David P. Olson

Osteoblastic cells regulate the haematopoietic stem cell niche

Stem cell fate is influenced by specialized microenvironments that remain poorly defined in mammals. To explore the possibility that haematopoietic stem cells derive regulatory information from bone, accounting for the localization of haematopoiesis in bone marrow, we assessed mice that were genetically altered to produce osteoblast-specific, activated PTH/PTHrP receptors (PPRs). Here we show that PPR-stimulated osteoblastic cells that are increased in number produce high levels of the Notch ligand jagged 1 and support an increase in the number of haematopoietic stem cells with evidence of Notch1 activation in vivo. Furthermore, ligand-dependent activation of PPR with parathyroid hormone (PTH) increased the number of osteoblasts in stromal cultures, and augmented ex vivo primitive haematopoietic cell growth that was abrogated by γ-secretase inhibition of Notch activation. An increase in the number of stem cells was observed in wild-type animals after PTH injection, and survival after bone marrow transplantation was markedly improved. Therefore, osteoblastic cells are a regulatory component of the haematopoietic stem cell niche in vivo that influences stem cell function through Notch activation. Niche constituent cells or signalling pathways provide pharmacological targets with therapeutic potential for stem-cell-based therapies.

An excitatory paraventricular nucleus to AgRP neuron circuit that drives hunger

Hunger is a hard-wired motivational state essential for survival. Agouti-related peptide (AgRP)-expressing neurons in the arcuate nucleus (ARC) at the base of the hypothalamus are crucial to the control of hunger. They are activated by caloric deficiency and, when naturally or artificially stimulated, they potently induce intense hunger and subsequent food intake. Consistent with their obligatory role in regulating appetite, genetic ablation or chemogenetic inhibition of AgRP neurons decreases feeding. Excitatory input to AgRP neurons is important in caloric-deficiency-induced activation, and is notable for its remarkable degree of caloric-state-dependent synaptic plasticity. Despite the important role of excitatory input, its source(s) has been unknown. Here, through the use of Cre-recombinase-enabled, cell-specific neuron mapping techniques in mice, we have discovered strong excitatory drive that, unexpectedly, emanates from the hypothalamic paraventricular nucleus, specifically from subsets of neurons expressing thyrotropin-releasing hormone (TRH) and pituitary adenylate cyclase-activating polypeptide (PACAP, also known as ADCYAP1). Chemogenetic stimulation of these afferent neurons in sated mice markedly activates AgRP neurons and induces intense feeding. Conversely, acute inhibition in mice with caloric-deficiency-induced hunger decreases feeding. Discovery of these afferent neurons capable of triggering hunger advances understanding of how this intense motivational state is regulated.

Central nervous system control of metabolism

Although it is a widely held thought that direct hormone action on peripheral tissues is sufficient to mediate the control of nutrient handling, the role of the central nervous system in certain aspects of metabolism has long been recognized. Furthermore, recent findings have suggested a more general role for the central nervous system in metabolic control, and have revealed the importance of a number of cues and hypothalamic circuits. The brains contributions to metabolic control are more readily revealed and play a crucial part in catabolic states or in hormone deficiencies that mimic starvation.

A neural basis for melanocortin-4 receptor regulated appetite

Pro-opiomelanocortin (POMC)- and agouti-related peptide (AgRP)-expressing neurons of the arcuate nucleus of the hypothalamus (ARC) are oppositely regulated by caloric depletion and coordinately stimulate and inhibit homeostatic satiety, respectively. This bimodality is principally underscored by the antagonistic actions of these ligands at downstream melanocortin-4 receptors (MC4R) in the paraventricular nucleus of the hypothalamus (PVH). Although this population is critical to energy balance, the underlying neural circuitry remains unknown. Using mice expressing Cre recombinase in MC4R neurons, we demonstrate bidirectional control of feeding following real-time activation and inhibition of PVHMC4R neurons and further identify these cells as a functional exponent of ARCAgRP neuron–driven hunger. Moreover, we reveal this function to be mediated by a PVHMC4R→lateral parabrachial nucleus (LPBN) pathway. Activation of this circuit encodes positive valence, but only in calorically depleted mice. Thus, the satiating and appetitive nature of PVHMC4R→LPBN neurons supports the principles of drive reduction and highlights this circuit as a promising target for antiobesity drug development.

Activation of Neural Pathways Associated with Sexual Arousal in Non-Human Primates

To evaluate brain activity associated with sexual arousal, fully conscious male marmoset monkeys were imaged during presentation of odors that naturally elicit high levels of sexual activity and sexual motivation.

Functional imaging of brain activity in conscious monkeys responding to sexually arousing cues

Olfactory cues can elicit intense emotional responses. This study used fMRI in male common marmoset monkeys to identify brain areas associated with sexual arousal in response to odors of ovulating female monkeys. Under light anesthesia, monkeys were secured in a specially designed restrainer and positioned in a 9.4 T magnetic resonance spectrometer. When fully conscious, they were presented with the scents of both ovariectomized and ovulating monkeys. The sexually arousing odors of the ovulating monkeys enhanced signal intensity in the preoptic area and anterior hypothalamus compared to the odors of ovariectomized monkeys. These data corroborate previous findings in monkeys based on invasive electrical lesion and stimulation techniques and demonstrate the feasibility of using non-invasive functional imaging on fully conscious common marmosets to study cue-elicited emotional responses.

An Obligate Role of Oxytocin Neurons in Diet Induced Energy Expenditure

Oxytocin neurons represent one of the major subsets of neurons in the paraventricular hypothalamus (PVH), a critical brain region for energy homeostasis. Despite substantial evidence supporting a role of oxytocin in body weight regulation, it remains controversial whether oxytocin neurons directly regulate body weight homeostasis, feeding or energy expenditure. Pharmacologic doses of oxytocin suppress feeding through a proposed melanocortin responsive projection from the PVH to the hindbrain. In contrast, deficiency in oxytocin or its receptor leads to reduced energy expenditure without feeding abnormalities. To test the physiological function of oxytocin neurons, we specifically ablated oxytocin neurons in adult mice. Our results show that oxytocin neuron ablation in adult animals has no effect on body weight, food intake or energy expenditure on a regular diet. Interestingly, male mice lacking oxytocin neurons are more sensitive to high fat diet-induced obesity due solely to reduced energy expenditure. In addition, despite a normal food intake, these mice exhibit a blunted food intake response to leptin administration. Thus, our study suggests that oxytocin neurons are required to resist the obesity associated with a high fat diet; but their role in feeding is permissive and can be compensated for by redundant pathways.

Gene knockout of Acc2 has little effect on body weight, fat mass, or food intake

Deletion of acetyl CoA carboxylase-2 (Acc2) reportedly causes leanness in the setting of hyperphagia. To determine the cellular basis for these effects, we generated a mouse model in which Acc2 can be selectively deleted by the action of Cre recombinase. Deletion of Acc2 from skeletal muscle, the predominant site of Acc2 expression, had no effect on body weight, food intake, or body composition. When Acc2 was inactivated in the germline, Acc2 knockout (Acc2KO) mice displayed no differences in body weight, food intake, body composition, or glucose homeostasis as compared to controls on chow or high fat diet. Total malonyl CoA content and fatty acid oxidation rates in skeletal muscle of Acc2KO mice were unchanged, suggesting metabolic compensation in response to the loss of Acc2. The limited impact of Acc2 deletion on energy balance raises the possibility that selective pharmacological inhibition of Acc2 for the treatment of obesity may be ineffective.

MC4R-expressing glutamatergic neurons in the paraventricular hypothalamus regulate feeding and are synaptically connected to the parabrachial nucleus

Significance Both in rodents and humans, melanocortin-4 receptors (MC4Rs) suppress appetite and prevent obesity. Unfortunately, the underlying neural mechanisms by which MC4Rs regulate food intake are poorly understood. Unraveling these mechanisms may open up avenues for treating obesity. In the present study we have established that MC4Rs on neurons in the paraventricular nucleus of the hypothalamus are both necessary and sufficient for MC4R control of feeding and that these neurons are glutamatergic and not GABAergic and do not express the neuropeptides oxytocin, corticotropin-releasing hormone, prodynorphin, or vasopressin. In addition, we identify downstream projections from these glutamatergic neurons to the lateral parabrachial nucleus, which could mediate the appetite suppressing effects. Activation of melanocortin-4 receptors (MC4Rs) restrains feeding and prevents obesity; however, the identity, location, and axonal projections of the neurons bearing MC4Rs that control feeding remain unknown. Reexpression of MC4Rs on single-minded 1 (SIM1)+ neurons in mice otherwise lacking MC4Rs is sufficient to abolish hyperphagia. Thus, MC4Rs on SIM1+ neurons, possibly in the paraventricular hypothalamus (PVH) and/or amygdala, regulate food intake. It is unknown, however, whether they are also necessary, a distinction required for excluding redundant sites of action. Hence, the location and nature of obesity-preventing MC4R-expressing neurons are unknown. Here, by deleting and reexpressing MC4Rs from cre-expressing neurons, establishing both necessity and sufficiency, we demonstrate that the MC4R-expressing neurons regulating feeding are SIM1+, located in the PVH, glutamatergic and not GABAergic, and do not express oxytocin, corticotropin-releasing hormone, vasopressin, or prodynorphin. Importantly, these excitatory MC4R-expressing PVH neurons are synaptically connected to neurons in the parabrachial nucleus, which relays visceral information to the forebrain. This suggests a basis for the feeding-regulating effects of MC4Rs.

NPY signaling inhibits extended amygdala CRF neurons to suppress binge alcohol drinking.

Binge alcohol drinking is a tremendous public health problem because it leads to the development of numerous pathologies, including alcohol abuse and anxiety. It is thought to do so by hijacking brain systems that regulate stress and reward, including neuropeptide Y (NPY) and corticotropin-releasing factor (CRF). The central actions of NPY and CRF have opposing functions in the regulation of emotional and reward-seeking behaviors; thus, dysfunctional interactions between these peptidergic systems could be involved in the development of these pathologies. We used converging physiological, pharmacological and chemogenetic approaches to identify a precise neural mechanism in the bed nucleus of the stria terminalis (BNST), a limbic brain region involved in pathological reward and anxiety behaviors, underlying the interactions between NPY and CRF in the regulation of binge alcohol drinking in both mice and monkeys. We found that NPY Y1 receptor (Y1R) activation in the BNST suppressed binge alcohol drinking by enhancing inhibitory synaptic transmission specifically in CRF neurons via a previously unknown Gi-mediated, PKA-dependent postsynaptic mechanism. Furthermore, chronic alcohol drinking led to persistent alterations in Y1R function in the BNST of both mice and monkeys, highlighting the enduring, conserved nature of this effect across mammalian species. Together, these data provide both a cellular locus and signaling framework for the development of new therapeutics for treatment of neuropsychiatric diseases, including alcohol use disorders.