Stability of dendritic mass during aestivation

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Abstract
In hot and dry weather, terrestrial snails withdraw into their shells and remain inactive for long periods of time. This phenomenon, known as aestivation, is the basis for our investigation of the effects of behavioral inactivity on neuronal structure. Several recent studies have shown that the level of afferent electrical activity is an important modifier of structure, even in adult animals. During aestivation, sensory stimulation (and therefore presumably afferent activity) is greatly reduced. We have tested the hypothesis that long-term behavioral inactivity causes a regression of dendrites. Two identified neurons of Achatina fulica were selected for study, the giant cerebral neuron (GCN) and RPall. The cells were viewed on 10-μm-thick sections after intracellular injection of hexamminecobalt chloride. They were reconstructed by using a video camera attached to a light microscope and a digitizing board resident in a microcomputer. Snails in the aestivated group were completely inactive for 8 weeks beginning at age 23 weeks. A quantitative analysis showed that there were no significant differences in either cell, in either the total mass of material or its distribution, comparing cells from the Aestivated snails and cells from the Younger snails (age 23 weeks) and the Older snails (age 33 weeks). These results suggest limits to the modifiability of neuronal structure.