Table 1.

Loss of SV2A does not affect synapse number or morphology

	Synapse density, 106 synapses/mm3	Bouton size, area in μm2	Active zone length, nm	Active zone thickness, nm	Vesicle clustering, vesicles/μm2	Vesicle number, mean per synapse	Vesicle diameter, nm
Wild type	668	217 ± 147 (86)	370 ± 25 (115)	7.5 ± 22 (115)	2.4 ± 0.5 (86)	19.1 ± 18.2 (114)	30.4 ± 9.4 (155)
SV2A knockout	620	290 ± 208 (88)	412 ± 19 (112)	6.7 ± 26.3 (103)	2.4 ± 0.9 (88)	21.5 ± 17.3 (110)	37.4 ± 9.4 (190)

The proximal dendritic region of CA3 hippocampal neurons, which receives mossy fiber input from dentate granule neurons and which has a predominance of asymmetric, presumed excitatory synapses, was photographed at ×42,750. Photographs were analyzed for the listed features as described under Methods. Data were obtained from three wild-type and three SV2A-knockout animals, except for the measure of synapse density, which was obtained from three wild types and two SV2A knockouts. Numbers in parentheses indicate the total number of synapses or vesicles analyzed.