RETURNYonago Acta medica 1992;35:192–208
Stress-Induced Increases in Dopamine and Glutamate in the Rat Retina
Takatoshi Hamahashi*†, Yoshinori Kamisaki* and Tadao Itoh*
*Department of Clinical Pharmacology and †Department of Ophthalmology, Faculty of Medicine , Tottori University, Yonago 683, Japan
In order to investigate the effects of stress on the dopaminergic neurons in the retina, Wistar rats were subjected to water-immersion restraint stress for l, 4 and 7 h. The 1-h stress caused 2.5- and 1.3-fold increases in the dopamine and glutamate (Glu) contents in the retina, respectively, and longer stress reduced them to prestress levels. In vitro incubation of the retina with Glu in the presence of 3,4-dihydroxy-phenylalanine caused a significant increase in the dopamine content. Moreover, intraocular administration of Glu caused dose-dependent increases in aromatic amino acid decarboxylase activity in the retina with an ED50 of 0.63 µmol. Kainate showed effects similar on Glu, but N-methyl-D-aspartate and quisqualate failed. When Glu antagonists were administered intraocularly together with Glu, the Glu-induced increase in the decarboxylase activity was inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione but not by D,L-2-amino-5-phosphonovaleric acid. These data suggest that at the early stages stress causes an increase in Glu and dopamine content in the retina, and that elevated Glu may stimulate dopamine synthesis probably through a kainate-type Glu receptor.
Key words: dopamine; glutamate; retina; stress