A comparison of the subnuclear and ultrastructural distribution of acetylcholinesterase and choline acetyltransferase in the rat interpeduncular nucleus.

The subnuclear and synaptic staining patterns for acetylcholinesterase (AChE) activity and choline acetyltransferase (ChAT) activity were studied in the rat interpeduncular nucleus (IPN) using histochemical and immunohistochemical methods. AChE reactivity was prominent in the neuropil of the rostral, lateral and dorsomedial subnuclei, whereas ChAT immunoreactivity was confined to axons and terminals in the rostral, intermediate and central subnuclei. AChE-positive somata were evident in all the subnuclear divisions of the IPN, and possessed reaction product in the rough endoplasmic reticulum and nuclear envelope. ChAT-positive somata were not present in the IPN. Characteristic axodendritic synapses in the rostral, intermediate and central subnuclei possessed ChAT immunoreactivity presynaptically, and AChE reactivity both pre- and postsynaptically. Other synaptic arrangements in the lateral subnucleus lacked ChAT-immunoreactive terminals, yet possessed prominent AChE reactivity. The results of the present study reveal that AChE reactivity and ChAT immunoreactivity are heterogeneously distributed among the subnuclear divisions of the rat IPN, and that AChE reactivity is present in both the cholinoceptive and noncholinoceptive subnuclei. Although neuronal colocalization of ChAT and AChE activity is not evident in the IPN, AChE-positive neurons are in receipt of putative cholinergic, as well as peptidergic, afferent inputs.