Conditioning, habituation and behavioral reorganization factors in chronic cocaine effects

Abstract

Rats were administered cocaine (50.0 mg/kg i.p.) daily for 7 days in a Pavlovian paradigm either immediately prior (paired group) or 30 min following (unpaired group) a 20-min placement in an open field test environment. After 7 days of drug withdrawal, the animals were retested 3 days apart, once with saline and once with cocaine (50 mg/kg). Measurement of locomotion as distance traversed (m) revealed a higher level of locomotion in the paired group on all test trials. Analysis of the paired vs. unpaired differences indicated an antihabituation effect of cocaine rather than a hyperlocomotion or a conditioned locomotor effect. Rotation pattern analysis for each animal showed a new frequency distribution of rotations across four categories of diameter size in the paired but not in the unpaired group by Day 5. This new pattern was characterized by a shift in skewness toward large greater than or equal to 55 cm diameter rotations. These qualitative changes in rotation pattern point to a context specific behavioral reorganization process in response to repeated cocaine drug treatment.