Crustacean Hyperglycemic Neuropeptides

The neurosecretory structures in the crustacean eyestalk areconsidered to be the source of factors regulating a considerablevariety of physiological processes. Although many hormonal "factors"have been postulated, only a few have been characterized indetail. Two pigmentary effector regulating neuropeptides havebeen completely characterized. A third substance, the hyperglycemichormone, has been isolated and characterized in terms of aminoacid composition. It is larger than the pigmentary effectorhormones (mol wt 6,000–7,000) and it is the first of theheretofore described invertebrate neurohormones that containsdisulfide bridges. Unlike the pigmentary effector hormones,the hyperglycemic neuropeptide exhibits species or systematicgroup specificity, recognizable by differences in amino acidcompositions and also expressed by lack of interspecific (orintergroup) biological activity. An antiserum permitted thedevelopment of a radioimmunoassay and immunocytochemical demonstrationof the hormone producing perikarya in decapods and in an isopod.Large immunopositive perikarya form a distinct group in themedulla terminalis ganglionic X-organ. This group sends a conspicuoustract of axons to the neurohemal organ, the sinus gland, wherethe hormone is stored in large quantities. It is believed tobe necessary for the regulation of resting levels of blood sugarand for elevation of blood sugar in situations of physiologicalneed. In general, however, the physiological mode of actionof the hormone is largely unknown.