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.

Brain grafts of cerebral ganglia have effectiveness in growth restoration of damaged Helix 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.

[Study of mitochondrial DNA in Helix land snails by PCR-RFLP]. / Etude de l'ADN mitochondrial d'espèces d'escargots du genre Helix par PCR-RFLP.

Sometimes the morphological criteria--used to distinguish between 4 land snails species (Helix pomatia, Helix lucorum, Helix aspersa aspersa and Helix aspersa maxima)--are little pronounced and ambiguous. We have selected mitochondrial DNA, a widely used molecular marker, in order to have a reliable technique of distinction between the 4 studied species. After extraction, mtDNA is amplified by PCR and digested with several enzymes. Among them, Dra I give restriction fragments of different length depending on species. So, owing to PCR-RFLP of mtDNA, we describe here a reliable method for identifying 4 snail species.

In vitro effect of the gonad of Helix aspersa (Mollusca) on galactogen synthesis in the albumen gland of either mated or virgin snails.

The gonad of Helix aspersa contains a factor which can stimulate in a dose-dependent manner galactogen synthesis in albumen gland explants cultured in vitro. The stimulatory activity appears to be greater when the gonad is predominantly male than when it is predominantly female. The albumen gland of virgin snails does not respond in vitro to the gonadal influence. The receptivity of the albumen gland to the galactogen synthesis stimulating effect of the gonad is increased after the first and second mating. It decreases at the third mating in correlation with the increase of the albumen gland maturation index.

[Influence of brain grafts on growth restoration of snail (Helix aspersa) deprived of the midbrain]. / Influence de greffes cérébrales dans la restauration de la croissance de l'escargot (Helix aspersa) privé de mesocerebrum.

Microsurgical removal of the mesocerebrum from the brain of juvenile snails stopped their growth whereas intracerebral implantation of desheathed cerebral ganglia (CG) re-established it. When the animals were grafted with CG from very young snails growth was much more stimulated than with CG from donors of the same age or from adults. Furthermore, young CG of juvenile fast growing specimens of the large species (Helix aspersa maxima) induced a higher growth rate than the CG of the ordinary small garden snails (Helix aspersa aspersa). Labelling of the neural grafts with the vital fluorescent dye fast blue enabled us to follow the repopulation of the lesioned area of the brain of the host during the functional integration of the implanted neurons into the circuits that control growth in snails.

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

1. The presence of insulin-like substances has been demonstrated by immunocytochemistry in the central nervous system of the snail Helix 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 of Helix aspersa, one may suggest that insulin could play a neuromodulatory or a neurotransmittory role in the central nervous system and might control the growth.

[Effect of cerebral ganglia and dorsal bodies on DNA synthesis induced by heat in the ovotestis of hibernating Helix aspersa ]. / Etude de l'action des ganglions cérébroïdes et des corps dorsaux sur la synthèse d'ADN induite par la chaleur dans l'ovotestis d'Helix aspersa en hibernation.

Brain extirpation of snails at the start of their natural hibernation increased the synthesis of DNA in spermatogonia when the animals were transferred from 5 to 25 degrees C for a 4-week period. This effect did not occur if animals were maintained at 5 degrees C. The reimplantation of brain (cerebral ganglia: CG + associated dorsal bodies: DB) in brain-ablated snails failed to correct the effects of brain extirpation. The implantation of either DB or CG in cerebrotomized hosts showed that, compared to shams, DB restored the level of DNA synthesis and spermatogonial proliferations whereas CG stimulated it. The CG and associated DB were therefore found to exert antagonistic effects which are responsible for the control of spermatogonial DNA synthesis in hibernating Helix aspersa.

[Asynchronous development of the genital tract in the snail, Helix aspersa, during growth and reproduction]. / Asynchronisme du développement du tractus génital de l'escargot Helix aspersa pendant la croissance et la reproduction.

During the growth of laboratory-raised Helix aspersa, the development of the albumen gland and spermoviduct was studied in relation to age, weight and different stages of reproduction such as mating and egg-laying. The results showed that the population can be divided into 2 categories because of different growth rates and asynchronous development of the genital tract. The fast-growing snails are larger and reach sexual maturity (female type maturity) in a shorter period than slow growing snails (male type maturity). During growth, the maturation of the genital tract was not directly proportional to the weight of the animal. Within each class of similar weight and age of population, 2 groups were identified; in one group, the genital tract was significantly less developed than in the other. This asynchrony of genital tract development could still be found between mating partners of the same weight, the genital tract could be 3 times smaller in one than in the other partner. However, this difference disappeared between mating and egg-laying. These observations suggest: that asynchronous development of the genital tract could be a strategy for the developing population of Helix aspersa; and that (a) mating factor(s) is (are) involved in the regulation of the growth and function of the genital tract.

Evidence for a light compensation of the inhibition of reproduction by low temperatures in the snail Helix aspersa. Ovotestis and albumen gland responsiveness to different conditions of photoperiods and temperatures.

Four combinations of photoperiods and temperatures have been tested on the reproduction and on the activity of the genital apparatus of the snail Helix aspersa. The results show some interaction between photoperiod and temperature and reveal a predominant effect of photoperiod that compensates for the negative effect of low temperatures. A combination of long day (LD, 18L:6D) and a temperature of 20 degrees C is the most favorable condition for egg-laying as well as for the effective functioning of the ovotestis and albumen gland. In contrast, during a short day (SD, 8L:16D), egg-laying is completely inhibited at 15 degrees C and partly inhibited at 20 degrees C; the differentiation of gametes can be observed in the ovotestis, but the mature oocytes are not released and thus they degenerate. In the albumen gland, an important synthetic activity is noticed, but cellular multiplication and the release of the secretory products decrease. These results suggest that short photoperiods induce inhibition of the (neuro)endocrine centers responsible for the control of both ovulation and egg-laying.

Inhibition of temperature-induced spermatogenic proliferation by a brain factor in hibernating Helix aspersa (Mollusca).

Ablation of the brain from hibernating Helix aspersa maintained at 25 degrees C causes a significant increase in the proliferation of male cells in the gonad, whereas the ablation of the optic tentacles has no effect. The brain, therefore, produces a factor which specifically inhibits the multiplication of spermatogonia and spermatocytes.

In the snail Helix aspersa the gonadotropic hormone-producing dorsal bodies are under inhibitory nervous control of putative growth hormone-producing neuroendocrine cells.

In many Stylommatophora, dorsal bodies (DB) consist of cell groups dispersed in the connective tissue surrounding the cerebral ganglia. It has previously been shown that in these animals the DB cells are under inhibitory nervous control. In the present tissue culture experiment on Helix aspersa it is shown that the axons innervating the DB cells originate from the peptidergic cerebral green cells (CeGC). It is argued that the observed morphological relationship between the CeGC and the DB--the CeGc produce a growth hormone, the DB a female gonadotropic hormone--reflects the antagonism between growth and reproduction which has often been reported for pulmonate snails.

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.

[Action of the extract from the optic tentacles of juvenile and adult snails on the in vivo development of the albumin gland of Helix aspersa]. / 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.

[Control of secretory activity of multifid glands by castration and grafting in the snail Helix aspersa]. / Etude du contrôle de l'activité sécrétrice des glandes multifides par castration et greffe chez l'escargot Helix aspersa.

Castration of juvenile snails results in a cessation of multified gland cell differentiation. Many months later, the cells still resemble polarized epithelial cells and show no signs of secretory activity. Transplantation of nondifferentiated cells from multifid gland of castrated snails into normal adults initiated secretory activity. The experiments show that the presence of the gonad is essential for the multifid glands to develop secretory activity and that its influence is mediated by an endocrine factor which is transported in the hemolymph.

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

Relative humidity affects the intercellular spaces and cell contacts of the kidney epithelium of the terrestrial snail Helix aspersa müller.

The effects of relative humidity on hemolymph osmolarity and on kidney ultrastructure are explored in Helix aspersa. The snails are active at 95% relative humidity and less active at 50% relative humidity. The hemolymph osmotic pressure increases with the decrease of relative humidity. Pericardial fluid and hemolymph collected from the heart contain similar amounts of total proteins, and both fluids display hemocyanin molecules in negatively stained preparations. When the snails are kept in an atmosphere of 95% relative humidity, numerous wide intercellular spaces are observed in the single-layered-kidney epithelium. The spaces are almost absent when the snails are kept at 50% relative humidity. It is suggested that prourine is formed through a paracellular junctional pathway across the single-layered kidney epithelium, and that the pericardial cavity is not the site of prourine formation. The septate junctions joining the kidney epithelial cells form a continuous belt of intimate contact in the paracellular pathway of prourine. Long septate junctions with many septa are present in the kidneys of snails from the atmosphere of 50% relative humidity, whereas short septate junctions with fewer septa are found in the kidneys of snails from the atmosphere of 95% relative humidity. It is possible that the longer septate junctions with many septa reduce prourine formation across the kidney sac epithelium.

[Stages of organogenesis and cytodifferentiation of the albumen gland in the snail Helix aspersa Muller]. / Les stades de l'organogenèse et la cytodifférenciation de la glande à albumen de l'escargot Helix aspersa Müller.

The differentiation of the albumen gland of the pulmonate stylommatophora Helix aspersa has been divided into five stages. An ultrastructural study showed, the differentiation of undifferentiated epithelial cells into two cell types: ciliated cells and secretory cells. The glandular differentiation of epithelial cells was characterized by the development of ergastoplasma and the Golgi apparatus which were both involved in protein and galactogen synthesis.

[Ultrastructural study of the differentiation of mammary buds during the fetal life of female mice]. / Etude ultrastructurale de la différenciation des bourgeons mammaires au cours de la vie foetale de souris femelles.

On mouse female fetuses, mammary gland bud development was studied ultrastructurally. This development is characterized by: - primary bud dichotomization into two secondary ductules, - lumen formation in the primary bud and in the secondary ductules. The lumen is formed by necrosis of central cells and around it cells are organized in an epithelium.

[Effects of actinomycin D combined with testosterone on regression of in vitro cultured mammary buds of the fetal mouse]. / Action de l'actinomycine D associée à la testostérone sur la régression des bourgeons mammaires de l'embryon de souris en culture in vitro.

Effects of actinomycin and testosterone, alone or associated, were studied on the regression of fetal mouse mammary gland cultivated in vitro to elucidate the role of testosterone on physiological mecanisms of target cells.

Ultrastructural study of the follicle cells in the freshwater gastropod Viviparus viviparus L.

The morphology and the role of the follicle cells of Viviparus viviparus were examined by means of light and electron microscopy. The follicle cells appear to contain glycogen and fat, and often lysosomes or heterogeneous inclusions. Therefore, they seem to be active in phagocytosis and storage. They are probably involved in the nutrition of the oocyte. Their role in the formation of a selectively permeable barrier is discussed.