Journal of Neuroscience, Vol 14, 3333-3340, Copyright © 1994 by Society for Neuroscience
Opposite responses of mesolimbic dopamine system to controllable and uncontrollable aversive experiences
S Cabib and S Puglisi-Allegra
Istituto di Psicobiologia e Psicofarmacologia, CNR Roma, Italy.
It has been previously shown that rodents exposed to stressful experiences
show a biphasic response of the mesolimbic dopamine (DA) system, that is,
initial increase of DA release followed by a decrease below control levels
(Puglisi-Allegra et al., 1991). Evidence is now presented showing that mice
exposed to a series of foot shocks show an increase of DA release in the
nucleus accumbens septi (NAS) if they are allowed to control the shock
experience (shocked condition) and a decrease of DA release in this brain
area if they are not allowed to exert any control (yoked condition). These
results indicate that escapable/controllable and inescapable/uncontrollable
aversive experiences elicit opposite responses from the mesolimbic DA
system. Mice exposed to the apparatus without receiving shock (sham
condition) show a time-dependent biphasic evolution mesolimbic DA release
in line with previous reports indicating that confinement in an unknown
environment represents a stressful experience for mice. Moreover, exposure
to the sham condition for a time comparable to the duration of shock and
yoked exposure induces a mesolimbic DA response only quantitatively
different from the response of the yoked group but qualitatively different
from the response of the shocked mice. These results suggest that in
environmental conditions that allow behavioral control, enhanced mesolimbic
DA release is maintained regardless of the intensity of the aversive
stimuli. On the other hand, evaluation of changes in acid DA metabolites
levels in the frontal cortex (FC) of mice exposed to the shocked, yoked,
and sham conditions suggests that stressful experiences characterized by a
different intensity of the aversive stimuli could elicit graded responses
in the FC DA system.(ABSTRACT TRUNCATED AT 250 WORDS)