THE SUPERIOR COLLICULUS RELAYS SIGNALS DESCENDING FROM THE VIBRISSAL MOTOR CORTEX TO THE FACIAL-NERVE NUCLEUS IN THE RAT

Electrical stimulation of the vibrissal motor cortex (VMCx), the superior colliculus and the facial nerve nucleus elicits vibrissal movements. A possibility of the superior colliculus as one of the relay nuclei between the VMCx and the facial nerve nucleus was investigated by injecting an anterograde neural tracer, Phaseolus vulgaris leucoagglutinin (PHA-L), into the physiologically identified VMCx and a retrograde tracer, cholera toxin B subunit (CTb), into the facial nerve nucleus in Wistar rats. In the lateral half of the superior colliculus, the termination field of axons from the VMCx overlapped with the distribution field of projection neurons to the facial nerve nucleus. In some cases, PHA-L-labeled terminal swellings were closely apposed to the somas of CTb-labeled neurons. We conclude that signals descending from the VMCx are relayed through the lateral half of the superior colliculus to the facial nerve nucleus.