Journal of Neuroscience, Vol 11, 3111-3123, Copyright © 1991 by Society for Neuroscience
Behavioral sensitization to kainic acid and quisqualic acid in mice: comparison to NMDA and substance P responses
XF Sun and AA Larson
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
Substance P (SP) and the excitatory amino acid (EAA) agonists NMDA, kainic
acid (KA), or quisqualic acid (Quis) each produce a transient, caudally
directed biting and scratching response (CBS) in mice after their
intrathecal injection. We have previously shown that repeated injections of
SP result in a decrease in the intensity of CBS, or desensitization. The
goals of the present study were (1) to determine whether desensitization
also develops to the CBS behavior produced by EAAs in the spinal cord, (2)
to characterize the role of interneurons in desensitization, and (3) to
examine possible interactions between EAAs and SP. While injection of NMDA
at 2 min intervals resulted in desensitization to its CBS behavioral
effect, behavioral responses to repeated injections of KA or Quis increased
in intensity, exhibiting sensitization. The NMDA antagonist
DL-2-amino-5-phosphonovaleric acid failed to alter sensitization to either
KA or Quis but inhibited behaviors produced by SP and NMDA, suggesting an
NMDA-mediated component in SP-induced behavior. Concanavalin A, which is
reported to block desensitization to the electrophysiologic effect of Quis,
blocked sensitization to the behavioral effects of both Quis and KA.
Strychnine, bicuculline, and 5-aminovaleric acid each inhibited
desensitization to SP and NMDA, supporting the notion of recruitment of
inhibitory transmitters in the attenuation of NMDA and SP activity.
Pretreatment with capsaicin selectively inhibited the development of
behavioral sensitization to KA, suggesting an involvement of small-
diameter C-fibers in the enhancement of responsivity to KA. Consistent with
this, pretreatment with SP selectively potentiated the CBS response to KA.
The potentiation of KA effects by SP and dependence of KA behavioral
sensitization on C-fiber activity suggest a possible mechanism by which
EAAs and SP may be involved in the mediation of pain.