Zhang B, Goldberger M E, Wu L F, Murray M
Department of Anatomy & Neurobiology, Medical College of Pennsylvania, Philadelphia 19129, USA.
Exp Neurol. 1995 Apr;132(2):186-93. doi: 10.1016/0014-4886(95)90024-1.
Projections to the dorsal horn change in adult mammals in response to complete or partial deafferentation. The number of synaptic terminals remains constant after complete lumbosacral deafferentation, indicating replacement of lost dorsal root terminals by newly formed terminals from spared intrinsic systems. The density of a spared central projection of a dorsal root is increased in dorsal horn after partial deafferentation, consistent with sprouting by the axons in the spared root. In this study, we have used electron microscopy to study morphological changes in a specific class of terminals in the dorsal horn induced by partial deafferentation. Complex terminals (CTs) in the dorsal horn originate exclusively from dorsal roots and are readily distinguished morphologically. The CTs and the postsynaptic densities (PSDs) associated with CTs were measured in lamina II at L5 and L6 in cats subjected to unilateral spared root (L6) dorsal rhizotomies and compared to CTs in the control side. Acutely following partial deafferentation, the number of CT profiles decreased. At more chronic survivals, the number of CT profiles were restored to normal levels, and both the number and the length of PSDs were increased. The changes in CTs and PSDs suggest sprouting and synaptogenesis by the spared dorsal root fibers that produce changes in the postsynaptic neuron. Spared root deafferentation thus elicits compensatory changes in presynaptic terminals of the spared root and also in their postsynaptic target neurons.
在成年哺乳动物中，背角的投射会因完全或部分传入神经阻滞而发生变化。在完全腰骶部传入神经阻滞后，突触终末的数量保持恒定，这表明失去的背根终末被来自保留的内在系统的新形成的终末所取代。在部分传入神经阻滞后，背根保留的中枢投射在背角中的密度增加，这与保留根中的轴突发芽一致。在本研究中，我们使用电子显微镜研究了部分传入神经阻滞诱导的背角中特定类型终末的形态学变化。背角中的复杂终末（CTs）仅起源于背根，并且在形态上很容易区分。在接受单侧保留根（L6）背根切断术的猫的L5和L6的II层中测量了CTs以及与CTs相关的突触后致密物（PSDs），并与对照侧的CTs进行比较。在部分传入神经阻滞后急性观察时，CT轮廓的数量减少。在更长时间的存活期，CT轮廓的数量恢复到正常水平，并且PSDs的数量和长度都增加了。CTs和PSDs的变化表明保留的背根纤维发生了发芽和突触形成，从而导致突触后神经元发生变化。因此，保留根传入神经阻滞会引发保留根的突触前终末及其突触后靶神经元的代偿性变化。
