Tissue & Cell, 2002 34 (2) 109–116 © 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0040-8166(02)00020-4, available online at http://www.idealibrary.com Tissue&Cell Immunocytochemical demonstration of glucagon-like peptides in Mytilus edulis cerebral ganglia and an in vitro effect of vertebrate glucagon on glycogen metabolism K. Kellner, C. Heude-Berthelin, M. Mathieu Abstract. Immunological detection of glucagon-like peptides was performed in the cerebral ganglia of the mussel Mytilus edulis using an anti-vertebrate glucagon antibody. Two clusters of positive neurosecretory cells were observed, as well as stained nervous fibers. The effect of vertebrate glucagon on glucose incorporation into glycogen of reserve cells was tested using an in vitro microplate bioassay. Optimal incubation conditions were previously defined and an inhibitory effect of porcine glucagon was obtained for concentrations ranging from 10 -6 to 10 -9 M. It is postulated that the glucagon-like peptide may be implicated in the regulation of glucose metabolism in bivalves. © 2002 Elsevier Science Ltd. All rights reserved. Keywords: glucagon, Mytilus edulis , mollusca, glycogen metabolism, immunocytochemistry, cerebral ganglia Introduction In temperate areas, marine bivalves follow an annual re- productive cycle with defined periods of gonadal matura- tion and spawning. Reproduction is generally associated with high energy consumption and weight loss during spawning may be considerable (Downing & Allen, 1987; Mathieu & Lubet, 1993). This sexual activity is dependent on the accu- mulation of abundant reserves, essentially during the sexual resting stage, and mobilisation of these reserves to support the reproductive effort. In Mytilidae, glycogen represents the major form of nutrient reserve (De Zwaan & Zandee, 1972; Gabbott, 1975, Bayne et al., 1982). In the mussel Mytilus edulis, two types of storage cells have been previously identi- Laboratoire de Biologie et Biotechnologies Marines, Université de Caen, Esplanade de la paix, Caen Cedex, France Received 12 June 2001 Accepted 27 March 2002 Correspondence to: Dr K. Kellner, Laboratoire de Biologie et Biotechnologies Marines, Université de Caen, Esplanade de la paix, 14032 Caen Cedex, France. Tel.: +33 2 31 53 80 18; Fax: +33 2 31 53 80 09; E-mail: kellner@ibba.unicaen.fr fied: the adipogranular cells (ADG cells) contain mainly lipid droplets, proteinic granules and glycogen particles, the vesic- ular connective tissue cells (VCT cells) or glycogen cells are specialised in glycogen storage (Froutin, 1937; Lubet, 1959; Lenoir et al., 1989). Both cell types co-exist in mantle tissue whereas only VCT cells are present in labial palps. In mussel populations of the European north-west coasts, the major spawning event occurs in February. Gabbott and Bayne (1973) have previously demonstrated that glycogen storage occurs in summer during the sexual resting stage, when nutrients are abundant, and that reserves are progres- sively mobilised in autumn and winter during gametogenetic development. In the mussel M. edulis, glycogen storage and mobilisation provides a good example of metabolic regulation by external and internal factors. Glycogen storage is mainly dependant on the free circulating glucose level: an elevation of glucose concentration increases glycogen synthetase activity (I form) in tissue slice preparations (Whittle & Gabbott, 1986). Mo- bilisation of reserves appears to be strictly correlated with the reproductive activity in mussels and a possible neuroen- docrine control of this breakdown must be taken into account. 109