Figure 2. Features that distinguish granule cells from semilunar granule cells. A, Illustration of a fully reconstructed granule cell shows the typical location of the somata in the granule cell layer (GCL) and compact dendritic spread in the molecular layer (ML). The axon (mossy fiber, thin line) is seen projecting in the hilus, toward CA3. Inset, Confocal image shows labeling for biocytin (left), Prox1 (middle), and the merged image (right), illustrating colabeling. Scale bar, 5 μm. B, Reconstruction of a biocytin-filled semilunar granule cell shows the location of somata in the ML and demonstrates the wider dendritic span compared with the granule cell in A. Note the high degree of branching of the SGC axon (thin line) in the hilus and projection to CA3. Inset, Confocal image of the somata of the SGC in B shows labeling for biocytin (left), Prox1 (middle), and the merged image (right), illustrating colabeling. Scale bar, 5 μm. C, Membrane voltage traces from the granule cell in A show the highly adapting firing pattern in response to +200 pA current injection and hyperpolarization during a −120 pA current injection. D, Current-clamp recordings from the semilunar granule cell in B illustrate the continuous firing with low adaptation during a +200 pA depolarizing current injection from a holding potential of −70 mV. Note that the hyperpolarization in response to a −120 pA current injection is smaller than in the granule cell in C. Inset, Expanded membrane voltage trace shows the slow ramp depolarization (arrowhead) and large, slow afterhyperpolarization (arrow) that are distinctive of SGCs. E, Summary histogram shows lower spike frequency adaptation ratio (i.e., higher adaptation) in granule cells compared with SGCs. F, Summary plot illustrates the low input resistance of SGCs compared with granule cells. *p < 0.05, Student's t test.