5-Hydroxytryptamine-induced synovial plasma extravasation is mediated via 5-hydroxytryptamine2A receptors on sympathetic efferent terminals.

5-Hydroxytryptamine (5-HT) is known to act in peripheral tissues to produce pain and inflammation, yet the mechanisms underlying 5-HT-induced inflammation have not been well studied. The present study uses a rat knee joint model of inflammation (synovial plasma extravasation) and molecular biological techniques to determine the site of action of 5-HT and the specific 5-HT receptor subtype mediating synovial 5-HT-induced plasma extravasation. 5-HT (1 microM) stimulates synovial plasma extravasation 7-fold above base-line levels. Surgical lumbar sympathectomy, but not C-fiber depletion by neonatal capsaicin, dramatically reduces 5-HT-induced synovial plasma extravasation (P