Temporal Properties of Cone ERGs of Pikachurin Null Mutant Mouse.

PURPOSE Pikachurin is an extracellular matrix-like protein located in the synaptic cleft of photoreceptors. Pikachurin null mutant (Pika-/-) mice have abnormal ON bipolar cell function. This study aimed to determine the contribution of the ON bipolar cell pathway (ON pathway) of Pika-/- mice to the flicker ERG response and, using vector analysis, identify how the contribution varies with the stimulus frequency. METHODS Flicker ERGs were recorded from wild-type (WT), Pika-/-, and mGluR6 null mutant (mGluR6-/-) mice. The frequency of stimulation was 3.906 to 31.250 Hz. The amplitude and phase of the fundamental components were obtained by harmonic and vector model analysis. The mGluR6-/- mice were used as a model wherein the ON pathway is known to be absent. RESULTS The amplitudes of the fundamental components of the Pika-/- mice were significantly smaller than those of WT mice for stimulation frequencies between 3.906 and 17.578 Hz. The phase of the fundamental components of the Pika-/- mice was between those of the WT and mGluR6-/- mice. Vector analyses showed that the functioning of the ON pathway of Pika-/- mice was 12% to 25% of that of the WT mice at low frequencies (i.e., <15.625 Hz); however, it was reduced to noise level at frequencies >17.578 Hz. CONCLUSIONS Vector model analysis can determine the degree of contribution of the ON pathway of Pika-/- mice to flicker ERG response and may be useful for determining the retinal function in mice models with abnormalities of the ON pathway.