While it is widely accepted that tonic and reflex changes in cardiac vagal activity play significant roles in cardiovascular function, little is known about the synaptic pathways in the brainstem responsible for the control of cardiac vagal neurons in the nucleus ambiguus (NA). In this study, we identified the principal post-synaptic receptors activated in cardiac vagal neurons upon stimulation of the nucleus tractus solitarius (NTS). Cardiac vagal neurons were identified by the presence of a retrograde fluorescent tracer and were visualized in rat brainstem slices. Perforated patch clamp techniques were used to record post-synaptic currents. NTS stimulation activated glutamatergic currents in cardiac vagal neurons with a typical delay of 8-18 ms. Post-synaptic responses were separated into NMDA and non-NMDA components using D-2-amino-5-phophonovalerate (AP5) and 6-cyano-7-nitroquinoxaline-2, 3-dione (CNQX), respectively. In conclusion, this study characterizes a monosynaptic glutamatergic pathway from NTS that activates NMDA and kainate/AMPA post-synaptic receptors in cardiac vagal neurons.
Copyright 1998 Elsevier Science B.V.