Motion of rodent macrovibrissae apparently lacks of peripheral control mechanism since their pad muscles appear to operate without muscle spindles feedback. It has been suggested that during vibrissae movement, mystacial pad skin receptors my provide a trigeminal proprioceptive input.

This study investigated in rats whether the trigeminal mesencephalic nucleus (TMnu) is involved in whisker pad proprioception.

Neuroanatomical experiments, using retrograde tracers injected into the mystacial pad and the masseter muscle, revealed three different subpopulations of trigeminal mesencephalic neurons: 1) those innervating the masseter muscle neuromuscolar spindles 2) those innervating the mystacial pad, and 3)those innervating both structures. Extracellular recordings, performed during spontaneous movement of the vibrissae, showed in the TMnu the presence of whisking neurons similar to those described in the trigeminal ganglion, with patterns of activation dependent on the type of spontaneous macrovibrissae movement. In particular, their spiking activity tonically increased during fan-like movements of the vibrissae and showed phasic bursting during their rythmic whisking. These neurons at the same time also responded to masseter muscle stretch.

In conlusion, results strongly support the hypothesis that TMnu also contains first-order neurons that relay spatial information related to whisker movement and location to trigeminal-cortical pathways.