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Fig. 5. Evidence for H2S involvement in trout gill chemoreceptors. (A)
Injection of 5 µmol H2S into the buccal cavity of an
unanesthetized 600 g trout previously implanted with a pressure cannula in,
and flow probe around, the bulbus arteriosus produces a bradycardia within 5 s
that mimics a hypoxic bradycardia. Pva, ventral aortic
pressure; CO cardiac output. (B) Heart rate following intrabuccal injection of
a 1 ml bolus of H2S in intact trout (black bars;
N=13–15) or trout with either the first (Gill 1; white bars;
N=7) or second (Gill 2; stippled bars; N=6) pair of gills
removed. Dashed lines indicate mean ± s.e.m. heart rate of all fish
prior to H2S. H2S produced a dose-dependent bradycardia
in control trout that was similar to that produced in trout with the second
pair of gills removed. Removal of the first pair of gills decreased
H2S sensitivity. 
Significantly different from
pre-H2S; *significantly different from intact trout
after H2S injection. The bradycardia at 5 and 10 mmol
l–1 is significantly (*) attenuated in trout with
the first pair of gills removed relative to the two other groups. Adapted from
Olson (Olson et al., 2008b),
with permission.
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