Journal of Neuroscience, Vol 15, 8031-8038, Copyright © 1995 by Society for Neuroscience
Opioid and adenosine peripheral antinociception are subject to tolerance and withdrawal
KO Aley, PG Green and JD Levine
Department of Anatomy, University of California, San Francisco 94143, USA.
The selective mu-opioid agonist, D-Ala2,N-Me-Phe4,Gly5-ol-enkephalin
(DAMGO), or the selective A1-adenosine agonist N6-cyclopentyladenosine
(CPA), when coinjected intradermally with prostaglandin E2 (PGE2), dose-
dependently inhibited PGE2-induced mechanical hyperalgesia in the rat
hindpaw, as determined by the Randall-Selitto paw-withdrawal test. Repeated
(hourly x 3) intradermal injections of DAMGO or CPA produced tolerance to
the antinociceptive effect of a fourth injection 1 hr later. Furthermore,
repeated (hourly x 3) intradermal injections of DAMGO produced
cross-tolerance to the antinociceptive effect of CPA, and repeated (hourly
x 3) intradermal injection of CPA produced cross- tolerance to the
antinociceptive effect of DAMGO. The demonstration of the bidirectional
cross-tolerance between the peripheral antinociceptive effects of DAMGO and
CPA supports the hypothesis that both these agents produced antinociception
by acting on the same cell, presumably the primary afferent nociceptor, and
that the development of tolerance involves changes downstream to activation
of mu-opioid and A1- adenosine receptors. The opioid antagonist naloxone,
which had no effect on paw-withdrawal threshold in normal paws, produced
withdrawal threshold in normal paws, produced withdrawal hyperalgesia in
DAMGO- tolerant paws. Furthermore, naloxone elicited a cross-withdrawal
hyperalgesia response in CPA-tolerant paws. Similarly, the A1-adenosine
antagonist 1,3-dipropyl-8-(2-amino-4- chlorophenyl)-xanthine (PACPX), which
had no effect on paw-withdrawal threshold in normal paws, elicited a
withdrawal hyperalgesia response in CPA-tolerant paws and cross-withdrawal
hyperalgesia responses in DAMGO-tolerant paws. These cross-dependence and
cross-withdrawal responses suggest that the development of dependence to
mu-opioid and A1-adenosine agonists involves changes in the same second
messenger system downstream to both mu-opioid and A1-adenosine receptor
activation.