of distribution for ethanol are an important factor in the tolerance displayed in the classical conditioning paradigm. It has been suggested that the conditioned compensatory response comprises the physiological response underlying "craving" for ethanol. This implies that an extinction procedure would be an effective treatment for the prevention of relapse.

The role of associative factors in tolerance to the hypothermic effects of morphine in mice

Associative learning theories of drug tolerance emphasize the importance of stimuli which predict drug administration. One such model holds that drug tolerance is due to the development of a conditional response (CR) which is directionally opposed to the unconditional response (UCR) to the drug. By virtue of their opposing natures, the overlapping occurrence of CR and UCR is seen as a diminished response, i.e., tolerance. The present experiments tested the predictions of this model using two doses of morphine, and included truly random controls to examine the role of excitatory and inhibitory conditioning in tolerance. Tolerance was greatest in mice administered morphine in the context of stimuli previously paired with drug administration, intermediate in random controls, and least or absent in mice administered the drug in the presence of cues paired with vehicle injections. No direct evidence of a compensatory CR which could offset morphine's hypothermic effect was obtained in placebo test sessions, nor was evidence for such a response obtained in cross-drug tests with amphetamine and apomorphine.

Temperature dependence of ethanol lethality in mice

The present study provides systematic evidence indicating a direct relationship between environmental temperature, rectal temperature and ethanol lethality. Male, C57 BL/6J mice, previously housed at room temperature (23 +/- 1 degree C), were injected intraperitoneally with 4.8 to 9.2 g kg-1 ethanol and then exposed for 24 h to ambient temperatures that did not appreciably exceed the thermally neutral range for sober mice (20 to 35 degrees C). There was a direct relationship between temperature and ethanol lethality at 8 and 24 h after injection. The 8 h LD50 increased by 64%, from 5.3 to 8.7 g kg-1, as environmental temperature decreased from 35 to 20 degrees C. The 24 h LD50 increased by 51%, from 5.3 to 8.0 g kg-1, across this temperature range. Each 5 degrees C reduction in ambient temperature induced a significant decrease in the rectal temperature of ethanol-injected mice. Mean rectal temperature ranged from 2.2 degrees C above baseline at an ambient temperature of 35 to 15 degrees C below baseline in the 20 degrees C environment. Ethanol induced a significant dose-related hypothermia in mice exposed to the 20, 25 and 30 degrees C environments but did not produce hypothermia in animals kept in the 35 degrees C environment. These findings indicate that the potency of potentially lethal ethanol doses varies with body temperature in accordance with partition and membrane expansion-fluidization theories of anaesthesia.

Behavioural tolerance to amphetamine and other psychostimulants: the case for considering behavioural mechanisms

An hypothesis is presented about the nature of behavioural tolerance in animals to stimulant drugs. It is suggested that, in many behavioural procedures, tolerance is due to behavioural adaptation to those drug effects which cause disruption of ongoing rewarded behaviour. This unitary hypothesis accounts for the available data on tolerance and cross-tolerance to stimulants more effectively than all of the other more conventional explanations which are based upon dispositional or functional concepts, the most common of which are described, evaluated, and found to be inadequate. Furthermore, it is suggested that attempts to explain tolerance in terms of changes in synaptic functioning are subject to very considerable problems of interpretation and that an analysis of behavioural mechanisms may be of greater value in understanding the process of behavioural tolerance. Evidence for the basic behavioural hypothesis is outlined in some detail, and a theoretical justification presented for its major assumptions. Operant studies of chronic stimulant effects on behaviour have often produced very complex patterns of data, considerable differences being reported both between subjects and between studies. A speculative model is presented which attempts to account for this pattern of data in tolerance studies.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)

Conditioned and unconditioned influences on body temperature and ethanol hypothermia in laboratory rats

Both a naive group and a group of chronically handled rats were observed to develop hyperthermia when their cages (rats in situ) were removed from their usual positions on cage rack shelving and placed upon the laboratory bench for a period of 60 minutes. That procedure apparently functioned as a stressful unconditioned stimulus for the naive group. The extent of hyperthermia was more pronounced in the chronic group, presumably owing to the classical conditioning of environmental cues to the stressful events that had repeatedly been associated in the past with placement of the cage onto the benchtop. Doses of naloxone (10 mg/kg) and of ethanol (1 g/kg) that normally produced negligible effects on body temperature were found to significantly reduce the hyperthermia that developed when cages were placed onto the benchtop. The hypothermic response to 2 g/kg of ethanol was lessened in both groups by placement of the cages onto the benchtop.

Effects of pentobarbital and cocaine in rats expecting pentobarbital

Rats received extensive exposure to pentobarbital in a distinctive environment, and were subsequently tested for tolerance to the sedative effects of pentobarbital either in the distinctive environment or in an environment previously associated only with saline. Rats tested when expecting pentobarbital (i.e., in the usual drug environment) were tolerant, but rats tested when not expecting the drug (i.e., in the saline environment) were not tolerant. These results extend demonstrations of conditional tolerance to the general behavioral arousal effects of a sedative hypnotic. Subsequently, the same rats were administered cocaine either when expecting pentobarbital or when not expecting pentobarbital. Rats administered cocaine when expecting pentobarbital exhibited more intense forms of cocaine-induced behavior than rats administered cocaine but not expecting pentobarbital. These results establish the phenomenon of conditional cross-potentiation between conditional drug states and unconditional drug-effects.

The role of conditional drug responses in tolerance to the hypothermic effects of ethanol

The role of predrug cues in tolerance to ethanol-induced hypothermia was investigated in two experiments. The results of Experiment 1 demonstrated that tolerance was displayed only when the drug was administered in conjunction with environmental stimuli that had, in the past, accompanied ethanol administration. A conditional hyperthermic response was elicited when a placebo, instead of ethanol, was administered in conjunction with the usual ethanol cues. Results of Experiment 2 suggested that tolerance to ethanol-induced hypothermia can be extinguished by repeated placebo injections. These results indicate that associative processes, previously demonstrated to modulate opiate tolerance, also modulate ethanol tolerance.