As part of an effort supported by the K. Lisa Yang Brain-Body Center, Fan Wang’s lab at the McGovern Institute has developed a technique that makes the mouse head transparent and visualizes the nervous system in unprecedented detail.

The team used a new “clearing” protocol, developed in collaboration with Life Canvas using the Smart SPIM microscope, to visualize all of the cholinergic neurons in the mouse’s head and neck. Cholinergic neurons use the neurotransmitter acetylcholine to send messages in the brain and body. In the peripheral nervous system, the cholinergic system encompasses somatic motor neurons (which originate in the central nervous system and project to the muscles) and autonomic neurons (a network of nerves throughout the body that control unconscious processes). The cholinergic autonomic neurons include all parasympathetic neurons (which carry signals that relax the body), a small number of sympathetic neurons (which regulate sweating responses), and subsets of neurons in the gut. Together these autonomic neurons regulate involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal. Despite its importance, the details of cholinergic innervation in the head remain poorly understood.
 
In this video, Wang’s team visualized all cholinergic neurons and their innervations using the choline acetyltransferase-Cre; Cre-dependent tdTomato reporter mouse (ChAT-Cre;Ai14). Cholinergic neurons here express a red fluorescent protein tdTomato. 
 
This video reveals an intricate pattern of innervation in the parasympathetic nervous system, which has never been seen in such detail before. In the head, the parasympathetic system extensively innervates the vascular system. This vascular innervation by the parasympathetic system is not observed in the rest of the body, suggesting that the parasympathetic system plays a unique role in controlling blood flow.
 
Video courtesy of Jun Takatoh and Fan Wang.