The Journal of Neuroscience, February 1, 2002, 22(3):1155-1164
Impaired Spatial Performance in Rats with Retrosplenial Lesions:
Importance of the Spatial Problem and the Rat Strain in Identifying
Lesion Effects in a Swimming Pool
K. Troy
Harker and
Ian Q.
Whishaw
Canadian Center for Behavioral Neuroscience, Lethbridge, Alberta,
T1K 3M4, Canada
Behavioral, electrophysiological, and anatomical evidence suggests
that retrosplenial (RS) cortex (areas RSA and RSG) plays a role in
spatial navigation. This conclusion has been questioned in recent work,
suggesting that it is damage to the underlying cingulum bundle (CG)
(areas CG and IG), and not RS, that disrupts spatial place learning
(Aggleton et al., 2000).
We revisited this issue by comparing Long-Evans rats, the strain used
in studies that report RS deficits, to Dark Agouti rats, the strain in
which no RS deficit has been reported. Rat groups with RS, RS + CG, or
no lesion were tested on a place task in a swimming pool, a test of
nonspatial and spatial learning, and a matching-to-place task, a
relatively selective test of spatial learning. Long-Evans rats given
RS and RS + CG lesions, either before or after training on the two
tasks, were impaired on both tasks, a deficit not attributable to
impaired visual acuity. Control Dark Agouti rats and RS Dark Agouti
rats, although not different on the place task, were both significantly
impaired relative to Long-Evans rats. The RS Dark Agouti group,
however, was also impaired on the matching-to-place task.
Thus, we show that RS cortex is part of an extended neural circuit
involved in spatial behavior in both Long-Evans and Dark Agouti rats,
but its role in the place task may be masked by an innate nonspatial
deficit in Dark Agouti rats. The results are discussed in relation to
the importance of assessing spatial learning with appropriate spatial
tests, the problems of interpretation posed by rat strain differences,
and the role of retrosplenial cortex in spatial behavior.
Key words:
cingulum bundle; Dark Agouti rat; learning and memory; Long-Evans rat; matching-to-place learning; Morris water task; place
learning; posterior cingulate; retrosplenial cortex; spatial
navigation; strain differences
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