Semilunar granule cells in the dentate gyrus represent a distinct type of granule cell, distinguished by their unique morphology and physiology. These cells are located within the inner molecular layer and the upper juxta-granule cell layer of the dentate gyrus. The presence of a smaller number of granule cells has also been observed in the outer molecular layer; however, the information regarding these cells is limited. In the present study, the perisomatic innervation that these two types of granule cells receive was characterized using confocal and electron microscopy. Our findings revealed that both semilunar granule cells and outer molecular layer granule cells receive substantial excitatory and inhibitory perisomatic contacts. The inhibitory contacts are derived from parvalbumin fast-spiking cells and cholecystokinin regular-spiking cells. The origin of excitatory contacts has been traced to hilar mossy cells and supramammillary afferents.
Rovira-Esteban et al. (Wed,) studied this question.