Burnett A, Gebhart G F
Department of Pharmacology, College of Medicine, University of Iowa, Iowa City 52242.
Brain Res. 1991 Apr 19;546(2):271-81. doi: 10.1016/0006-8993(91)91491-i.
The present study examined the role of the A5 catecholamine-containing cell group in descending modulation of the nociceptive tail-flick (TF) reflex and regulation of blood pressure and heart rate in rats lightly anesthetized with pentobarbital. Systematic mapping studies throughout the A5 cell group, rostral to caudal, showed that electrical stimulation in and near the A5 cell group at intensities as low as 25 microA was sufficient to inhibit the tail-flick (TF) reflex without producing a significant pressor response. Microinjections of glutamate into the same sites to selectively activate cell bodies also produced inhibition of the TF reflex and were accompanied by significant decreases in blood pressure (mean, -23 +/- 4.7 mmHg, n = 21) and non-significant decreases in heart rate (-7.6 +/- 11 bpm). Intrathecal administration of the receptor antagonists phentolamine, yohimbine, prazosin, methysergide, naloxone or atropine revealed that descending inhibition from the A5 cell group produced by electrical stimulation is mediated in part by spinal opioid and alpha-adrenoceptors. Increases in stimulation thresholds in the A5 cell group for inhibition of the TF reflex of 28.3 and 24.1% were produced by intrathecal pretreatment with phentolamine and naloxone, respectively. None of the other receptor antagonists produced significant increases in stimulation thresholds in the A5 cell group for inhibition of the TF reflex. Resting blood pressure and heart rate were not affected by the receptor antagonists.
本研究考察了含A5儿茶酚胺的细胞群在戊巴比妥轻度麻醉的大鼠中对伤害性甩尾（TF）反射的下行调制以及血压和心率调节中的作用。对整个A5细胞群从吻侧到尾侧进行系统的定位研究表明，在A5细胞群及其附近以低至25微安的强度进行电刺激足以抑制甩尾（TF）反射，而不会产生明显的升压反应。向相同部位微量注射谷氨酸以选择性激活细胞体也会抑制TF反射，并伴有血压显著下降（平均为-23±4.7 mmHg，n = 21）和心率无显著下降（-7.6±11次/分钟）。鞘内注射受体拮抗剂酚妥拉明、育亨宾、哌唑嗪、麦角新碱、纳洛酮或阿托品表明，电刺激产生的来自A5细胞群的下行抑制部分由脊髓阿片受体和α-肾上腺素能受体介导。鞘内分别用酚妥拉明和纳洛酮预处理后，A5细胞群抑制TF反射的刺激阈值分别提高了28.3%和24.1%。其他受体拮抗剂均未使A5细胞群抑制TF反射的刺激阈值显著升高。静息血压和心率不受受体拮抗剂的影响。
