Fine structure of the rostral pars distalis follicle cells in homotransplanted pituitaries of rainbow trout, Salmo gairdneri

The effects of N-methyl-D,L-aspartate and gonadotropin-releasing hormone on in vitro growth hormone release in steroid-primed immature rainbow trout, Oncorhynchus mykiss

In the present study we investigated the effects of 17 beta-estradiol (E2) and 5 alpha-dihydrotestosterone (5 alpha DHT) on the ability of the glutamate agonist, N-methyl-D,L-aspartate (NMA), to stimulate growth hormone (GH) release from perifused pituitary glands of sexually immature rainbow trout (Oncorhynchus mykiss). Two weeks after steroid hormone implantation, pituitary glands were removed from the fish and challenged with NMA (10(-8) M) in a perifusion unit. NMA rapidly and significantly elevated GH release from perifused pituitary fragments taken from all treatment groups, and there was a main effect of in vivo steroid hormone treatment on the in vitro GH response to NMA. To examine the relationship between NMA and gonadotropin-releasing hormone on GH release, pituitaries from E2- and 5 alpha DHT-primed and control fish were exposed to a single pulse of salmon gonadotropin-releasing hormone (sGnRH) which also elicited a significant elevation in GH release from perifused pituitary fragments, although the response in the E2- and 5 alpha DHT-primed fish was significantly smaller (P < 0.05) than that for the NMA challenge. Administration of a specific GnRH antagonist, D-pGlu1,D-Phe2,D-Trp3,6-LHRH, did not affect the GH response to NMA, whereas administration of the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid blocked the GH response to NMA. These data suggest that NMA acts to stimulate GH release directly at the level of the somatotroph, likely through the NMDA receptor and not through increased release of GnRH.

The development of monoclonal antibodies against salmon (Oncorhynchus kisutch and O. keta) pituitary hormones and their immunohistochemical identification

Monoclonal antibodies (MCAs) directed against several salmon pituitary hormones were generated by the fusion of myeloma cells with spleen cells from mice that had been immunized with either chum salmon (Oncorhynchus keta) growth hormone (GH) or prolactin (PRL), or one of two purified protein preparations from coho salmon (O. kisutch) pituitaries. Hybridoma were cloned by limiting dilution and screened for MCA production using immunohistochemical procedures. MCAs were generated that bound specifically to GH, PRL, or gonadotropic cells. MCAs were generated that bound to either fine granular material or large globular inclusions in the cytoplasm of the "classical" strongly PAS-positive globular gonadotropic cell type found in mature fish. This suggests that these MCAs are directed against gonadotropin II (GTH II). A MCA was also generated that bound both granular and globular material in the globular gonadotrops and granular material in the weakly PAS-positive vesicular gonadotrops in pituitaries from mature fish and to a cell type in immature rainbow trout pituitaries which is tentatively identified as the gonadotropin I (GTH I) cell type. This MCA did not bind to thyrotrops in immature rainbow trout pituitaries.

Hypothalamic control of prolactin release in the rainbow trout,Salmo gairdneri: in vitro studies

Hypothalamic control of prolactin (PRL) release in immature rainbow troutSalmo gairdneri was investigated using anin vitro perifusion system of the rostral pars distalis. Hypothalamic extract of trout induced a dose-dependent stimulation of PRL release. A similar effect was observed when infusing the medium from a 24h static incubation of the hypothalamus. Extracts from different control tissues (muscle, liver, gut) did not changein vitro release, thus confirming the specificity of this stimulatory effect. Hypothalamic extract from adult male rat, known to contain PRL release inhibiting factors, stimulatedin vitro PRL secretion in rainbow trout. This suggests that PRL cells are predominantly influenced by PRL releasing factors. Measurement of TRH and serotonin content in trout hypothalamus indicated consistent physiological levels of these two factors. HPLC studies of hypothalamic extract showed that immunoreactive - TRH eluted at the same place as labelled TRH standard. Moreover, pizotifen, a serotonin antagonist, partially inhibited the stimulation observed with trout hypothalamic extract. These results suggest that, in immature rainbow trout, PRL release is under stimulatory hypothalamic control and that serotonin and probably TRH play a major role in this control.

Prolactin and growth hormone secretion during long-term incubation of the pituitary pars distalis of mature chum salmon, Oncorhynchus keta

The effects of hypotonicity of the medium on prolactin (PRL) and growth hormone (GH) release from the pars distalis (PD) of mature chum salmon pituitary were examined during culture for 4 days. Large amounts of PRL and GH were released during the first 6 hr and secretion decreased rapidly thereafter. The amounts of GH released as well as the residual content in PD were 10 times greater than those of PRL. There was no difference in PRL or GH release between the PD incubated in isotonic medium (325 mOsm) and those in hypotonic medium (250 mOsm) even during the first 6 hr. Female PD secreted more PRL than male PD during the first 6 hr, whereas a sex difference was not observed in GH release. Considerable amounts of both PRL and GH remained in the PD at the end of the culture period. The amount of PRL released during 4 days of culture from female PD (37-39%) was greater than that from male PD (23-26%), and the amount of GH released was less in females (28-32%) than that in males (53-54%). Release of PRL and GH appears to be mainly under stimulatory hypothalamic control in the mature chum salmon.

The effect of prolactin on fanning behavior in the male three-spined stickleback, Gasterosteus aculeatus L

The effect of administration of homologous prolactin on fanning behavior, an important aspect of parental care in sticklebacks and many other teleost fish, was studied. Prolactin was administered by implantation of an additional pituitary prolactin lobe in the dorsal body musculature of males with a nest without eggs. The low but rather constant level of fanning behavior is significantly increased from Day 6 to Day 12 after administration of the prolactin lobe. The implantation has no noticeable effects on cell and nuclear size or on the ultrastructure of the in situ prolactin cells of the recipient fish. Recovered prolactin lobe implants show two categories of prolactin cells. The major category consists of cells that are well developed and, similar to in situ prolactin cells, show structural signs of high secretory activity. The other prolactin cell category in the implants shows signs of cellular involution. Ten days after implantation, the first category predominates, and 16 days after implantation the second category. Prolactin lobe implantation increases the number of mucocytes in the epithelium of the skin, in particular at Day 10, and to a lesser extent at Day 16. This is considered evidence for a transient rise in blood prolactin levels in the recipient fish. We conclude that prolactin stimulates fanning behavior in male sticklebacks.

Plasma and pituitary prolactin levels in rainbow trout during adaptation to different salinities

The development of a highly specific radioimmunoassay for salmonid prolactin (PRL) using chinook salmon PRL allowed us to study plasma and pituitary PRL profiles in large sedentary rainbow trout (Salmo gairdneri) transferred from fresh water to seawater and vice versa. Plasma osmotic pressure and chloride levels were also measured for 3 weeks following change of salinity. Within 1 day after transfer to full seawater we observed a plasma PRL decrease, which stayed significantly lower (3-5 ng/ml) than the fresh water control group (10-15 ng/ml) during the entire experiment. Pituitary PRL content showed an initial abrupt increase, but after 3 weeks in seawater pituitary PRL content had decreased to the same level as in the fresh water control group. On the contrary, transfer from seawater to fresh water was followed within 1 day by a rise in plasma PRL levels, which stayed high (10-15 ng/ml) after 3 weeks in fresh water. Simultaneously, pituitary PRL content decreased significantly. These results may indicate an important role of PRL in fresh water adaptation of sedentary rainbow trout.

Immunocytochemistry of gonadotropic cells and identification of cell types in ultrathin cryosections of the pituitary of the rainbow trout, Salmo gairdneri

The most frequently occurring cell types in the pars distalis of the pituitary gland of the rainbow trout, (i) the lactotropic, (ii) the gonadotropic, and (iii) the somatotropic cells, were identified in cryosections. Their morphological characteristics were compared with those of Epon-embedded material. Cell location, cell form, position of the nucleus, arrangement of rough endoplasmic reticulum and sizes of secretory granules proved to be useful parameters for identification. The size distribution of secretory granules of corresponding cells in cryosections and Epon sections proved to be similar. Additionally, both the immunoferritin and the unlabeled antibody enzyme method were applied for the immunocytochemical labeling of gonadotropic hormone-producing cells in cryosections. Anti-salmon-GTH as well as anti-carp-GTH serum showed the presence of GTH in both the smaller and the larger granules of the classical GTH cells, but also produced a reaction in TSH cells. Labelling of TSH cells was absent when using anti-beta-carp-GTH. Specificity of the reaction depended upon the degree of dilution of the anti-GTH serum. Results with dilutions of 1:4,000 and 1:8,000 in the unlabeled antibody enzyme method, and of 1:8,000 up to 1:32,000 in the immunoferritin technique were optimal. Acid phosphatase activity in the smaller granules was demonstrated by enzyme cytochemistry in Epon sections. The relationship of the presence of hormone in these granules is discussed. The high sensitivity of the immunocytochemical labeling procedure is discussed with respect to cryo-ultramicrotomy.

Effects of external osmolality, calcium and prolactin on growth and differentiation of the epidermal cells of the cichlid teleost Sarotherodon mossambicus

Osmolality and concentrations of divalent cations--calcium, and to a lesser extent magnesium--of the water are the main environmental factors that determine development and degree of mucification of the skin epithelium of Sarotherodon mossambicus. Epithelial thickness and number of mucocytes in fish exposed to low (freshwater level) concentrations of calcium and magnesium are directly related to the height of the osmotic gradient between water and blood plasma. No such relationship is found in fish exposed to a high (seawater level) concentration of calcium in the water, irrespective of the height of the osmotic gradient. The results strongly indicate that the effects of osmolality and divalent cations are indirect, and mediated by prolactin, since administration of ovine or fish prolactin stimulates growth and multiplication of the cells of the basal layer of the epidermis, and promotes the differentiation of the mucocytes.