OPIOID RECEPTORS ON PERIPHERAL SENSORY AXONS

Opioid receptors have been demonstrated by Light microscopic technique s in fine cutaneous nerves in naive animals. The present study extends these findings by showing that 29 and 38% of unmyelinated cutaneous s ensory axons can be immunostained for mu- or delta-opioid receptors re spectively. Local cutaneous injection of DAMGO, a mu-opioid ligand, am eliorates the nociceptive behaviors caused by local cutaneous injectio n of glutamate, a purely nociceptive chemical stimulus showing that th e mu-receptors are functional. By contrast the delta-opioid ligand [2- D-penicillamine, 5-D-penicillamine]enkephalin (DPDPE) had no effect on these behaviors. These findings indicate a wider function for opioid receptors in naive animals than previously envisioned. (C) 1997 Elsevi er Science B.V.