5-HT acting on 5-HT1/2 receptors does not participate in the in vitro hypoxic respiratory depression

The involvement of serotoninergic mechanisms in the central respiratory dep ression produced by hypoxia was studied in the newborn rat brainstem-spinal cord preparation. The respiratory frequency measured by the C4 ventral roo t activity was recorded. 5-HT (30 muM) superfusion elicited a rapid increas e in respiratory frequency, prevented by a treatment with methysergide (a 5 -HT1/2 receptor antagonist) (40 muM). To investigate the possible participa tion of 5-HT in hypoxic respiratory depression, this concentration of methy sergide was added to the bathing medium during hypoxia. Methysergide did no t modify the decrease in respiratory frequency produced by hypoxia. In orde r to ensure that other 5-HT subtype receptors were not involved in hypoxic respiratory depression, 5-HT was added to the bath during hypoxic-methyserg ide tests; no effect on respiratory frequency was observed. These results s uggest that in the newborn rat brainstem-spinal cord preparation, serotonin ergic mechanisms are not involved in the elaboration of the in vitro respir atory response to hypoxia. (C) 2001 Elsevier Science Ireland Ltd and the Ja pan Neuroscience Society. All rights reserved.