Figure 1.
(A–D) Photomicrographs taken with a 40× objective of PV-IR neurons in the subfields of the rat hippocampus. (A) Dentate Gyrus: short arrows indicate two PV-IR interneurons; one in the hilus and the other is inside the GCL. PV-IR fibers can be seen passing through both the hilus and the GCL where they are densely distributed in a ‘honeycombed’ fashion around granule cell somatas which are PV-IR negative. (B) CA3/2 subfield: several PV-IR interneurons are visible in both stratum pyramidale and oriens; an arrow indicates a darkly stained example in stratum oriens, and arrowheads indicate two examples of interneurons in the pyramidal layer. Unstained pyramidal neurons are responsible for the clear, ‘honeycombed’ appearance similar to the GCL. (C) CA1 subfield: a PV-IR interneuron located in the pyramidal layer is marked with an arrowhead; a PV-IR located just inside the stratum oriens is indicated by an arrow. (D) Subiculum: several PV-IR interneurons are clearly visible in the pyramidal layer. The location of an unstained pyramidal cell, surrounded by darkly stained contacts formed by the axons of PV-IR interneurons, is indicated by the arrow. Scale bars = 50 μm.