Peripheral targeting of the trigeminal ganglion via the infraorbital foramen as a therapeutic strategy

A unique interventional approach for modulating sensory signaling involves targeting neurons in the sensory ganglia through use of pharmacological or gene therapies. This has previously been accomplished in the trigeminal system via stereotactic ganglionic microinjections. However, this procedure can be time consuming and requires expensive stereotactic equipment. The current paper describes a percutaneous approach for injecting the trigeminal ganglion with an electrical-stimulation needle inserted through the infraorbital foramen, infraorbital canal and foramen rotundum. The needle tip was positioned in the ganglion by eliciting a twitch in the ipsilateral masseter following electrical stimulation. The technique was imaged using computerized tomography and methylene blue dye to verify the site of the injection. We validated this technique by reproducing the results from our prior study that involved injection of resiniferatoxin (RTX) into the trigeminal ganglion using the stereotactic approach. Both techniques for intraganglionic injection of RTX produced a specific deletion of C-fiber neurons, as demonstrated by inhibition of neurogenic-induced plasma extravasation and behavioral assays. Thus, we propose a novel and simple technique for studying mechanisms of peripheral sensory modulation of orofacial pain via direct application of drugs, tracers or viral vectors around trigeminal sensory neuronal cell bodies. This technique minimizes trauma to brain structures that may have an impact on pain perception.