An ultrastructural study of the activation of the endocrine dorsal bodies in the snail Helix aspersa by mating

Abstract

The ultrastructural organization of the dorsal bodies of Helix aspersa was studied using serial sections. The dorsal body cells, which were found in groups of two to six in the connective tissue surrounding the brain, contacted each other and formed a network. They were innervated by two types of axons. Type I axons conformed with those described in earlier studies as inhibitory and originating from the cerebral green cells. Type II axons contained secretory granules that were morphologically distinct from and smaller than type I granules. Between the dorsal body cells and both axon types, localized modifications of the membrane were evident. Virgin snails, which grew faster (wet weight) than mated snails, did not lay viable eggs. A comparative morphometric analysis of the dorsal bodies of virgin and mated snails showed that in the latter there was an increase in the numbers of mitochondria, secretory granules, and Golgi bodies, with a concomitant decrease in the numbers of lipid droplets. However, no difference was found in the numbers of profiles of exocytotic release of secretory granules with the use of tannic acid methods. Mating, obligatory for oviposition of viable eggs, appeared to cause ultrastructural changes consistent with increased synthesis and release of the dorsal body hormone essential for vitellogenesis, ovulation, and, consequently, egg laying.