COMPARISONS OF DOSE-DEPENDENT EFFECTS OF SYSTEMIC MORPHINE ON FLEXIONREFLEX COMPONENTS AND OPERANT AVOIDANCE RESPONSES OF AWAKE NONHUMAN-PRIMATES

Electromyographic activity and the force of reflex and operant respons es were recorded following administration of morphine. Low doses facil itated reflex responses to input from A-delta afferents but not from A -beta input. Higher doses inhibited A-delta responses but not A-beta r esponses. Operant avoidance responses to visual cues were unchanged. T hus, depending on the dose, nociceptive reflexes were facilitated or i nhibited, without associated effects on non-nociceptive input or on mo tor output.