Title : Optogenetic neuromodulation of allodynia and hyperalgesia pain responses in rodent model
Abstract:
Introduction: While pain is the body’s normal physiological response to tissue damage, it is a significant contributor to worldwide disability as well as physical and psychological distress. These deleterious effects are typically dictated by the duration and intensity of pain. Current methods of managing acute and chronic pain largely comprise the utility of controlled opioid medications, which have obvious adverse effects. Chronic pain management may involve alternative techniques such as electronic stimulation and non-narcotic pharmacology such as the use of anticonvulsant drugs for neuropathic pain. However, pain relief from these atypical methods may be variable depending on the patient. Pain is a complex process – involving numerous neurological structures that are integrated into a stepwise fashion from peripheral sensation to central processing. At the level of the spine, the dorsal horn is responsible for the integration of multiple ascending afferent fibers relaying nociceptive pain from their specific dermatomal nerve roots. As such, this location in the pathway of sensation provides a unique opportunity to provide analgesia through alternative methods without the aforementioned deleterious effects associated with current methods.
Methods: Previously, we successfully demonstrated that through the direct stimulation of inhibitory neurons within the Anterior Cingulate Cortex and Dorsal Root Ganglion expressing channelrhodopsin-2, experimental mice could experience significant pain reduction. In this experiment, wild-type mice were used as controls while two experimental groups existed. In one group, a highly sensitive optogenetic actuator Multi-Characteristic Opsin was specifically expressed in inhibitory (GABAergic) neurons via a Glutamic Acid Decarboxylase (GAD) promoter within the epidural space. Another experimental group (HOU) also used a highly sensitive opsin, but this protein was expressed in stimulatory (Glutamatergic) neurons and is expressed via a tryptophan hydroxylase 2 (TPH2) promoter. Using an injection of functionalized gold nanorods (fGNRs) with HOU and MCO-encoding DNA, we were able to induce the expression of HOU and MCO in target areas of the nervous system by illuminating them with concentrated bursts of attuned light.
Our novel Bluetooth Optogenetic Pain Modulator device provided optogenetic stimulation with red (630 nm) light at various frequencies and intensities. We used a meshed cage with the Von Frey Assay to measure the pain responses of the Mice. Allodynia was measured via perpendicular monofilament contact, whereas hyperalgesia was modeled by pinprick contact to the hind paw. Reflexive pain responses (Von Frey Assays) were measured over time with a complex pain scoring system that included hind paw retraction, hind paw licking, and spatial preferences.
Results: Optogenetic stimulation of the pain pathways within the epidural space led to a significant reduction in pain in both experimental groups, MCO and HOU groups. In the initial phase, there were significant reductions in pain in both experimental groups not seen in the control groups. Finally, the MCO group experienced more excellent sustenance of pain relief throughout the experiment, while the HOU group demonstrated significant spikes at 30 and 50 minutes. Altogether, these data suggest that in the MCO and HOU groups, optogenetic stimulation within the epidural space provides effective pain relief when compared to controls.
Conclusion: These findings support optogenetic modulation within the epidural space as a potential mechanism of pain reduction.
What will the audience learn from your presentation?
- The pathways involved in pain sensation and their ability to undergo neuromodulation
- Gene delivery of opsin proteins via functional gold nanorods
- The Von Frey assay and its utility for pain responses of allodynia and hyperalgesia in a model for neuropathic pain
