Vasopressin-Mediated Modulation of Trigeminal Reflexes in Rats

In experiments on rats under urethane anesthesia, we studied how microinjections of vasopressin into the spinal trigeminal nucleus influence jaw-opening reflexes (JOR): nociceptive JOR, induced by stimulation of the tooth pulp, and non-nociceptive JOR, evoked by stimulation of A fibers of the infraorbital nerve. It was shown that injection of 10 M vasopressin resulted in a pronounced decrease (by 45-50%) in the nociceptive JOR amplitude for 25-30 min, whereas the non-nociceptive JOR dropped only by 8-10% for 11-13 min. It is concluded that vasopressin predominantly affects the nociceptive JOR; this fact is obviously related to a central analgesic effect of this peptide.