AMYGDALOID NORADRENALINE IS INVOLVED IN THE SENSITIZATION OF THE ACOUSTIC STARTLE RESPONSE IN RATS

The present study examined the role of noradrenaline (NA) in the centr al nucleus of the amygdala (cA) in the sensitization of the acoustic s tartle response (ASR) in rats. In the first experiment, local microinj ections of 0, 0.5, 1, 2 nmol of the alpha(2)-adrenergic antagonist yoh imbine into the cA increased the magnitude of the ASR in a dose-depend ent way. In the second experiment, foot shocks were applied to increas e the ASR amplitude (sensitization). Local microinjections of 0, 4, 8, 16 nmol of the alpha(2)-adrenergic agonist ST-91 into the cA dose dep endently decreased the sensitizing effects of foot shocks on the ampli tude of the ASR. It is conjectured that yohimbine increases and ST-91 decreases local NA release by acting at presynaptic autoreceptors. The present data suggest that the release of NA in the cA is involved in the mediation of the sensitizing effects of foot shocks on the ASR.