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Sniff adjustment in an odor discrimination task in the rat: analytical or synthetic strategy?

Courtiol E, Lefèvre L, Garcia S, Thévenet M, Messaoudi B, Buonviso N - Front Behav Neurosci (2014)

Bottom Line: We found that sniffing variations were not only a matter of odorant sorption properties and that the same odorant was sniffed differently depending on the odor pair in which it was presented.These results suggest that rather than being adjusted analytically, sniffing is instead adjusted synthetically and depends on the pair of odorants presented during the discrimination task.Our results show that sniffing is a specific sensorimotor act that depends on complex synthetic processes.

View Article: PubMed Central - PubMed

Affiliation: Centre de Recherche en Neurosciences de Lyon, Equipe Olfaction: du codage à la mémoire, CNRS UMR 5292-INSERM U1028-Université Lyon1 Lyon, France.

ABSTRACT
A growing body of evidence suggests that sniffing is not only the mode of delivery for odorant molecules but also contributes to olfactory perception. However, the precise role of sniffing variations remains unknown. The zonation hypothesis suggests that animals use sniffing variations to optimize the deposition of odorant molecules on the most receptive areas of the olfactory epithelium (OE). Sniffing would thus depend on the physicochemical properties of odorants, particularly their sorption. Rojas-Líbano and Kay (2012) tested this hypothesis and showed that rats used different sniff strategies when they had to target a high-sorption (HS) molecule or a low-sorption (LS) molecule in a binary mixture. Which sniffing strategy is used by rats when they are confronted to discrimination between two similarly sorbent odorants remains unanswered. Particularly, is sniffing adjusted independently for each odorant according to its sorption properties (analytical processing), or is sniffing adjusted based on the pairing context (synthetic processing)? We tested these hypotheses on rats performing a two-alternative choice discrimination of odorants with similar sorption properties. We recorded sniffing in a non-invasive manner using whole-body plethysmography during the behavioral task. We found that sniffing variations were not only a matter of odorant sorption properties and that the same odorant was sniffed differently depending on the odor pair in which it was presented. These results suggest that rather than being adjusted analytically, sniffing is instead adjusted synthetically and depends on the pair of odorants presented during the discrimination task. Our results show that sniffing is a specific sensorimotor act that depends on complex synthetic processes.

No MeSH data available.


Sorption is not the only parameter that determines global sniffing variations. (A) Global sampling parameters (mean ± s.e.m.), Sd (left), and Ns (right), for non-enantiomer odor pair: hept (green)/iso (black) n = 150. (B) Modulation of respiratory parameters in the first, second, and third cycles for hept/iso. From top to bottom: mean (± s.e.m.) normalized ID, IPF, and ED. Same colors as in (A). The number of trials for each odorant and cycle in hept/iso pair is: ncycle 1 = 150, ncycle 2 = 137, ncycle 3 = 65. Data were analyzed using a paired t-test; *p < 0.05; and ***p < 0.001.
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Figure 5: Sorption is not the only parameter that determines global sniffing variations. (A) Global sampling parameters (mean ± s.e.m.), Sd (left), and Ns (right), for non-enantiomer odor pair: hept (green)/iso (black) n = 150. (B) Modulation of respiratory parameters in the first, second, and third cycles for hept/iso. From top to bottom: mean (± s.e.m.) normalized ID, IPF, and ED. Same colors as in (A). The number of trials for each odorant and cycle in hept/iso pair is: ncycle 1 = 150, ncycle 2 = 137, ncycle 3 = 65. Data were analyzed using a paired t-test; *p < 0.05; and ***p < 0.001.

Mentions: In a second step, we analyzed sniffing strategies when the animals had to discriminate between odorants that had similar sorption properties but were non-enantiomers (Figure 4). Here, we surprisingly observed more heterogeneous results; the odorants of the LS/LS pair (cum/cyc) were sampled similarly, but the odorants of the HS/HS pair (hept/mbz) were sampled differently. As shown in Figure 4, both global sampling parameters [Figure 4A, Sd: t(165) = −0.513, p = 0.6084; Ns: t(165) = −0.985, p = 0.3261] and fine parameters (Figure 4B, right) of individual sniffs were similar for cum and cyc. In contrast, both the Sd and Ns were significantly different between HS odorants hept and mbz [Figure 4A, Sd: t(167) = −4.295, p < 0.001; Ns: t(167) = −3.553, p < 0.001]. When we examined each cycle individually (Figure 4B, left), we observed only a few differences between hept and mbz with only one significant difference in the ID during the third cycle [t(143) = −2.691, p < 0.01]. Thus, for the two different pairs of odorant molecules used that were non-enantiomers, we did not observe a sorption-based rule; molecules could be sniffed either similarly or differently even if they were endowed with similar sorption properties. This finding suggests that sorption is not the only parameter involved in sniffing adjustment and is confirmed by results from another pair of odorants, hept/iso, which have similar sorption properties (HS/HS, see Table 1) but differ in their vapor pressure. The results presented in Figure 5 reveal that both global sampling parameters [Figure 5A, Sd: t(149) = 7.603, p < 0.001; Ns: t(149) = 10.049, p < 0.001] and fine parameters of individual sniffs [Figure 5B, IPF second cycle: t(136) = 3.551, p < 0.001; third cycle: t(64) = 6.962, p < 0.001; ED first cycle: t(149) = −2.553, p < 0.05; second cycle: t(136) = −7.941, p < 0.001; third cycle: t(64) = −7.952, p < 0.001] were significantly different between hept and iso. Thus, vapor pressure seems to enhance differences between sniffing strategies.


Sniff adjustment in an odor discrimination task in the rat: analytical or synthetic strategy?

Courtiol E, Lefèvre L, Garcia S, Thévenet M, Messaoudi B, Buonviso N - Front Behav Neurosci (2014)

Sorption is not the only parameter that determines global sniffing variations. (A) Global sampling parameters (mean ± s.e.m.), Sd (left), and Ns (right), for non-enantiomer odor pair: hept (green)/iso (black) n = 150. (B) Modulation of respiratory parameters in the first, second, and third cycles for hept/iso. From top to bottom: mean (± s.e.m.) normalized ID, IPF, and ED. Same colors as in (A). The number of trials for each odorant and cycle in hept/iso pair is: ncycle 1 = 150, ncycle 2 = 137, ncycle 3 = 65. Data were analyzed using a paired t-test; *p < 0.05; and ***p < 0.001.
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Related In: Results  -  Collection

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Show All Figures
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Figure 5: Sorption is not the only parameter that determines global sniffing variations. (A) Global sampling parameters (mean ± s.e.m.), Sd (left), and Ns (right), for non-enantiomer odor pair: hept (green)/iso (black) n = 150. (B) Modulation of respiratory parameters in the first, second, and third cycles for hept/iso. From top to bottom: mean (± s.e.m.) normalized ID, IPF, and ED. Same colors as in (A). The number of trials for each odorant and cycle in hept/iso pair is: ncycle 1 = 150, ncycle 2 = 137, ncycle 3 = 65. Data were analyzed using a paired t-test; *p < 0.05; and ***p < 0.001.
Mentions: In a second step, we analyzed sniffing strategies when the animals had to discriminate between odorants that had similar sorption properties but were non-enantiomers (Figure 4). Here, we surprisingly observed more heterogeneous results; the odorants of the LS/LS pair (cum/cyc) were sampled similarly, but the odorants of the HS/HS pair (hept/mbz) were sampled differently. As shown in Figure 4, both global sampling parameters [Figure 4A, Sd: t(165) = −0.513, p = 0.6084; Ns: t(165) = −0.985, p = 0.3261] and fine parameters (Figure 4B, right) of individual sniffs were similar for cum and cyc. In contrast, both the Sd and Ns were significantly different between HS odorants hept and mbz [Figure 4A, Sd: t(167) = −4.295, p < 0.001; Ns: t(167) = −3.553, p < 0.001]. When we examined each cycle individually (Figure 4B, left), we observed only a few differences between hept and mbz with only one significant difference in the ID during the third cycle [t(143) = −2.691, p < 0.01]. Thus, for the two different pairs of odorant molecules used that were non-enantiomers, we did not observe a sorption-based rule; molecules could be sniffed either similarly or differently even if they were endowed with similar sorption properties. This finding suggests that sorption is not the only parameter involved in sniffing adjustment and is confirmed by results from another pair of odorants, hept/iso, which have similar sorption properties (HS/HS, see Table 1) but differ in their vapor pressure. The results presented in Figure 5 reveal that both global sampling parameters [Figure 5A, Sd: t(149) = 7.603, p < 0.001; Ns: t(149) = 10.049, p < 0.001] and fine parameters of individual sniffs [Figure 5B, IPF second cycle: t(136) = 3.551, p < 0.001; third cycle: t(64) = 6.962, p < 0.001; ED first cycle: t(149) = −2.553, p < 0.05; second cycle: t(136) = −7.941, p < 0.001; third cycle: t(64) = −7.952, p < 0.001] were significantly different between hept and iso. Thus, vapor pressure seems to enhance differences between sniffing strategies.

Bottom Line: We found that sniffing variations were not only a matter of odorant sorption properties and that the same odorant was sniffed differently depending on the odor pair in which it was presented.These results suggest that rather than being adjusted analytically, sniffing is instead adjusted synthetically and depends on the pair of odorants presented during the discrimination task.Our results show that sniffing is a specific sensorimotor act that depends on complex synthetic processes.

View Article: PubMed Central - PubMed

Affiliation: Centre de Recherche en Neurosciences de Lyon, Equipe Olfaction: du codage à la mémoire, CNRS UMR 5292-INSERM U1028-Université Lyon1 Lyon, France.

ABSTRACT
A growing body of evidence suggests that sniffing is not only the mode of delivery for odorant molecules but also contributes to olfactory perception. However, the precise role of sniffing variations remains unknown. The zonation hypothesis suggests that animals use sniffing variations to optimize the deposition of odorant molecules on the most receptive areas of the olfactory epithelium (OE). Sniffing would thus depend on the physicochemical properties of odorants, particularly their sorption. Rojas-Líbano and Kay (2012) tested this hypothesis and showed that rats used different sniff strategies when they had to target a high-sorption (HS) molecule or a low-sorption (LS) molecule in a binary mixture. Which sniffing strategy is used by rats when they are confronted to discrimination between two similarly sorbent odorants remains unanswered. Particularly, is sniffing adjusted independently for each odorant according to its sorption properties (analytical processing), or is sniffing adjusted based on the pairing context (synthetic processing)? We tested these hypotheses on rats performing a two-alternative choice discrimination of odorants with similar sorption properties. We recorded sniffing in a non-invasive manner using whole-body plethysmography during the behavioral task. We found that sniffing variations were not only a matter of odorant sorption properties and that the same odorant was sniffed differently depending on the odor pair in which it was presented. These results suggest that rather than being adjusted analytically, sniffing is instead adjusted synthetically and depends on the pair of odorants presented during the discrimination task. Our results show that sniffing is a specific sensorimotor act that depends on complex synthetic processes.

No MeSH data available.