Functional alpha7-containing nicotinic acetylcholine receptors localize to cell bodies and proximal dendrites in the rat substantia nigra pars reticulata.

The substantia nigra pars reticulata (SNr) is the primary output nucleus for the basal ganglia (BG) in the rat. The SNr is reciprocally connected with the pedunculopontine tegmental nucleus (PPN) in the brainstem, which provides cholinergic innervation to most BG nuclei. The cholinergic input into the BG is considered to be important because PPN activity is altered in Parkinson's disease (PD), a neurological disorder involving the BG, and cholinergic pharmacotherapy is beneficial in alleviating some of its symptoms. In order to better understand the role of cholinergic input to the BG, we examined the effects of nicotinic acetylcholine receptor (nAChR) activation in the GABAergic neurons in slices through juvenile rat SNr. With the aide of subtype selective antagonists, we found that SNr neurons express the alpha7 subtype of nAChRs, the function of which we assessed using the whole cell patch-clamp recording technique. Besides alpha7 nAChRs, GABAergic SNr neurons also contained functional non-alpha7 nAChRs. Using local photolysis of caged carbachol, a broad-spectrum cholinergic agonist, we mapped alpha7 nAChR-mediated currents along the visible extent of filled SNr neurons and found that alpha7 nAChRs can be functionally detected as far as 60 microm away from the soma. Our data are paving the way to a better understanding of the physiological roles of nAChRs in the BG.