Figure 3.

Differential expression of HCN1 mRNA in specific regions of hippocampal formation from autopsy (AUT) and severe HS epileptic tissue. The distribution of HCN1 mRNA-expressing individual neurons in the CA1-CA2 region (A-D) and the dentate gyrus (E, F) is demonstrated using nonradioactive in situ hybridization (see Materials and Methods). Low-magnification views (A, B) show robust HCN1 mRNA signal in CA1 pyramidal cells (as well as in stratum oriens interneurons; arrows) of autopsy-derived hippocampus (A) compared with sparser HCN1-expressing cells (and drastic reduction of neuronal density; Fig. 1) in epileptic sclerotic hippocampus (B). C, D, Higher magnification demonstrates reduced HCN1 mRNA signal over the CA1 pyramidal cell layer in HS (D) compared with AUT (C) tissue. Signal over individual remaining pyramidal cells is faint, whereas strong HCN1 mRNA expression is observed in presumed interneurons bordering the layer (arrows). E, F, Compared with AUT dentate gyrus (E), GCL from HS hippocampus (F) is depleted, yet HCN1 mRNA expression is clearly apparent in remaining neurons located well within the GCL (arrows). HCN1 mRNA-expressing hilar neurons (E, arrowheads) are virtually absent in the epileptic severe HS material (F). Scale bars: A, B, 150 μm; C-F, 30 μm. CA, Cornu ammonis; H, hilus.