NMDA RECEPTOR INVOLVEMENT IN NEUROPLASTIC CHANGES INDUCED BY NEONATAL
CAPSAICIN TREATMENT IN TRIGEMINAL SUBNUCLEUS CAUDALIS (MEDULLARY DORSAL HORN)
NOCICEPTIVE NEURONS OF ADULT RATS.
CHEN YU CHIANG, JAMES W. HU, AND BARRY J. SESSLE.
Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6,
Canada.
APStracts 4:167N, 1997.
ABSTRACT
This study examined whether (1) the neonatal loss of C-fiber afferents results
in neuroplastic changes in the mechanoreceptive field (RF) properties and
spontaneous activity of nociceptive neurons in trigeminal subnucleus caudalis
(medullary dorsal horn) of adult rats, and (2) N-methyl-D-aspartic acid (NMDA)
receptor mechanisms are involved in these neuroplastic changes. Compared to
vehicle-treated (i.e., control, CON) rats, capsaicin-treated (CAP) rats showed
a marked increase in neuronal spontaneous activity and RF size per se, but
these neuroplastic changes could be significantly reduced by MK-801 (1 mg/kg,
i.v.), a non-competitive NMDA receptor antagonist; RF size and spontaneous
activity remained unchanged in CON rats following MK-801 and in CAP rats
following vehicle (saline, i.v.). Administration of 7-chlorokynurenic acid (5
_g/10 _l, i.t.), an antagonist of strychnine-insensitive glycine binding sites
on the NMDA receptor, also significantly reduced neuronal RF size and
spontaneous activity in CAP rats, but not in CON rats. These data provide
evidence that C-fiber afferents play a role in shaping the properties of
nociceptive neurons and that the neuroplastic changes involve NMDA receptor
mechanisms.
Received 16 October 1996; accepted in final form 24 July 1997.
APS Manuscript Number J814-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997