Behavioral sensitization to nicotine in female and male rats.

Behavioral sensitization to nicotine has been studied in both male and female rats, but studies up to now have been difficult to compare due to different experimental conditions. Including both sexes in scientific research is of great importance since clinical data indicate gender differences both in response to nicotine and in ability for smoking cessation. The aim of the present study was to compare behavioral sensitization and body-weight gain to two chronic doses of nicotine in female and male Wistar rats housed in unisex conditions. The rats received daily subcutaneous injections of vehicle or nicotine (0.2 or 0.4 mg/kg, free base) and locomotor activity was measured at days 1, 7, 14, 21, 28 and 37 after administration of vehicle or nicotine (0.4 mg/kg). On day 45, all rats received an injection of nicotine. Body weights were monitored throughout the experiment. All rats receiving nicotine developed a sensitized response to the locomotor stimulatory effects of the drug. Male and female rats displayed a similar effect on horizontal and rearing activity after treatment with nicotine. Acute nicotine treatment induced a depressed rearing activity in male, but not female, rats; however, after chronic treatment the rats displayed a sensitized response. Furthermore, females treated with nicotine gained less weight compared to controls, while no such effect was seen in males. In conclusion, the present study does not support findings suggesting sex differences in development of behavioral sensitization to nicotine, while it demonstrates differences in nicotine-induced effects on weight gain in female and male rats.