H. Vanpraag et al., DISSOCIATION OF MOTOR HYPERACTIVITY AND SPATIAL MEMORY DEFICITS BY SELECTIVE HIPPOCAMPAL-LESIONS IN THE NEONATAL RAT, Journal of cognitive neuroscience, 6(4), 1994, pp. 321-331
Hippocampal lesions can disrupt the acquisition of new memories and te
nd to increase motor activity. Although hyperactivity may affect explo
ration, it is unclear how these performance variables contribute to th
e learning deficit and it is also not known which brain structures are
involved. The present study provides evidence for a dissociation betw
een activity and memory Following unilateral or bilateral electrolytic
lesions of the hippocampus in neonatal rats, we assessed open field b
ehavior and performance of discrete trials alternation in a T-maze. Wh
en tested 6 and 20 weeks postoperatively, rats subjected to bilateral
lesions were hyperactive. Their performance in the discrete trials alt
ernation task was impaired. In contrast, rats subjected to unilateral
lesions did not display an increase in motor activity, but were still
deficient in performance on the T-maze. To define whether these behavi
oral changes were accompanied by secondary changes in structures that
project to the hippocampus, we studied the function of the septum and
locus coeruleus after the lesions. Septal choline acetyltransferase (C
AT, the acetylcholine-synthesizing enzyme) activity was reduced and ty
rosine hydroxylase (TH, the rate-limiting enzyme in catecholamine bios
ynthesis) activity in noradrenergic Ic neurons was increased after bot
h the unilateral and bilateral lesion. Therefore, these changes map co
ntribute to the memory impairment but are not necessarily related to m
otor hyperactivity. We conclude that a deficit in spatial memory is no
t attributable to altered performance variables such as activity. Furt
hermore, spatial memory deficits in both the unilateral and bilateral
lesion paradigms may be associated with changes in septal and Ic funct
ion.