Bhide P G, Frost D O
Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02129, USA.
J Comp Neurol. 1999 Aug 16;411(1):119-29.
Permanent, novel retinal projections to the principal thalamic somatosensory (ventrobasal) or auditory (medial geniculate) nuclei can be produced in adult hamsters if the superior colliculus is ablated bilaterally and the somatosensory and auditory lemniscal axons are transected unilaterally on the day of birth. We studied the development of those novel projections by labeling retinal axons with the fluorescent tracer 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate to examine the relative roles of intrinsic factors and axon-target interactions in the specification of retinal axon connections. Our principal findings are as follows: (1) In hamsters operated on the day of birth to produce the novel retinal projections, retinal ganglion cell axons projecting to the ventrobasal or medial geniculate nuclei develop in three morphologically distinct stages, i.e., elongation, collateralization, and arborization, as do retinal axons projecting to the dorsal lateral geniculate nucleus, the principal thalamic visual nucleus, in normal hamsters. (2) In both the ventrobasal and medial geniculate nuclei of operated hamsters, as in the dorsal lateral geniculate nucleus of normal hamsters, collateral branches were initially formed by retinal ganglion cell axons in both the superficial and internal components of the optic tract and only collaterals from the superficial component formed permanent projections. (3) The retinofugal axon terminal arbors in the ventrobasal and medial geniculate nuclei of mature, operated hamsters resemble the same three morphologic classes that are observed in the lateral geniculate nucleus of normal hamsters, although their absolute size appears to be altered. These data suggest that both superficial and internal optic tract axons can produce thalamic collaterals during development but that only superficial optic tract axons can permanently retain thalamic collaterals. Furthermore, the same morphologic types of retinofugal axons appear to contribute to normal and surgically induced retinal projections.
如果在成年仓鼠出生当天双侧切除上丘，并单侧切断体感和听觉丘系轴突，就可以产生永久性的、新的视网膜投射至丘脑主要体感（腹侧基底）或听觉（内侧膝状体）核。我们通过用荧光示踪剂1,1'-二辛基-3,3,3',3'-四甲基吲哚羰花青高氯酸盐标记视网膜轴突，研究这些新投射的发育过程，以检验内在因素和轴突-靶标相互作用在视网膜轴突连接特异性中的相对作用。我们的主要发现如下：（1）在出生当天接受手术以产生新视网膜投射的仓鼠中，投射至腹侧基底或内侧膝状体核的视网膜神经节细胞轴突，与正常仓鼠中投射至丘脑主要视觉核背外侧膝状体核的视网膜轴突一样，在形态上经历三个不同阶段，即伸长、侧支形成和分支形成。（2）在手术仓鼠的腹侧基底核和内侧膝状体核中，与正常仓鼠的背外侧膝状体核一样，视网膜神经节细胞轴突最初在视束的浅层和深层成分中都形成侧支，但只有浅层成分的侧支形成永久性投射。（3）成熟的手术仓鼠腹侧基底核和内侧膝状体核中的视网膜传出轴突终末分支，与正常仓鼠外侧膝状体核中观察到的三种形态学类型相似，尽管它们的绝对大小似乎有所改变。这些数据表明发育过程中视束浅层和深层轴突都能产生丘脑侧支，但只有视束浅层轴突能永久性保留丘脑侧支。此外，相同形态学类型的视网膜传出轴突似乎对正常和手术诱导的视网膜投射都有贡献。
