Contribution of mGluR5 to different components of the rat dark-adapted electroretinogram

Objective To investigate the contribution of the metabotropic glutamate receptor 5 (mGluR5) to the different components of the rat dark-adapted electroretinogram (ERG). Methods This was an experimental study. After 12 h dark adaptation, RCS-rdy+-p+ rats were subretinally injected with the 200 μmol agonist (R, S)-2-chloro-5-hydroxyphenylglycine (CHPG) and 200 μmol antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP). The same volume of phosphate buffered saline (PBS) was injected into the fellow eye for comparison. The dark-adapted ERGs were recorded by a series of flashes [-4.5, -2.5, -0.5, -0.02, 0.5, and 1 log(cd×m/s-2)]. Output data were exported and compared by paired t-tests. Results In the CHPG group, the amplitudes of the a- and b-waves at all light intensities (except the lowest intensity) were significantly decreased compared with the PBS-injected eyes. The parameters of Rmax and Vmax were also significantly decreased, but sensitivities of the a- and b-waves, the b-wave to a-wave ratio, and the oscillatory potentials (OPs) were unchanged when compared with the PBS-injected eyes. In the MPEP group, the amplitudes of the a- and b-waves at all light intensities (except the lowest intensity) were significantly increased compared with the PBS-injected eyes. The parameters of Rmax and Vmax were also significantly increased, but the sensitivities of the a- and b-waves, the b-wave to a-wave ratio, and OPs were unchanged when compared with the PBS-injected eyes. Conclusion The mGluR5 agonist CHPG decreased the amplitudes of the ERG a- and b-waves. This suggests that mGluR5 regulates the light responses of the outer retina. Key words: Metabotropic glutamate receptor 5; Electroretinogram; (R, S)-2-chloro-5-hydrox- yphenylglycine; 2-methyl-6- (phenylethynyl) -pyridine