a, Schematic representation of active conditioned medium generation (left). Proliferation index (EdU+ and DAPI co-positive nuclei/total DAPI+ nuclei) of pHGG cells (SU-pcGBM2) exposed to plain medium (aCSF), optogenetically stimulated Nlgn3 wild-type cortical slice conditioned medium, or optogenetically stimulated Nlgn3 knockout cortical slice conditioned medium (F = 30.8, P < 0.001). b, c, Proliferation index of patient-derived paediatric cortical glioblastoma (SU-pcGBM2) cells as measured by EdU incorporation 24 h after in vitro exposure to recombinant human NLGN1 at concentrations ranging from 0 to 100 nM (b) or recombinant human NLGN4X or NLGN4Y at 100 nM (c). n = 3 wells per condition. All data are mean ± s.e.m. *P < 0.05, ***P < 0.001, one-way ANOVA with Tukey’s post hoc test for multiple comparisons. n.s. indicates P > 0.05.