Strain and sex alter effects of stress and nicotine on feeding, body weight, and HPA axis hormones

Gender and genotype result in differential sensitivity to stress and to nicotine. Male and female Sprague–Dawley and Long–Evans rats exhibit different behavioral responses to immobilization stress and to chronically-administered nicotine, suggesting that these animals may be useful to model human variability in stress and nicotine sensitivity. It is possible that differences in sensitivity of the hypothalamo–pituitary–adrenocortical (HPA) axis might account for these sex and strain differences. This experiment examined corticosterone (CORT) and adrenocorticotropin hormone (ACTH) responses of male and female Sprague–Dawley (n=117) and Long–Evans (n=120) rats administered 0, 6, or 12 mg/kg/day nicotine for 14 days; half of each treatment group was exposed to immobilization stress (20 min/day). Feeding and body weight also were measured. Nicotine increased CORT and ACTH levels of Sprague–Dawley females only. Stress increased CORT and ACTH levels of all groups except for Long–Evans females. Nicotine and stress decreased feeding and body weight with greatest effects in Long–Evans females. CORT, feeding, and body weight were positively correlated among stressed females. These findings suggest that strain differences in HPA axis, body weight, and feeding responses to nicotine and to stress are robust among females but not among males. CORT reactivity and female sex hormones may explain these differences.