The bioelectric field of the pattern electroretinogram in the mouse

To compare the bioelectric field associated with the pattern electroretinogram (PERG) with that of the flash electroretinogram (FERG) in the mouse.

PERGs and FERGs were recorded from each eye in 32 C57BL/6J mice using corneal silver loops referenced to a subcutaneous needle on the back of the head. PERG stimuli were horizontal gratings of 0.05 cycles per degree and 98% contrast reversing 2 times per second. Light-adapted FERG stimuli were bright strobe flashes. Stimuli were presented either monocularly or binocularly. In some experiments, TTX was injected in one eye and saline in the contralateral eye.

The PERG recorded from the contralateral, occluded eye had slightly larger amplitude (1.14 ×, P < 0.01) and longer latency (+1.57 ms, P < 0.01) compared with the ipsilateral eye. Under binocular stimulation, the PERG amplitude was much larger (1.67 ×, P < 0.01) than the monocular amplitude. TTX injected in the stimulated eye drastically reduced the PERG in both eyes. Monocular FERGs were recordable from the stimulated eye only and were moderately reduced by TTX. Binocular and monocular FERGs had similar amplitudes.

PERG and FERG generate different bioelectric fields in the mouse. The PERG bioelectric field is consistent with a dipole model whose axis is orthogonal to the eye axis, whereas the standard dipole model for the FERG is coaxial. Possible sources of the PERG bioelectric field are unmyelinated optic nerve axons adjacent to the sclera. Results provide new insights on the generators of the PERG signal and its alterations in mouse models of glaucoma and optic nerve diseases.