Figure 1.

Morphological and electrophysiological characteristics of dissociated hippocampal neurons expressing the human disease variants in Stxbp1 null mouse neurons. (A) Schematic overview of some of the previously discovered STXBP1 truncations, deletions and missense mutations in human patients showing the seven mutations tested in colour-coded boxes. (B) Dissociated cortical neurons were stained for Munc18-1, dendritic marker MAP2 and synaptic marker synaptobrevin (VAMP). Examples represent Stxbp1 null neurons expressing wild-type Munc18-1 (WT), C180Y or M433R. (C–G) Morphological and synaptic characteristics of Munc18-1 wild-type neurons, Stxbp1^+/− neurons and null mutant neurons expressing one of the human disease variants: (C) mean synapse density calculated as the ratio of synapse number and total dendritic length. (D) Mean soma Munc18-1 level. (E) Mean synaptic Munc18-1 level. (F and G) Mean somatic and synaptic syntaxin-1 level. (H) Example traces of evoked release from wild-type neurons, Stxbp1 null neurons expressing C180Y and M433R upon a single action potential stimulation. (I) Mean EPSC amplitude expressed as the ratio of the wild-type value. (J) Paired-pulse ratio (calculated as the ratio of second EPSC and first EPSC) depending on the pulse interval. (K) Frequency of spontaneous release normalized to the wild-type values. (L). Amplitude of spontaneous release normalized to the wild-type values. (M) Example traces of spontaneous release in Stxbp1 null neurons expressing Munc18-1 wild-type, C180Y or M433R human variants. (N) The size of the readily releasable pool derived from back extrapolation of cumulative total charge released during 40 Hz train, 100 APs. The number of analysed cells is indicated in the bars. *P < 0.05, **P < 0.01, ***P < 0.001 versus infected wild-type control. Explanation of statistical analysis is provided in the Supplementary material. mEPSC = mini excitatory postsynaptic current; RRP = readily releasable pool.