Fig. 6: Morphological properties of granule cells in the Islands of Calleja.

a, b A representative granule cell is shown in the Islands of Calleja. This neuron was filled with biocytin during whole-cell patch-clamp recording in the acute coronal slice preparation. The same slice was live-stained with 300 nM Fluo-CAR for the correlated visualization of drug-binding sites and the morphological features of the granule cell. Note that the arborization of the granule cell strictly follows the unique shape of the Islands of Calleja. One of its processes preferentially branches in the hilar subregion, whereas two other major processes arborize in the granular subregion. b 3D reconstruction of the same granule cell. The neuronal process that enters the Fluo-CAR-rich hilar subregion is marked in yellow and hereinafter referred to as the hilar process. The other neurites that remain restricted to the granular subregion are termed the granular processes (blue). c–h Correlated light and electron microscopy was used to determine the integrity of the acute slice preparations used for PharmacoSTORM staining and helped to determine the morphological features of hilar and granular processes. c A representative light micrograph of a biocytin-filled granule cell soma (arrow) in the granular subregion of the Islands of Calleja and its hilar process that has numerous varicosities within the hilus. Inset shows two bouton-like structures (b₁, b₂) at higher magnification from the boxed area. d Electron microscopic images of consecutive serial sections demonstrate that the two boutons (b₁, b₂) are filled with synaptic vesicles, and form symmetric synaptic specializations (arrowheads) on a dendrite (d, pseudo-colored in yellow). e High-magnification electron micrograph of the synapse from the boxed area in (d). f Another biocytin-filled granule cell (arrow) is shown together with its granular process. g Electron microscopic image of the boxed area in (f). h High-magnification electronmicrographs of boxed areas in (g), showing afferent boutons (pseudo-colored in cyan) forming chemical synapses (arrowheads) on the granular process of the granule cell. Panels display representative micrographs from three biologically independent experiments.