Modulation of TRPV1 Function in Sensory Neuropathy

Abstract

This thesis examined how and why TRPV1 function is being modulated in

sensory neuropathy and explored the potential of its rescue in the urinary bladder of STZ-­‐induced diabetic rats. Diabetes induced a rapid decline in TRPV1 function and changes in neurogenically mediated electrically-­‐evoked responses together with a gradual decline in muscarinic function. Diabetic bladder was also deficient in muscarinic and TRPV1 organ bath temperature-­‐induced changes but not in those affecting spontaneous contractile activity. Exposure to a potential neuropathy causative agent, methylglyoxal was studied and its mechanism of action explored through the use of TRPA1 ligands. Methylglyoxal exposure mimicked some of the effects of diabetes on TRPV1, neurogenic electrically evoked responses and muscarinic function. Methylglyoxal effects were seen to be partly through TRPA1 receptor activation but other as yet undefined pathways were also involved. Use of TRPA1 ligands revealed an unexpected complexity of the interaction of the TRPA1 receptor with TRPV1. Finally the potential of reversing the diminished TRPV1 response was examined through the use of three known sensitising agents, bradykinin, NGF and insulin. Bradykinin was the only agent seen to reverse the TRPV1 diminished response back up to to control equivalent levels and through the use of bradykinin selective ligands, it was seen that the dual activation of BK-­‐1 and BK-­‐2 receptor was necessary to rescue the TRPV1 response. The likely mechanism of action of bradykinin was through prostaglandin production as indomethacin blocked TRPV1 rescue. In the acute stage of diabetes, TRPV1 function is downregulated and may be caused by exposure to a neuropathy-­‐causing metabolite such as methylglyoxal. The TRPV1 function still retains plasticity at this acute stage because function could be enhanced back to control levels by bradykinin receptor activation : a potential for early therapeutic intervention.