Hemicholinium-3 binding sites in subnuclei of the rat interpeduncular nucleus: quantitative in vitro autoradiography

The interpeduncular nucleus (IPN) receives dense cholinergic input from the medial habenulae (MH) via the fasciculus retroflexus (FR). This projection is known to terminate in the rostral, central and intermediate subnuclei. Correspondingly, the concentration of hemicholinium-3 (HC-3) binding sites in these subnuclei was equal to or greater than that reported in any other brain areas. Moderate values in the distal FR and in the lateral subnuclei indicate that choline uptake sites are located on nonterminal portions of MH afferent axons as well. Possible relationships of HC-3 binding to the unusual metabolic properties of FR and IPN, and to the distribution of choline acetyltransferase-containing axons and terminals in FR and IPN are suggested.