Gustatory Responses of the Hamster Mesocricetus auratus to Various
Compounds Considered Sweet by Humans
VICKTORIA DANILOVA, 1 GÖRAN HELLEKANT, 1 JEAN-MARIE TINTI, 2 AND CLAUDE NOFRE 2
1
Animal Health and Biomedical Sciences, The University of Wisconsin-Madison, Madison, Wisconsin 53706; and
2
Université Claude Bernard, Faculté de Médecine Alexis Carrel, 69372 Lyon, France
INTRODUCTION
The hamster was for 40 years a recurrent animal model
in taste research (Carpenter 1956; Cummings et al. 1996;
Fishman 1957; Formaker and Frank 1996; Frank 1972, 1973;
Frank et al. 1987, 1988; Frank and Nowlis 1989; Hanamori
et al. 1988; Hellekant and Roberts 1983; Hyman and Frank
1981; Noma et al. 1974; Ogawa et al. 1968, 1969; Rehnberg
et al. 1990).
However, during these 40 years it also became increasingly evident that there are major differences in the sense
of taste among mammalian species. Taste differences were
especially documented in primate sweet taste where many
differences can be related to the phylogeny (Glaser et al.
1995; Hellekant and Danilova 1996; Hellekant et al. 1997a;
Nofre et al. 1996). However, between nonprimate species
profound differences also exist in taste (cf. Jakinovich and
Sugarman 1988 and Kare 1961), although these differences
were not studied as systematically as in primates. Therefore
one purpose here is to improve our understanding of differences in taste across species by testing in hamsters the taste
of a number of compounds considered sweet by humans.
Another purpose of this study relates to data in primate
research demonstrating that two hedonically opposed groups
of taste fibers can be distinguished (Danilova et al. 1998;
Hellekant et al. 1997a,b). One group, the S-fibers, responds
most and best to compounds humans consider sweet, although by no means do all compounds sweet to humans
evoke a response in these S-fibers. Activity in the other
group, the Q-fibers, elicits a rejection to the compound that
caused the activity. The final hedonical response is the result
of these two opposing activities in the same way as sympathetic and parasympathetic activity determine the autonomic
response. This study determines how applicable this idea is
to the hamster by relating the neural with the behavioral
responses to a large number of compounds.
METHODS
Chemicals
Table 1 lists the solutions used in the electrophysiological and
behavioral experiments. Twenty-six of these compounds are sweet
to humans, as indicated in the right column. Figure 1 presents the
structure of some of the more unusual sweeteners.
The compounds were dissolved in distilled water for the twobottle preference (TBP) and conditioned taste aversion (CTA)
experiments and in artificial hamster saliva for electrophysiological
experiments. The composition of the artificial saliva was based on
the composition of pilocarpine-stimulated natural hamster saliva
(Rehnberg et al. 1992) and was made from 6.6 mM NaHCO3 ,
15 mM KCl, 28 mM KHCO3 , pH 8.5. Because 10 mM quinine
hydrochloride (QHCl) did not dissolve in the saliva, it was dissolved in distilled water. Precipitation also prevented the use of Dand L-asparagine over 24-h periods in the TBP tests.
Electrophysiology
The recordings were obtained from the chorda tympani proper
(CT) nerve of nine golden hamsters, Mesocricetus auratus, of both
sexes, 7- to 10-mo old. Anesthesia was initiated with 0.1 ml im
Innovar followed by 0.1 ml pentobarbital sodium, 15 mg/ml im
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Danilova, Vicktoria, Göran Hellekant, Jean-Marie Tinti, and
Claude Nofre. Gustatory responses of the hamster Mesocricetus
auratus to various compounds considered sweet by humans. J.
Neurophysiol. 80: 2102–2112, 1998. The taste of 30 compounds
was studied in the golden hamster with three different methods:
single-fiber recordings, two-bottle preference (TBP), and conditioned taste aversion (CTA) tests. On the whole, the results showed
that the sense of taste in the hamster differs in many respects from
that in humans because, of 26 tested compounds known as sweet
to humans, 11 had no taste or tasted differently. The results also
supported the notion that activity in S-fibers elicits liking and activity in Q- or H-fibers rejection. Specifically hierarchial cluster analysis of 36 single fibers from the chorda tympani proper nerve separated N-, H-, and S-clusters consisting of 11 sucrose-, 14 NaCl-,
and 11 citric-best fibers. Ace-K, cyanosuosan, N-4-cyanophenylN *-cyanoguanidineacetate (CCGA), D-tryptophan, N-3,5-dichlorophenyl-N *-(S)-a-methylbenzylguanidineacetate (DMGA), saccharin, SC-45647, and suosan stimulated only the S-fibers, were
significantly preferred in TBP tests, and generalized to sucrose in
the CTA tests. Ethylene glycol stimulated the N-fibers in addition
to the S-fibers. This explains its generalization to sucrose in CTA.
Its toxicity may contribute to its rejection in TBP tests. Sodium
cyclamate stimulated a few N- but no S-fibers, which may explain
the nondiscriminatory TBP and CTA results. Glycine elicited its
largest response in the S-fibers, although it also stimulated other
fibers. The resulting mixed taste sensation may explain why it was
not preferred in TBP, although it generalized to sucrose in the
CTA. Alitame, aspartame, N-4-cyanophenylcarbamoyl-L-aspartyl(R)-a-methylbenzylamine (CAM), N-4-cyanophenylcarbamoyl(R, S)-3-amino-3-(3,4-methylenedioxyphenyl) propionic acid
(CAMPA), N-(S)-2-methylhexanoyl-L-glutamyl-5-amino-2-pyridinecarbonitrile (MAGAP), N-1-naphthoyl-L-glutamyl-5-amino2-pyridinecarbonitrile (NAGAP), NHDHC, superaspartame, and
thaumatin were among the compounds considered sweet by humans that gave no response, were not discriminated in the TBP
test, and gave no generalization in the CTA tests.
GUSTATORY RESPONSES OF HAMSTER TO SWEETENERS
TABLE
1.
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List of solutions used in electrophysiological and behavioral experiments with hamsters
Solutions for Single CT
Fibers Recordings
NaCl, 70 mM
Citric acid, 20 mM
L-Asparagine, 333 mM
QHCl, 10 mM
L-Tryptophan, 19.5 mM
Solutions for CTA
Experiments
L-Asparagine,
L-Tryptophan, 19.5 mM
ADGA, 25 mM
NHDHC, 0.48 and 0.72 mM
CAM, 0.176 and 0.86 mM
Alitame, 0.15 and 1.5 mM
Aspartame, 2.7 and 15 mM
Superaspartame, 60 and 400 mM
NAGAP, 24.8 mM
Thaumatin, 1.4 and 12.7 mM
MAGAP, 27.7 and 166 mM
Cyclamate-Na, 10, 25, and 50 mM
CAMPA, 28 and 280 mM
Dulcin, 1.6 mM
TGC, 0.165 mM
D-Tryptophan, 19.5 mM
Saccharin, 1.6 mM
Ethylene glycol, 2.86 M
Acesulfame-K, 4 mM
Suosan, 1.13 mM
CCGA, 0.205 mM
Sucrose, 0.2 M
DMGA, 27.3 mM
Cyanosuosan, 2.14 mM
CGA, 0.76 mM
SC-45647, 43.4 mM
Glycine, 0.89 M
333 mM
L-Tryptophan, 19.5 mM
ADGA, 25 mM
NHDHC, 0.48 mM
CAM, 0.176 mM
Alitame, 0.15 mM
Asparatame, 2.7 mM
Superaspartame, 60 mM
NAGAP, 24.8 mM
Thaumatin, 1.4 mM
MAGAP, 27.7 mM
Cyclamate-Na, 10 mM
CAMPA, 28 mM
Dulcin, 1.6 mM
TGC, 0.165 mM
D-Tryptophan, 19.5 mM
Saccharin, 1.6 mM
Ethylene glycol, 2.86 M
Acesulfame-K, 4 mM
D-Asparagine, 0.333 mM
Suosan, 1.13 mM
CCGA, 0.205 mM
Sucrose, 0.2 M
DMGA, 27.3 mM
Cyanosuosan, 2.14 mM
CGA, 0.76 mM
SC-45647, 43.4 mM
Glycine, 0.89 M
Potency in Human Compared With Sucrose
Bitter/sweet 0.21 (0.376%) (Haefeli and Glaser 1990)
Bitter (Haefeli and Glaser 1990)
10,0001 (2%) (Nofre et al. 1990)
9051 (5%) (DuBois et al. 1991)
1,5001 (2%) (Nofre and Tinti 1987)
2,955 1 (5%) (DuBois et al. 1991)
1961 (5%) (DuBois et al. 1991)
3,9001 (5%) (Nofre and Tinti 1993b)
30,0001 (2%) (Nofre and Tinti 1993b)
14,2851 (5%) (DuBois et al. 1991)
20,0001 (2%) (Nofre and Tinti 1993a)
311 (5%) (DuBois et al. 1991)
15,0001 (2%) (Nofre et al. 1996)
2501 (2%) (Paul 1922)
3,0001 (2%) (Tinti et al. 1981)
351 (0.376%) (Shallenberger 1993)
4401 (5%) (DuBois et al. 1991)
0.491 (3%) (Shallenberger 1993)
1401 (5%) (DuBois et al. 1991)
2.51 (0.376%) (Shallenberger 1993)
9501 (2%) (Petersen and Müller, 1948)
7,0001 (2%) (Nofre et al. 1989)
120,0001 (2%) (Nofre et al. 1990)
6501 (2%) (Tinti et al. 1982)
2,7001 (2%) (Nofre et al. 1989)
28,0001 (Nofre et al. 1990)
0.81 (2%) (DuBois et al. 1991)
Values in parentheses are sucrose concentrations used for comparison. CT, chorda tympani proper; TBP, two-bottle preference; CTA, conditioned
taste aversion.
and then was maintained with pentobarbital intravenously as
needed. The trachea was cannulated, and body temperature, heart,
and respiratory rates were continuously monitored.
The right CT was dissected free from the point where it joins
the lingual nerve to the tympanic bulla, where it was cut. Singlefiber impulses were recorded with an impulse-amplitude analyzer,
which displayed adjustable upper and lower levels. It triggered a
pulse when a nerve impulse exceeded the lower but not the upper
level. These pulses were processed by an IBM-PC computer. The
custom-made software controlled stimulus delivery and stored intervals between pulses together with information on the presented
stimulus.
The solutions were delivered over the anterior part of the
tongue by a computerized system described earlier ( Hellekant
and Roberts 1995 ) . Each stimulation lasted for 5 s with 40-s
rinsing time between stimulations. Hamster artificial saliva
rinsed the tongue between stimulations ( Rehnberg et al. 1992 ) .
The stimuli and rinses were maintained and delivered at constant
temperature ( 347C ) .
The spontaneous activity before each stimulation was deducted from the responses. We define here spontaneous activity
as the impulse activity preceding the stimulation during rinsing
of the tongue with artificial saliva for 5 s. A cluster was considered to be responsive to a stimulus if the nerve impulse rate
during the first 5 s of stimulation was larger than 2 times SD of
the spontaneous activity of the cluster. Cluster and multidimensional ( MDS ) analyses were performed on the responses of 36
fibers to 31 stimuli ( SYSTAT for Macintosh, Version 5.2 ) . The
hierarchical cluster analysis measured the intercluster similarity
with the use of the Pearson correlation coefficient, and the cluster analysis proceeded according to the average linkage method.
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To facilitate comparisons with data from other species and studies, the responses of CT fibers to the four basic stimuli (NaCl,
citric acid, QHCl, and sucrose) were used to categorize each fiber
by its best stimulus (Frank 1973) and to calculate the breadth of
responsiveness (H) for each fiber. H was calculated according to
the formula H Å 0 Kpi log pi , where K is a scaling constant (1.6)
and pi is the proportional response each of the four basic stimuli
(Smith and Travers 1979).
TBP experiments
A total of 28 adult hamsters of both sexes, housed individually, served as subjects. Each stimulus was tested with seven
animals. Their intake of water and a stimuli was recorded during
four consecutive 24-h periods with graduated cylinders switched
at each measurement. In each hamster the preference ratio was
calculated for each 24-h period as the amount of a tastant consumed divided by the total amount of liquid consumed from
both cylinders. The mean daily preference ratios were then calculated for each hamster. Thus equal consumption of both liquids yields a preference ratio of 0.5; complete preference yields
a preference ratio of 1.
Results were first assessed with the use of analysis of variance.
Then a two-tailed t-test was used to compare mean preference ratios
to 0.5, and, for all cases in the following text where significance is
indicated, P values are õ0.01.
CTA experiments
Twelve conditioned and eight control adult hamsters of both
sexes served as subjects. Their consumption was measured as num-
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NHDHC, 0.48 mM
CAM, 0.176 mM
Alitame, 0.15 mM
Aspartame, 2.7 mM
Superaspartame, 60 mM
NAGAP, 24.8 mM
Thaumatin, 1.4 mM
MAGAP, 27.7 mM
Cyclamate-Na, 10 mM
CAMPA, 28 mM
Dulcin, 1.6 mM
TGC, 0.165 mM
D-Tryptophan, 19.5 mM
Saccharin, 1.6 mM
Ethylene glycol, 2.86 M
Acesulfame-K, 4 mM
D-Asparagine, 0.333 mM
Suosan, 1.13 mM
CCGA, 0.205 mM
Sucrose, 0.2 M
DMGA, 27.3 mM
Cyanosuosan, 2.14 mM
CGA, 0.76 mM
SC-45647, 43.4 mM
Glycine, 0.89 M
Solutions for TBP Experiments
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V. DANILOVA, G. HELLEKANT, J.-M. TINTI, AND C. NOFRE
ber of licks from 16 different bottles mounted in a carousel. Each
lick broke an infrared beam positioned between the animal and the
bottle in use and triggered one count by the computer. The first
lick started a timer that presented the bottle for 30 s.
After a session in which the hamsters were trained to drink water
through the apparatus, the animals were water deprived for 24 h
and then offered 0.2 M sucrose solution (conditioning stimulus).
After consumption of sucrose, 1.5 ml of 0.3 M LiCl (unconditioning stimulus) was injected intraperitoneal within 5–15 min. The
control animals underwent the same routine as conditioned animals
but without LiCl injections. After a 1-day recovery period we tested
if the animals were successfully conditioned. If they drank as much
sucrose as before first conditioning, we again injected them with
LiCl. Two to four injections were necessary to produce conditioning.
The CTA test was carried without water deprivation. Each animal was tested with three cycles that each included distilled water,
sucrose, and sweeteners presented at random.
The level of drinking differed between animals. To use the re-
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sults from different animals, the consumption of sweeteners had
to be normalized to a ‘‘standard.’’ For each animal we considered
the average number of licks of water during three cycles as the
standard and assigned it the value 100%. Then for each hamster,
consumption of all stimuli was expressed in percentage of this
standard. The data were then averaged for the control and conditioned animals.
With the use of a t-test for independent samples we analyzed
the difference in consumption by control and conditioned animals.
A P õ 0.01 value was considered a significant difference in the
statistical analysis.
RESULTS
Single-fiber responses in hamster chorda tympani
Figure 2 shows an example of the nerve impulses recorded
from single CT taste fiber HA94M25E classified as an Sfiber by the hierarchial analysis below. We present here only
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FIG . 1. Structures of SC-45647, N-4-cyanophenylguanidineacetate (CGA), cyanosuosan, N-3,5-dichlorophenyl-N *-(S)a-methylbenzylguanidineacetate (DMGA), N-4-cyanophenyl-N*-cyanoguanidineacetate (CCGA), TGC, N-4-cyanophenylcarbamoyl-(R,S)-3-amino-3-(3,4-methylenedioxyphenyl) propionic acid (CAMPA), N-(S)-2-methylhexanoyl-L-glutamyl5-amino-2-pyridinecarbonitrile (MAGAP), N-1-naphthoyl-L-glutamyl-5-amino-2-pyridinecarbonitrile (NAGAP), N-4-cyanophenylcarbamoyl-L-aspartyl-(R)-a-methylbenzylamine (CAM), and N-4-azidophenyl-N *-diphenylmethylguanidineacetate
(ADGA).
GUSTATORY RESPONSES OF HAMSTER TO SWEETENERS
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a part of the recordings from this unit. However, it is evident
that sucrose, suosan, N-4-cyanophenyl-N*-cyanoguanidineacetate (CCGA), SC-45647, N-4-cyanophenylguanidineacetate (CGA), cyanosuosan, N-3,5-dichlorophenyl-N *-(S)a-methylbenzylguanidineacetate (DMGA), and to some
extent NaCl gave a response, but citric acid, QHCl, alitame,
superaspartame, N- ( S ) -2-methylhexanoyl-L-glutamyl-5amino-2-pyridinecarbonitrile ( MAGAP ) , N-1-naphthoylL-glutamyl-5-amino-2-pyridinecarbonitrile ( NAGAP ) ,
N-4-cyanophenylcarbamoyl-L-aspartyl-(R)-a-methylbenzylamine
(CAM), and sodium cyclamate did not.
Figure 3 shows an overview of the responses to all compounds in all 36 CT fibers. The legend included in Fig. 3
relates the area of the circles with the nerve responses over
the first 5 s of stimulation. Open circles indicate a suppression of the nerve activity during a stimulation. The fibers
were ordered along the y-axis in groups, starting with the
fibers responding best to NaCl, followed by the fibers mainly
stimulated by citric acid and QHCl and finally a group of
sucrose-best fibers.
The breadth of tuning (H) for the NaCl-best fibers was
0.23 (SE Å 0.05), for citric acid-best 0.66 (SE Å 0.04),
and for sucrose-best 0.41 (SE Å 0.07). This shows that the
NaCl-best fibers are more narrowly tuned than the other
types.
Hierarchical cluster analysis
The responses of the 36 CT fibers in Fig. 3 were subjected
to a hierarchical cluster analysis. Our analysis distinguished
three major clusters consisting of 11 S-fibers, 14 N-fibers,
and 11 H-fibers. The result is represented as a dendrogram
in Fig. 4 with the identity number of the fiber and response
category on the basis of its best response to the four basic
solutions listed on the left side.
Average response profiles
Figure 5 shows the average response profiles of these
three clusters. The stimuli were listed along the x-axis, and
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the average impulse activity measured over 5 s was plotted
along the y-axis. The error bars illustrate the SE of these
averages. We will present each cluster.
N-CLUSTER. This cluster included 14 units and was the
largest one. Figure 5A shows that the N-cluster was characterized by strong responses to NaCl but also to ethylene
glycol. These fibers did not respond to bitter compounds.
Among the compounds that taste sweet to humans, only
Na-cyclamate, ethylene glycol, and glycine elicited a strong
responses in these fibers; responses to other stimuli were not
significant. The average spontaneous activity of the 14 Ncluster fibers was 9.39 (SE Å 1.92) imp/5 s.
H-CLUSTER. Figure 5B shows the average response profile
of 11 units. Citric acid elicited the best response, and QHCl
and L-asparagine gave significant responses. NaCl also stimulated this cluster, although responses were not strong. Most
compounds sweet to humans did not stimulate the H-cluster
fibers, with exception of ethylene glycol, glycine, and Dasparagine. The average spontaneous of the H-cluster was
4.02 (SE Å 0.77) imp/5 s.
S-CLUSTER. Figure 5C shows massive responses to some
but not all of the compounds sweet to humans. Thus all
compounds from dulcin to glycine elicited a significant response according to our criteria for a response. The remaining sweeteners from NHDHC to MAGAP did not elicit
any activity; responses to cyclamate and N-4-cyanophenylcarbamoyl-(R,S)-3-amino-3-(3,4-methylenedioxyphenyl)
propionic acid (CAMPA) were insignificant. The latter applies also to the activity recorded during stimulation with
NaCl, citric acid, and L-asparagine. For all S-fibers the average spontaneous activity before stimulation was 14.2 (SE Å
4.2) imp/5 s.
Multidimensional scaling
On the basis of a correlation matrix of the stimuli and to
present the relationships between stimuli used, we performed
multidimensional scaling. The spatial representation of the
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FIG . 2. Recordings from the chorda tympani (CT) S-cluster fiber HA94M25E. Onset and offset of stimuli are shown as
changes in bar code.
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FIG . 3. An overview of the response profiles of 36 single CT fibers with the use of topographical method. The area of
the circles represents impulse activity over the first 5 s of stimulation. Open circles, inhibition; absence of a mark shows
that data are missing. The stimuli were arranged along the x-axis in order of salty, sour, bitter, and sweet. The fibers were
arranged along the y-axis in groups: NaCl-, acid-, and sucrose-best fibers.
similarities among 30 stimuli is shown in Fig. 6. The stress
value is 0.072.
Sucrose, suosan, cyanosuosan, CAMPA, CGA, TGC, dulcin, acesulfame-K, saccharin, SC-45647, CCGA, DMGA,
D-tryptophan, and D-asparagine formed a tight group separate from the other stimuli. Another group included NaCl
together with cyclamate and ethylene glycol. Citric acid, Lasparagine, and QHCl were segregated from sweeteners and
sodium salts by dimension 2. The closeness between QHCl
and citric acid is evident. The nine stimuli that elicited no
response are scattered between the groups; eight of these
compounds are sweet to humans.
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Results of TBP tests
Figure 7 presents the results with TBP in hamsters with the
compounds arranged in order of increasing intake. Except for
L-tryptophan, all compounds used in the TBP tests taste
sweet to humans. Some compounds were presented in two
or three concentrations (see Table 1).
On the basis of the intake all stimuli can be divided into
three groups. One group was significantly rejected. It comprised ethylene glycol and L-tryptophan. The second group
was neither preferred nor rejected as indicated by the statistical test showing that the intake of the two bottles did not
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Results of CTA tests
Figure 8 shows the extent of generalization between intake
of sucrose and one of the compounds listed along the x-axis
according to the procedure described under METHODS . The
circles (control hamsters) and squares (conditioned hamsters) illustrate the number of licks for each compound expressed in percentage of number of licks when offered plain
water. In the control group the means varied from 82% (for
suosan) to 134% (for glycine).
In Fig. 8 the stimuli were arranged from the most rejected
to the least rejected compound by the conditioned hamsters.
As expected the consumption of sucrose was most suppressed
(13.9% of water intake) followed by all the compounds that
elicited a response in the S-fibers (P õ 0.01). As in previous
figures these compounds are highlighted in Fig. 8.
FIG . 4. Result of hierarchical cluster analysis of the response profiles
for 36 CT fibers. Intercluster similarity was measured with the Pearson
correlation coefficient, and the cluster analysis proceeded according to the
average linkage method. Number and response category of the fiber on the
basis of its response to the 4 basic solutions are listed on the left. N, H,
and S stand for NaCl-, citric acid-, sucrose-best fibers.
differ from the 0.5 level. This suggests that hamsters do not
discriminate between water on one side and MAGAP, N-4azidophenyl-N *-diphenylmethylguanidineacetate (ADGA),
superaspartame, cyclamate, aspartame, alitame, glycine,
CAMPA, NAGAP, thaumatin, NHDHC, and CAM on the
other.
To evaluate the possible influence of concentration, these
stimuli were also tested at concentrations higher than in the
electrophysiological experiments. Only one compound gave
different results; 101 higher concentration of CAMPA was
preferred over water.
The third group was significantly preferred and included
saccharin, D-tryptophan, CGA, SC-45647, DMGA, CCGA,
acesulfame-K, dulcin, sucrose, TGC, suosan, and cyanosuosan. The highlighted compounds are sweeteners that elicited
a response in S-fibers. As can be seen, only two compounds
that stimulate the S-fibers were shunned in the TBP tests.
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The aim of this study was to investigate how a number
of compounds, known as sweet to humans, taste to the hamster. We used three different approaches in our attempts to
elucidate this: single-fiber recordings from the CT nerve,
TBP and CTA tests.
It seems that together these three techniques can provide
us with information how a tastant tastes to an animal species.
The electrophysiological method provides information as to
whether a compound has taste or not. If a compound does
not elicit any impulse activities in the taste nerve, it has no
taste. If single-fiber responses are obtained, comparisons of
these responses with those of other compounds reveal how
similar their tastes are.
The TBP method shows how much the hamsters prefer
the compounds over water but gives no information about
the taste quality of the stimuli. On the other hand, our assumption is that compounds with a sucroselike taste are liked
by hamsters.
The CTA technique here showed to what extent the hamsters generalized from their aversion to sucrose to the other
stimuli. From this we conclude that the amount of suppression mirrors the taste similarities between the compound in
question and sucrose.
Table 2 summarizes the results of all experiments and
draws conclusions about the taste of each compound in the
hamsters.
Compounds that did not stimulate CT fibers
The electrophysiology identified compounds that did not
stimulate any of the CT fibers. These were L-tryptophan
and eight sweeteners: alitame, aspartame, CAM, MAGAP,
NAGAP, NHDHC, superaspartame, and thaumatin.
These sweeteners were neither preferred nor rejected over
water in TBP experiments, and their consumption was not
suppressed in CTA experiments. Thus we conclude that alitame, aspartame, CAM, MAGAP, NAGAP, NHDHC, superaspartame, and thaumatin in concentrations used here do not
taste sweet for hamsters.
It is unlikely that these compounds might stimulate Sfibers in glossopharyngeal or superior laryngeal nerves.
However, the population of sucrose-best fibers in these two
nerves is small, and sucrose is a rather ineffective stimulus
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DISCUSSION
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FIG . 5. Average response profiles of N-cluster (A),
H-cluster (B), and S-cluster (C) of hamster CT fibers.
Error bars are SE. Hatched columns, salts; open columns, acids; shaded columns, bitter compounds; black
columns, sweeteners. Numbers within parentheses show
number of fibers tested with each compound.
GUSTATORY RESPONSES OF HAMSTER TO SWEETENERS
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for the glossopharyngeal or superior laryngeal nerves (Dickman and Smith 1988; Hanamori et al. 1988). Hamster CT
neurons provide the main information about sweeteners’ and
sodium salts’ tastes, whereas NG neurons play a major role
in description of bitter and acid stimuli (Frank and Nowlis
1989). Thus we can conclude that the results of the three
methods are congruent and that these compounds are tasteless to hamsters.
FIG . 7. Results of the two-bottle preference (TBP) test. Data were averaged for 7–9 hamsters individually tested during
4 consecutive days. Sweeteners eliciting responses in S-cluster fibers are in bold type. Error bars are SE. Line shows
preference ratio level 0.5. *, significant difference from preference ratio 0.5.
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FIG . 6. Distribution of 30 stimuli in a 3-D space resulting from multidimensional scaling. Distribution was calculated
with Pearson correlation coefficient between stimuli across 36 CT fibers. Kruskal stress value is 0.072.
2110
V. DANILOVA, G. HELLEKANT, J.-M. TINTI, AND C. NOFRE
Figure 7 shows that L-tryptophan was avoided in the TBP
experiments, indicating an aversive taste sensation. It is possible that L-tryptophan stimulates Q-fibers in the glossopharyngeal nerve. Results of previous CTA experiments support
this conclusion because hamsters show reciprocal generalization between 50 mM L-tryptophan and 1 mM QHCl (Yamamoto et al. 1988). Thus it is likely that L-tryptophan has
to the hamster a slight quinine/acidlike taste, the same as it
has to humans (Haefeli and Glaser 1990; Schiffman 1976).
Compounds that stimulated any CT fibers except S-cluster
fibers
The rest of the stimuli elicited significant responses in
single CT fibers. The electrophysiology distinguished stimuli
that did not elicit responses in S-fibers from those which
did. As mentioned we distinguished three clusters. This corroborates previous studies (Frank 1973, 1988), which
showed similar clusters.
The compounds that did not stimulate the S-fibers included cyclamate and L-asparagine. Cyclamate, which was
in form of sodium salt, stimulated the N-fibers, was neither
preferred nor rejected in TBP test, and was not avoided in
CTA experiments. The conclusion is supported by the finding that 25 mM cyclamate generalizes to NaCl in CTA
(Nowlis et al. 1980). However it was also shown that 25
mM cyclamate generalizes to sucrose in CTA (Nowlis et al.
1980). When we tested 25 and 50 mM cyclamate in TBP
tests, the animals did not prefer it. This indicates that, even
if S-fibers would respond to higher concentrations of cyclamate, the responses of N-fibers of CT would determine the
/ 9k2c$$se38
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reaction of the whole organism. Thus hamsters may taste 10
mM cyclamate as similar to NaCl.
L-Asparagine stimulated only the H-fibers, and its consumption was not suppressed in CTA. We suggest that, to
hamsters, L-asparagine tastes similar to acids.
Compounds that stimulated more than S-cluster fibers
The next group of compounds included sweeteners that
stimulated more than one cluster: D-asparagine, glycine, and
ethylene glycol. We suggest that different clusters of fibers
provide information about different taste qualities.
D-Asparagine elicited responses in the S- and H-fibers.
Unfortunately TBP data are missing, but the hamsters generalized from sucrose to D-asparagine, which indicates that it
exerts a mixed sucrose- and acidlike taste.
Glycine stimulated fibers in every cluster. Thus it elicits
a mixed taste. The suppression of its consumption in CTA
suggests that its taste has a sucroselike component. This
conclusion is supported by earlier studies showing reciprocal
generalization between 0.1 M sucrose and 0.6 M glycine
(Nowlis et al. 1980; Yamamoto et al. 1988). On the other
hand the complexity of its taste is demonstrated by its generalization to HCl (Nowlis et al. 1980). Because neither preference nor rejection was recorded in the TBP experiments
here, it is likely that the effects on S- and H-fibers balanced
each other.
Ethylene glycol is a highly toxic compound. Consequently
postingestive signals may explain the discrepancy between
the generalization to sucrose in our CTA tests and the rejection in the TBP experiments. On the other hand, ethylene
glycol stimulated both the N- and S-fibers (Fig. 3). It is
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FIG . 8. Consumption of sweeteners by conditioned and control groups of hamsters. Number of licks of each sweetener
was normalized to consumption of water for each animal and expressed in percentages. Data were averaged for 8 control
and 9–11 conditioned animals. Sweeteners eliciting responses in S-cluster fibers are in bold type. Error bars are SE. Significant
difference between 2 groups: * P õ 0.05, ** P õ 0.01.
GUSTATORY RESPONSES OF HAMSTER TO SWEETENERS
TABLE
2.
2111
Summary table for the results of the all experiments in hamsters
NHDHC
CAM
Alitame
Aspartame
Superaspartame
NAGAP
Thaumatin
MAGAP
ADGA
Cyclamate
CAMPA
Dulcin
TGC
D-Tryptophan
Saccharin
Ethylene glycol
NS; also in H fibers
No response
No response
No response
No response
No response
No response
No response
No response
No response
—
Response in N fibers
Response in 4/9 fibers*
Response (not strong)
Response (not strong)
Response
Response
Response; also in N fibers
—
—
—
—
—
—
—
—
—
—
—
—
Yes
Yes
Yes
Yes
Yes
—
Acesulfame-K
D-Asparagine
Response
Response; also in H fibers
Yes
Yes
Suosan
CCGA
Sucrose
DMGA
Cyanosuosan
CGA
SC-45647
Glycine
Response
Response
Response
Response
Response
Response
Response
Responses in all fibers
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
L-Asparagine
L-tryptophan
Reaction in TBP Test
Result in CTA
Test
Conclusion About Taste
—
No suppression
Not sweet, may be similar to citric acid
Aversion
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference*/**
No suppression
Not sweet
No preference
No suppression
Not sweet
No preference*/**
No suppression
Not sweet, may be similar to NaCl
Preference**/no preference* No suppression* Might be sweet at high concentration
Preference
No suppression
Sweet not like sucrose
Preference
No suppression
Sweet not like sucrose
Preference
Suppression
Sweet like sucrose
Preference
Suppression
Sweet like sucrose
Aversion
Suppression
Mixed taste, sweet like sucrose and
may be similar to NaCl
Preference
Suppression
Sweet like sucrose
—
Suppression
Mixed taste, sweet like sucrose and
may be similar to citric aicd
Preference
Suppression
Sweet like sucrose
Preference
Suppression
Sweet like sucrose
Preference
Suppression
Sweet like sucrose
Preference
Suppression
Sweet like sucrose
Preference
Suppression
Sweet like sucrose
Preference
No suppression
Sweet not like sucrose
Preference
Suppression
Sweet like sucrose
No preference
Suppression
Mixed taste, not only sweet like
sucrose taste
MDS, multidimensional analysis; NS, not significant; see Table 1 for other definitions. * Low concentration; ** high concentration.
possible that the strong response in N-fibers was the cause
for the rejection because hamsters reject NaCl in TBP tests
(Hettinger and Frank 1990). Ethylene glycol also generalized to sucrose in our CTA experiments. This can be explained by its substantial response in the S-fibers. Thus it
has both a sucrose- and NaCl-like taste to hamsters.
Compounds that stimulated only S-cluster fibers
The last group of stimuli included compounds that stimulated only S-cluster fibers. Hamsters liked all these compounds in TBP experiments. The CTA experiments separated these sweeteners into two groups. The consumption of
ace-K, cyanosuosan, CCGA, D-tryptophan, DMGA, saccharin, SC-45647, and suosan was suppressed, indicating that
the hamsters generalized from sucrose to these compounds.
Thus these compounds taste like sucrose.
The consumption of CGA, dulcin, and TGC was not suppressed in CTA. Although both dulcin and TGC evoked
significant responses in the S-fibers, these responses were
smaller than those of the other sweeteners (Fig. 5C). It is
possible that we used concentrations of dulcin (1.6 mM)
and TGC (0.16 mM) that were too low. CGA was the only
compound that gave contradictory results. Because of several
circumstances, one of these being lack of compound, we
were unable to repeat the CTA tests for CGA.
CAMPA presents a special case. In CTA and TBP experiments with low concentration (28 mM), the hamsters
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showed no reaction. However, 101 higher concentration of
CAMPA was preferred in the TBP. This is in contrast to all
the other compounds tested with more than one concentration in TBP tests (Table 2). Furthermore, CAMPA at 28
mM stimulated four of nine S-cluster fibers, although the
average response was not significant. MDS analysis positioned it together with stimuli that taste like sucrose. This
indicates that the concentration of CAMPA used for electrophysiology was below the behavioral threshold for hamsters.
At higher concentrations it might be sweet to hamsters.
These results further support the hypothesis that activity
in S-fibers stimulates intake (Rehnberg et al. 1990) and
activity in Q-fibers rejection. The results show that, by combining single-fiber nerve recordings and TBP and CTA methods, it is possible to gain insight on how an unknown compound may taste to an animal species. The results of all
compounds can be explained by the assumption that activity
in S-fibers will evoke a preference and activity in H-/Qfibers rejection, whereas the behavioral effects of N-fiber
activity are species related.
Address for reprint requests: G. Hellekant, Animal Health and Biochemical Sciences, The University of Wisconsin-Madison, 1655 Linden Dr., Madison, WI 53706-1581.
Received 29 December 1997; accepted in final form 3 June 1998.
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