Does Substance P Enhance Synaptic Transmission at NTS Synapses?
These data were obtained from extracellular recordings of action-potential responses obtained from NTS neurons in the whole animal and from whole-cell patch-clamp recordings obtained from NTS neurons in a coronal brainstem slice preparation. The slice contained the caudomedial NTS, the same region studied in vivo, and the peripheral (including vagal) afferent fibers in the TS. To determine whether exogenous substance P can enhance the transmission of input from peripheral vagal afferent C fibers, we compared the action-potential responses of NTS neurons evoked by electrical stimulation of the vagal afferent C fibers before and during iontophoretic application of substance P in vivo. The findings are illustrated in the example in Figure 4A. Under control conditions, 30 sequential stimuli applied to the ipsilateral vagus nerve at intensities to activate C fibers evoked 16 action potentials for a 53% action-potential response rate. During the iontophoresis of substance P in amounts that d
