Changes in the numbers and distribution of calretinin in the epileptic rat hippocampus

OBJECTIVE: To examine calretinin (CR)-containing interneurons that degenerate in the hippocampus in post status epilepticus (SE) rats at different time points.

METHODS: This study was conducted at the Central South University, Xiangya Hospital, Hunan Province, P.R. China between September 2008 and January 2010. Pilocarpine-induced SE was chosen as a model to generate chronic epileptic rats. To determine whether hippocampal neuronal populations are affected by hippocampal seizures, immunohistochemical assays were performed in brain sections obtained from age-matched control (n=50) and epileptic rats (n=170). Nissl stain was used to observe pathological changes of the hippocampus.

RESULTS: Our results revealed the most dramatic cell loss to be in the hilar, cornu Ammonis (CA)1, and CA3 areas in the epileptic rats. Quantitative analysis revealed significant differences between control and epileptic rats in the number of CR-positive interneurons. These interneurons were distributed in the hilar, CA1, and CA3 areas and in the dentate gyrus of both control and epileptic rats, but was more numerous in the hippocampus of normal rats. However, a transient increase of CR-positive interneurons was observed in the CA1 between 7 and 15 days post SE. The CR interneurons were mostly located in the hilar and CA1 for epileptic rats, and in the hilus for control rats.

CONCLUSION: Our data suggest that a different proportion of inhibitory interneurons was observed in the epileptic rat hippocampus, as their numbers differ from controls. These results indicate that the inhibitory circuits in the hippocampus may represent a compensatory response with a role to balance the enhanced excitatory input in the region.