Responses of Gustatory Cells in the Nucleus of the Solitary Tract of the
Hamster following NaCl or Amiloride Adaptation.
Smith, David V., Hongyang Liu, and Mark B. Vogt.
Department of Anatomy, University of Maryland School of Medicine, Baltimore
MD 21201-1559 and Department of Molecular and Cellular Physiology, University
of Cincinnati College of Medicine, Cincinnati OH 45267.
APStracts 3:0015N, 1996.
SUMMARY AND CONCLUSIONS
1. The responses of single NST neurons in the hamster were recorded to an
array of Na + and non-Na + stimuli under each of three adaptation conditions:
distilled H 2 O, 0.032 M NaCl, and 10 [mu]M amiloride. Each adapting solution
flowed for 60 sec prior to delivery of one of seven test stimuli: 0.032 M
NaCl, NaNO 3 , and Na-gluconate, 0.1 M KCl and sucrose, 1 mM HCl, and 3 mM
quinine hydrochloride (QHCl). Stimuli were dissolved in distilled H 2 O (H 2 O
and NaCl adaptation conditions) or 10 [mu]M amiloride (amiloride adaptation
condition). 2. Both amiloride treatment and NaCl adaptation reduced responses
to the Na + stimuli. The effects of NaCl adaptation were generally greater
than those of amiloride and the responses to the Na + salts were reduced by
NaCl adaptation in every cell that responded to NaCl, regardless of its best-
stimulus classification. Amiloride treatment suppressed the responses to Na +
salts with larger anions (NaNO 3 and Na-gluconate) more than the response to
NaCl. 3. Unlike amiloride treatment, NaCl adaptation also reduced responses to
several non-Na + stimuli (KCl, HCl, and QHCl). This effect occurred primarily
in the NaCl-best neurons that were most highly responsive to NaCl and which
showed a postexcitatory suppression following NaCl. This suppression has been
observed in recordings from the chorda tympani nerve in both rats and hamsters
and in taste receptor cell responses recorded in situ in the rat. If it is a
receptor phenomenon, these data would imply that some NaCl-sensitive receptor
cells are also responsive to these non-Na + electrolytes. 4. The effects of
amiloride on the responses to Na + stimuli were not limited to NaCl-best
neurons, but occurred in sucrose-best cells as well. These results suggest
that the sucrose-best cells in the NST receive converging input from sucrose-
and NaCl-best chorda tympani fibers, since there is little Na + sensitivity in
the peripheral sucrose-best fibers and the amiloride sensitivity is restricted
to NaCl-best chorda tympani fibers. The responses to NaCl in the few HCl- and
QHCl-best NST neurons were not affected by amiloride. 5. Rinsing the tongue
with amiloride for 60 sec resulted in a reduction in the baseline response
rate of NST cells. This effect occurred primarily in NaCl- and sucrose-best
NST neurons and implies that much of the spontaneous activity in these
brainstem cells arises from amiloride-sensitive channel activity in the
peripheral receptor cells. 6. The results of human psychophysical studies show
very different effects of NaCl adaptation and amiloride treatment. Adaptation
to NaCl produces a robust and specific reduction in the saltiness of all
salts. The present results show that NaCl adaptation reduces the responses of
all cells sensitive to NaCl. Treatment of the human tongue with amiloride
produces a proportionately smaller reduction in the response to NaCl than it
does in rodents and it appears to have no effect on saltiness. Rather,
amiloride has been shown to specifically reduce the sour side taste of NaCl,
Na-gluconate, and LiCl. Therefore, conclusions about the effects of amiloride
on taste quality based on rodent electrophysiology are questionable.
Received 2 August 1995; accepted in final form 28 December 1995.
APS Manuscript Number J500-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96