DISSOCIATIONS IN DOPAMINE RELEASE IN MEDIAL PREFRONTAL CORTEX AND VENTRAL STRIATUM DURING THE ACQUISITION AND EXTINCTION OF CLASSICAL AVERSIVE-CONDITIONING IN THE RAT
Ls. Wilkinson et al., DISSOCIATIONS IN DOPAMINE RELEASE IN MEDIAL PREFRONTAL CORTEX AND VENTRAL STRIATUM DURING THE ACQUISITION AND EXTINCTION OF CLASSICAL AVERSIVE-CONDITIONING IN THE RAT, European journal of neuroscience, 10(3), 1998, pp. 1019-1026
Dual perfusion in vivo brain microdialysis was used to monitor extrace
llular levels of dopamine in the medial prefrontal cortex and ventral
striatum during the acquisition and extinction of a classical aversive
conditioning paradigm in rats. The main finding was a dissociation in
the pattern of release in the two brain areas. The first stimulus-foo
tshock pairing elicited large increases in cortical dopamine over base
line levels that were much greater than the increases elicited by diff
erent stimuli of equivalent salience that were unpaired with footshock
. In contrast, dopamine levels in ventral striatum were unchanged unde
r these conditions. Over the next two pairings, there was a decline in
the cortical response and an increase in the response in ventral stri
atum. The first presentation of the aversive conditioned stimulus in a
separate context elicited the largest response in ventral striatum. P
ost-conditioning, the cortical response to the conditioned stimulus wa
s smaller than that elicited by the initial stimulus-footshock pairing
and was equivalent in magnitude to that elicited by stimuli unpaired
with footshock. Over the final two conditioned stimuli presentations,
in the absence of the footshock reinforcer (extinction), responses dec
lined in both brain areas. Simultaneous monitoring of behaviour indica
ted that the neurochemical events were accompanied by effective aversi
ve learning, as indexed by conditioned freezing responses. The data ar
e discussed in terms of the hypothesis that medial prefrontal cortex i
s especially engaged during novel circumstances which may, potentially
, require new learning, whilst ventral striatal dopamine more closely
follows the expression of conditioned responding during learning and e
xtinction.