- 1Whole-cell voltage-clamp recordings in an in vitro brainstem-cranial nerve explant preparation were used to assess the local circuitry activated by vagal input to nucleus tractus solitarii (NTS) neurones in immature rats.
- 2All neurones that responded to vagal stimulation displayed EPSCs of relatively constant latency. Approximately 50 % of these also demonstrated variable-latency IPSCs, and ∼31 % also displayed variable-latency EPSCs to vagal stimulation. All neurones also had spontaneous EPSCs and IPSCs.
- 3Evoked and spontaneous EPSCs reversed near 0 mV and were blocked by the glutamate AMPA/kainate receptor antagonists 6,7-nitroquinoxaline-2,3-dione (DNQX) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) at rest. Evoked EPSCs had rapid rise times (< 1 s) and decayed monoexponentially (τ= 2.04 ± 0.03 ms) at potentials near rest.
- 4At holding potentials positive to ∼−50 mV, a slow EPSC could be evoked in the presence of DNQX or CNQX. This current peaked at holding potentials near −25 mV and was blocked by the NMDA receptor antagonist dl-2-amino-5-phosphonovaleric acid (AP5). It was therefore probably due to activation of NMDA receptors by vagal afferent fibres.
- 5Fast IPSCs reversed near −70 mV and were blocked by the GABAA receptor antagonist bicuculline. In addition, bicuculline enhanced excitatory responses to vagal stimulation and increased spontaneous EPSC frequency. Antagonists to AMPA/kainate receptors reversibly blocked stimulus-associated IPSCs and also decreased the frequency of spontaneous IPSCs.
- 6These findings suggest that glutamate mediates synaptic transmission from the vagus nerve to neurones in the immature NTS by acting at non-NMDA and NMDA receptors. NTS neurones may also receive glutamatergic and GABAergic synaptic input from local neurones that can be activated by vagal input and/or regulated by amino acid inputs from other brainstem neurones.1. Whole-cell voltage-clamp recordings in an in vitro brainstem-cranial nerve explant preparation were used to assess the local circuitry activated by vagal input to nucleus tractus solitarii (NTS) neurones in immature rats.