The role of the eyestalk in sodium metabolism in the crayfish Pacifastacus leniusculus Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/df65vb47w

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  • In freshwater the crayfish, Pacifasticus leniusculus, maintains sodium balance by absorbing sodium against a large concentration gradient. The site of uptake is the gills. The rate of uptake is regulated and can be increased by depleting the animals of sodium Neither the mechanism of sodium transport or the regulatory mechanism is understood for any invertebrate. Sodium balance in vertebrates is known to be at least partially regulated by hormones. It is conceivable that the crayfish regulates sodium balance in an analogous fashion. The eyestalks were studied as a possible source of such hormones. The immediate effects of eyestalk removal on an average crayfish of twenty grams are (1) a net uptake of sodium amounting to about 96 μeg in three days, (2) a negligible uptake of water and (3) a significant decrease in the sodium and chloride concentrations in the blood. The first two effects can be attributed to handling stress, for they also occurred in sham operated animals and animals handled to the same extent as animals without eyestalks. The third effect was characteristic of animals without eyestalks. It is concluded that the eyestalks may exert some control over the exchanges of sodium and chloride between the blood and some yet unidentified "salt-pool" in the animal. Crayfish lose sodium when transferred from pond water to flowing or frequently changed distilled water. The initial rate of loss is approximately 0.07 μeq/g/hr. However, after a latent period of 72 hours, this is reduced by one half. This "depletion response" is not affected by eyestalk removal. Salt-depletion activates the sodium transport system so that when salt-depleted crayfish are returned to dilute solutions of NaCl they take up net quantities of sodium at a rapid rate (maximum 0.3 μeq/g/hr), and thus restore their sodium balance. This "uptake response" is also not influenced by eyestalk removal. These data suggest that the eyestalks are not important in regulating the exchange of sodium between the internal and external medium. Sections of the eyestalks from crayfish which had been salt depleted and salt loaded were examined for neurosecretion and compared with sections from control animals. No differences were observed.
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