Effects of morphine on evoked potentials recorded from the amygdala by tooth pulp stimulation in cats

Effects of intravenously administered morphine on the evoked potentials of the amygdala elicited by tooth pulp stimulation were examined in cats. The various evoked potentials were observed in regions of the amygdala such as nucleus amygdaloideus centralis (pars lateralis), nucleus amygdaloideus basalis (pars magnocellularis), nucleus amygdaloideus basalis (pars parvocellularis) and nucleus amygdaloideus lateralis. Evoked potentials were significantly decreased by morphine in four of the recorded regions. Morphine had no effect on the latency at any site of the amygdala observed. Depressant effects of morphine on evoked potentials were antagonized by naloxone in all 14 cats. This study indicates that there is a receptive field of pain in the amygdala which undoubtedly plays a role in emotion.