AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 3 869-R873, Copyright © 1997 by American Physiological Society
Possible nicotinic receptor-mediated modulation of synaptic transmission in nucleus of the solitary tract
T. Shiraki, A. Toyoda, H. Sugino, A. Hori and S. Kobayashi
Department of Neuroscience, Graduate School of Human and Environmental Studies, Kyoto University, Japan.
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.
