Single neurons in the spinal trigeminal and dorsal column nuclei project to both the cochlear nucleus and the inferior colliculus by way of axon collaterals: a fluorescent retrograde double-labeling study in the rat.

A number of single neurons in the spinal trigeminal nucleus (STN) and the dorsal column nucleus (DCN) were found to project simultaneously to the cochlear nucleus (CoN) and the external cortex of the inferior colliculus (ICe) by way of axon collaterals. Each rat was injected with Fluoro-Gold (FG) into CoN on one side and with tetramethylrhodamine-dextran amine (TMR-DA) into ICe on the side ipsilateral or contralateral to the FG injection. In these rats, a number of neuronal cell bodies in DCN and the interpolar and caudal subnuclei of STN were double-labeled retrogradely with both FG and TMR-DA, mainly on the side ipsilateral to the FG injection into CoN. These neurons in STN and DCN might mediate somatosensory inputs simultaneously to the two lower brainstem nuclei, CoN and ICe, which constitute the relays of the auditory pathway.