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Abstract: In the present study, we characterized differential expressions of phosphorylated Ca2+/calmodulin-dependent protein kinase IIα (pCaMKIIα) and phosphorylated extracellular signal-regulated protein (pERK) in the mouse hippocampus induced by various nociceptive stimuli. In an immunoblot study, s.c. injection of formalin and intrathecal (i.t.) injections of glutamate, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1 β) significantly increased pCaMKIIα expression in the hippocampus, but i.p. injections of acetic acid did not. pERK1/2 expression was also increased by i.t. injection of glutamate, TNF-α, and IL-1β but not by s.c. injections of formalin or i.p. injections of acetic acid. In an immunohistochemical study, we found that increased pCaMKIIα and pERK expressions were mainly located at CA3 or the dentate gyrus of the hippocampus. In a behavioral study, we assessed the effects of PD98059 (a MEK 1/2 inhibitor) and KN-93 (a CaMKII inhibitor) following i.c.v. administration on the nociceptive behaviors induced by i.t. injections of glutamate, pro-inflammatory cytokines (TNF-α or IL-1β), and i.p. injections of acetic acid. PD98059 as well as KN-93 significantly attenuated the nociceptive behavior induced by glutamate, pro-inflammatory cytokines, and acetic acid. Our results suggest that (1) pERKα and pCaMK-II located in the hippocampus are important regulators during the nociceptive processes induced by s.c. formalin, i.t. glutamate, i.t. pro-inflammatory cytokines, and i.p. acetic acid injection, respectively, and (2) the alteration of pERK and pCaMKIIα in nociceptive processing induced by formalin, glutamate, pro-inflammatory cytokines and acetic acid was modulated in a different manner. [Copyright &y& Elsevier]

We examined proopiomelanocortin (POMC) mRNA and beta-endorphin expression in the hypothalamus of mice after various nociceptive stimuli. The time-course study (10 min, 30 min, 1 h, 2 h, and 10 h) showed that the POMC mRNA level significantly increases from 1 h after s.c. formalin injection and returns to the control level at 10 h. Intrathecal (i.t.) substance P (SP) injection also increases the hypothalamic POMC mRNA level from 1 h to 10 h. However, i.t. glutamate injection did not affect the hypothalamic POMC gene expression at all time points. We found that the POMC mRNA after s.c. formalin injection was located in the arcuate nucleus of the hypothalamus. In the same manner, beta-endorphin immunoreactivity was also increased in the hypothalamic arcuate nucleus. The expression of phosphorylated extracellular signal-regulated protein kinase 1/2 (pERK1/2), phosphorylated calcium/calmodulin-dependent protein kinase-IIalpha (pCaMK-IIalpha) protein and phosphorylated IkappaB (pIkappaB) protein was increased by s.c. formalin injection at various time points. We also found that increased pERK1/2, pCaMKIIalpha and pIkappaB protein after s.c. formalin injection was mainly located in the arcuate nucleus of hypothalamus in which cells containing beta-endorphin after s.c. formalin injection also express pERK1/2, pCaMK-IIalpha and pIkappaB immunoreactivity. In addition, formalin-induced POMC mRNA expression was significantly reduced by 10 min, pretreatment with i.c.v. PD98059 (mitogen-activated protein kinase (MAPK) pathways inhibitor; 6.6 mug) and KN93 (pCaMK-II inhibitor; 20 mug). In conclusion, POMC mRNA expression in the arcuate nucleus of the hypothalamus was increased by inflammatory pain stimuli, in which pERK1/2, pCaMK-IIalpha and NFkappaB may play an important role in the expression of the hypothalamic POMC gene and beta-endorphin expression.