Localization of catecholamines in the eyes and other tissues of Aplysia

A green fluorescence indicative of catecholamines (CA) was localized in the secondary cells (nonreceptor neurons), neuropile and optic nerve of the eye and other tissues in Aplysia by using the formaldehyde-induced fluorescence method for the demonstration of biogenic amines. The specificity of the induced fluorescence was confirmed by its absence in tissue not exposed to formaldehyde vapor, relatively rapid decay upon exposure to UV light and its chemical reduction by sodium borohydride. The fluorescence was greatly reduced in eyes treated with reserpine (depletes serotonin and catecholamines). Furhter confirmation that the green fluorescence in the eye was due to a CA and not to serotonin was obtained by showing that it was decreased or eliminated by alpha-methyl-para-tyrosine (an inhibitor of catecholamine synthesis), increased by incubation in dopamine and exhibited a peak emission (470 nm) characteristic of CA fluroescence. CA fluorescence was also observed in the neuropiles of the cerebral, pedal, pleural and parieto-visceral ganglia and in cells in the pedal ganglion, statocyst, mantle, anterior tentacles and siphon. The finding of CA in secondary neurons of the eye was unusual since CA-containing cells have not been observed in other gastropod eyes. The distribution of CA in Aplysia, in tissue other than the eye, is similar to that of other gastropod molluscs.