Effect of activation of 5-HT1A receptors at the ventral medulla on phrenic nerve activity.

The purpose of this study was to determine the effects of the 5-HT1A receptor agonist, 8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide (8-OH-DPAT), on respiratory activity (phrenic nerve activity) following application to the ventral medullary surface in the cat. In addition, in order to determine if the action of 8-OH-DPAT was localized to structures at the ventral medulla, we examined the distribution of [3H]8-OH-DPAT to other brain regions and to the peripheral circulation. 8-OH-DPAT (0.0625-8 micrograms) produced a dose-related increase in respiratory rate when applied at either the intermediate or caudal areas on the ventral surface of the medulla. The maximal change in respiratory rate was 9 +/- 2 and 8 +/- 1 breaths/min at the intermediate and caudal areas, respectively. Integrated phrenic nerve amplitude was not significantly affected at these sites except at the 8 micrograms dose where it was decreased. No change in phrenic nerve activity was observed with 8-OH-DPAT application at the rostral area. [3H]8-OH-DPAT was not found to distribute to other brain regions or to the peripheral circulation following application to the ventral medullary surface. The results of this study suggest that 8-OH-DPAT causes changes in respiratory activity, primarily respiratory rate, by acting on neuronal structures at the ventral surface of the medulla.