ホルマリン誘発侵害刺激に対する中枢神経系の反応：pCREB免疫陽性細胞数の経時的変化

It is widely accepted that females are more sensitive to nociceptive stimuli than males. In the previous study, we showed that there were sex differences in the response of CNS to formalin-induced nociceptive stimuli by checking the expression of pCREB as a marker of neural activity in the accumbens nucleus (ACB) and the bed nucleus of the stria terminalis including the lateral (BSTL) and the medial subdivisions (BSTM). In the ACB and the BSTL, the number of cells expressing pCREB in female rats was increased 5 min after formalin injection but not in male rats. In the present study, we examined time-course changes in the number of cells expressing pCREB in adult male rats and female rats at proestrus. Rats were injected with saline or 2% formalin into the planter surface of the right hindpaw, and they were killed 10, 30, and 120 min after the injection. Their brains were served to immunocytochemistry and the number of cells expressing pCREB in the ACB, BSTL, and BSTM was counted. In all areas examined, the number of cells expressing pCREB in formalin-injected rats was not different from that in saline-injected rats at any time point, irrespective of the sex. It is suggested 1) that the ACB and BSTL are activated only during acute phase and not during later phases of behavioral responses to nociceptive stimuli in female rats and 2) that the ACB and BSTL are refractory to nociceptive stimuli through all phases in male rats. [Jpn J Physiol 55 Suppl:S168 (2005)]