Possible nicotinic receptor-mediated modulation of synaptic transmission in nucleus of the solitary tract.

Signal transmission from afferent nerves to neurons in the nucleus of the solitary tract (NTS) may be mediated partially by nicotinic acetylcholine receptors (nAChRs). Here, we investigated nAChR-mediated signal transmission using rat NTS slices. First, we characterized nAChRs by obtaining patch-clamp recordings from NTS neuronal cell bodies. Under whole cell voltage-clamp conditions at -60 mV, application of nicotine induced an inward current, and this effect was blocked by hexamethonium. In outside-out patch recordings, nicotine was seen to induce a hexamethonium-sensitive single-channel current. Second, we investigated nAChR-mediated signal transmission. Fast synaptic transmission mediated by nAChRs was not detected. The action of diffusible acetylcholine (ACh) on nAChRs was then tested using the outside-out patches excised from NTS neurons as probes for ACh. When the patch was placed at a distance of 20-30 microm from the cell body, single-channel currents were recorded, and these were inhibited by hexamethonium. The frequency of channel opening was increased by high-extracellular potassium concentration solution suggesting the voltage-dependent release ofACh that acts on nAChRs. These results suggested that nAChR-mediated signal transmission from sensory afferents to NTS neurons is in part mediated by diffusible ACh.