350-μm side-view optical probe for imaging the murine brain in vivo from the cortex to the hypothalamus

Miniature endoscopic probes offer a solution for deep brain imaging by overcoming the limited depth of intravital microscopy. We describe a small-diameter (350 μm) graded-index optical probe with a side-view design for in vivo cellular imaging of the mammalian brain. The side-view probe provides a unique view of the vertical network of neurons and penetrating blood vessels. At a given insertion site, the translational and rotational scanning of the probe provides access to a large tissue area (>1  mm(2)) across the cortex, hippocampus, thalamus, and hypothalamus.