Ontogeny of oxytocin-like immunoreactivity in the cuttlefish, Sepia officinalis, central nervous system.

In vertebrate species, the neuropeptide oxytocin (OT) has been implicated in neural and behavioral development. Although several OT-like peptides have been characterized in invertebrate species, the ontogenesis of the OT-like system has not yet been described in these species. Thus, the aim of the present study was to perform an immunohistochemical investigation of the spatiotemporal distribution of OT-like elements in the central nervous system (CNS) of a decapod cephalopod mollusc, the cuttlefish, Sepia officinalis, during the first 3 months of postembryonic development. On the day of birth, OT-like immunoreactivity was detected throughout the whole CNS. Some nervous structures (e.g. the magnocellular lobes) exhibited a stained pattern in newborns similar to that reported in our previous study in adult cuttlefish whereas other lobes (e.g. the vertical lobe complex) showed maturation during the first weeks of life. Finally, at the age of 60 days, the general pattern of staining in the CNS was comparable to the adult distribution. The putative roles of the OT-like system with regard to the development of some behaviors in juvenile cuttlefish are discussed. The present study provides a neurochemical basis for the investigation of postnatal development of complex behaviors in cephalopods and suggests, for the first time in an invertebrate species, important organizational effects for the OT-like system in the course of the first weeks of life.