Double dissociation of the behavioural effects of R(+) 7-OH-DPAT infusionsin the central and basolateral amygdala nuclei upon Pavlovian and instrumental conditioned appetitive behaviours
Pk. Hitchcott et Gd. Phillips, Double dissociation of the behavioural effects of R(+) 7-OH-DPAT infusionsin the central and basolateral amygdala nuclei upon Pavlovian and instrumental conditioned appetitive behaviours, PSYCHOPHAR, 140(4), 1998, pp. 458-469
Dopaminergic cell bodies located within the ventral mesencephalon innervate
the amygdaloid complex, a region critically involved in the attribution of
affective significance to environmental stimuli. Recently, we have shown t
hat post-session intra-amygdala administration of a Dg dopamine receptor ag
onist enhances selectively the acquisition of an appetitive conditioned res
ponse. In the present study, we have investigated the potential involvement
of the central nucleus and the basolateral nuclei of the amygdala in media
ting this effect. Thus, rats were trained to associate an arbitrary stimulu
s (CS+) with the availability of 10% sucrose reward. Post-session infusions
of the D-3 receptor-preferring agonist, R(+) 7-OH-DPAT, were made into eit
her the central nucleus or basolateral nuclei. Acquisition of a conditioned
approach response was enhanced by R(+) 7-OH-DPAT infusions within the cent
ral nucleus, but not within the basolateral nuclei. Drug infusions into eit
her region failed to affect approach behaviour elicited by presentation of
a control stimulus (CS-), explicitly unpaired with sucrose reward. The effe
cts of pre-test infusions of R(+) 7-OH-DPAT on the instrumental properties
of the stimuli were then determined. Rats were presented with two novel lev
ers, depression of one lever resulted in presentation of the CS+, while pre
sentation of the CS- was contingent upon depression of the other lever. Rat
es of response upon each lever as well as the ability of the conditioned st
imuli subsequently to elicit conditioned approach behaviour were recorded.
Data revealed a double dissociation of the effects of R(+) 7-OH-DPAT on the
expression of the Pavlovian and instrumental properties of the reward-rela
ted stimulus. Thus, within the central nucleus R(+) 7-OH-DPAT dose-dependen
tly attenuated expression of the conditioned approach response, but had no
effect upon instrumental responding maintained by the conditioned reward. I
n contrast, within the basolateral nuclei, R(+) 7-OH-DPAT had no effect upo
n expression of conditioned approach behaviour, but abolished selectively t
he ability of the reward-associated stimulus to support the acquisition of
a novel instrumental response. Hence, these data indicate that distinct reg
ions of the amygdaloid complex process distinct aspects of conditioned appe
titive behaviours.