Lucien Gomot

In vitro metabolism of androstenedione and identification of endogenous steroids in Helix aspersa.

In vitro metabolism of androstenedione in gonads of juvenile and adult Helix aspersa has been investigated. The conversion of [3H]androstenedione into testosterone, 5 alpha-dihydrotestosterone, androsterone, and estriol was demonstrated. In juvenile animals testosterone (59.8%) is the major metabolite whereas in adult animals androsterone (18.8%) is. The following endogenous steroids have been identified by gas chromatography-mass spectrometry in adult gonads: androsterone, dehydroepiandrosterone, androstenedione, 3 alpha-androstanediol, estrone, estradiol-17 beta, and estriol. The levels of testosterone, 5 alpha-dihydrotestosterone, androstenedione, and progesterone have been measured by RIAs in gonads and hemolymph. Their levels vary with the physiological stage: the gonadal and circulating levels of testosterone decrease with the sexual maturation whereas the 5 alpha-dihydrotestosterone increases. These differences observed in metabolism and in level of steroids between the juvenile and the adult snails allow us to suppose that these steroids have a biological role.

Immunocytochemical localization of insulin-related peptide(s) in the central nervous system of the snail Helix aspersa Müller: involvement in growth control.

Summary1.The presence of insulin-like substances has been demonstrated by immunocytochemistry in the central nervous system of the snailHelix aspersa.2.The immunopositivity has been observed especially in the large perikarya of the mesocerebral green cells [the cerebral green cells (CeGC) stained in green by the alcian blue: alcian yellow technique].3.The removal of either the mesocerebrum or the CeGC stops the growth of the snail and induces the increase of the glycogen content in the mantle edge.4.Our results show the existence of insulin-like material in the neurosecretory cells. Previous data having demonstrated the presence of specific binding sites to insulin in the cephalic ganglia ofHelix aspersa, one may suggest that insulin could play a neuromodulatory or a neurotransmittory role in the central nervous system and might control the growth.

Etude in vitro de l'influence des corps dorsaux sur l'ovogenèse d'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.

Allogeneic and xenogeneic grafts in pulmonate gastropod molluscs: fates of neural transplants.

Neural intracerebral allo- and xenografts in pulmonate gastropods demonstrated a variation in the tolerance of neural xenogeneic grafts that was dependent on the phylogenetic distance between the donor and the host. Like allografts, neural congeneric xenografts (Hp/Haa and H1/Haa) of cerebral ganglia (CG) were tolerated and restored growth in juvenile mesocerebrum-deprived (Haa) snails. However, CG neural xenografts between different genera of stylommatophorans (Achatina fulica/Haa) or between genera of different orders (Lymnaea stagnalis: Basommatophora/Haa: Stylommatophora) revealed an interspecific histoincompatibility. These results, compared with those described by other authors, suggest that gastropods possess mechanisms for the recognition of non-self that depend on the organ considered and the phylogenetic distance separating host and donor. Research should now attempt to identify the factors responsible for graft destruction.

Mating and 20-hydroxyecdysone cause increased galactogen synthesis in the albumen gland explants of Helix aspersa (mollusca)

Abstract 1. 1. Mating causes a significant increase in [14G]glucose incorporation into newly synthesized galactogen by albumen gland explants of Helix aspersa. 2. 2. 20-Hydroxyecdysone, irrespective of the concentration used did not increase galactogen synthesis in albumen gland explants in virgin snails. 3. 3. In mated snails immediately following egg-laying, 20-hydroxyecdysone at a concentration of 10−8M caused significant increase in galactogen synthesis in albumen gland explants. 4. 4. In mated snails prior to egg-laying, a 10−7 M concentration of 20-hydroxyecdysone was required for the maximum increases of [14C]glucose uptake into galactogen. 5. 5. These results suggest that 20-hydroxyecdysone plays a hormonal role in controlling galactogen synthesis in the albumen gland of H. aspersa.

Brain grafts of cerebral ganglia have effectiveness in growth restoration of damagedHelix aspersa mesocerebrum

The microsurgical extirpation of the mesocerebrum from the brain of fast-growing juvenile snails (Helix aspersa aspersa: H.a.a.) stops their growth. This suggests that neurosecretory cells of the mesocerebrum secrete a growth hormone. Neural grafting has been used as a tool to restore the impaired growth function after mesocerebrum removal in juvenile H.a.a snails. The transplantation of desheathed cerebral ganglia (CG) (i.e. CG with their glioconjunctive outer covering removed), into the place where the mesocerebrum had been re-established growth which depended on the age of the donors. For the grafts of H.a.a CG into H.a.a, it was CG from the youngest donors that restored growth best. However, the CG of adult snails still conserved a slight growth-stimulating activity. Transplantation of the CG from the large, fast-growing sub-species H. aspersa maxima (H.a.m), into the brain of H.a.a with mesocerebrum removed induced faster growth than the H.a.a CG probably because of a more abundant secretion of growth hormone. Our results show that intracerebral CG grafts are well tolerated in snails and that labeling of the neurones of the transplanted CG with a vital fluorescent stain (Fast blue), allowed the observation, over several months, of their integration into the lesion zone of the host brain.

Length of hibernation and the brain's influence on temperature-induced spermatogenic DNA synthesis in Helix aspersa

Abstract 1. 1. In ovotestis of hibernating snails, the male cell line is very sensitive to temperature. An elevated temperature from 5 to 25°C induces spermatogenic DNA synthesis and formation of spermatids and spermatozoa in 4 weeks. 2. 2. The DNA synthesis gradually increases in male cell line with the lengthening of hibernation. 3. 3. Brain removal produces a marked increase of DNA synthesis after 1 and 6 months of hibernation (× 3.5 and 3.3) but not after 12 months.

Action of epigenetic factors on the expression of hermaphroditism in the snail Helix aspersa

Abstract 1. 1. The gonad of Helix aspersa has a dual origin: the germinal line differentiates early during the embryonic life whereas small mesenchymal cells give rise to the non-germinal auxiliary cells. 2. 2. The differentiation of gametes is controlled by environmental and (neuro)endocrine factors. Among the external parameters, photoperiod and temperature are particularly important. 3. 3. For the internal regulation of gametogenesis, in vitro and in vivo experiments show a predominant role of the cerebral ganglia: neurons of the mesocerebrum control the spermatogonial multiplication while the endocrine dorsal bodies control oocyte growth. 4. 4. The evidence of two subpopulations during Helix growth seems to be related to an interindividual complementarity which is necessary for reproduction.

Influence de la température sur le déroulement de l'ovogenèse chez l'escargot Helix aspersa

Abstract The influence of temperature on oogenesis was investigated in snails (Helix aspersa) maintained for 4 weeks in inactive conditions after several months of hibernation at 5°C. At temperatures between 5 and 25°C, differentiation of young oocytes proceeded. Vitellogenesis, on the contrary, is temperature-dependent as low temperatures strongly inhibited the second vitellogenic stage. It is suggested that the effect of temperature on oocyte growth may be mediated by the endocrine dorsal bodies.

Action de l'extrait de tentacules oculaires d'Escargots juveniles et adultes sur le développement in vivo de la glande à albumen d'Helix aspersa

Injected optic tentacle homogenates in Helix aspersa were shown to cause a decrease in growth rate and albumen gland development. The effects of optic tentacles removed from young animals and from adult animals were compared. In young animals, injections of adult optic tentacle homogenate resulted in a reduction in both growth rate and albumen gland weight. In older adult animals injected with adult optic tentacle homogenate, growth and albumen gland development decreased, but not to the same extent as in young animals. In contrast, the inhibitory effect of the young tentacle homogenate was inverted. The possible source of a tentacular factor is discussed in relation to its possible origin in other investigated pulmonates, and also the mechanism of the homogenates heterochronic action.