Foong F W, Terman G, Duggan A W
Eur J Pharmacol. 1985 Oct 22;116(3):239-48. doi: 10.1016/0014-2999(85)90158-x.
In barbiturate anaesthetized cats, electrical stimulation in the periaqueductal grey (PAG) selectively inhibited the excitation of multireceptive dorsal horn neurons by noxious heating of the skin or by electrical stimulation of unmyelinated primary afferents. Intravenous methysergide (0.2-1.0 mg/kg) had opposing effects on uninhibited responses, increasing excitation by noxious heat but reducing responses to C fibre stimulation. Evidence was obtained that the increases to noxious heat resulted from increased firing of peripheral nociceptors secondary to decreased cutaneous blood flow. Intravenous methysergide reduced inhibition from PAG stimulation. When administered electrophoretically from micropipettes however, methysergide did not reduce such inhibition. The mechanism whereby systemic methysergide reduces PAG spinal inhibition is unknown and cannot necessarily be related to a blockade of spinally released 5-hydroxytryptamine.
在巴比妥类麻醉的猫中，中脑导水管周围灰质（PAG）的电刺激选择性地抑制了皮肤有害热刺激或无髓初级传入纤维电刺激对多感受性背角神经元的兴奋作用。静脉注射麦角新碱（0.2 - 1.0毫克/千克）对未受抑制的反应有相反的作用，增加有害热刺激引起的兴奋，但减少对C纤维刺激的反应。有证据表明，有害热刺激引起的反应增加是由于皮肤血流量减少继发外周伤害感受器放电增加所致。静脉注射麦角新碱可减少PAG刺激引起的抑制作用。然而，当通过微量移液器进行电泳给药时，麦角新碱并不会减少这种抑制作用。全身应用麦角新碱减少PAG对脊髓抑制作用的机制尚不清楚，且不一定与脊髓释放的5 - 羟色胺的阻断有关。
