In vivo recordings from rat geniculate ganglia: taste response properties of individual greater superficial petrosal and chorda tympani neurones

Abstract

Coding of gustatory information is complex and unique among sensory systems; information is received by multiple receptor populations located throughout the oral cavity and carried to a single central relay by four separate nerves. The geniculate ganglion is the location of the somata of two of these nerves, the greater superficial petrosal (GSP) and the chorda tympani (CT). The GSP innervates taste buds on the palate and the CT innervates taste buds on the anterior tongue. To obtain requisite taste response profiles of GSP neurones, we recorded neurophysiological responses to taste stimuli of individual geniculate ganglion neurones in vivo in the rat and compared them to those from the CT. GSP neurones had a distinct pattern of responding compared to CT neurones. For example, a small subset of GSP neurones had high response frequencies to sucrose stimulation, whereas no CT neurones had high response frequencies to sucrose. In contrast, NaCl elicited high response frequencies in a small subset of CT neurones and elicited moderate response frequencies in a relatively large proportion of GSP neurones. The robust whole-nerve response to sucrose in the GSP may be attributable to relatively few, narrowly tuned neurones, whereas the response to NaCl in the GSP may relate to proportionately more, widely tuned neurones. These results demonstrate the diversity in the initial stages of sensory coding for two separate gustatory nerves involved in the ingestion or rejection of taste solutions, and may have implications for central coding of gustatory quality and concentration as well as coding of information used in controlling energy, fluid and electrolyte homeostasis.

Anion size modulates salt taste in rats

“…In the present study, we recorded single-cell spike discharges from the geniculate ganglion to a battery of taste solutions representing the four basic taste qualities, and to concentration series of NaCl and Nagluconate. Single cell responses were examined in detail, especially between 500 and 1,000 ms, when rats discriminate taste quality and intensity (Geran and Spector 2000b;Halpern and Tapper 1971) and longer recording intervals (5 s) for consistency with our laboratory's prior studies (Breza et al 2007;Breza et al 2010;Lundy and Contreras 1999) and those in the literature (Geran and Travers 2006; Smith and Travers 1979;Sollars and Hill 2005). Parallel whole nerve studies were performed to compare our results with previous studies using similar methods.…”

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

“…The overall goal was to examine sensory coding of the afferent input and not the basic biology of the GG neurons. Similar to earlier investigations, GG/CT neuron responses can be "grouped" as NaCl specialist, NaCl generalist and HCl generalist (Lundy and Contreras 1999;Sollars and Hill 2005). When additional stimuli were added, the resulting classification of GG neuron responses changed (Sollars and Hill 2005), so that many of the GG neurons that were classified as salt (NaCl) specialist in fact responded to NH 4 Cl also.…”

“…We did not follow the classification of chemosensory responses identified by prior investigations of GG/CT neurons (Lundy and Contreras 1999;Sollars and Hill 2005). In particular, we did not identify the "salt specialist" classification of response sensitivity.…”

“…When additional stimuli were added, the resulting classification of GG neuron responses changed (Sollars and Hill 2005), so that many of the GG neurons that were classified as salt (NaCl) specialist in fact responded to NH 4 Cl also. Not surprisingly, in data from responses of GG/CT single neurons, a similar distribution of broad response profiles has been demonstrated (Lundy and Contreras 1999;Sollars and Hill 2005).…”

“…Arguing that, because single-axon recordings from the CT involve sectioning of the nerve that results in injury and limits recording time, Boudreau recorded extracellularly from GG neurons while stimulating the tongue with a range of chemical stimuli (Boudreau et al 1971(Boudreau et al , 1985. The Boudreau approach was later used by the laboratories of Contreras and Hill to reexamine responses of rat GG neurons and determine their sensitivity to chemical stimulation of the tongue (Lundy and Contreras 1999) and soft palate (Sollars and Hill 2005). The overall goal was to examine sensory coding of the afferent input and not the basic biology of the GG neurons.…”