ENHANCED STIMULUS-REWARD LEARNING BY INTRAAMYGDALA ADMINISTRATION OF A D-3 DOPAMINE-RECEPTOR AGONIST

The amygdala is considered to be a critical neural substrate underlyin g the formation of stimulus-reward associations, and is known to recei ve substantial innervation from dopaminergic neurons located within th e ventral mesencephalon. However, relatively little is known about the function of the mesoamygdaloid dopamine projection in stimulus-reward learning, Recently, we have found post-session intra-amygdala microin jections of cl-amphetamine to enhance appetitive Pavlovian conditionin g as assessed ill a discriminative approach task, In the present study we have examined the effects of dopamine receptor agonists possessing relative selectivity for the D-1, D-2 and D-3 receptor subtypes in or der to examine more fully the role of the mesoamygdaloid dopamine proj ection in stimulus-reward learning. Thus, subjects were trained to ass ociate an initially neutral stimulus (CS+) with 10% sucrose reward (US ), A second, control stimulus (CS-) was also presented but never paire d with sucrose reward, In order to measure specifically the conditione d response to CS+/CS- presentation, responding during CS and US presen tations was measured separately. Immediately following each training s ession, subjects received bilateral intra-amygdala infusion of 0.1, 1 or 10 nmol/side of SKF-38393, quinpirole or 7-OH-DPAT. Infusions of SK F-38393 or quinpirole were without effect on CS+ approach. However, po st-session intra-amygdala infusions of 7-OH-DPAT enhanced selectively CS+ approach in a dose-dependent fashion. No dose of any drug affected CS- approach, US behaviours, or measures of extraneous behaviour. Sub sequent acquisition of a novel conditioned instrumental response was a lso unaffected. Thus, the present data indicate a selective involvemen t of the D-3 dopamine receptor subtype in the modulation of stimulus-r eward learning by the mesoamygdaloid dopamine projection.