Fig. 7. The effect of the nitric oxide synthase inhibitor L-NAME (10^–5 mol l^–1) on 5-hydroxytryptamine (5-HT)-induced clearance rates during the winter. Treatments are either gills that were exposed to 5-HT or gills exposed to both 10^–5 mol l^–1 L-NAME and 5-HT; the ratios are as described in the text. Data are means ± s.e.m.; sample size ranged from 6 to 14. At 10^–5 mol l^–1 5-HT, the means are significantly different (P<0.05).