Spinal cord injuries (SCI) result in a devastating loss of function and chronic central
pain syndromes frequently develop in the majority of these patients. The present study uses a rodent spinal hemisection model of SCI in which mechanical and
thermal allodynia develops by 24 days after injury. Post-operative paw withdrawal responses to low threshold and high threshold mechanical stimuli compared to pre-operative responses (4.78, 9.96, and 49.9 mN) were increased and were statistically significant (p<0.05) for both forelimbs and hindlimbs indicating the development of
mechanical allodynia. By contrast, post-operatively, the temperature at which paw withdrawal accompanied by paw lick occurred was significantly decreased (p<0.05), indicating the development of
thermal allodynia. The intrathecal application of either D-AP5, a competitive
NMDA receptor antagonist, or
NBQX-disodium
salt, a competitive non-
NMDA AMPA/
kainate receptor antagonist, alleviated the
mechanical allodynia and lowered the threshold of response for the high threshold mechanical stimuli in a dose-dependent manner, and these decreases were statistically significant (p<0.05). By contrast, neither the D-AP5 nor the
NBQX produced a statistically significant change in the
thermal allodynia behavior in either forelimbs or hindlimbs in the hemisected group. No significant changes in locomotion scores, and thus no sedation, were demonstrated by the hemisected group for the doses tested. These data support the potential efficacy of competitive
excitatory amino acid receptor antagonists in the treatment of chronic central
pain, particularly where input from low threshold mechanical afferents trigger the onset of the painful sensation. Furthermore, these data suggest a role for both
NMDA and non-
NMDA receptors in the development of
plastic changes in the spinal cord that provide the underlying mechanisms for central
neuropathic pain.