LOSS OF DORSAL-ROOT GANGLION-CELLS CONCOMITANT WITH DORSAL-ROOT AXON SPROUTING FOLLOWING SEGMENTAL NERVE LESIONS

Tight ligation of the fifth and sixth lumbar segmental nerves in the r at provides a model of neuropathic pain. We used this model to assess the changes in primary afferent input to the dorsal hem in neuropathic pain syndromes. Dorsal roots and ganglia were examined for up to 32 w eeks following segmental nerve ligation. Stereologic and morphometric techniques revealed a notable decrease in the numbers of dorsal root g anglion cells and unmyelinated dorsal root axons by six weeks post-inj ury. By 32 weeks following segmental nerve ligations, the numbers of d orsal root ganglion cells have dropped to 50% of pre-ligation levels w hile the numbers of dorsal root axons have increased to normal levels predominantly due to sprouting of myelinated fibres. These findings in dicate that although there is a great loss of dorsal root ganglion cel ls, there is dramatic sprouting of myelinated fibres and possibly some sprouting of unmyelinated fibres in the dorsal roots. Additionally, a difference in the responses of unmyelinated and myelinated fibres to this peripheral nerve injury is revealed. These changes in dorsal root ganglion cells and their central axons may underlie certain aspects o f abnormal pain syndromes because of changes in the types and quantity of input the dorsal horn receives. (C) 1997 IBRO. Published by Elsevi er Science Ltd.