A QUANTITATIVE-ANALYSIS OF THE MICROGLIAL CELL REACTION IN CENTRAL PRIMARY SENSORY PROJECTION TERRITORIES FOLLOWING PERIPHERAL-NERVE INJURYIN THE ADULT-RAT

The time course of the microglial cell reaction in central nervous sys tem primary sensory projection territories has been examined following peripheral nerve injury in the adult rat using qualitative and quanti tative analysis of immunoreactivity with the monoclonal antibody OX-42 , which recognises the complement receptor CR3. The regions examined i ncluded the gracile nucleus, the column of Clarke and the spinal cord dorsal horn (superficial and deep laminae separately) after unilateral sciatic nerve transection, and the spinal trigeminal nucleus followin g unilateral infraorbital nerve transection. In all territories examin ed a qualitative increase in OX-42 immunoreactivity was observed 24 h postlesion. Further, quantitative analysis revealed an exponential dev elopment of the OX-42 immunoreactivity, with a peak at one week postle sion, thereafter showing a slow exponential decline. Our results show that the signal (or signals) that induces the microglial cell response in primary sensory projection territories is rapid in comparison to p reviously described central degenerative changes following peripheral nerve lesions (transganglionic degeneration). These findings are compa tible with the hypothesis that activated microglia play a pathogenetic role in the development of transganglionic degeneration.