Adaptation and tolerance of invertebrate nervous systems to osmotic stress

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AbstractBoth the osmotic and ionic concentration changes accompanying a salinity alteration might be expected to have profound effects on neuronal physiology, especially in euryhaline animals. We have examined the effects of salinity change and followed the subsequent adaptation to that change by an invertebrate neuron. The spontaneous activity of the follower cell of the cardiac ganglion of Limulus polyphemus is altered during salinity stress. The membrane potential is depolarized, the burst frequency is altered and the impulse pattern within each burst is disrupted following hypoosmotic stress. With time in the reduced salinity, adaptation occurs and both the membrane potential and the burst pattern return to control levels. Further, all these changes are due to osmotic variation with no detectable ionic component. Coincident with the adaptation of the electrical characteristics of these follower cells is an efflux of intracellular free amino acids which in turn, presumably, is regulating cell volume. Thus, this temporal correlation suggests that the electrical adaptation is dependent upon the cell volume regulatory mechanisms of the neurons.