(A,J) Representative images of third-instar larval muscle 4 NMJs immunostained with an antibody against BRP. Scale bars: 2μm. (D,M) Representative traces of eEJC, mEJC and paired-pulse (inter stimulus interval (ISI) of 10ms) measurements at third-instar larval muscle 6/7 NMJs. Scale bars: eEJC, paired-pulse traces 10ms, 20mV; mEJC traces 250ms, 2mV. (A,D) Spn mutant phenotype is suppressed by Syd-1 heterozygosity as shown through quantification of (B) BRP spot area (C) BRP density (E) eEJC amplitudes (H) Quantal content and (I) Paired pulse ratio (10ms ISI). (F) mEJC amplitudes are unaltered and (G) mEJC frequency phenotype is not suppressed. (J,M) Syd-1 mutant phenotype is suppressed by Spn heterozygosity as shown through quantification of (K) BRP spot area (L) BRP density (N) eEJC amplitudes (O) mEJC amplitudes (P) mEJC frequency (Q) Quantal content (R) Paired pulse ratio (10ms ISI). See also figures S1 and S2, and table S1.