Chronic nicotine administration increases tyrosine hydroxylase selectivity in the rat hippocampus

Acute nicotine treatment increases catecholamine synthesis selectively in the nucleus accumbens, hypothalamus and hippocampus of the rat. In the hippocampus, but not in the other areas mentioned, or in the caudate, chronic pretreatment with nicotine for 28 days potentiates this response. In the present study we have investigated the effects of acute treatment with the same dose of nicotine (0.8 mg/kg s.c.), and of chronic pretreatment with this dose, on the in vitro activity of tyrosine hydroxylase, the rate limiting enzyme for catecholamine synthesis. Tyrosine hydroxylase was not altered by acute nicotine, but was increased by about 2-fold, selectively in the hippocampus, by the chronic pretreatment. These results show that nicotine treatment increases the capacity for noradrenaline synthesis in the hippocampus; taken with our previous results they indicate that this capacity is not manifest until an acute challenge occurs. This effect of nicotine on tyrosine hydroxylase is consistent with nicotinic receptor mediation of central transsynaptic induction.