Serotonergic modulation of nicotine-induced kinetic tremor in mice.

We previously demonstrated that nicotine elicited kinetic tremor by elevating the neural activity of the inferior olive via α7 nicotinic acetylcholine (nACh) receptors. Since α7 nACh receptors reportedly facilitate synaptic monoamine release, we explored the role of 5-HT receptors in induction and/or modulation of nicotine tremor. Treatment of mice with nicotine induced kinetic tremor that normally appeared during movement. The 5-HT agonist, 8-hydroxydipropylaminotetraline (8-OH-DPAT), significantly enhanced nicotine-induced tremor and the action of 8-OH-DPAT was antagonized by WAY-100135 (5-HT antagonist). In addition, the cerebral 5-HT depletion by repeated treatment with p-chlorophenylalanine did not reduce, but rather potentiated the facilitatory effects of 8-OH-DPAT. In contrast, the 5-HT agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI), significantly attenuated nicotine tremor, which was antagonized by ritanserin (5-HT antagonist). The 5-HT agonist SR-57227 did not affect nicotine-induced tremor. Furthermore, when testing the direct actions of 5-HT antagonists, nicotine tremor was inhibited by WAY-100135, but was unaffected by ritanserin, ondansetron (5-HT antagonist) or SB-258585 (5-HT antagonist). These results suggest that postsynaptic 5-HT receptors are involved in induction of nicotine tremor mediated by α7 nACh receptors. In addition, 5-HT receptors have an inhibitory modulatory role in induction of nicotine tremor.