The influence of environment on the induction of sensitization to the psychomotor activating effects of intravenous cocaine in rats is dose-dependent

Abstract

The acute psychomotor response and development of sensitization to amphetamine is attenuated if i.p. injections are given in the cage where a rat lives relative to when injections are given in a novel but physically identical test environment. Furthermore, when the environmental cues predicting i.p. injections are completely eliminated by using remotely activated i.v. injections in the home cage, 1.0 mg/kg amphetamine produces a very small acute response and no sensitization. The same treatments do produce sensitization if i.v. injections are signaled by placement of the rat in a novel test cage. The present experiment was designed to determine if there is a similar effect of environmental condition on the response to i.v. cocaine, and to what extent the effect may be dose-dependent. This was accomplished by comparing the psychomotor activating effects (rotational behavior) of repeated i.v. administrations of one of eight doses of cocaine (0.0, 0.3, 0.6, 1.2, 2.4, 3.6, 4.8, or 7.2 mg/kg) given in the home cage, with infusions of the same doses given in a novel test cage. There was no effect of environment on the acute psychomotor response to cocaine. There was, however, a significant effect of environment on the induction of sensitization. A higher dose of cocaine was required to induce sensitization when i.v. administrations were given in the home cage than when they were given in a physically identical but novel test environment. At high doses, however, cocaine induced sensitization regardless of environmental condition. The results suggest that the effect of this environmental manipulation is to shift the dose-effect curve for the induction of sensitization, and support the notion that the ability of psychostimulant drugs to induce sensitization can be modulated by the circumstances surrounding drug administration.

Estrogen Influences Cocaine-Induced Blood Oxygen Level-Dependent Signal Changes in Female Rats

“…Both conditions surrounding psychostimulant administration and the route of administration can affect the behavioral response to these drugs (Browman et al, 1998) and perhaps neuronal activity (Porrino, 1993). Thus, external stimuli, such as a needle prick after intraperitoneal administration and the cage environment in which cocaine pretreatment was given, are not expected to significantly contribute to evoking neuronal activity in the present study.…”

The Neural Consequences of Repeated Cocaine Exposure Revealed by Functional MRI in Awake Rats

“…Both conditions surrounding psychostimulant administration and the route of injection can affect the behavioral response to these drugs (Browman et al, 1998), and can vary the magnitude of neuronal activity (Porrino, 1993). External stimuli, such as a peripheral injections and the cage environment where cocaine pretreatment was given, are not expected to significantly contribute to evoking neuronal activity in the present study.…”

Manipulations During the Second, but not the First, Week of Life Increase Susceptibility to Cocaine Self-Administration in Female Rats

“…Rats selected to proceed to SA were anesthetized with a ketamine (100 mg/kg), xylazine (20 mg/kg), and acepromazine (20 mg/kg) solution in a 1-ml/kg volume. A chronic indwelling catheter was placed into the external jugular vein using procedures described previously (Browman et al, 1998;Crombag et al, 1996;Robinson et al, 2001;Weeks, 1972). Briefly, a silicone catheter (0.012 00 Â 0.025 00 Â 0.0065 00 ; A-M Systems, Inc., Carlsborg, WA) was inserted into the external jugular vein and passed s.c. to an infusion port mounted between the shoulder blades, similar in design to that described by Caine et al (1993).…”