Immunocytochemical localization of enkephalin and substance P in retina and eyestalk neurones of lobster

Abstract

Enkephalin and substance P are two peptides found in vertebrate nervous systems that have been intensively studied with regard to cellular distribution and receptor mechanisms^1–3. Invertebrate nervous systems, which are extremely useful in elucidating general principles of neural functions^4–6, can also be used as models for the analysis of peptidergic mechanisms^7,8. The accessibility, regularity, small number and relatively large size of the neural components of one such system, the crustacean compound eye, have facilitated the accumulation of detailed information about their anatomy^9–11 and physiology^12–14, and provided insight into basic principles of intercellular communication^12–14. We report here that immunoreactivity of enkephalin and substance P can be localized to specific neural elements in the visual system of the spiny lobster, Panulirus interruptus. Our observations suggest that this highly organized, simple in vivo system may be a convenient model to evaluate the cellular mechanisms of these peptides. Although several neuropeptides have been localized in vertebrate retinal inter-neurones¹⁵, our results are the first to detect a known peptide in primary photoreceptors.