Crustacean Hyperglycemic Neuropeptides

Abstract

The neurosecretory structures in the crustacean eyestalk are considered to be the source of factors regulating a considerable variety of physiological processes. Although many hormonal “factors” have been postulated, only a few have been characterized in detail. Two pigmentary effector regulating neuropeptides have been completely characterized. A third substance, the hyperglycemic hormone, has been isolated and characterized in terms of amino acid composition. It is larger than the pigmentary effector hormones (mol wt 6,000–7,000) and it is the first of the heretofore described invertebrate neurohormones that contains disulfide bridges. Unlike the pigmentary effector hormones, the hyperglycemic neuropeptide exhibits species or systematic group specificity, recognizable by differences in amino acid compositions and also expressed by lack of interspecific (or intergroup) biological activity. An antiserum permitted the development of a radioimmunoassay and immunocytochemical demonstration of the hormone producing perikarya in decapods and in an isopod. Large immunopositive perikarya form a distinct group in the medulla terminalis ganglionic X-organ. This group sends a conspicuous tract of axons to the neurohemal organ, the sinus gland, where the hormone is stored in large quantities. It is believed to be necessary for the regulation of resting levels of blood sugar and for elevation of blood sugar in situations of physiological need. In general, however, the physiological mode of action of the hormone is largely unknown.