Axonal regeneration through a peripheral nerve implanted into a brain cavity.

A cavity was prepared in the rat parietal cortex by suction, filled with gel foam and left for 3 weeks during which time it became highly vascularised. Into this 3-week-old capillary bed a 5 mm length of autologous common peroneal nerve was implanted. Animals were killed at various time intervals up to 7 months after implantation of the nerve segment. The ultrastructural features of the vascular bed before and after implantation of the nerve segment were compared. In the absence of a peripheral nerve implant no axons were found within the cavity. However, at 5 weeks after implantation numerous axon-like profiles and capillaries containing fenestrations were observed within the implant. Eight weeks after implantation of the peripheral nerve both myelinated and non-myelinated axons were observed within the implant and in the surrounding capillary bed. No obvious increase in the number of axons was observed with increasing time periods. To investigate the origin of the axons within the vascular bed and/or implant the fluorochrome true blue was injected into the cavity 7 months after implantation of the nerve. Three days later selected areas of the brain, the trigeminal, superior cervical and otic ganglia were examined for retrogradely labelled fluorescent cells. Labelled cells were found adjacent to the cavity and in the ipsilateral trigeminal and superior cervical ganglia. The significance of these results in relation to the enhancement of axonal regeneration from the damaged central nervous system (CNS) is discussed.