Vasopressin and oxytocin in the rat spinal cord: analysis of their role in the control of nociception.

Lesions of the hypothalamic paraventricular nucleus depleted immunoreactive (ir)-vasopressin (VP) and -oxytocin (OT) from rat spinal cord but failed to modify nociceptive thresholds. Further, intrathecal introduction of VP and OT into the cord failed either to influence nociceptive thresholds or to modify the antinociceptive action of morphine. However, doses of VP as low as 20 ng caused, in contrast to OT, a hind-limb muscular flaccidity and respiratory disturbances. Rats suffering from chronic arthritis did not, finally, reveal any alterations in levels or ir-VP or ir-OT in the spinal cord. Is is concluded that spinal pools of VP and OT are derived from the paraventricular nucleus and do not play a major role in nociceptive processes in the spinal cord. A role of spinal VP in motor and, possibly autonomic control is, nevertheless, indicated.