THE OLFACTORY SYSTEM OF THE EMBRYONIC COMMON CUTTLEFISH, SEPIA OFFICINALIS

Abstract

Olfactory systems across the animal kingdom have several inter-phyletic similarities, such as glomeruli, which have been well studied in some vertebrates and arthropods. Comparisons in a third taxon, such as the large-brained cephalopods, could help to elucidate the evolution of these commonalities. I used immunohistochemistry and in situ hybridization on embryos of Sepia officinalis, the common cuttlefish, to map the organization of their olfactory system. I first demonstrated that histamine is a neurotransmitter in a class of olfactory sensory neurons by examining staining from anti-histamine and a custom histidine decarboxylase mRNA probe. To update classic descriptions of the cephalopod brain, I used antibodies and riboprobes against FMRFamide, serotonin, APGWamide, acetylated α-tubulin, and synaptotagmin, in addition to structural stains including phalloidin and DiI. My findings cast doubt upon the hypothetical presence of glomeruli in all molluscs and clarify our understanding of how the sense of olfaction evolved.