Evaluation of carbon dioxide induction methods for the euthanasia of day-old cull broiler chicks

This study was conducted to evaluate the efficacy of 5 different CO2 euthanasia induction techniques for day-old cull chicks in minimizing distress and inducing a rapid loss of sensibility and death. Each induction treatment was characterized for concentration change over time, maximum concentration, and time to reach maximum. Sixteen chicks were euthanized with the gradual treatments to establish validity of treatment. Then, all 5 treatments were evaluated for effect on distress, insensibility, and death. Day-of-hatch cull chicks (n = 110) were euthanized in pairs by either immersion into 100% CO2 or gradual induction to 100% CO2 at displacement rates of 7, 14, 21, or 28% of chamber volume added per min (% vol/min). CO2 concentration was measured at chick level. Live focal observations and video recordings were used to assess latency to behavioral responses: head shaking (HS) and gasping (GS) as indicators of distress; loss of posture (LOP) as an indicator of insensibility; and cessation of rhythmic breathing (CRB) and movement (COM), indicating death. All behaviors occurred at the earliest with immersion compared to gradual treatments, and time between first signs of distress and LOP was shorter for immersion than gradual treatments. Gradual treatments showed a linear decrease in latency to HS, GS, and LOP as displacement rate increased. Latency to CRB decreased quadratically with increasing displacement rate, while COM decreased linearly. Within gradual treatments, HS and GS occurred at CO2 concentrations between 0.43 and 1.14%, LOP between 11.1 and 17.5%, while CRB and COM occurred between 61.8 and 78.4%. Overall, immersion induced distress, insensibility, and death significantly faster and with the shortest interval between distress and insensibility. For gradual treatment, insensibility and death occurred faster with increasing displacement rates. Behavioral signs of distress were observed with all treatments, and occurred at concentrations lower than those causing insensibility. In conclusion, immersion into 100% CO2 environment resulted in the shortest time of distress and fastest time to death compared to gradual displacement rates of any speed measured.

Biological role of the pars intermedia in lower vertebrates

The most obvious function of the pars intermedia in lower vertebrates is the secretion of melanocyte-stimulating hormone (MSH) for the purpose of pigmentary control. In some amphibia, elasmobranchs and teleosts, the histological study of the pars intermedia, the radioimmunoassay of pituitary and plasma MSH and the effects of hypophysectomy and of MSH injection suggest that the activity of the pars intermedia is regulated to satisfy the needs of cryptic colour change. MSH secretion is associated with dispersion of melanin granules and with melanogenesis. However, in other teleost species, both the evidence from pituitary cytology and the failure to respond to MSH injection suggest that pigmentary change is not regulated by changes in the plasma titres of MSH. Results discussed here indicate that MSH alone may be inadequate for pigmentary control. Evidence for non-pigmentary functions of the pars intermedia is circumstantial and fragmentary. It is based on cytological observations of altered pars intermedia activity under certain conditions, and on observations of physiological changes that accompany increased melanotropic activity. Such function include effects of plasmas titres of cortisol in teleosts, resistance to adrenaline-induced hyperglycaemia in toads, and effects on neural activity in fish and amphibia. Evidence for pars intermedia involvement in osmoregulation is briefly discussed.

Differences in arginine vasotocin gene transcripts and cortisol secretion in trout with high or low endogenous melanin-concentrating hormone secretion

Previous studies on trout suggest that melanin-concentrating hormone (MCH) acts at both hypothalamic and pituitary levels to restrain the release of adrenocorticotropic hormone and hence cortisol during stress. Using in situ hybridization, the present work examined whether high rates of MCH secretion were associated with changes in the synthesis of arginine vasotocin (AVT), one of the corticotropin secretogogues. It also examined whether high endogenous MCH secretion restrains cortisol secretion during intense as well as mild stress, and how exogenous MCH affects the rise in plasma cortisol following injection stress. Trout were reared in black- or white-coloured tanks for 1 year or more to achieve maximal differences in MCH secretion. Following a mild stress, cortisol secretion was greater in black-reared fish with low MCH secretion which is in line with previous findings but, following a more severe stress, plasma cortisol concentrations were similar in the two groups. Injection of MCH into black-adapted fish restrained the stress-induced rise in plasma cortisol concentration during the first hour but did not affect final cortisol values. In two separate experiments, AVT mRNA levels were significantly lower in the hypothalamus of black-reared fish. Possible explanations for this include a greater negative-feedback restraint by cortisol, which is likely to rise higher in black-adapted fish during the moderate, daily stresses of aquarium life; or the possibility that exposure to a white background may be psychologically stressful, stimulating AVT transcription. The possibility that MCH directly stimulates AVT transcription cannot be excluded but seems less likely. The results suggest that while MCH may restrain the release of hypothalamo-pituitary stress hormones under moderately stressful conditions, it does not restrain AVT synthesis.

The distribution of melanin-concentrating hormone in the lamprey brain

In addition to its novel, colour-regulating hormonal role in teleosts, the melanin-concentrating hormone (MCH) serves as a neuromodulatory peptide in all vertebrate brains. In gnathostome vertebrates, it is produced in several neuronal cell groups in the hypothalamus. The present work examines the organisation of the MCH system in the brain of lampreys, which separated from gnathostome vertebrates at an early stage in evolution. In all three lamprey genera examined-Petromyzon, Lampetra, and Geotria spp.-MCH perikarya were found in one major anatomical site, the periventricular dorsal hypothalamic nucleus of the posterior hypothalamus. Axons from these cell bodies projected medially into the ventricular cavity, and laterally to the neuropile of the lateral hypothalamus. From here, they extended anteriorly and posteriorly to the fore- and hindbrain. Other fibres extended dorsomedially to the habenular nucleus. In Lampetra, but not in Petromyzon, MCH fibres were seen in the pituitary neurohypophysis, most prominantly above the proximal pars distalis. The hypothalamic region in which the MCH perikarya are found forms part of the paraventricular organ (PVO), which is rich in monoamines and other neuropeptides. The association of MCH neurones with the PVO, which occurs also in many other nonmammalian vertebrates, may reflect the primary location of the MCH system. These MCH neurones were present in ammocoetes, postmetamorphic juveniles, and adults. They were more heavily granulated in adults than in young lampreys but showed no marked change in secretory appearance associated with metamorphosis or experimental osmotic challenge to indicate a role in feeding or osmoregulation. In sexually maturing Lampetra fluviatilis, however, a second group of small MCH neurones became detectable in the telencephalon, suggesting a potential role in reproduction and/or behaviour.

The effect of leptin on luteinizing hormone release is exerted in the zona incerta and mediated by melanin-concentrating hormone

The adipose hormone, leptin, not only restrains appetite, but also influences energy expenditure. One such influence is to promote sexual maturation and fertility. The neuromodulatory circuits that mediate this effect are not well known but the present study suggests that one mediator could be melanin-concentrating hormone (MCH). We show that the long-form receptor (Ob-Rb) is expressed in the zona incerta of the rat and that administration of leptin (both 0.5 microg and 1.0 microg/side) into this area of ovariectomized, oestrogen-primed rats stimulated the release of luteinizing hormone (LH) within 1 h, the effect enduring for a further 1 h. Injections of leptin into the arcuate nucleus induced a smaller, transient rise in LH while injections into the paraventricular and ventromedial nuclei were without effect. MCH neurones are present in the zona incerta and administration of this hormone into the medial preoptic area (mPOA) stimulates LH release, therefore we investigated the possibility that MCH might mediate this effect of leptin. An injection of MCH antiserum into mPOA prevented the rise in LH normally induced by leptin injected into the zona incerta. In addition, melanocortin receptor antagonists ([D-Arg8]ACTH(4-10) and [Ala6]ACTH(4-10)), previously shown to inhibit the stimulatory effect of MCH on LH release, also inhibited the effect of leptin. We propose that one route by which leptin may promote reproductive activity is by enhancing MCH release from fibres within the mPOA. Speculative mechanisms for the action of MCH include the following possibilities: MCH may be acting on the specific MCH receptor which in turn interacts with a melanocortin or melanocortin-like receptor; MCH may bind directly to one of the melanocortin receptors; or melanocortin antagonists may interact with the MCH receptor.

The effects of acute and chronic stresses on vasotocin gene transcripts in the brain of the rainbow trout (Oncorhynchus mykiss)

Secretion of adrenocorticotropic hormone (ACTH) from the fish pituitary, which occurs in times of stress, is stimulated by several hypothalamic neuropeptides, one of which is arginine vasotocin (AVT). This study investigates whether gene expression for AVT is up-regulated during acute or chronic stress. Rainbow trout (Oncorhynchus mykiss) were subjected to one of two forms of acute stress-either 2 h confinement followed by 2 h recovery, or capture and transfer to low water for 2 min followed by 4 h recovery in their home tank before autopsy. In other experiments, these stresses were repeated daily for 5 or 6 days (chronic stress). Quantification of AVT transcript prevalence in the parvocellular and magnocellular neurones of the preoptic nucleus after in situ hybridization was used as a monitor of the AVT gene response to stress. The results showed that acute confinement, but apparently not brief low-water stress, significantly increased AVT transcript prevalence in a group of parvocellular perikarya. When applied repeatedly, both forms of stress caused habituation, such that the AVT hybridization signal remained at control or even lower levels despite elevated pro-opiomelanocortin transcripts in the corticotropes and raised plasma cortisol concentrations. The AVT hybridization signal in the magnocellular perikarya showed no significant response to either acute or chronic stress. The results support the idea that these parvocellular AVT neurones are involved in ACTH stimulation during acute stress, and that the system habituates to chronic stresses.

Melanin-concentrating hormone, melanocortin receptors and regulation of luteinizing hormone release

Melanin-concentrating hormone (MCH) is a neuropeptide, identified by its ability to either mimic or antagonize the melanin-dispersing action of alpha-melanocyte stimulating hormone (alphaMSH) on skin melanophores. MCH and alphaMSH also have antagonistic actions in the brain affecting feeding behaviour, aggression, anxiety, arousal and reproductive function through the release of luteinizing hormone (LH). It is not clear, however, how they exert their opposite effects in the central nervous system (CNS). One possibility is that they act via a common receptor. In this study we have examined the effect of a number of MC receptor antagonists, with relative selectivity for the MC3, 4 and 5 subtypes, on the actions of MCH on LH release. We confirmed that bilateral administration of MCH (100 and 200 ng/side) into the medial preoptic area of oestrogen-primed (oestradiol benzoate 5 microgram) ovariectomized anaesthetized rats, stimulated the release of LH. This effect was blocked by the concomitant administration into the medial preoptic area of the MC4/5 antagonist ([D-Arg8]ACTH(4-10) and the MC3/5 antagonist ([Ala6]ACTH(4-10)-both at 500 ng/side-but not by the MC3/4 antagonist, SHU9119 (200 ng/side). Furthermore, the MC3 agonist [Nle3]-gamma2 MSH failed to affect LH release. These results indicate that the MC3 and MC4 receptors are not involved in mediating the action of MCH but are consistent with an action via the MC5 subtype. Preputial glands, which express MC5 receptors, were also stimulated by MCH which is in keeping with this idea. In HEK293 cells transfected with the MC5 receptor MCH increased the production of IP3. However, it was much less potent than alphaMSH and unlike alphaMSH, had no effect on the production of cAMP. MCH (10-10 to 10-5 M) also failed to displace I125NDP-MSH from cells transfected with MC5 receptors indicating that it was not acting as a competitive antagonist and its binding site was distinct from that of alphaMSH. Thus while MCH may function as an agonist at the MC5 receptor, its stimulation of LH release is more likely to be mediated via a specific MCH receptor that has common properties with the MC5 receptor.

The influence of gonadal steroids on pre-pro melanin-concentrating hormone mRNA in female rats

Melanin-concentrating hormone (MCH) may have a regulatory role in the control of luteinizing hormone (LH) release. We have investigated if gonadal steroids induce changes in the expression of pre-pro MCH (ppMCH) that are associated with changes in the pattern of LH release. Using quantitative in-situ hybridization histochemistry we have determined the effect of administration of either oestradiol benzoate (5 microg/rat) or oestradiol benzoate followed 44 or 48 h later by progesterone (0.5 mg/rat) to ovariectomized rats on the expression of ppMCH in the medial and lateral zona incerta and the lateral hypothalamus. The prevalence of ppMCH transcripts in the intact female rat at 12.00 and 19.00 h on proestrus and the first day of dioestrus was also examined. Oestrogen reduced the intensity of hybridization signal for ppMCH mRNA and this was associated with both a decrease in the number of cells in which the message was detected in the medial zona incerta and a negative feedback effect on LH release in ovariectomized rats. Progesterone administration to oestradiol benzoate-primed rats did not alter the reduced expression in the medial zona incerta in spite of its positive feedback effect on LH release. We suggest that progesterone may act only on post-translational events. Expression in the MCH cell bodies of the lateral zona incerta were not affected but there was a transient decrease 4 h after progesterone treatment in the oestradiol benzoate-primed rats in expression in the lateral hypothalamus. No changes in ppMCH mRNA were seen in intact animals on proestrus or the first day of dioestrus indicating that gonadal steroids are not important in the modulation of ppMCH gene expression during the oestrous cycle. In other steroid-dependent physiological situations, however, oestrogen may influence the expression of ppMCH in a subpopulation of cell bodies in the medial zona incerta.

Rainbow trout (Oncorhynchus mykiss) urotensin-I: structural differences between urotensins-I and urocortins

In bony fishes, both corticotropin-releasing factor (CRF) and urotensin-I play a role in the regulation of interrenal glucocorticoid release. The rainbow trout, Oncorhynchus mykiss, is a useful model for understanding the mechanisms of stress and the hypothalamo-pituitary-interrenal axis because of its phylogenetic position at the base of the euteleostei and its popularity as a food fish. Urotensin-I may act as a glucocorticoid releaser in a mechanism phylogenetically older than that of CRF. The structural and functional relationships of trout urotensin-I have been investigated. The transcript was cloned from a trout brain hypothalamic cDNA library. A single positive clone was isolated and sequenced. It possesses 3218 bases and has the longest 3' untranslated region of all urotensins-I and CRF transcripts found to date. In comparison to the other fish orthologues, it has the closest sequence identity to the mammalian urocortins. The transcript appears to be differentially processed in brain and urophysis as determined by Northern blot analysis and the presence of polyadenylation signals in the 3' untranslated region. Synthetic trout urotensin-I activated both human CRF-R1 and -R2 receptor-transfected CHO cells with a potency similar to that of white sucker (Catostomus commersoni) urotensin-I. Both fish neuropeptides possessed an order of magnitude less potency than human urocortin in CRF-R2 transfected cells.

Diurnal changes in the expression of genes encoding for arginine vasotocin and pituitary pro-opiomelanocortin in the rainbow trout (Oncorhynchus mykiss): correlation with changes in plasma hormones

Using quantitative in-situ hybridization, this study monitored diurnal changes in the abundance of the gene transcripts of two corticotropin-releasing peptides, arginine vasotocin (AVT) and isotocin in hypothalamic neurones, and of pro-opiomelanocortin (POMC) mRNA in the pituitary of the rainbow trout (Oncorhynchus mykiss). A significant diurnal pattern of gene expression was only displayed in the hypothalamus by the parvocellular AVT neurones of the preoptic nucleus. Abundance of AVT mRNA in these neurones was low at lights on (06.00 h), increased during the morning to reach a plateau of peak values between 14.00 h and 22.00 h, and then declined during the dark phase. This pattern was the inverse of that shown by plasma cortisol values. Changes in AVT transcript abundance are also considered in terms of the reported diurnal change in circulating AVT concentration. Pituitary and hypothalamic AVT peptide content did not change. Transcripts of both POMC genes (POMC-A and POMC-B) were monitored in pituitary corticotropes and melanotropes. Only POMC-A mRNA was detected in corticotropes where it showed no diurnal change in abundance. Transcripts of both POMC genes were found in the melanotropes, although, judging from autoradiographic intensity, POMC-A mRNA predominated. Both genes showed diurnal differences in their transcription with POMC-A mRNA showing peak values at 10.00 h and a nadir at 02.00 h, while POMC-B mRNA showed an inverse pattern. The results indicate that the two POMC genes can be independently regulated.

Behavioral effects of neuropeptide E-I (NEI) in the female rat: interactions with alpha-MSH, MCH and dopamine

The behavioral and neurochemical effects of NEI, and its interaction with alpha-MSH or MCH were investigated in the ventromedial nucleus (VMN) and medial preoptic area (MPOA) in female rats (bilateral administration, 100 ng in 0.5 microliter/side). NEI in the VMN (but not in the MPOA) stimulated exploratory behavior, increased anxiety and reduced dopamine and DOPAC release. The behavioral effects were antagonized by alpha-MSH. NEI stimulated female sexual receptivity in the MPOA. In the VMN, NEI did not have any effect on sexual activity, but partially antagonized the stimulatory effect of MCH. These results show that NEI in the hypothalamus participates in the regulation of behavior, possibly through dopaminergic mediation.

Stimulatory effect of melanin-concentrating hormone on luteinising hormone release

Alpha-melanocyte-stimulating hormone (alpha-MSH) and melanin-concentrating hormone (MCH) are two peptide neurotransmitters widely distributed in the mammalian brain, the former originating mainly from cell bodies in the arcuate nucleus and the latter from cell bodies in the zona incerta and lateral hypothalamus. Within the hypothalamus they innervate the pre-optic area, median eminence (ME) and ventromedial nucleus (VMN). Both peptides stimulate sexual behaviour and in this report we have investigated their effect on another gonadal steroid-dependent function, luteinising hormone (LH) release. alpha-MSH, MCH or a combination of the two were injected bilaterally (100 ng/side) into either the medial pre-optic area (MPOA), ME, or VMN of anaesthetised (Saffan 3 ml/kg i.p.) rats that had previously been ovariectomised and adrenalectomised (O+A) and then primed with 5 microg/rat s.c. oestradiol benzoate (OB), 48 h before peptide administration. MCH stimulated LH release when applied to the MPOA and ME; alpha-MSH was inhibitory in the ME and in this model was ineffective in the MPOA. Neither peptide was effective in the VMN. The two peptides were then injected into the MPOA of O+A rats primed with OB followed 48 h later by 0.5 mg/rat s.c. progesterone, which normally induces an LH surge. alpha-MSH, but not MCH, inhibited this induced rise in LH. Administration of anti-MCH antiserum (0.5 microg/side neat serum) also had an inhibitory effect on LH release in this model. These results show that MCH has a stimulatory effect on LH release when administered into the ME and MPOA. In the MPOA, this may be physiologically significant since blocking endogenous MCH with an anti-MCH antiserum inhibits LH release. On the other hand, alpha-MSH has an inhibitory effect on LH release in the MPOA and ME. In the teleost skin these two peptides are functionally antagonistic; it seems that a similar antagonism exists between their effects on LH release.

Responses of melanin-concentrating hormone mRNA to salt water challenge in the rainbow trout

Melanin-concentrating hormone (MCH) is a structurally conserved neuropeptide, produced in the hypothalamus of all vertebrates where it probably serves as a central neurotransmitter/neuromodulator. In teleost fish it is also a neurohypophysial hormone with peripheral effects on skin colour but its central effects are less well understood. In mammals, MCH mRNA abundance changes in response to salt-loading or dehydration, suggesting an involvement in salt or water balance. The present study has used in situ hybridization to investigate the response of the MCH neurons in the rainbow trout (Oncorhynchus mykiss) to progressive changes in ambient salinity. In trout, MCH perikarya are found in two hypothalamic sites: predominantly in the nucleus lateralis tuberis (NLT) and, to a lesser extent, in neurons above the lateral ventricular recess (LVR). Immersion in 50% salt water (SW) for 24 h had no effects on MCH transcripts, plasma osmotic pressure (OP) or cortisol concentrations, but after 24 h in 80% SW, plasma OP and cortisol were raised and MCH transcripts in the NLT were significantly increased (159% of controls, p < 0.01). LVR-MCH neurons remained unaffected. However, after 24 h in 100% SW, MCH mRNA was significantly reduced in both groups of neurons (NLT -62% of controls, p < 0.001; LVR -33% of control, p < 0.001). These responses were transient and were no longer apparent after 6 days in 100% SW, despite the fact that plasma OP and cortisol levels continued to rise. The relative importance of osmotic disturbance and stress on the differential responses of the 2 groups of MCH neurons to changing salinity is discussed, together with a consideration of the potential role of MCH in osmoregulation.

Expression of MCH and POMC genes in rainbow trout (Oncorhynchus mykiss) during ontogeny and in response to early physiological challenges

The expression of the neuropeptide melanin-concentrating hormone (MCH) in two groups of hypothalamic neurones (NLT- and LVR-MCH neurones), and POMC in the pituitary corticotropes and melanotropes, has been examined in rainbow trout larvae using immunocytochemistry and quantitative in situ hybridization. The aim was to establish at what stage in ontogeny these cells first respond to two physiological challenges-background color and stress. Trout reared in black or white trays showed adaptive skin pigmentary changes at 10 days posthatching, when fish in a pale environment abruptly exhibited melanin aggregation from a prior dispersed state, although the pigment cells were already competent to respond to adrenalin and MCH in vitro at 3 days. Immunoreactive MCH was detectable in the neurohypophysis at hatching and MCH mRNA in the NLT-MCH neurones (which project to the pituitary) was enhanced at 7 days in the white-reared trout. Immunostainable POMC was also present in the pars intermedia at hatching but their POMC mRNA was unaffected by tank color until 28 days, when it was enhanced in the black-reared trout. It is suggested that early pigment concentration depends on neural signals from the sympathetic nervous system in conjunction with MCH from the NLT rather than on a reduction in alphaMSH secretion from the pars intermedia. MCH mRNA in the LVR-MCH neurones was increased on a pale environment only 28 days after hatching, suggesting that these cells play little role in the early adaptive pigment response. Previous studies on the ontogeny of cortisol secretion indicate the hypothalamopituitary-interrenal axis can respond to stress by about 14 days. However, the pituitary ACTH cells showed no stress-induced changes in POMC mRNA until 28 days. ACTH release may therefore be dissociated from POMC transcription in the early stages of development. The LVR- and NLT-MCH neurones were both stimulated by stress, LVR-MCH mRNA responding by 14 days and NLT-MCH mRNA by 21 days. Melanotrope POMC mRNA was reduced by stress but the physiological significance of this is not known.

Melanin-concentrating hormone (MCH) antagonizes the effects of alpha-MSH and neuropeptide E-I on grooming and locomotor activities in the rat

The intraventricular (i.c.v.) administration of the neuropeptide melanocyte stimulating hormone (alpha-MSH) is known to elicit a series of behaviors in the rat which include excessive grooming and other motor activities. In bony fish, the pigmentary effects of alpha-MSH can be antagonized by the neuropeptide melanin-concentrating hormone (MCH). We therefore examined whether MCH or its sister peptide neuro-peptide E-I (NEI), derived from the same precursor molecule, would modulate the effect of alpha-MSH on grooming and motor activity in the rat, or perhaps elicit some responses of their own. Rats were injected i.c.v. with either artificial cerebrospinal fluid, alpha-MSH, MCH, NEI, or with two peptides together, and behavioral responses were monitored over the next 65 min. The i.c.v. injection of 1 microgram MSH significantly enhanced grooming behavior. NEI at the same dose increased grooming, rearing, and locomotor activities. MCH alone had no behavioral effects but it annulled the behavioral responses induced by either alpha-MSH or NEI. alpha-MSH also antagonized the locomotor and rearing behavior induced by NEI. The physiological significance of these observations is discussed.

In the trout, CRH and AVT synergize to stimulate ACTH release

Anterior pituitaries of the rainbow trout (Oncorhynchus mykiss) were incubated with graded concentrations of arginine vasotocin (AVT) or synthetic rat corticotrophin-releasing hormone (rCRH-41), alone or in combination, and the ACTH secreted into the medium was measured by a sensitive cytochemical bioassay. The aim was to determine the relative potencies of the two secretogogues and whether, in this fish species, they act synergistically. Rat CRF-41 and AVT both produced concentration-dependent increases in ACTH release. The minimum effective concentration for both peptides was approximately 1 nM but, at higher concentrations, the efficacy of CRF-41 was greater than that of AVT. Clear evidence of synergy between the two peptides was obtained. The response of the trout thus falls in line with observations in mammals and contrasts with findings for the goldfish.

Evidence that cortisol may protect against the immediate effects of stress on circulating leukocytes in the trout

Rainbow trout stressed by an intraperitonal injection of saline displayed reduced phagocytic activity of their spleen and head-kidney macrophages within 3 hr. Phagocytic activity was similarly depressed by injecting noradrenalin, but was maintained in fish injected with the adrenergic blocking agent phentolamine, suggesting that endogenous catecholamines are involved in this stress response. Since stress may increase the number of circulating granulocytes, it is proposed that noradrenalin, released during stress, causes the liberation of active macrophages from the lymphocytic tissue, the remaining macrophages therefore showing a lowered phagocytic index. Cortisol injection, like phentolamine, prevented the depressive effect of stress on the phagocytic index but did not antagonize the depressive effect of exogenous noradrenalin. It is suggested that the stress-induced release of endogenous catecholamines may be prevented by cortisol. Injection stress caused a decline in the number of circulating lymphocytes/thrombocytes, indicating their retrafficking into some other tissue. This was opposed by cortisol and by high doses of noradrenalin. It is proposed that cortisol or noradrenalin may oppose, directly or indirectly, the expression of adhesion molecules which are normally induced after stress.

Developmental changes in melanin-concentrating hormone in Rana temporaria

Melanin-concentrating hormone (MCH) is a vertebrate neuropeptide produced in hypothalamic neurons. In bony fish, such as trout, MCH acts as a neurohypophysial hormone which, once released into the circulation, acts on pigmented skin cells with the result that the fish turns pale to camouflage itself against a light colored background. In other animals the role of MCH is not clearly established but it appears to be a neuromodulator/transmitter within the central nervous system rather than a hormone. The present study examines MCH function in the grass frog, Rana temporaria. Using immunocytochemistry the location and morphology of irMCH neurons were followed, from tadpole to adult frog. In adult R. temporaria a group of MCH neurons appeared to comprise small and large-celled populations located in the ventral and dorsal infundibular regions, respectively. A group of MCH neurons in the preoptic area is proposed, although the perikarya were rarely immunostainable. Immunoreactive fibers were seen in various areas of the brain, including the olfactory lobes, optic tecta, habenular nucleus, and spinal cord. Immunoreactive MCH cells were only visible in midmetamorphic climax stages, and cellular morphology suggested low secretory activity until the animal first emerged onto land at which time nuclear size and granulation increased significantly. No such increase was observed in equivalent stages of the South African clawed toad, Xenopus laevis, an animal which is fully aquatic throughout its life in contrast to R. temporaria which is terrestrial.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of environmental colour and diurnal phase on MCH gene expression in the trout

Melanin-concentrating hormone (MCH) gene expression in the brain of rainbow trout, reared and maintained in either pale or black-coloured tanks, was studied using in situ hybridization histochemistry. MCH transcripts were most prevalent in the magnocellular neurones of the nucleus lateralis tuberis (NLT), which project to the pituitary gland. They were also present, although at much lower levels, in dorsally projecting parvocellular neurones, sited more posteriorly above the lateral ventricular recess (LVR). In the NLT the most intense hybridization signal was seen over the pituitary stalk; above the LVR, the most active neurones were located caudally. In both the NLT and above the LVR, MCH hybridization signal was 4-fold stronger in white-reared fish than in black-reared fish. There was also a marked diurnal variation in MCH expression in both sites, with high levels at 16.00 h and lower levels at 04.00 h. The results show that gene activity in both hormonal (NLT) and neuromodulator/neurotransmitter (LVR) MCH neurones is induced by pale environmental colour and that MCH gene activity is subject to pronounced diurnal variation.

Seasonal and photoperiod-induced changes in the secretion of alpha-melanocyte-stimulating hormone in Soay sheep: temporal relationships with changes in beta-endorphin, prolactin, follicle-stimulating hormone, activity of the gonads and growth of wool and horns

Blood plasma concentrations of alpha-melanocyte-stimulating hormone (alpha-MSH), beta-endorphin (beta-END), prolactin and follicle-stimulating hormone (FSH), and associated changes in the size of the testes, and growth of the horns and pelage were measured in male (n = 8), castrated male (n = 5) and female (n = 9) Soay sheep. The animals were born in April and kept outdoors near Edinburgh (56 degrees N) during the first two years of life. In all groups there was a close association between the weekly changes in the plasma concentrations of alpha-MSH and beta-END; the molar ratio in mean concentrations was close to 1:1. The blood plasma concentrations of both hormones varied markedly with season with a 3- to 10-fold increase in concentrations from the minimum in winter to the maximum in autumn. The seasonal peak occurred in September in the first year of life as juveniles, and between July (males) and September (females) in the second year when the animals were sexually mature. The plasma concentrations of ACTH did not vary in parallel with the seasonal changes in the concentrations of alpha-MSH (measured only in males); the molar ratio for the concentrations of alpha-MSH:ACTH was 1:0.12. The seasonal increase in the concentrations of alpha-MSH occurred 1-3 months after the seasonal increase in the concentrations of prolactin and the associated growth in horns and pelage, and slightly before, or coincident with the seasonal increase in the concentrations of FSH and the growth in the testes. In a second experiment, the same parameters were measured in a group of adult male Soay sheep (n = 8) housed indoors under an artificial lighting regimen of alternating 16-week periods of long (16 h light: 8 h darkness) and short days (8 h light: 16 h darkness). In this situation, there was a clearly defined photoperiod-induced cycle in the plasma concentrations of alpha-MSH with a 25-fold increase from a minimum under long days to a maximum under short days. The concentrations of beta-END varied in close parallel with the changes in alpha-MSH, and the temporal associations with the changes in the other pituitary hormones were similar to those observed in animals housed outdoors. Overall, the results support the view that alpha-MSH is co-secreted with beta-END from the melanotrophs in the pars intermedia of the pituitary gland, and that the secretory activity of the melanotrophs changes markedly with season, increasing in summer and autumn, and decreasing in winter and spring.(ABSTRACT TRUNCATED AT 400 WORDS)

Melanin-concentrating hormone binding to mouse melanoma cells in vitro

An analogue of human melanin-concentrating hormone (MCH) suitable for radioiodination was designed in which Tyr13 was replaced by Phe and Val19 by Tyr. The resulting monoiodinated [125I] [Phe13,Tyr19]-MCH radioligand was biologically active and led to the discovery of high-affinity binding sites on mouse B16-F1, G4F and G4F-7 melanoma cells. Saturation binding analysis with G4F-7 cells revealed 1090 MCH receptors per cell and a KD of 1.18 x 10(-10) mol/l. Receptors for MCH were also found on rat PC12 phaeochromocytoma cells, human RE melanoma cells and COS-7 cells. Competition binding analyses with other peptides such as alpha-MSH, NPY and PACAP demonstrated that MCH receptor binding is specific. rANF(1-28) was found to be a weak competitor of MCH, indicating topological similarities between MCH and rANF(1-28) when interacting with MCH receptors.

The effect of various stresses, corticosteroids and adrenergic agents on phagocytosis in the rainbow trout Oncorhynchus mykiss

The effect of acute and chronic stress on the phagocytic activity of putative macrophages from the rainbow trout. Oncorhynchus mykiss has been assessed, using an in vitro phagocytic index, in which the average number of engulfed yeast cells in a population of phagocytes is determined. An injection stress given under light anaesthesia, or a longer noise stress combined with confinement, both significantly reduced, within 3 h, the level of phagocytic activity of macrophages from the spleen and pronephros. Daily injection stress over six days had a lesser effect on the proportion of phagocytically active cells even though plasma cortisol levels were equally raised. Daily dexamethasone injection depressed the proportion of phagocytically active cells more than saline injection. In these in vivo experiments, it was not possible to determine whether stress and steroids depressed the phagocytic activity of individual macrophages or caused the active macrophages to migrate out of the spleen and pronephros. Administration of cortisol (200 nM) to trout macrophages in vitro failed to depress phagocytic activity within a 3h period but both α- and β-adrenergic agonists (10 μM) were usually depressive. It is proposed that the autonomic nervous system may be an early regulator of macrophage phagocytosis following stress and that corticosteroids only exert their suppressive effect on macrophage activity in the longer term.

Melanin-concentration hormone updated functional considerations

The melanin-concentrating hormone (MCH) is a vertebrate neuropeptide produced in hypothalamic perikarya whose fibers project to most regions of the brain and into the spinal cord. Its role as a neurohypophyseal color-change hormone is peculiar to teleost fish, but recent studies in mammals suggests that MCH itself, and other peptides derived from the same precursor, may participate in multiple functions in the central nervous system, modulating behavior and the perception of sensory information. Recent hybridization studies in mammals have greatly increased our understanding of the response of the MCH system to environmental factors, such as osomotic challenge, lactation, stress, and changes in corticosteroid levels. Further studies in lower vertebrates are needed to highlight the physiologically important functions that have led to the structural conservation of the MCH peptide during vertebrate evolution.

The effect of photoperiod on plasma levels of melanin-concentrating hormone in the trout

The neurohypophysial melanin-concentrating hormone, MCH, plays a role in adaptive colour change in teleost fishes inducing pallor when the fish is placed in pale-coloured surroundings. The present study shows that its plasma concentration, measured in groups of white-adapted fish, is not uniformly high throughout the day but follows a clear diurnal pattern. Over a 24 h cycle, plasma concentrations rise gradually during the morning to reach peak values around the middle of the photophase, after which they decline significantly before night. Lowest concentrations are observed during the dark period. This pattern was observed under a long photoperiod in summer and a short photoperiod in winter. The peak was shifted within a week of changing the onset of either light or dark. When dawn was delayed by 6 h for fish held under short photoperiod conditions, then peak concentrations were attained 6 h precociously. Fish from a long photoperiod placed in constant light showed a pattern of MCH release which approximated to the normal over the first 24 h period but plasma values then became raised and periodicity was no longer discernible. Plasma hormone concentrations were much reduced in trout kept in black coloured tanks in which nocturnal and daytime values differed, but significant differences during the photophase were not demonstrable. The results suggest that an illuminated white background can initiate the early morning release of MCH, and that an endogenous pacemaker underlies the pattern of MCH secretion.

The Biosynthesis of Melanin-Concentrating Hormone in Trout Kept Under Different Conditions of Background Colour and Stress, as Determined by an in vitro Method

The aim of this study was to develop a method to monitor the synthetic activity of neurons which secrete the neurohypophysial melanin-concentrating hormone (MCH), a hormone implicated in two separate physiological roles in fish-pigmentary regulation and the response to stress. Trout hypothalamic fragments, containing the MCH neuronal cell bodies, were incubated in vitro in a medium including [(35) S]methionine. Labelled MCH-related products were separated by immunoprecipitation. Gel electrophoresis showed that radioactive methionine was incorporated into MCH precursors and into mature MCH, much as in vivo. Thus, de novo hormone synthesis continues in vitro. Trout reared at a fish-farm and adapted to black or white tanks for 39 days displayed nearly a 2-fold difference in their rate of methionine incorporation. Transferring fish from a black to a white background also doubled the rate of incorporation within 7 days and this rate increased only very slightly during the following 3 weeks. The rate of methionine incorporation by tissue from trout reared in black tanks was very depressed, and 4-fold lower than that of fish reared in white tanks, suggesting that very long-term adaptation to one or other background has increasingly marked effects on the activity and perhaps the number of synthetically active neurons. Stress also influenced the rate of methionine incorporation: a mild daily stress was stimulatory but more frequent stress had an inhibitory effect in many cases. The effects of daily dexamethasone administration were inconclusive. It is suggested that these differences in methionine incorporation reflect the relative rates of MCH synthesis in vivo, and that the method is useful to investigate conditions which modulate the biosynthesis of MCH in the trout.

The effect of rearing rainbow trout on black or white backgrounds on their secretion of melanin-concentrating hormone and their sensitivity to stress

Rainbow trout were reared in black or off-white coloured tanks for up to 18 months of age to achieve maximum differences in the synthesis of the neuropeptide, melanin-concentrating hormone (MCH). White-reared fish had greatly increased MCH concentrations in their pituitary glands, in their MCH perikarya and in the presumptive neuromodulatory fibres of the dorsal hypothalamus/thalamus when compared with black-reared and commercially reared trout. Following transfer to brighter white tanks, white-reared fish showed a significant increase in plasma MCH concentration and a reduction of MCH in the pituitary and MCH perikarya. The additional challenge of repeated stress further increased plasma MCH concentration in these fish and also reduced MCH in the dorsal hypothalamus/thalamus. In black-reared fish transferred to white tanks, plasma MCH concentrations were significantly raised after transfer, although they were lower after 11 days than in white-reared counterparts. Transfer from black to white background caused a fall in the MCH concentration in all regions--pituitary gland, perikarya and dorsal hypothalamus/thalamus; if transfer was accompanied by repeated stress, the hormone in the pituitary gland and MCH perikarya became so depleted that plasma MCH concentrations declined. Within each experimental situation (control, background transfer and transfer with stress) there was in inverse correlation between plasma MCH concentrations of black- and white-reared fish and the cortisol concentration. MCH had no direct effect on the secretion of cortisol by interrenal tissue but incubated hypothalami, in which endogenous MCH had been immunoabsorbed, provided evidence that MCH can depress the release of corticotrophin-releasing bioactivity.

The influence of repeated stress on the release of melanin-concentrating hormone in the rainbow trout

Melanin-concentrating hormone (MCH) is a neurohypophysial peptide that induces pigmentary pallor in teleosts and which is released when the fish are placed on a white background. An additional effect of the peptide is the depression of ACTH and hence cortisol secretion during moderate stress. The present work on rainbow trout shows that plasma MCH concentrations, while unaffected by a single stress, are raised by repeated stress (1 ml saline injected i.p. without anaesthesia) and remain high for several hours thereafter. The response to stress is observed only in white-adapted fish and not in fish kept in black-coloured tanks, when MCH release is normally low. Plasma concentrations of MCH vary diurnally but stress induces an equivalent incremental rise in plasma MCH, whether administered in the middle or towards the end of the photophase. The stress-induced rise in MCH concentrations is prevented by treatment with dexamethasone. The results support the suggestion that the modulatory effect of MCH on the hypothalamopituitary-interrenal axis of fish might be enhanced under conditions of stress.

Structure-activity studies with fragments and analogous of salmonid melanin-concentrating hormone

A number of cyclic and linear fragments and analogues of MCH were synthesized and their biological potencies tested using the isolated carp scale melanophore assay. In this system the cyclic portion MCH(5-14) exhibited only 0.1% bioactivity, which was markedly enhanced by the addition of the exocyclic sequences MCH(15-17) and MCH(1-4). The exocyclic sequence itself, MCH(1-4,15-17), had minimal activity, however. Substitution of Tyr11 with phenylalanine reduced the potency of the ring structure MCH(5-14) by about 4-fold. Substitution of Gly8 with D-alanine reduced the potency of MCH(5-14) 16-fold, while both substitutions together caused a still more marked reduction (200-fold) in bioactivity. Linearized fragments of MCH, extending from MCH(15-17) to [Cys(Acm)5,14]MCH(1-17), showed a progressive increase in potency. The linearized forms of MCH, MCH(5-17) and MCH(5-14), were approximately 100-fold or less potent than their cyclic forms. The significant increases in bioactivity produced by the addition of the C- and N-terminal exocyclic sequence even to these linearized forms further emphasizes the importance of these regions for interaction at the receptor site.

The biosynthesis of melanin-concentrating hormone in a fish

Abstract This work investigated the biosynthesis of a neurohypophysial hormone, melanin-concentrating hormone (MCH), in the trout. Sephadex G-75 chromatography showed the presence of several large MCH-immunoreactive molecules in hypothalamic and pituitary gland extracts, with different retention times on high-performance liquid chromatography from the mature MCH(1-17). About 10% of the total MCH-immunoreactivity in the hypothalamus was attributable to large molecular weight forms but these contributed less than 1% to the immunoreactivity in the neurointermediate lobe. Both [(35) S]methionine and [(3) H]leucine were injected into the hypothalamus near the MCH perikarya (nucleus lateralis tuberis region) of anaesthetized fish, after which the fish were killed at intervals of up to 8 h post-injection and the basal hypothalami, pituitary pars distales and neurointermediate lobes were extracted in acid. MCH-related immunoprecipitates from these extracts were fractionated by sodium dodecyl sulphate polyacrylamide gel electrophoresis or by Sephadex G-50 chromatography. The results show the incorporation of radiolabel into 15.3 K and 11.3 K precursors within 0.75 h, and their conversion, via several smaller intermediates, to a molecule resembling MCH(1-17). The results are discussed in relation to the known cDNA sequence of salmon MCH. Labelled MCH first appeared in the neurointermediate lobe 4 h after injection, giving an estimated transit rate of 0.4 mm/h.

Melanin-concentrating hormone: a structural and conformational study based on synthesis, biological activity, high-field NMR, and molecular modeling techniques

A series of Melanin-concentrating hormone (MCH) fragments have been synthesized and their biological activities compared with the parent peptide. The substructural units, 5-14 linear and 5-14 cyclic, have been used as models for MCH-- H-Asp1-Thr-Met-Arg-Cys-Met-Val-Gly-Arg HO-Val17-Glu-Trp-Cys-Pro-Arg-Tyr-Val in 1H-nmr conformational studies. Conformational features predicted by molecular dynamics analyses find support in the nmr experiments.

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.

The measurement of melanin-concentrating hormone in trout blood

Two methods are described for measuring the titres of melanin-concentrating hormone (MCH) in trout plasma. One involves the extraction of MCH from 1-ml plasma onto C18 Sep Pak cartridges, after which the eluted peptide is measured by conventional radioimmunoassay. In the alternative method, antibodies are bound onto immunobeads which are added to 0.5 ml plasma. After incubation for 24 hr, the beads are washed to remove the plasma and are incubated with 125I-labelled MCH; the following day, the labelled beads are separated by centrifugation, washed, and counted. The relative advantages of each method is discussed. Using these two methods, it is shown that the plasma concentration of the hormone is significantly higher in fish from white tanks (greater than 50 pmol/litre) than in fish from black tanks (approximately 10 pmol/litre) or those kept in the dark (approximately 5 pmol/litre). The plasma concentration of MCH changes rapidly when trout are moved from one coloured background to another, indicating its involvement in physiological colour change.

Melanin concentrating hormone. I. Influence of nerves and hormones on the control of trout melanophores

When melanophores on trout scales are cultured in vitro they show a transitory melanin concentration, which can be prevented by addition to the medium of the alpha adrenergic blocker, phentolamine. This indicates the release of endogenous nor-epinephrine from local nerve terminals. This initial phase of melanin aggregation is followed by redispersion and then by a second, more gradual melanin concentration over several days, which is not antagonized by phentolamine. A final melanophore index of between 2-2.5 is attained which may be the resting state of trout melanophores. Using short-term cultured melanophores which have passed the phase of endogenous nor-epinephrine release, it is shown that exogenous nor-epinephrine will interact synergistically with the melanin-concentrating hormone to achieve full melanin concentration. Evidence is discussed for believing that in the trout, such synergy is necessary to achieve maximum pallor in vivo.

An immunological study of the secretory activity of neurons producing melanin-concentrating hormone in a teleost

The melanin-concentrating hormone is a general vertebrate neurosecretory peptide which, in bony fish, serves as a neurohypophysial hormone influencing pigmentary changes in response to background colour. Young carp were reared for six months in white- or black-coloured tanks to determine how this would influence the development of the neurons producing the peptide. Cytological criteria and radioimmunoassay of tissue extracts showed that the background markedly influenced the synthetic activity of these neurons. In carp reared in black tanks, the perikarya were small and poorly granulated, with small nuclei and often undetectable nucleoli. Transfer of such fish to a white tank for six days caused no significant change in hormone content but cytological criteria suggested an increased activity of some of the neurons. In fish reared on a white background, over 50% of these neurons showed a greatly enhanced synthetic activity, while radioimmunoassays showed significantly higher concentrations of immunoreactive peptide in their hypothalami but not in their pituitary glands. After such fish were moved to black tanks for six days, the neuropeptide content of the hypothalamus and pituitary gland was significantly increased. Histologically, this was reflected in the amount of immunostainable granulation in both sites but cell nuclear size was not decreased. These changes are interpreted in terms of changes of hormone synthesis and release. The observations provide evidence that the activity of many but not necessarily all of the neurons producing melanin-concentrating hormone in the carp hypothalamus is controlled by background colour.

Melanin concentrating hormone. IV. Development of a sensitive solid-phase radioimmunoassay for melanin-concentrating hormone

A two-step solid-phase radioimmunoassay for melanin-concentrating hormone (MCH) was developed for direct determination of the hormone in plasma samples. To this end, synthetic MCH was coupled to bovine thyreoglobulin and the complex was injected into rabbits. Specific antisera of high titer were obtained which did not crossreact with other hormones. The IgGs were chemically linked to immunobeads, an acrylamide/acrylic acid polymer matrix. In the first step, plasma MCH was immunoextracted by incubation of diluted plasma samples with anti-MCH immunobeads. In the second step, the washed polymer was incubated with radioiodinated MCH tracer for titration of non-occupied sites. This procedure made it possible to determine as little as 4 pg MCH per ml of plasma. Application of the radioimmunoassay to plasma levels of black or white background-adapted trout showed a marked difference in circulating MCH: while trout on a black background contained a mean value of 29 +/- 5.6 pg/ml, animals on a white background had 106 +/- 19 pg/ml. These findings strengthen the hypothesis that MCH is directly involved in the control of color change of teleost fishes. By contrast, there was no detectable salmonid MCH immunoreactivity in rat or human plasma.

Localisation and identification of melanocyte-stimulating hormones in the fish brain

The existence of melanocyte-stimulating hormone (MSH) in fish brains was investigated by a range of techniques: radioimmunoassay, HPLC, bioassay, and immunocytochemistry. Immunoreactive alpha MSH (ir alpha MSH) was detected by radioimmunoassay in all regions of carp and trout brains, with the highest concentration in the basal hypothalamus. In trout, ir alpha MSH cell bodies were located by immunocytochemistry only periventricularly, in the medial basal hypothalamus near the third ventricle, whereas in the carp ir alpha MSH staining was seen both in periventricular cells and also in some of the magnocellular neurones in the lateral hypothalamus. When white-adapted fish were transferred to a black tank for 6 days, the melanin-concentrating hormone (MCH) content of the basal hypothalamus of both carp and trout increased 2- and 4.6-fold, respectively, but the alpha MSH content did not change in either species. Analysis by HPLC of pituitary gland, hypothalamic, and optic tectal extracts revealed that the pituitary contains desacetyl, monoacetyl, and diacetyl alpha MSH, although the ratio of these forms differed in the two species. The hypothalamus and optic tectum, however, contained predominantly the desacetyl form of alpha MSH. Bioassays for MSH in the HPLC fractions revealed the existence of presumptive beta MSH in both the pituitary and hypothalamus. An argument is advanced that the periventricular ir alpha MSH neurones are homologous with the proopiomelanocortin cells of the arcuate nucleus in mammals, and that the immunocytochemical alpha MSH-like activity in the MCH neurones may not be authentic alpha MSH.

Melanin-concentrating hormone (MCH) immunoreactive hypophysial neurosecretory system in the teleost Poecilia latipinna: light and electron microscopic study

Neurons containing immunoreactivity for melanin-concentrating hormone (MCH) were located in the brain of the teleost Poecilia latipinna by light microscopic (peroxidase antiperoxidase) and electron microscopic (immunogold) methods. Neuronal cell bodies were found in the tuberal hypothalamus, mostly within the nucleus lateralis tuberis, pars lateralis, containing MCH-immunoreactive granules up to 150 nm in diameter. From here bundles of immunoreactive fibers could be traced through the preoptic area as far forward as the olfactory bulb, and through the posterior hypothalamus up into the pretectal thalamus and midbrain. The main projection was, however, to the neurohypophysis, where MCH fibers were observed to form contacts with pituicytes, basement membranes around blood vessels, and the endocrine cells of the pars intermedia. Occasionally MCH-immunoreactive terminals were also seen near the corticotrophs of the rostral pars distalis. These results support the hypothesis that MCH may act as a systemic hormone, a central neurotransmitter, and a modulator of pituitary function.

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.

Structural studies of nerve terminals containing melanin-concentrating hormone in the eel, Anguilla anguilla

Eels were adapted to black- or white-coloured backgrounds and the pituitary glands were prepared for light and electron microscopy. Immunocytochemical staining was used to study the distribution of the neurohypophysial melanin-concentrating hormone in the neurointermediate lobe. The hormone was located in small, elliptical, electron-opaque neurosecretory granules, measuring approximately 120 x 90 nm. The neurones terminated on blood vessels in the centre of the neurohypophysis and on the basement membrane separating neural and intermediate lobe tissues. The results of both light and electron immunocytochemistry and of radioimmunoassay are consistent with a higher rate of hormone release from eels adapted to white backgrounds than from those adapted to black backgrounds. In addition to this, when fish that had been adapted to white tanks were transferred to black tanks, there was an accumulation of irMCH in the gland and an increased numerical density of secretory granules at nerve terminals. These results reinforce the proposal that MCH is released during adaptation to a white background, to cause melanin concentration and to inhibit MSH release, and that its release is halted in black-adapted fish.

Ultrastructural demonstration that melanin-concentrating hormone-like and alpha-melanocyte-stimulating hormone-like immunoreactive molecules coexist in the same neurosecretory granules

Using immunocytochemical methods at the electron microscope level, immunoreactivity for both melanin-concentrating hormone (MCH) and alpha-melanocyte-stimulating hormone (alpha-MSH) has been demonstrated in the carp neurohypophysis. A double-labelling technique, using colloidal gold probes of different sizes showed that immunoreactivity to both molecules coexists within the same neurosecretory granules in some neurones, while in other neurones the granules exhibit only MCH-like immunoreactivity. These observations suggest that the two immunoreactivities are attributable to separate molecules; if they are derived from the same precursor molecule, then this must be cleaved differently in the two sets of neurones. The absence of adrenocorticotropic hormone (ACTH)-like immunostaining in any neurosecretory granule might suggest the alpha-MSH-like molecule is not derived from the conventional pro-opiomelanocortin precursor.

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.

Melanin concentrating hormone inhibits the release of alpha MSH from teleost pituitary glands

A radioimmunoassay was developed for salmonid melanin concentrating hormone (MCH) and used to measure immunoreactive (ir)MCH in the hypothalamus and pituitary of trout (Salmo gairdneri) and eels, (Anguilla anguilla) maintained under different regimes of background color. In trout, 95% of the total irMCH was located in the pituitary gland. The amount of MCH in both pituitary and hypothalamus was increased when white-adapted trout were transferred to a black background. In eels, a similar change of background led to an accumulation of MCH in the pituitary but not in the hypothalamus. The results suggest that MCH is released from the neurohypophysis in association with physiological color change. Neurointermediate lobes of trout and eels released both ir alpha MSH and irMCH when they were cultured in vitro. The release of alpha MSH was significantly enhanced when endogenous MCH was immunoabsorbed by MCH antiserum added to the culture medium. The results indicate that MCH can induce pallor in fish not only by its peripheral effect on the melanophores but also by an inhibitory action on the release of alpha MSH from the pituitary.

Effects of chronic administration of melanin-concentrating hormone on corticotrophin, melanotrophin, and pigmentation in the trout

This paper reports the effects of salmonid melanin-concentrating hormone (MCH), administered via an Alzet minipump, on pigmentation and secretion of pituitary melanotrophin (MSH) and corticotrophin (ACTH) by black-adapted, adult rainbow trout. The drug induced melanin concentration in the skin melanophores and prevented melanogenesis. Both the cytological appearance of the pituitary pars intermedia and determinations of plasma alpha-MSH suggest that MCH prevented the increase in secretory activity of the melanotrophic cells seen normally in black-adapted trout. Resting plasma cortisol titres were similar in all groups of fish but anterior pituitary glands taken from stressed, MCH-treated fish released less ACTH in vitro than those from corresponding saline-treated fish.

Effect of melanin concentrating hormone on pigment and adrenal cells in vitro

Highly purified synthetic salmonid melanin concentrating hormone (MCH) and some analogs were investigated for their ability to concentrate the pigment in scale melanophores of the Chinese grass carp, Ctenopharyngodon idellus, to produce melanin dispersion in frog or lizard melanophores and to inhibit alpha-MSH in its action on mouse melanoma and rat adrenal glomerulosa cells in vitro. In the grass carp, MCH produced half-maximal pigment aggregation at 6 X 10(-11) M and its oxidized form at 7 X 10(-11) M. Replacement of the two methionines at position 3 and 6 with norvaline lowered the potency by a factor of 2.7 and with propargylglycine by a factor of about 7. Linear, Cys5,14-Acm-protected MCH was a full agonist of MCH but with a 345-fold lower potency. Iodinated MCH showed similar, low activity. In tetrapods, salmonid MCH and its analogs displayed only marginal pigment dispersion at concentrations greater than 10(-5) M. Alkali-treatment of MCH increased the pigment-dispersing potency by a factor of about 30 whereas the activity for pigment aggregation in the grass carp was destroyed. At high concentrations (10(-6), 10(-5) M) MCH also stimulated tyrosinase activity in B-16 mouse melanoma cells but did not modify the effects of alpha-MSH in this system. By contrast, when tested on rat adrenal glomerulosa cells, salmonid MCH had no effect alone but at a concentration of greater than 10(-10) M it slightly reduced corticosterone production by an alpha-MSH concentration of 10(-7) M. Aldosterone production was not affected and MCH did not influence the response to ACTH.

Salmonid melanin-concentrating hormone inhibits corticotrophin release

Melanin-concentrating hormone (MCH) is a neural peptide associated with colour change in fishes. We show here that it also inhibits corticotrophin (ACTH) secretion. Synthetic salmonid MCH at a concentration of 100pmol/l reduced the in-vitro release of ACTH by pars distales (pDs) taken from stressed trout. At lower concentrations (10pmol/l) the peptide inhibited CRF-41-induced secretion of ACTH by pDs removed from unstressed trout, while at higher concentrations (10nmol/l) it reduced the corticotrophic response of rat pituitary tissue to CRF-41.