AMYGDALA AND HIPPOCAMPUS CONTROL DISSOCIABLE ASPECTS OF DRUG-ASSOCIATED CONDITIONED REWARDS

Limbic innervation of the nucleus accumbens via the ventral subiculum/ hippocampus and basolateral area of the amygdala has been shown to de termine dissociable aspects of behaviour controlled by stimuli associa ted with natural rewards. However, the respective contributions of the ventral subiculum and amygdala to behaviour governed by drug-associat ed stimuli remain to be determined. Experiments consisted of two phase s: drug-stimulus training, and subsequent stimulus-only testing. Initi al training sessions were of two alternating forms. During drug sessio ns, responding upon one lever resulted in an infusion of 1 mu g d-amph etamine into the nucleus accumbens, whilst during saline sessions d-am phetamine was replaced with saline. Each infusion (drug or saline) was preceded with either a light, or tone. Responding upon a control leve r had no programmed consequences. Following training, the levers were retracted, and instead two novel vertical bars were extended from the chamber ceiling. Movement of one bar produced the drug-associated stim ulus, whilst the alternative bar produced the saline-associated stimul us. Infusions of the AMPA receptor antagonist CNQX into the ventral su biculum or basolateral area of the amygdala (0, 0.2, 2.0 nmol) were ma de immediately before the start of each session. Intra-basolateral are a of the amygdala CNQX reduced responding upon the drug-associated sti mulus bar, but at the same time increased responding upon the saline-a ssociated stimulus bar. By contrast, intra-ventral subiculum CNQX redu ced drug-associated stimulus responding selectively. Neither manipulat ion affected levels of activity within the operant chamber extraneous to the bar-pushing response. Hence, the basolateral area of the amygda la appeared to have determined the degree of discriminative control ex erted over behaviour by the drug-associated stimulus, whilst the ventr al subiculum is suggested to have determined the efficacy of the condi tioned reward.