Lateral Hypothalamic Mc3R-Expressing Neurons Modulate Locomotor Activity, Energy Expenditure, and Adiposity in Male Mice.

The central melanocortin system plays a crucial role in the control of energy balance. Although the decreased energy expenditure and increased adiposity of melanocortin-3 receptor (Mc3R)-null mice suggest the importance of Mc3R-regulated neurons in energy homeostasis, the roles for specific subsets of Mc3R neurons in energy balance have yet to be determined. Because the lateral hypothalamic area (LHA) contributes to the control of energy expenditure and feeding, we generated Mc3rcre mice to determine the roles of LHA Mc3R (Mc3RLHA) neurons in energy homeostasis.

Specific subpopulations of hypothalamic leptin receptor-expressing neurons mediate the effects of early developmental leptin receptor deletion on energy balance.

Objective: To date, early developmental ablation of leptin receptor (LepRb) expression from circumscribed populations of hypothalamic neurons (e.g., arcuate nucleus (ARC) Pomc- or Agrp-expressing cells) has only minimally affected energy balance.

ERα in Tac2 Neurons Regulates Puberty Onset in Female Mice.

A variety of data suggest that estrogen action on kisspeptin (Kiss1)-containing arcuate nucleus neurons (which coexpress Kiss1, neurokinin B (the product of Tac2) and dynorphin (KNDy) neurons restrains reproductive onset and function, but roles for estrogen action in these Kiss1 neurons relative to a distinct population of rostral hypothalamic Kiss1 neurons (which does not express Tac2 or dynorphin) have not been directly tested. To test the role for estrogen receptor (ER)α in KNDy cells, we thus generated Tac2(Cre) and Kiss1(Cre) knock-in mice and bred them onto the Esr1(flox) background to ablate ERα specifically in Tac2-expressing cells (ERα(Tac2)KO mice) or all Kiss1 cells (ERα(Kiss1)KO mice), respectively. Most ERα-expressing Tac2 neurons represent KNDy cells.

TRAP-seq defines markers for novel populations of hypothalamic and brainstem LepRb neurons.

Objective: Leptin acts via its receptor (LepRb) on multiple subpopulations of LepRb neurons in the brain, each of which controls specific aspects of energy balance. Despite the importance of LepRb-containing neurons, the transcriptome and molecular identity of many LepRb subpopulations remain undefined due to the difficulty of studying the small fraction of total cells represented by LepRb neurons in heterogeneous brain regions. Here we sought to examine the transcriptome of LepRb neurons directly and identify markers for functionally relevant LepRb subsets.

Individual Differences in Cue-Induced Motivation and Striatal Systems in Rats Susceptible to Diet-Induced Obesity.

Pavlovian cues associated with junk-foods (caloric, highly sweet, and/or fatty foods), like the smell of brownies, can elicit craving to eat and increase the amount of food consumed. People who are more susceptible to these motivational effects of food cues may have a higher risk for becoming obese. Further, overconsumption of junk-foods leading to the development of obesity may itself heighten attraction to food cues.

Taste responsiveness to sweeteners is resistant to elevations in plasma leptin.

There is uncertainty about the relationship between plasma leptin and sweet taste in mice. Whereas 2 studies have reported that elevations in plasma leptin diminish responsiveness to sweeteners, another found that they enhanced responsiveness to sucrose. We evaluated the impact of plasma leptin on sweet taste in C57BL/6J (B6) and leptin-deficient ob/ob mice.

Ventral tegmental area neurotensin signaling links the lateral hypothalamus to locomotor activity and striatal dopamine efflux in male mice.

Projections from the lateral hypothalamic area (LHA) innervate components of the mesolimbic dopamine (MLDA) system, including the ventral tegmental area (VTA) and nucleus accumbens (NAc), to modulate motivation appropriately for physiologic state. Neurotensin (NT)-containing LHA neurons respond to multiple homeostatic challenges and project to the VTA, suggesting that these neurons could link such signals to MLDA function. Indeed, we found that pharmacogenetic activation of LHA NT neurons promoted prolonged DA-dependent locomotor activity and NAc DA efflux, suggesting the importance of VTA neurotransmitter release by LHA NT neurons for the control of MLDA function.

A parabrachial-hypothalamic cholecystokinin neurocircuit controls counterregulatory responses to hypoglycemia.

Hypoglycemia engenders an autonomically mediated counterregulatory (CR)-response that stimulates endogenous glucose production to maintain concentrations within an appropriate physiological range. Although the involvement of the brain in preserving normoglycemia has been established, the neurocircuitry underlying centrally mediated CR-responses remains unclear. Here we demonstrate that lateral parabrachial nucleus cholecystokinin (CCK(LPBN)) neurons are a population of glucose-sensing cells (glucose inhibited) with counterregulatory capacity.

Leptin-inhibited PBN neurons enhance responses to hypoglycemia in negative energy balance.

Hypoglycemia initiates the counter-regulatory response (CRR), in which the sympathetic nervous system, glucagon and glucocorticoids restore glucose to appropriate concentrations. During starvation, low leptin levels restrain energy utilization, enhancing long-term survival. To ensure short-term survival during hypoglycemia in fasted animals, the CRR must overcome this energy-sparing program and nutrient depletion.

Leptin acts via lateral hypothalamic area neurotensin neurons to inhibit orexin neurons by multiple GABA-independent mechanisms.

The adipocyte-derived hormone leptin modulates neural systems appropriately for the status of body energy stores. Leptin inhibits lateral hypothalamic area (LHA) orexin (OX; also known as hypocretin)-producing neurons, which control feeding, activity, and energy expenditure, among other parameters. Our previous results suggest that GABAergic LHA leptin receptor (LepRb)-containing and neurotensin (Nts)-containing (LepRb(Nts)) neurons lie in close apposition with OX neurons and control Ox mRNA expression.

Leptin acts independently of food intake to modulate gut microbial composition in male mice.

Shifts in the composition of gut bacterial populations can alter host metabolism and may contribute to the pathogenesis of metabolic disorders, including obesity. Mice deficient in leptin action are obese with altered microbiota and increased susceptibility to certain intestinal pathogens. Because antimicrobial peptides (AMPs) secreted by Paneth cells represent a major mechanism by which the host influences the gut microbiome, we examined the mRNA expression of gut AMPs, several of which were decreased in leptin receptor (LepR)-deficient db/db mice, suggesting a potential role for AMP modulation of microbiota composition.

Leptin action through hypothalamic nitric oxide synthase-1-expressing neurons controls energy balance.

Few effective measures exist to combat the worldwide obesity epidemic(1), and the identification of potential therapeutic targets requires a deeper understanding of the mechanisms that control energy balance. Leptin, an adipocyte-derived hormone that signals the long-term status of bodily energy stores, acts through multiple types of leptin receptor long isoform (LepRb)-expressing neurons (called here LepRb neurons) in the brain to control feeding, energy expenditure and endocrine function(2-4). The modest contributions to energy balance that are attributable to leptin action in many LepRb populations(5-9) suggest that other previously unidentified hypothalamic LepRb neurons have key roles in energy balance.

Leptin action via LepR-b Tyr1077 contributes to the control of energy balance and female reproduction.

Leptin action in the brain signals the repletion of adipose energy stores, suppressing feeding and permitting energy expenditure on a variety of processes, including reproduction. Leptin binding to its receptor (LepR-b) promotes the tyrosine phosphorylation of three sites on LepR-b, each of which mediates distinct downstream signals. While the signals mediated by LepR-b Tyr1138 and Tyr985 control important aspects of energy homeostasis and LepR-b signal attenuation, respectively, the role of the remaining LepR-b phosphorylation site (Tyr1077) in leptin action has not been studied.

Molecular mapping of mouse brain regions innervated by leptin receptor-expressing cells.

Leptin acts via the long form of the leptin receptor (LepRb) on specialized sets of neurons in the brain to modulate diverse functions in concert with energy stores. Previous studies have revealed the distribution of LepRb-expressing neurons in the brain but not the regions to which LepRb neurons project to mediate downstream leptin actions. We utilized LepRb-cre in combination with cre-inducible enhanced green fluorescent protein (EGFP) and farnesylated EGFP (EGFPf) mouse reporter strains to visualize LepRb neurons and their projections, respectively, throughout the brain.

Leptin signaling modulates the activity of urocortin 1 neurons in the mouse nonpreganglionic Edinger-Westphal nucleus.

A recent study systematically characterized the distribution of the long form of the leptin receptor (LepRb) in the mouse brain and showed substantial LepRb mRNA expression in the nonpreganglionic Edinger-Westphal nucleus (npEW) in the rostroventral part of the midbrain. This nucleus hosts the majority of urocortin 1 (Ucn1) neurons in the rodent brain, and because Ucn1 is a potent satiety hormone and electrical lesioning of the npEW strongly decreases food intake, we have hypothesized a role of npEW-Ucn1 neurons in leptin-controlled food intake. Here, we show by immunohistochemistry that npEW-Ucn1 neurons in the mouse contain LepRb and respond to leptin administration with induction of the Janus kinase 2-signal transducer and activator of transcription 3 pathway, both in vivo and in vitro.

Large litter rearing enhances leptin sensitivity and protects selectively bred diet-induced obese rats from becoming obese.

Because rearing rats in large litters (LLs) protects them from becoming obese, we postulated that LL rearing would protect rats selectively bred to develop diet-induced obesity (DIO) from becoming obese by overcoming their inborn central leptin resistance. Male and female DIO rats were raised in normal litters (NLs; 10 pups/dam) or LLs (16 pups/dam) and assessed for anatomical, biochemical, and functional aspects of leptin sensitivity at various ages when fed low-fat chow or a 31% fat high-energy (HE) diet. LL rearing reduced plasma leptin levels by postnatal day 2 (P2) and body weight gain by P8.

Ventral tegmental area leptin receptor neurons specifically project to and regulate cocaine- and amphetamine-regulated transcript neurons of the extended central amygdala.

Leptin acts via its receptor (LepRb) to regulate neural circuits in concert with body energy stores. In addition to acting on a number of hypothalamic structures, leptin modulates the mesolimbic dopamine (DA) system. To determine the sites at which LepRb neurons might directly influence the mesolimbic DA system, we examined the distribution of LepRb neurons and their projections within mesolimbic brain regions.

Insufficiency of Janus kinase 2-autonomous leptin receptor signals for most physiologic leptin actions.

Objective: Leptin acts via its receptor (LepRb) to signal the status of body energy stores. Leptin binding to LepRb initiates signaling by activating the associated Janus kinase 2 (Jak2) tyrosine kinase, which promotes the phosphorylation of tyrosine residues on the intracellular tail of LepRb. Two previously examined LepRb phosphorylation sites mediate several, but not all, aspects of leptin action, leading us to hypothesize that Jak2 signaling might contribute to leptin action independently of LepRb phosphorylation sites.

Three weeks of postweaning exercise in DIO rats produces prolonged increases in central leptin sensitivity and signaling.

In rats selectively bred to develop diet-induced obesity (DIO) 3 wk of postweaning exercise reduces weight and adipose regain for 10 wk after exercise cessation, despite intake of 31% fat high-energy (HE) diet. To test the hypothesis that this effect is due to increased central leptin sensitivity, 4-wk-old DIO rats were fed the HE diet and left sedentary (Sed), exercised for 3 wk, and then remained sedentary for 10 additional weeks (Ex/Sed) or continued exercise for a full 13 wk (Ex). After 3 wk, leptin (5 mg/kg ip) induced a 36% decrease in 24-h food intake in Ex rats, while Sed rats had no change in 24-h intake.

Hypothalamic neural projections are permanently disrupted in diet-induced obese rats.

The arcuate nucleus of the hypothalamus (ARH) is a key component of hypothalamic pathways regulating energy balance, and leptin is required for normal development of ARH projections. Diet-induced obesity (DIO) has a polygenic mode of inheritance, and DIO individuals develop the metabolic syndrome when a moderate amount of fat is added to the diet. Here we demonstrate that rats selectively bred to develop DIO, which are known to be leptin resistant before they become obese, have defective ARH projections that persist into adulthood.

Three weeks of early-onset exercise prolongs obesity resistance in DIO rats after exercise cessation.

We assessed the effect of early-onset exercise as a means of preventing childhood obesity using juvenile male rats selectively bred to develop diet-induced obesity (DIO) or to be diet resistant (DR) when fed a 31% fat high-energy diet. Voluntary wheel running begun at 36 days of age selectively reduced adiposity in DIO vs. DR rats.

Role of exercise in the central regulation of energy homeostasis and in the prevention of obesity.

Many of the small percentage of previously obese humans who successfully maintain weight loss report high levels of physical activity, suggesting a role for exercise in the maintenance of their lower body weights. The rat model of diet-induced obesity (DIO) has been particularly useful, since it shares several common characteristics with human obesity and, unlike the human condition, allows a thorough investigation of the effects of exercise on the central pathways which regulate energy homeostasis. In rats with DIO, voluntary wheel running selectively reduces adiposity without causing a compensatory increase in energy intake.