Fig. 6. Dose- and stage-dependent changes in fictive lung and buccal burst frequency during application of increasing concentration of the ₂-adrenoceptor agonist clonidine (Clo). Clo application was followed by a 30-90 min wash-out period. (A) Data expressed as a percentage change from baseline lung values, and (B) data expressed as a percentage change from baseline buccal values. In A, lung burst frequency responses were measured in pre-(triangles; N=9) and metamorphic tadpoles (squares; N=7), and adult frogs (circles; N=12). For fictive buccal burst frequency responses (B), mean data were obtained in pre-(N=9) and metamorphic tadpoles (N=6), and adult frogs (N=2). Adults were excluded from the statistical analysis since the number of replicates was too low; for this group, data are displayed without error bars. Values are expressed as means ± s.e.m. ^*Values statistically different from baseline, P<0.05. ^**Values statistically different from baseline, P<0.10. Values statistically different from corresponding values from the pre-metamorphic group, P<0.05.