Expression of aquaporin-9 immunoreactivity by catecholaminergic amacrine cells in the rat retina

Aquaporins are involved in the maintenance of ionic and osmotic balance in the central nervous system and in the eye. Whereas the expression of aquaporin-9 immunoreactivity in the brain has been described for catecholaminergic neurons and glial cells, the expression of aquaporin-9 in the neural retina is unclear. We examined the distribution of aquaporin-1 and -9 immunoreactivities in retinas of the rat. Aquaporin-9 immunoreactivity was expressed exclusively by tyrosine hydroxylase (TH) positive amacrine cells, while aquaporin-1 immunoreactivity was expressed by photoreceptor cells and by TH negative amacrine cells. The staining pattern of aquaporin-9 did not change up to 4 weeks after pressure-induced transient retinal ischemia. It is concluded that catecholaminergic, putatively dopaminergic, amacrine cells of the retina express aquaporin-9.