Norekian T P
Department of Zoology, Arizona State University, Tempe 85287-1501, USA.
J Neurophysiol. 1997 Jul;78(1):308-20. doi: 10.1152/jn.1997.78.1.308.
The holoplanktonic pteropod mollusk Clione limacina has a unique startle system that provides a very fast, ballistic movement of the animal during escape or prey capture behaviors. The startle system consists of two groups of large pedal motoneurons that control ventral or dorsal flexions of the wings. Although startle motoneurons innervate the same musculature used during normal swimming, they are independent of the swim central pattern generator and swim motoneurons. This study demonstrates that a cerebral startle (Cr-St) interneuron, which provides prominent excitatory inputs to startle motoneurons, plays a very important role in coordination of the startle and swimming neural systems. The Cr-St interneuron produces, simultaneously with monosynaptic excitatory inputs to dorsal startle motoneurons, monosynaptic inhibitory inputs to all types of swim neurons, including interneurons of the central pattern generator, general excitor motoneurons, small motoneurons, and modulatory pedal serotonergic wing neurons. The inhibitory synaptic transmission between the Cr-St interneuron and swim interneurons and motoneurons, as well as excitatory transmission between the Cr-St interneuron and startle motoneurons, appears to be cholinergic because it is blocked by the cholinergic antagonists atropine and d-tubocurarine, mimicked by exogenous acetylcholine in very low concentrations, and enhanced by the cholinesterase inhibitor eserine (physostigmine). The Cr-St-neuron-mediated inhibitory inputs to the swimming system are strong enough to completely terminate swimming activity while the Cr-St interneuron is active. Mechanosensory inputs are capable of triggering Cr-St neuron firing at rates sufficient to suppress fictive swimming in reduced preparations. Thus the Cr-St interneuron can temporally remove the swimming system from the control over the swim musculature while simultaneously activating the startle system to produce a powerful, short-latency response.
终生浮游的翼足类软体动物——海若螺，拥有独特的惊吓系统，该系统能使动物在逃避或捕食行为中产生非常快速的弹射运动。惊吓系统由两组大型足运动神经元组成，它们控制着翼的腹侧或背侧弯曲。尽管惊吓运动神经元支配正常游泳时所使用的相同肌肉组织，但它们独立于游泳中枢模式发生器和游泳运动神经元。本研究表明，向惊吓运动神经元提供显著兴奋性输入的脑惊吓（Cr-St）中间神经元，在惊吓和游泳神经系统的协调中起着非常重要的作用。Cr-St中间神经元在向背侧惊吓运动神经元产生单突触兴奋性输入的同时，也向所有类型的游泳神经元产生单突触抑制性输入，包括中枢模式发生器的中间神经元、一般兴奋运动神经元、小型运动神经元和调节性足5-羟色胺能翼神经元。Cr-St中间神经元与游泳中间神经元和运动神经元之间的抑制性突触传递，以及Cr-St中间神经元与惊吓运动神经元之间的兴奋性传递，似乎都是胆碱能的，因为它被胆碱能拮抗剂阿托品和d-筒箭毒碱阻断，能被极低浓度的外源性乙酰胆碱模拟，并被胆碱酯酶抑制剂毒扁豆碱增强。Cr-St神经元介导的对游泳系统的抑制性输入足够强大，足以在Cr-St中间神经元活跃时完全终止游泳活动。机械感觉输入能够以足以抑制简化标本中虚拟游泳的速率触发Cr-St神经元放电。因此，Cr-St中间神经元可以在时间上使游泳系统脱离对游泳肌肉组织的控制，同时激活惊吓系统以产生强大的、潜伏期短的反应。
