A Multidisciplinary Approach to Simultaneously Monitoring Real-Time Neuronal Activity and Pain Behaviors During Optogenetic Stimulation of Brain Neurons in Freely Moving Mice

BACKGROUND: Highlighted by the current opioid epidemic, identifying novel therapies to treat chronic trigeminal neuropathic pain is a critical need. To develop these treatments, it is necessary to have viable targets in the brain to act on. Historically, neural tracing studies have been extremely useful in determining connections between brain areas but do not provide information about the functionality of these connections. Combining optogenetics and behavioral observation allows researchers to determine whether a particular brain area is involved in the regulation of such behavior. The addition of multi-channel electrophysiological recording provides information on real-time neuronal activity in the specific neuronal pathway. METHODS: Male C57/BL/6J mice (8-week-old) underwent either chronic constriction injury of infraorbital nerve (CCI-ION) or a sham surgery and were injected with either channelrhodopsin (ChR2) or a control virus in the hypothalamic A11 nucleus. Two weeks after CCI-ION, they were tested in real-time place preference (RTPP), while neuronal activity in the spinal trigeminal nucleus caudalis (Sp5C) was recorded. RESULTS: Optogenetic excitation of the A11 neurons results in more time spent in the stimulation chamber during RTPP testing. Additionally, stimulation of the A11 results in a greater number of neuronal activity increase in the Sp5C in animals with the injection of AAV carrying ChR2 compared to animals injected with a control virus or that underwent a sham surgery. CONCLUSION: In vivo multi-channel electrophysiological recording, optogenetic stimulation, and behavioral observation can be combined in a mouse model of chronic trigeminal neuropathic pain to validate brain areas involved in the modulation of such pain.