Optical Activation or Silencing of Neural Activaty in Neurons that Regulate Energy Balance in the Hypothalamus

Abstract

Hypothalamic neurons defined by the expression of RIPCre transgene have been suggested to control body weight. However, which RIPCre neurons regulate energy expenditure, and via release of which neurotransmitter, is presently unknown. This study revealed that acute activation of arcuate RIPCre neurons innervated NTS/DMV-projecting neurons in the paraventricular hypothalamus. Thus, as additional neurons to those expressing POMC or AgRP, RIPCre neurons in the arcuate play important roles in regulating energy expenditure via releasing GABA. To assess the mechanism and function of RIPCre neurons, animals with disrupted neurotransmitter release (GABA or glutamate) from these neurons were generated by crossing RIPCre transgenic mice with lox-vGAT(vesicular GABA transporter) or lox-vGlut2 (vesicular glutamate transporter) mice. Combined with patch-clamp recordings, and channelrhodopsin2-assisted circuits mapping (CRACM), this study has explored the neural circuitry involving ARC-RIPCre neurons in regulating energy expenditure. On the other hand, the Cre-dependent halorhodopsin (eNpHR 3.0) expression has been tested following AAV-injection into the arcuate of Agrp-ires-Cre mice. In brain slice preparations, it has been confirmed that yellow light repeatedly and reversibly hyperpolarizes and silences AgRP neurons expressing NpHR. Our study suggests that the ChR2/Halo system constitutes a powerful toolbox enabling photostimulation and photoinhibition in genetically-specified neurons, enabling the systematic analysis of neural circuits.