Visualization of activity-regulated BDNF expression in the living mouse brain using non-invasive near-infrared bioluminescence imaging

Mamoru Fukuchi,Nami Hagiwara,Ryohei Saito,Shojiro Maki,Hironori Izumi,Satoru Mitazaki,Hisashi Mori,Yumena Nakajima

doi:10.1186/s13041-020-00665-7

Abstract

Altered levels of brain-derived neurotrophic factor (BDNF) have been reported in neurologically diseased human brains. Therefore, it is important to understand how the expression of BDNF is controlled under pathophysiological as well as physiological conditions. Here, we report a method to visualize changes in BDNF expression in the living mouse brain using bioluminescence imaging (BLI). We previously generated a novel transgenic mouse strain, Bdnf-Luciferase (Luc), to monitor changes in Bdnf expression; however, it was difficult to detect brain-derived signals in the strain using BLI with d-luciferin, probably because of incomplete substrate distribution and light penetration. We demonstrate that TokeOni, which uniformly distributes throughout the whole mouse body after systematic injection and produces a near-infrared bioluminescence light, was suitable for detecting signals from the brain of the Bdnf-Luc mouse. We clearly detected brain-derived bioluminescence signals that crossed the skin and skull after intraperitoneal injection of TokeOni. However, repeated BLI using TokeOni should be limited, because repeated injection of TokeOni on the same day reduced the bioluminescence signal, presumably by product inhibition. We successfully visualized kainic acid-induced Bdnf expression in the hippocampus and sensory stimulation-induced Bdnf expression in the visual cortex. Taken together, non-invasive near-infrared BLI using Bdnf-Luc mice with TokeOni allowed us to evaluate alterations in BDNF levels in the living mouse brain. This will enable better understanding of the involvement of BDNF expression in the pathogenesis and pathophysiology of neurological diseases.

Highlights

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, is fundamentally involved in a variety of functions in the developing and mature brain [1]
To compare the detection of bioluminescence signals produced by each substrate, we administered each substrate to Bdnf-Luc mice under inhalation anesthesia and measured bioluminescence signals (Fig. 1b)
Endogenous BDNF is highly abundant in the brain; strong bioluminescence signals were expected from the brain

Summary

Introduction

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, is fundamentally involved in a variety of functions in the developing and mature brain [1]. We previously generated a novel transgenic mouse strain termed BdnfLuciferase (Luc) to monitor changes in Bdnf expression in vivo as well as in vitro, using a firefly Luc as an imaging probe [15, 16]. Because levels of Luc can be evaluated by measuring bioluminescence produced by reaction with a substrate, such as D-luciferin, the most popular and commonly used substrate for in vitro and in vivo BLI, changes in Bdnf expression can be evaluated by detecting bioluminescence signals. We previously detected signals from brain regions after the systematic injection of TokeOni into Bdnf-Luc mice; the signals were detected by an invasive method (we removed the skin to expose the skull before in vivo imaging) [16], and it is still unclear whether changes in Bdnf expression under physiological conditions can be visualized by noninvasive in vivo BLI

Methods

Results

Conclusion