Neuroendocrine control of water balance in the decapod crustacean, Thalamita crenata

Abstract

The involvement of the central nervous system in hydromineral regulation of decapod crustaceans has been demonstrated in the past, yet the control of this regulation has not been fully explored. It has been postulated that a neuroendocrine mechanism may control water and mineral movements in steady state animals and that neurosecretory products produced and secreted from the central nervous system may be the factors responsible for this control. Two factors contained in the ventral ganglion and brain of the brackish water crab Thalamita crenata Latreille were separated into water soluble and acetone soluble fractions. When these fractions were bioassayed in crayfish and crabs, it was found that the acetone soluble fraction contained a biologically active compound which, when injected into the assay animal, caused an increased influx of tritiated water into the animal; the water soluble fraction produced a decrease in water influx after injection. Neither the acetone soluble nor the water soluble fractions had an effect on sodium-22 influx. This increase and decrease of tritium influx was also demonstrated by perfusing the gill chambers of the crab with the isotopic medium; the acetone soluble fraction increased the influx while the water soluble fraction caused a decrease. By isolating the intestine of the crayfish, it was observed that the acetone soluble fraction increased the lumen to haemolymph tritiated water flux; the water soluble fraction did not cause a change in the flux rate. The water soluble fraction which produced a decrease in water influx in whole animals was partially purified by column chromatography. Semi-pure fractions were obtained by separation with a Sephadex G-25 to G-10 gel series. Further purification was obtained by eluting the Sephadex G-10 activity-containing fraction through CM Sephadex ion exchange gel utilizing a continuous ionic strength concentration gradient. The active material was a small molecular weight polypeptide. Substances other than these central nervous system factors were bioassayed for their effect on water and sodium influx. Acetylcholine, norepinephrine, glutamic acid, and vertebrate neurohypophyseal octapeptides did not alter the rate of the influx of water or sodium. 5-hydroxytryptamine and pericardial organ extract increased sodium-22 influx while ecdysone appeared to increase the influx of tritiated water. It is proposed that these two factors found in the central nervous system and which affect the influx of tritiated water are important in the maintenance of the osmotic steady state of decapod crustaceans. These factors modify the permeability to water of the gills and intestine to maintain the osmotic balance of these animals.