CARDIOVASCULAR EFFECTS OF THE LOCAL INJECTION OF 5,7-DIHYDROXYTRYPTAMINE INTO THE NODOSE GANGLIA AND NUCLEUS-TRACTUS-SOLITARIUS IN AWAKE FREELY MOVING RATS

The role of the nucleus tractus solitarius (NTS) serotonergic afferents in cardiovascular (CV) regulation is yet to be established. However, several findings suggest that in this nucleus the serotonergic endings coming from the nodose ganglia (NG) are involved in the control of blood pressure (BP). The purpose of the present study was to identify the CV effects of the destruction of this NG-NTS serotonergic pathway. For that, the BP, BP variability (BPV) and heart rate (HR) effects of the local microinjection of 5,7-dihydroxytryptamine (5,7-DHT), into the NG and NTS were investigated in awake freely moving rats. The local degeneration of serotonergic elements was associated with a significant decrease in the 5-HT and 5-hydroxyindole acetic acid levels within the NG and NTS in 5,7-DHT treated rats. In addition, the microinjection of the neurotoxin in both structures produced a transient and significant increase in BP. This effect was of greater amplitude and associated with an increase in BPV in NG lesioned rats. These results may indicate that the NG-NTS serotonergic pathway participates in the transfer of the messages arising from the aortic baroreceptors. However, the vagal component of the baroreflex assessed with the phenylephrine test was not significantly modified in NG lesioned animals as compared to controls. Consequently, if the present data suggest that the NG-NTS serotonergic pathway plays a depressor role in BP regulation, its involvement in the reflex CV responses triggered by the stimulation of the aortic baroreceptors has yet to be established.