TRKA, CGRP AND IB4 EXPRESSION IN RETROGRADELY LABELED CUTANEOUS AND VISCERAL PRIMARY SENSORY NEURONS IN THE RAT

The pattern of trkA expression in relation to other neurochemical mark ers (CGRP and IB4) was investigated in primary sensory neurones innerv ating either the skin or bladder. Retrograde tracing using the fluores cent marker Fast Blue was performed followed by histochemistry. A grea ter proportion of visceral afferents compared with cutaneous afferents were trkA-immunoreactive (75% and 43%, respectively). CGRP expression correlated with trkA expression in that it was higher in visceral aff erents than cutaneous afferents (69% and 51%, respectively). IB4 expre ssion was negatively correlated with trkA expression, being lower in v isceral afferents compared with cutaneous afferents (29% and 43%, resp ectively). The results emphasise the heterogeneity of trkA expression (and hence nerve growth factor sensitivity) in afferents innervating d ifferent targets, and furthermore suggest that it is predominantly the CGRP-expressing population of primary afferents that express trkA.