Interactions between cutaneous afferent inputs to a withdrawal reflex in the decerebrated rabbit and their control by descending and segmental systems
Interactions between cutaneous afferent inputs to a withdrawal reflex in the decerebrated rabbit and their control by descending and segmental systems
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DOI：
10.1016/s0306-4522(02)00093-3
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发表时间：
2002-01-01
期刊：
影响因子：
3.3
通讯作者：
Stuart, E
中科院分区：
文献类型：
--
作者：
Clarke, RW;Eves, S;Stuart, E
以往的研究表明，激活足跟的伤害性传入引起一种脊髓上机制，该机制受肾上腺素能下行抑制的调节，增强了内侧腓肠肌(MG)运动神经元的戒断反射。为了验证这一观点，我们在去大脑兔身上研究了1赫兹电刺激腓肠神经Aβ、Aβ和C纤维轴突诱发MG反射的时间演变。反射被分析在三个时间段，估计符合来自Abeta-(阶段1)、ADelta-(阶段2)和C-纤维(阶段3)输入的传入驱动。刺激Adelta型和C型纤维使所有反射的时间总和显著增加。α(2)-肾上腺素能受体拮抗剂RX 821002((2-(2，3-dihydro-2-methoxy-1，4-benzodioxin-2-yl)-4，5-dihydro-1-H-imidazole)-HCl)(鞘内注射1100毫克)和α(2)激动剂右美托咪定(1-30杯I.T.)抑制所有反射本身，但这些药物对时间总和的影响次于基线兴奋性的变化。当刺激C-纤维时，AT-甲基-D-天冬氨酸(NMDA)受体拮抗剂地佐西平(i mg i.t.)减少了第二阶段和第三阶段的时间总和，但不减少了第一阶段反射。在没有药物的情况下，L1的棘化增加了第二相和第三相反射，但对第一相没有影响，而在RX 821002之后，棘化导致I相反应减少，但在以后的阶段没有显著变化。在地佐西平存在的情况下，旋转仅导致3相反射的小幅减少。在所有情况下，尖晶化实际上都废除了时间总和。在脊髓化的动物中，地佐西平选择性地减少了晚反射。和阿片类拮抗剂纳洛酮(100毫克I.T.)本实验揭示了腓肠-MG反射通路的一些新的和重要的特征：(I)细小传入轴突的活动增强了所有随后传入输入的反射产生潜力，从而允许所有来自腓肠野的传入驱动有助于脚跟的收缩；(Ii)该反射通路的内源性肾上腺素能控制是完全非选择性的；(Iii)存在一种非肾上腺素能的下行抑制成分，它选择性地作用于MG反射反应的晚期成分，该成分特别针对通过NMDA受体的传递；(Iv)这种反射的时间总和依赖于NMDA受体依赖和非依赖的机制：以及(V)这种时间总和在某种程度上依赖于下行通路的完整性。(C)2002年IBRO。爱思唯尔科学有限公司出版。版权所有。
Previous studies have suggested that activation of nociceptive afferents from the heel recruits a supraspinal mechanism, which is modulated by adrenergic descending inhibition, that augments withdrawal reflexes in medial gastrocnemius (MG) motoneurones. To test this idea, we have studied the temporal evolution of reflexes evoked in MG by electrical stimulation of sural nerve Abeta-, Adelta- and C-fibre axons at 1 Hz, in decerebrated rabbits. Reflexes were analysed in three time bands, estimated to accord to afferent drive from Abeta- (phase 1), Adelta- (phase 2) and C-fibre (phase 3) inputs. Stimulation of Adelta- and C-fibres gave significant temporal summation of all reflexes. The alpha(2)-adrenoceptor antagonist RX 821002 ((2-(2,3-dihydro-2-methoxy-1,4-benzodioxin-2-yl)-4,5-dihydro-1-H-imidazole)-HCl) (1100 mug intrathecal (i.t.)) potentiated, and the alpha(2)-agonist dexmedetomidine (1-30 mug i.t.) depressed all reflexes per se but the effects of these drugs on temporal summation were secondary to changes in baseline excitability. When C-fibres were stimulated, the AT-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (I mg i.t.) reduced temporal summation of phase 2 and 3 but not phase I reflexes. Spinalisation at L1 in the absence of drugs increased phase 2 and 3 reflexes but had no effect on phase 1, whereas spinalisation after RX 821002 resulted in decreased phase I responses with no significant change in later phases. Spinalisation in the presence of dizocilpine resulted in small reductions in phase 3 reflexes only. In all cases spinalisation virtually abolished temporal summation. In spinalised animals, dizocilpine selectively reduced late reflexes. and the opioid antagonist naloxone (100 mug i.t.) augmented all reflexes but gave rise to temporal subtraction of reflexes when C-fibres were stimulated.The present experiments have revealed a number of novel and important features of the sural-MG reflex pathway: (i) activity in fine afferent axons augments the reflexogenic potential of all subsequent afferent input, thereby allowing all afferent drive from the sural field to contribute to withdrawal of the heel; (ii) endogenous adrenergic control of this reflex pathway is completely non-selective; (iii) there is a non-adrenergic element of descending inhibition that is selective for the late components of MG reflex responses, and this element is directed particularly against transmission through NMDA receptors; (iv) temporal summation in this reflex is dependent on NMDA receptor-dependent and -independent mechanisms: and (v) this temporal summation is in some way dependent on the integrity of descending pathways. (C) 2002 IBRO. Published by Elsevier Science Ltd. All rights reserved.