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Absence of cocaine sensitization in OVX female rats is not due to cocaine dosage

Female rats show higher locomotor activity in response to cocaine than males. Estradiol is partly responsible for this enhanced cocaine‐induced hyperactivity. The present study was designed to determine the dose and/or length of exposure to cocaine necessary to induce behavioral sensitization in ovariectomized female rats. Rats were ovariectomized, half received a Silastic implant filled with estradiol benzoate (OVX‐EB); the other half received an empty implant (OVX). For 5 consecutive days rats received a daily cocaine injection (10, 15 or 30 mg/kg). On days 1, 5, and 13 animals were tested for their locomotor response to cocaine. Another group of animals received a repeated cocaine exposure of 10 days. Their locomotor response to cocaine was recorded on days 1, 5, 10, and 18. Manipulations of dose and length of exposure to cocaine did not induce behavioral sensitization in OVX rats. These results show that estradiol is necessary for female rats to develop behavioral sensitization to cocaine.