Figure 9.
Serotonin and substance P in concert are required to generate and maintain the respiratory rhythm and motor output in situ. Antagonism of 5-HT1,2 receptors with the nonselective receptor antagonist MeSG (20 μm) did not affect inspiratory rhythm generation, as shown by the lack of effect on inspiratory burst frequency (XII/PN), but strongly reduced PN and XII nerve burst amplitudes. Addition of the NK-1 antagonist SR (20 μm) nearly eliminated all inspiratory burst activity, as shown by the significant large decreases in burst frequency and amplitudes. This suggests that endogenous 5-HT and NK-1 receptor activation work in concert to generate and maintain inspiratory activity in situ. Error bars indicate SEM.