A Microfluidic Approach to Investigate Changes in Functional Properties of Nociceptive Axons Underlying Inflammatory Pain States

Abstract

The lack of analgesics available for the management of chronic pain is attributed to our limited understanding of the molecular mechanisms responsible for this debilitating condition. Our current understanding of pain mechanisms is primarily based on extrapolation from observations of the dorsal root ganglia (DRG) cell body. However, our knowledge of the functional properties of nociceptive nerve terminals and axons, where the pain response is initiated, is still lacking.
To address this gap in our understanding, I established an in vitro microfluidic (MFC)-based model to investigate functional properties of nociceptive axons in isolation from the cell soma. This platform made it possible to model peripheral sensitisation in response to a combination of inflammatory mediators (IM) including prostaglandin E2 (PGE2), bradykinin, histamine and serotonin. Two types of functional sensitisation were identified in isolated IM-treated nociceptive axons using this model: 1. enhanced magnitude of axonal responses, and 2. increased number of responders were observed in response to chemical stimuli, compared to vehicle-treated groups. We propose this MFC-based in vitro platform as a novel model to study peripheral inflammatory sensitisation, delivering an improved capacity to understand the major axonal molecular players of inflammatory pain conditions.
PGE2 is a widely-known pain mediator, and the most abundantly produced eicosanoid lipid in inflamed tissue. Despite the pivotal role of PGE2 in the genesis of neuropathic and inflammatory pain, the underlying molecular mechanisms are yet unclear. The developed MFC-based model was exploited to decipher axonal mechanisms responsible for changes in nociceptor function induced by PGE2. PGE2 directly depolarised the axonal membrane resulting in persistent neuronal activity, observed even after removal of the PGE2 stimulus. This points towards the basis of clinical ongoing pain patients experience, which persists despite resolution of inflammation. Using pharmacological strategies, we identify Nav1.8 channels and the cAMP/PKA signalling pathway as important mediators of PGE2-induced persistent neuronal activity.

Date of Award	2018
Original language	English
Awarding Institution	King's College London
Supervisor	Peter McNaughton (Supervisor) & Ramin Raouf (Supervisor)