Unga A. Unmehopa

Distribution of MT1 melatonin receptor immunoreactivity in the human hypothalamus and pituitary gland: colocalization of MT1 with vasopressin, oxytocin, and corticotropin-releasing hormone.

Melatonin is implicated in numerous physiological processes, including circadian rhythms, stress, and reproduction, many of which are mediated by the hypothalamus and pituitary. The physiological actions of melatonin are mainly mediated by melatonin receptors. We here describe the distribution of the melatonin receptor MT1 in the human hypothalamus and pituitary by immunocytochemistry. MT1 immunoreactivity showed a widespread pattern in the hypothalamus. In addition to the area of the suprachiasmatic nucleus (SCN), a number of novel sites, including the paraventricular nucleus (PVN), periventricular nucleus, supraoptic nucleus (SON), sexually dimorphic nucleus, the diagonal band of Broca, the nucleus basalis of Meynert, infundibular nucleus, ventromedial and dorsomedial nucleus, tuberomamillary nucleus, mamillary body, and paraventricular thalamic nucleus were observed to have neuronal MT1 receptor expression. No staining was observed in the nucleus tuberalis lateralis and bed nucleus of the stria terminalis. The MT1 receptor was colocalized with some vasopressin (AVP) neurons in the SCN, colocalized with some parvocellular and magnocellular AVP and oxytocine (OXT) neurons in the PVN and SON, and colocalized with some parvocellular corticotropin‐releasing hormone (CRH) neurons in the PVN. In the pituitary, strong MT1 expression was observed in the pars tuberalis, while a weak staining was found in the posterior and anterior pituitary. These findings provide a neurobiological basis for the participation of melatonin in the regulation of various hypothalamic and pituitary functions. The colocalization of MT1 and CRH suggests that melatonin might directly modulate the hypothalamus–pituitary–adrenal axis in the PVN, which may have implications for stress conditions such as depression. J. Comp. Neurol. 499:897–910, 2006.

Estrogen receptor‐α distribution in the human hypothalamus in relation to sex and endocrine status

The present study reports the first systematic rostrocaudal distribution of estrogen receptor‐α immunoreactivity (ERα‐ir) in the human hypothalamus and its adjacent areas in young adults. Postmortem material taken from 10 subjects (five male and five female), between 20 and 39 years of age, was investigated. In addition, three age‐matched subjects with abnormal levels of estrogens were studied: a castrated, estrogen‐treated 50‐year‐old male‐to‐female transsexual (T1), a 31‐year‐old man with an estrogen‐producing tumor (S2), and an ovariectomized 46‐year‐old woman (S8). A strong sex difference, with more nuclear ERα‐ir in women, was observed rostrally in the diagonal band of Broca and caudally in the medial mamillary nucleus. Less robust sex differences were observed in other brain areas, with more intense nuclear ERα‐ir in men, e.g., in the sexually dimorphic nucleus of the medial preoptic area, paraventricular nucleus, and lateral hypothalamic area, whereas women had more nuclear ERα‐ir in the suprachiasmatic nucleus and ventromedial nucleus. No nuclear sex differences in ERα were found, e.g., in the central part of the bed nucleus of the stria terminalis. In addition to nuclear staining, ERα‐ir appeared to be sex‐dependently present in the cytoplasm of neurons and was observed in astrocytes, plexus choroideus, and other non‐neuronal cells. ERα‐ir in T1, S2, and S8 suggested that most of the observed sex differences in ERα‐ir are “activational” (e.g., ventromedial nucleus/medial mamillary nucleus) rather than “organizational.” Species similarities and differences in ERα‐ir distribution and possible functional implications are discussed. J. Comp. Neurol. 454:115–139, 2002.

Estrogen‐receptor‐β distribution in the human hypothalamus: Similarities and differences with ERα distribution

This study reports the first systematic rostrocaudal distribution of estrogen receptor beta immunoreactivity (ERβ‐ir) in the human hypothalamus and adjacent areas in five males and five females between 20–39 years of age and compares its distribution to previously reported ERα in the same patients. ERβ‐ir was generally observed more frequently in the cytoplasm than in the nucleus and appeared to be stronger in women. Basket‐like fiber stainings, suggestive for ERβ‐ir in synaptic terminals, were additionally observed in various areas. Men showed more robust nuclear ERβ‐ir than women in the medial part of the bed nucleus of the stria terminalis, paraventricular and paratenial nucleus of the thalamus, while less intense, but more nuclear, ERβ‐ir appeared to be present in, e.g., the BSTc, sexually dimorphic nucleus of the medial preoptic area, diagonal band of Broca and ventromedial nucleus. Women revealed more nuclear ERβ‐ir than men of a low to intermediate level, e.g., in the suprachiasmatic, supraoptic, paraventricular, infundibular, and medial mamillary nucleus. These data indicate potential sex differences in ERβ expression. ERβ‐ir expression patterns in subjects with abnormal hormone levels suggests that there may be sex differences in ERβ‐ir that are “activational” rather than “organizational” in nature. Similarities, differences, potential functional, and clinical implications of the observed ERα and ERβ distributions are discussed in relation to reproduction, autonomic‐function, mood, cognition, and neuroprotection in health and disease. J. Comp. Neurol. 466:251–277, 2003.

Hypocretin and Melanin-Concentrating Hormone in Patients with Huntington Disease

To evaluate whether hypocretin‐1 (orexin‐A) and melanin‐concentrating hormone (MCH) neurotransmission are affected in patients with Huntington disease (HD), we immunohistochemically stained hypocretin and MCH neurons and estimated their total numbers in the lateral hypothalamus of both HD patients and matched controls. In addition, hypocretin‐1 levels were determined in prefrontal cortical tissue and post‐mortem ventricular cerebrospinal fluid (CSF) using a radioimmunoassay. The total number of hypocretin‐1 neurons was significantly reduced by 30% in HD brains (P = 0.015), while the total number of MCH neurons was not significantly altered (P = 0.100). Levels of hypocretin‐1 were 33% lower in the prefrontal cortex of the HD patients (P = 0.025), but ventricular CSF levels were similar to the control values (P = 0.306). Neuronal intranuclear and cytoplasmic inclusions of mutant huntingtin were present in all HD hypothalami, although with a variable distribution across different hypothalamic structures. We found a specific reduction in hypocretin signaling in patients with HD as MCH cell number was not significantly affected. It remains to be shown whether the moderate decrease in hypocretin neurotransmission could contribute to clinical symptoms. As the number of MCH‐expressing neurons was not affected, alterations in MCH signaling are unlikely to have clinical effects in HD patients.

Diminished aromatase immunoreactivity in the hypothalamus, but not in the basal forebrain nuclei in Alzheimer's disease

In previous studies we have shown in Alzheimers disease (AD) an enhanced nuclear estrogen receptor (ER) alpha expression in the cholinergic basal forebrain nuclei, i.e. the vertical limb of the diagonal band of Broca (VDB) and the nucleus basalis of Meynert (NBM), and in a number of hypothalamic nuclei, i.e. the supraoptic nucleus (SON), the infundibular nucleus (INF), the medial mamillary nucleus (MMN). We aimed at determining whether the increase in nuclear ERalpha seen in AD patients was related to a rise in local production of estrogens by aromatase (P-450arom), which is a key enzyme that catalyzes the biosynthesis of estrogens from precursor aromatizable androgens. We confirmed for the first time the presence of aromatase mRNA in neurons and glial cells in the human NBM and the tuberomamillary nucleus by RT-QPCR using laser microdissection. Enhanced aromatase immunoreactivity (ir) was indeed observed in the NBM in AD. However, in contrast a decreased aromatase-ir was found in the SON, INF and MMN of AD patients. In addition, P-450arom-ir was clearly diminished in ependymal and choroid plexus cells in AD. While an increase in aromatase-ir was found in the NBM and SON during normal aging, a decrease in staining was observed in the MMN. No sex differences in young control, elderly control or AD patients were present in any of the nuclei studied. In conclusion, brain P-450arom-ir and the relationship of its regulation with plasma sex steroid levels, estrogen and androgen receptors in the human hypothalamus and basal forebrain are region-specific.

A direct androgenic involvement in the expression of human corticotropin-releasing hormone

We investigated the possibility of a direct action of androgens on the expression of the human corticotropin-releasing hormone (CRH), which plays a central role in the hypothalamic–pituitary–adrenal (HPA)-axis. Colocalization of CRH and nuclear/cytoplasmic androgen receptor (AR) was found in neurons of the paraventricular nucleus (PVN) in the human hypothalamus. A potential androgen-responsive element (ARE) in the human CRH promoter was subsequently analyzed with bandshifts and cotransfections in neuroblastoma cells. In the presence of testosterone, recombinant human AR bound specifically to the CRH-ARE. Expression of AR in combination with testosterone repressed CRH promoter activity through the ARE. We conclude that androgens may directly affect CRH neurons in the human PVN via AR binding to the CRH-ARE, which may have consequences for sex-specific pathogenesis of mood disorders.

Increased arginine vasopressin mRNA expression in the human hypothalamus in depression : A preliminary report

BACKGROUND Elevated arginine vasopressin (AVP) plasma levels have been observed in major depression, particularly in relation to the melancholic subtype. Two hypothalamic structures produce plasma vasopressin: the supraoptic nucleus (SON) and the paraventricular nucleus (PVN). The aim of this study was to establish which structure is responsible for the increased vasopressin plasma levels in depression. METHODS Using in situ hybridization, we determined the amount of vasopressin messenger ribonucleic acid (mRNA) in the PVN and SON in postmortem brain tissue of nine depressed subjects (six with the melancholic subtype) and eight control subjects. RESULTS In the SON, a 60% increase of vasopressin mRNA expression was found in depressed compared with control subjects. In the melancholic subgroup, AVP mRNA expression was significantly increased in both the SON and the PVN compared with control subjects. CONCLUSIONS We found increased AVP gene expression in the SON in depressed subjects. This might partly explain the observed increased vasopressin levels in depression.

Functional neuroanatomy of thyroid hormone feedback in the human hypothalamus and pituitary gland

A major change in thyroid setpoint regulation occurs in various clinical conditions such as critical illness and psychiatric disorders. As a first step towards identifying determinants of these setpoint changes, we have studied the distribution and expression of thyroid hormone receptor (TR) isoforms, type 2 and type 3 deiodinase (D2 and D3), and the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) in the human hypothalamus and anterior pituitary. Although the post-mortem specimens used for these studies originated from patients who had died from many different pathologies, the anatomical distribution of these proteins was similar in all patients. D2 enzyme activity was detectable in the infundibular nucleus/median eminence (IFN/ME) region coinciding with local D2 immunoreactivity in glial cells. Additional D2 immunostaining was present in tanycytes lining the third ventricle. Thyrotropin-releasing hormone (TRH) containing neurons in the paraventricular nucleus (PVN) expressed MCT8, TRs as well as D3. These findings suggest that the prohormone thyroxine (T4) is taken up in hypothalamic glial cells that convert T4 into the biologically active triiodothyronine (T3) via the enzyme D2, and that T3 is subsequently transported to TRH producing neurons in the PVN. In these neurons, T3 may either bind to TRs or be metabolized into inactive iodothyronines by D3. By inference, local changes in thyroid hormone metabolism resulting from altered hypothalamic deiodinase or MCT8 expression may underlie the decrease in TRH mRNA reported earlier in the PVN of patients with critical illness and depression. In the anterior pituitary, D2 and MCT8 immunoreactivity occurred exclusively in folliculostellate (FS) cells. Both TR and D3 immunoreactivity was observed in gonadotropes and to a lesser extent in thyrotropes and other hormone producing cell types. Based upon these neuroanatomical findings, we propose a novel model for central thyroid hormone feedback in humans, with a pivotal role for hypothalamic glial cells and pituitary FS cells in processing and activation of T4. Production and action of T3 appear to occur in separate cell types of the human hypothalamus and anterior pituitary.

Hypothalamic oxytocin mRNA expression and melancholic depression.

K Nieselt, A Schmitt, T Bertsch, K Fassbender, R Spanagel, H Northoff and PJ Gebicke-Haerter Department of Psychopharmacology, Central Institute of Mental Health, Mannheim, Germany; Department of Transfusion Medicine, University of Tuebingen, Tuebingen, Germany; Department of Psychosomatic, Westpfalzklinikum, Kaiserslautern, Germany; Department of Information and Cognitive Sciences, Center for Bioinformatics Tuebingen, University of Tuebingen, Tuebingen, Germany; Department of Psychiatry, Central Institute of Mental Health, Mannheim, Germany; Clinic Nuremberg, Institute of Clinical Chemistry and Laboratory Medicine, Nuremberg, Germany and Department of Neurology, University of Saarland, Homburg/Saar, Germany E-mail: peter.gebicke@zi-mannheim.de These authors contributed equally to this work

Alterations in the histaminergic system in Alzheimer's disease: a postmortem study

Histamine is produced by the hypothalamic tuberomamillary nucleus (TMN). We studied its involvement in Alzheimers disease (AD) by in situ hybridization of histidine decarboxylase (HDC), the key enzyme of histamine production, in 9 AD patients and 9 controls. Additionally, messenger (m) RNA levels of the 4 histamine receptors (H(1-4)R) and of the enzyme involved in histamine metabolism, histamine methyltransferase (HMT), were determined by quantitative polymerase chain reaction (qPCR) in the prefrontal cortex (PFC) in the course of AD (n = 49). Moreover, alterations in glia markers were studied. HDC-mRNA levels in the TMN were unchanged in AD, despite of the reduced number of Nissl-stained neurons (p = 0.001). However, a decrease in HDC-mRNA was observed in its medial part (mTMN; p = 0.047). In the course of AD only females had increased prefrontal cortex expression of histamine receptor-3 (H(3)R) (p = 0.007) and histamine methyltransferase-mRNA (p = 0.011) and of the glia markers, glial fibrillary acidic protein-mRNA, vimentin-mRNA and proteolipid protein-mRNA. These findings indicate the presence of regional changes in the TMN that are at least partly gender-dependent.