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Brain Research 772 1997 181–190
Research report
Modulation of anxiety-related behaviours following lesions of the prelimbic
or infralimbic cortex in the rat
Anthony L. Jinks
1
, Iain S. McGregor
)
Department of Psychology, A19, UniÕersity of Sydney, Sydney, NSW 2006, Australia
Accepted 17 June 1997
Abstract
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A series of experiments examined behavioural and autonomic aspects of stress and anxiety in rats subjected to either: 1 electrolytic
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lesions of the infralimbic cortex subregion of the medial prefrontal cortex; 2 electrolytic lesions of the prelimbic cortex subregion of the
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medial prefrontal cortex; 3 sham lesions of infralimbic or prelimbic cortex sham control ; or 4 no lesions control . In exploration-based
models of anxiety, infralimbic- or prelimbic-lesioned rats spent less time in the centre of an open field and less time on the exposed arms
of an elevated plus maze, indicating increased anxiety. Locomotor activity was normal in the lesioned rats when tested in a non-stressful
enclosed environment. In a step-down passive avoidance task, infralimbic-lesioned rats stepped down more quickly than controls onto a
grid floor where they had been shocked 24 h previously. Prelimbic-lesioned rats were no different to controls on this test, although they
showed greater latencies to step down onto the grid floor during conditioning. In a final experiment, indirect calorimetry was used to
show that both infralimbic- and prelimbic-lesioned rats have essentially normal alterations in oxygen consumption and energy substrate
utilisation when exposed to brief footshock. Thus, the impaired passive avoidance in infralimbic-lesioned rats cannot be attributed to
decreased nociception. It is concluded that both the prelimbic and infralimbic regions play a role in anxiety, and that this role may be
subtly differentiated. In particular, the infralimbic cortex may have a specific role in mediating the inhibition of behaviours associated
with aversive outcomes. q1997 Elsevier Science B.V.
Keywords: Medial prefrontal cortex; Infralimbic cortex; Prelimbic cortex; Anxiety; Respiratory quotient; Passive avoidance; Autonomic; Rat
1. Introduction
Despite systematic investigation over the past two
decades, the exact function of the medial prefrontal cortex
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MPC remains something of an enigma. According to
numerous recent studies involving rats, the MPC plays a
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role in memory 12,21,30,52 , attention 13,43 , emotion
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19,26,29,38,41,42,44 , autonomic control 2,48,54 and
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response initiation 25,43 . In addition, abnormal MPC
function has been consistently implicated in human psy-
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chopathology including schizophrenia 1,56 , sociopathy
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14 , obsessive–compulsive disorder 1,4 and depression
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5,8 . However, in neither species, does there appear to be
)
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Corresponding author. Fax: q61 2 9351-2603; E-mail:
iain@psych.su.oz.au
1
Present address: The Centre For Advanced Food Research, Univer-
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sity of Western Sydney Hawkesbury , Bourke Street, Richmond, NSW
2753, Australia.
a definitive answer to the question of what the MPC
actually ‘does’.
The MPC is classically defined as the cortical projec-
tion of the mediodorsal nucleus of the thalamus and in the
rat includes at least four subregions, the medial precentral
cortex, anterior cingulate cortex, prelimbic cortex and in-
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fralimbic cortex 23,33,35 . Numerous lesion studies of the
MPC have been conducted over the past two decades,
mostly using rats as subjects. However, there has been
large variability in the size and placement of lesions within
MPC subregions across studies. Thus, it might be inferred
that the heterogeneity in MPC function exhibited in the
recent literature to some extent reflects the variability in
MPC subregions targeted for destruction.
Differentiation of function across MPC subregions has
only recently become a theme in the neurobehavioural
literature, and has proceeded with particular reference to
emotion and memory. With respect to emotion, Ledoux
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and colleagues 41,42 have shown that dorsal MPC le-
0006-8993r97r$17.00 q 1997 Elsevier Science B.V. All rights reserved.
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PII S0006-8993 97 00810-X