[The effect of the cephalic complex (eyestalks-brain) on the development of infantile and juvenile gonads of Arion subfuscus Drap. (Gasteropoda, Pulmonata) cultured in vitro]

The neuroendocrine mechanism responsible for sexual inversion of the gonad in the protandrous hermaphroditic mollusc, Crepidula fornicata L

An in vitro investigation has clarified the neuroendocrine mechanism responsible for the differentiation of the female gonad in the protandrous hermaphrodite Crepidula fornicata. The male gonads were used as target organs; in some experiments they were brought to a uniform resting state by prior decerebration of donor animals. When isolated in culture, most of the male gonad degenerates, leaving only the stem cells lining the wall of the acini. No ovarian autodifferentiation has been observed. A masculinizing factor, released by the nervous ganglia during the male phase, controls spermatogonial mitosis and maintenance of male differentiation. A feminizing factor, secreted by the nervous ganglia during sex inversion and the female phase and present in the hemolymph, initiates oogonial mitosis and female differentiation in the male phase gonad.

Evidence for neurosecretory control of the optic gland in terrestrial pulmonates

The optic gland in terrestrial pulmonates secretes gonadotropic hormone. The present study investigates the fine structure of the optic gland to clarify the control of secretion. Animals used were the slug, Limax marginatus, and the snail, Euhadra peliomphala. The optic gland cell has a process and the cytoplasm is filled with large granules about 750-1300 nm in diameter with a thin cortex in L. marginatus and 800-1700 nm delimited by a thick peripheral layer in E. peliomphala. These gland cells are characterized by well-developed granular endoplasmic reticulum. Granule formation was seen in the region of the Golgi apparatus. During the breeding season, the medial neurosecretory cells of the brain are active in the production and release of secretory materials. Although no neurosecretory cell bodies occur in the tentacular ganglion, neurosecretory axons penetrate into the optic gland cells. Cobalt filling reveals that axons of the medial neurosecretory cells project to the tentacular ganglion, near the optic gland. These results suggest that the optic gland is controlled by a neurohormone originating from the medial neurosecretory cells of the brain.

[In vitro study of the influence of dorsal bodies on oogenesis in Helix aspersa Müll]

Infantile gonads of Helix aspersa were cultured in vitro for 13 days, alone, associated with dorsal bodies, or with cerebral ganglia (surrounded by connective tissue containing the dorsal bodies). The results demonstrate the stimulatory effect of the dorsal bodies on oocyte growth and suggest that the cerebral ganglia have an inhibitory influence on dorsal body activity and/or on oocyte development.

Male gonadotrophic factor in brain and blood of photoperiodically stimulated slugs

A pulmonate male gonadotrophic factor (MGF) has been described that is released from cerebral ganglia of male-phase slugs (Limax maximus). This factor produces, directly or indirectly, an increase in spermatogonial proliferation as determined by in vivo incorporation of [3H]thymidine into gonadal DNA. In the present investigation MGF activity was demonstrated in saline homogenates of male-phase cerebral ganglia by injecting homogenates into immature slugs for 5 consecutive days and assaying gonadal [3H]thymidine incorporation on Day 7. Dose-response data indicate that daily administration of as little as 0.1 brain equivalent can produce a significant stimulation in incorporation. Comparison of brain homogenates from immature (short-day) and male-phase (long-day) animals has shown that male-phase cerebral ganglia contain substantially more MGF activity than immature ganglia. Similar injection experiments using slug blood plasma showed that activity is present in male-phase blood but not in the blood of short-day immatures. MGF activity in long-day brain homogenates and blood plasma was found to be associated with a molecular weight fraction of 50 to 100 kDa obtained by ultrafiltration. Activity could be reduced or destroyed by treatment with trypsin or by heating. The present findings suggest that MGF is a proteinaceous factor of substantial size. It appears that both the synthesis and the secretion of MFG are stimulated in slugs that are in their male developmental phase as a result of prior exposure to long-day photoperiods.

Stimulation of spermatogonial DNA synthesis in slug gonad by a factor released from cerebral ganglia under the influence of long days

Incorporation of [3H]thymidine into gonadal DNA was shown to increase 1 week after implantation into an immature slug (Limax maximus) of a "brain" (circumesophageal ring of ganglia) from a male-phase donor. Light microscope autoradiography revealed that in stimulated gonads labeling was localized primarily in the nuclei of spermatagonia. Implant-stimulated spermatogonial DNA synthesis was found to depend upon implantation of supraesophageal (cerebral) ganglia. Neither subesophageal ganglia implants nor immature supraesophageal implants had an effect. Thymidine incorporation could also be stimulated by exposure of slugs to long-day lightcycles (LD 16:8) for 3 to 4 weeks. Similar duration of long-day treatment was also adequate to trigger male-phase development even after animals were returned to short days (LD 8:16). The results are consistent with the view that 3 to 4 weeks of long-day lightcycles are required to promote irreversibly the release from slug cerebral ganglia of a male-phase gonadotropic factor which directly or indirectly promotes spermatogonial proliferation.