Fig. 6. Effect of the NO donors SNP and SNAP on the 5-HT-stimulated light response. White bars are 5-HT controls (0.03 mmol l^–1 5-HT). Injection of either 5-HT and SNP (0.3 mmol l^–1) or 5-HT and SNAP (0.3 mmol l^–1) results in a significantly lower L_tot than injection of 5-HT per se (A, P<0.05). 5-HT controls from September (2004) and December (2004) were combined in the SNAP analysis. Injection of 5-HT and SNAP (0.3 mmol l^–1) results in a significantly lower RLP_max (B) and a significantly higher t_ip (C) than injection of 5-HT per se (P<0.05). SNP did not affect these parameters. Number of replicates (non-converging data in brackets, not included in the analysis): SNP treatment: 5-HT, N=8 (1); 5-HT+SNP (0.03 mmol l^–1), N=5; 5-HT+ SNP (0.3 mmol l^–1), N=6 (2); SNAP treatment: 5-HT L_tot, N=18 (1); 5-HT RLP_max, t_ip, N=10; 5-HT+SNAP, N=8 (1); error bars indicate s.e.m.