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.