(A) Synaptic terminal endocytosis was analyzed in WT and MPS-IIIA DIV14 hippocampal neurons by quantification of incorporated FM1-43 dye fluorescence in ~300 individual boutons (taken from 4-5 coverslips for each group). Fluorescence intensities were expressed as arbitrary units (A.F.U.) and displayed both as a distribution and as mean values ± s.e.m. 