Pharmacological targeting of glutamatergic neurons within the brainstem for weight reduction.

Food intake and body weight are tightly regulated by neurons within specific brain regions, including the brainstem, where acute activation of dorsal raphe nucleus (DRN) glutamatergic neurons expressing the glutamate transporter Vglut3 (DRNVglut3) drive a robust suppression of food intake and enhance locomotion. Activating Vglut3 neurons in DRN suppresses food intake and increases locomotion, suggesting that modulating the activity of these neurons might alter body weight. Here, we show that DRNVglut3 neurons project to the lateral hypothalamus (LHA), a canonical feeding center that also reduces food intake. Moreover, chronic DRNVglut3 activation reduces weight in both leptin-deficient (ob/ob) and leptin-resistant diet-induced obese (DIO) male mice. Molecular profiling revealed that the orexin 1 receptor (Hcrtr1) is highly enriched in DRN Vglut3 neurons, with limited expression elsewhere in the brain. Finally, an orally bioavailable, highly selective Hcrtr1 antagonist (CVN45502) significantly reduces feeding and body weight in DIO. Hcrtr1 is also co-expressed with Vglut3 in the human DRN, suggesting that there might be a similar effect in human. These results identify a potential therapy for obesity by targeting DRNVglut3 neurons while also establishing a general strategy for developing drugs for central nervous system disorders.

Functional analysis of distinct populations of subthalamic nucleus neurons on Parkinson's disease and OCD-like behaviors in mice.

The subthalamic nucleus (STN) is a component of the basal ganglia and plays a key role to control movement and limbic-associative functions. STN modulation with deep brain stimulation (DBS) improves the symptoms of Parkinson's disease (PD) and obsessive-compulsive disorder (OCD) patients. However, DBS does not allow for cell-type-specific modulation of the STN. While extensive work has focused on elucidating STN functionality, the understanding of the role of specific cell types is limited. Here, we first performed an anatomical characterization of molecular markers for specific STN neurons. These studies revealed that most STN neurons express Pitx2, and that different overlapping subsets express Gabrr3, Ndnf, or Nos1. Next, we used optogenetics to define their roles in regulating locomotor and limbic functions in mice. Specifically, we showed that optogenetic photoactivation of STN neurons in Pitx2-Cre mice or of the Gabrr3-expressing subpopulation induces locomotor changes, and improves locomotion in a PD mouse model. In addition, photoactivation of Pitx2 and Gabrr3 cells induced repetitive grooming, a phenotype associated with OCD. Repeated stimulation prompted a persistent increase in grooming that could be reversed by fluoxetine treatment, a first-line drug therapy for OCD. Conversely, repeated inhibition of STNGabrr3 neurons suppressed grooming in Sapap3 KO mice, a model for OCD. Finally, circuit and functional mapping of STNGabrr3 neurons showed that these effects are mediated via projections to the globus pallidus/entopeduncular nucleus and substantia nigra reticulata. Altogether, these data identify Gabrr3 neurons as a key population in mediating the beneficial effects of STN modulation thus providing potential cellular targets for PD and OCD drug discovery.

Regulation of Energy Expenditure by Brainstem GABA Neurons.

Homeostatic control of core body temperature is essential for survival. Temperature is sensed by specific neurons, in turn eliciting both behavioral (i.e., locomotion) and physiologic (i.e., thermogenesis, vasodilatation) responses. Here, we report that a population of GABAergic (Vgat-expressing) neurons in the dorsolateral portion of the dorsal raphe nucleus (DRN), hereafter DRNVgat neurons, are activated by ambient heat and bidirectionally regulate energy expenditure through changes in both thermogenesis and locomotion. We find that DRNVgat neurons innervate brown fat via a descending projection to the raphe pallidus (RPa). These neurons also densely innervate ascending targets implicated in the central regulation of energy expenditure, including the hypothalamus and extended amygdala. Optogenetic stimulation of different projection targets reveals that DRNVgat neurons are capable of regulating thermogenesis through both a "direct" descending pathway through the RPa and multiple "indirect" ascending pathways. This work establishes a key regulatory role for DRNVgat neurons in controlling energy expenditure.

Functional analysis reveals differential effects of glutamate and MCH neuropeptide in MCH neurons.

OBJECTIVES: Melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus (LH) regulate food intake and body weight, glucose metabolism and convey the reward value of sucrose. In this report, we set out to establish the respective roles of MCH and conventional neurotransmitters in these neurons. METHODS: MCH neurons were profiled using Cre-dependent molecular profiling technologies (vTRAP). MCHCre mice crossed to Vglut2fl/flmice or to DTRfl/flwere used to identify the role of glutamate in MCH neurons. We assessed metabolic parameters such as body composition, glucose tolerance, or sucrose preference. RESULTS: We found that nearly all MCH neurons in the LH are glutamatergic and that a loss of glutamatergic signaling from MCH neurons from a glutamate transporter (VGlut2) knockout leads to a reduced weight, hypophagia and hyperkinetic behavior with improved glucose tolerance and a loss of sucrose preference. These effects are indistinguishable from those seen after ablation of MCH neurons. These findings are in contrast to those seen in mice with a knockout of the MCH neuropeptide, which show normal glucose preference and do not have improved glucose tolerance. CONCLUSIONS: Overall, these data show that the vast majority of MCH neurons are glutamatergic, and that glutamate and MCH signaling mediate partially overlapping functions by these neurons, presumably by activating partially overlapping postsynaptic populations. The diverse functional effects of MCH neurons are thus mediated by a composite of glutamate and MCH signaling.

Lack of exacerbation of neurodegeneration in a double transgenic mouse model of mutant LRRK2 and tau.

LRRK2 (leucine-rich repeat kinase) mutations constitute the most common cause of familial Parkinson's disease (PD). Microtubule-associated protein tau mutations cause a group of neurodegenerative diseases termed tauopathies. Genome-wide association studies show that, after α-synuclein, polymorphisms in the tau gene have the second strongest genetic association with PD. In a proportion of PD patients with LRRK2 mutations, and in several transgenic animal models of LRRK2, tau hyperphosphorylation and aggregation, rather than α-synuclein aggregation, are the most prominent neuropathologic findings. To further examine the relationship between LRRK2 and tau, we crossed LRRK2 R1441G BAC transgenic mice (Mus musculus) with tau P301S mutant transgenic mice and characterized their behavioral, neuropathological and biochemical phenotypes. We found that the combination of the two mutations does not increase tau hyperphosphorylation or aggregation nor does it exacerbate the behavioral and pathological deficits previously described in the tau P301S mice. The double-mutant mice had no shortening of lifespan and no worsening of motor or memory deficits. There was no increase in the aggregation of tau or α-synuclein. Dopaminergic neuron cell counts and striatal levels of dopamine and its metabolites were unaltered. There was no exacerbation of cell loss, microgliosis or astrogliosis in multiple brain regions. These results suggest that LRRK2 and tau do not interact to exacerbate behavioral, biochemical or pathological abnormalities in neurodegeneration and that LRRK2 and tau exert their pathogenic effects through independent mechanisms.