Perceptual and motor effects of morphine and buprenorphine in baboons

The effects of morphine and buprenorphine on auditory perceptual discrimina tions and response latency ("reaction time") in baboons are compared. The t ask employed synthetic human vowel sounds that art: readily generated in th e laboratory, and closely approximate natural baboon "grunt" vocalizations [J. Acoust. Sec. Am. 101 (1997) 2951]. Baboons pressed a lever to produce o ne repeating "standard" vowel, and released the lever only when one of four other "comparison" vowels occasionally occurred in place of the standard v owel. The percentage of correct detections and median reaction time for eac h comparison were measured following intramuscular drug administrations of morphine (0.01-1.8 mg/kg) and buprenorphine (0.00032-0.032 mg/kg). Both mor phine and buprenorphine impaired vowel discriminability, and greater impair ments occurred for those comparison vowels that were mon similar in formant structure to the standard vowel. Morphine increased reaction time in all b aboons, and buprenorphine increased reaction time in two of three baboons. Morphine's perceptual effects occurred within 20-30 min following drug admi nistration; buprenorphine's perceptual effects occurred 50-100 min followin g drug administration. Morphine and buprenorphine did not differ in the tim e course of their maximal reaction time effects. The results demonstrate th at both morphine and buprenorphine can impair auditory discriminations invo lving human vowel sounds in baboons, as well as lengthen reaction times to the stimuli. (C) 2001 Elsevier Science Inc. All rights reserved.