Augmented Constitutive CREB Expression in the Nucleus accumbens and Striatum May Contribute to the Altered Behavioral Response to Cocaine of Adult Mice Exposed to Cocaine in utero

Neuroadaptations occurring in the mesolimbic dopamine pathway following recurrent exposure to drugs of abuse have been correlated with a behavioral phenomenon known as behavioral sensitization. We have developed an animal model of prenatal cocaine exposure and, using a postnatal sensitization protocol, have examined the subsequent sensitivity of offspring to cocaine. Pregnant Swiss Webster dams were injected twice daily from embryonic day 8 to 17, inclusive, with cocaine (COC40: administered cocaine HCl at a dose of 40 mg/kg/day, and COC20: administered cocaine HCl at a dose of 20 mg/kg/day), or saline (SAL). The SPF40 group (saline pair-fed), a nutritional control group, was ‘pair-fed’ with COC40 dams. Activity was recorded for 30 min during a 3-day saline habituation, a 14-day ‘initiation’ phase, when animals received cocaine (15 mg/kg) or saline every other day, and following a 21-day ‘withdrawal’ period when all mice were challenged with cocaine. COC40 offspring, as compared with SAL controls, did not habituate to a novel environment, demonstrated increased cocaine-induced stereotypy on Coc 1 (first cocaine injection), and blunted locomotor sensitization on challenge as measured by the percentage of each animal’s baseline locomotion. Tissue samples of the nucleus accumbens (NAc) and striatum (Str) of all four prenatal treatment groups were examined to determine whether alterations in the transcription factor CREB or glutamate receptor subunit, GluR1, induced by prenatal cocaine treatment may have contributed to the altered behavioral responses. Immunoblot quantitation revealed significantly increased constitutive CREB expression in the NAc and Str of COC40 mice as compared with SAL controls. Such alterations in constitutive CREB levels may contribute to some of the behavioral differences reported in adult mice exposed to cocaine in utero.