Abstract
Purpose :
Zebrafish regenerate their retinas following damage, resulting in restoration of function (McGinn et al., 2018 J Neurosci). Behavioral measures of visual function are restored more rapidly following a lesion that destroys inner retinal neurons and spares photoreceptors (PR) and glia (selective lesion; SL), than following a lesion that destroys all retinal neurons and spares only glia (extensive lesion; EL) (Sherpa et al., 2014 Dev Neurobiol). Here we evaluate recovery of visual function through characterization of the electroretinogram (ERG) over time following each type of retinal damage.
Methods :
Right eyes of zebrafish (6mo–1.5yrs, both sexes) were lesioned with intravitreal injection of 10µM (EL) or 2µM (SL) ouabain, with left eyes as unlesioned controls. Function of retinal circuitry was analyzed at selected recovery times using ERG recordings in live zebrafish (n=3-13/timepoint). Eyes were then harvested for histological analyses of PKCα+ ON bipolar cells (BP) and parvalbumin (PARV)+ amacrine cell (AC) processes within the deep sublaminae of the inner plexiform layer (IPL), which receive input from ON BPs.
Results :
A qualitative study of ERG waveforms focused on the “post-photoreceptor response” (PPR) to assess BP function and PR-BP connectivity, which in a healthy retina is dominated by the b-wave or ON BP response. There was a rapid reduction in amplitude of the PPR after both EL and SL, though the reduction was greater for EL. During early stages of functional recovery after each lesion type, we observed a deviated waveform, consistent with emergence of a d-wave (OFF BP response) elicited at light termination. At later time points (EL: 45 days post-injury (DPI), SL: 21DPI), the PPR amplitude increased and peaked sooner after the light stimulus compared to earlier DPIs, suggesting emergence of the b-wave. Later sampling times (EL: 60-90DPI, SL: 80DPI) continued to show PPRs with reduced amplitude and deviated waveforms, suggesting physiological abnormalities may persist. PKCα+ ON BP terminals and PARV+ AC processes became more reliably positioned within the deep sublaminae of the INL over recovery time after each lesion type.
Conclusions :
ERG waveform topography suggests that PR-OFF BP component/connectivity may functionally recover and mature earlier during regeneration compared to the PR-ON BP component. Analysis with cell-specific markers suggests the gradual restoration of ON BP circuitry during regeneration.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.