INHIBITION OF THE TAIL-FLICK REFLEX FOLLOWING MICROINJECTION OF MORPHINE INTO THE AMYGDALA

RECENT evidence indicates that the amygdala plays a critical role in t he activation of Drain stem antinociceptive systems during stress. In the present experiment, bilateral microinjection of morphine sulfate ( 10 mug) into the amygdala of pentobarbital-anesthetized rats resulted in a time-dependent elevation in latency of the tail flick reflex evok ed by radiant heat. The most effective sites within the amygdala were in or immediately adjacent to the basolateral nucleus. The relative am plitude of the tail flick reflex did not differ as a function of repea ted testing or morphine treatment. These results suggest that importan t forebrain inputs which normally activate endogenous antinociceptive systems in behaving animals may be manipulated and studied in detail u sing the anesthetized rat.