The Journal of Neuroscience, July 1, 1999, 19(13):5482-5492
Chronic Pain is Associated with Increased TrkA Immunoreactivity
in Spinoreticular Neurons
Sophie
Pezet1,
Brigitte
Onténiente1,
Gaël
Grannec1, and
Bernard
Calvino1, 2
1 Institut National de la Santé et de la
Recherche Médicale U421, Institut Mondor de Médecine
Moléculaire, Faculté de Médecine, F-94010
Créteil Cedex, France, and 2 Faculté des
Sciences, Université de Paris XII, F-94010 Créteil Cedex,
France
Repetitive noxious stimulation leads to permanent adaptive changes
of central pathways involved in the genesis and integration of
nociception. Several classes of neurotrophic factors that affect brain
plasticity are also involved in the regulation of sensory functions in
adulthood. To investigate a putative role of nerve growth factor (NGF)
in central plasticity linked to chronic pain, modifications in
immunoreactivity (IR) for the high-affinity NGF receptor, TrkA, were
studied at spinal levels in a rat model of inflammatory chronic pain,
adjuvant-induced arthritis (AIA). We report a specific increase in the
number of TrkA-IR profiles in laminae V-VI at lumbar levels L3 and L4
in arthritic rats. Tract tracing using FluoroGold injections in the
ventrobasal complex of the thalamus and in the brainstem showed that
these increased TrkA-IR profiles are spinoreticular neurons. Dual
labeling with calcitonin gene-related peptide or substance P showed
that TrkA-IR neurons were mainly located in projection fields of small-
to medium-sized primary afferent fibers, which convey nociceptive inputs. These results suggest that TrkA-containing neurons of the
spinal dorsal horn participate in the first central relay of
transmission of nociceptive information to supraspinal centers. Enhanced numbers of TrkA-IR neurons during AIA strongly support the
hypothesis of a participation of NGF in adaptive mechanisms of central
nociceptive pathways observed in chronic pain states.
Key words:
nerve growth factor; NGF; TrkA; adjuvant-induced
arthritis; substance P; CGRP; spinal cord; rat
Copyright © 1999 Society for Neuroscience 0270-6474/99/19135482-11$05.00/0