Pharmacological characterization of the effects of 5-hydroxytryptamine and different prostaglandins on peripheral sensory neurons in vitro.

The excitatory and sensitizing properties of 5-HT and different prostaglandins (PGD2, PGE1, PGE2, PGF2 alpha, PGI2 and PGI2-analogue, cicaprost) were characterized on an in vitro preparation of the neonatal rat spinal cord with functionally attached tail. Prolonged (10 min) perfusion of the tail with 5-hydroxy-tryptamine (5-HT, 0.5-10 microM) or any of the tested prostaglandins (0.1-5 microM) did not evoke an excitatory response recorded from a lumbar ventral root, but significantly enhanced responses of peripheral nociceptors to thermal and chemical (bradykinin, capsaicin) stimuli. PGD2 did not induce such an enhancement. Following sensitization of peripheral nociceptors with low concentrations of bradykinin or capsaicin, 5-HT (1-10 microM) evoked a ventral root response. Using specific 5-HT-receptor agonists and antagonists, 5-HT-evoked excitation was determined to be mediated via a 5-HT1-like receptor while 5-HT-induced sensitization involved 5-HT2 receptors.