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Arizona Research Laboratories, Division of Neurobiology, University of Arizona, Tucson, Arizona 85721
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ABSTRACT |
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 Abstract
 Introduction
Methods
Results
Discussion
References
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Glendinning, John I. and Thomas T. Hills. Electrophysiological evidence for two transduction pathways within a bitter-sensitive taste receptor. J. Neurophysiol. 78: 734-745, 1997. Among the sapid stimuli, those that elicit bitter taste are the most abundant and structurally diverse. To accommodate this diversity, animals are thought to use multiple bitter transduction pathways. We examined the role of individual taste receptor cells (TRCs) in this transduction process by focusing on one of the taste organs, or chemosensilla, of a caterpillar (Manduca sexta). This chemosensillum (the lateral styloconicum) contains four functionally distinct TRCs: the salt, sugar, inositol, and deterrent TRCs, which are known to respond strongly to, in respective order, salts, sugars, inositol, and compounds humans describe as bitter. Using an extracellular recording technique, we tested three hypotheses for how a structurally diverse array of bitter compounds (salicin, caffeine, and aristolochic acid) could excite the same chemosensillum: several TRCs within the lateral styloconica respond to the bitter compounds; only the deterrent TRC responds to the bitter compounds, through a single transduction pathway; and only the deterrent TRC responds to the bitter compounds, but through multiple transduction pathways. To discriminate among these hypotheses, we tested five predictions. The first addressed how many TRCs within the lateral styloconica responded to the bitter compounds. Subsequent predictions were based on the results of the test of the first prediction and assumed that only the deterrent TRC responded to these compounds. These latter predictions addressed whether the bitter compounds acted through one or multiple transduction pathways. We obtained evidence consistent with the third hypothesis: only the deterrent TRC responded to the bitter compounds; the temporal patterns of firing and concentration-response curves elicited by caffeine and salicin were similar to each other, but different from those elicited by aristolochic acid; the patterns of sensory adaptation and disadaptation elicited by caffeine and salicin were similar to each another, but different from those elicited by aristolochic acid; reciprocal cross-adaptation occurred between caffeine and salicin, but not between aristolochic acid and caffeine or aristolochic acid and salicin; and the responsiveness of individual deterrent TRCs to caffeine and salicin correlated significantly, whereas that to aristolochic acid and caffeine or aristolochic acid and salicin did not. Taken together, these results indicate that the deterrent TRC contains at least two excitatory transduction pathways: one responds to caffeine and salicin and the other to aristolochic acid. To our knowledge, this is the first direct support for the existence of two bitter transduction pathways within a single TRC.
One distinctive feature of chemosensory systems is that they respond to a large number of structurally unrelated compounds. They appear to accomplish this feat through a multitude of transduction pathways (e.g., receptor sites, second messenger cascades, and ion channels) in their receptor cells (Ache 1994
Insects, diets, and taste stimuli
We obtained caterpillars from the Manduca rearing facility at the Division of Neurobiology, University of Arizona, where they were fed a wheat-germ based diet and maintained under established protocols at 25°C with a 16 L:8D photoperiod (Bell and Joachim 1976 Electrophysiological recording procedure
Like most caterpillars, M. sexta has eight bilateral pairs of gustatory chemosensilla associated with its mouth parts, and they all occur outside its cibarial cavity (i.e., mouth). As compared with vertebrate taste buds, these insect "taste buds" have a simple structure: each contains three to four dendritic processes, which arise from cell bodies located at the base of the chemosensillum. Tastants gain access to these processes by diffusing through a tiny pore at the tip of the chemosensillum. When tastants reach the receptor membrane at the distal end of the dendritic processes, they are thought to induce inward current across the membrane and thereby elicit spiking near the cell body (Morita 1959
How many TRCs are activated by the bitter compounds? (test of first prediction)
If all three bitter compounds stimulate the same TRC within the lateral styloconica (i.e., the deterrent TRC), then binary mixtures of the bitter compounds should activate only the deterrent TRC and cause it to fire at a higher rate than either compound individually (e.g., van Loon and van Eeuwijk 1989 Responses of the deterrent TRC to different concentrations of the bitter compounds (test of second prediction)
If each of the three bitter compounds stimulates the deterrent TRC through different transduction pathways, then we predicted that each should elicit different concentration-response curves and temporal patterns of firing (see Table 1). For example, bitter compounds that act directly on ion-gated channels in TRC membranes (e.g., quinine in salamanders) (Kinnamon 1992 Patterns of adaptation and disadaptation to the bitter compounds in the deterrent TRC (test of third prediction)
If each of the three bitter compounds stimulates the deterrent TRC through different transduction pathways, then we predicted they would produce different patterns of adaptation and disadaptation (see Table 1). This prediction derives from the observation that specific transduction pathways often exhibit characteristic patterns of sensory adaptation (e.g., Ozaki and Amakawa 1992 Patterns of cross-adaptation among the bitter compounds in the deterrent (test of fourth prediction)
If each of the three bitter compounds stimulated the deterrent TRC through different transduction pathways, then we predicted that sensory adaptation to one bitter compound would not cross-adapt to the others (see Table 1). Cross-adaptation between two of the bitter compounds would indicate that both activate a common pathway, whereas a significant lack of cross-adaptation would indicate that both activate independent pathways. Cross-adaptation is an accepted and effective technique for evaluating the independence of transduction processes or binding sites within chemosensory cells (e.g., Caprio and Byrd 1984 Does the response of individual deterrent TRCs to the bitter compounds covary? (test of fifth prediction)
If each of the three bitter compounds stimulated the deterrent TRC through different transduction pathways, then we predicted that the responsiveness of the deterrent TRC to one bitter compound would not covary with its responsiveness to the others (see Table 1). On the contrary, significant covariance would indicate that the compounds act through a common transduction pathway.
How many TRCs are activated by the bitter compounds?
Binary mixtures of the bitter compounds strongly activated only one TRC in all of the lateral styloconica studied. Based on the distinctive temporal pattern of firing, we inferred that it was the deterrent TRC that responded (Fig. 2). Visual inspection of the traces (e.g., Fig. 2, C and D) reveals that the salt TRC also fired infrequently, presumably in response to the 0.1 M KCl present in the stimulating solution. That the salt TRC was not responding to the bitter compounds is demonstrated by the fact that its response (i.e., firing rate) to the binary mixtures was indistinguishable from that to solutions containing only one bitter compound (Fig. 2, C and D). Finally, the firing rates of the deterrent TRC (during the initial 500 ms of stimulation) were significantly higher in response to the binary mixture of aristolochic acid and caffeine than to either compound alone and to the binary mixture of salicin and caffeine than to either compound alone (Fig. 2, A and B; Table 2).
Responses of the deterrent TRC to different concentrations of the bitter compounds
Aristolochic acid elicited a qualitatively different temporal pattern of firing in the deterrent TRC than did caffeine or salicin. For all concentrations of aristolochic acid tested, the number of spikes during the first 100 ms was low but increased markedly over the next 900 ms (Fig. 4A). Further, the shape of the time-response curve changed with concentration: it was linear at concentrations
Patterns of adaptation and disadaptation to the bitter compounds in the deterrent TRC
All three compounds elicited patterns consistent with sensory adaptation (Fig. 6, A-C,
Patterns of cross-adaptation among the bitter compounds in the deterrent TRC
We obtained evidence of cross-adaptation between some but not all of the compounds. For example, the normal response of the deterrent TRC to aristolochic acid was not affected by adaptation to salicin or caffeine (Fig. 8, A and B). Likewise, the normal response of the deterrent TRC to salicin or caffeine was not affected by adaptation to aristolochic acid (Fig. 8, C and E). In all of these tests, the two-way ANOVA revealed no significant effect of repeated stimulation, or interaction between repeated stimulation and time, on the firing rate (Table 4). There was a significant effect of time in all comparisons, however, which confirms the result of the previous experiment: that aristolochic acid, caffeine, and salicin reliably elicit sensory adaptation in the deterrent TRC.
Does the response of individual deterrent TRCs to the bitter compounds covary?
The sensory responses of the deterrent TRC to caffeine and salicin were significantly correlated (r = 0.71, df = 38, P
We initially proposed three alternative hypotheses to explain how the lateral styloconica could respond to three compounds that are as structurally diverse as caffeine, salicin, and aristolochic acid. The first hypothesis was that several TRCs within the lateral styloconica mediated the response to these compounds. If this was the case, then we predicted that binary mixtures of the bitter compounds would activate more than one TRC. However, this was not the case; only the deterrent TRC responded to the binary mixtures, and it did so at a significantly higher firing rate than was elicited by either of the bitter compounds alone. A key assumption of this prediction was that more than one TRC within the lateral styloconica could fire vigorously at the same time. To evaluate this assumption, we tested binary mixtures of each bitter compound with known ligands of the inositol and sugar TRCs. In this latter experiment, at least two TRCs responded vigorously to the binary mixtures. Taken together, these results lead us to conclude that the three bitter compounds stimulate the deterrent TRC exclusively.
Functional significance
We can envision several ways that herbivores like M. sexta could benefit from having multiple bitter transduction pathways within the same TRC. One stems from the finding that the mixture of caffeine and aristolochic acid elicited about 1.7 times as many spikes/second as either compound alone, whereas the mixture of caffeine and salicin elicited only ~1.3 times as many spikes/second as either component alone (Table 2, Fig. 2). Given that caffeine and aristolochic acid stimulate different transduction pathways, our findings indicate that simultaneous activation of two pathways within the same deterrent TRC increases the chances of M. sexta detecting mixtures of bitter and potentially toxic compounds. The ecological relevance of this hypothesis is demonstrated by the facts that plant tissues often contain complex mixtures of bitter compounds (Rouseff 1990
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
; Dione and Dubin 1994; Kinnamon and Cummings 1992; Spielman et al. 1992). Although the existence of these different pathways is well documented, their functional organization across populations of taste or olfactory receptor cells within animals is not. For example, it is unclear how many transduction pathways are expressed within individual receptor cells, how extensively different pathways within the same receptor cell overlap in terms of their molecular receptive ranges, and whether the coexistence of multiple transduction pathways within receptor cells increases or decreases an animal's ability to discriminate between different classes of compounds. These issues are critical to our understanding of how chemosensory systems encode natural chemical signals.
). Moreover, there is speculation that interactions between these transduction pathways may facilitate olfactory coding and the detection of low concentrations of odorants in complex mixtures (Ache 1994; Restrepo et al. 1996). The situation in the gustatory system, however, is less clear because only a few studies have addressed this issue. The most definitive study reported that sweet-sensitive taste receptor cells (TRCs) in rats can express at least two transduction pathways: one responds to sucrose and the other to nonnutritive sweeteners (Bernhardt et al. 1996). Here, we further explore the functional organization of transduction pathways within the gustatory system but focus on pathways that are activated by compounds humans describe as bitter.
). That animals accommodate this diversity through a multitude of specific bitter transduction pathways is supported by findings from several experimental paradigms. Psychophysical and electrophysiological studies reveal that attenuating the gustatory response to one bitter compound, through habituation (Glendinning and Gonzalez 1995) or sensory adaptation (McBurney and Bartoshuk 1973; McBurney et al. 1972; Sato and Sugimoto 1995), generalizes to some, but not all, novel bitter compounds. In addition, inbred strains of mice differ greatly in taste sensitivity to bitter compounds, and these interstrain differences are explained most parsimoniously by a model involving multiple transduction pathways (Whitney and Harder 1994). Finally, biochemical and physiological studies of bitter-sensitive TRCs also support the existence of several transduction pathways (Kinnamon and Cummings 1992; Ruiz-Avila et al. 1995; Spielman et al. 1992). Virtually nothing is known, however, about the functional organization of these different transduction pathways across the population of bitter-sensitive TRCs.
). In addition, one can study the response properties of individual TRCs in intact preparations through noninvasive recording techniques (Gothilf and Hanson 1994). Because the responses of individual TRCs within a chemosensillum can be discriminated reliably from one another based on their respective temporal patterns of firing, one can study homologous TRCs from different animals (e.g., see Glendinning 1996). Finally, most insect chemosensilla contain one TRC that responds to a structurally diverse range of compounds that humans characterize as bitter, and it is usually called the deterrent TRC (Blaney and Simmonds 1988; Chapman et al. 1991; Dethier 1973); stimulation of this TRC is associated with taste-rejection (Schoonhoven et al. 1992). Despite these experimentally favorable attributes, little is known about how insect chemosensilla respond to bitter compounds.
). However, it should be noted that there have been no reports to date of more than one deterrent TRC within the same chemosensillum.
; Kumazawa et al. 1988; Kurihara 1972), or binding of the bitter ligand to one of several membrane-bound receptors, which are all coupled to a common second-messenger system (e.g., Shimada 1975; Shimada et al. 1974).
,5-cyclic monophosphate (cAMP) and Ca2+ uptake and the other to nonnutritive sweeteners with an increase in IP3 and Ca2+-release (Bernhardt et al. 1996). Even though there is evidence for similar transduction pathways within bitter-sensitive TRCs of mammals [one involving an increase in IP3 and Ca2+-release (Akabas et al. 1988; Spielman et al. 1996) and the other a decrease in cAMP and Ca2+ uptake (Kolesnikov and Margolskee 1995)], no investigator, to our knowledge, has yet determined whether both of these pathways can coexist within the same bitter-sensitive TRC.
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TABLE 1.
Predictions taken from alternative hypotheses about how several structurally distinct bitter compounds could elicit spiking within the same chemosensillum
).
METHODS
Abstract
Introduction
Methods
Results
Discussion
References
). We used caterpillars 2 days after completing their molt to the fifth stadium. All caterpillars were naive to the test compounds before testing. To control for any potential differences among caterpillars from different egg batches, we interspersed individuals from each batch across experimental treatments.
; Glendinning, unpublished data), elicit rapid taste-rejection in M. sexta (de Boer et al. 1977; Wrubel and Bernays 1990; Glendinning, unpublished data), and taste bitter to humans (Glendinning 1994). Even though neither of these compounds occurs in normal food plants of M. sexta (i.e., plants within the Solanaceae) (Harborne and Baxter 1993), they nevertheless occur in plants within the geographic range of M. sexta and thus might be encountered by free ranging individuals.
). These bipolar sensory neurons extend directly to the subesophageal ganglion in the CNS.
; Schoonhoven et al. 1992). Each TRC responds to its best stimuli with a characteristic temporal pattern of firing: that from the salt TRC is temporally irregular, that from the inositol TRC is strongly phasic-tonic; that from the sugar TRC is less strongly phasic-tonic; and that from the deterrent TRC is predominantly tonic, with a variable latency of onset (Fig. 1, A-D). Owing to the distinctive nature of each TRC's temporal pattern of firing, we were able to discriminate them readily.
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FIG. 1.
Typical neural records from 4 taste receptor cells (TRC) within lateral styloconic sensilla. Traces illustrate temporal pattern of firing by salt and sugar TRCs in response to 100 mM KCl (A), sugar TRC to 75 mM glucose (B), inositol TRC to 0.5 mM inositol (C), and deterrent TRC to 50 mM salicin (D). Because 100 mM KCl was present in all solutions (for conductivity), all neural records contain variable number of spikes from salt TRC; these spikes are indicated ( 
).
). In brief, this method involved anesthetizing the caterpillar by sealing it within a grounded vial containing 0.1 M KCl (with its head protruding) and then placing a recording/stimulating electrode over the tip of one of its lateral styloconica. Because the recording electrode contained the tastant solution, we could stimulate and record from the deterrent TRC simultaneously.
) and an AC-coupled amplifier-filter system with a band-pass set at 130-1,200 Hz. We digitized and stored neural records directly onto a computer with a software program called SAPID Tools (Smith et al. 1990).
3 min between successive stimulations of the same sensillum. In all cases, we quantified the number of action potentials generated from 10 ms after contact with the sensillum; the actual length of recording varied among recordings. To minimize solvent evaporation at the tip of the recording/stimulating electrode, we drew fluid from the tip with a piece of filter paper <7 s before each stimulation.
; Glendinning, unpublished data).
) (see Table 1). If the bitter compounds stimulate different TRCs, then binary mixtures of the bitter compounds should activate more than one TRC.
) might be expected to elicit a response more rapidly than those that act through second messenger systems (e.g., IP3 in mice) (Spielman et al. 1996). If the bitter compounds act on the same transduction pathway, then the temporal patterns of firing that they elicit, and their concentration-response curves should be similar.
). If all bitter compounds stimulate the same transduction pathway, then we predicted that each compound would elicit similar patterns of adaptation and disadaptation.
0.05).
; Daniel et al. 1994; Hazelbauer et al. 1987; Rehnberg et al. 1989; Sato and Sugimoto 1995; Shimada 1987).
RESULTS
Abstract
Introduction
Methods
Results
Discussion
References
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FIG. 2.
Sensory responses of deterrent TRC to binary mixtures of caffeine and aristolochic acid or caffeine and salicin. We present mean ± SE temporal pattern of firing in response to 0.001 mM aristolochic acid alone, 0.5 mM caffeine alone, and the mixture of both (A), or 3 mM salicin alone, 0.5 mM caffeine alone, and the mixture of both (B). Representative neural records from data in A and B are provided in C and D, respectively (all traces in C and D are from the same chemosensillum). Spikes from salt TRC are indicated with arrowheads. Results in A and B are derived from 12 deterrent TRCs, each from different caterpillars. See Table 2 for statistical analysis of these data.
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TABLE 2.
Sensory response of the deterrent TRC to various stimulants
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FIG. 3.
Sensory responses of different TRC to solutions containing single component stimuli (A; 0.5 mM caffeine, 0.5 mM inositol, or 75 mM glucose), a binary mixture (B) of 0.5 mM caffeine and 0.5 mM inositol, and a binary mixture (C) of 0.5 mM caffeine and 75 mM glucose. In A, only 1 TRC fired regularly and rapidly: deterrent, inositol, and glucose TRC, respectively. However, in traces in B and C, 2 TRCs are firing regularly and rapidly, creating a complex temporal pattern of spiking. Unusually large spikes in these latter traces correspond to instances where 2 TRCs fired synchronously. To facilitate interpretation of these complex neural records, we have provided neural record at top and inferred location of spikes from different TRCs below. Note similarity in temporal pattern of firing of each TRC between traces containing single component stimuli and those containing binary mixtures. Spikes from salt TRC were observed only in traces within A, and they are indicated ( ).
1 µM and asymptotic at higher concentrations. The time-response curves for caffeine and salicin also exhibited delayed onset, but they all reached their maximal firing rate 100-200 ms after stimulus contact and then decreased gradually and linearly during the subsequent 800 ms (Fig. 4, B and C).
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FIG. 4.
Temporal pattern of firing (mean number of spikes per 100 ms) by deterrent TRC in response to a range of concentrations of aristolochic acid (A), caffeine (B), and salicin (C). Each line represents a different concentration (actual values are provided to right of each line). Resultsare derived from 12 deterrent TRCs (each from a different caterpillar), andeach TRC was stimulated with full range of concentrations. Note thaty-axis scale for A differs from that for B and C.
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FIG. 5.
Concentration-response curves (number of spikes/s) for deterrent TRC in response to aristolochic acid, caffeine and salicin (means ± SE). For more details, see Fig. 4.
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FIG. 7.
Representative neural records from sensory adaptation and disadaptation experiment. For more details, see Fig. 6. Spikes from the salt TRC are indicated with arrowheads.
). The initial response to caffeine and salicin (i.e., stimulation 1) began vigorously but then decreased with time to a level that was ~50% of the maximal firing rate. Even though the initial response to aristolochic acid took several seconds to reach its maximal firing rate, the firing rate subsequently decreased to a level ~50% of the maximum. In addition, the deterrent TRC failed to disadapt to all three bitter compounds during the 30 s gap between stimulations 1 and 2; this is revealed by a comparison of lines containing versus 
(Fig. 6, A-C).
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FIG. 6.
Test for sensory adaptation and disadaptation of deterrent TRC to 3 bitter compounds: 0.1 mM aristolochic acid (A), 5 mM caffeine (B), and 50 mM salicin (C). We indicate adaptation protocol in top right portion of figure. In each panel, we provide mean ± SE number of spikes per 500-ms bin during stimulation 1 ( ) and stimulation 2 (). These data are based on response of 15 deterrent TRCs, each from different caterpillars. We inferred adaptation if firing rate decreased significantly with time during stimulation 1 and disadaptation if temporal pattern of firing during stimulation 2 did not differ significantly from that during stimulation 1. See Table 3 for a statistical analysis of these results.
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TABLE 3.
Analysis of the tests for adaptation and disadaptation in Fig. 6, A-C
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FIG. 8.
Test for cross-adaptation between 0.1 mM aristolochic acid, 5 mM caffeine, and 50 mM salicin in deterrent TRC. We illustrate cross-adaptation protocol at top of figure. A and B: adaptation to salicin and caffeine affected normal response to aristolochic acid. C and D: adaptation to aristolochic acid and caffeine affected normal response to salicin. E and F: adaptation to aristolochic acid and salicin affected normal response to caffeine. Response variable is mean ± SE number of spikes per 500-ms bin. We inferred cross-adaptation when response to test compound before adaptation differed significantly from that after adaptation. See Table 4 for a statistical analysis of these results. Each panel is derived from 12 to 16 deterrent TRCs, each from different caterpillars.
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TABLE 4.
Analysis of the cross-adaptation tests in Fig. 8, A-F
0.05/3), whereas those to caffeine and aristolochic acid (r = 0.34, df = 38, P >0.05/3) or salicin and aristolochic acid (r = 0.33, df = 38, P > 0.05/3) were not (Fig. 9,A-C). Thus these results demonstrate that the responsiveness of the deterrent TRC to caffeine and salicin covaries, but that to aristolochic acid and the other compounds does not.
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FIG. 9.
Correlations of sensory response of individual deterrent TRCs to caffeine (5 mM), salicin (50 mM), and aristolochic acid (0.1 mM). Correlation in A is significant (P 0.05/3), but those in B and C are not (P > 0.05/3). Line of equality (- - -) and Pearson product-moment correlation coefficient (r) are provided in each panel. All correlations involved the same 40 deterrent TRCs (each from different caterpillars).
DISCUSSION
Abstract
Introduction
Methods
Results
Discussion
References
; Cromarty and Derby 1997; Hyman and Frank 1980). It is calculated as Rab/(Ra + Rb), where a and b represent the two chosen tastants at response-matched concentrations, Ra and Rb represent the response magnitudes (i.e., total spikes during 500 ms) to a and b, respectively, and Rab represents the response magnitude to the binary mixture of a and b. Accordingly, if the two components stimulate a receptor cell through independent pathways, then the response to the mixture should equal the sum of the response to the single components (i.e., the ICI would be statistically indistinguishable from 1). If the two components activate the same transduction pathway, the response to the mixture should be greater or less than the sum of the single components (i.e., the ICI would be significantly greater or <1).
0.05), we determined whether either of these means differed significantly from 1. Whereas the mean ICI for the mixture of caffeine and salicin was significantly <1 (t(9) = 7.96), that for the mixture of caffeine and aristolochic acid did not differ from 1 (t(9) = 1.60). Thus these findings reinforce the conclusion that the deterrent TRC contains at least two independent transduction pathways.
) and that many of these compounds are toxic at low concentrations (Holyoke and Reese 1987).
). Thus given that the molecular receptive range of any given transduction pathway is limited, the expression of multiple transduction pathways within each deterrent TRC may be the most parsimonious way to expand the range of bitter and potentially toxic compounds to which a caterpillar's gustatory system can respond.
; Bernays and Cornelius 1992; Glendinning 1994; Harley and Thorsteinson 1967). Rejection of all foods that strongly stimulate the deterrent TRC may cause insects to taste-reject many harmless and potentially nutritious foods. However, if two transduction pathways within a TRC produce different temporal patterns of firing, and if the CNS can discriminate between these two patterns of firing, then the CNS may still be able to distinguish between spikes produced by the different transduction pathways. The results of this study present an ideal situation for evaluating this idea with an associative learning test: whereas caffeine and salicin elicited rapid spiking almost immediately after stimulation (i.e., within 50 ms), aristolochic acid elicited a pattern of spiking that gradually increased with time and did not plateau until several seconds after stimulation.
; Pietra et al. 1972) and at higher levels in the gustatory system (Di Lorenzo and Schwartzbaum 1982). However, the functional significance of these findings is unclear because no one has demonstrated that the vertebrate CNS can utilize this temporal information as a basis for discriminating between compounds.
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ACKNOWLEDGEMENTS |
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We thank R. Chapman and D. Morton for advice throughout this study; E. Bernays, C. Derby, S. Kinnamon, and V. Shields for valuable editorial comments; and M. Truong for help collecting the electrophysiological data.
This project was supported by the National Institute of Deafness and Other Communication Disorders Grant 5 R29 DC-02416-02 and training grant number BIR-9220332 from the National Science Foundation Program in Interdisciplinary Science.
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FOOTNOTES |
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Present address and address for reprint requests: J. I. Glendinning, Dept. of Biological Sciences, Barnard College, Columbia University, 3009 Broadway, New York 10027-6598. E-mail: jglendinning{at}barnard.columbia.edu
Received 24 January 1997; accepted in final form 1 April 1997.
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Abstract
Introduction
Methods
Results
Discussion
References
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J. Glendinning, S Ensslen, M. Eisenberg, and P Weiskopf Diet-induced plasticity in the taste system of an insect: localization to a single transduction pathway in an identified taste cell J. Exp. Biol., January 8, 1999; 202(15): 2091 - 2102. [Abstract] [PDF]
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