ARTIFICIAL SWEETENERS, NaCl, AND KCl STIMULATE PERIPHERAL TRIGEMINAL

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ARTIFICIAL SWEETENERS, NaCl, AND KCl STIMULATE
PERIPHERAL TRIGEMINAL NERVE CHEMORECEPTORS Vajini
N. Atukorale, Matthew W. Greene, and Wayne L.
Silver Department of Biology, Wake Forest
University, Winston-Salem, NC 27109 atukvn5_at_wfu.e
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Introduction The trigeminal nerve provides
sensory information from the eyes, nose, and
mouth. It is a multisensory nerve, responding to
a variety of irritants in the environment.
Several receptor proteins associated with the
trigeminal nerve mediate these responses.
Artificial sweeteners, which are of obvious
economic importance, are reported to be
irritating at high concentrations. As irritants
they should stimulate the trigeminal nerve. The
present study examined peripheral trigeminal
nerve responses to increasing concentrations of
three artificial sweeteners (Sodium Saccharin,
Sodium Cyclamate, and Acesulfame K), NaCl, and
KCl.
Conclusions The artificial sweeteners tested,
Sodium Saccharin, Sodium Cyclamate, and
Acesulfame K, elicit graded responses (with
respect to increasing concentrations) from the
ethmoid branch of the trigeminal nerve.
Artificial sweeteners stimulate TRPV1 receptors
(capsaicin, irritant receptors) (Riera et al.,
2006) and T2R receptors (bitter receptors) (Kuhn
et al., 2004) in vitro. As both of these receptor
proteins are associated with trigeminal nerves
(Dinh et al., 2003 Finger et al., 2003), either
or both may contribute to the trigeminal nerve
responses to the sweeteners tested. NaCl and
KCl also elicited responses from the trigeminal
nerve. Therefore, Na and K may have played a
role in the response to the sweeteners tested.
However, the thresholds for NaCl and KCl were
higher than those of the sweeteners, suggesting
that the sweeteners must be stimulatory by
themselves. Future experiments will examine
trigeminal nerve responses to the sweeteners in
the presence of TRPV1 and T2R receptor blockers.
Methods Rats were anesthetized with urethane
(ethyl carbamate 1 g/kg injected i.p.). Two
cannulae were inserted into the trachea of each
rat. One cannula allowed the rat to breathe room
air. The second cannula, inserted into the
nasopharynx, was connected via a pump to a
reservoir containing Ringers solution. Stimuli
(1.0 ml) were injected into the flow of Ringers
(10 ml/min), which was allowed to drip from the
rats nose. Rats were restrained in a head holder
and the ethmoid nerve was exposed and placed on a
pair of platinum-iridium wire hook electrodes.
Multiunit neural activity from the ethmoid
nerve was summated using an averaging circuit.
The data were analyzed by taking the maximum
height of the integrated response after stimulus
delivery. Responses are reported as a percentage
of the standard response to 10µM capsaicin.
Concentrations are reported for the injected
solutions.
Figure 2. Stimuli Tested
Capsaicin
Literature Cited Finger TE, Böttger B, Hansen A,
Anderson KT, Alimohammadi H, and Silver WL.
(2003) Solitary chemoreceptor cells in the nasal
cavity serve as sentinels of respiration. PNAS.
1008981-8986. Dinh, Q.T., Groneberg, D.A.,
Mingomataj, E., Peiser, C., Heppt, W., Dinh, S.,
Arck,  P.C., Klapp, B.F., and Fischer, A.
(2003) Expression of substance P and vanilloid
receptor (VR1) in trigeminal sensory neurons
projecting to the mouse nasal mucosa.
Neuropeptides 37, 245-250. Kuhn C, Bufe B, Winnig
M, Hofmann T, Frank O, Behrens M, Lewtschenko T,
Slack JP, Ward CD, Meyerhof W. (2004). Bitter
taste receptors for Saccharin and Acesulfame K.
J Neurosci. 24 10260-10265. Riera C, Damak S,
Coutre JL. (2006). Food flavors and the sweetener
Saccharin activate the transient receptor
potential vanilloid subtype 1 (TRPV1) channel.
Chem Senses. 31 A49-A50.
Acesulfame-K (potassium salt)
Sodium Saccharin
Sodium Cyclamate
NaCl
KCl
Figure 1. Electrophysiological setup. Stimuli
(1.0 ml) were delivered via a syringe into
Ringers solution flowing through the rats nose.
Responses were digitized and recorded on an IBM
computer with Acknowledge software (Biopac).
Figure 2. Stimuli tested.
Figure 3. Multiunit, integrated responses to the
stimuli tested at increasing concentrations.
Figure 4. Concentration-response curves for
the stimuli tested. Responses are reported as a
percent of the response to 10 µM capsaicin.
Error bars have been omitted for clarity. N4