Morphological and functional evidences for TRPM8 expression in the mouse retina

Abstract

Purpose : Novel transgenic mice expressing fluorescent reporters associated to TRP channels have improved morphological studies of protein location. Here we report the expression of TRPM8 cold-transducing ion channel in a subset of retinal neurons. This study also aims to study the function of TRPM8 in the retina.

Methods : Retinas from TRPM8-EYFP and TRPM8-KO mice were used to detect by immunofluorescence Calretinin, Calbindin, Parvalbumin, Tyrosine hydroxylase, Choline acetyl transferase, GAD 65/67 and mGluR2. Prior to morphological analysis, WT and KO mice were examined by electroretinography (ERG) and optomotor tests to evaluate the functional role of TRPM8 in the retina. ARVO statements for the use of animals were followed.

Results : We described a population of TRPM8-positive amacrine cells with cell bodies distributed in the internal nuclear layer (INL) and ganglion cell layer (GCL), forming two densely packed neuropil layers coincident with ChAT+ sublayers 2 and 4 of the inner plexiform layer (IPL). Retinal amacrine cells from TRPM8-KO mice did not express TRPM8 protein or mRNA and were less numerous than in WT mice. Electroretinographic analysis showed alterations in oscillatory potentials and b-wave in KO mice. Optomotor test showed impaired movement discrimination in KO mice compared with WT.

Conclusions : A subtype of amacrine cells expressing TRPM8 channels has been identified. It appears unlikely that TRPM8 channels expressed by these neurons are involved in cold detection. In contrast, the expression of ChAT and the alterations in oscillatory potentials strongly suggest that about 60% of these cells may be starburst-like cells and could be involved in directional selectivity.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.