Gatesy S M, English A W
Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322.
Dev Dyn. 1993 Mar;196(3):174-82. doi: 10.1002/aja.1001960304.
In adult rats, each neuromuscular compartment of the lateral gastrocnemius muscle (LG) is exclusively innervated by a primary branch of the LG nerve. In neonates, however, a small percentage of LG cells receives inputs from more than one primary nerve branch; these inputs are known as cross-compartmental. Cross-compartmental inputs are normally lost from the medial compartment of LG (LGm) by the 8th postnatal day. To investigate the mechanisms involved in the elimination of cross-compartmental inputs, muscle fibers in the LGm compartment were denervated by cutting the LGm nerve branch in 1-4 day old rat pups and in adult rats. We then assessed the degree of cross-compartmental innervation within the "denervated" compartment using intracellular recordings from neonatal muscle fibers or immunohistochemical staining for nerve cell adhesion molecule (N-CAM) and neurofilament protein in adult muscles. Following LGm axotomy in neonates, cross-compartmental innervation is more extensive than in controls and is present as late as 20 days after birth. Thus, in the absence of "native" LGm axons, neonatal cross-compartmental inputs proliferate by axonal sprouting and the formation of new synapses on vacant LGm fibers. In contrast, axotomized adults do not form new cross-compartmental inputs over the same time period. The differential response of neonates and adults to muscle nerve branch denervation is evidence for the existence of some form of compartment-specific recognition. We propose that compartmental identity either arises or becomes relatively more potent during ontogeny and normally acts selectively to eliminate foreign axons and deter the formation of new cross-compartmental inputs.
在成年大鼠中，外侧腓肠肌（LG）的每个神经肌肉区室仅由LG神经的一个初级分支支配。然而，在新生大鼠中，一小部分LG细胞会接收来自不止一个初级神经分支的输入；这些输入被称为跨区室输入。跨区室输入通常在出生后第8天从LG的内侧区室（LGm）消失。为了研究参与消除跨区室输入的机制，通过切断1 - 4日龄幼鼠和成年大鼠的LGm神经分支，使LGm区室的肌纤维失神经支配。然后，我们使用新生肌纤维的细胞内记录或成年肌肉中神经细胞粘附分子（N - CAM）和神经丝蛋白的免疫组织化学染色，评估“失神经支配”区室内跨区室神经支配的程度。在新生大鼠中切断LGm轴突后，跨区室神经支配比对照组更广泛，并且在出生后20天仍存在。因此，在没有“天然”LGm轴突的情况下，新生跨区室输入通过轴突发芽和在空置的LGm纤维上形成新突触而增殖。相比之下，成年大鼠轴突切断后在相同时间段内不会形成新的跨区室输入。新生大鼠和成年大鼠对肌肉神经分支去神经支配的不同反应证明了某种形式的区室特异性识别的存在。我们提出，区室特性要么在个体发育过程中产生，要么变得相对更强，并且通常选择性地作用于消除外来轴突并阻止新的跨区室输入的形成。
