Effect of prolonged nicotine infusion on response of rat catecholamine biosynthetic enzymes to restraint and cold stress

There is a paradoxical relationship between nicotine and stress. To help elucidate their relationship on catecholamine biosynthesis, rats were infused with nicotine for 7-14 days before exposure to cold or restraint stress. Nicotine (5 mg/kg/day, 14 days) did not alter basal plasma corticosterone or its elevation with 24 h cold stress, but prevented corticosterone elevation following 2 h restraint stress. In adrenal medulla (AM), response of dopamine β-hydroxylase (DBH), but not tyrosine hydroxylase (TH) mRNA, to both stressors was attenuated in nicotine-infused rats. In locus coeruleus (LC), restraint stress elevated TH and DBH mRNA in saline-, but not in nicotine-infused rats. Cold stress triggered a similar response of TH and DBH mRNAs in LC with and without nicotine infusion. With shorter nicotine infusion (8 mg/kg/day, 7 days), TH mRNA in AM was not induced by restraint stress on one (1×) or two (2×) consecutive days nor was DBH mRNA in AM or LC by 2×. The findings demonstrate that constant release of nicotine can modulate, or even prevent, some stress responses at the level of the HPA axis and gene expression of catecholamine biosynthetic enzymes in LC and AM.