Jankowska E, Slawinska U, Hammar I
Department of Physiology, Göteborg University, 405 30 Göteborg, Sweden.
J Physiol. 2002 Jul 1;542(Pt 1):301-14. doi: 10.1113/jphysiol.2001.014076.
The aim of the study was to verify the hypothesis that trisynaptic actions of group II muscle afferents upon motoneurones are, at least in part, mediated by dorsal horn interneurones exciting the same intermediate zone interneurones that are interposed in disynaptic pathways from group II afferents. Population EPSPs (field potentials) and responses of individual interneurones evoked by group II afferents in the dorsal horn and in the intermediate zone were analysed in order to assess the possibility of a causal relationship between them. When direct actions of group II afferents in the intermediate zone were abolished by presynaptic inhibition, distinct later components of field potentials and delayed interneuronal responses were induced at latencies 0.5-1 ms longer than those seen originally. Both the latency and a marked temporal facilitation define these later group II actions as being evoked disynaptically. Under the same conditions, single stimuli activated more than one half of dorsal horn interneurones, and the second and third stimuli activated all of these interneurones. Responses of dorsal horn interneurones preceded disynaptically evoked responses of intermediate zone interneurones. The study indicates that intermediate zone interneurones may be activated by group II afferents both directly and via dorsal horn interneurones and that synaptic actions of group II afferents upon these interneurones, and their subsequent actions upon motoneurones, may be modulated in parallel at the level of intermediate zone and dorsal horn interneurones.
Ⅱ类肌传入纤维对运动神经元的三突触作用至少部分是由背角中间神经元介导的，这些中间神经元兴奋了那些插入到来自Ⅱ类传入纤维的双突触通路中的相同中间带中间神经元。分析了Ⅱ类传入纤维在背角和中间带诱发的群体兴奋性突触后电位（场电位）以及单个中间神经元的反应，以评估它们之间存在因果关系的可能性。当通过突触前抑制消除Ⅱ类传入纤维在中间带的直接作用时，会诱发场电位明显的后期成分和延迟的中间神经元反应，其潜伏期比最初观察到的长0.5 - 1毫秒。潜伏期和明显的时间易化都将这些后期的Ⅱ类作用定义为由双突触诱发。在相同条件下，单个刺激激活了超过一半的背角中间神经元，而第二个和第三个刺激激活了所有这些中间神经元。背角中间神经元的反应先于中间带中间神经元的双突触诱发反应。该研究表明，中间带中间神经元可能被Ⅱ类传入纤维直接激活，也可能通过背角中间神经元激活，并且Ⅱ类传入纤维对这些中间神经元的突触作用以及它们随后对运动神经元的作用，可能在中间带和背角中间神经元水平上受到并行调节。
