Peripherally grafted human foetal dorsal root ganglion cells extend axons into the spinal cord of adult host rats by circumventing dorsal root entry zone astrocytes.

Human foetal dorsal root ganglia were grafted in place of native lumbar dorsal root ganglia in adult rat hosts. Between 4 weeks and 4 months later, the dorsal root entry zone (DREZ) in the grafted roots showed extensive peripheral outgrowth of astrocytic processes, in contrast to the normal 'smooth' interface between the peripheral and central nervous system compartments of the DREZ. Fibres originating from the grafted neurones and approaching the DREZ changed their direction of growth and entered the spinal cord through the pia by following blood vessels, grew into the grey matter and ramified there. These findings suggest that the DREZ astrocytes in vivo are non-permissive not only to mature peripheral regenerating axons, but also to growing axons from immature neurones.