Feldman D H
Department of Physiology, University of California, School of Medicine, San Francisco 94143.
J Neurosci. 1988 Nov;8(11):4367-78. doi: 10.1523/JNEUROSCI.08-11-04367.1988.
B cells and C cells in frog lumbar sympathetic ganglia are specifically innervated by preganglionic B fibers and C fibers, respectively. To explore the mechanisms underlying the formation of these specific synapses, electrophysiological studies were made of sprouting and regenerating synaptic connections following interruption of the preganglionic pathways. Studies were also made of developing connections in tadpole ganglia. After partial denervation (by selective interruption of B fibers), the C fibers sprouted and innervated B cells. When B fibers regenerated, they reinnervated B cells only, and within several weeks, C fiber synapses on B cells were no longer found. After complete denervation (by interruption of both B and C fibers) specific synaptic connections were eventually restored. At least 2 experimentally separable processes underlie this specificity: First, there is a preference for appropriate connections from the outset of reinnervation, seen even in the absence of competition between the 2 groups of preganglionic fibers. Despite this preference, however, some inappropriate synapses are formed. Second, those inappropriate synapses that do arise are eliminated when appropriate synapses are allowed to reform, as a result of competitive interactions between the 2 preganglionic fiber groups. In normally developing tadpole ganglia, B and C cells were not readily distinguishable. The great majority of tadpole neurons were found to be innervated exclusively by either B or C fibers. Some neurons were innervated by both preganglionic fiber groups, a situation virtually never found in adult ganglia. It thus appears that in normal development, as in reinnervation, innervation is by and large selective; inappropriate synapses may form, but they are eliminated during maturation, presumably through competitive interactions.
青蛙腰交感神经节中的B细胞和C细胞分别由节前B纤维和C纤维特异性支配。为了探究这些特异性突触形成的潜在机制，对节前通路中断后突触连接的发芽和再生进行了电生理研究。还对蝌蚪神经节中正在发育的连接进行了研究。在部分去神经支配（通过选择性中断B纤维）后，C纤维发芽并支配B细胞。当B纤维再生时，它们仅重新支配B细胞，并且在几周内，B细胞上的C纤维突触不再被发现。在完全去神经支配（通过中断B和C纤维）后，特异性突触连接最终得以恢复。至少有两个实验上可分离的过程构成了这种特异性：首先，从重新支配开始就存在对适当连接的偏好，即使在两组节前纤维之间不存在竞争的情况下也是如此。然而，尽管有这种偏好，仍会形成一些不适当的突触。其次，当适当的突触能够重新形成时，那些确实出现的不适当突触会由于两组节前纤维之间的竞争性相互作用而被消除。在正常发育的蝌蚪神经节中，B细胞和C细胞不容易区分。发现绝大多数蝌蚪神经元仅由B纤维或C纤维单独支配。一些神经元由两组节前纤维支配，这种情况在成年神经节中几乎从未发现。因此，似乎在正常发育过程中，如同在重新支配过程中一样，支配在很大程度上是选择性的；可能会形成不适当的突触，但它们在成熟过程中会被消除，大概是通过竞争性相互作用。
