High-resolution intravital imaging of the murine hypothalamus using GRIN lenses and confocal microscopy.

Intravital studies of cellular morphology in structures such as the hypothalamus are challenging because of their location at the bottom of the brain. Here, we describe an intravital imaging protocol based on gradient refractive index (GRIN) lenses in conjunction with confocal microscopy to inspect fluorescent cells at high resolution in deep-brain areas. The approach relies on implanted guide-tubes for the interchangeable use of GRIN lenses, thereby allowing imaging at different magnifications and increasing the effective field of view. For complete details on the use and execution of this profile, please refer to Butiaeva et al. (2021).

Leptin receptor-expressing pericytes mediate access of hypothalamic feeding centers to circulating leptin.

Knowledge of how leptin receptor (LepR) neurons of the mediobasal hypothalamus (MBH) access circulating leptin is still rudimentary. Employing intravital microscopy, we found that almost half of the blood-vessel-enwrapping pericytes in the MBH express LepR. Selective disruption of pericytic LepR led to increased food intake, increased fat mass, and loss of leptin-dependent signaling in nearby LepR neurons. When delivered intravenously, fluorescently tagged leptin accumulated at hypothalamic LepR pericytes, which was attenuated upon pericyte-specific LepR loss. Because a paracellular tracer was also preferentially retained at LepR pericytes, we pharmacologically targeted regulators of inter-endothelial junction tightness and found that they affect LepR neuronal signaling and food intake. Optical imaging in MBH slices revealed a long-lasting, tonic calcium increase in LepR pericytes in response to leptin, suggesting pericytic contraction and vessel constriction. Together, our data indicate that LepR pericytes facilitate localized, paracellular blood-brain barrier leaks, enabling MBH LepR neurons to access circulating leptin.