Smith C L, Frank E
Department of Neurobiology, University of Pittsburgh, School of Medicine, Pennsylvania 15261.
J Comp Neurol. 1988 Mar 1;269(1):96-108. doi: 10.1002/cne.902690108.
Sensory neurons in dorsal root ganglia of frogs project to areas of the spinal cord they do not normally innervate following removal of adjacent ganglia at tadpole stages (Frank and Westerfield, J. Physiol. (Lond.) 324:495-505, '82b). A possible explanation of this phenomenon is that sensory neurons project to wider areas of the spinal cord in tadpoles than in adult frogs and that partial deafferentation causes the retention of these widespread projections. Therefore, the specificity of sensory projections to the spinal cord in tadpoles was assessed by staining individual dorsal roots with horseradish peroxidase. Thoracic sensory neurons project to thoracic segments of the spinal cord and to the brainstem in tadpoles, like thoracic sensory neurons in adult frogs. They rarely arborize in the brachial region even at stages when no other sensory fibers arborize at this level. Furthermore, their projections are restricted to the dorsal horn at all stages. Conversely, hypoglossal sensory neurons, which project into the intermediate gray matter in the adult, also project to this area in tadpoles. The finding that sensory neurons in tadpoles only project to areas of the spinal cord that they innervate in the adult suggests that the novel projections observed following partial deafferentation of the spinal cord are actually induced by the operation. An additional finding was that forelimb afferents, which project to an area extending from the obex to midthoracic levels in adult frogs, arborize at rostral spinal levels and at thoracic levels several stages before they form projections to the region around their own dorsal root. These differences in the stages at which projections to different levels of the spinal cord develop suggest that local properties of the spinal cord may control the timing of sensory fiber arborization.
在蝌蚪阶段切除相邻神经节后，青蛙背根神经节中的感觉神经元会投射到它们通常不会支配的脊髓区域（Frank和Westerfield，《生理学杂志》（伦敦）324:495 - 505，1982年b期）。对这一现象的一种可能解释是，蝌蚪中的感觉神经元投射到脊髓的区域比成年青蛙中的更广泛，部分去传入神经作用导致这些广泛的投射得以保留。因此，通过用辣根过氧化物酶对单个背根进行染色，评估了蝌蚪中感觉投射到脊髓的特异性。蝌蚪中的胸段感觉神经元投射到脊髓的胸段和脑干，就像成年青蛙中的胸段感觉神经元一样。即使在没有其他感觉纤维在此水平分支的阶段，它们也很少在臂部区域分支。此外，它们的投射在所有阶段都局限于背角。相反，成年时投射到中间灰质的舌下感觉神经元在蝌蚪中也投射到该区域。蝌蚪中的感觉神经元仅投射到它们在成年时支配的脊髓区域这一发现表明，脊髓部分去传入神经作用后观察到的新投射实际上是由手术诱导的。另一个发现是，成年青蛙中投射到从闩部到胸段中部区域的前肢传入神经，在它们形成向其自身背根周围区域的投射之前的几个阶段，就在脊髓头端水平和胸段水平分支。向脊髓不同水平的投射发育阶段的这些差异表明，脊髓的局部特性可能控制感觉纤维分支的时间。
