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 pituitar

Hypothalamic NPY and agouti-related protein are increased in human illness but not in Prader-Willi syndrome and other obese subjects

Animal studies have demonstrated the importance of orexigenic NPY and agouti-related protein (AGRP) hypothalamic neurons, which are inhibited by the adipocyte hormone leptin, in the regulation of body weight and neuroendocrine secretion. We have examined NPY and AGRP neurons in postmortem human hypothalami from controls, Prader-Willi syndrome and other obese subjects, using quantitative immunocytochemistry (ICC) and in situ hybridization, to identify causes of leptin resistance in human obesity. Using combined ICC and in situ hybridization, AGRP, but not POMC, was colocalized with NPY in infundibular nucleus neurons. Infundibular nucleus (including median eminence) NPY ICC staining or mRNA expression, and AGRP ICC staining, increased with premorbid illness duration. NPY ICC staining and mRNA expression were reduced in obese subjects, but AGRP ICC staining was unchanged, correcting for illness duration. This suggests normal responses of NPY and AGRP neurons to peripheral signals, such as leptin and insulin, in human illness and obesity. The pathophysiology of obesity and illness-associated anorexia appear to lie in downstream or separate neuronal circuits, but the infundibular neurons may mediate neuroendocrine responses to illness. The implications for pharmacological treatment of human obesity are discusse

Estrogen-receptor-beta distribution in the human hypothalamus: Similarities and differences with ER alpha distribution

This study reports the first systematic rostrocaudal distribution of estrogen receptor beta immunoreactivity (ERbeta-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 ERalpha in the same patients. ERbeta-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 ERbeta-ir in synaptic terminals, were additionally observed in various areas. Men showed more robust nuclear ERbeta-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, ERbeta-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 ERbeta-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 ERbeta expression. ERbeta-ir expression patterns in subjects with abnormal hormone levels suggests that there may be sex differences in ERbeta-ir that are "activational" rather than "organizational" in nature. Similarities, differences, potential functional, and clinical implications of the observed ERalpha and ERbeta distributions are discussed in relation to reproduction, autonomic-function, mood, cognition, and neuroprotection in health and disease. (C) 2003 Wiley-Liss, In

The effects of overnight nutrient intake on hypothalamic inflammation in a free-choice diet-induced obesity rat model

Consumption of fat and sugar induces hyperphagia and increases the prevalence of obesity and diabetes type 2. Low-grade inflammation in the hypothalamus, a key brain area involved in the regulation of energy homeostasis is shown to blunt signals of satiety after long term high fat diet. The fact that this mechanism can be activated after a few days of hyperphagia before apparent obesity is present led to our hypothesis that hypothalamic inflammation is induced with fat and sugar consumption. Here, we used a free-choice high-fat high-sugar (fcHFHS) diet-induced obesity model and tested the effects of differential overnight nutrient intake during the final experimental night on markers of hypothalamic inflammation. Male Wistar rats were fed a control diet or fcHFHS diet for one week, and assigned to three different feeding conditions during the final experimental night: 1) fcHFHS-fed, 2) fed a controlled amount of chow diet, or 3) fasted. RT-qPCR and Western blot were utilized to measure hypothalamic gene and protein expression, of cytokines and intermediates of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Lastly, we investigated the effects of acute fat intake on markers of hypothalamic inflammation in fat-naïve rats. fcHFHS/fcHFHS rats consumed more calories, increased adipose tissue, and showed elevated expression of hypothalamic inflammation markers (increased phosphorylation of NF-κB protein, Nfkbia and Il6 gene expression) compared to chow/chow rats. These effects were evident in rats consuming relative high amounts of fat. Removal of the fat and sugar, or fasting, during the final experimental night ameliorated hypothalamic inflammation. Finally, a positive correlation was observed between overnight acute fat consumption and hypothalamic NF-κB phosphorylation in fat-naïve rats. Our data indicate that one week of fcHFHS diet, and especially the fat component, promotes hypothalamic inflammation, and removal of the fat and sugar component reverses these detrimental effects

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

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. 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. 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. We found increased AVP gene expression in the SON in depressed subjects. This might partly explain the observed increased vasopressin levels in depressio

Ultrastructural localization and expression of TRPM1 in the human retina

Transient receptor potential subfamily melastatin (TRPM)1 cation channels of retinal ON-bipolar cells are modulated via a mGluR6 (GMR6) signaling cascade. While light-microscopy shows these channels are located on the tips of ON-bipolar cells dendrites, near rod and cone synaptic ribbons, TRPM1 localization at the electron-microscope level is currently not described. The authors report here the ultrastructural localization of TRPM1 in the human retina. TRPM1 was localized in postmortem human retinas by immunohistochemistry at both the light and electron microscope levels. Additionally, TRPM1 expression was studied using in situ hybridization, laser dissection microscopy, and PCR techniques. TRPM1-immunoreactivity was located on the dendrites and soma of ON-bipolar cells at the light microscope level. At the electron microscope level TRPM1-immunoreactivity was located on the tips of ON-bipolar cell dendrites that were invaginating cone pedicles and rod spherules. In addition, TRPM1-immunoreactivity was occasionally found on the rod spherules ribbons, suggesting that at least a proportion of rods may also express TRPM1. In situ hybridization showed TRPM1 encoding RNA in inner nuclear layer somata and in some photoreceptors. The presence of TRPM1-RNA in photoreceptors was confirmed by PCR in pure photoreceptor material obtained with a laser dissection microscope. In the human retina TRPM1 is expressed on ON-bipolar cell dendrites that invaginate photoreceptor terminals. TRPM1 is also expressed on the synaptic ribbons of a subclass of rods, suggesting a dual function for TRPM1 in the ON-pathwa

A Free-Choice High-Fat High-Sugar Diet Alters Day-Night Gene Expression in Reward-Related Brain Areas in Rats

Under normal light-dark conditions, nocturnal rodents consume most of their food during the dark period. Diets high in fat and sugar, however, may affect the day-night feeding rhythm resulting in a higher light phase intake. In vitro and in vivo studies showed that nutrients affect clock-gene expression. We therefore hypothesized that overconsuming fat and sugar alters clock-gene expression in brain structures important for feeding behavior. We determined the effects of a free-choice high-fat high-sugar (fcHFHS) diet on clock-gene expression in rat brain areas related to feeding and reward and compared them with chow-fed rats. Consuming a fcHFHS diet for 6 weeks disrupted day-night differences in Per2 mRNA expression in the nucleus accumbens (NAc) and lateral hypothalamus but not in the suprachiasmatic nucleus, habenula, and ventral tegmental area. Furthermore, short-term sugar drinking, but not fat feeding, upregulates Per2 mRNA expression in the NAc. The disruptions in day-night differences in NAc Per2 gene expression were not accompanied by altered day-night differences in the mRNA expression of peptides related to food intake. We conclude that the fcHFHS diet and acute sugar drinking affect Per2 gene expression in areas involved in food reward; however, this is not sufficient to alter the day-night pattern of food intake

The effect of diet interventions on hypothalamic nutrient sensing pathways in rodents

The hypothalamus plays a fundamental role in regulating homeostatic processes including regulation of food intake. Food intake is driven in part by energy balance, which is sensed by specific brain structures through signaling molecules such as nutrients and hormones. Both circulating glucose and fatty acids decrease food intake via a central mechanism involving the hypothalamus and brain stem. Besides playing a role in signaling energy status, glucose and fatty acids serve as fuel for neurons. This review focuses on the effects of glucose and fatty acids on hypothalamic pathways involved in regulation of energy metabolism as well as on the role of the family of peroxisome proliferator activated receptors (PPARs) which are implicated in regulation of central energy homeostasis. We further discuss the effects of different hypercaloric diets on these pathways

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

In previous studies we have shown in Alzheimer's 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. (C) 2004 Elsevier Inc. All rights reserve

Thyroid hormone receptor expression in the human hypothalamus and anterior pituitary

In the present study, we describe for the first time the distribution of thyroid hormone receptor (TR) isoforms in the human postmortem hypothalamus and anterior pituitary using immunocytochemistry. We used a set of polyclonal antisera raised against the specific isoforms of the human TR. The distribution of TR alpha1, alpha2, beta1, and beta2 was studied in consecutive sections of six hypothalami and pituitaries. Staining intensity showed strong interindividual variation but was consistently present in the infundibular nucleus, paraventricular nucleus, and supraoptic nucleus. In addition, strong TR immunoreactivity was observed in the anterior pituitary. Neuropeptide Y and proopiomelanocortin mRNA-positive cells in the infundibular nucleus, which were studied in three other hypothalami, appeared not to express Tits, and thus, the neurons expressing TRs in the human mediobasal hypothalamus remain to be characterize