Effects of intrathecal BAM22 on noxious stimulus-evoked c-fos expression in the rat spinal dorsal horn

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• 作者：Zeng ; Xueai ; Huang ; Hao ; Hong ; Yanguo
• 关键词：Sensory systems ; Pain modulation ; pharmacology ; BAM22 ; Formalin test ; Noxious heat ; c-Fos-like immunoreactivity ; Opioid receptor ; Sensory neuron-specific receptor
• 刊名：Brain Research
• 出版年：2004
• 出版时间：December 3, 2004
• 年：2004
• 卷：1028
• 期：2
• 页码：170-179
• 全文大小：1.90 M

文摘

The effects of bovine adrenal medulla 22 (BAM22), a cleaved product of proenkephalin A, were investigated on the noxious stimulus-evoked expressions of spinal c-fos-like immunoreactivity (FLI). Heat (51 ??C) applied to the tail evoked FLI predominantly in laminae I???II of the sacral spinal cord. Intrathecal (i.t.) BAM22 at a dose of 7 nmol decreased the expressions of the heat-evoked FLI by 68 % , 64 % and 56 % in laminae I???II, III???IV and V???VI, respectively, and the decrease pattern was comparable to that induced by i.t. morphine (10 ??g). Naloxone (1 mg/kg, i.p.) significantly enhanced the heat-evoked FLI in laminae III???VI, prevented the morphine-induced inhibition, and decreased the potencies of BAM22 in laminae I???II and V???VI by 23???40 % . Higher dose of naloxone (10 mg/kg, i.p.) also partially reduced the BAM22-induced suppression. Following intraplantar injection of formalin (2.5 % ), FLI neurons were preferentially distributed not only in laminae I???II but also in laminae III???IV and V???VI of segments L4???L5. Pretreatment with BAM22 (7 nmol, i.t.) reduced the formalin-evoked FLI neurons by 72 % , 61 % and 58 % , in laminae I???II, III???IV and V???VI, respectively. Naloxone (1 mg/kg. i.p.) enhanced the formalin-evoked expressions of FLI in laminae III???VI and decreased the potencies of BAM22 by 22???38 % in laminae I???II and V???VI. The present study provided evidence at a cellular level showing that opioid and non-opioid effects of BAM22 on nociceptive processing in acute and persistent pain models were associated with modulation of noxious stimulus-evoked activity of the spinal dorsal horn neurons.