Development of morphine dependence in rats: lack of effect of previous ingestion of other drugs

Differential epigenetic changes in the hippocampus and prefrontal cortex of female mice that had free access to cocaine

Alterations in gene expression within the neural networks of prefrontal cortex (PFC) and hippocampus (HPC) are known to contribute to behavioural phenotypes associated with drug intake. However, the functional consequences of regulated expression patterns of Fosb and Crem (cAMP response element modulator) in both brain regions in response to volitional intake of cocaine in social environment is yet to be explored. Here, we first exposed young adult mice to cocaine (300 mg/L) and water concurrently for 30 days in the IntelliCage to investigate consumption preference, and subsequently for 28 days during which persistent motivated drug seeking behaviours were examined. Thereafter, locomotor activity and memory performance of the mice were assessed. DNA methylation status in the promoters of Fosb and Crem genes were also evaluated. We show that mice that had extended access to cocaine exhibited motivational deficit and demonstrated decreased locomotor activity and intact recognition memory. These changes were accompanied by hypomethylation or hypermethylation in the promoters of Fosb and Crem genes in the PFC and HPC of the cocaine-experienced mice, respectively. Together, these findings correlate the molecular changes to behavioural effects of the treatment and further suggests a possible activation of prefrontal cortical networks by social interaction episodes in the IntelliCage which possibly enhanced behavioural control that dampens mice sensitivity to cocaine rewards. Furthermore, our data delineate the molecular response of Crem and Fosb to oral cocaine in group-housed mice and demonstrates differential regulation of activities within the substrate brain regions studied.

P-hydroxy-norephedrine as a possible mediator causing the reduction of oral intake of D-amphetamine in rats

In rats D-amphetamine is predominantly metabolized by hydroxylation to p-hydroxy-norephedrine (p-HNE); in guinea pigs, however, by deamination to benzoic acid. After 2-3 days on dosages of 1 mg/kg per day and more rats begin to reduce their oral intake of the stimulant whereas guinea pigs do not. In the present study we examined the hypothesis that the formation of p-HNE in the CNS is partially responsible for this aversion. To determine the elimination of D-amphetamine and the increase in p-HNE, groups of male Wistar rats were given various doses (0.5-5 mg/kg per day) of D-amphetamine in their drinking water intragastrically and intravenously. D-Amphetamine in the brain was determined by radioimmunoassay, p-HNE by high performance liquid chromatography followed by electrochemical detection. In contrast to the concentration of D-amphetamine, the p-HNE-content is independent of the route of administration; after oral treatment it showed a linear increase. The results reveal that p-HNE induces the aversion to the stimulant and that the ratio of D-amphetamine to its metabolite determines the onset of this aversion. No p-HNE was found in the brain of guinea pigs. Guinea pigs do not show any aversion to drinking D-amphetamine solutions, even in high dosages.

The influence of brain catecholamines on 'drug taking behaviour' relative to oral self-administration of d-amphetamine by rats

Oral administration of 5 mg/kg of d-amphetamine to adult Wistar rats caused brain NE to decrease to approx. 80% of the control level during 4-24 h after acute treatment and slowly further to 65% after 24 days of self-administration via drinking water. The norepinephrine (NE)-reducing effect was first recognized at 1 mg/kg and appeared to peak at 5 mg/kg of d-amphetamine. Brain dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were only shortly affected. Neither iprindole nor desipramine altered the effect of amphetamine on brain NE. DA was decreased by both inhibitors depending on the duration of pre-treatment. Iproniazid and alpha-methyl-p-tyrosine antagonized and potentiated respectively the amphetamine effect on NE- and DA-concentration after 4 days of simultaneous treatment. In the free choice experiment (water vs. 0.005% d-amphetamine solution) rats developed an aversion to amphetamine. The number of rats taking the drug and the consumption by rats still drinking it declined gradually from 100% and approx. 3 mg/kg/day to 50% and approx. 1.5 mg/kg/day, respectively, during 18 days. The time course of the developing aversive reaction to oral amphetamine ran approximately parallel to that of NE-depletion. Iprindole and desipramine intensified, iproniazid and propranolol weakened, while alpha-methyl-p-tyrosine and haloperidol hardly influenced the aversive effect of amphetamine. It is concluded that the development of aversive behaviour in response to oral d-amphetamine is mediated not only through the depleting effect of amphetamine on NE stores but also by its direct stimulation at beta-adrenergic receptors in the CNS.

Self-administration of barbiturates and benzodiazepines: a review

Studies of barbiturate and benzodiazepine self-administration are categorized by species and route of administration. Reinforcement, defined as self-administration of drug greater than of a non-drug control, has been demonstrated most often in studies employing the IV route, and there has been greater reliability in this result for a given drug among barbiturates rather than among benzodiazepines. Most studies of PO self-administration in rodents have not demonstrated reinforcement, despite a number of behavioral manipulations to induce drug intake. Studies of PO barbiturate self-administration in monkeys have demonstrated reinforcement but recent studies of PO benzodiazepine self-administration in baboons have not, although physical dependence was demonstrated. Reinforcement via the IG route has not been reliably demonstrated. Behavioral variables, including interreinforcement interval and drug self-administration history, appear to be important determinants of whether or not reinforcement will be demonstrated, particularly among the benzodiazepines; but the range of conditions under which behavioral and pharmacological variables interact to promote or lessen the likelihood of self-administration of these drugs remains to be determined experimentally.

(+)-Amphetamine oral 'drug taking behavior' in naive and tolerant rats

The drinking behavior of naive rats changes predictably in a free choice experiment involving water vs. 0.02%, 0.01% and 0.003% (+)-amphetamine solutions: The higher the concentration of the amphetamine solution, the sooner a number of rats quit drinking it, and the less is ingested by those still drinking it. Physically dependent rats having undergone three withdrawals immediately reject (+)-amphetamine solution in a free choice test with water available. The avoidance of withdrawal symptoms does not motivate further self-administration. Therefore, (+)-amphetamine self-administered in drinking water is neither a reinforcer for naive nor for physically dependent rats in sustaining drug taking behavior. In acute and chronic experiments, the transition from increased motor activity to stereotypical behavior could be demonstrated and evidence was produced that tolerance develops to the (+)-amphetamine-induced increase in motor activity.

Benzodiazepine dependence

Dependence to benzodiazepines is difficult to induce in animals but has been induced by high doses in man. Case reports of benzodiazepine dependence are rare compared with the usage of these drugs, but provide no proper epidemiological framework for the estimation of risk. Patients taking these drugs for four months or more may develop symptoms on withdrawal, characterized by anxiety, dysphoria, malaise, depersonalization, and by perceptual changes such as hyperacusis and unsteadiness. In our first study we compared four patients withdrawing from high doses of benzodiazepines with six patients withdrawing from therapeutic doses. In all patients the typical withdrawal syndrome was noted and was equal in intensity in both groups. In the second study, long-term, normal-dose benzodiazepine treatment was discontinued in 24 patients believed to be dependent on their medication. The withdrawal was gradual, placebo-controlled and double-blind. All experienced some form of withdrawal reaction, which ranged from anxiety and dysphoria to moderate affective and perceptual changes. Symptom ratings rose as the drugs were discontinued, but usually subsided to pre-withdrawal levels over the next two to four weeks. Electroencephalograhic (EEG) changes comprised marked reduction in fast-wave activity as the drugs were withdrawn, and an improvement in psychological performance was noted. It is concluded that a risk of dependencies present in all patients taking benzodiazepines even in therapeutic doses for more than a few months. Caution is urged in the prescribing of these drugs.

Alcohol and taste-mediated learning

Taste-mediated learning is relevant to the alcohol consumption patterns of animals. This review concludes that taste aversion learning has thus far prevented development of an animal model of alcoholism. The presence of a taste cue, lack of control over alcohol administration, and high alcohol concentrations or dosages all facilitate the development of alcohol aversions. There is little evidence that taste preference learning is involved in the development of alcohol dependence. Data from taste-mediated learning research with animals are consistent with drinking patterns of human alcoholics.

Learned taste aversion to saccharin produced by orally consumed d-amphetamine

Rats were presented with solutions containing both saccharin and d-amphetamine and the development of taste aversions to solutions of either or both of these substances was studied. In Experiment 1 it was found that taste aversions developed to solutions of saccharin (1 mg/ml) which contained amphetamine at concentrations of 0.01, 0.03 and 0.1 mg/ml. Experiment 2 showed that a taste aversion conditioned to a solution of saccharin (2 mg/ml) and amphetamine (0.2 mg/ml) generalised to solutions containing saccharin at concentrations between 0.625 and 20 mg/ml but not to a solution containing only amphetamine. In the third experiment it was found that the degree of generalisation of a taste aversion to lower saccharin concentrations depended upon the concentration used during conditioning trials. When the conditioning concentration was 0.625 mg/ml the aversion generalised to concentrations as low as 0.075 mg/ml but when a 10 mg/ml solution was used for conditioning the aversion did not generalise to concentrations below 2 mg/ml. The characteristics of taste aversions conditioned with orally consumed amphetamine are similar to those of conditioning involving injections of the drug.

Effects of chronic d-amphetamine treatment on schedule-controlled behavior

The effect of d-amphetamine added to the drinking water on the rate of conditioned lever pressing by rats was determined using fixed-ratio 30 (FR-30) and fixed-interval 2-min (FI-2) schedules of food presentation. After 32 days of gradual increase in drug concentration the average drug ingestion was 13 mg/kg/day. In tests with various doses of d-amphetamine injected before and after the chronic ingestion regimen, the rate-decreasing effects of d-amphetamine on FR responding were attenuated after chronic treatment, indicating development of a two- to three-fold tolerance. However, the rate-decreasing effect of d-amphetamine on FI responding was not altered by chronic ingestion. Since acute amphetamine treatment reduced the reinforcement frequency under the FR but not the FI schedule, these results are consistent with the hypothesis that a 'behavioral tolerance' will develop most readily to drug effects that decrease the frequency of reinforcement. Upon removal of d-amphetamine from the drinking water there was some increase in the rate of FR responding, but no change in FI responding.

Preference for morphine and drug-seeking behavior in morphine dependent rats

We have already reported that morphine pretreated rats prefered morphine-admixed food during choice trials with the two cup method. In the present work, we utilized both the five and two cup methods and observed the preference for morphine in rats forcedly pretreated with the drug and the increasing rate of preference for the drug in rats where the feeding time was limited. In morphine pretreated rats, preference rate for morphine was 61.2 +/- 3.0% with the five cup method and 61.8 +/- 3.3% with the two cup method during the choice trials. In rats that were limitedly treated with morphine, each preference rate for morphine during choice trials rapidly increased in the five cup method, i.e. 5.5 leads to 14.4 leads to 31.7 leads to 43.6 leads to 61.2%, and the preference rate for morphine stabilized at approximately 60 percent. Findings with the two cup method were similar. After the preference for morphine was stabilized at the 60 percent level, morphine was given subcutaneously and it was found that the preference rate was dependent on the dose injected. When the drug-admixed concentration was changed from 1 mg/g food to 0.5 and 2 mg/g food, the preference rate changed in parallel with the concentration. When the number of food cups containing morphine-admixed food was changed from 1/5 to 2/5, 3/5 and 4/5 food cup, the preference rate was not effected. These studies clearly demonstrate drug-seeking behavior in rats. In the process of preference for morphine, morphine treatment enhances spontaneous intake of morphine-admixed food.

The effect of housing and gender on morphine self-administration in rats

To determine the effect of housing conditions on morphine self-administration, rats isolated in standard laboratory cages and rats living socially in a large open box (8.8 m2) were given morphine in solution (0.5 mg/ml) as their only source of fluid for 57 days. They were then exposed to a series of 3-day cycles previously shown by Nichols et al. (1956) to increase self-administration of morphine in caged rats. On morphine/water choice days late in the period of forced consumption, between the Nichols cycles, and during a subsequent period of abstinence, the isolated rats drank significantly more morphine solution than the social rats, and the females drank significantly more morphine solution than the males. During the four choice days in the Nichols Cycle Period the isolated rats increased their consumption, but the socially housed animals decreased theirs.

Amphetamine-induced taste aversion demonstrated with operant behaviour

Amphetamine can be used to condition strong taste aversions, but little is known about the possible effects of flavour-amphetamine pairings on operant behaviour. Rats were trained to press bars for water reinforcers delivered after every 40 responses (FR 40). Flavoured reinforcers were then substituted for the water and post-session injections of amphetamine (1 mg/kg) were given. Even a single flavour-amphetamine pairing produced some decrement in responding for that flavour, whereas three flavour-amphetamine pairings almost completely suppressed responding. In the same rats, a flavour which was paired with saline injections did not suppress responding. Flavour-amphetamine pairings can therefore have a powerful influence on operant behaviour and the different outcomes of flavour-conditioning and self-administration procedures cannot be attributed simply to the type of response required from the rat.

d-Amphetamine and adjunctive drinking in rats

In the first experiment four food-deprived rats developed high levels of adjunctive water drinking during daily sessions of intermittent food pellet delivery. When the water was removed and a solution of d-amphetamine sulfate (0.01 mg/ml) put in its place, adjunctive drinking was disrupted towards the end of each session although the rats ingested doses of approximately 0.5 mg/kg daily for over 40 sessions. Consumption of the d-amphetamine solution was increased by injections of several doses of alpha-methyl-p-tyrosine (AMPT). In a second experiment injections of d-amphetamine (0.25, 0.5, 1.0, 2.0 mg/kg) were found to reduce adjunctive water consumption in six rats. It was also found that the actions of the two highest doses of d-amphetamine were reduced by pretreatment with a dose of AMPT (100 mg/kg), which itself slightly reduced levels of drinking. These results suggest that, although adjunctive drinking may be a useful technique for inducing rats to self-administer d-amphetamine, the amount of drug consumed is limited by a direct action of the drug on drinking.

Factors influencing flavour aversions conditioned with amphetamine in rats

Rats would not drink distinctively flavoured solutions after their previous ingestion had been followed by injection of amphetamine (1 mg/kg). In the same rats, intake of flavoured solutions followed by saline injections was not suppressed. Providing the rats with cues as to the location of flavoured solutions paired with amphetamine did not alter either the speed of development or the final severity of the aversion. Neither increasing the interval between presentation of the flavour and injection of amphetamine, nor decreasing baseline drinking levels, altered the final degree of aversion. The aversion became progressively weaker as the dose of amphetamine was reduced, but it was detectable at doses as low as 0.1 mg/kg. Further decreases in dose did not enhance intake of flavours paired with amphetamine, even when combined with reductions in baseline drinking brought about by reduced fluid deprivation and flavour palatability. The results are discussed in relation to the conditions in which amphetamine has been shown to exhibit either rewarding or aversive properties.

Acquired preference for morphine but no d-amphetamine as a result of saccharine adulteration

Consumption of morphine sulfate and d-amphetamine was studied in two groups of rats. In a choice situation, preference for both drugs remained low after 46 days of drinking. In two additional groups morphine and d-amphetamine solutions were prepared with 1% saccharine. Morphine drinking was significantly increased by saccharine adulteration, whereas drinking of amphetamine solutions decreased. Addition of saccharine to morphine solutions increased drinking in more than a simple additive way. Saccharine facilitates the acquisition of drug-directed behavior. The slope of the acquisition trials for the morphine-saccharine group was significantly different from horizontal (O-slope) and significantly different from the slope found for the morphine without saccharine group.

Morphine suppression of ethanol withdrawal in mice

The acute administration of morphine, alcohol or dopamine results in a pronounced suppression of the convulsions produced by alcohol in mice. The suppressive action of morphine on alcohol withdrawal in the mouse apparently is not a product of morphine intoxication, but rather to some other specific interaction between alcohol and morphine in the central nervous system. The conclusion suggest that dopamine may play a significant role as a modulator in convulsions produced during alcohol withdrawal.

Morphine dependent behaviour in rats: some clinical implications

An animal model of morphine dependence is described, in which rats learned to overcome their aversion to solutions of morphine and eventually drank such solutions in preference to water on choice trials. Selected aspects of the acquisition, maintenance, and elimination of this type of morphine dependent behaviour were studied and the findings are discussed in terms of their relevance to man.