Expression of water channel aquaporin-4 during experimental syringomyelia: laboratory investigation

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.

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.

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.

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.