Fig. 5. Effects of glutamate microinjections in the medullary Raphé on fictive lung ventilation frequency. (A-C) Responses were measured in brainstem preparations from (A) pre-metamorphic tadpoles, (B) metamorphic tadpoles, and (C) adult bullfrogs under control conditions [artificial cerebrospinal fluid (aCSF) only; open diamonds)] and in the presence of a 5-HT₃ receptor antagonist (Tropisetron; closed circle). Note that the tropisetron concentration required to affect the frequency response (when present) decreased during development. (D,E) A between stage-group comparison was performed by expressing the frequency response following glutamate microinjection (1 nl pre- and metamorphic tadpoles; 5 nl adult frogs) as (D) the percentage change from baseline, and (E) the percentage change from baseline expressed as the percentage of the maximum lung burst frequency produced by each preparation. The black bars represent the control response (aCSF); the grey bars represent the response in the presence of the 5-HT₃ antagonist (when necessary). Values are expressed as means ± s.e.m. Asterisks indicate values statistically different from baseline values (no stimulation) at *P<0.05 and **P<0.01.