Distribution of fibres reacting with an alpha-endorphin antiserum in the neurohypophysis of Carassius auratus and Cyprinus carpio

Immunocytochemical demonstration of melanin-concentrating hormone and proopiomelanocortin-like products in the brain of the trout and carp

Immunocytochemistry on frozen sections revealed that in both the trout and the carp, parvocellular neurones located in the medial basal hypothalamus (medial nucleus lateralis tuberis) were immunostained by antisera against three molecules known to be derived from the proopiomelanocortin (POMC) molecule, viz: alpha-melanocyte-stimulating hormone (alpha MSH), ACTH, and salmonid NPP--the whole N-terminal sequence preceding ACTH in the POMC precursor. Axons from these neurones extended into various regions of the brain but did not appear to project into the pituitary gland. Antiserum against salmonid melanin-concentrating hormone (MCH) immunostained magnocellular neurones in the lateral basal hypothalamus (lateral nucleus lateralis tuberis). Axons from some of these neurones projected into the brain while other axons extended into the pituitary gland. In the carp, but not in the trout, some MCH neurones were also immunostained by antisera against alpha MSH but not by antisera against the other POMC molecules.

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.

Hypothalamo-pituitary-interrenal responses to opioid substances in the trout. I. Effects of morphine on the release in vitro of corticotrophin-releasing activity from the hypothalamus and corticotrophin from the pituitary gland

The effects of morphine and naloxone on the secretion in vitro of corticotrophin (ACTH) and and corticotrophin-releasing factor (CRF) by the pars distalis and hypothalamus, respectively, have been studied in the trout. The spontaneous in vitro secretion of corticotrophin by the pars distalis is depressed significantly by the addition of high concentrations of morphine (10(-6)-10(-7) mol/litre) to the incubation medium. The effect is naloxone reversible. Morphine does not influence the response of the pituitary tissue to exogenous CRF41, suggesting that the inhibitory influence of the opiate is exerted primarily on the CRF nerve terminals within the pars distalis and not on the corticotrophs. At considerably lower concentrations (10(-10)-10(-8) mol/litre) morphine stimulates the release of CRF from the isolated trout hypothalamus in vitro. Its effects are dose-dependent and antagonized by naloxone. The results suggest that two anatomically and pharmacologically distinct populations of opioid receptors mediate opposing actions of morphine on the hypothalamo-pituitary-corticotrophic system in the trout.

Hypothalamo-pituitary-interrenal responses to opioid substances in the trout. II. Effects of morphine and D-Ala2, Met5-enkephalinamide on plasma cortisol titres in vivo

The influence of morphine, D-Ala2, Met5-enkephalinamide (DALA), and naloxone on plasma cortisol titres has been studied in vivo in fingerling and adult trout. The responses were complex and variable. A single ip injection of morphine or DALA into fingerlings usually resulted in a rise in plasma cortisol after 0.5 hr followed by a fall below control values within 2 hr. In similar experiments with adult trout, only an inhibitory effect was observed. Naloxone reduced the rise in plasma cortisol following saline injection, but only when the hypothalamo-pituitary-interrenal response was intense. The antagonist also blocked the morphine-induced rise in cortisol secretion. Prolonged morphine treatment diminished both the postinjection and stress-induced secretion of cortisol in adult fish. Morphine had no effect on the spontaneous or ACTH-induced secretion of cortisol by interrenal tissue incubated in vitro. The results support the concept of inhibitory and stimulatory sites of action by opiates and opioid substances on the hypothalamo-pituitary-interrenal axis. These findings are discussed with reference to the action of morphine on hypothalamic and pituitary tissue of the trout in vitro and with the opioid control of hypothalamo-pituitary-adrenal function in mammals.

Occurrence of beta-endorphin-like immunoreactivity in the brain of the teleost, Boops boops

By immunocytochemical methods the present study describes beta-endorphin-like immunoreactive substance in the brain of Boops boops. Beta-Endorphin-like neurons and fibers were detected in both dorsal and ventral components of the preoptic nucleus and in the nucleus lateralis tuberis. This localization has been discussed in relation to the presence, in the same area, of a well-defined neurosecretory system involved in hypophysial regulation. A beta-endorphin-like immunoreaction was also detected in the Purkinje cells and in processes within the cerebellum molecular layer. Although this last finding remains enigmatic it may suggest a neuromodulatory activity for cerebellum beta-endorphin-like substance. No immunoreaction was observed when the specific antiserum was absorbed with corresponding antigen and with beta-LPH. These tests led to the conclusion that the immunostaining reaction might correspond to a beta-endorphin- or lipotropin-like reaction. Further, the present results show the phylogenetic antiquity of a beta-endorphinergic or lipotropinergic system in the brain, with a stable evolutionary history as a hypophysial regulatory factor or neuromodulatory agent.