Control of growth by the neurosecretory hormone of the light green cells in the freshwater snail Lymnaea stagnalis

Abstract

An experimental study has been made of the role of the endocrine centres in the cerebral ganglia of the freshwater pulmonate L. stagnalis on body growth, growth of body parts, locomotion, feeding and oviposition. Cauterization of the neurosecretory light green cells (LGC) of rapidly growing juvenile snails resulted in a markedly retarded body growth, which could be restored by implantation of cerebral ganglia containing LGC. From these results it is concluded that the LGC produce a growth hormone. Cauterization or reimplantation of dorsal bodies (DB), or of the neurosecretory caudodorsal cells (CDC) or bright green cells (BGC) had no effect on body growth. Cauterization of the lateral lobes (LL) resulted in giant growth, suggesting that the LL have a growth retarding effect. LGC removal also resulted in a clear retardation of the growth of all body parts, whereas reimplantation of LGC restored normal growth. Since the DB specifically stimulate the growth of the female accessory sex organs, and the CDC have an opposite effect, it is concluded that the effect of the growth hormone of the LGC on the female organs requires the presence of the gonadotropins produced by the DB and the CDC. None of the centres had an effect on locomotion. Compared with the increase in food consumption of the normally growing control snails, the snails without LGC ate less, but food consumption was normal after reimplantation of LGC. It is concluded that the growth hormone has an indirect effect, via growth and metabolism, on feeding activity. Cauterization of DB resulted in cessation of oviposition. Previous results have shown that this is due to a cessation of vitellogenesis. Oviposition was resumed after reimplantation of DB. CDC removal also resulted in cessation of oviposition, probably because ovulation had been blocked. LL removal resulted in a gradual decline in ovipository activity, suggesting that a second function of the LL is the stimulation of egg production. In contrast to the more specific effects on reproduction of these centres, the LGC have a more general and probably indirect positive effect on the rate of ovipository activity via the stimulation of growth.