Aging of neurons in the mollusc Lymnaea stagnalis small parietal ganglion: a morpho-functional comparison in the same neuron

The aim of this study was to compare the functional and structural changes in similarly identified neurons of the small parietal ganglion in 56 molluscs ( Lymnaea stagnalis) of two age groups: adult (10–12 months) and old (20–22 months). No age changes were found in the values of membrane potential, resistance of the neuronal membrane, amplitude, duration, or rate of increase of the anterior action potential front. With aging, the thresholds of direct stimulation were significantly increased, the rate of action potential repolarization decreased, and the amplitude of trace hyperpolarization decreased. The most marked age-dependent changes were observed in the frequency of neuronal spontaneous activity. A clear relationship was established between the frequency of action potentials of the neuron and its structure in adult and old individuals alike. In the molluscs of both age groups, the neurons with a high frequency of action potential displayed ultrastructural features of high activity in the organelles involved in protein biosynthesis. The cytoplasm of these neurons was filled with numerous ribosomes and had a well-developed rough endoplasmic reticulum. The structure of cells with low spontaneous activity in old molluscs differed considerably from that of the corresponding neurons of the adult individuals. The former had significantly marked morphological signs of reduction of the protein-synthesizing processes, as well as of destructive and dystrophic changes. A decrease in the lability of neurons may be an important mechanism of aging.