Brain Research Bulletin 71 (2006) 91–96 Localization of ZnT7 and zinc ions in mouse retina— Immunohistochemistry and selenium autometallography Xin Wang a , Zhan-You Wang a,∗ , Hui-Ling Gao a , Gorm Danscher b , Liping Huang c a Department of Histology and Embryology, China Medical University, Shenyang 110001, PR China b Department of Neurobiology, University of Aarhus, DK 8000 Aarhus C, Denmark c Western Human Nutrition Research Center, Agriculture Research Service, United States Department of Agriculture, USA Received 15 June 2006; received in revised form 11 July 2006; accepted 7 August 2006 Available online 31 August 2006 Abstract Zinc transporter 7 (ZnT7, Slc30a7), a member of the Slc30 family, is involved in mobilizing zinc ions from the cytoplasm into the Golgi apparatus. In the present study, we examined the distribution and localization of ZnT7 and the labile zinc ions in the mouse retina using immunohistochemistry and in vivo zinc–selenium autometallography (ZnSe AMG ). Our results showed that ZnT7 is abundantly expressed in the ganglion cells and pigment epithelial cells of the mouse retina. ZnT7 is also expressed in the amacrine cells and the layer of optic fibers of the mouse retina, but to a lesser extent. Weak staining of ZnT7 was detected in the inner plexiform layer, outer plexiform layer, and outer segment of the photoreceptors. However, ZnT7 was not detected in the outer nuclear layer and inner segment of the photoreceptors. A high level of labile zinc pool was detected in the pigment epithelial cells, the inner segment of the photoreceptors, and the marginal region of the inner nuclear layer. Less amount of labile zinc ions were detected in the ganglion cells of the retina. These observations strongly suggest that ZnT7 may play critical roles in retinal zinc homeostasis and that chelatable zinc pools may have multiple functions in the retina. © 2006 Elsevier Inc. All rights reserved. Keywords: Zinc; ZnT7; Zinc transporter; Retina; Mouse 1. Introduction Zinc is an essential trace metal which plays critical roles in biological processes of the body. In brain, approximately 90% of total zinc is tightly bound in metalloenzymes and other zinc-containing proteins, where zinc serves as a cofactor for enzymatic activities or for maintaining the three-dimensional structure of proteins [6,4]. The remaining 10% of total zinc is called chelatable zinc, because it presents as free or loosely bound ions. These chelatable zinc ions, most of which are local- ized in a population of synaptic vesicles of the so-called zinc enriched (ZEN) terminals, can be detected by both fluorescence and autometallographic (AMG) techniques. The fluorescence techniques including TSQ and Zinquin staining are suitable for low magnification approaches while the AMG techniques are ∗ Corresponding author. Tel.: +86 24 23256666 5305; fax: +86 24 23256666 5305. E-mail address: wangzy@mail.cmu.edu.cn (Z.-Y. Wang). excellent for detecting nM levels of chelatable zinc ions in tis- sues [17,10,51,16,9]. The telencephalon contains large amount of zinc enriched neuronal somata and terminals. Neocortex and hippocampal regions of brain contain the highest zinc enriched neuronal terminals in the human brain. These zinc enriched neuronal terminals are glutaminergic [31,32,12]. During synaptic vesi- cle exocytosis, vesicular zinc is co-released with glutamate into the synaptic space [3,21,2]. It has been suggested that these zinc ions modulate the activities of the excitatory N-methyl- d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid (AMPA) receptors localized on the postsynaptic membrane ([49,35]). In addition, studies also showed that most zinc enriched terminals in the spinal cord and cerebellum are either GABAergic or glycinergic [44–46]. Zinc is abundant in the mammalian retina [20]. Several studies have demonstrated that cellular zinc ions were local- ized in the inner segment of the photoreceptors, the outer and inner plexiform layers, and inner nuclear layer [1]. However, the ultrastructural evidence of the exact zinc localization is 0361-9230/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.brainresbull.2006.08.002