PLEASURE-ATTENUATION OF STARTLE IS DISRUPTED BY LESIONS OF THE NUCLEUS-ACCUMBENS

THE nucleus accumbens (NAC) and the amygdala have been implicated in p rocesses by which reinforcers control instrumental behaviour. Reinforc ement has both motivational and motor components, and it is necessary to differentiate between these two aspects. The acoustic startle respo nse (ASR) is attenuated in the presence of a secondary reinforcer. In contrast to other paradigms used for investigating mechanisms of rewar d, the ''pleasure-attenuated startle'' (PAS) paradigm indicates the re warding properties of a treatment by an attenuation rather than by rei nforcement of a response, thus allowing determination of the motivatio nal impact of a treatment independent from its motor stimulating effec ts. Here, we report that the ASR was attenuated in the presence of a p ositive conditioned stimulus in sham-operated animals and in rats with lesions of the amygdala, but not in animals bearing 6-hydroxydopamine lesions of the NAC. These findings suggest that the catecholaminergic innervation oi the NAC is important for behavioural control by condit ioned reward.