Meeting Abstract
Research on squid chromatophores has been largely restricted to loliginids, a family of primarily coastal species whose displays rely heavily on spatial patterning. Comparatively little work has been done on the pelagic ommastrephids, the family that includes Dosidicus gigas. This species displays dynamic “flickering” characterized by seemingly chaotic activity of chromatophores that can be rapidly inhibited before an episode of coordinated flashing. In this study we investigated the innervation of chromatophores in Dosidicus, particularly serotonergic pathways, in order to compare features with those in loliginids where 5-HT has inhibitory effects. We used topical application of 5-HT with skin preparations from Dosidicus (and the loliginid Doryteuthis opalescens) to study functional effects and immunohistochemistry to visualize serotonergic axons in the chromatophore system. We found that chromatophore activity in D. gigas was more sensitive to 5-HT and that the extent of serotonergic innervation is greatly reduced in comparison to D. opalescens. These features correspond to a different level of spontaneous chromatophore activity in skin preparations from D. gigas and D. opalescens as well as in the living animal. Chronic denervation of chromatophores in D. opalescens leads to complete degeneration of serotonergic axons and the appearance of spontaneous waves of chromatophore activity that are inhibited by 5-HT, similar to activity normally observed in D. gigas. We suggest that the sparse serotonergic innervation in Dosidicus results in minimal resting inhibition that facilitates flickering, and that the extensive serotonergic innervation in D. opalescens leads to strong inhibition of spontaneous, coordinated chromatophore activity in the normal, innervated condition.
