Activation of ChAT+ neuron in dorsal motor vagus (DMV) increases blood glucose through the regulation of hepatic gene expression in mice

The brain and peripheral organs communicate through hormones and neural connections. Proper communication is required to maintain normal whole-body energy homeostasis. In addition to endocrine system, from the perspective of neural connections for metabolic homeostasis, the role of the sympathetic nervous system has been extensively studied, but understanding of the parasympathetic nervous system is limited. The liver plays a central role in glucose and lipid metabolism. This study aimed to clarify the innervation of parasympathetic nervous system in the liver and its functional roles in metabolic homeostasis. The liver-specific parasympathetic nervous system innervation (PNS) was shown by tissue clearing, immunofluorescence and transgenic mice at the three-dimensional histological level. The parasympathetic efferent signals were manipulated using a chemogenetic technique and the activation of ChAT+ parasympathetic neurons in dorsal motor vagus (DMV) results in the increased blood glucose through the elevated hepatic gluconeogenic and lipogenic gene expression in the liver. Thus, our study showed the evidence of ChAT+ parasympathetic neurons in the liver and its role for hepatic parasympathetic nervous signaling in glucose homeostasis through the regulation of hepatic gene expression.

Lateral hypothalamic leptin receptor neurons drive hunger-gated food-seeking and consummatory behaviours in male mice

For survival, it is crucial for eating behaviours to be sequenced through two distinct seeking and consummatory phases. Heterogeneous lateral hypothalamus (LH) neurons are known to regulate motivated behaviours, yet which subpopulation drives food seeking and consummatory behaviours have not been fully addressed. Here, in male mice, fibre photometry recordings demonstrated that LH leptin receptor (LepR) neurons are correlated explicitly in both voluntary seeking and consummatory behaviours. Further, micro-endoscope recording of the LH^LepR neurons demonstrated that one subpopulation is time-locked to seeking behaviours and the other subpopulation time-locked to consummatory behaviours. Seeking or consummatory phase specific paradigm revealed that activation of LH^LepR neurons promotes seeking or consummatory behaviours and inhibition of LH^LepR neurons reduces consummatory behaviours. The activity of LH^LepR neurons was increased via Neuropeptide Y (NPY) which acted as a tonic permissive gate signal. Our results identify neural populations that mediate seeking and consummatory behaviours and may lead to therapeutic targets for maladaptive food seeking and consummatory behaviours.

Chemogenetic stimulation of the parasympathetic nervous system lowers hepatic lipid accumulation and inflammation in a nonalcoholic steatohepatitis mouse model

AIMS

The role of the parasympathetic nervous system (PNS) in the pathogenesis of nonalcoholic steatohepatitis (NASH) is largely unknown. In this study, the effect of PNS modulation on NASH was investigated using chemogenetics.

MAIN METHODS

A streptozotocin (STZ) and high-fat diet (HFD)-induced NASH mouse model was used. To activate or inhibit the PNS, chemogenetic human M3-muscarinic receptor coupled with either Gq or Gi protein-containing viruses was injected into the dorsal motor nucleus of the vagus at week 4 and clozapine N-oxide was administered intraperitoneally for a week from week 11. Three groups (PNS-stimulation, PNS-inhibition, and control) were compared in terms of heart rate variability (HRV), histological lipid droplet area, nonalcoholic fatty liver disease activity score (NAS), the area of F4/80-positive macrophages, and biochemical responses.

KEY FINDINGS

The STZ/HFD-treated mouse model showed typical histological characteristics of NASH. HRV analysis confirmed that PNS-stimulation and PNS-inhibition groups had significantly higher and lower PNS activity, respectively (both P < 0.05). The PNS-stimulation group showed a significantly smaller hepatic lipid droplet area (14.3 % vs. 20.6 %, P = 0.02) and lower NAS (5.2 vs. 6.3, P = 0.047) than the control group. The area of F4/80-positive macrophages was significantly smaller in the PNS-stimulation group than in the control group (4.1 % vs. 5.6 %, P = 0.04). The PNS-stimulation group showed a lower serum aspartate aminotransferase level than the control group (119.0 vs. 356.0 U/L, P = 0.04).

SIGNIFICANCE

In STZ/HFD-treated mice, chemogenetic stimulation of the PNS significantly reduced hepatic fat accumulation and inflammation. The hepatic PNS may play a pivotal role in the pathogenesis of NASH.