Differential contributions of vasopressin V1A and oxytocin receptors in the amygdala to pain-related behaviors in rats

Neuroplastic changes in the amygdala account for emotional-affective aspects of pain and involve neuropeptides such as calcitonin gene-related peptide and corticotropin-releasing factor. Another neuropeptide system, central arginine vasopressin, has been implicated in neuropsychiatric disorders, but its role in pain-related emotional expression and neuroplasticity remains to be determined. Here, we tested the hypothesis that arginine vasopressin in the amygdala contributes to pain-related emotional-affective responses, using stereotaxic applications of arginine vasopressin and antagonists for G-protein coupled vasopressin V1A and oxytocin receptors in adult male Sprague-Dawley rats. In normal animals, arginine vasopressin increased audible and ultrasonic vocalizations and anxiety-like behavior (decreased open-arm preference in the elevated plus maze). The facilitatory effects were blocked by a selective V1A antagonist (SR 49059, Relcovaptan) but not by an oxytocin receptor antagonist (L-371,257). L-371,257 had some facilitatory effects on vocalizations. Arginine vasopressin had no effect in arthritic rats (kaolin/carrageenan knee joint pain model). SR 49059 inhibited vocalizations and anxiety-like behavior (elevated plus maze) in arthritic, but not normal, rats and conveyed anxiolytic properties to arginine vasopressin. Arginine vasopressin, SR 49059, and L-371,257 had no significant effects on spinal reflexes. We interpret the data to suggest that arginine vasopressin through V1A in the amygdala contributes to emotional-affective aspects of pain (arthritis model), whereas oxytocin receptors may mediate some inhibitory effects of the vasopressin system.