Abstract
In the central nervous system, melastatin transient receptor potential (TRPM) channels function as receptors for the neurosteroid pregnenolone sulfate (PregS). The expression and function of TRPM3 has been explored in adult retina, though its role during development is unknown. We found, during the second postnatal week in mice, TRPM3 immunofluorescence labeled distinct subsets of inner retinal neurons, including a subset of retinal ganglion cells (RGCs), similar to what has been reported in the adult. Labeling for a TRPM3 promoter-driven reporter confirmed expression of the TRPM3 gene in RGCs and revealed additional expression in nearly all Müller glial cells. Using two-photon calcium imaging, we show that PregS and the synthetic TRPM3 agonist CIM0216 induced prolonged calcium transients in RGCs, which were mostly absent in TRPM3 knockout (KO) mice. These prolonged calcium transients were not associated with strong membrane depolarizations but induced cFOS expression. To elucidate the impact of PregS-activation of TRPM3 on retinal circuits we took two sets of physiological measurements. First, PregS induced a robust increase in the frequency but not amplitude of spontaneous postsynaptic currents (PSCs). This increase was absent in the TRPM3 KO mice. Second, PregS induced a small increase in cell participation and duration of retinal waves, but this modulation persisted in TRPM3 KO mice, indicating PregS was acting on wave generating circuits independent of TRPM3 channels. However, baseline frequency of retinal waves was reduced in the TRPM3 KO mice. Together, these results indicate that functional TRPM3 channels impact spontaneous synaptic activity and retinal waves during development.
Significance statement TRPM3, a heat sensitive ion channel found throughout the CNS, also functions as a receptor for the neurosteroid Pregnenolone Sulfate (PregS). In the hippocampus and cerebellum, TRPM3 has been shown to have a functional role as a steroid receptor during development. We show that, in the developing retina, TRPM3 responds to PregS, producing prolonged calcium transients in a subset of retinal ganglion cells (RGCs) and increasing the frequency of spontaneous synaptic current onto RGCs. The PregS-mediated increase in spontaneous synaptic activity was absent in the TRPM3 KO retina. In addition, the absence of TRPM3 signaling reduced wave frequency. Thus, we show that TRPM3 and the endogenous neurosteroid, PregS, function in modulating spontaneous activity in the retina during development.
Footnotes
Authors report no conflict of interest.
CW was supported by NIHF31GM122278, P30EY010572, S10OD023695, JT was supported by NSF Predoctoral Fellowship, FC-H was supported by NIH F31EY028022, CWM was supported by NIH R01EY022369, and MBF was supported by NIH RO1EY019498 and RO1EY013528, and NIH P30EY003176.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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