Temporal properties of cone ERGs of Pikachurin null mutant mouse

Abstract

Purpose : Pikachurin is an extracellular matrix-like protein located in the synaptic cleft of the photoreceptors, and pikachurin null mutant (Pika^-/-) mice have abnormal ON bipolar cell function. The purpose of this study was to determine the contribution of the ON bipolar cell pathway (ON pathway) of Pika^-/- mice to the flicker ERGs and to identify how the contribution varies with the stimulus frequency using vector analysis.

Methods : Flicker ERGs were recorded from wild type (WT), Pika^-/-, and mGluR6 null mutant (mGluR6^-/-) mice. The frequency of stimulation ranged from 3.906 Hz to 31.250 Hz. The amplitude and phase of the fundamental components were obtained by harmonic analysis and vector model analysis. The mGluR6^-/- mice were used as a model in which the ON pathway is well known to be absent.

Results : The amplitudes of the fundamental components of the Pika^-/- mice were significantly smaller than those of WT for stimulation frequencies between 3.906 to 17.578 Hz. The phase of the fundamental components of the Pika^-/- mice was between the phases of the WT and mGluR6^-/- mice.Vector analyses showed that the function of ON pathway of Pika^-/- mice was about 12 to 25% of that of the WT mice at lower frequencies < 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 the flicker ERGs, and it may be a useful method to determine the retinal function in mice models with abnormalities of the ON pathway.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Representative vectors obtained from the amplitudes and phases of fundamental components of the flicker ERGs of the WT, Pika^-/-, and mGluR6^-/- mice at 5.859 Hz , 11.718 Hz , 17.578 Hz , and 23.438 Hz . The length and direction of the arrows indicate the mean amplitudes and phases respectively. The vectors of the WT, Pika^-/-, mGluR6^-/- are shown. To estimate the contribution of the ON pathway of Pika^-/- mice, the vector of the mGluR6^-/- mice was subtracted from that of the Pika^-/- mice. To estimate the contribution of the ON pathway of WT mice , the vector of the mGluR6^-/- mice was subtracted from that of the WT mice.