The subnuclear organization of acetylcholinesterase-containing neurons in the interpeduncular nucleus of rats.

The interpeduncular nucleus (IPN) is a heterogeneous structure comprised of seven subnuclei which differ with regard to their cytoarchitecture, synaptology, connectivity, and content of neuropeptides and biogenic amines. In the present study, we used Butcher's pharmacohistochemical regimen to assess the subnuclear distribution and staining intensity of acetylcholinesterase (AChE)-containing neurons in the IPN. Although AChE-positive somata were present in every subnucleus, their staining intensity differed within and between the subnuclei. The most intensely stained somata were found in the apical and central subnuclei; however, they comprised only 10-25% of the total population of AChE-positive somata in these subnuclei. Heavily stained somata were observed in the apical, central, and lateral subnuclei; moderately stained somata in the central, lateral, intermediate, and rostral subnuclei; and lightly stained somata in the lateral, intermediate, rostral, dorsal lateral, and rostral lateral subnuclei. The present findings indicate that AChE-containing neurons are differentially distributed between subnuclei of the IPN.