Expression of water channel aquaporin-4 during experimental syringomyelia

Laboratory investigation

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Object

Aquaporins (aqp) are protein channels providing water transport across cell membranes. The main member of this family expressed in the CNS is aqp-4. The pattern and amount of expression of this channel suggest a dominant role in bulk water movement into the nervous tissue. It has also been shown to play a role in several water balance disorders in the CNS. In this study, the authors investigated the possible role of aqp-4 in syringomyelia.

Methods

Twenty-five male Wistar-Hannover rats were divided into experimental (20 rats) and control (5 rats) groups. Syringomyelia was induced in the experimental group by kaolin injection into the cisterna magna. Eight weeks later, the animals were killed, and their spinal cords were removed. Central canal dilations were noted in all experimental animals. Immunohistochemistry and Western blot analysis were performed to evaluate aqp-4 expression.

Results

Both groups demonstrated positive immunoreactive signals to aqp-4. Western blot analysis revealed a slight decrease in the mean aqp-4 value in the experimental group; however, the difference did not reach statistical significance (p > 0.05). Immunohistochemical analysis showed a similar pattern and intensity of aqp-4 staining in both groups.

Conclusions

The results of this study indicate that aqp-4 most likely does not play a major role in chronic syringomyelia. Its slight downregulation during the initial stage of syrinx formation is possibly a compensatory mechanism. This effect is not present during the late stage of syringomyelia, and aqp-4 is most likely not involved in the pathophysiology of syrinx cavity formation.

Abbreviations used in this paper: aqp = aquaporin; TBST = Trisbuffered saline with Tween.

Article Information

Address correspondence to: Kamran Aghayev, M.D., Neuro-Oncology Program, H. Lee Moffitt Cancer Center, 12902 Magnolia Drive, Tampa, Florida 33612. email: kamranag@gmail.com.

Please include this information when citing this paper: published online June 17, 2011; DOI: 10.3171/2011.5.SPINE10303.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Photographs of spinal cords obtained immediately after removal from the spinal canal.

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    Photomicrographs showing syringomyelia induced by kaolin injection in samples obtained in control (A, C, and E) and experimental (B, D, and F) animals. A and B: Spinal cord specimens. Note the difference between the central canal sizes. C and D: Central canal specimens. Note the ependymal disruption and denuding in the experimental sample. E and F: Aqp-4 immunostaining. H & E (A–D), original magnification × 10 (A–F).

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    Schematic representation of aqp-4 expression in the CNS.

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