Identification of Hypothalamic Sites that Control Puberty Onset and Sexual Maturation.

This dissertation seeks to identify hypothalamic neuronal populations that regulate puberty onset and sexual maturation as part of the hypothalamic-pituitary-gonadal (HPG) axis. The HPG axis integrates a variety of signals, including the adipose-derived hormone leptin and the gonadal steroid hormone estradiol. These hormones function either as permissive signals (leptin) or stimulatory signals (estradiol) to affect commencement and progression of puberty, as well as to maintain adult fertility. First, we investigated the role of direct leptin action through its receptor LepRb in neurons expressing Nos1. Based on previous data, we hypothesized that the reproductive axis would be significantly affected by genetic ablation of LepRb from Nos1-expressing neurons. The deletion resulted in only slightly delayed sexual maturation in females and unaffected overall fertility. Additionally, these mice are profoundly obese and have disrupted energy balance. Thus, leptin action on Nos1-expressing neurons is not critical for fertility, but is necessary for proper energy balance. Second, we determined whether direct estrogen action through estrogen receptor alpha (ER-alpha) on arcuate nucleus (ARC) kisspeptin neurons is required for estrogen negative feedback. In females, loss of ER-alpha from either ARC kisspeptin or all kisspeptin neurons resulted in a similar phenotype of precocious puberty and incomplete sexual maturation. While both conditional knockouts exhibit reduced negative feedback, there is remaining estrogen negative feedback, likely at the level of the pituitary gland. Thus, while ARC kisspeptin neurons may not be the only neuronal population involved in estrogen negative feedback in females, ER-alpha in these neurons is critical for restraint of puberty onset and normal reproductive function. Finally, we assessed whether ARC kisspeptin neurons were critical for estrogen negative feedback in the male mouse. Surprisingly, we found that negative feedback was more severely affected in male mice lacking ER-alpha in all kisspeptin neurons than in mice lacking ER-alpha specifically in ARC kisspeptin neurons. Here, we have identified sites of leptin and estrogen action within the hypothalamus whose function is to modulate the reproductive axis. Future work should focus on the mechanism, potentially through modulation of GnRH neuron function, whereby loss of LepRb or ER-alpha affects puberty onset, sexual maturation and fertility.PHDNeuroscienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102412/1/mgreenw_1.pd

Nucleus of the Solitary Tract Serotonin 5-HT2C Receptors Modulate Food Intake

The authors wish to thank members of staff of the Medical Research Facility, University of Aberdeen, Ms. Raffaella Chianese and Dr. Susan Jalicy, for technical assistance. PX330 and PX552 plasmids were a gift from Prof. Feng Zhang (Massachusetts Institute of Technology, Massachusetts, USA). DREADD vectors were a gift from Prof. Bryan Roth (University of North Carolina at Chapel Hill, North Carolina, USA). PomcDsRED and PomcNEO mice were a gift from Prof. Malcolm Low (University of Michigan, Michigan, USA). Codes to analyze operant-responding for food were a gift from Dr. Vladimir Orduña Trujillo (National Autonomous University of Mexico, Mexico). This work was supported by the Wellcome Trust (L.K.H.; WT098012), Wellcome Trust and the University of Aberdeen (G.D.; 105625/Z/14/Z), Biotechnology and Biological Sciences Research Council (L.K.H., BB/K001418/1, BB/N017838/1; and J.J.R., BB/K017772/1), Medical Research Council (J.J.R., MR/L002620/1; G.D., MR/P009824/1; L.K.H., J.J.R., G.D., MC/PC/15077), British Society of Neuroendocrinology (G.D.), NIH and the Marilyn H. Vincent Foundation (M.G.M.; DK056731, DK034933).Peer reviewedPublisher PD

Sex difference in physical activity, energy expenditure and obesity driven by a subpopulation of hypothalamic POMC neurons.

OBJECTIVE: Obesity is one of the primary healthcare challenges of the 21st century. Signals relaying information regarding energy needs are integrated within the brain to influence body weight. Central among these integration nodes are the brain pro-opiomelanocortin (POMC) peptides, perturbations of which disrupt energy balance and promote severe obesity. However, POMC neurons are neurochemically diverse and the crucial source of POMC peptides that regulate energy homeostasis and body weight remains to be fully clarified. METHODS: Given that a 5-hydroxytryptamine 2c receptor (5-HT2CR) agonist is a current obesity medication and 5-HT2CR agonist's effects on appetite are primarily mediated via POMC neurons, we hypothesized that a critical source of POMC regulating food intake and body weight is specifically synthesized in cells containing 5-HT2CRs. To exclusively manipulate Pomc synthesis only within 5-HT2CR containing cells, we generated a novel 5-HT 2C R (CRE) mouse line and intercrossed it with Cre recombinase-dependent and hypothalamic specific reactivatable Pomc (NEO) mice to restrict Pomc synthesis to the subset of hypothalamic cells containing 5-HT2CRs. This provided a means to clarify the specific contribution of a defined subgroup of POMC peptides in energy balance and body weight. RESULTS: Here we transform genetically programed obese and hyperinsulinemic male mice lacking hypothalamic Pomc with increased appetite, reduced physical activity and compromised brown adipose tissue (BAT) into lean, healthy mice via targeted restoration of Pomc function only within 5-HT2CR expressing cells. Remarkably, the same metabolic transformation does not occur in females, who despite corrected feeding behavior and normalized insulin levels remain physically inactive, have lower energy expenditure, compromised BAT and develop obesity. CONCLUSIONS: These data provide support for the functional heterogeneity of hypothalamic POMC neurons, revealing that Pomc expression within 5-HT2CR expressing neurons is sufficient to regulate energy intake and insulin sensitivity in male and female mice. However, an unexpected sex difference in the function of this subset of POMC neurons was identified with regard to energy expenditure. We reveal that a large sex difference in physical activity, energy expenditure and the development of obesity is driven by this subpopulation, which constitutes approximately 40% of all POMC neurons in the hypothalamic arcuate nucleus. This may have broad implications for strategies utilized to combat obesity, which at present largely ignore the sex of the obese individual

Activation of Ventral Tegmental Area 5-HT2C Receptors Reduces Incentive Motivation

FUNDING AND DISCLOSURE The research was funded by Wellcome Trust (WT098012) to LKH; and National Institute of Health (DK056731) and the Marilyn H. Vincent Foundation to MGM. The University of Michigan Transgenic Core facility is partially supported by the NIH-funded University of Michigan Center for Gastrointestinal Research (DK034933). The remaining authors declare no conflict of interest. ACKNOWLEDGMENTS We thank Dr Celine Cansell, Ms Raffaella Chianese and the staff of the Medical Research Facility for technical assistance. We thank Dr Vladimir Orduña for the scientific advice and technical assistance.Peer reviewedPublisher PD

Molecular Mapping of the Neural Pathways Linking Leptin to the Neuroendocrine Reproductive Axis

Leptin communicates with the neuroendocrine reproductive axis via multiple populations of LepRb neurons that lie afferent to both Kiss1 and GnRH neurons