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Gap junctions in olfactory neurons modulate olfactory sensitivity.

Zhang C - BMC Neurosci (2010)

Bottom Line: Electroolfactogram recordings showed decreased olfactory responses to octaldehyde, heptaldehyde and acetyl acetate in OlfDNCX compared to WT.Furthermore, pharmacologically uncoupling of gap junctions reduces olfactory activity in subsets of ORNs.These data suggest that gap junctional communication or hemichannel activity plays a critical role in maintaining olfactory sensitivity and odor perception.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, Chicago, IL 60616, USA. zhangc@iit.edu

ABSTRACT

Background: One of the fundamental questions in olfaction is whether olfactory receptor neurons (ORNs) behave as independent entities within the olfactory epithelium. On the basis that mature ORNs express multiple connexins, I postulated that gap junctional communication modulates olfactory responses in the periphery and that disruption of gap junctions in ORNs reduces olfactory sensitivity. The data collected from characterizing connexin 43 (Cx43) dominant negative transgenic mice OlfDNCX, and from calcium imaging of wild type mice (WT) support my hypothesis.

Results: I generated OlfDNCX mice that express a dominant negative Cx43 protein, Cx43/β-gal, in mature ORNs to inactivate gap junctions and hemichannels composed of Cx43 or other structurally related connexins. Characterization of OlfDNCX revealed that Cx43/β-gal was exclusively expressed in areas where mature ORNs resided. Real time quantitative PCR indicated that cellular machineries of OlfDNCX were normal in comparison to WT. Electroolfactogram recordings showed decreased olfactory responses to octaldehyde, heptaldehyde and acetyl acetate in OlfDNCX compared to WT. Octaldehyde-elicited glomerular activity in the olfactory bulb, measured according to odor-elicited c-fos mRNA upregulation in juxtaglomerular cells, was confined to smaller areas of the glomerular layer in OlfDNCX compared to WT. In WT mice, octaldehyde sensitive neurons exhibited reduced response magnitudes after application of gap junction uncoupling reagents and the effects were specific to subsets of neurons.

Conclusions: My study has demonstrated that altered assembly of Cx43 or structurally related connexins in ORNs modulates olfactory responses and changes olfactory activation maps in the olfactory bulb. Furthermore, pharmacologically uncoupling of gap junctions reduces olfactory activity in subsets of ORNs. These data suggest that gap junctional communication or hemichannel activity plays a critical role in maintaining olfactory sensitivity and odor perception.

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OlfDNCX display altered responses to odorants. A. A photograph of the turbinates in a mouse showing EOG recording sites. Endoturbinates are indicated by roman ordinals. The approximate locations for EOG recordings are indicated. B. Typical EOG responses for octaldehyde (solid line) and benzaldehyde (dotted line) in wild type mice (WT) and in OlfDNCX in Position 1. Duration of the stimulation and the response magnitude are as indicated. C. Dose-response relationships for peak EOG responses to octaldehyde (normalized to responses of 100 μM benzaldehyde) in OlfDNCX (open circle) and their WT littermates (solid circle). Significant differences between the two groups are indicated by asterisks (*, p < 0.05; **, p < 0.01; n = 11).
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Figure 3: OlfDNCX display altered responses to odorants. A. A photograph of the turbinates in a mouse showing EOG recording sites. Endoturbinates are indicated by roman ordinals. The approximate locations for EOG recordings are indicated. B. Typical EOG responses for octaldehyde (solid line) and benzaldehyde (dotted line) in wild type mice (WT) and in OlfDNCX in Position 1. Duration of the stimulation and the response magnitude are as indicated. C. Dose-response relationships for peak EOG responses to octaldehyde (normalized to responses of 100 μM benzaldehyde) in OlfDNCX (open circle) and their WT littermates (solid circle). Significant differences between the two groups are indicated by asterisks (*, p < 0.05; **, p < 0.01; n = 11).

Mentions: Because I suspected that modulation of odor responses by gap junctions would be of a relatively small magnitude, and because there was a large variation in the absolute magnitude of the EOG responses to an odorant from mouse to mouse, I measured the response to one odorant normalized to the response of another odorant (normalized response), as has been routinely done in EOG recordings in rat [44]. EOG recordings were conducted at ventral (Position 1) and dorsal (Position 2) positions (indicated in Figure 3A) because an earlier study shows that Cx43 is more abundantly expressed in Position 1 than in Position 2 [23]. I started with stimulation of benzaldehyde, 1,8-cineole, and octaldehyde at the concentration of 100 μM. It appeared that olfactory responses to octaldehyde were consistently lower in OlfDNCX, compared to WT, when recorded from Position 1 (Figure 3B). Indeed, when I quantified the response magnitudes of octaldehyde by normalizing to those of benzaldehyde, the normalized responses were significantly different between OlfDNCX and WT (p < 0.0001) (Figure 3B, Table 3). The ratios of cineole to benzaldehyde did not differ between OlfDNCX and WT in Position 1 (Table 3). In contrast, no significant differences were found between OlfDNCX and WT for EOG responses recorded from Position 2, an area expressing limited Cx43. In the statistical analysis, p values were adjusted to correct for multiple comparisons by using the false discovery rate procedure [45]. Table 4 lists normalized olfactory response magnitudes to 2,5-dimethyl pyrazine, ethyl acetate and heptaldehyde recorded from Position 1. The olfactory responses of ethyl acetate and heptaldehyde were lower in OlfDNCX compared to WT, when they were normalized to those of benzaldehyde.


Gap junctions in olfactory neurons modulate olfactory sensitivity.

Zhang C - BMC Neurosci (2010)

OlfDNCX display altered responses to odorants. A. A photograph of the turbinates in a mouse showing EOG recording sites. Endoturbinates are indicated by roman ordinals. The approximate locations for EOG recordings are indicated. B. Typical EOG responses for octaldehyde (solid line) and benzaldehyde (dotted line) in wild type mice (WT) and in OlfDNCX in Position 1. Duration of the stimulation and the response magnitude are as indicated. C. Dose-response relationships for peak EOG responses to octaldehyde (normalized to responses of 100 μM benzaldehyde) in OlfDNCX (open circle) and their WT littermates (solid circle). Significant differences between the two groups are indicated by asterisks (*, p < 0.05; **, p < 0.01; n = 11).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2944353&req=5

Figure 3: OlfDNCX display altered responses to odorants. A. A photograph of the turbinates in a mouse showing EOG recording sites. Endoturbinates are indicated by roman ordinals. The approximate locations for EOG recordings are indicated. B. Typical EOG responses for octaldehyde (solid line) and benzaldehyde (dotted line) in wild type mice (WT) and in OlfDNCX in Position 1. Duration of the stimulation and the response magnitude are as indicated. C. Dose-response relationships for peak EOG responses to octaldehyde (normalized to responses of 100 μM benzaldehyde) in OlfDNCX (open circle) and their WT littermates (solid circle). Significant differences between the two groups are indicated by asterisks (*, p < 0.05; **, p < 0.01; n = 11).
Mentions: Because I suspected that modulation of odor responses by gap junctions would be of a relatively small magnitude, and because there was a large variation in the absolute magnitude of the EOG responses to an odorant from mouse to mouse, I measured the response to one odorant normalized to the response of another odorant (normalized response), as has been routinely done in EOG recordings in rat [44]. EOG recordings were conducted at ventral (Position 1) and dorsal (Position 2) positions (indicated in Figure 3A) because an earlier study shows that Cx43 is more abundantly expressed in Position 1 than in Position 2 [23]. I started with stimulation of benzaldehyde, 1,8-cineole, and octaldehyde at the concentration of 100 μM. It appeared that olfactory responses to octaldehyde were consistently lower in OlfDNCX, compared to WT, when recorded from Position 1 (Figure 3B). Indeed, when I quantified the response magnitudes of octaldehyde by normalizing to those of benzaldehyde, the normalized responses were significantly different between OlfDNCX and WT (p < 0.0001) (Figure 3B, Table 3). The ratios of cineole to benzaldehyde did not differ between OlfDNCX and WT in Position 1 (Table 3). In contrast, no significant differences were found between OlfDNCX and WT for EOG responses recorded from Position 2, an area expressing limited Cx43. In the statistical analysis, p values were adjusted to correct for multiple comparisons by using the false discovery rate procedure [45]. Table 4 lists normalized olfactory response magnitudes to 2,5-dimethyl pyrazine, ethyl acetate and heptaldehyde recorded from Position 1. The olfactory responses of ethyl acetate and heptaldehyde were lower in OlfDNCX compared to WT, when they were normalized to those of benzaldehyde.

Bottom Line: Electroolfactogram recordings showed decreased olfactory responses to octaldehyde, heptaldehyde and acetyl acetate in OlfDNCX compared to WT.Furthermore, pharmacologically uncoupling of gap junctions reduces olfactory activity in subsets of ORNs.These data suggest that gap junctional communication or hemichannel activity plays a critical role in maintaining olfactory sensitivity and odor perception.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, Chicago, IL 60616, USA. zhangc@iit.edu

ABSTRACT

Background: One of the fundamental questions in olfaction is whether olfactory receptor neurons (ORNs) behave as independent entities within the olfactory epithelium. On the basis that mature ORNs express multiple connexins, I postulated that gap junctional communication modulates olfactory responses in the periphery and that disruption of gap junctions in ORNs reduces olfactory sensitivity. The data collected from characterizing connexin 43 (Cx43) dominant negative transgenic mice OlfDNCX, and from calcium imaging of wild type mice (WT) support my hypothesis.

Results: I generated OlfDNCX mice that express a dominant negative Cx43 protein, Cx43/β-gal, in mature ORNs to inactivate gap junctions and hemichannels composed of Cx43 or other structurally related connexins. Characterization of OlfDNCX revealed that Cx43/β-gal was exclusively expressed in areas where mature ORNs resided. Real time quantitative PCR indicated that cellular machineries of OlfDNCX were normal in comparison to WT. Electroolfactogram recordings showed decreased olfactory responses to octaldehyde, heptaldehyde and acetyl acetate in OlfDNCX compared to WT. Octaldehyde-elicited glomerular activity in the olfactory bulb, measured according to odor-elicited c-fos mRNA upregulation in juxtaglomerular cells, was confined to smaller areas of the glomerular layer in OlfDNCX compared to WT. In WT mice, octaldehyde sensitive neurons exhibited reduced response magnitudes after application of gap junction uncoupling reagents and the effects were specific to subsets of neurons.

Conclusions: My study has demonstrated that altered assembly of Cx43 or structurally related connexins in ORNs modulates olfactory responses and changes olfactory activation maps in the olfactory bulb. Furthermore, pharmacologically uncoupling of gap junctions reduces olfactory activity in subsets of ORNs. These data suggest that gap junctional communication or hemichannel activity plays a critical role in maintaining olfactory sensitivity and odor perception.

Show MeSH
Related in: MedlinePlus