Influence of sex and female hormones on nicotine-induced changes in locomotor activity in rats

The acute and chronic effects of nicotine (0.4 mg/kg SC) on locomotor activ ity in photocell cages have been compared in male, female, and ovariectomiz ed hooded rats. In Experiment 1, female rats displayed higher locomotion th an males (n = 12); acutely, nicotine-reduced locomotion, and this effect wa s slightly larger in females than males. Daily administration of nicotine f or 21 days produced a similar, gradual increase in activity in both sexes. Tests then confirmed greater activity in females than males and as a functi on of previous chronic exposure to nicotine (n = 6); there was an activatin g effect of nicotine challenge but no interaction of nicotine effects with sex. In Experiment 2, ovariectomized rats were primed with 17-beta-estradio l (50 mu g/kg SC) and progesterone (2.5 mg/kg SC) or vehicle only. Acute ad ministration of nicotine reduced activity in both groups similarly (n = 12) . After nicotine daily for 21 days, there was increased activity as a funct ion of both chronic nicotine and hormonal priming, and challenge with nicot ine increased activity (n = 6). The effects of these challenges with nicoti ne were also slightly greater, as a function of previous nicotine exposure and priming. As a whole, these experiments showed robust effects of acute a nd chronic nicotine administration, sex, and hormonal priming; neither sex nor gonadal hormones had marked influences on changes in locomotor activity produced by nicotine. (C) 1998 Elsevier Science Inc.