RESEARCH ON POLYCHAETE ANNELID OSMOREGULATORY PEPTIDE(S) BY IMMUNOCYTOCHEMICAL AND PHYSIOLOGICAL APPROACHES - COMPUTER RECONSTRUCTION OF THE BRAIN AND EVIDENCE FOR A ROLE OF ANGIOTENSIN-LIKE MOLECULES IN NEREIS (HEDISTE) DIVERSICOLOR OF MULLER

Immunohistochemical and physiological studies were carried out on Nere is (Hediste) diversicolor OF Muller in order to obtain evidence concer ning the neuroendocrine control of polychaete osmoregulation. The occu rrence in this animal of peptides immunologically related to mammalian angiotensin II and I (AII and AI) and oxytocin (OT) was demonstrated in the brain and the ventral nerve cord (VNC) perikarya and nerve fibr es as well as in a few peripheral structures (peripheral nerves, epith elial cells, nuchal organ, intestine and nephridia). The exact localiz ation of immunoreactive cells was achieved by serial sections of brain and ventral nerve cord followed by a three-dimensional reconstruction of brain ganglionic nuclei using the CATIA ('Conception Assistee Trid imensionnelle Inter Active') Dassault system program. Injections of po lyclonal antisera against AII or OT provoked a partial inhibition of t he increase in body weight in Nereis exposed to hypo-osmotic medium. T he effect of a-All seemed more pronounced than that of a-OT. In a subs equent test, injections of synthetic AII and AII-amide (peptide recent ly isolated from an achaete (Salzet et al (1995) J Biol Chem 270, 1575 -1582) enhanced the increase in body weight and, therefore, strenghthe ned the hypothesis of the neuroendocrine control of Nereis osmoregulat ion. The antidiuretic effect of both synthetic peptides in this study was indicative of the exact role of Nereis endogenous molecule(s). AII was less potent than its amidated form. If Al-like can easily be stru ck off the list of putative endogenous osmoregulaory factors, the role of OT-like substance in Nereis osmoregulation, which is partially dem onstrated in this study, needs to be clarified by further physiologica l experiments using injection of synthetic peptide(s) or endogenous su bstance(s). All these results are discussed and compared to those rece ntly obtained in an achaete annelid (Salzet er al (1993) Brain Res 631 , 247-255; Salzet et al (1993) Brain Res 601, 173-184; Salzet et al (1 995) J Biol Chem 270, 1575-1582.