Regulation of Release and Mode of Action of Crustacean Chromatophorotropins

Abstract

Pigment movements in crustacean chromatophores are regulated by pigment-concentrating and pigment-dispersing neurosecretory hormones. The release of these hormones from the neurosecretory system is thought to be controlled by neural signals. Although the exact cellular sources of chromatophorotropins and the nature of synaptic input to the neurosecretory system remain unresolved, recent pharmacological studies on fiddler crabs indicate that certain biogenic amines contribute to the release of some of the chromatophorotropins. The current evidence suggests that: 5-hydroxytryptamine stimulates the release of RPDH (red pigment dispersing hormone), dopamine triggers the release of RPCH (red pigment concentrating hormone), and norepinephrine stimulates the release of BPDH/MDH (black pigment/melanin dispersing hormone). Nothing is known of the regulation of release of leucophorotropins and xanthophorotropins. Like most other peptide hormones, crustacean chromatophorotropins are thought to exert their effect by first binding to receptors on the cell surface and then triggering a series of events leading to cellular responses, but the details are far from clear. Recent work suggests that hormone-induced pigment movements may be modulated/mediated by alterations in cyclic nucleotide levels and/or by changes in Ca2+ distribution or flux. Both cyclic nucleotides and Ca2+ may modulate motility by regulating the integrity and/or function of cytoskeletal elements, but the details of this mechanism and the precise roles of cytoskeletal elements in the pigment-translocating process remain unresolved.