Reinnervation of rat Pacinian corpuscles after nerve crush during the postcritical period of development.

The ultrastructure of crural Pacinian corpuscles was examined after sciatic nerve crush performed in 7- to 20-day-old rats, i.e. during the postcritical period of development when the corpuscles no longer degenerate after axotomy but cease growing. The aim of our study was to assess the innervation pattern and structural changes of the corpuscles following transient denervation and subsequent reinnervation during their maturation and growth. Reinnervated corpuscles were examined by electron microscopy from 2.5 months after nerve crush onwards. After sciatic nerve crush at 7 days of age, the corpuscles are mostly reinnervated with multiple axon terminals, each of them enclosed within a newly formed inner core. The axial multiple cores are in part covered by a layer of concentric inner core lamellae and surrounded by a capsule, both structures having survived from the original corpuscle. After nerve crush at 10 days of age, reinnervated Pacinian corpuscles usually contain, in their axial region, a denervated remainder of the original core together with a few regenerated axon terminals enclosed within new inner cores. These axial structures are surrounded by a layer of concentric lamellae of the original core which may accommodate some regenerated terminals. Additional axon terminals with their small inner cores may be found at the outer aspect of the composite core beneath the capsule. When the nerve is crushed in 15-day-old rats, the inner core which is already well developed remains preserved by the time of reinnervation, and regenerating axons grow in between the original lamellae inducing only moderate neoformation of 2-3 lamellar layers which enclose the terminals. After crushing the sciatic nerve in 20-day-old rats, formation of new inner core lamellae is minimal and regenerated terminals become accommodated between the original lamellar of the core as is the case in adult animals. Regeneration of new inner cores and reinnervation of the preserved lamellar structure thus characterize the recovery of Pacinian corpuscles following reinnervation after nerve crush during the postcritical period of their development.