Secondary
mechanical allodynia resulting from a thermal stimulus (52.5 degrees C for 45s) is blocked by intrathecal (i.t.) pretreatment with
calcium-permeable
AMPA/KA receptor antagonists, but not
NMDA receptor antagonists. Spinal sensitization is presumed to underlie thermal stimulus-evoked secondary
mechanical allodynia. We investigated whether this spinal sensitization involves activation and phosphorylation of
calcium-dependent
protein kinases (PKA, PKC and CaMKIIalpha), and examined if the noxious stimulus increases phosphorylated
AMPA GLUR1 (pGLUR1 Ser-845 and pGLUR1 Ser-831). Secondary
mechanical allodynia after thermal stimulation was not altered by i.t. pretreatment with control vehicles (saline or 5%
DMSO). Comparable
allodynia was observed after pretreatment with a selective CaMKIIalpha inhibitor (17 and 34nmol
KN-93). In marked contrast, pretreatment with either a PKA (10nmol
H89) or PKC (30nmol
chelerythrine) inhibitor blocked
allodynia. Western immunoblot analyses supported behavioral findings and revealed a thermal stimulus-evoked increase in spinal phosphorylated PKA and PKC, but not CaMKIIalpha. There was no increase in any of the total
protein kinases. Although thermal stimulation did not change either pGLUR1 Ser-845 or pGLUR1 Ser-831, it was associated with an increase in cytosolic total GLUR1. Pretreatment with a selective
calcium-permeable
AMPA/KA receptor antagonist (5nmol
joro spider toxin), but not an
NMDA receptor antagonist (25nmol d-2-amino-5-phosphonovalerate, AP-5), blocked thermal stimulus-evoked increases in phosphorylated PKA and PKC, in addition to increased cytosolic GLUR1. These findings indicate that spinal sensitization in the thermal stimulus model does not involve CaMKIIalpha activation or
AMPA GLUR1 receptor phosphorylation, and differs from that occurring in NMDAr-dependent
pain states.