Plummer K L, Behan M
Department of Anatomy, University of Wisconsin-Madison 53706.
J Comp Neurol. 1993 Dec 15;338(3):458-74. doi: 10.1002/cne.903380309.
We studied the development of corticotectal synaptic terminal boutons and synapses by making injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into area 17 of visual cortex in kittens ranging from newborn to 12 weeks of age and in adults. The location and extent of the injection site, and labeled corticotectal axon terminals in the superficial layers of the superior colliculus were demonstrated histochemically with the cobalt-glucose oxidase diaminobenzidine reaction. During the first 2 weeks after birth, the majority of labeled profiles resembled axonal growth cones, or structures intermediate in morphology between growth cones and synaptic terminals, while very few corticotectal axon terminals forming well-defined synaptic contacts were observed. Labeled synaptic terminals in kittens at 1 and 2 weeks of age were small, contained very few synaptic vesicles, which were usually restricted to the contact zone, and exhibited few mitochondria. By 4 and 6 weeks after birth, a well-developed population of synaptic terminals was established; however, growth cones and intermediate profiles were still numerous. At 8 weeks of age synaptic terminals were morphologically mature, and growth cone-like profiles were no longer observed. To study quantitative changes in synapse development we used the disector method to obtain unbiased estimates of the density and number of corticotectal synaptic terminals and synapses; both the density and number of terminals and synapses increased steadily throughout postnatal development. These results suggest that the corticotectal projection develops by the progressive elaboration of synapses, as opposed to synapse overproduction and subsequent elimination.
我们通过将与辣根过氧化物酶（WGA-HRP）偶联的小麦胚凝集素注射到新生至12周龄小猫以及成年猫的视皮层17区，研究了皮质顶盖突触终末小体和突触的发育。注射部位的位置和范围，以及上丘表层中标记的皮质顶盖轴突终末，通过钴-葡萄糖氧化酶二氨基联苯胺反应进行组织化学显示。在出生后的前2周，大多数标记的形态类似于轴突生长锥，或形态介于生长锥和突触终末之间的结构，而观察到形成明确突触联系的皮质顶盖轴突终末很少。1周和2周龄小猫的标记突触终末很小，含有很少的突触小泡，这些小泡通常局限于接触区，并且线粒体很少。到出生后4周和6周时，已建立了发育良好的突触终末群体；然而，生长锥和中间形态仍然很多。在8周龄时，突触终末在形态上成熟，不再观察到生长锥样形态。为了研究突触发育的定量变化，我们使用了分割法来获得皮质顶盖突触终末和突触密度及数量的无偏估计；在出生后的整个发育过程中，终末和突触的密度及数量均稳步增加。这些结果表明，皮质顶盖投射是通过突触的逐步精细形成而发育的，而不是通过突触的过度产生和随后的消除。
