Nicotine-induced Fos expression in the pedunculopontine mesencephalic tegmentum in the rat

The aim of this study was to assess the effects of a single dose of nicotin e (NIC, 0.3 or 1.0 mg/kg, s.c.), after survival times of 30, 60 or 120 min, on immediate early gene expression in the pedunculopontine mesencephalic t egmentum (PMT), using Fos-immunocytochemistry. Either doses of NIC strongly increased Fos-immunoreactivity in both the ped unculopontine tegmental nucleus (PPTg) and the laterodorsal tegmental nucle us (LDTg), as compared to the saline controls, at 30 min and 60 min. In com parison, the effects of NIC-induced Fos expression in the caudate-putamen ( CP) were not as strong as the ones observed in the PPTg and LDTg. In fact, at 30 min the 0.3 mg/kg dose of NIC did not induce Fos-expression, unlike t he PPTg and LDTg. The CP response was more noticeable in the mediodorsal th an in the laterodorsal region. Double-labelling studies using Fos-immunoreactivity and NADPH-diaphorase hi stochemistry for cholinergic cells in the PPTg and LDTg revealed that, in g eneral, cholinergic neurons had Fos negative nuclei, although double-labell ed neurons were occasionally seen in the PPTg. In conclusion, systemically administered NIC activates the neuronal populat ion of the PPTg and the LDTg possibly by directly targeting nicotinic recep tors that may be located in non-cholinergic neurons. We postulate that acti vation of these non-cholinergic neurons modulates the activity of cholinerg ic cells in the PMT, which in turn may alter dopamine release in the mesoli mbic system. (C) 2000 Elsevier Science Ltd. All rights reserved.