PERIPHERALLY GRAFTED HUMAN FETAL 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 lumba r 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 nerv ous system compartments of the DREZ. Fibres originating from the graft ed neurones and approaching the DREZ changed their direction of growth and entered the spinal cord through the pia by following blood vessel s, grew into the grey matter and ramified there. These findings sugges t that the DREZ astrocytes in vivo are non-permissive not only to matu re peripheral regenerating axons, but also to growing axons from immat ure neurones.