Gonadal steroid hormone regulation of proopiomelanocortin gene expression in neurons that innervate the median eminence of the rat

Photoperiodically driven transcriptome-wide changes in the hypothalamus reveal transcriptional differences between physiologically contrasting seasonal life-history states in migratory songbirds

We investigated time course of photoperiodically driven transcriptional responses in physiologically contrasting seasonal life-history states in migratory blackheaded buntings. Birds exhibiting unstimulated winter phenotype (photosensitive state; responsive to photostimulation) under 6-h short days, and regressed summer phenotype (photorefractory state; unresponsiveness to photostimulation) under 16-h long days, were released into an extended light period up to 22 h of the day. Increased tshβ and dio2, and decreased dio3 mRNA levels in hypothalamus, and low prdx4 and high il1β mRNA levels in blood confirmed photoperiodic induction by hour 18 in photosensitive birds. Further, at hours 10, 14, 18 and 22 of light exposure, the comparison of hypothalamus RNA-Seq results revealed transcriptional differences within and between states. Particularly, we found reduced expression at hour 14 of transthyretin and proopiomelanocortin receptor, and increased expression at hour 18 of apolipoprotein A1 and carbon metabolism related genes in the photosensitive state. Similarly, valine, leucine and isoleucine degradation pathway genes and superoxide dismutase 1 were upregulated, and cocaine- and amphetamine-regulated transcript and gastrin-releasing peptide were downregulated in the photosensitive state. These results show life-history-dependent activation of hypothalamic molecular pathways involved in initiation and maintenance of key biological processes as early as on the first long day.

Cross-Talk between Metabolism and Reproduction: The Role of POMC and SF1 Neurons

Energy homeostasis and reproduction require tight coordination, but the mechanisms underlying their interaction are not fully understood. Two sets of hypothalamic neurons, namely pro-opiomelanocortin (POMC) neurons in the arcuate nucleus and steroidogenic factor-1 (SF1) neurons in the ventromedial hypothalamic nucleus, are emerging as critical nodes where metabolic and reproductive signals communicate. This view is supported by recent genetic studies showing that disruption of metabolic signals (e.g., leptin and insulin) or reproductive signals (e.g., estradiol) in these neurons leads to impaired regulation of both energy homeostasis and fertility. In this review, we will examine the potential mechanisms of neuronal communication between POMC, SF1, and gonadotropin-releasing hormone neurons in the regulation of metabolism and reproduction.

Role of melanocortin in the long-term regulation of energy balance: lessons from a seasonal model

Siberian hamsters express photoperiod-regulated seasonal cycles of body weight and food intake, providing an opportunity to study the role of melanocortin systems in regulating long-term adaptive changes in energy metabolism. These hamsters accumulate intraperitoneal fat reserves when kept in long summer photoperiods, but show a profound long-term decrease in food intake and body weight when exposed to a short winter photoperiod. Icv administration of a MC3/4-R agonist (MTII) potently suppresses food intake in hamsters in both the obese and lean state, indicating the potential for melanocortin systems to regulate energy metabolism in the hypothalamus of the Siberian hamster. Icv treatment with the melanocortin antagonist SHU9119 increases food intake in both seasonal states. Moreover, hamsters bearing neurotoxic lesions, which destroy the majority of POMC expressing neurons in the arcuate nucleus are still able to show seasonal regulation of body weight. These studies in a seasonal model substantiate the view that endogenous melanocortin systems exert a tonic inhibition of food intake in mammals. The observations that this melanocortin tone occurs to a similar extent in both an anabolic state induced by a long day photoperiod, and in a catabolic state induced by a short day photoperiod, suggests that alterations in endogenous melanocortin tone are not the primary cause of the lipolysis, weight-loss and hypophagia which characterize the establishment of the short day-induced overwintering state.

POMC-derived peptides and their biological action

It has long been known that a large number of POMC-related peptides are found in skin. In this introduction I describe the formation of POMC-derived peptides in various tissues to indicate that processing is largely tissue-dependent. I focus on the peptides from the N-terminal fragment, such as gamma-MSH, ACTH and alpha-MSH, and beta-lipopropin as well as beta-endorphin. I touch on the factors that control the synthesis of the various peptides, which are now numerous and varied, and again are tissue specific. The biologic activity of the peptides generated from POMC are described in relation to their possible action in skin. In addition, I describe a new class of peptides induced in skin following injury and which are of great interest.

Arcuate nucleus of the hypothalamus: effects of age and sex

The arcuate nucleus of the hypothalamus (ARN) is involved in a variety of functions known to be sexually dimorphic and altered by aging. Although the effects of sex and age on the synaptic organization and neurochemistry of the ARN have been extensively analyzed, data regarding sex-related differences and age-induced effects on the total number of neurons and volume of the ARN in adult and aged male and female rats are controversial. To address this issue, we have quantitatively analyzed the ARN of male and female Wistar rats aged 6 and 24 months. The optical fractionator, the optical rotator, and the Principle of Cavalieri were used as the estimators of the total number of neurons, mean nuclear volume of ARN neurons, and volume of the ARN, respectively. In addition, a Golgi study was carried out to analyze the dendritic trees of its neurons. We found that in young adult rats, the volume of the ARN is 0.9 mm3 in males and 0.7 mm3 in females, whereas the total number of neurons is 100 x 10(3) in males and 86 x 10(3) in females. ARN neurons of males and females have identical mean nuclear volumes, which we estimated to be 300 microm3. No significant effects of age were found in these parameters, both in males and in females. In adult rats, no sex-related differences were detected in the number of dendritic segments and in the total dendritic length, but the dendritic branching density and the spine density were greater in females than in males. In aged rats there was a significant reduction in the number of dendritic segments, in the total dendritic length, and in the branching and spine densities that, although evident in both sexes, was more marked in females. Our results show that the total number of neurons and the volume of the ARN are sexually dimorphic in adult and aged rats and that neither of these parameters is altered by aging. Conversely, aging induces regressive changes in the dendritic arborizations of ARN neurons of males and females and abolishes the sexual dimorphic pattern of their organization.