Fan Ruey-Jane, Friesen W Otto
Department of Biology, University of Virginia, Charlottesville, 22904, USA.
J Comp Neurol. 2006 Jan 10;494(2):290-302. doi: 10.1002/cne.20818.
Sensory feedback from stretch receptors, neurons that detect position or tension, is crucial for generating normal, robust locomotion. Among the eight pairs of putative stretch receptors associated with longitudinal muscles in midbody segments of medicinal leeches, only the ventral stretch receptor has been characterized in detail. To achieve the identification of all such receptors, we penetrated large axons in the nerve roots of nerve cords from adult leeches with dye-filled (Alexa Fluor hydrazide) electrodes. We identified the terminal arborizations of two additional putative stretch receptors with axons in anterior nerve roots and four more such receptors with axons in posterior roots of midbody ganglia. The axons are nonspiking and are individually identifiable by their entry point into the CNS; their projections within the neuropile; the pattern, extent, and orientation of their terminal branches; and the characteristics of small "spike-like" events. At least two of these axons undergo membrane potential oscillations that are phase locked to the swimming rhythm expressed in nerve cord-body wall preparations and, at a different phase angle, also in isolated nerve cords. Thus the membrane potentials of at least two axons are phasically modulated by the periphery and hence could provide cycle-by-cycle sensory input to coordinate swimming activity. One of these neurons has a soma associated with the dorsal body wall and hence is a putative stretch receptor in dorsal longitudinal muscle. Thus the traveling body wave expressed by swimming leeches may be regulated by sensory feedback from both ventral and dorsal longitudinal muscles.
来自伸展感受器（即检测位置或张力的神经元）的感觉反馈对于产生正常、有力的运动至关重要。在与药用水蛭身体中段纵向肌肉相关的八对假定伸展感受器中，只有腹侧伸展感受器得到了详细的表征。为了识别所有此类感受器，我们用充满染料（Alexa Fluor酰肼）的电极刺入成年水蛭神经索神经根中的大轴突。我们识别出另外两个假定伸展感受器的终末分支，其轴突位于前神经根中，还有四个此类感受器的轴突位于身体中段神经节的后根中。这些轴突不产生动作电位，可通过它们进入中枢神经系统的入口点、在神经纤维网内的投射、终末分支的模式、范围和方向以及小“尖峰样”事件的特征来单独识别。这些轴突中至少有两个会经历膜电位振荡，这些振荡与神经索-体壁标本中表达的游泳节律锁相，并且在不同的相位角下，在分离的神经索中也是如此。因此，至少两个轴突的膜电位受到外周的相位调制，从而可以提供逐周期的感觉输入来协调游泳活动。其中一个神经元的胞体与背侧体壁相关，因此是背侧纵向肌肉中的一个假定伸展感受器。因此，游泳水蛭所表现出的行进体波可能受到来自腹侧和背侧纵向肌肉的感觉反馈的调节。
