Receptive field size, chemical and thermal responses, and fiber conduction velocity of rat chorda tympani geniculate ganglion neurons

Abstract

Yokota Y, Bradley RM. Receptive field size, chemical and thermal responses, and fiber conduction velocity of rat chorda tympani geniculate ganglion neurons. J Neurophysiol 115: 3062-3072, 2016. First published March 30, 2016 doi:10.1152/jn.00045.2016.-Afferent chorda tympani (CT) fibers innervating taste and somatosensory receptors in fungiform papillae have neuron cell bodies in the geniculate ganglion (GG). The GG/CT fibers branch in the tongue to innervate taste buds in several fungiform papillae. To investigate receptive field characteristics of GG/CT neurons, we recorded extracellular responses from GG cells to application of chemical and thermal stimuli. Receptive field size was mapped by electrical stimulation of individual fungiform papillae. Response latency to electrical stimulation was used to determine fiber conduction velocity. Responses of GG neurons to lingual application of stimuli representing four taste qualities, and water at 4°C, were used to classify neuron response properties. Neurons classified as SALT, responding only to NaCl and NH 4 Cl, had a mean receptive field size of six papillae. Neurons classified as OTHER responded to salts and other chemical stimuli and had smaller mean receptive fields of four papillae. Neurons that responded to salts and cold stimuli, classified as SALT/ THERMAL, and neurons responding to salts, other chemical stimuli and cold, classified as OTHER/THERMAL, had mean receptive field sizes of six and five papillae, respectively. Neurons responding only to cold stimuli, categorized as THERMAL, had receptive fields of one to two papillae located at the tongue tip. Based on conduction velocity most of the neurons were classified as C fibers. Neurons with large receptive fields had higher conduction velocities than neurons with small receptive fields. These results demonstrate that GG neurons can be distinguished by receptive field size, response properties and afferent fiber conduction velocity derived from convergent input of multiple taste organs. taste; taste bud; geniculate ganglion; chemosensory; chorda tympani PRIMARY AFFERENT NEURONS OF the chorda tympani nerve (CT) convey information to the central nervous system about sensory properties of food. CT fibers have cell bodies in the geniculate ganglion (GG) and respond to chemical, thermal and mechanical properties of oral stimuli (Finger et al. 2005;Fishman 1957;Kumari et al. 2015). Despite the obvious importance of their neurobiological and sensory roles, there is no comprehensive understanding of the full nature of the basic biology of GG neurons. As one example of the lack of information about GG/CT neuron biology, consider how primary afferents conveying skin sensation have been classified based on their peripheral targets (cutaneous, articular and visceral afferents), conduction velocity (afferent axon size and myelination), response properties (sensory modality and intensity thresholds) and neurochemical phenotype (such as peptide expression) (Lawson 2002;Le Pichon and Chesler 2014;McMahon and Priestley...

The transcription factor Phox2b distinguishes between oral and non‐oral sensory neurons in the geniculate ganglion

“…As many of these neurons are gustatory, this implies that neurons in the palate may innervate a greater number of taste receptor cells than neurons in the tongue. However, as some tongue afferents are somatosensory in function (Yokota & Bradley, ), another possibility is that there are more somatosensory neurons innervating the tongue via the chorda tympani compared with the palate via the greater superficial petrosal.…”

Oral thermosensing by murine trigeminal neurons: modulation by capsaicin, menthol and mustard oil

“…Thermal sensations in the oral cavity are ascribed to activation of somatosensory (trigeminal) afferent fibres, although gustatory afferent nerves and sensory neurons in the geniculate ganglion have long been known also to respond to thermal stimuli (Zotterman, , ; Fishman, ; Lundy & Contreras, ; Yokota & Bradley, , ). Interest in oral thermoreception dates back to the earliest studies obtained with single fibre recording methodologies (Zotterman, ).…”

Oral thermosensing by murine trigeminal neurons: modulation by capsaicin, menthol, and mustard oil

“…Thermal sensations in the oral cavity are ascribed to activation of somatosensory (trigeminal) afferent fibres, although gustatory afferent nerves and sensory neurons in the geniculate ganglion have long been known also to respond to thermal stimuli (Zotterman, 1935(Zotterman, , 1936Fishman, 1957;Lundy & Contreras, 1999;Yokota & Bradley, 2016. Interest in oral thermoreception dates back to the earliest studies obtained with single fibre recording methodologies (Zotterman, 1935).…”