Striatal lesions change the behavioral effects of morphine in cats

Cats injected with a relatively low single dose of morphine sulfate (0.5-3.0 mg/kg i.p.) exhibit a long-lasting group of behaviors which we quantified via a time-sampling video technique. The dominant events are complex head movements accompanied by discrete paw, ear and body movements with the animal in a quiet posture, all of which appeared to be visually mediated. Cats with extensive lesions of the caudate nuclei do not show this profile; instead they show unspecific locomotor activity proportional to the size of the ablation and to the dose of morphine. These effects are blocked by naloxone in both intact and lesioned animals. The robustness of these results indicate that (i) the striatum is involved in the behavioral effects of morphine, and (ii) that the cat is a useful, sensitive model for the study of the behavioral effects of opiates.