Rate of production and release of chromatophorotropins in crustaceans

Abstract

It is now well accepted that the crustacean chromatophores are largely controlled by the condition of light and by hormonal effectors, the chromatophorotropins, which are the product of neurosecretory systems. Distribution of these “hormones” can be measured by bioassay methods in the freshwater prawn Palaemon paucidens. The red pigment-dispersing hormone (RPDH) is mainly localized in ganglionic tissues such as the supraesophageal ganglion or the “brain” (BR) and thoracic ganglion (ThG), whereas the tritocerebral commissure (TrC) is the source of the most potent red pigment-concentrating hormone (RPCH). Other nervous tissues, including the eyestalk (ES) and circumesophageal connectives (CC), contain both these hormones, but in smaller amounts. Two questions arise from these results: Is an RPDH present in the BR chemically identical with corresponding substances contained in other tissues? And, is there a relationship between the two, physiologically antagonistic hormones which coexist within a tissue? The prawns, when placed on a specially devised “neutral” background, manifest a diurnal variation in chromatophoral behavior under natural light: they are darker by day than at night. Chromatophorotropins contained in several nervous tissue-extracts from such animals were shown to have a definite rhythm of potency. The BR contained more RPDH during daytime than at night time, whereas the ES contained more RPDH during night than by day. On the other hand, amounts of the RPCH present in the TrC changed little during the 24-hour period. These results seem to show (1) that the BR-RPDH, after synthesis, is released promptly into circulation to bring about dispersion of red pigment, and (2) that the TrC, containing the RPCH at about the same level throughout the 24-hour period, does not play a principal role in diurnal variation of bodily color in Palaemon. Bioassay of particular tissue extracts from the prawns that had previously received other tissue extracts gives interesting features of the relationship between hormones of different origins. Thus, a significant decrease in potency was noticed of the BR-RPDH in animals that had received injection of the ES extracts, suggesting that the ES contains a substance which liberates the tissue-bound RPDH of the BR. On the contrary, the potency of the ES-RPCH increased greatly after the animals received the TrC extracts, suggesting that the TrC-RPCH is transported to the ES before its release into circulation. The nauplius eye is suggested as the site of another hormonal factor that might be involved in physiology of chromatophorotropins. The evidence to support this concept is discussed.