ELSEVIER Neuroscience Letters 198 (1995) 165-168 $1111 Differential expression of glial fibrillary acidic protein (GFAP) in the retinae and visual cortices of rats with experimental renal hypertension T.K. Lam a, W.Y. Chan a,*, Guo-Bi Kuang b, Hong Wei b, Alisa S.W. Shum a, D.T. Yew a aDepartment of Anatomy, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong bDepartment of Anatomy, Sun Yat Sen University of Medical Sciences, Guangzhou, People's Republic of China Received 3 July 1995; revised version received 29 August 1995; accepted 29 August 1995 Abstract To examine the expression of the GFAP protein in the retina and visual cortex under normal and pathological conditions, hyperten- sion was induced in adult male Sprague-Dawley rats by applying silver clips onto renal arteries and the change in GFAP expression was followed by Western blotting and immunocytochemical staining. One week after operation when the induced hypertension was at the initial stage, GFAP expression in the retina was reduced to half of the sham control. By 4 weeks, when consistent hypertension was developed, a further decrease irl the level of GFAP expression in the retina to one third of the sham control was observed. Immunocyto- chemical staining showed that the number of GFAP-positive cells in the nerve fiber layer of the retina of the hypertensive rat was re- duced to less than one third of the sham control. However, similar changes in GFAP expression in the visual cortex of hypertensive rats were not observed. This study represents the first report to date on GFAP expression in the retina and visual cortex and includes dis- cussion of the possible mechanisms through which GFAP expression is mediated. Keywords: Glial fibrillary acidic protein; Retina; Cerebral cortex; Astrocyte; Experimental hypertension; Rat; Renal artery Glial fibrillary acidic protein (GFAP) has been widely documented as the chief constituent in the astrocytes and is a major component of their intermediate filaments (10nm diameter [12]). These filaments are present in both the fibrous and protoplasmic astrocytes [4-7,12]. The GFAP protein is brain specific and not species spe- cific and therefore can bevisualized immunologically in a number of species with the exception of rabbit, guinea pig and cow which produce only very faint reactions [13]. In the retina and the cerebral cortex, astrocytes have been suggested to induce or participate in the formation of blood-brain or blood-retina barriers with the endothelial cells of the capillaries [3,8,15]. Furthermore, in the retina, the astrocytes seem to perform many roles, e.g. wrapping around ganglion cell axons [14], contacting other macro- glial cells (e.g. Miiller cells) to form adherent junctions [9] and also play a role in potassium buffering [11] and in neuronal signalling [2]. As the astrocytes have a close relationship with both blood vessels and nerve fibers, it * Corresponding author. Tel: +852 26096895; fax: +852 26035031/ 26096895. is of particular interest to know whether there are any changes in the astrocytes when the blood pressure changes. In this study, we report a de novo change of the GFAP, one of the major constituent molecules of the as- trocyte, in the retina but not the visual cortex after induc- tion of renal hypertension. Histological examination showed that there was a reduction in the number of astro- cytes in the nerve fiber layer of the retina four weeks after the induction of the hypertension. Hypertension was induced by applying silver clips with an internal diameter of 0.3 mm onto renal arteries on both sides of the animals through paramedian incisions under light ether anesthesia [16]. Male Sprague-Dawley rats (n = 32) about 4 months old were used as experimen- tal animals while another 24 rats were sham-operated. They were then sacrificed 1 week or 4 weeks after opera- tion. The blood pressures were measured prior to opera- tion and before sacrifice by an electronic device (Shang- hai, China) through the tail artery as in previous studies [ 17]. A pilot study showed that the systolic blood pressure increased more significantly in magnitude than the dia- stolic pressure although they followed a similar pattern of 0304-3940/95/$09.50 © 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0304-3940(95)1 1984-2