Nerve growth factor increases sensitivity to bradykinin, mediated through B2 receptors, in capsaicin-sensitive small neurons cultured from rat dorsal root ganglia.

To examine the effects of nerve growth factor (NGF) on the response to bradykinin (BK) of primary afferent neurons, intracellular recordings were obtained from small (< 30 microm) and large (> or = 35 microm) neurons in rat dorsal root ganglia (DRG). The response to BK in the small neurons was tested in 23 freshly dissociated neurons (dissociated group), 37 neurons cultured in the absence of NGF (no-NGF group) and 117 neurons in the presence of NGF (NGF group). Application of BK (10(-7) or 10(-5) M) induced a depolarization in a small number of neurons in the freshly dissociated (13%) and the no-NGF (11%) groups. After cultivation with NGF, the percentage of neurons that were depolarized by BK significantly increased to 46% after 2 days of cultivation. In the NGF group, the percentage of neurons sensitive to BK was significantly greater among capsaicin (CAP)-sensitive than among CAP-insensitive neurons (48 vs 20%). This BK-induced depolarization was completely blocked by a B2 receptor antagonist, but not a B1 receptor antagonist. With large neurons, in contrast, NGF did not increase the percentage that were BK-sensitive (9% in the dissociated group vs 0% after being cultured 2 days with NGF). These results demonstrate that NGF increases sensitivity to BK, mediated through B2 receptors only, in capsaicin-sensitive small neurons cultured from rat DRGs.