Fig. 2.

Morphology of biocytin-filled neurons in the OML. Three representative examples of OML interneurons are illustrated showing dendritic variability. A, Interneuron recorded and filled in a postnatal day 17 (P17) hippocampal slice with a fusiform morphology. The soma is located in the middle third of the OML. B, Multipolar interneuron from a P13 rat situated near the hippocampal fissure. The very short thin dendrites are confined to the OML. The main axon is marked by the open arrow, and projecting collaterals are marked by filled arrows. C, Pyramidal-like interneuron recorded and filled at P11, located in the inner third of the OML. The long apical dendrite descends into the hilar region via the granule cell layer. D, Single fiber (arrows) crossing the hippocampal fissure (hf).E, Photo montage of a displaced granule cell recorded and filled at P17. The soma is located in the inner third of the OML, and the main axon (open arrow) descends through the granule cell layer, giving rise to several collaterals (filled arrows) within the hilar region. In all micrographs the hippocampal fissure (hf) is delineated by the dashed line. GCL, Granule cell layer; H, hilar region; iml, inner molecular layer of the dentate gyrus; ml, molecular layer of the subiculum; oml, outer molecular layer of the dentate gyrus. Scale bars: in A–C, E, 50 μm; in D, 25 μm.