Rats can acquire conditional fear of faint light leaking through the acrylic resin used to mount fiber optic cannulas

Abstract

Rodents are exquisitely sensitive to light and optogenetic behavioral experiments routinely introduce light-delivery materials into experimental situations, which raises the possibility that light could leak and influence behavioral performance. We examined whether rats respond to a faint diffusion of light, termed caplight, which emanated through the translucent dental acrylic resin used to affix deep-brain optical cannulas in place. Although rats did not display significant changes in locomotion or rearing to caplight in a darkened open field, they did acquire conditional fear via caplight-footshock pairings. These findings highlight the potential confounding influence of extraneous light emanating from light-delivery materials during optogenetic analyses.

Carbon-mixed dental cement for fixing fiber optic ferrules prevents visually triggered locomotive enhancement in mice upon optogenetic stimulation

“…Unspecific behavioral effects, i.e. effects which can be observed even in the absence of opsins, induced by light leakage in optogenetic experimental setups have been often underestimated and there have been only a few studies which directly addressed this issue ( Guo et al., 2014 ; Eckmier et al., 2016 ). Nonetheless, several authors suggested various methods to minimize light leakage in order to prevent unintended potential behavioral effects of light leakage.…”

“…There have been, however, only a few studies which addressed this issue in their behavioral experiments. Studies using rats showed that rats can acquire conditional fear by pairing footshock with faint light leakage from the dental cement, termed “caplight” ( Eckmier et al., 2016 ), although locomotion was not or only marginally influenced by light leakage ( Guo et al., 2014 ; Eckmier et al., 2016 ). In another study, Horibe and colleagues directly exposed mother mice and pups to blue LED without implementing optogenetics and saw no influence on maternal care or pups’ brain function development, except that retinas of mother mice were damaged ( Horibe et al., 2017 ).…”

“…In another study, Horibe and colleagues directly exposed mother mice and pups to blue LED without implementing optogenetics and saw no influence on maternal care or pups’ brain function development, except that retinas of mother mice were damaged ( Horibe et al., 2017 ). Importantly, those studies conducted in the darkness, which corresponds to the active phase of nocturnal animals such as mice, also reported no apparent influences on mice locomotive behaviors ( Eckmier et al., 2016 ). In contrast to these previous reports, we observed that caplight did influence mouse locomotive behaviors, and replacing conventional dental cement with the one mixed with carbon abolishes such confounding influences from the caplight.…”

And Then There Was Light: Perspectives of Optogenetics for Deep Brain Stimulation and Neuromodulation

“…Whether electric, microfluidic or optical, any application must take into account the diffusion and depth of penetration. Although only mentioned in animals, light leaks might influence an implant (Eckmier et al, 2016 ), considering that near infra-red spectroscopy is a technique based on light transmission through scalp, skull and brain (Benaron et al, 2000 ). Optic implants are new and require a specific encapsulation still lacking chronic evaluation (Rossi et al, 2015 ).…”

Scalable and modular wireless-network infrastructure for large-scale behavioural neuroscience

“…This presence inherently alters the observed system. This 'observer effect' is both widespread and often underappreciated in behavioural neuroscience [1][2][3][4][5] . Furthermore, coordinating experiments with large numbers of experimental subjects with precise control is exceptionally challenging, thus making reproducible and repeatable high-throughput in vivo experiments difficult.…”