P2 nucleotide receptors in peripheral nerve trunk

There is considerable interest in the possibility that ATP may function as a peripheral pain mediator Most of the studies underlying this idea are ele ctrophysiological recordings from sensory cell bodies, as nociceptive axons with diameters of 1 to 3 mum are not accessible by intracellular electroph ysiological methods. However, the most important region for conduction of n ociceptive information is thin axons in the peripheral nerve trunk. These n ociceptive axons are in close contact with ensheathing Schwann cells, which also cannot easily be studied in situ by conventional recording techniques . In this review we describe new methods that have been used to study the e ffects of ATP on unmyelinated axons and Schwann cells in intact peripheral nerve preparations. Threshold tracking of compound C fibre potentials and c onfocal calcium imaging revealed that extracellular ATP has rapid excitator y effects on both axons and Schwann cells in peripheral nerve trunk. Thereb y, at least four different ionotropic and metabotropic P2 receptors were se parated by pharmacological profiles. These receptors (P2X(2/3) on unmyelina ted axons; P2Y(1), P2Y(2), and P2X(7) on Schwann cells) would allow for rap id interactions between axons and Schwann cells. it is suggested that purin ergic signalling in peripheral nerve trunk contributes not only to pain tra nsduction but might be involved in mechanosensitivity, inflammation, prolif eration, and demyelination. Drug Dev. Res. 52:83-88, 2001. (C) 2001 Wiley-L iss, Inc.