Spinal distribution of c-Fos activated neurons expressing enkephalin in acute and chronic pain models

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• 作者：Mehdi Hossaini ; Liron S. Duraku ; Somesh K. Kohli ; Joost L.M. Jongen ; Jan C. Holstege
• 关键词：Pain ; Enkephalin ; Inflammation ; Neuropathic ; Fos ; Spinal
• 刊名：Brain Research
• 出版年：16 January, 2014
• 年：2014
• 卷：1543
• 期：Complete
• 页码：83-92
• 全文大小：6372 K

文摘

The endogenous opioid enkephalin is known to inhibit spinal nociceptive transmission. Here we investigated activation of spinal enkephalinergic neurons by determining the proportions of c-Fos expressing (activated) spinal neurons that were enkephalinergic after different acute and chronic peripheral nociceptive stimuli. The number of c-Fos-activated neurons in the dorsal horn was increased after hind paw injection of capsaicin, formalin or complete Freund's adjuvant (CFA, 1.5 hrs - 4 days). The numbers of these neurons that were enkephalinergic increased after paraformaldehyde, and at 20 hrs, but not 1.5 hrs or 4 days post-CFA as compared to saline. In the spared nerve injury (SNI) model of neuropathic pain, c-Fos expression was increased acutely (2 hrs) and chronically (2 weeks), and a greater number of these were enkephalinergic in the nerve-injured animals acutely compared to controls (sham-SNI). Combining all acute (=2 hrs) versus chronic (鈮?0 hrs) treatment groups, there was a significant decrease in the percentage of activated neurons that were enkephalinergic in superficial layers, but a significant increase in the deeper layers of the dorsal horn in the chronic treatment group. It is concluded that the overall percentage of c-Fos activated neurons that contained enkephalin was not significantly different between acute and chronic pain phases. However, the shift in localization of these neurons within the spinal dorsal horn indicates a noxious stimulus directed activation pattern.