Morphine analgesia following its infusion into different liquor spaces in rat brain.

Infusion of morphine (1 microgram) into the lateral ventricle, fourth ventricle, subarachnoid space beneath the brainstem, and cisterna magna, produces analgesia. The analgesia was tested with tail-flick response with radiant heat stimulus. Of all the liquor spaces, the structures on the ventral surface of the brainstem caudal to the fossa interpeduncularis appear to be the most sensitive site for the analgesic action elicited from the ventral surface of the brainstem is discussed.