Fig. 3. (A) The effects of continuous infusion of control saline (unfilled bars; N=8) or rapidly switching to saline containing nicotine (10^–5 mol l^–1; filled bars; N=8) or nicotine plus a cocktail of 10^–3 mol l^–1 hexamethonium and 10^–5 mol l^–1 atropine (cross-hatched bars; N=8) on catecholamine secretion in an in situ perfused posterior cardinal vein preparation of rainbow trout Oncorhynchus mykiss. (B) After 10 min, the preparations were electrically stimulated using a frequency of 1 Hz and maximal catecholamine secretion rates were determined under the various conditions. An asterisk denotes a statistically significant difference from the `pre-switch' (Pre) value; a dagger represents a significant difference from the secretion rate after 10 min.