Glucose is the essential energy source for the brain, whose deficit, triggered by energy deprivation or therapeutic agents, can be fatal. Increased appetite is the key behavioral defense against hypoglycemia; however, the central pathways involved are not well understood. Here, we describe a glucoprivic feeding pathway by tyrosine hydroxylase (TH)-expressing neurons from nucleus of solitary tract (NTS), which project densely to the hypothalamus and elicit feeding through bidirectional adrenergic modulation of agouti-related peptide (AgRP)-and proopiomelanocortin (POMC)-expressing neurons. Acute chemogenetic inhibition of arcuate nucleus (ARC)-projecting NTS TH neurons or their target, AgRP neurons, impaired glucoprivic feeding induced by 2-Deoxy-D-glucose (2DG) injection. Neuroanatomical tracing results suggested that ARC-projecting orexigenic NTS TH neurons are largely distinct from neighboring catecholamine neurons projecting to parabrachial nucleus (PBN) that promotes satiety. Collectively, we describe a circuit organization in which an ascending pathway from brainstem stimulates appetite through key hunger neurons in the hypothalamus in response to hypoglycemia.

No abstract

Background: Melanin-concentrating hormone (MCH)-expressing neurons have been implicated in regulation of energy homeostasis and reward, yet the role of their electrical activity in short-term appetite and reward modulation has not been fully understood. Objectives: We investigated short-term behavioral and physiological effects of MCH neuron activity manipulations. Methods: We used optogenetic and chemogenetic approaches in Pmch-cre transgenic mice to acutely stimulate/inhibit MCH neuronal activity while probing feeding, locomotor activity, anxiety-like behaviors, glucose homeostasis, and reward. Results: MCH neuron activity is neither required nor sufficient for short-term appetite unless stimulation is temporally paired with consumption. MCH neuronal activation does not affect short-term locomotor activity, but inhibition improves glucose tolerance and is mildly anxiolytic. Finally, using two different operant tasks, we showed that activation of MCH neurons alone is sufficient to induce reward. Conclusions: Our results confirm diverse behavioral/physiological functions of MCH neurons and suggest a direct role in reward function.

Prader-Willi Syndrome (PWS) is a neurodevelopmental disorder causing social and learning deficits, impaired satiety and severe childhood obesity. Genetic underpinning of PWS involves deletion of a chromosomal region with several genes, including MAGEL2, which is abundantly expressed in the hypothalamus. Of appetite regulating hypothalamic cell types, both AGRP and POMC-expressing neurons contain Magel2 transcripts but the functional impact of its deletion on these cells has not been fully characterized. Here, we investigated these key neurons in Magel2-null mice in terms of the activity levels at different energy states as well as their behavioral function. Using cell type specific ex vivo electrophysiological recordings and in vivo chemogenetic activation approaches we evaluated impact of Magel2 deletion on AGRP and POMC-neuron induced changes in appetite. Our results suggest that POMC neuron activity profile as well as its communication with downstream targets is significantly compromised, while AGRP neuron function with respect to short term feeding is relatively unaffected in Magel2 deficiency.

No abstract