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Gustatory modulation of the responses of trigeminal subnucleus caudalis neurons to noxious stimulation of the tongue in rats
Author(s) -
Boucher Yves,
Felizardo Rufino,
Klein Amanda H.,
Carstens Mirela I.,
Carstens Earl
Publication year - 2013
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.12282
Subject(s) - neuroscience , noxious stimulus , stimulation , tongue , diffuse noxious inhibitory control , chemistry , anatomy , nociception , psychology , medicine , pathology , receptor , biochemistry
Certain tastants inhibit oral irritation by capsaicin, whereas anesthesia of the chorda tympani ( CT ) enhances oral capsaicin burn. We tested the hypothesis that tastants activate the CT to suppress responses of trigeminal subnucleus caudalis ( V c) neurons to noxious oral stimuli. In anesthetized rats, we recorded V c unit responses to noxious electrical, chemical (pentanoic acid, 200 μ m ) and thermal (55 °C) stimulation of the tongue. Electrically evoked responses were significantly reduced by a tastant mix and individually applied N a C l, monosodium glutamate ( MSG ), and monopotassium glutamate. Sucrose, citric acid, quinine and water (control) had no effect. Pentanoic acid‐evoked responses were similarly attenuated by N a C l and MSG , but not by other tastants. Responses to noxious heat were not affected by any tastant. Transection and/or anesthesia of the CT bilaterally affected neither V c neuronal responses to electrical or pentanoic acid stimulation, nor the depressant effect of N a C l and MSG on electrically evoked responses. Calcium imaging showed that neither N a C l nor MSG directly excited any trigeminal ganglion cells or affected their responses to pentanoic acid. GABA also had no effect, arguing against peripheral effects of GABA , N a C l or MSG on lingual nocicepive nerve endings. The data also rule out a central mechanism, as the effects of N a C l and MSG were intact following CT transection. We speculate that the effect is mediated peripherally by the release from taste receptor cells (type III ) of some mediator(s) other than GABA to indirectly inhibit trigeminal nociceptors. The results also indicate that the CT does not exert a tonic inhibitory effect on nociceptive V c neurons.