Visual function in guinea pigs: behavior and electrophysiology

Guinea pig visual function is characterised based on behavioural and electrophysiological measures and retinal ganglion cell density is examined to further develop the guinea pig as a model of human ocular conditions.

Guinea pigs are an important model of human ocular conditions. Here, guinea pig spatial frequency discrimination, pattern and full-field photopic electroretinography (ERG), and retinal ganglion cell distribution were investigated.

Adult guinea pigs (n = 6) were included. Optomotor responses to square-wave gratings from 0.3 to 2.4 cycles per degree (cpd) were assessed. Pattern ERG responses were recorded using square-wave gratings from 0.025 to 0.25 cpd at 100% contrast, alternating at a temporal frequency of 1.05 Hz. Full-field ERG responses were recorded using a 10.0 cd.s/m² flash. Ganglion cell density was determined histologically from retinal whole mounts.

Maximum spatial frequency discrimination was 1.65 ± 0.49 cpd for stimuli rotating temporally to nasally and 0.75 ± 0.16 cpd for stimuli rotating nasally to temporally. For pattern ERG, a maximum amplitude of 3.50 ± 1.16 µV for the first negative to positive peak (N1P1) was elicited with a 0.025 cpd grating, and 2.5 ± 0.1 µV for the positive to second negative peak (P1N2) was elicited with a 0.05 cpd grating. For full-field ERG, a-wave amplitude was 19.2 ± 4.24 µV, b-wave amplitude was 33.6 ± 8.22 µV, and the PhNR was 24.0 ± 5.72 µV. Peak retinal ganglion cell density was 1621 ± 129 cells/mm², located 1-2 mm superior to the optic nerve head.

Guinea pigs show directional selectivity for stimuli moving in the temporal to the nasal visual field. Guinea pigs demonstrate a quantifiable PhNR in the full-field ERG and negative and positive waveforms in the pattern ERG. The visual streak is located in the superior retina.