Cat trigeminal neurons innervated from the planum nasale: their medullary location and their responses to mechanical stimulation.

Experiments were performed to determine whether the receptors of the glabrous skin of the cat planum nasale (PN) could function in tactile analysis. Trigeminal projection sites of the PN were first identified using transganglionic transport of wheat germ agglutinin-horseradish peroxidase and horseradish peroxidase. Restricted projection sites were identified in this way among the interstitial neurons of the trigeminal tract, in the dorsal horn of the medulla, in subnucleus interpolaris and to a lesser extent in subnucleus oralis. Electrophysiological recording in the trigeminal spinal nucleus confirmed the major neuroanatomical findings and confirmed the paucity of PN projections to the trigeminal system. Most neurons innervated from the PN have small receptive fields, are rapidly adapting and responsive to PN vibration at amplitudes as low as 10 micros. Neurons could be entrained at frequencies below 80 Hz. This upper limit for entrainment presumably reflects the lack of pacinian corpuscles in the PN. A limited number of slowly adapting neurons were found, but only responded to PN displacements of 400 microns and above. The data suggest that the PN can function in tactile analysis to a limited degree. The significance of these findings is considered with respect to the organization of neural systems controlling head movement.