PLASMA COCAINE LEVELS AND LOCOMOTOR-ACTIVITY AFTER SYSTEMIC INJECTIONIN VIRGIN AND IN LACTATING MATERNAL FEMALE RATS

We have determined the temporal pattern of plasma cocaine levels and i ncreased activity that result from acute systemic injections of cocain e to female rats in two different endocrine and behavioral states, in nonmaternal virgins and in lactating maternal dams. Plasma levels of c ocaine as well as ambulatory and rearing activity were determined ever y 30 min for a total of 300 min after subcutaneous injections of eithe r 10, 20, or 40 mg/kg of cocaine. Virgin females had no prior drug his tory, whereas lactating, maternal dams had received two cocaine inject ions before activity testing. Within 30 min after an injection, cocain e in the plasma and activity were substantially elevated, and generall y remained so for 270-300 min. Overall, plasma cocaine levels and acti vity were well correlated and followed a predictable dose-response pat tern. The onset, peak, duration, and decline of activity corresponded generally to the onset, peak, duration, and decline of plasma cocaine. For virgins, mean ambulatory activity increased 2.5-4.0-fold over bas eline, whereas in lactating females activity increased 5-11-fold over baseline. Stereotypy did not occur. Although the general responsivity of these females to cocaine was very similar to that reported for male s, there are differences in the timing of peak activity and the return of activity to baseline when the virgins and the lactating dams are c ompared to each other and to reports by others on male rats. These dat a support the hypothesis that endocrine or behavioral state may influe nce the responsiveness of animals to cocaine. (C) 1998 Elsevier Scienc e Inc.