Ž . Molecular Brain Research 76 2000 341–346 www.elsevier.comrlocaterbres Research report Retinal lesions induce differential changes in the expression of flip and flop isoforms of the glutamate receptor subunit GluR1 in the chick optic tectum Raquel S. Pires a , Nancy A. Rebouc ¸as a , Robert M. Duvoisin b , Luiz R.G. Britto a, ) a Department of Physiology and Biophysics, Institute of Biomedical Sciences, UniÕersity of Sao Paulo, AÕ. Prof. Lineu Prestes, 1524, 05508-900 Sao ˜ Paulo S.P., Brazil b Margaret M. Dyson Vision Research Institute, Departments of Ophthalmology and Cell Biology, Weill Medical College of Cornell UniÕersity, New York, NY 10021, USA Accepted 4 January 2000 Abstract A sensitive RNase protection assay was employed to determine the levels of mRNA encoding the GluR1 subunit flip and flop isoforms in the chick optic tectum and forebrain. We found that the flip GluR1 mRNA predominates in the forebrain, whereas the flop variant is more strongly expressed in the optic tectum. A temporal analysis of GluR1 variants in the embryonic and adult chick brain revealed that the flip isoform is more highly expressed at E12 than at P15–21, whereas mRNA levels of the flop isoform are higher at P15–21 than at E12. To study the effect of deafferentation on GluR1 expression, unilateral retinal lesions were performed. Two days later the mRNA levels of GluR1 flip and flop variants were decreased in the deafferented tectum, especially for the flop isoform. However, 7 days after the lesion, the mRNA levels of both GluR1 isoforms were increased, especially for the flip isoform. These results reveal an important control of the retinal input upon the expression of the different GluR1 isoforms. Furthermore, they indicate a differential spatial and temporal regulation of the flip and flop splice variants, suggesting the existence of a mechanism regulating differential splicing or possibly differential RNA stability. q 2000 Elsevier Science B.V. All rights reserved. Keywords: AMPA; Neurotransmitter; Receptor subunit; Splice variant; Visual pathway 1. Introduction Ž . The AMPA-type glutamate receptors GluRs are the primary mediators of fast excitatory synaptic transmission in the vertebrate brain. They are composed of tetrameric assemblies of four protein subunits, named GluR1-4 w x 13,21 . Each of these subunits can exist in two alterna- tively spliced forms, termed flip and flop, which differ in their functional properties, regional distribution and preva- w x lence during development in the rat brain 10,23 . Recent molecular studies have shown that the avian AMPA recep- tors share extensive sequence homology with mammalian w x receptors 12,14 . This homology extends to the flip and flop alternative splicing variants, suggesting functional and w x regional distribution similarities 19,20 . In both E17 chicks and P1–15 rats, flip splice variants of GluR1-3 predomi- ) Corresponding author. Fax: q55-11-818-7426; e-mail: lrbritto@usp.br nate in the forebrain and flop splice variants of GluR1 and w x 2 are more prevalent in the midbrain 19 . Despite the similarities between AMPA receptors of mammals and birds, little is known about the developmental changes of chick GluRs and the expression patterns of each GluR isoform after experimental manipulations of the visual pathways, such as retinal deafferentation. Previous im- munohistochemistry and immunoblotting data have shown that the expression of GluR1 and GluR2r3 subunits were decreased in the deafferented chick optic tectum 2 days after a retinal lesion and were followed by an increased w x level of these subunits after 7 days 17 . As part of a general effort to characterize the regulation and distribu- tion of GluR expression in the avian visual system, we have used RNase protection assays to investigate the ex- pression patterns of flip and flop isoforms of GluR1 mRNA in the chick optic tectum in response to retinal lesions and to analyze the spatial and temporal variations of mRNA levels for each GluR1 isoform. 0169-328Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-328X 00 00016-4