ENDOCRINE MECHANISMS IN CRAYFISH, WITH EMPHASIS ON REPRODUCTION AND NEUROTRANSMITTER REGULATION OF HORMONE-RELEASE

The neuroendocrine system of crustaceans, crayfish in particular, has been extensively studied. As among vertebrates, a wide variety of processes are hormonally regulated, including reproduction, growth, carbohydrate metabolism and color changes. The sinus gland, a neurohemal organ in the crayfish eyestalk, is the major neuroendocrine center. Herein, crayfish reproductive cycles and their hormonal control, particularly by the gonad-stimulating and gonad-inhibiting hormones, are a major focus. In addition, the aminergic and peptidergic neuroregulators identified in crayfish central nervous organs that either have been or likely may be shown to have neurotransmitter/neuromodulator roles in controlling hormone release are discussed with respect to localization and identified roles.