Figure 5.

Comparison of ChR2-eYFP labeling in control and pilocarpine (Pilo)-treated mice following viral vector injection in s. oriens of SOM-Cre mice. A, B, In a control mouse, numerous neurons in s. oriens (O) of CA1 are labeled for eYFP, with very limited cell body labeling in s. pyramidale (P) and s. radiatum (R). A dense plexus of labeled fibers is evident in s. lacunosum-moleculare (LM) but does not extend into the adjacent molecular layer (M) of the dentate gyrus. No labeling is evident in the granule cell layer (G) or hilus (H). In a pilocarpine-treated mouse, similar eYFP labeling is evident in s. oriens and s. lacunosum moleculare, but, in contrast to the control, substantial labeling extends into the outer molecular layer of the dentate gyrus. C, D, At higher magnification, limited numbers of eYFP-labeled fibers are present in the outer molecular layer in the control mouse. In contrast, a rich plexus of labeled fibers is evident throughout the outer two-thirds of the molecular layer in a pilocarpine-treated mouse. E, Labeled fibers in the molecular layer of a pilocarpine-treated mouse exhibit numerous small swellings separated by thin labeled segments, suggesting axons with en passant terminals. Scale bars: A, B, 100 μm; C, D, 25 μm; E, 10 μm.