Letters2 August 2005Regulation of Body Weight by Proopiomelanocortin Peptides in Humans: Lessons from the Nelson SyndromeRajagopal V. Sekhar, MD, J. Clay Goodman, MD, Ashok Balasubramanyam, MD, Jeffrey B. Tatro, PhD, and Emese Mihaly, PhDRajagopal V. Sekhar, MDFrom Baylor College of Medicine, Houston, TX 77030; Tufts University School of Medicine, Boston, MA 02111; and Semmelwies University Medical School, 1088 Budapest, Hungary.Search for more papers by this author, J. Clay Goodman, MDFrom Baylor College of Medicine, Houston, TX 77030; Tufts University School of Medicine, Boston, MA 02111; and Semmelwies University Medical School, 1088 Budapest, Hungary.Search for more papers by this author, Ashok Balasubramanyam, MDFrom Baylor College of Medicine, Houston, TX 77030; Tufts University School of Medicine, Boston, MA 02111; and Semmelwies University Medical School, 1088 Budapest, Hungary.Search for more papers by this author, Jeffrey B. Tatro, PhDFrom Baylor College of Medicine, Houston, TX 77030; Tufts University School of Medicine, Boston, MA 02111; and Semmelwies University Medical School, 1088 Budapest, Hungary.Search for more papers by this author, and Emese Mihaly, PhDFrom Baylor College of Medicine, Houston, TX 77030; Tufts University School of Medicine, Boston, MA 02111; and Semmelwies University Medical School, 1088 Budapest, Hungary.Search for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/0003-4819-143-3-200508020-00021 SectionsAboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail TO THE EDITOR:Background: Melanocortins (α-melanocyte-stimulating hormone [MSH] and adrenocorticotropic hormone [ACTH]), in addition to their melanocyte-stimulating actions, may regulate energy balance through hypothalamic melanocortin-4 receptors (MC4Rs). In mice, deletion of the proopiomelanocortin (POMC) or MC4R genes leads to obesity, whereas administration of MC4R agonists (for example, MSH) causes weight loss (1). In humans, inactivating mutations of the POMC (2) or MC4R (3) genes can cause obesity, but there is no evidence that increased melanocortin action can cause weight loss.In the Nelson syndrome, rapid growth of an adrenocorticotrophic pituitary adenoma following bilateral adrenalectomy causes extreme elevation of melanocortin levels ...References1. Seeley RJ, Drazen DL, Clegg DJ. The critical role of the melanocortin system in the control of energy balance. Annu Rev Nutr. 2004;24:133-49. [PMID: 15189116] CrossrefMedlineGoogle Scholar2. Krude H, Biebermann H, Luck W, Horn R, Brabant G, Gruters A. Severe early-onset obesity, adrenal insufficiency and red hair pigmentation caused by POMC mutations in humans. Nat Genet. 1998;19:155-7. [PMID: 9620771] CrossrefMedlineGoogle Scholar3. Vaisse C, Clement K, Durand E, Hercberg S, Guy-Grand B, Froguel P. Melanocortin-4 receptor mutations are a frequent and heterogeneous cause of morbid obesity. J Clin Invest. 2000;106:253-62. [PMID: 10903341] CrossrefMedlineGoogle Scholar4. Mountjoy KG, Mortrud MT, Low MJ, Simerly RB, Cone RD. Localization of the melanocortin-4 receptor (MC4-R) in neuroendocrine and autonomic control circuits in the brain. Mol Endocrinol. 1994;8:1298-308. [PMID: 7854347] MedlineGoogle Scholar5. Hagan MM, Rushing PA, Schwartz MW, Yagaloff KA, Burn P, Woods SC, et al. Role of the CNS melanocortin system in the response to overfeeding. J Neurosci. 1999;19:2362-7. [PMID: 10066286] CrossrefMedlineGoogle Scholar Author, Article, and Disclosure InformationAuthors: Rajagopal V. Sekhar, MD; J. Clay Goodman, MD; Ashok Balasubramanyam, MD; Jeffrey B. Tatro, PhD; Emese Mihaly, PhDAffiliations: From Baylor College of Medicine, Houston, TX 77030; Tufts University School of Medicine, Boston, MA 02111; and Semmelwies University Medical School, 1088 Budapest, Hungary.Editor's Note: The lead author of the following Clinical Observation was one of a dozen Associates of the American College of Physicians selected to present a clinical vignette at the 2003 Annual Session in San Diego. We are proud to present this case report through a special arrangement with the Council of Associates of the College.Acknowledgment: The authors thank Margaret Entwistle for technical expertise.Grant Support: By National Institutes of Health grants DK59537 and HL73696 to Dr. Balasubramanyam and grant MH44694 to Dr. Tatro.Disclosures: None disclosed. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails Metrics 2 August 2005Volume 143, Issue 3Page: 238-239KeywordsAdrenalectomyAdrenocorticotropic hormoneBlood plasmaBody mass indexBody weightObesityPituitary tumorsScarsWeight gainWeight loss ePublished: 2 August 2005 Issue Published: 2 August 2005 Copyright & PermissionsCopyright © 2005 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...

Immunohistochemical single‐ and double‐labeling studies were performed on the hypothalami of postmortem human brains to elucidate the distribution of corticotropin‐releasing hormone (CRH)‐immunoreactive (IR) neuronal elements and their interaction with the neuropeptide Y (NPY)‐ergic neuronal system. The great majority of CRH‐IR perikarya were found in the paraventricular nucleus (PVN), whereas a considerable number of CRH‐IR neurons were also observed in the periventricular and infundibular nuclei. The dorsomedial nucleus and the perifornical region contained only scattered CRH‐IR neurons. Dense CRH‐IR fiber networks were found throughout the hypothalamus. However, the medial preoptic, the dorsolateral part of the supraoptic, the suprachiasmatic, the ventromedial, and the different mammillary nuclei showed a relative paucity of fibers. The terminal fields of NPY‐IR axons overlapped the distribution of CRH‐IR neurons in the hypothalamus. NPY‐IR axon varicosities were juxtaposed to both dendrites and perikarya of the majority of CRH‐IR neurons residing in the paraventricular, periventricular, and infundibular nuclei. These neurons were frequently contacted by multiple NPY axons that either formed baskets around their perikarya or completely ensheathed the emanating CRH dendrites. Because NPY and agouti‐related protein (AGRP) are co‐contained in neurons of the human infundibular nucleus, we used AGRP as a marker of NPY fibers originating exclusively from the infundibular nucleus. Only a small proportion of CRH neurons in the PVN was contacted by AGRP‐IR axon varicosities, suggesting that NPY‐IR innervation of CRH neurons in the PVN derive mainly from regions outside the infundibular nucleus. The present morphological findings support the view that NPY regulates the CRH system of the human hypothalamus and therefore at least some of the effects of NPY on metabolic, autonomic, and endocrine functions may be mediated through CRH. J. Comp. Neurol. 446:235–243, 2002. © 2002 Wiley‐Liss, Inc.

Recent evidence suggests that neuropeptide Y (NPY), originating in neurons in the hypothalamic arcuate nucleus, is an important mediator of the effects of leptin on the central nervous system. As these NPY neurons innervate hypophysiotropic neurons in the hypothalamic paraventricular nucleus (PVN) that produce the tripeptide, TRH, we raised the possibility that NPY may be responsible for resetting of the hypothalamic-pituitary-thyroid (HPT) axis during fasting. To test this hypothesis, the effects of intracerebroventricularly administered NPY on circulating thyroid hormone levels and proTRH messenger RNA in the PVN were studied by RIA and in situ hybridization histochemistry, respectively. NPY administration suppressed circulating levels of thyroid hormone (T(3) and T(4)) and resulted in an inappropriately normal or low TSH. These alterations were associated with a significant suppression of proTRH messenger RNA in the PVN, indicating that NPY infusion had resulted in a state of central hypothyroidism. Similar observations were made in NPY-infused animals pair fed to the vehicle-treated controls. These data are reminiscent of the effect of fasting on the thyroid axis and indicate that NPY may play a major role in the inhibition of HPT axis during fasting.

Our previous study has shown that prothyrotropin-releasing hormone (proTRH) gene expression is increased in the ventrolateral periaqueductal gray (PAG) neurons following precipitated morphine withdrawal and continues to be activated even 24 h after withdrawal. We have hypothesized that peptide products of proTRH may participate in the recovery from morphine withdrawal. To identify neuroanatomical substrates of the proposed action of proTRH-derived peptides originating from the ventrolateral PAG proTRH neurons, projections of these neurons were investigated by a series of anterograde and retrograde tract-tracing experiments. First, Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected in the ventrolateral PAG in Sprague–Dawley rats. Following transport of the tracer, simultaneous immunolabeling for PHA-L and proTRH peptides was performed and mapped in discrete brain regions. PHA-L-immunoreactive (IR) fibers showing preterminal and terminal-like arborization that contained proTRH were identified in the dorsolateral and lateral PAG, deep layer of superior colliculus (CS), parafascicular nucleus (PF), ventromedial zona incerta (ZI) and at the border of the locus coeruleus (LC) and Barrington’s nucleus. Scattered double-labeled fibers were present in the lateral septal nucleus, ventromedial preoptic nucleus, lateral hypothalamus, perifornical area and in the periventricular region at the diencephalon/midbrain junction. The retrogradely transported marker, cholera toxin β-subunit (CTb) was then injected in the dorsolateral PAG, CS, PF, ZI and medial to the LC. Double-labeled perikarya for both CTb and proTRH in the ventrolateral PAG were found for each region injected with CTb, corroborating the findings by the anterograde tracing experiment. These studies demonstrate that proTRH neurons in the ventrolateral PAG project to several regions of the brain that are involved in autonomic and behavioral regulation and thereby, may function as an integrating center to coordinate responses to opiate withdrawal.

1Tupper Research Institute and Department of Medicine, Division of Endocrinology, Diabetes, Metabolism, and Molecular Medicine, New England Medical Center, Boston, Massachusetts 02111, 2Department of Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary 1083, 3Department of Community Health, Tufts University School of Medicine, Boston, Massachusetts 02111, 4Department of Medicine, Division of Endocrinology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, and 5Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts 02111

We recently demonstrated that three arcuate nucleus-derived peptides, neuropeptide Y (NPY), agouti-related protein (AGRP), and alphaMSH, are contained in axon terminals that heavily innervate hypophysiotropic TRH neurons in the rat brain and may contribute to the altered set-point of the hypothalamo-pituitary-thyroid axis during fasting. To determine whether a similar regulatory system exists in human brain, we performed a series of immunohistochemical studies using antisera against NPY, AGRP, alphaMSH, and TRH in adult hypothalami obtained within 15 h of death. Numerous small to medium-sized, fusiform and multipolar NPY-, AGRP-, and alphaMSH-immunoreactive (-IR) cells were widely distributed throughout the rostro-caudal extent of the infundibular (arcuate) nucleus. A similar distribution pattern was found for NPY- and AGRP-IR neurons in the arcuate nucleus, whereas alphaMSH-IR cells appeared to form a separate cell population. By double labeling fluorescent immunohistochemistry, 82% of NPY neurons cocontained AGRP, and 87% of AGRP neurons coexpressed NPY. No colocalization was found between alphaMSH- and AGRP-IR neurons. NPY-, AGRP-, and alphaMSH-containing axons densely innervated the hypothalamic paraventricular nucleus and were found in close juxtaposition to TRH-synthesizing cell bodies and dendrites. These studies demonstrate that in man, the NPY-, AGRP-, and alphaMSH-IR neuronal systems in the infundibular and paraventricular nuclei are highly reminiscent of that observed in the rat and may similarly be involved in regulating the hypothalamo-pituitary-thyroid axis in the human brain.

Type 2 iodothyronine deiodinase, an enzyme involved in the conversion of thyroxin to the biologically active 3,5, 3'-triiodothyronine, is highly concentrated in a group of specialized ependymal cells, tanycytes, lining the wall and floor of the third ventricle. As this distribution is highly reminiscent of the distribution of cells containing the phosphatase inhibitor, DARPP-32, we raised the possibility that these two proteins may coexist in tanycytes and that DARPP-32 may modulate type 2 deiodinase activity by regulating the phosphorylation state of the cAMP regulatory factor, CREB. To address this question, double-labeling histochemical studies were performed for type 2 deiodinase mRNA and DARPP-32 immunoreactivity (IR), or DARPP-32- and CREB-IR in the same tissue sections. Type 2 deiodinase mRNA was found in the cell bodies of all DARPP-32-immunolabeled tanycytes. Both type 2 deiodinase mRNA and DARPP-32-IR also extended into tanycyte processes that ramified in the arcuate nucleus and median eminence, in close association with blood vessels and portal capillaries. In contrast, type 2 deiodinase mRNA was not present in the same cells that contained DARPP-32-IR in the pituitary gland. All tanycytes containing DARPP-32-IR also contained CREB-IR in their nucleus. Since type 2 deiodinase activity can be induced by substances that increase cAMP, we hypothesize that DARPP-32 may regulate the activity of type 2 deiodinase by prolonging the activation of CREB. Selectivity for the colocalization of these factors to tanycytes but not the pituitary gland, may explain the heterogeneous response of type 2 deiodinase activity in these two loci in response to specific stimuli such as fasting.

The hypothalamic arcuate nucleus has an essential role in mediating the homeostatic responses of the thyroid axis to fasting by altering the sensitivity of prothyrotropin-releasing hormone (pro-TRH) gene expression in the paraventricular nucleus (PVN) to feedback regulation by thyroid hormone. Because agouti-related protein (AGRP), a leptin-regulated, arcuate nucleus-derived peptide with alpha-MSH antagonist activity, is contained in axon terminals that terminate on TRH neurons in the PVN, we raised the possibility that alpha-MSH may also participate in the mechanism by which leptin influences pro-TRH gene expression. By double-labeling immunocytochemistry, alpha-MSH-IR axon varicosities were juxtaposed to approximately 70% of pro-TRH neurons in the anterior and periventricular parvocellular subdivisions of the PVN and to 34% of pro-TRH neurons in the medial parvocellular subdivision, establishing synaptic contacts both on the cell soma and dendrites. All pro-TRH neurons receiving contacts by alpha-MSH-containing fibers also were innervated by axons containing AGRP. The intracerebroventricular infusion of 300 ng of alpha-MSH every 6 hr for 3 d prevented fasting-induced suppression of pro-TRH in the PVN but had no effect on AGRP mRNA in the arcuate nucleus. alpha-MSH also increased circulating levels of free thyroxine (T4) 2.5-fold over the levels in fasted controls, but free T4 did not reach the levels in fed controls. These data suggest that alpha-MSH has an important role in the activation of pro-TRH gene expression in hypophysiotropic neurons via either a mono- and/or multisynaptic pathway to the PVN, but factors in addition to alpha-MSH also contribute to the mechanism by which leptin administration restores thyroid hormone levels to normal in fasted animals.

Because cocaine- and amphetamine-regulated transcript (CART) coexists with α-melanocyte stimulating hormone (α-MSH) in the arcuate nucleus neurons and we have recently demonstrated that α-MSH innervates TRH-synthesizing neurons in the hypothalamic paraventricular nucleus (PVN), we raised the possibility that CART may also be contained in fibers that innervate hypophysiotropic thyrotropin-releasing hormone (TRH) neurons and modulate TRH gene expression. Triple-labeling fluorescentin situhybridization and immunofluorescence were performed to reveal the morphological relationships between pro-TRH mRNA-containing neurons and CART- and α-MSH-immunoreactive (IR) axons. CART-IR axons densely innervated the majority of pro-TRH mRNA-containing neurons in all parvocellular subdivisions of the PVN and established asymmetric synaptic specializations with pro-TRH neurons. However, whereas all α-MSH-IR axons in the PVN contained CART-IR, only a portion of CART-IR axons in contact with pro-TRH neurons were immunoreactive for α-MSH. In the medial and periventricular parvocellular subdivisions of the PVN, CART was co-contained in ∼80% of pro-TRH neuronal perikarya, whereas colocalization with pro-TRH was found in <10% of the anterior parvocellular subdivision neurons. In addition, >80% of TRH/CART neurons in the periventricular and medial parvocellular subdivisions accumulated Fluoro-Gold after systemic administration, suggesting that CART may serve as a marker for hypophysiotropic TRH neurons. CART prevented fasting-induced suppression of pro-TRH in the PVN when administered intracerebroventricularly and increased the content of TRH in hypothalamic cell cultures. These studies establish an anatomical association between CART and pro-TRH-producing neurons in the PVN and demonstrate that CART has a stimulatory effect on hypophysiotropic TRH neurons by increasing pro-TRH gene expression and the biosynthesis of TRH.

During fasting, corticotropin-releasing hormone (CRH) mRNA decreases in the hypothalamic paraventricular nucleus (PVN), but the mechanism by which this takes place is not well understood. To test the hypothesis that the melanocortin system may be involved in the regulation of CRH mRNA in the PVN during fasting, the effect of intracerebroventricularly administered α-melanocyte stimulating hormone (MSH) on CRH mRNA in the PVN was studied in fasted animals by in situ hybridization histochemistry. Whereas fasting suppressed CRH mRNA levels in the PVN, α-MSH at doses of 150 and 300 ng every 6 h for 64 h prevented the fasting-induced suppression of CRH gene expression in the PVN. These data indicate that the suppression of α-MSH synthesis may be responsible for the decreased CRH gene expression in the PVN during fasting.

The central regulation of the preovulatory LH surge requires a complex sequence of interactions between neuronal systems that impinge on LH-releasing hormone (LHRH)-synthesizing neurons. The reported absence of estrogen receptors (ERs) in LHRH neurons indicates that estrogen-receptive neurons that are afferent to LHRH neurons are involved in mediating the effects of this steroid. We now present evidence indicating that central histaminergic neurons, exclusively located in the tuberomammillary complex of the caudal diencephalon, serve as an important relay in this system. Evaluation of this system revealed that 76% of histamine-synthesising neurons display ERalpha-immunoreactivity in their nucleus; furthermore histaminergic axons exhibit axo-dendritic and axo-somatic appositions onto LHRH neurons in both the rodent and the human brain. Our in vivo studies show that the intracerebroventricular administration of the histamine-1 (H1) receptor antagonist, mepyramine, but not the H2 receptor antagonist, ranitidine, can block the LH surge in ovariectomized estrogen-treated rats. These data are consistent with the hypothesis that the positive feedback effect of estrogen in the induction of the LH surge involves estrogen-receptive histamine-containing neurons in the tuberomammillary nucleus that relay the steroid signal to LHRH neurons via H1 receptors.