Lesions in the dentate hilum and CA2/CA3 regions of the rat hippocampus produce cognitive deficits that correlate with site-specific glial activation.

Thirty male rats pressed a lever three times (FR3) when a stimulus light (sD) was off to obtain sucrose pellets. They were then evenly divided into sham Controls versus groups lesioned bilaterally in the hippocampus by stercotaxic injection of ibotenic acid into the dentate hilum (HIL) or the CA2/CA3 region (CA2/3). On measures of recall of the FR3-sD task taken during the initial 30 min of a postlesion test session, the CA2/3 and especially the HIL groups showed significant (p < .05) impairments relative to the Controls. During an ensuing 30-min period, rats were reshaped to criterion, beginning at FR1, and no appreciable intergroup differences were noted on this schedule or at FR1-sD. At FR2-sD, the HIL but not the CA2/3 group showed some impairment relative to Controls. At FR3-sD, both the CA2/3 and HIL groups had impaired task performance. An immunocytochemical index of glial activation showed higher reactivity in CA2/3 or the dentate hilum among CA2/3 or HIL animals, respectively, that was associated with the degree to which they showed an FR3-sD performance deficit.