Comparison of structural and functional age changes in identified neurons of molluscLymnaea stagnalis

Abstract

Experiments on adult (aged 10–12 months) and old (aged 20–22 months) molluscsLymnaea stagnalis were aimed at comparison of functional and structural changes in identified neurons of the lesser parietal ganglion. No age changes were observed in the membrane potential of a neuron, in the resistance of its membrane, or in the amplitude, duration, and rate of rise of the leading edge of the action potential. With age, thresholds for direct stimulation of a neuron increased substantially, the repolarization phase of the action potential slowed down, and the amplitude of the afterhyperpolarization decreased. The most pronounced age changes were revealed in the characteristics of background neuronal activity. A distinct correlation was observed between the frequency of background spikes in a neuron and the state of its structures, both in adult and in old individuals. In the molluscs of both age groups the neurons with a high frequency of spike generation featured high activity of the protein-biosynthesizing system. In contrast, the structure of cells with a low firing frequency in old molluscs differed significantly from that of the neurons with similar activity in adult individuals, first of all, by substantially pronounced morphological manifestations of the suppression of protein-synthesizing processes, as well as by catabolic and destructive-dystrophic changes.