Neuronal Tract Tracing in the Rat Trigeminal Sensory System

Understanding anatomical circuitries promotes the development of novel therapeutics to manage neurological pathologies. Tract tracing is a neuroanatomical approach that allows visualization of neural pathways. Wheat germ agglutinin (WGA) is a transsynaptic tracer taken up by neurons and passed to other networked neurons. WGA can be conjugated to a fluorescent dye (WGA-488) to be observed with a microscope. The goal of our study was to develop methodology using WGA-488 to visualize connectivity of the sensory nerves of the face into brainstem nuclei. We injected various volumes of 1% WGA-488 into the rat cheek or the jaw joint. Post-mortem sensory ganglia and brainstem were collected 3- or 7-days later, sectioned, and analyzed with a microscope. We found that 50 μL WGA-488 was observed in the trigeminal ganglia and several brainstem nuclei at 3-days post-tracer injection. This methodology can now be used to characterize the functional neurochemistry of the orofacial sensory neurons.