Localization of substance P-like, leucine-enkephalin-like, methionine-enkephalin-like, and FMRFamide-like immunoreactivity in the eyestalk of the fiddler crab, Uca pugilator

Abstract

The occurrence and distribution of substance P (SP)-like, methionine-(Met)- and leucine-(Leu)-enkephalin-like, and FMRFamide-like immunoreactivities were determined in the neuroendocrine complex of the eyestalk of the fiddler crab, Uca pugilator, by immunocytochemistry. SP-like immunoreactivity was found in the optic peduncle, sinus gland, medulla externa, medulla interna, lamina ganglionaris, and retinular cells. Met-enkephalin-like and Leu-enkephalin-like immunoreactivity was observed in most of the retinular cells, optic peduncle, sinus gland, medulla terminalis, and lamina ganglionaris. However, Met-enkephalin-like, but no Leu-enkephalin-like, immunoreactivity was seen in the medulla terminalis X-organ. FMRFamide-like immunoreactivity could be seen in all parts of the eyestalk except in the sinus gland, lamina ganglionaris, and retinular cells. FMRF-amide-like activity was especially strong in the three chiasmatic regions connecting the optic ganglia. The possibility that these four peptides may function as neuroregulators in the fiddler crab is discussed.

Crustacean neuropeptides

“…While Carcinus maenas is the only crustacean from which enkephalins have been fully characterized, biochemical/ immunohistochemical data suggest they are broadly conserved in the taxon [129][130][131][132][133][134][135][136]; these data also suggest that the enkephalins function both as locally released autocrines/ paracrines and circulating hormones in crustaceans.…”

Physiological functions of FMRFamide‐like peptides (FLPs) in crustaceans

“…The appearance of FLI in several regions within the eyestalks of the fiddler crab Uca pugilator suggested that FLPs might function as neurotransmitters or as neurohormones (Fingerman et al, 1985). Subsequently, injection of FMRFamide and other neuropeptides into intact fiddler crabs was shown to produce dark adaptation by stimulating the release of distal retinal pigment dark-adapting hormone from the eyestalk neuroendocrine complex (Kulkami and Fingerman, 1987).…”

Crustacean Molting: Regulation and Effects of Environmental Toxicants

“…Fingerman et al [45] reported the presence of two types of peptides methionine-enkephalin and leucineenkephalin from neuroendocrine complex of eyestalk of fiddler crab U. pugilator. Later, based on experimental evidences proved the role of opioids like methionine-enkephalin as a neurotrasmitter that regulates the secretion of hyperglycemic hormone in fiddler crab U. pugilator, movement of red pigment molecules that regulates chromatophores and on ovarian maturation in U. pugilator.…”