Innervation of the maxillary vibrissae in mice as revealed by anterograde and retrograde tract tracing.

Vibrissae are a unique sensory system of mammals that is characterized by a rich and diverse innervation involved in numerous sensory tasks with the potential for species-specific differences. In the present study, indocarbocyanine dyes (DiI and PTIR271) and confocal microscopy were combined to study the innervation of the mystacial vibrissae and vibrissa-specific sensory neuron distribution in the maxillary portion of the trigeminal ganglion of the mouse. The deeper regions of the vibrissa cavernous sinus (CS) contained a dense plexus of free nerve endings, possibly of autonomic fibers. The superficial part of this sinus displayed a massive array of corpuscular endings. Innervation in the region of the ring sinus consisted of Merkel endings and different morphological variances of lanceolate endings. The region of the inner conical body had a circular plexus of free nerve endings. In addition to confirming previous observations obtained by a variety of other techniques and ultrastructural studies, our studies revealed denser terminal receptor endings in a different distribution pattern than previously demonstrated in studies using the rat. We also revealed the distribution of sensory neurons in the trigeminal ganglion using retrograde tracing with fluorescent tracers from two nearby vibrissae. We determined that the populations of sensory neurons innervating the two vibrissae were largely overlapping. This suggests that the somatotopic maps of vibrissal projections reported at the different levels in the neuraxis are not faithfully reproduced at the level of the ganglion.