Effects of estradiol and mammalian LHRH on the ultrastructure of the pars distalis of the eel.

Male silver eels were injected with estradiol-17 beta (E2) to induce the development of gonadotropic (GTH) cells. They were subsequently injected with luteinizing hormone-releasing hormone (LHRH). Exocytotic figures and the lysis of some large globules and granules were observed. Morphometric studies showed a significant increase in the percentage of vacuoles after 4 and 6 injections of LHRH and a slight but significant decrease of granules. This response did not, however, occur in all GTH cells which never appeared completely degranulated and did not reach a vesicular stage. Hemi-pituitaries of E2-pretreated eels were incubated with or without LHRH (20 min to 2 h). Although typical exocytoses were not detected, an increased number of small granules near the basal lamina and lytic processes (globules with a raspberry-shaped structure, granules with variable electron density) were observed in the LHRH-incubated hemi-pituitaries compared with those kept in a control medium. The structure of GTH cells and their response to LHRH has been studied only under conditions of artificial stimulation, and their functional similarity to GTH cells of spontaneously maturing eels is discussed. Large female eels had unstimulated GTH cells. Growth hormone (STH), thyrotropic (TSH) and prolactin (PRL) cells were stimulated after E2 and LHRH. As with GTH cells, they regressed slowly after treatment was discontinued.

Cytological and ultrastructural changes in the pituitary pars distalis of the goldfish kept in calcium-free environments.

The cytology and ultrastructure of the pars distalis, mainly that of prolactin (PRL) cells, were investigated in goldfish adapted to fresh water (FW) or deionized water (DW) for 20 and 40 days, or gradually adapted to 1/3 artificial sea water (ASW) or 1/3 Ca-free sea water. When compared to PRL cells of goldfish kept in FW, those of goldfish adapted to DW did not show signs of increased activity. The lack of exocytotic activity and the low development of various organelles suggested that cell activity was slightly reduced. In 1/3 ASW, PRL cells were smaller and less active. In 1/3 Ca-free ASW, PRL cells appeared slightly stimulated compared with those of fish in 1/3 ASW. The Golgi area was more developed and a few lamellae of endoplasmic reticulum were observed in some cell islets. However, there was no significant difference between PRL cells of goldfish kept in 1/3 Ca-free ASW and in FW. In 1/3 ASW, which is isosmotic to the blood, thyrotrophs (TSH cells) corticotrophs (ACTH cells) and somatotrophs (STH cells) were not clearly affected. In DW, these cells and their nuclei were significantly enlarged. Their stimulation was also evident in 1/3 Ca-free ASW; values for cellular and nuclear areas were maximal in this environment and significantly higher than those of fish in FW and 1/3 ASW. These data suggest that in addition to the PAS-positive cells of the pars intermedia, highly stimulated in Ca-free environments, other cell types of the pars distalis may be involved in osmoregulation, and that the role of PRL cells is not primordial in the goldfish.

Light and electron microscopic identification of gonadotrophic cells in the pituitary gland of the goldfish by means of immunocytochemistry.

Immunocytochemical techniques were used at the light and electron microscopical levels in order to localize and to characterize the gonadotrophs in the goldfish pituitary gland by means of antibodies to carp gonadotrophin (c-GTH) or its subunit (c-GTH beta). At the light microscopical level antibodies to c-GTH reacted weakly with cells located in the rostral pars distalis (RPD) and strongly with cells of the proximal pars distalis (PPD). The labeling was restricted to the proximal pars distalis when antibodies to c-GTH beta were employed. The PAP and colloidal-gold postembedding procedures demonstrated that two cell types of the PPD react with both immune sera. These cells correspond to the so-called globular and nonglobular basophils of the goldfish pituitary. The labeling was located over the small secretory granules and the large globules. A relationship was noted between the intensity of the labeling and the electron density of the globules.

Existence of dopaminergic neurons in the preoptic region of the goldfish.

Three morphofunctional techniques for the detection of biogenic monoamines have been used in order to find evidence for the presence of dopaminergic neurons in the preoptic region of the goldfish. The formaldehyde-induced fluorescence technique and the immunohistochemical demonstration of tyrosine hydroxylase allowed the detection of cell bodies containing catecholamines in the ventral and lateral walls of the preoptic recess of the goldfish. Specific antibodies indicated that at least part of these perikarya contain dopamine. Evidence for the projection of these neurons to the pituitary are given. These results support the assumption that dopamine, originating from the preoptic region, may act as a gonadotrophin release-inhibiting factor in goldfish.

Immunocytochemical localization of luteinizing hormone-releasing hormone in the brain of the goldfish Carassius auratus.

Using an indirect immunofluorescence technique, LH-RH was localized in the brain of the goldfish (Carassius auratus). Immunoreactive cell bodies were inconsistantly found in two hypothalamic nuclei: the anteroventral nucleus preopticus periventricularis (npp) and the posterior nucleus lateralis tuberis (nltp). Numerous immunoreactive fibers were observed in hypothalamic as well as in the extrahypothalamic parts of the brain and in the proximal pars distalis of the pituitary gland. Our results are discussed in relation to the neuroendocrine control of the pituitary gonadotropic function in teleosts.

[Homologous radioimmunoassay of a hypothalamic factor stimulating salmon pituitary gonodatropic function (sGnRH)]. / Dosage radio-immunologique homologue d'un facteur hypothalamique de stimulation de la fonction gonadotrope hypophysaire de saumon s-Gn-RH.

A radioimmunoassay for Salmon Gn-RH p-gly-His-Trp-Ser-Tyr-Gly-Trp- Leu-Pro-Gly) (NH2) has been developed with a sensitivity of 7 pg/assay tube. The system allows the specific detection of an immunological GnRH related substance in the brain and pituitary of three teleost species but not in an elasmobranch the Dogfish. these results are discussed and some Gn-RH contents of the organs are proposed.

Ultrastructural identification of catecholaminergic fibers in the goldfish pituitary. A high-resolution radioautographic study after in vitro 3H-dopamine administration.

The monoaminergic innervation of the goldfish pituitary gland was studied by means of light- and electron-microscopic radioautography after in vitro administration of 3H-dopamine. The tracer was specifically incorporated and retained by part of the type-B fibers innervating the different lobes of the pituitary. In the rostral pars distalis labeled fibers were most frequently observed in contact with the basement membrane separating the neurohypophysis and the adenohypophysis. In the proximal pars distalis and the pars intermedia, labeled profiles were detected in the neural tissue and in direct contact with the different types of secretory cells. According to the previous data concerning the uptake and retention of tritiated catecholamines in the central nervous system, it is assumed that the labeled fibers are mainly catecholaminergic (principally dopaminergic). This study provides morphological evidence for a neuroendocrine function of catecholamines in the goldfish.

Response of prolactin cells in the goldfish adapted to diluted seawater with or without calcium.

The activity of prolactin (PRL) cells was investigated in goldfish gradually adapted to diluted (30%) artificial seawater (ASW) or directly immersed in 23% ASW and in similar saline solutions free of calcium. When Ca2+ is omitted, PRL cells appear slightly more active than those in saline solutions with calcium, nuclear areas having intermediate values between those in freshwater (FW) and those in diluted SW. Nuclear areas are also slightly larger in Mg-free SW. Other signs of stimulation are not apparent. These data are compared to those obtained in other teleost species. The lack of stimulation in PRL cells of goldfish adapted to deionized water (DW) suggests that calcium plays a minor role in controlling prolactin secretion in this teleost.

[Ultrastructure of prolactin cells and survival of Gambusia sp. (teleost fish) in deionized water enriched in calcium or sodium]. / Ultrastructure des cellules à prolactine et survie de Gambusia sp. (poisson téléostéen) en eau désionisée enrichie en calcium ou en sodium.

The ultrastructure of the prolactin (PRL) cells of Gambusia was studied in animals kept in deionized water (EDes) and in EDes supplemented either with Ca2+ (10,2 and 15,3 mM) or with Na+ (10,2 and 15,3 mM). In environments supplemented with CaCl2 the maximal survival was 40 days. The stimulation of PRL cells was similar to that described in EDes. On the contrary, in environments supplemented with NaCl, 50% of the animals are still alive after 45 days. PRL cells are slightly stimulated and their ultrastructural aspect is similar to that observed in controls kept in freshwater. The significance of these results is discussed in relation with our present knowledge of the pituitary control of osmoregulation in teleost fish.

Serotonin in the brain of the goldfish, Carassius auratus. An immunocytochemical study.

The distribution of immunoreactive serotonin (5-HT) was investigated in the brain and pituitary gland of the goldfish with the use of indirect immunofluorescence technique. Immunoreactive cerebrospinal fluid-contacting neurons were found in the nucleus recessus lateralis and in the nucleus recessus posterioris of the hypothalamus. Additional immunoreactive neurons were observed ventro-lateral to the posterior commissure in the nucleus dorsolateralis thalami. This group of cell bodies extends posteriorly as far as the rostral midbrain tegmentum. At the level of the isthmus, numerous immunoreactive cell bodies were located medially between the fiber bundles of the fasciculus longitudinalis medialis. Finally, a few isolated immunoreactive cells were observed in the medulla oblongata. In the pituitary gland, immunoreactive fibers and cells were found primarily in the pars distalis. The origin of the numerous fibers of the telencephalon is not clear, however, they may arise from the perikarya located in the raphe region. The general organization of the ascending and descending 5-HT-systems of the teleost brain appears to be similar to that described in mammals.

Ultrastructural changes in the pars intermedia of the goldfish kept in calcium-free environments.

The PAS-positive-calcium-sensitive (Ca-s) cells of the pars intermedia (PI) were studied in goldfish kept in fresh water (FW), deionized water (DW), 1/3 sea water (SW) and 1/3 Ca-free SW. Ultrastructural studies show that Ca-s cells of control goldfish kept in FW have a low activity with elongated or deeply indented nuclei. This activity is slightly reduced after 19 days in 1/3 SW. A considerable stimulation of most Ca-s cells is noted in goldfish kept in DW for 20 or 40 days. The stimulation is similar in 1/3 Ca-free SW, but it affects sometimes a smaller percentage of cells and may be less marked in peripheral areas of the PI. Exocytotic figures are more numerous in Ca-s cells of goldfish in 1/3 Ca-free SW than in DW. A basal lamina is rarely present and direct contacts between PI cells and nervous tissue are frequent, although a single synaptic contact with a type B fiber was observed. MSH cells are not affected in goldfish kept in DW. They are stimulated in 1/3 Ca-free SW: the physiological significance of this response remains unclear. Few agranular (Agr) cells are scattered in the PI. Evident changes are not observed in the different environments. The present ultrastructural data support the hypothesis that the Ca-s cells of the PI secrete a factor involved in calcium regulation in some teleosts.

[1st immunocytochemical application of an anti-dopamine antibody in the study of the central nervous system]. / Première application immunocytochimique d'un anticorps antidopamine à l'étude du système nerveux central.

An antibody against dopamine was raised in Rabbits by means of an immunogen constituting dopamine coupled to bovine serum albumin by formaldehyde. These antibodies were applied to frozen sections of Goldfish (Carassius auratus) brain fixed by 4% paraformaldehyde. The localisation of immunoreactive structures corresponded to regions rich in dopamine detected by histofluorescence. The specificity of this antiserum tested with the aid of dopamine analogues coupled with a carrying protein different from that of the antibody, indicates its validity as a method for the detection of dopaminergic neurons.

[Immunocytochemical distribution of somatostatin in the forebrain of two teleosts, the goldfish (Carassius auratus) and Gambusia sp (author's transl)]. / Localisation immunocytochimique de la somatostatine dans le cerveau antérieur et l'hypophyse de deux Téléostéens, le cyprin (Carassius auratus) et Gambusia sp.

Using immunofluorescence somatostatin was localized in the forebrain of the Goldfish and Gambusia. Immunoreactive cell bodies were detected in the nucleus preopticus periventricularis (NPP), the nucleus lateralis tuberis (NLT) and a dorsomedial nucleus at the level of the posterior nucleus anterioris periventricularis (NAPv) and of the rostral part of the nucleus ventromedialis thalami (NVM). In the pituitary, immunoreactive terminals were restricted at the proximal pars distalis.

Ultrastructural changes in the calcium-sensitive (PAS-positive) cells of the pars intermedia of eels kept in deionized water and in normal and concentrated sea water.

The ultrastructure of the calcium-sensitive (Ca-s) (PAS-positive) cells of the pars intermedia was investigated in eels kept in hypo- and hyperosmotic environments. Although the cells were moderately active in fresh water (FW), they were highly stimulated in deionized water (DW) and displayed an enlarged Golgi apparatus, a distinct rough endoplasmic reticulum, few secretory granules, some microtubules and an extended area of contact with the basal lamina that separates nervous and glandular tissues. Some mitosing cells were seen. A similar picture was observed in eels kept in sea water (SW) for 45 days, returned to FW and subsequently to DW for 21 days. In SW (20 and 33%), and particularly in concentrated SW (50, 60 and 63%), the Ca-s cells were inactive. Their granules were significantly smaller than in eels kept in FW, and the area of contact with the basal lamina was greatly reduced. However, signs of granule-release were seen in eels adapted to 50 and 60% SW. Nerve fibers rarely contacted the Ca-s cells and did not synapse with them. The ultrastructural data support the hypothesis that the Ca-s cells of Anguilla, like those of Carassius, are involved in ionic regulation. MSH cells were not greatly affected by the present experiments.

[Ultrastructure of neurons of nucleus preopticus and pars lateralis of the nucleus lateralis tuberis in Gambusia (Teleosta poeciliidae)]. / Ultrastructure des neurones du noyau préoptique et de la pars lateralis du noyau latéral du tuber chez Gambusia (Téléostéen poeciliidae).

The nucleus preopticus (NPO) and the pars lateralis of the nucleus lateralis tuberis (NLT) have been examined at the ultrastructural level. In the NPO two types of large neurons occur, both containing 140-150 nm secretory granules. The pars lateralis of the NLT contains only one cell type with similar granules. Both of these nuclei may be the source of type A fibres innervating the gonadotropic cells of Gambusia.

Serotoninergic control of MSH secretion in the eel. Ultrastructural study after 5-hydroxytryptophan treatment.

Injection of 5-HTP induces a melanodisperson ; MSH cells are markedly stimulated :hormone synthesis (development of Golgi area and endoplasmic reticulum) and release (reduction of secretory granules) are observed. This stimulatory serotoninergic pathway seems antagonistic to the dopaminergic system that inhibits MSH secretion in the eel.

[Ultrastructure of prolactin cells of three Mugilidae during adaptation to fresh-water (author's transl)]. / Etude ultrastructurale des cellules à prolactine chez trois espèces de mugilides au cours de l'adaptation à l'eau douce.

The behaviour of three species of Mugilidae (Mugil ramada, Crenimugil labrosus and Mugil auratus) during adaptation to fresh water is very different. Those differences may be explain by variants of their prolactin cells activity. The adaptation of Mugil ramada and Crenimugil labrosus to fresh water is easy and last over a long time; the prolactin cells, with a slow activity in sea water, become during adaptation more active. In Mugil auratus in sea water, prolactin cells present already a sign of strong activity. After transfert in fresh water, they appear to be unable to increase their activity. The adaptation of this species is difficult and short-lasting.