Table 4.

Studies assessing the relationship between AQPs and olfaction.

Authors and Reference	Study Design	Species and/or Tissue Type	Detection Method	Target AQPs	Results/Conclusion
Solbu et al. [56]	Animal tissue study	Rats and mice (olfactory mucosa)	Immunofluorescence staining, immunogold electron microscopy	AQP1, -3, -4, -5	AQP5 is present at the apical surface of the olfactory epithelium, and an intricate network of fine AQP1-positive fibroblast processes surrounds Bowman’s glands.
Sørbø et al. [73]	Animal tissue study	Rats (nasal epithelium and glomerulus of the olfactory bulb)	RT-PCR, immunoblotting, immunohistochemistry	AQP4	AQP4 is strongly expressed in the glomerulus, the synaptic unit of the olfactory bulb, suggesting a role for AQP4 in olfactory function.
Lu et al. [57]	Animal tissue study	Mice (AQP4-null mice vs. wild-type mice)	Immunocytochemistry, immunofluorescence	AQP4	The olfactory epithelium of AQP4-null mice appeared outwardly normal, but did not express AQP4, exhibited a 12-fold reduction in osmotic water permeability, and showed impaired olfaction.
Ablimit et al. [58]	Animal tissue study	Rats (VNO)	Immunofluorescence microscopy, immunoelectron microscopy	AQP1, -2, -3, -4, -5, -6, -7, -9, -10, -11	The localization of AQPs in the VNO is distinct from that in the olfactory mucosa. AQP4 was specifically detected in neuronal sensory cells, which is also a unique feature among neuronal cells.
Merigo et al. [74]	Animal tissue study	Mice (VNO vs. olfactory mucosa)	RT-PCR, immunoblotting, ELISA	AQP2, -3, -4, -5	In the olfactory epithelium, AQP2, AQP3, and AQP4 appeared at E14 and AQP5 at E17, and all persisted until adulthood except AQP2, which was no longer found in olfactory epithelium after P15. In the VNO–SE, AQP2 appeared at E14 and was absent after P15, as was also observed in the olfactory epithelium; instead, AQP4 was expressed in the VNO–SE from E18 to P60, and AQP3 and AQP5 were absent throughout.
Shields et al. [59]	In vivo animal study, in vitro cultured cell study	Mice	Immunoblotting, immunohistochemistry	AQP1	AQP1 is expressed in lamina propria of the nasal cavity, OEG in the main olfactory bulb, and in primary cultured olfactory bulb cells.

AQP, aquaporin; qRT-PCR, quantitative reverse transcription polymerase chain reaction; VNO, vomeronasal organ; E, embryonic day; P, postnatal day; VNO–SE: vomeronasal–sensory epithelium; OEG, olfactory ensheathing glia.