Systemic or Intra-accumbens Injection of D-amphetamine Delays Habituation to a Tone Stimulus in Rats

Dopamine release within the nucleus accumbens shell is suggested to control the salience of environmental stimuli, and previous research has shown that the indirect dopamine agonist D-amphetamine can alter the salience of both aversive and neutral stimuli. In experiment 1, the effect of systemic injection of D-amphetamine (0.5, 1 mg/kg) on fear conditioning to a tone was assessed in an 'off-baseline' conditioned suppression procedure using several footshock intensities. Although the effects of amphetamine on conditioning were unclear, the results indicated a deficit of simple tone habituation in amphetamine-treated rats. In experiment 2, habituation of the orienting reaction to a tone was assessed by the progressive reduction of lick suppression upon repeated presentation of the auditory stimulus. D-Amphetamine delayed tone habituation, whether administered systemically (0.5, 1 mg/kg) or into the nucleus accumbens shell (3, 10 microg/0.5 microl). These data are consistent with electrophysiological and neurochemical data demonstrating the role of nucleus accumbens dopamine in novelty processing. The relevance of the data to latent inhibition is discussed.