Increases in tyrosine hydroxylase messenger RNA in the locus coeruleus after a single dose of nicotine are followed by time-dependent increases in enzyme activity and noradrenaline release.

We have utilized biochemical, molecular biological, and functional neurochemical measurements to investigate the integrated and long-term effects of a single dose of nicotine on the noradrenergic system in the central nervous system of the rat, from enzyme induction to transmitter release. We have found that a single systemic injection of nicotine (0.8 mg/kg) increases messenger RNA for the rate-limiting enzyme in the synthesis of catecholamines, tyrosine hydroxylase, two to six days later in the noradrenergic cell body region, the locus coeruleus (and not in the dopaminergic cell body regions, substantia nigra and ventral tegmental area). This was then followed by a time-dependent increase in enzyme activity, measured in vitro, in terminal regions of the ascending dorsal noradrenergic bundle up to four weeks later. Functionally, the increase in tyrosine hydroxylase activity in the terminals four weeks after a single administration was associated with an increase in the capacity to release noradrenaline in the hippocampus, measured using in vivo microdialysis in freely moving animals. This occurred in response to an acute systemic nicotine injection (0.4 mg/kg) but not to a local, intrahippocampal, challenge with 250 microM nicotine. These experiments have revealed a long-term effect of nicotine on noradrenergic activity in the central nervous system, associated with induction of tyrosine hydroxylase. This is accompanied by a time-dependent increase in terminal tyrosine hydroxylase activity and an increase in noradrenaline release.