It has been recently shown that tracer injection in the rat whisker pad induces trigeminal mesencephalic neurons (TMne) labelling. Furthermore, it has been demonstrated that these neurons, respond to spontaneous vibrissae movements with several patterns.

It has been proposed that trigeminal mesencephalic nucleus (TMnu) contains first-order neurons that relay spatial information related to whisker movement and location to trigeminal-cortical pathways.

In this study to better characterize whisker pad afference to the TMnu, the evoked responses of TMne to electrical stimulation of the facial nerve were analyzed.

After its surgical isolation, the facial nerve was cut close to the whisker pad, and its peripheral branch was electrically stimulated in order to induce a deflection of the ipsilateral macrovibrissae. Following cerebellum exposition, extracellular recordings were performed in the TMnu in basal conditions and during facial nerve stimulation. Histological localization of the recording site was performed at the end of the experiment.

Results showed that facial nerve electrical stimulation induced several patterns of response with a latency of 3–5 msec of the TMne localized in the medio-caudal part of the nucleus.

In conclusion, these findings seem to confirm our previous hypothesis that TMnu is involved not only in masseter proprioception and parodontal ligaments sensitivity, but also in whisker pad proprioception.