The effect of chronic self-administration of d-amphetamine on food intake, locomotor activity, and C14-leucine incorporation into cerebral cortex protein

Opioid influence on some aspects of stereotyped behavior induced by repeated amphetamine treatment

Rats were administered repeated IP injections of dl-amphetamine (AMPH) according to a chronic escalating dose schedule (three doses per 24 hr, for four days, two days or one day). Animals treated for four days exhibited a diminished oral stereotypy in response to a challenge of 12 mg/kg AMPH or 2 mg/kg SC apomorphine (APO), 72 hr after withdrawal. Pretreatment with 2 mg/kg IP naloxone (NAL) during the period of chronic AMPH administration prevented the reduction in oral stereotypy induced by AMPH or APO. No differences were detected among the mean of stereotypy scores from the different treatments in response to a challenge dose of 6 mg/kg AMPH. Neurochemical data showed that NAL pretreatment reversed the depletion of striatal dopamine content induced by chronic AMPH. When repeated injections of AMPH were given only one day, the diminished stereotypy response to AMPH or APO was not observed. Animals treated simultaneously with 1 mg/kg IP morphine or 5 micrograms/kg IP beta-endorphin and repeated AMPH injections for one day, showed a reduced stereotyped response to AMPH or APO. These results suggest that opioid peptides are involved in the mechanisms underlying the decrease in oral behaviors following AMPH treatment.

Volitional oral intake of nicotine in tupaias: drug-induced alterations

Non-deprived, unstressed tree shrews (Tupaia belangeri) preferred nicotine solution (10 mg/l nicotine tartrate) over water in a free-choice situation. This drug-taking behaviour was stable over 14 months. Several drugs, most of which known to attenuate ethanol consumption in other species, in doses that did not alter locomotive behavior, significantly reduced the volitional nicotine intake in tupaias.

(+)-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.

The effect of long-term amphetamine administration on the activity of dopaminergic neurons of the substantia nigra

Spontaneously active neurons from the pars compacta region of the substantia nigra were studied in chloral hydrate anesthetized, immobilized rats which had been pretreated with daily intraperitoneal saline or D-amphetamine injections according to several schedules. The spontaneous firing rates of these neurons were not altered by any of the pretreatment regimens. In addition, the intravenous dose of D-amphetamine sulfate which was required to reduce the spontaneous firing rate of these cells by at least 50% (threshold dose) was not modified by amphetamine pretreatment. There was a significant positive linear correlation between the threshold dose and the initial spontaneous firing rate of the neurons from animals pretreated with multiple saline injections, but not from those receiving long-term D-amphetamine. These results demonstrate that there are no alterations in the sensitivity of dopaminergic neurons to amphetamine under conditions known to produce the enhanced effects of the drug on motor behaviors which develop during multiple injections.

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.

On the interaction of drugs with the cholinergic nervous system. I. Tolerance to phencyclidine derivatives in mice: pharmacological characterization

Phencyclidine [1(1-phenylcylohexyl) piperidine] and cyclohexamine [1(1-phenylcyclohexyl) ethylamine) were used as model psychotropic drugs to study the phenomenon of tolerance in mice. The behavioral effects of these drugs were measured by forced motor activity using the rotarod test. Tolerance develops progressively with chronic treatment at a rate and to a degree that are dose-dependent. The optimal conditions for tolerance induction are s.c. administration with 4-h intervals. The process of tolerance development is expressed in concomitant changes in five indices chosen for its quantification: ED50 values, duration, duration-dose dependency, critical falling time, and body weight. All these changes were found to be totally reversible, with no carry-over between two consecutive tolerance cycles. It was established that cyclohexamine is a better tolerance-inducer than phencylidine, although the nature of the tolerance developed for both drugs is qualitatively similar.