Role of 5-HT2A/C receptors in serotonergic modulation of respiratory motor output during tadpole development.

We tested the hypothesis that 5-HT(2A/C) receptors contribute to the modulation of respiratory motor output elicited by serotonin bath-application in the in vitro brainstem preparation from bullfrog tadpoles. Preparations were superfused with (1) a selective 5-HT(2A/C) receptor agonist (DOI, 0.5-25 microM) or (2) 5-HT in presence of a non-selective 5-HT(2A/C) receptor antagonist (methysergide maleate, 10 microM). Stage-related differences in 5-HT(2A/C) modulation were assessed by performing experiments on two groups: pre- and post-metamorphic tadpoles. 5-HT(2A/C) receptor activation with DOI did not alter either gill or lung burst frequency. Methysergide did not prevent the gill burst frequency attenuation elicited by 5-HT. Our results show no apparent contribution of the 5-HT(2A/C) receptor subtypes to the serotonergic modulation of either gill- or lung-related neural activity in either group. While 5-HT(2A/C) receptors are involved in the modulation of respiratory motor output in mammals, these receptor subtypes do not appear to play a significant role in this species.