ATROPHY AND DEGENERATION OF PEPTIDERGIC NEURONS AND CESSATION OF EGG-LAYING IN THE AGING POND SNAIL LYMNAEA-STAGNALIS

The morphology of the neuroendocrine caudodorsal tells (CDCs), which a re involved in the regulation of female reproduction in the pond snail Lymnaea stagnalis, was studied in young (200 to 234 days of age) and old (400 to 500 days) animals. Lucifer Yellow fills of ventral CDCs sh owed that in young animals ventral CDCs branch ipsilaterally as well a s contralaterally in the cerebral commissure. In old animals these bra nches were reduced at different degrees and in some cases even lacking completely, leaving only an axon crossing the commissure. Immunocytoc hemical stainings with antibodies against CDC peptides (CDCH-I and alp ha CDCP) corroborated the finding that ventral CDCs degenerate. Among the other types of CDCs (dorsal, lateral), degeneration was found as w ell, The immunocytochemical findings showed that in old animals the ax on terminals of the CDCs were strongly stained, indicating that they a re packed with secretory vesicles containing peptides. It was also fou nd that these darkly stained, peptide-containing axon terminals protru ded into the perineurium. These findings suggest that accumulation of peptides in tile terminals of the CDCs of old animals may be due to th e impaired release. The relationship between atrophy and degeneration of CDCs and cessation of egg-laying activity in Lymnaea is discussed. (C) 1996 John Wiley & Sons, Inc.