Compensatory hippocampal neurogenesis in the absence of cognitive impairment following experimental hippocampectomy in adult rats

Abstract

Temporal lobe epilepsy (TLE) is the commonest type of focal epilepsy in adult humans. In refractory TLE, patients are indicated for unilateral resection of the affected hippocampus (hippocampectomy), which generally does not cause any cognitive impairment. Once adult hippocampus is a region of endogenous neurogenesis, we have hypothesized that a compensatory increase in hippocampal neurogenesis might occur in the remaining hippocampus after unilateral hippocampectomy. To test this hypothesis, we performed unilateral hippocampectomy in adult Wistar rats (n=12). Sham animals were not hippocampectomized (n=6). Animals were deeply anesthetized and adjacent cortex and hippocampus of the left hemisphere were completely removed. They were perfused at 15 (G15, n=6) or 30 (G30, n=6) days post-surgery. Behavioral tests were performed to address possible cognitive impairments. We did not find any cognitive impairment in the hippocampectomized animals. Histopathology was performed using thionine staining and mature neurons and migratory neuroblasts were immunolabeled using anti-NeuN and anti-doublecortin (DCX) antibodies, respectively. The remaining hippocampus presented higher numbers of DCX positive cells compared to control (p<0.001) at both G15 and G30. The results suggest increased compensatory adult neurogenesis following experimental unilateral hippocampectomy in adult rats, which may contribute to absence of cognitive impairments.