Reassessing morphine effects in cats: I. Specific behavioral responses in intact and unilaterally brain-lesioned...

Behavioral responses to single low doses of morphine (0.5-3.0 mg/kg IP) were measured in intact cats and in cats with removal of one cerebral hemisphere or one caudate nucleus. Responses were dose-dependent and formed 3 stages: (1) autonomic stage (0-15 min postdrug): with vocalization, salivation, licking, swallowing, retching and vomiting; (2) quiet stage (15-60 min postdrug): sitting, fixed gaze, mydriasis, and pricked pinnae; (3) head movement stage (from 30-60 min postdrug and decreasing by the 5th hr): fully aroused but mostly sitting; showing discrete, complex head movements of a visual-tracking type with pouncing/avoidance paw movements, and with irregular, dose-dependent bouts of rocking, pivoting, and backing. Sleep, grooming, micturition and defecation were suppressed. In hemispherectomized cats the frequency of head movements was increased only towards the side of the ablation, and there was a strong bias for body turning to that side together with a significant bias to move the ispilateral paw. None of these biases were significant in cats with a unilateral caudate ablation. We conclude that the cat is an excellent model for behavioral morphine studies when dose levels below those inducing "feline mania" are used. CNS sites underlying these responses are discussed.