Immunocytological detection and localization of a peptide reacting with an alpha-endorphin antiserum in the corticotropic and melanotropic cells of the trout pituitary (Salmo irideus Gibb)

Opioid binding sites in the fish brain: an autoradiographic study

Cryostat sections of trout brains were incubated with tritiated opioid ligands (5 nM [3H]etorphine or 4 nM D-[3H]Ala2, Met5 enkephalinamide) with the initial aim of locating opioid binding sites associated with the hypothalamo-pituitary axis. Naloxone-displaceable binding was observed in all regions of the brain, with a density ranking order of cerebellum greater than telencephalon greater than optic tectum greater than hypothalamus greater than brain stem greater than pituitary gland. Within the hypothalamus and pituitary gland binding was unexpectedly low, apart from a slightly enhanced binding anteriorly in the preoptic region and posteriorly associated with presumptive sensory fibres. A similar distribution of opioid binding sites was seen in the eel and lamprey brain. The high level of opioid binding in the cerebellum permitted a tentative identification of opioid subtypes using [3H]etorphine binding to membrane preparations from trout cerebellum. Scatchard analysis indicated the presence of a single class of high-affinity binding sites with a density of 0.38 pmol/mg protein and affinity constant (KD) of 2.6 nM. Displacement by unlabelled ligands suggested the existence of mu and/or kappa receptors.

Identification and distribution of the cell types in the pituitary gland of Austromenidia laticlavia (Teleostei, Atherinidae)

By using antisera against human pituitary hormones in immunocytochemistry in combination with classical cytochemical techniques, we have been able to identify the different cell types in the adenohypophysis of the Austromenidia laticlavia and to determine their location. Antisera against prolactin and growth hormones did not stain cells in the pituitary of Austromenidia, whereas antisera against beta-endorphin, LH, and beta-TSH selectively cross-reacted with cells which have a specific location within the adenohypophysis. The beta-endorphin antiserum stained the periodic acid-Schiff (PAS)-negative cells in the pars intermedia and also, though faintly, the PAS-negative cells in the internal border of the rostral pars distalis (RPD). Human beta-TSH antiserum showed a discrete population of small PAS-positive cells in the proximal pars distalis (PPD). Antiserum against human LH stained PAS-positive cells located in the most ventral zone of the PPD and around the pars intermedia (PI). The distribution of the different cell types is similar to that of other teleosts. The phylogenetic implications of the degree of cross-reactivity of the antisera against human pituitary hormones with specific cells of the teleost fish pituitary is discussed.

Stress-induced elevation of plasma alpha-MSH and endorphin in brown trout, Salmo trutta L

Handling and confinement caused a pronounced elevation in the plasma cortisol levels of brown trout. This response was more rapid, and the elevation greater, at 13.4 than at 5 degrees although basal cortisol levels were also higher at the warmer water temperature. The large increase in plasma cortisol caused by handling and confinement was not accompanied by any changes in the plasma levels of either alpha-MSH or endorphin. However, when handling and confinement was combined with a thermal shock, not only was there a rapid and pronounced elevation in plasma cortisol, but there were also concomitant and sustained rises in the plasma levels of both alpha-MSH and endorphin. The levels of a alpha-MSH and endorphin induced by the thermal shock were considerably higher than those recorded in long-term, black-adapted brown trout, the only other circumstance in fish known to cause an elevation of the plasma levels of these two peptides. These results indicate that handling and confinement only activated the corticotrophs of the pars distalis, not the melanotrophs of the neurointermediate lobe, whereas when combined with a thermal shock, both cell types were activated.

Immunocytochemical identification of the proopiocortin-producing cells in the chum salmon pituitary with antisera to endorphin and NH2-terminal peptide of salmon proopiocortin

The proopiocortin-containing cells were identified immunocytochemically in the chum salmon pituitary using specific antibodies raised against NH2-terminal peptide (sNPP) and COOH-terminal peptide, endorphin (sEP), of salmon proopiocortin. Immunoreactivity for both sNPP and sEP was observed in the same cells, melanotrops, in the pars intermedia. In the pars distalis, on the other hand, corticotrops were stained only with antibody to sNPP but not with that to sEP. The present results indicate that proopiocortin or a precursor molecule for NH2-terminal peptide and endorphin is biosynthesized in both melanotrops of the pars intermedia and corticotrops of the pars distalis. However, the absence of immunoreactivity of corticotrops with sEP antibody suggests that the processing of the precursor molecule in the pars distalis differs significantly from that in the pars intermedia in the chum salmon pituitary as the processings established in the two lobes in the mammalian pituitaries.

The distribution of some proopiomelanocortin-related peptides in the pituitary gland of the rainbow trout, Salmo gairdneri

Acid extracts of neurointermediate lobe (NIL) and pars distalis (PD) of the pituitary gland of the rainbow trout were radioimmunoassayed for alpha-melanocyte-stimulating hormone (alpha-MSH), beta-melanocyte-stimulating hormone (beta-MSH), adrenocorticotrophin (ACTH), and endorphin. The majority of the alpha-MSH, beta-MSH, and endorphin was present in the NIL; the small amount of these peptides present in the PD may be native to this lobe, or may be due to slight contamination with NIL material--it is not possible to distinguish between these possibilities at present. All the ACTH was present in the PD. These results support the hypothesis that throughout the vertebrates proopiomelanocortin is cleaved to smaller peptides in the NIL than it is in the PD.

Gastro-intestinal and neurohormonal peptides in the alimentary tract and cerebral complex of Ciona intestinalis (Ascidiaceae)

Polypeptide-hormone producing cells were localized in the alimentary tract and cerebral ganglion of Ciona intestinalis using cytochemical, immunocytochemical and electron-microscopical methods. Antisera to the following peptides of vertebrate type were employed: bombesin, human prolactin (hPRL), bovine pancreatic polypeptide (PP), porcine secretin, motilin, vasoactive intestinal polypeptide (VIP), beta-endorphin, leu-enkephalin, met-enkephalin, neurotensin, 5-hydroxytryptamin (5-HT), cholecystokinin (CCK), human growth (GH), ACTH, corticotropin-like intermediate lobe peptide (CLIP) and gastric inhibitory peptide (GIP). Immunoreactive cells were found both in the alimentary tract epithelium and in the cerebral ganglion for bombesin, PP, substance P, somatostatin, secretin and neurotensin. Additionally, in the cerebral ganglion only, there were cells immunoreactive for beta-endorphin, VIP, motilin and human prolactin. 5-HT positive cells, however, were restricted to the alimentary tract. No immunoreactivity was obtained either in the cerebral ganglion or in the alimentary tract with antibodies to leu-enkephalin, met-enkephalin, CCK, growth hormone, ACTH, CLIP and GIP. Prolactin-immunoreactive and pancreatic polypeptide-immunoreactive cells were argyrophilic with the Grimelius' stain and were found in neighbouring positions in the cerebral ganglion. At the ultrastructural level five differently granulated cell types were distinguished in the cerebral ganglion. Granules were present in the perikarya as well as in axons. The possible functions of the peptides as neurohormones, neuroregulators and neuromodulators are discussed.

Immunocytological study on the differentiation of chick and quail adenohypophysis epithelial rudiments, grafted or cultivated in vitro: evidence for polypeptidic hormones

Epithelial rudiments of adenohypohysis were removed from chick and quail embryos between days 3 and 5 of development. Chick rudiments were grafted for 11--13 days onto the chorioallantoic membrane of decapitated chick embryo hosts. Quail rudiments were cultivated in vitro for 6 days. Both grafted and cultivated Rathke's pouches differentiated into adenohypophyseal tissue. The adenohypophyseal tissue cultured on chorio-allantoic membrane exhibited cells reacting with the following immune sera: anti-beta-(1--24)ACTH, anti-alpha-(17--39)-ACTH, anti-alpha-endorphin, anti-beta-endorphin and anti-beta-LPH, which also gave a positive reaction when applied to adenohypophysis of corresponding age which had differentiated in situ. In situ, corticotrophs were located exclusively in the cephalic lobe of adenohypophysis. Therefore, the differentiation of corticotrophs in the whole graft, i.e., from both cephalic and caudal lobes of Rathke's pouch, showed that the cells of the caudal lobe, or at least some of them, were uncommitted when the rudiment was removed. In vitro, tissue derived from Rathke's pouch contained cells reacting with antibodies to beta-(1--24)-ACTH, alpha-(17--39)-ACTH, and beta-LPH, as did adenohypophysis from quail embryos of corresponding age (9--10 days), differentiated in situ. The differentiation of quail Rathke's pouch in vitro corroborates that differentiation can occur without influence from hypothalamus and, moreover, shows that at least some kinds of cells can differentiate without influence exerted by any other encephalic factors, and in the absence of mesenchyme. The question arises whether fibroblastic cells derived from Rathke's pouch cells act as feeder-cells and/or secrete some factors promoting differentiation.

Responses of MSH and prolactin cells to 5-hydroxytryptophan (5-HTP) in amphibians and teleosts

Injection of 5-hydroxytryptophan (5-HTP), a precursor of serotonin, induces dispersion of melanin in the amphibians, Pleurodeles waltlii (Urodela) and Xenopus laevis (Anura), in the goldfish, Carassius auratus, and in the carp, Cyprinus carpio. It is accompanied by a dispersion of erythrophore pigments. In the pituitaries of Pleurodeles and goldfish, a stimulation of MSH cells, characterized by a significant nuclear hypertrophy, is also observed; in Carassius, MSH cells may become degranulated. Serotonin appears to exert a stimulating effect on MSH release in lower vertebrates. Swimming behavior is disturbed in the goldfish and the carp; gaseous metabolism in the swim-bladder may be affected by injection of 5-HTP, as previously reported in the eel. Prolactin (PRL) cells appear activated, but remain granulated in the treated goldfish. No clear response of PRL cells to injection of 5-HTP can be observed in Pleurodeles. A possible role of serotonin in Pleurodeles submitted to an experimental aeroionization is briefly discussed.

Radioimmunoassay of methionine(5)-enkephalin sulphoxide: phylogenetic and anatomical distribution

A sensitive and specific radioimmunoassay (RIA) for the oxidised form of methionine(5)-enkephalin (Met(5)-Enk), Met(5)-Enk sulphoxide (Met(5)-Enk-S), has been developed. Antisera were raised in rabbits against Met(5)-Enk coupled to carrier proteins with glutaraldehyde or carbodiimide. Displacement of (125I) Met(5)-Enk bound to antiserum by Met(5)-Enk was poor, but Met(5)-Enk-S displayed good displacement suggesting that the Met(5)-Enk immunogen was oxidised to Met(5)-Enk-S and that the antisera were formed against this compound. The sensitivity of the RIA for Met(5)-Enk-S was 0.02 pmole/tube using the most sensitive antiserum. The antisera showed negligible cross-reactivity with leucine(5)-enkephalin and with both native and oxidised endorphins. Cross-reactivity was between 15% and 28% with the fragment Met(5)-Enk (2--5) sulphoxide and between 9% and 25% with D-Ala(2)-Met(5)-Enk sulphoxide. The antisera showed less than 0.01% cross-reactivity with other Met(5)-Enk fragments and naturally occurring neuropeptides. Tissue extracts were oxidised with hydrogen peroxide prior to assay. Met(5)-Enk-S immunoreactivity (IMR) was detected in brain, pituitary gland, pancreas, and intestine extracts of the rat, chicken, toad and teleost, and in cerebral-suboesophageal ganglion extracts of the snail. All tissue extracts showed parallelism in serial dilution to synthetic mammalian Met(5)-Enk-S, suggesting possible immunological identity. The results indicate that spontaneous oxidation of Met(5)-Enk immunogen occurs such that antisera are produced against the sulphoxide analogue of Met(5)-Enk, and may account for the relative insensitivity of some published RIAs using Met(5)-Enk standard. Our findings demonstrate a wide phylogenetic and anatomical distribution of Met(5)-Enk IMR.