REINNERVATION OF RAT PACINIAN CORPUSCLES AFTER NERVE CRUSH DURING THEPOSTCRITICAL PERIOD OF DEVELOPMENT

The ultrastructure of crural Pacinian corpuscles was examined after sc iatic nerve crush performed in 7- to 20-day-old rats, i.e. during the postcritical period of development when the corpuscles no longer degen erate after axotomy but cease growing. The aim of our study was to ass ess the innervation pattern and structural changes of the corpuscles f ollowing transient denervation and subsequent reinnervation during the ir maturation and growth. Reinnervated corpuscles were examined by ele ctron microscopy from 2.5 months after nerve crush onwards. After scia tic nerve crush at 7 days of age, the corpuscles are mostly reinnervat ed with multiple axon terminals, each of them enclosed within a newly formed inner core. The axial multiple cores are in part covered by a l ayer of concentric inner core lamellae and surrounded by a capsule, bo th structures having survived from the original corpuscle. After nerve crush at 10 days of age, reinnervated Pacinian corpuscles usually con tain, in their axial region, a denervated remainder of the original co re together with a few regenerated axon terminals enclosed within new inner cores. These axial structures are surrounded by a layer of conce ntric lamellae of the original core which may accommodate some regener ated terminals. Additional axon terminals with their small inner cores may be found at the outer aspect of the composite core beneath the ca psule. When the nerve is crushed in 15-day-old rats, the inner core wh ich is already well developed remains preserved by the time of reinner vation, and regenerating axons grow in between the original lamellae i nducing only moderate neoformation of 2-3 lamellar layers which enclos e the terminals. After crushing the sciatic nerve in 20-day-old rats, formation Of new inner core lamellae is minimal and regenerated termin als become accommodated between the original lamellae of the core as i s the case in adult animals. Regeneration of new inner cores and reinn ervation of the preserved lamellar structure thus characterize the rec overy of Pacinian corpuscles following reinnervation after nerve crush during the postcritical period of their development.