Immunohistochemical localization of alpha-melanocyte stimulating hormone (alpha-MSH) in the human hypothalamus

Hedgehog Pathway Activation Alters Ciliary Signaling in Primary Hypothalamic Cultures

Primary cilia dysfunction has been associated with hyperphagia and obesity in both ciliopathy patients and mouse models of cilia perturbation. Neurons throughout the brain possess these solitary cellular appendages, including in the feeding centers of the hypothalamus. Several cell biology questions associated with primary neuronal cilia signaling are challenging to address in vivo. Here we utilize primary hypothalamic neuronal cultures to study ciliary signaling in relevant cell types. Importantly, these cultures contain neuronal populations critical for appetite and satiety such as pro-opiomelanocortin (POMC) and agouti related peptide (AgRP) expressing neurons and are thus useful for studying signaling involved in feeding behavior. Correspondingly, these cultured neurons also display electrophysiological activity and respond to both local and peripheral signals that act on the hypothalamus to influence feeding behaviors, such as leptin and melanin concentrating hormone (MCH). Interestingly, we found that cilia mediated hedgehog signaling, generally associated with developmental processes, can influence ciliary GPCR signaling (Mchr1) in terminally differentiated neurons. Specifically, pharmacological activation of the hedgehog-signaling pathway using the smoothened agonist, SAG, attenuated the ability of neurons to respond to ligands (MCH) of ciliary GPCRs. Understanding how the hedgehog pathway influences cilia GPCR signaling in terminally differentiated neurons could reveal the molecular mechanisms associated with clinical features of ciliopathies, such as hyperphagia-associated obesity.

Hypothalamic malonyl-CoA and the control of food intake

Fatty acid metabolism is implicated in the hypothalamic control of food intake. In this regard, malonyl-CoA, an intermediate in fatty acid synthesis, is emerging as a key player. Malonyl-CoA in the hypothalamus has been proposed as an anorectic mediator in the central control of feeding. A large body of evidence demonstrates that modulating hypothalamic activities of malonyl-CoA metabolic enzymes impacts food intake. Malonyl-CoA action appears to play a significant role in the intracellular signaling pathways underlying leptin anorectic effect in the arcuate nucleus. Ghrelin's hypothalamic effect on feeding may also involve the change in malonyl-CoA metabolism. Hypothalamic malonyl-CoA levels are altered in response to fasting and refeeding, suggesting physiological relevance of the changes in malonyl-CoA level in the controls of feeding and energy balance. Malonyl-CoA inhibits the acyltransferase activity of carnitine palmitoyltransferase-1 (CPT-1), and CPT-1 was considered as a downstream effector in hypothalamic malonyl-CoA effect on feeding. However, recent evidence has not been entirely consistent with this notion. In the arcuate nucleus, the inhibition of CPT-1 acyltransferase activity does not play an important role in the feeding effect of either leptin or cerulenin (a fatty acid synthase inhibitor) that requires the increase in malonyl-CoA level. Alternatively, the brain isoform of CPT-1 (CPT-1c) may act as a downstream target in the malonyl-CoA signaling pathways. CPT-1c does not possess a typical acyltransferase activity, and the exact molecular function of this protein is currently unknown. Recent data indicate it is involved in ceramide metabolism. Of relevance, in the arcuate nucleus, CPT-1c may link malonyl-CoA to ceramide metabolism to affect food intake.

Unraveling the central proopiomelanocortin neural circuits

Central proopiomelanocortin (POMC) neurons form a potent anorexigenic network, but our understanding of the integration of this hypothalamic circuit throughout the central nervous system (CNS) remains incomplete. POMC neurons extend projections along the rostrocaudal axis of the brain, and can signal with both POMC-derived peptides and fast amino acid neurotransmitters. Although recent experimental advances in circuit-level manipulation have been applied to POMC neurons, many pivotal questions still remain: how and where do POMC neurons integrate metabolic information? Under what conditions do POMC neurons release bioactive molecules throughout the CNS? Are GABA and glutamate or neuropeptides released from POMC neurons more crucial for modulating feeding and metabolism? Resolving the exact stoichiometry of signals evoked from POMC neurons under different metabolic conditions therefore remains an ongoing endeavor. In this review, we analyze the anatomical atlas of this network juxtaposed to the physiological signaling of POMC neurons both in vitro and in vivo. We also consider novel genetic tools to further characterize the function of the POMC circuit in vivo. Our goal is to synthesize a global view of the POMC network, and to highlight gaps that require further research to expand our knowledge on how these neurons modulate energy balance.

NPY and VGF immunoreactivity increased in the arcuate nucleus, but decreased in the nucleus of the Tractus Solitarius, of type-II diabetic patients

Ample animal studies demonstrate that neuropeptides NPY and α-MSH expressed in Arcuate Nucleus and Nucleus of the Tractus Solitarius, modulate glucose homeostasis and food intake. In contrast is the absence of data validating these observations for human disease. Here we compare the post mortem immunoreactivity of the metabolic neuropeptides NPY, αMSH and VGF in the infundibular nucleus, and brainstem of 11 type-2 diabetic and 11 non-diabetic individuals. α-MSH, NPY and tyrosine hydroxylase in human brain are localized in the same areas as in rodent brain. The similar distribution of NPY, α-MSH and VGF indicated that these neurons in the human brain may share similar functionality as in the rodent brain. The number of NPY and VGF immuno positive cells was increased in the infundibular nucleus of diabetic subjects in comparison to non-diabetic controls. In contrast, NPY and VGF were down regulated in the Nucleus of the Tractus Solitarius of diabetic patients. These results suggest an activation of NPY producing neurons in the arcuate nucleus, which, according to animal experimental studies, is related to a catabolic state and might be the basis for increased hepatic glucose production in type-2 diabetes.

Distribution, subcellular localization and identity of immunoreactive alpha-melanotropin in the pituitary gland and brain

In homogenates of adult human or rat hypothalamic tissue, immunoreactive alpha-MSH (alpha-MSHi) is concentrated in synaptosomes, suggesting that it is localized in neurons. This conclusion is supported by immunohistochemical results on the localization of alpha-MSHi in the brain. The function of alpha-MSHi in the hypothalamus is undefined but the amount of alpha-MSH in this tissue increases in young rats and decreases in old rats. There is little alpha-MSHi in pituitary glands from human abortuses before the 15th gestational week. Thereafter the amount of alpha-MSHi in the anterior and neurointermediate lobes increases appreciably. When acetic acid extracts of each lobe were analysed by high-pressure liquid chromatography the alpha-MSHi in extracts of the anterior lobe had a retention time equal to that of desacetyl alpha-MSH; little if any alpha-MSHi had a retention time identical to that of desacetyl alpha-MSH; alpha-MSH, if present in these extracts, appeared to be a minor component. A similar analysis of extracts of adult human hypothalamic tissue yielded results suggesting that the alpha-MSHi in this tissue is also attributable largely to desacetyl alpha-MSH.

Neuropeptides in hypothalamic neuronal disorders

A few examples of hypothalamic, peptidergic disorders leading to clinical signs and symptoms are presented in this review. Increased activity of corticotropin-releasing hormone (CRH) neurons in the paraventricular nucleus (PVN) and decreased activity of the vasopressin neurons in the biological clock and of the thyroxine-releasing hormone (TRH) neurons in the PVN contribute to the signs and symptoms of depression. In men, the central nucleus of the bed nucleus of the stria terminalis (BSTc) is about twice as large and contains twice as many somatostatin neurons as in women. In transsexuals this sex difference is reversed, pointing to a role of this structure in gender. Luteinizing hormone-releasing hormone (LHRH) neurons are formed in the fetal olfactory placade and migrate along the terminal nerve fibers into the hypothalamus. In Kallmann's syndrome the migration process of the LHRH (gonadotropin-releasing hormone) neurons is aborted, which explains the joint occurrence of hypogonadotropic hypogonadism and anosmia in this syndrome. In postmenopausal women, the neurons of the infundibular nucleus hypertrophy and become hyperactive because of the disappearance of the estrogen feedback and contain hyperactive peptidergic neurons. Climacteric flushes may be caused by hyperactivity of the neurokinin-B or LHRH neurons in this nucleus. The hypocretin (orexin) neurons in the perifornical area are involved in sleep. In narcolepsy with cataplexy, a loss of these neurons, probably due to an autoimmune process, is found. Obese subjects with a mutation in the gene that encodes for leptin, the preproghrelin gene, or the alpha-melanocyte-stimulating hormone (alpha-MSH) gene have been described. Decreased numbers and activity of the oxytocin neurons in the PVN may be responsible for the absence of satiety in Prader-Willi syndrome. Moreover, a glucocorticoid receptor polymorphism is associated with obesitas and dysregulation of the hypothalamus-pituitary-adrenal axis. In contrast, two single nucleotide polymorphisms (SNPs) of the AGRP gene have been associated with anorexia nervosa.

Marked distributional difference of alpha-melanocyte-stimulating hormone (alpha-MSH)-like immunoreactivity in the brain between two elasmobranchs (Scyliorhinus torazame and Etmopterus brachyurus): an immunohistochemical study

Application of alpha-MSH immunohistochemistry to the brain of elasmobranchs (Scyliorhinus torazame and Etmopterus brachyurus) demonstrated a marked species difference concerning the distribution of the alpha-MSH-like molecule in the brain. In S. torazame, alpha-MSH-like immunoreactive cells were present in the hypothalamus, mainly in the tuberculum posterius and the nucleus lateralis tuberis, and also in the distal and neurointermediate lobes of the hypophysis. Labeled varicose fibers were densely distributed in the hypothalamus, but they were sparse or absent in other portions of the brain. In striking contrast to the results for S. torazame, the immunoreactivity in the E. brachyurus brain was associated exclusively with the glial system, represented by astrocytes and tanycytes, throughout the central nervous system; no immunoreactivity was found in the neuronal elements. In the E. brachyurus hypophysis, the labeled cells were present in the distal and intermediate lobes, similarly to their presence in S. torazame, but in the intermediate lobe the immunoreactivity was confined to the peripheral cell cord closely adjacent to the neural lobe. The present findings are the first as regards the occurrence of alpha-MSH-like immunoreactivity in the glial system of the central nervous system of vertebrates and suggest diversity of expression and/or processing of proopiomelanocortin in the brain of elasmobranchs.

Melanotropic peptides in the mammalian brain: the melanin-concentrating hormone

Melanin-concentrating hormone (MCH) has been identified in neurons of the mammalian brain. This review summarizes some current information regarding the cell biology of this neuropeptide and the topography of MCH-immunoreactive (-IR) neurons in several species including mouse, rat, hamster, guinea pig, rabbit, dog and monkey; and atlas of MCH-IR neurons in the hypothalamus and subthalamus of the brain of guinea pig is presented. Based upon the location of this MCH cell group, it is hypothesized that they may be functionally involved in circuits of extrapyramidal motor systems from striatal centers to the thalamus and cerebral cortex and to the midbrain and spinal cord.

Isolation and structural characterization of peptides related to alpha- and gamma-melanocyte-stimulating hormone (MSH) from the frog brain

Peptides that are derived from the processing of proopiomelanocortin were isolated in pure form from the brain of the frog Rana ridibunda. The primary structure of the most abundant of those peptides was established as: Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val. This amino acid sequence is identical to that of mammalian and frog pituitary alpha-melanocyte-stimulating hormone (MSH) and the peptide co-eluted with synthetic desacetyl alpha-MSH, indicating that it is COOH-terminally alpha-amidated. A second component, which exhibited a shorter retention time, co-eluted with the glycine-extended form of desacetyl alpha-MSH [ACTH(1-14)]. The primary structure of the third peptide isolated in pure form from the brain extract was established as: Lys-Tyr-Val-Met-Ser-His-Phe-Arg-Trp-Asn-Lys-Phe-NH2. This sequence corresponds to Lys-gamma 1-MSH as predicted from the nucleotide sequence of frog proopiomelanocortin. The presence of substantial amounts of desacetyl alpha-MSH and Lys-gamma 1-MSH in the frog brain supports the concept that, in amphibia, melanotropins may act as neurotransmitters and/or neuromodulators as well as hormonal peptides.

Characterization of alpha-melanocyte-stimulating hormone (alpha-MSH)-like peptides in discrete regions of the rat brain. In vitro release of alpha-MSH from perifused hypothalamus and amygdala

The neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is synthesized by discrete populations of hypothalamic neurons which project in different brain regions including the cerebral cortex, hippocampus and amygdala nuclei. The purpose of the present study was to identify the alpha-MSH-immunoreactive species contained in these different structures and to compare the ionic mechanisms underlaying alpha-MSH release at the proximal and distal levels, i.e. within the hypothalamus and amygdala nuclei, respectively. The molecular forms of alpha-MSH-related peptides stored in discrete areas of the brain were characterized by combining high-performance liquid chromatography (HPLC) separation and radioimmunoassay detection. In mediobasal and dorsolateral hypothalamic extracts, HPLC analysis confirmed the existence of a major immunoreactive peak which co-eluted with the synthetic des-N alpha-acetyl alpha-MSH standard. In contrast, 3 distinct forms of immunoreactive alpha-MSH, which exhibited the same retention times as synthetic des-, mono- and di-acetyl alpha-MSH, were resolved in amygdala nuclei, hippocampus, cortex and medulla oblongata extracts. The proportions of acetylated alpha-MSH (authentic alpha-MSH plus diacetyl alpha-MSH) contained in these extrahypothalamic structures were, respectively, 78, 80, 60 and 92% of the total alpha-MSH immunoreactivity. In order to compare the ionic mechanisms underlaying alpha-MSH release from hypothalamic and extrahypothalamic tissues, we have investigated in vitro the secretion of alpha-MSH by perifused slices of hypothalamus and amygdala nuclei. High potassium concentrations induced a marked increase of alpha-MSH release from both tissue preparations. However, a higher concentration of KCl was required to obtain maximal stimulation of amygdala nuclei (90 mM) than hypothalamic tissue (50 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Proopiomelanocortin (POMC)-related peptides in the brain of the rainbow trout, Salmo gairdneri

We have investigated the presence of ACTH, alpha-MSH and beta-endorphin, three peptides which derive from the multifunctional precursor protein proopiomelanocortin (POMC) in the brain of the rainbow trout Salmo gairdneri. Using both the indirect immunofluorescence and peroxidase-antiperoxidase techniques, a discrete group of positive cells was identified in the hypothalamus, within the anterior part of the nucleus lateralis tuberis. alpha-MSH-containing neurons represented the most abundant immunoreactive subpopulation. Coexistence of alpha-MSH, ACTH and beta-endorphin was observed in the lateral part of the nucleus. ACTH- and beta-endorphin-containing cells were mainly distributed in the rostral and caudal regions of the nucleus. In the medial portion of the nucleus lateralis tuberis, numerous cells were only stained for alpha-MSH. Moderate to dense plexuses of immunoreactive fibers were observed in the ventral thalamus and the floor of the hypothalamus. Some of these fibers projected towards the pituitary. The concentrations of ACTH, alpha-MSH and beta-endorphin-like immunoreactivities were measured in microdissected brain regions by means of specific radioimmunoassays. Diencephalon, mesencephalon and medulla oblongata extracts gave dilution curves which were parallel to standard curves. The highest concentrations of POMC-derived peptides were found in the diencephalon (alpha-MSH: 4.28 +/- 0.43 ng/mg prot.; ACTH: 1.08 +/- 0.09 ng/mg prot.; beta-endorphin: 1.02 +/- 0.1 ng/mg prot.), while lower concentrations were detected in the mesencephalon, medulla oblongata and telencephalon. The present results demonstrate that various peptides derived from POMC coexist within the same cell bodies of the fish hypothalamus. Taken together, these data suggest that expression and processing of POMC in the fish brain is similar to that occurring in pituitary melanotrophs.

Involvement of voltage-operated calcium channels in alpha-melanocyte-stimulating hormone (alpha-MSH) release from perifused rat hypothalamic slices

The contribution of voltage-operated calcium (VOC) channels in the mechanism of release of alpha-melanocyte-stimulating hormone (alpha-MSH) from hypothalamic neurons was investigated using perifused rat hypothalamic slices. The stimulatory effect of potassium (50 mM) on alpha-MSH release was completely blocked by cadmium (1 mM) a calcium competitor which indifferently blocks T-, L-and N-type VOC channels. To determine the nature of calcium conductances involved in K+-evoked alpha-MSH release, we have investigated the effect of a VOC channel agonist and 3 antagonists on the secretion of the neuropeptide. Administration of synthetic omega-conotoxin fraction GVIA (1 microM), a peptide toxin which blocks both N- and L-type VOC channels, reduced by 33% K+-induced alpha-MSH release. In contrast, the 1,4-dihydropyridine (DHP) antagonist nifedipine, at concentrations up to 100 microM, did not affect the response of hypothalamic alpha-MSH neurons to depolarizing concentrations of KCl. In addition, the secretion of alpha-MSH induced by high K+ concentrations was not reduced by nifedipine (10 microM) in the presence of diltiazem (1 microM), a benzothiazepine derivative which increases the affinity of the DHP antagonist for L-type VOC channels. The DHP agonist BAY K 8644 (0.1-10 microM) did not modify the early phase of the response of alpha-MSH neurons to K+-induced depolarization. In contrast BAY K 8644 (1 or 10 microM) significantly prolonged the duration of K+-induced alpha-MSH release. This sustained release of alpha-MSH induced by BAY K 8644 (10 microM) was totally suppressed by nifedipine (10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Alpha-melanocyte-stimulating hormone (alpha-MSH) in the brain of the cartilagenous fish. Immunohistochemical localization and biochemical characterization

The distribution of immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) in the central nervous system and pituitary of the elasmobranch fish Scyliorhinus canicula was determined by the indirect immunofluorescence and the peroxidase-antiperoxidase methods using a highly specific antiserum. Perikarya containing alpha-MSH-like immunoreactivity were localized in the dorsal portion of the posterior hypothalamus, mainly in the tuberculus posterioris and sacci vasculosus nuclei. Immunoreactive alpha-MSH cell bodies were found in the dorsal wall and ventral region of the caudal part of the tuberculum posterioris. These structures were densely innervated by fine beaded immunoreactive fibers. Some alpha-MSH immunoreactive cells were occasionally detected in the ventral part of the nucleus periventricularis. Scattered cell bodies and fibers were also observed in the dorsal wall of the posterior recess. Outside the hypothalamus very few fibers were detected in the dorsal thalamus and mesencephalon. No immunoreactivity was found in any other parts of the brain. The alpha-MSH immunoreactive material localized in the brain was characterized by combining high-performance liquid chromatography (HPLC) analysis and radioimmunological detection. Brain and pituitary extracts exhibited displacement curves which were parallel to that obtained with synthetic alpha-MSH. The concentrations of alpha-MSH immunoreactive material were determined in 5 different regions of the brain. The highest concentration was found in the hypothalamus. HPLC analysis resolved two major forms of immunoreactive alpha-MSH in the hypothalamus, which had been same retention times as des-N alpha-acetyl-alpha-MSH and its sulfoxide derivative. These results provide the first evidence for the presence of alpha-MSH-like peptides in the fish brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Melanin-concentrating hormone (MCH) is colocalized with alpha-melanocyte-stimulating hormone (alpha-MSH) in the rat but not in the human hypothalamus

Melanin-concentrating hormone (MCH)-containing neurons have recently been localized in the dorsolateral region of the rat hypothalamus, an area where the second alpha-MSH system is found which contains only alpha-MSH and none of the pro-opiomelanocortin (POMC)-related peptides. In order to study the morphological relationships between the MCH and alpha-MSH neuronal systems, we have studied the immunocytochemical localization of both MCH and alpha-MSH in the rat hypothalamus. The same study was also performed in the human hypothalamus where there is only one alpha-MSH system which contains alpha-MSH as well as the other POMC-related peptides (first alpha-MSH system). In the rat dorsolateral hypothalamus, we could demonstrate that most neuronal cell bodies stained for MCH also contained immunoreactive alpha-MSH. In the human hypothalamus, neuronal cell bodies stained for MCH were observed only in the periventricular area whereas cell bodies containing alpha-MSH were exclusively located in the infundibular (arcuate) nucleus. In the rat, immunoelectron microscopy showed labelling for MCH in the dense core vesicles of positive neurons and double-staining techniques clearly demonstrated that both immunoreactive MCH and alpha-MSH could be consistently detected in the same dense core vesicles. These ultrastructural studies then suggest that these two peptides should be released simultaneously from neurons located in the rat dorsolateral hypothalamus.

Immunocytochemical evidence for alpha-melanocyte-stimulating hormone in the hypothalamus of the frog Rana esculenta

The distribution of immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) within the brain of the frog, Rana esculenta, has been studied on adjacent serial sections using an indirect immunofluorescence technique. Immunoreactive cell bodies are found in the anterior part of the preoptic nucleus and in some ventral subependymal cerebrospinal fluid-contacting elements, and in the nucleus infundibularis ventralis. Numerous alpha-MSH-like immunoreactive fibers are present in the preoptic area, in the pars ventralis of the tuber cinereum, and in the outer layer of the median eminence. This staining pattern is completely eliminated after preabsorbing the antiserum with the corresponding antigen, but blocking tests with alpha-MSH-related peptides do not lead to any change in the immunoreaction. From these results it may be inferred that an alpha-MSH-like system is present in the hypothalamic neurosecretory area of R. esculenta, and is probably related to its hypophysiotropic functions. The results are compared to the distribution of alpha-MSH within the hypothalamus of reptiles and mammals.

Localization of melanin-concentrating hormone-like immunoreactivity in the brain and pituitary of the frog Rana ridibunda

The distribution of melanin-concentrating hormone (MCH) in the central nervous system of the frog Rana ridibunda was determined by the indirect immunofluorescence technique using antibodies against synthetic salmon MCH, generated in rabbits. The most prominent group of MCH-like containing perikarya was detected in the preoptic nucleus. Comparatively, a moderate number of cell bodies was observed in the dorsal infundibular nucleus and in the ventral thalamic area. Brightly immunofluorescent nerve bundles were found in the preoptic nucleus and in the ventral infundibular nucleus, coursing towards the internal zone of the median eminence and the pituitary stalk. An intense network of immunofluorescent fibers was localized in the neural lobe of the pituitary. The subcellular localization of MCH-like material was studied in the neurohypophysis using the immunogold technique. It was demonstrated that MCH-like material was contained in dense core vesicles (80-90 mm in diameter) within specific nerve terminals. The present findings indicate that, in amphibians, MCH-like peptide is located in specific hypothalamic neurons. Our data suggest that MCH may be released by neurohypophyseal nerve endings as a typical neurohormone.

Localization and identification of alpha-melanocyte-stimulating hormone (alpha-MSH) in the frog brain

The distribution of alpha-melanocyte-stimulating hormone (alpha-MSH) in the central nervous system of the frog Rana ridibunda was determined by immunofluorescence using a highly specific antiserum. alpha-MSH-like containing perikarya were localized in the infundibular region, mainly in the ventral hypothalamic nucleus. A rich plexus of immunoreactive fibers directed towards the ventral telencephalic region was detected. Reverse-phase high-performance liquid chromatography and radioimmunoassay were used to characterize alpha-MSH-like peptides in the frog brain. Chromatographic separation revealed that immunoreactive alpha-MSH coeluted with synthetic des-N alpha-acetyl alpha-MSH, authentic alpha-MSH and their sulfoxide derivatives. The heterogeneity of alpha-MSH-like material in the frog brain was in marked contrast with the figure observed in the intermediate lobe of the pituitary gland where only des-N alpha-acetyl alpha-MSH is present. These findings support the existence of discrete alpha-MSH immunoreactive neurons in the frog brain containing both desacetyl and authentic alpha-MSH.

Hypothermic and antipyretic effects of ACTH (1-24) and alpha-melanotropin in guinea-pigs

Intracerebroventricular administration of adrenocorticotropin (ACTH 1-24) and alpha-melanotropin (alpha-MSH), peptides which occur naturally in brain induced dose-related hypothermia in guinea-pigs at room temperature (21 degrees C) and also produced greater hypothermia at low (10 degrees C) ambient temperature. However, when the experiments were repeated in a warm (30 degrees C) environment, no effect on body temperature was observed. These results indicate that the peptides did not reduce the central set-point of temperature control. The hypothermia induced by ACTH and alpha-MSH was not mediated via histamine H1- or H2-receptors and serotonin since the H1-receptor antagonist, mepyramine, the H2-receptor antagonist, cimetidine, and the serotonin antagonist, methysergide, had no antagonistic effects. The peptides were antipyretic since they reduced pyrogen-induced-fever and hyperthermia due to prostaglandin E2, norepinephrine and dibutyryl cAMP, at a dose which did not affect normal body temperature. The powerful central effects of these peptides on normal body temperature, fever and hyperthermia, together with their presence of the brain regions important to temperature control, suggest that they participate in thermoregulation.

Biological and immunological characterization of alpha-melanocyte-stimulating hormone (alpha-MSH) in two neuronal systems of the rat brain

Recent immunocytochemical studies have demonstrated the existence of two different neuronal systems containing alpha-MSH-like material in the brain: one originating from the arcuate nucleus and the other one from the dorsolateral hypothalamus. The aim of the present study was to further characterize alpha-MSH in these two discrete regions of the rat diencephalon. Intracerebroventricular administration of colchicine resulted in a marked decrease in the number of ACTH and beta-endorphin nerve fibers and a significant reduction in ACTH and beta-endorphin content in the dorsolateral hypothalamus. Conversely, colchicine treatment did not alter alpha-MSH, ACTH or beta-endorphin content in the arcuate nucleus and did not significantly affect alpha-MSH concentration in the dorsal region. Reverse-phase high-performance liquid chromatography showed that the major alpha-MSH-like compound localized in the dorsal hypothalamus co-migrated exactly with synthetic alpha-MSH, whereas the arcuate nucleus contained 5 peptides cross-reacting with alpha-MSH antibodies, 4 of them being different from standard alpha-MSH. Significant amounts of biologically active melanotropin, which migrated on Sephadex G-25 columns like synthetic alpha-MSH, were also detected in both the arcuate nucleus and dorsolateral hypothalamus. Taken together, these data demonstrate that the alpha-MSH cell bodies located in the dorsolateral hypothalamus specifically produce authentic alpha-MSH, whereas the alpha-MSH cell bodies in the arcuate nucleus also contain ACTH, beta-endorphin and several peptides immunologically related but not identical to alpha-MSH.

Further studies on the identification of neurons containing immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) in the rat brain

In order to identify more accurately the organelles containing immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) in the rat brain, attempts were made to improve the ultrastructural preservation of the neural tissue used for immunostaining of the peptide. With the post-embedding staining technique, the quality of the preservation was not adequate since only low concentrations (0.2-0.5%) of OsO4 could be used for postfixation. Higher concentrations of OsO4 completely destroyed the antigenicity of alpha-MSH. With the pre-embedding technique in which the immunostaining is performed prior to postfixation with OsO4, a good preservation could be obtained making possible the identification of organelles and classification of endings containing immunoreactive alpha-MSH. In the dendrites, the staining was rather diffuse without any clear association with organelles. In the endings, the staining was mostly restricted to dense core vesicles with some degree of diffusion in the cytoplasm. None of the positive endings were seen making synaptic contact. These results support the hypothesis that alpha-MSH could be released in sites other than the classical synaptic junction and act as a local hormone.

Effect of hypophysectomy and pituitary stalk transection on alpha-melanocyte-stimulating hormone-like immunoreactivity in the brain of the frog, Rana ridibunda Pallas

The existence of an alpha-MSH-like molecule in the frog brain led us to investigate the role of the pituitary gland in the maintenance of the alpha-MSH content in 3 different regions of the brain. Acetic acid extracts of hypothalamus, rhombencephalon and telencephalon were analyzed by means of a highly specific radioimmunoassay for alpha-MSH in normal, sham-operated, pituitary disconnected and hypophysectomized frogs. Transection of the pituitary stalk gave rise to a significant decrease in alpha-MSH content in the intermediate lobe of the pituitary gland (-71% after 3 days), but did not affect alpha-MSH content in the distal lobe or in the brain. Eight days after total hypophysectomy, an alpha-MSH immunoreactive compound, co-eluting with synthetic alpha-MSH on Sephadex G-25, was found in the 3 brain regions studied. Removal of the whole pituitary gland did not significantly modify alpha-MSH content in the hypothalamus and the telencephalon. A slight increase in alpha-MSH was even observed in the rhombencephalon of hypophysectomized animals. Furthermore, no modification in alpha-MSH immunoreactivity occurred in any region of hypophysectomized animals. These results demonstrate the existence of alpha-MSH-like material in the brain of Rana ridibunda and establish that brain alpha-MSH in the frog is not of pituitary origin.

Characterization of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in human brain tissue

Adult human hypothalamic tissue was analyzed for the presence of products generated by post-cleavage processing of ACTH 1-13. The displacement curve generated by immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in extracts (5 M acetic acid or acidified ethanol) of adult human hypothalamic tissue was parallel to the alpha-MSH radioimmunoassay standard curve, and alpha-MSHi eluted as a single peak on Sephadex G-10, G-25, and G-50 columns in a manner identical to that of synthetic alpha-MSH. The alpha-MSHi was clearly distinguishable in its mobility on Sephadex G-50 columns from such peptides as beta-MSH, luteinizing hormone releasing hormone, and ACTH. After high performance liquid chromatography of extracts of hypothalamic tissue from young as well as aged men and women, we found that the major peak of alpha-MSHi (75-95% of total alpha-MSHi) coeluted with desacetyl alpha-MSH (ACTH 1-13 amide) rather than alpha-MSH. We suggest that desacetyl alpha-MSH, rather than alpha-MSH, is the predominant alpha-MSHi in adult human brain tissue.

Hypothermic and antipyretic effects of centrally administered ACTH (1--24) and alpha-melanotropin

ACTH (1--24) and alpha-melanotropin (alpha-MSH), peptides previously shown to influence body temperature when administered centrally and to occur naturally in brain regions important to temperature control, were injected intracerebroventricularly (ICV) in rabbits. The peptides in doses of 1.25, 2.5 and 5.0 micrograms produced dose-related hypothermias in a 23 degrees C environment, and greater decreases in body temperature when the experiments were repeated in the cold (10 degrees C), but the largest dose had no effect on temperature in the heat (30 degrees C). These results indicate that the peptides do not reduce the central set-point of temperature control. Rather, they appear to selectively inhibit heat conservation and production responses. Five microgram of ACTH reversed vasoconstriction and inhibited rises in temperature caused by leukocytic pyrogen (LP) given IV and ICV. The same dose of alpha-MSH also reduced fever produced by IV and ICV LP, but the reduction was not as great as after ACTH. Both peptides (5 micrograms) also reduced temperature rises and vasoconstriction caused by ICV PGE2. ACTH reduced d-amphetamine-induced hyperthermia without altering vasoconstriction which suggests that this peptide can reduce temperature rises by inhibiting heat production alone. One of the most important findings was that the peptides are antipyretic in that they reduce fever at doses (0.25 microgram, ICV) that do not affect normal temperature. The powerful effects of these peptides on resting body temperature, hyperthermia and fever, together with their presence in brain tissue important to temperature control, suggest that the endogenous central peptides participate in thermoregulation, perhaps by limiting fever and influencing normal temperature.

Release of alpha-melanocyte stimulating hormone into rat and human cerebrospinal fluid in vivo and from rat hypothalamus slices in vitro

The release of alpha-melanocyte stimulating hormone (alpha-MSH) from central nervous system neurons was investigated and demonstrated in vivo and in vitro. alpha-MSH immunoreactivity in rat and human cerebrospinal fluid (CSF) is comprised of deacetylated alpha-MSH, alpha-MSH and the methionine sulfoxide forms of these peptides. The sulfoxides are formed artifactually upon extraction. alpha-MSH in rat CSF is unaffected by hypophysectomy but is markedly increased by electrical stimulation of the mesencephalic central gray. These data indicate that CSF alpha-MSH is primarily of neuronal origin, alpha-MSH is also released in a calcium dependent manner from hypothalamic slices in vitro. The fact that the release of alpha-MSH is stimulated by veratridine and inhibited by tetrodotoxin demonstrates the necessity for neuronal sodium influx for alpha-MSH release. The presence of an alpha-MSH neurosecretory process supports a neurotropic role for this peptide in the central nervous system.

Evidence that N-acetylation regulates the behavioral activity of alpha-MSH in the rat and human central nervous system

alpha-MSH immunoreactive peptides were fractionated and characterized in rat and human brain and rat pituitary by reversed phase high pressure liquid chromatographic techniques. alpha-MSH and deacetylated alpha-MSH were two major naturally existing peptides in both brain and pituitary gland. Subsequent experiments examined the roles of these two peptides in neuronal function. The alpha-MSH was clearly more effective than deacetylated alpha-MSH in improving performance on a visual discrimination task after intraperitoneal administration and in inducing excessive grooming after intraventricular administration. The difference in behavioral potency may be explained by the fact that alpha-MSH was much more resistant to peptidase degradation than was deacetylated alpha-MSH. N-acetylation of alpha-MSH may be an effective regulatory process for modulating the behavioral potency of the secretory product of alpha-MSH-containing pituitary cells and neurons.

Identification of a second category of alpha-melanocyte-stimulating hormone (alpha-MSH) neurons in the rat hypothalamus

An immunocytochemical localization of alpha-melanocyte-stimulating hormone (alpha-MSH) as well as ACTH and a fragment (16K) of the common precursor of ACTH and beta-lipotropin (beta-LPH) was performed in rat brain. Two different groups of neuronal cell bodies showing alpha-MSH-like immunoreactivity (alpha-MSH-LI) were observed in the hypothalamus. One group of neurons located in the arcuate nucleus was shown to contain not only alpha-MSH-LI, but also ACTH and the 16K fragment. A second category of alpha-MSH-LI-containing neurons was characterized by the complete absence of staining for ACTH and 16K fragment. These neurons were mainly located in the dorsal-lateral portion of the hypothalamus. Immunoelectron microscopy showed that immunostaining for alpha-MSH was restricted to dense core vesicles in the positive perikarya. Nerve fibers staining for alpha-MSH (but not for ACTH and 16K fragment) were also observed outside the ACTH-beta-LPH pathway, especially in the cortex, caudate-putamen nucleus and hippocampus. These findings strongly suggest the presence of two different neuronal systems reacting with antibodies to alpha-MSH.

Demonstration of an endogenous circadian rhythm of alpha-melanocyte stimulating hormone in the rat pineal gland

alpha-Melanocyte stimulating hormone (alpha-MSH) has been identified and characterized in the rat pineal gland by a combination of immunochemical and high pressure liquid chromatographic techniques. The immunoreactivity in pineal extracts was separated into two chromatographic components. The major component had a retention time identical to that of alpha-MSH while the minor component eluted just slightly before standard alpha-MSH. Male rats maintained in a 12 h photoperiod demonstrated a marked circadian rhythm in pineal alpha-MSH concentration. Concentrations that peaked at 07.00 h, 1 h after the lights were turned on, were greater than 5 times the nadir which occurred at 01.000 h. Animals house in chronic dark for 7 days maintained the diurnal variation of alpha-MSH concentrations. However, in chronically dark housed rats, the peak shifted to 05.000 h and was greater than 10 times the nidir of this rhythm and approximately 4 time the peak at 07.00 in alternating light/dark conditions. Rats exposed to chronic light for 7 days maintained a pineal alpha-MSH rhythm although the amplitude of the peak was significantly decreased compared to the rhythm in animals housed in alternating light/dark conditions. Neither hypophysectomy nor superior cervical ganglionectomy had any effect on the alpha-MSH rhythm. Lesion of the arcuate nucleus, the major source of alpha-MSH-containing nerves in the brain, did not significantly affect pineal alpha-MSH concentrations. These data demonstrate a circadian alpha-MSH rhythm in the rat pineal and suggest an alpha-MSH involvement in the rhythmic processes of the pineal gland.

Central administration of peptides alters thermoregulation in the rabbit

Sixteen peptides were injected intracerebroventricularly to test their effects on rectal temperature of rabbits in a thermoneutral environment. In initial tests 5 micrograms alpha-MSH, ACTH(1--24), oxytocin, vasopressin and glucagon altered body temperature while ACTH(1--10), cholecystokinin, contraceptive tetrapeptide, gastrin, insulin, interferon, leupeptin, LHRH, panhibin (somatostatin), and proctolin did not. Bombesin also altered body temperature but in no consistent direction. In further tests on the effective peptides 1.25--5.0 micrograms alpha-MSH and ACTH(1--24) produced dose-related decreases in rectal temperature as great as 1.0 degrees C. The same doses of oxytocin and glucagon produced small, prolonged hyperthermias which did not exceed 0.4 degrees C. Vasopressin caused rapid development of small increases in rectal temperature; temperature returned to normal in 2--3 hr. The results suggest that five of the peptides tested may have roles in central mediation of normal body temperature, hypothermia, hyperthermia and fever.

Distribution of alpha-melanocyte-stimulating hormone in the rat brain: evidence that alpha-MSH-containing cells in the arcuate region send projections to extrahypothalamic areas

The distribution and concentration of alpha-MSH in the rodent brain has been determined by radioimmunoassay. The limbic system contained substantial quantities of alpha-MSH. Forty per cent of the alpha-MSH present in the brain was localized in the hypothalamus, with the highest concentration of alpha-MSH in the arcuate nucleus. More than 40% of the extrahypothalamic alpha-MSH in the brain was found in the following areas: midbrain (16%), preoptic area (13%), septum (7%), and thalamus (7%). To determine the source of the hypothalamic and extrahypothalamic alpha-MSH, the anterior hypothalamic preoptic area of the brain was surgically separated from more caudal diencephalic structures, and the arcuate region of the hypothalamus was surgically isolated from the remainder of the brain. Following these deafferentations, no significant reduction in hypothalamic alpha-MSH levels was observed; however, a significant reduction in extrahypothalamic alpha-MSH level was demonstrated. This dramatic decrease of alpha-MSH in extrahypothalamic areas of the rodent brain strongly suggests that the bulk of the extrahypothalamic alpha-MSH arises from neuronal perikarya in the arcuate region. These findings are consistent with the hypothesis that a population of neuronal cell bodies producing alpha-MSH originate in the arcuate region of the hypothalamus and that they send axonal projections to many areas of the limbic system and brain stem.

Identification and distribution of alpha-melanotropin in discrete regions of the cat brain

The distribution of alpha-melantropin-like material (alpha-MSH) was demonstrated in rat brain using a microdissection technique combined with radioimmunoassay. Highest concentrations of alpha-MSH were noted in the hypothalamus and preoptic area. Particularly high concentrations were observed in the arcuate nucleus, median eminence, suprachiasmatic nucleus, periventricular nucleus and the medial preoptic nucleus. The thalamic paraventricular nucleus also contained high alpha-MSH concentrations. Moderate to low concentrations were noted in other thalamic, septal, amygdaloid and midbrain nuclei. Low concentrations were observed in cortical and striatal regions.

Pituitary hormones in brain: where, how, and why?

Peptide and protein hormones usually considered as being of pituitary origin have been detected within the central nervous system by means of radioimmunoassay, bioassay, and immunocytochemical techniques. Intracerebral administration of some of these hormones or fragments thereof elicit behavioral responses, suggesting that they may have a physiological role similar to that described for other peptidergic neurotransmitter or neuromodulator substances. Evidence available for some of these hormones indicates that they are synthesized within the central nervous system and that their regulation may differ from that of their pituitary counterparts.

Subcellular localization of immunoreactive alpha-melanocyte stimulating hormone in human brain

The regional and subcellular distribution of immunoreactive alpha-melanocyte stimulating hormone (alpha-MSHi) in the post mortem adult human brain was investigated. alpha-MSHi was highly concentrated in medial basal hypothalamic tissue (1.02 ng/mg protein). Lower levels of alpha-MSHi were present in the optic chiasm and mammillary bodies, 0.08 and 0.11 ng/mg protein, respectively. The concentrations of alpha-MSHi in cerebellum and frontal cerebral cortex were 1/1,000th that of the medial basal hypothalamus. When medial basal hypothalamic homogenates were subjected to discontinuous or continuous sucrose density gradients, alpha-MSHi was found to be associated primarily with subcellular particles which resembled isolated nerve terminals, i.e., synaptosomes. Low to undetectable amounts of alpha-MSHi were found in the cytosol or the myelin/microsome fraction of the gradients. The results of these studies are consistent with the view that alpha-MSH is a neuronal peptide in the human brain.