Effect of optogenetic activation of superior salivatory nucleus on the choroidal thickness

Abstract

Purpose : The choroid is known to receive abundant innervation from the central nervous system (Reiner A, et al., Prog Retin Eye Res. 2018). Retrograde histological data have shown that parasympathetic input to the choroid traces back to the superior salivatory nucleus (SSN) (Li C, et al., Front Neuroanat. 2015). In the present study, we aimed to explore the effect of optogenetic activation of SSN cholinergic neurons on the choroidal thickness.

Methods : Cre-inducible adeno-associated virus expressing channelrhodopsin-2 fused with mCherry was injected into the left SSN of ChAT-IRES-Cre mice (ChAT-Cre, which express Cre recombinase in cholinergic neurons) (n = 4). Fiber optics were implanted above the left SSN one week after virus injection. Choroidal thickness was measured using Spectral Domain (SD)-OCT before and after each minute of LED illumination (470 nm wavelength, 10 Hz frequency). The stimulation lasted for 10 minutes. After 10 minutes of LED illumination, mice were immediately euthanized. Eye samples were taken, fixed, and then embedded in paraffin. Sagittal eye sections were HE stained to observe the structure of the choroid.

Results : Two minutes after the start of LED illumination, expansion of several blood-vessel-like areas was observed under live monitoring of the SD-OCT choroid image of the left eye (ipsilateral to optogenetic activation), which persisted until the end of illumination. Quantitative analysis of SD-OCT images revealed a significant increase in choroidal thickness in the left eye (before vs. after illumination: 28.4 ± 0.75 μm vs. 30.5 ± 1.43 μm, two-tailed Student’s t-test, P = 0.043). In HE stained sagittal eye sections, the choroid of the left eye (ipsilateral to optogenetic activation) was significantly thicker than the right eye (contralateral to optogenetic activation). The expansion was observed in the entire choroidal layers including the choriocapillaris.

Conclusions : After optogenetic activation of the unilateral SSN, thickening of the choroid in the ipsilateral eye was observed.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.