Effects of brain extracts on oocyte maturation in Helisoma (Pulmonata:Mollusca)

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Abstract
Normal oocyte development and the effects of brain extract injections on egg laying and on oocyte ultrastructure were investigated in 2 populations of Helisoma: an egg-laying population (H. duryi) and a non-egg-laying, overwintering population (H. trivolvis). Oocyte development in H. duryi resembles that in other pulmonate molluscs. Endocytotic profiles occur in maturing oocytes but not in young (previtellogenic) oocytes. Injected horseradish peroxidase (HRP) and ferritin were in the follicular space and between follicle cells 2-3 h after injection. Ultrastructural evidence indicates that these tracers are taken up by maturing oocytes, but not by young oocytes or follicle cells. In non-egg-laying H. trivolvis large oocytes lack endocytotic profiles although a follicular space and many yolk granules may be present. Injection of extracts of dorsal bodies or subesophageal ganglia from H. duryi induces egg laying in H. trivolvis within a few days. Injection of dorsal body extract into non-egg-laying animals induces the appearance of many endocytotic profiles in large oocytes. Endocytotic uptake of yolk components probably is stimulated by dorsal body extract.