Cocaine conditioning and sensitization: The habituation factor
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.
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