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Fig. 3. Effects of electrical stimulation of medullary Raphé neurons 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 circles). Note that the tropisetron
concentration required to affect the frequency response (when present)
decreases during development. (D,E) Stage-dependent lung burst frequency
responsiveness to medullary Raphé stimulation expressed as the
percentage change from baseline of the frequency response following 20 Hz
stimulation (D), and as percentage change from baseline expressed as the
percentage of the maximum lung burst frequency produced by each preparation
(E). The black bars represent the control response (aCSF) and 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;
indicates
a value significantly different from control at P<0.01.