(a) Schematic of NLGN2 and 3 showing positions of chimera. Yellow are critical dimerization residues, pink is splice site A, grey SP is signal peptide, and black TM is transmembrane domain. (b) Scatter plot showing that adding NLGN2 onto the NLGN3 extracellular region up to the 623rd residue fails to enhance IPSCs (p=0.4229, n = 16). (c) Scatter plot showing that adding up to the 180th residue also fails to enhance IPSCs (p=0.2754, n = 10). (d) Scatter plot showing that adding up to the 52nd residue is successful at conferring NLGN function at inhibitory synapses and enhancing IPSCs (**p=0.002, n = 10) (e) Expression of further chimeric constructs identifies a domain between residue 52–180 on NLGN2 that is sufficient to confer the ability to enhance IPSCs to NLGN3 (**p=0.0039, n = 9). Within this region, we also expressed only (f) the region between 52–164 (**p=0.0098, n = 10) or (g) residues corresponding to differences in splice site A (164–180) (p=0.0522, n = 12). (h) Summary graph. While the chimeric construct NLGN2-52-164-NLGN3 showed enhancement of IPSCs compared to untransfected control cells, the level of potentiation was significantly less than what we see with full-length NLGN2 (*p=0.0152). For panels b-g, open circles are individual pairs, filled circle is mean ± s.e.m. Black sample traces are control, green are transfected. Scale bars represent 100 pA and 50 ms. For panel h, graph plots mean transfected amplitude ± s.e.m, expressed as a percentage of control amplitude. Significance above each column represents pairwise comparison between transfected and untransfected cells. See also Figure 3—figure supplement 1.