Structure and synaptic function of local reflex circuit for crayfish uropod motor control system

研究的目的是了解局部回路神经元的功能作用和与行为环境有关的神经回路的基本组织。机械刺激克氏原螯虾的尾扇会引起“飞镖”样的回避反应。小龙虾闭上了两只尾足，向前走，腹部伸展。尾足动物的运动是由局部回路神经元介导的，包括非尖峰和尖峰的局部中间神经元和上行中间神经元。通过同时使用细胞内记录和染色，详细研究了回避反应中与非尖峰局部中间神经元的突触连接。一些非尖峰的局部中间神经元直接接受来自毛发传入的兴奋性外感受输入。上升和尖峰的局部中间神经元也通过化学突触接受传入的直接输入。运动神经元与传入神经之间没有直接联系，毛发传入神经也没有直接抑制联系。来自毛发传入的抑制性输入通过突起的局部中间神经元介导传递到非突起的中间神经元。来自毛发传入的间接兴奋输入也通过节间上行间神经元传递到非尖峰间神经元。一些非尖峰间神经元与其他非尖峰间神经元之间存在兴奋性或抑制性联系。非尖峰局部中间神经元的膜电位变化通过化学递质的逐渐释放而有效地改变尾足运动神经元的膜电位。

The aim of research is to understand the functional role of local circuit neurones and fundamental roganization of neural circuit relating to behavioral context. Mechanical stimulation of the tailfan in crayfish procambarus clarkii elicits a "dart" -like avoidance reaction. The crayfish closed both uropods and walks forward with extension of the abdomen. The movement of the uropod is mediated by local circuit neurones, including nonspiking and spiking local interneurones and ascending interneurones.Synaptic connection to and from nonspiking local interneurones in the avoidance reaction is investigated in detail by using simultaneous intracellular recordings and stainings. Some nonspiking local interneurones received excitatory exteroceptive sensory inputs directly from hair afferents. Boththe ascending and spiking local interneurones also received direct inputs from the afferents via chemical synapses. Neither direct connection between motor neurones and afferents nor direct inhibitory connection from hair afferents were detected.Inhibitory inputs from hair afferents were transmitted ento nonspiking interneurones via mediated by spiking local interneurones. Indirect excitatory inputs from hair afferents were also transmitted into nonspiking interneurones by intersegmental ascending interneurones. Some nonspiking interneurones made either excitatory or inhibitory connection with other nonspiking interneurones. Membrane potential change of nonspiking local interneurones was, in turn, effective to change the membrane potential of uropod motor neurones by means of gradual release of chemical transmitters.