Fig. 7. Effect of the NOS inhibitor L-NAME on the 5-HT-stimulated light response. White bars are 5-HT controls (0.03 mmol l^–1 5-HT). Injection of L-NAME (3.0 mmol l^–1) together with 5-HT gave a significantly higher L_tot (P<0.05), compared with the 5-HT control (A). As this treatment was performed in two different months (November and April) a two-factor ANOVA with `treatment' and `month' as factors was used to determine the effect of L-NAME. Month had no significant effect on L_tot. The lower concentrations of L-NAME used had no effect on the L_tot of the 5-HT response. In September and April the 5-HT and L-NAME treatment (0.3 and 3.0 mmol l^–1 L-NAME, respectively) gave a slower response with longer t_ip (B) and a higher RLP_max (C) compared with the 5-HT control (P<0.05). Number of replicates (non-converging data in brackets, not included in the analysis): 5-HT, June, N=10 (1); 5-HT+L-NAME, June, N=8; 5-HT, Sept., N=10 (2); 5-HT+L-NAME, Sept., N=9; 5-HT, Nov., N=9 (1); 5-HT+L-NAME, Nov., N=9 (2); 5-HT, Apr., N=14 (4); 5-HT+L-NAME, Apr., N=15; error bars indicate s.e.m.