Cocaine conditioning and sensitization: The habituation factor

https://doi.org/10.1016/j.pbb.2006.04.017Get rights and content

Abstract

The behavioral and neurobiological impact of cocaine can be strongly influenced by the environmental context in which the cocaine effects are experienced. In this report, we present the results of an experimental study in which the effects of environmental context in terms of novelty/familiarity upon locomotor stimulant effects of cocaine were examined. In the first phase of the study, two groups of naïve rats (N = 10/group) received either cocaine (10 mg/kg) or saline immediately prior to a 20-min test in a novel open-field environment. After three daily cocaine/saline test sessions, both groups received a saline test to evaluate cocaine conditioned drug effects. In the second phase, two groups (N = 10/group) were administered a 20-min saline test 1 day prior to receiving the same cocaine and saline testing regimen as in the first phase. Cocaine sensitization effects were not observed when the cocaine treatments were initiated in a novel environment but were observed when the same cocaine treatments were preceded 1 day by a single 20-min test environment exposure. The maximal locomotion sensitization effects observed, however, did not exceed the locomotor stimulant effects induced by cocaine administered in a novel environment. Thus, the cocaine sensitization manifested following a brief 20-min exposure to the test environment 1 day prior to cocaine administration represented a reversal of an inhibitory habituation effect. Cocaine-conditioned effects were also observed in both phases. These cocaine conditioned effects approximated, but did not exceed, the activation effects generated by a novel environment.

Section snippets

Animals

Forty naive male Sprague-Dawley rats from Taconic Farms (Germantown, NY), 4 months old and weighing approximately 400 g at the start of the experiments were used. Upon arrival, the animals were housed in individual 48 × 27 × 20 cm3 clear polycarbonate cages in a climate-controlled room at 22–24 °C with a 12-h dark and 12-h light cycle. During the 1st week after arrival, all animals were handled and weighed daily for 7 days. During the second week the animals received three injections (i.p.) of 0.9%

Results

Fig. 1A,B presents the results of the first phase of the experiment in which cocaine (10.0 mg/kg) treatments were initiated in a novel environment. As is apparent from Fig. 1A, the cocaine treatment had a marked locomotor stimulant effect on distance traversed. Group differences over the three cocaine test sessions were statistically significant (F1/18 = 27.7, P < 0.001) but the group × test session interaction was not significant (F2/36 = 0.21, P > 0.05). The non-significant group × test session

Discussion

The findings in the present studies are relevant to both cocaine sensitization and cocaine conditioned drug effects. We found that when the cocaine treatments were initiated in a novel environment locomotor sensitization effects were not observed; on the other hand, one brief prior exposure to the test environment 1 day before the cocaine treatments were administered was sufficient to promote the development of sensitization. For non-drug animals, one exposure to the test environment also

Acknowledgements

This work was supported by NIDA grant DA RO1 05366 and a VA Merit Review Grant.

References (21)

There are more references available in the full text version of this article.

Cited by (0)

View full text