The cytology of human Pacinian corpuscles: evidence for sprouting of the central axon.

During the course of the studies on non-traumatized Pacinian corpuscles from normal human adults, we have frequently encountered corpuscles which have an 'apparently multiple' innervation in both light and electron microscopic preparations. On closer inspection of serial sections for both light and electron microscopy, these 'apparently multiple' axon terminals have been found in fact to be branches of the main central axon within the inner core of the corpuscle. Sprouting occurred at the trunk or at the extreme tip of the main axon, and such sprouts extended in various directions from the central axon throughout the inner core, producing tortuous and complex patterns of this 'multiple' innervation. These axonal sprouts do not have separate inner cores separated from one another, but rather are embedded in a common inner core. The presence of a common inner core thus differentiates normal axonal sprouts from the experimentally or pathologically produced multiple innervation that results form regeneration of axons in a previously denervated corpuscle. We conclude that the inner core of Pacinian corpuscles is a unique micro-environment promoting sprouting of sensory axon in the normal human adult as well as juvenile Pacinian corpuscles.