Immunocytochemical identification of peptidergic neurons in compartment 4 of the supraesophageal ganglion of the leech Theromyzon tessulatum (O.F.M.)

Abstract

The use of polyclonal antibodies directed against mammalian peptide hormones and of monoclonal antibodies raised against molecules of supraesophageal ganglion neurons of the leech Theromyzon tessulatum has led to the identification of more than half of the 30 neurons present in compartment 4 of the supraesophageal ganglion. Six cellular types were characterized at stage 3B of the life cycle: (1) a group of four or five large angiotensin II and γ-melanocyte stimulating hormone (γ-MSH) immunopositive cells also immunoreactive with monoclonal antibodies Tt-7 and Tt-159 (cells of class I), (2) a group of five small growth hormone releasing factor (GRF) positive cells, (3) three motilin-positive cells, (4) one met-enkephalin-positive cell, (5) one oxytocin-positive cell that also immunoreacts with monoclonal antibody Tt-1, and (6) one vasopressin-positive cell immunoreactive with monoclonal antibody Tt-9. This study shows the heterogeneity of the neurons constituting compartment 4 and demonstrates that most of them have secretions of a peptidergic nature. The co-localization of epitopes recognized by anti-γ-MSH and anti-angiotensin II is demonstrated in cells of class I. The number of immunoreactive cells found in compartment 4 is not always constant and can vary for the following reasons: (i) changes in the physiological status of the leech, as is the case with anti-GRF and anti-motilin, (ii) individual variations for some cellular types (cells of class I), (iii) variability in the situation of the connective-tissue septum separating compartments 4 and 5.