Gustatory Neuron Types in Rat Geniculate Ganglion

• Published in: Journal of neurophysiology 1999-12, Vol.82 (6), p.2970-2988
• Main Authors: Lundy, Robert F., Jr, Contreras, Robert J
• Format: Article
• Language: English
• Subjects: Animals; Chorda Tympani Nerve - cytology; Chorda Tympani Nerve - drug effects; Cluster Analysis; Diuretics - pharmacology; Electric Stimulation; Electrodes, Implanted; Extracellular Space - physiology; Female; geniculate ganglion; Geniculate Ganglion - cytology; Geniculate Ganglion - physiology; Hot Temperature; In Vitro Techniques; Male; Neurons, Afferent - physiology; Rats; Rats, Sprague-Dawley; Signal Transduction - drug effects; Stereotaxic Techniques; Stimulation, Chemical; sucrose; Taste - physiology; Tongue - innervation
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.1999.82.6.2970

Department of Psychology, Florida State University, Tallahassee, Florida 32306-1270 Lundy Jr., Robert F. and Robert J. Contreras. Gustatory Neuron Types in Rat Geniculate Ganglion. J. Neurophysiol. 82: 2970-2988, 1999. We used extracellular single-cell recording procedures to characterize the chemical and thermal sensitivity of the rat geniculate ganglion to lingual stimulation, and to examine the effects of specific ion transport antagonists on salt transduction mechanisms. Hierarchical cluster analysis of the responses from 73 single neurons to 3 salts (0.075 and 0.3 M NaCl, KCl, and NH 4 Cl), 0.5   M sucrose, 0.01 M HCl, and 0.02 M quinine HCl (QHCl) indicated 3 main groups that responded best to either sucrose, HCl, or NaCl. Eight narrowly tuned neurons were deemed sucrose-specialists and 33 broadly tuned neurons as HCl-generalists. The NaCl group contained three identifiable subclusters: 18 NaCl-specialists, 11 NaCl-generalists, and 3 QHCl-generalists. Sucrose- and NaCl-specialists responded specifically to sucrose and NaCl, respectively. All generalist neurons responded to salt, acid, and alkaloid stimuli to varying degree and order depending on neuron type. Response order was NaCl > HCl = QHCl > sucrose in NaCl-generalists, HCl > NaCl >   QHCl > sucrose in HCl-generalists, and QHCl = NaCl = HCl > sucrose in QHCl-generalists. NaCl-specialists responded robustly to low and high NaCl concentrations, but weakly, if at all, to high KCl and NH 4 Cl concentrations after prolonged stimulation. HCl-generalist neurons responded to all three salts, but at twice the rate to NH 4 Cl than to NaCl and KCl. NaCl- and QHCl-generalists responded equally to the three salts. Amiloride and 5-( N,N -dimethyl)-amiloride (DMA), antagonists of Na + channels and Na + /H + exchangers, respectively, inhibited the responses to 0.075 M NaCl only in NaCl-specialist neurons. The K + channel antagonist, 4-aminopyridine (4-AP), was without a suppressive effect on salt responses, but, when applied alone in solution, it evoked a response in many HCl-generalists and one QHCl-generalist neuron so tested. Of the 39 neurons tested for their sensitivity to temperature, 23 responded to cooling and chemical stimulation, and 20 of these neurons were HCl-generalists. Moreover, the responses to the four standard stimuli were reduced progressively at lower temperatures in HCl- and QHCl-generalist neurons, but not in NaCl-specialists. Thus sodium channels and Na + /H + exchangers appear to be exp