NERVE GROWTH-FACTOR AND NT-5 INDUCE INCREASED THERMAL SENSITIVITY OF CUTANEOUS NOCICEPTORS IN-VITRO

1. Perfusion of the receptive field (RF) of C - or A delta-fiber nocic eptors with nerve growth factor (NGF) in an in vitro preparation of th e rat saphenous nerve with functionally attached skin induced a signif icant decrease in heat threshold without changing mechanical or cold s ensitivity. 2. NGF-induced thermal sensitization was absent after sali ne perfusion and in skin taken from mast-cell depleted animals, hence confirming a role for mast cells in NGF-induced thermal hyperalgesia. 3. Neurotrophin-5 (NT-5) also induced a small but significant reductio n in heat threshold without affecting mechanical sensitivity. It is sp eculated that NT-5 exerts its action either directly on the trkA recep tor, as with NGF or alternatively through trkB receptors located on sy mpathetic efferents or on small diameter afferents.