Distal Retinal Pigment of the Fiddler Crab,Uca pugilator: Release of the Dark-Adapting Hormone by Methionine Enkephalin and FMRFamide

The neuropeptides methionine enkephalin and FMRFamide, when injected into intact fiddler crabs, Uca pugilator, produce dark adaptation of the distal retinal pigment. Furthermore, both neuropeptides stimulate release of distal retinal pigment dark-adapting hormone activity from the isolated eyestalk neuroendocrine complex. It is hypothesized that both neuropeptides, when injected into intact fiddler crabs, act only indirectly on the distal retinal pigment, by stimulating release of this dark-adapting hormone.     

Cellular Aspects of the Control of Physiological Color Changes in Crustaceans

SYNOPSIS. Red chromatophores(erythrophores) of the prawn, Palaemonetesvulgaris, are controlled by pigment—dispersing and -concentratinghormones. Recent experiments on the modes of action of thesehormones are described, followed by a theory which satisfactorilyexplains the data. Red pigment-concentrating hormone is dependentupon sodium ions for a strong response to occur. There is asimilar dependency of red pigment—dispersing hormone uponcalcium ions. Ouabain inhibits the response to red pigment—concentratinghormone; tetrodotoxin enhances it. Erythrophores with maximallydispersed pigment had a transmembrane potential of 55±15mv inside negative in one series of experiments and 56±4mv in another. No appreciable changes in permeability occurwhen depolarizing and hyperpolarizing currents are passed througha microelectrode within the chromatophore. Red pigmentconcentratinghormone causes hyperpolarization of the transmembrane potential.The magnitude of hyperpolarization is directly related to thedegree of pigment concentration. Adenosine 3`;, 5`-monophosphate(cyclic AMP) causes dispersion of the red pigment but has nopigment-concentrating effect. The primary action of red pigmentconcentratinghormone is most likely stimulation of a pump which exchangessodium ions from inside the chromatophore with potassium ionsfrom the outside, whereas red pigment-dispersing hormone quitelikely stimulates entry of calcium ions into the chromatophore.     

Endocrine Mechanisms in Crayfish, with Emphasis on Reproduction and Neurotransmitter Regulation of Hormone Release

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

In vivo stimulation of ovarian development in the red swamp crayfish,Procambarus clarkii (Girard), by 5-hydroxytryptamine

Summary

The possibility that biogenic amines affect ovarian development in the red swamp crayfish, Procambarus clarkii, was investigated. Females were administered 15 μg/g body weight (bw) of norepinephrine, dopamine, 5-hydroxytryptamine (5-HT) or octopamine on days 1, 5 and 10 and were sacrificed on day 15. Crayfish given 5-HT showed significant increases in ovarian index (30.5%) and oocyte size (34.0%) over the concurrent controls, while norepinephrine, dopamine and octopamine did not significantly affect either the ovarian index or oocyte size. Significantly more labeling by ¹⁴C-leucine of ovarian proteins was found in ovaries of crayfish that were injected with 5-HT in vivo, but when ovarian lobes from crayfish that had not been injected with 5-HT were incubated in vitro with 5-HT added to the incubation medium, no significant change in the level of incorporation of ¹⁴C-leucine into ovarian proteins occurred.

The 5-HT receptor blocker LY53857 (25 μg/g bw) retarded ovarian development. The 5-HT releaser fenfluramine and the 5-HT potentiator fluoxetine (both 15 μg/g bw) were also used. Crayfish given fenfluramine, fluoxetine, fenfluramine plus 5-HT or fluoxetine plus 5-HT showed significant increases of ovarian index (24.0–102.8%), oocyte size (20.0–87.4%) and in vitro ¹⁴C-leucine labeling of ovarian proteins (30.6–123.6%) over the concurrent controls. The ovaries of crayfish that received the 5-hydroxytryptaminergic neurotoxin 5,6-dihydroxytryptamme (10 μg/g bw) did not show any significant change as compared with the initial control. These findings are consistent with the hypothesis that 5-HT, which is present in the central nervous system of Procambarus clarkii, exerts its stimulatory effect on the ovary of this crayfish indirectly by triggering release of the ovary-stimulating hormone.     

The Physiology and Pharmacology of Crustacean Chromatophores

The color change system of crustaceans is being investigatedalong a broad front. The techniques being used include physiological,pharmacological, biochemical, immunocytochemical, and ultrastructuralones. The problems investigators are seeking answers to includethe cellular bases for pigment granule translocation, the numberand specificity of the chromatophorotropic hormones responsiblefor the color changes, and the identity of the neuroregulators(neurotransmitters and neuromodulators) that control the releaseof these hormones. With respect to the cellular bases of pigmentgranule translocation, microtubules and a microtrabecular latticeare prime candidates as organelles that might be responsiblefor the pigment granule movements. Pigment dispersing and pigmentconcentrating neuropeptides have been identified. Some exhibitno specificity with respect to the chromatophore type they activate.Others show high specificity, affecting only one specific typeof chromatophore, such as the melanophore. Several putativeneuroregulator candidates have been identified as possibly havinga role in controlling chromatophorotropic hormone release. Theseinclude 5-hydroxytryptamine, dopamine, norepinephrine, octopamine,and gamma-aminobutyric acid. Some, like the first three, stimulatehormone release, whereas the latter two have inhibitory actions.