Abstract
Fluorescence imaging devices have been indispensable in elucidating the workings of the brain in living animals, including unrestrained, active ones. Various devices are available, each with their own strengths and weaknesses in terms of many factors. We have developed CMOS-based needle-type imaging devices that are small and lightweight enough to be doubly implanted in freely moving mice. The design also allowed angled implantations to avoid critical areas. We demonstrated the utility of the devices by using them on GCaMP6 mice in a formalin test experiment. Simultaneous implantations to the capsular-lateral central amygdala (CeLC) and dorsal raphe nucleus (DRN) were proven to be safe and did not hinder the execution of the study. Analysis of the collected calcium signaling data, supported by behavior data, showed increased activity in both regions as a result of pain stimulation. Thus, we have successfully demonstrated the various advantages of the device in its application in the pain experiment.
Highlights
Fluorescence imaging brain implants have been indispensable to the field of neurobiology
The complementary metal-oxide semiconductor (CMOS) imaging chips, designed by our laboratory, were cleaned by submersion in acetone (Fujifilm Wako), twice, and in isopropanol (Fujifilm Wako) for 5 min each. They were each mounted on a polyimide, gold-circuitprinted flexible printed-circuit substrate (FPC) substrate (Taiyo Industrial) taped on a glass slide using a thin layer of epoxy resin [low viscosity epoxy resin Z-1 (N), CraftResin]
No notable complications on the welfare of the experimental mice were encountered during the duration of the study
Summary
Fluorescence imaging brain implants have been indispensable to the field of neurobiology. Their use has given much insight of the inner workings of the brain in vivo (Grienberger and Konnerth, 2012). There are a number of types of such devices than can be safely used in living, active animals without compromising the process of a study. These animals are genetically encoded to express fluorescent calcium indicators that signal neuron firing, in a process referred to as calcium signaling. Though all types have their advantages, they have limitations that must be acknowledged when considering their use. Selecting the appropriate tool can mean the success or failure of doing a study
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