Sensitization to stereotypy in DBA/2J but not C57BL/6J mice with repeated cocaine.

The present study investigated the effects of seven repeated daily injections of 32 mg/kg cocaine on stereotyped behaviors (repetitive locomotion, rearing, and head bobbing) in two genetically distinct strains of mice. An initial injection of cocaine induced no stereotypy in either DBA/2J or C57BL/6J mice. Following the fourth daily injection, cocaine induced stereotypies in DBA/2J mice (11.33 +/- 4.40) compared to saline controls (2.67 +/- 1.54). Cocaine-induced stereotypy in DBA/2J mice was further enhanced following the seventh daily injection (19.83 +/- 4.39) as compared to saline controls (0.67 +/- 0.54). No cocaine-induced stereotypy was observed in C57BL/6J mice following any injection. Eighth day saline challenges of cocaine-sensitized mice did not induce stereotypy. Eighth day cocaine challenges of saline-treated mice induced no stereotypy in either strain. The current study demonstrates that sensitization to cocaine can be influenced by genotype and suggests that genetically defined animals may be useful in elucidating mechanisms underlying sensitization and tolerance to cocaine.