Dissociation of cold-water swin and morphine analgesia in Brattleboro rats with diabetes insipidus

The present study examined whether vasopressin mediated the analgesic response to morphine and cold-water stress by comparing the analgesic responses of homozygous Brattleboro rats with diabetes insipidus with those of normal rats of the same strain of similar weight. Brattleboro rats exhibited hypersensitive responses to foot shock which were brought back to within normal limits by systemic administration of arginine vasopressin and desamino-D-arginine vasopressin. While Brattleboro rats failed to display an analgesic response to cold-water swim stress, they displayed a normal analgesic response to morphine. These results provide further evidence for dissociation of pain-inhibitory mechanisms into opioid and non-opioid components, and suggests that vasopressin might be involved in the elucidation of the latter component.