Ramírez V, Ulfhake B
Department of Anatomy, Karolinska Institutet, Stockholm, Sweden.
Brain Res Dev Brain Res. 1991 Oct 21;62(2):189-202. doi: 10.1016/0165-3806(91)90166-g.
The postnatal development of dendrite anatomy in alpha-motoneurons intracellularly labeled with horseradish peroxidase (HRP), innervating the intrinsic muscles of the sole of the foot (IFS MNs) in the cat, was investigated. The number of dendrites per neuron was about 11 and did not change from birth to adult. The number of branches per dendrite decreased during the same period by 20-25%. The net elimination of dendritic branches appeared to occur at distal branching points, as revealed by topological analysis. The dendritic branching pattern tended to be asymmetric at birth and the net decrease in dendritic branching postnatally did not alter this pattern. The length of preterminal branches (PTB) increased by a factor of 2, while terminal branch (TB) length increased by a factor of 3.3 postnatally. The large increase in TB length was attributed to both longitudinal growth and an apparent lengthening caused by resorption of distal branches during development. Dendritic length in the transverse spinal cord plane increased in parallel with the overall growth of the parent spinal cord segment, while dendritic growth along the rostro-caudal axis exceeded, by about one order of magnitude, dendritic growth in the transverse plane. Average branch diameter doubled from birth to adult. The decrease in branch diameter across branching points did not obey satisfactorily to the 'power rule' of Rall. However, the 1.5 power ratio of daughters-to-parents branch dropped from 1.18 to 1.08 between 3 weeks of age and adult. Tapering was evident in both PTBs and TBs. The rate of taper did not change postnatally. From birth onwards, 'local' branch diameter correlated closely with amount of membrane area and combined length of the dendritic branches located distal to the 'supporting' parent branch. These relations were similar in all age groups and are suggested to be properties intrinsic to the IFS MNs. The local branch diameter also co-varied with the number of distal dendritic branches, but in this case there was a systematic shift in the relationship with increasing postnatal age. It appears that the local diameter in IFS MN dendrites is a key indicator of the size of the distal dendritic arborization.
研究了用辣根过氧化物酶（HRP）细胞内标记的、支配猫足底固有肌的α运动神经元（IFS MNs）树突解剖结构的产后发育情况。每个神经元的树突数量约为11个，从出生到成年没有变化。在此期间，每个树突的分支数量减少了20% - 25%。拓扑分析显示，树突分支的净消除似乎发生在远端分支点。出生时树突分支模式往往不对称，产后树突分支的净减少并未改变这种模式。终末前分支（PTB）的长度增加了1倍，而终末分支（TB）的长度在产后增加了3.3倍。TB长度的大幅增加归因于纵向生长以及发育过程中远端分支吸收导致的明显延长。脊髓横平面内的树突长度与母脊髓节段的整体生长平行增加，而沿头尾轴的树突生长比横平面内的树突生长超出约一个数量级。平均分支直径从出生到成年增加了一倍。跨分支点的分支直径减小情况并不完全符合拉尔的“幂律”。然而，子代与亲代分支的1.5幂比在3周龄到成年之间从1.18降至1.08。PTB和TB中都明显存在变细现象。变细速率在产后没有变化。从出生起，“局部”分支直径与位于“支撑”亲代分支远端的膜面积和树突分支总长度密切相关。这些关系在所有年龄组中都相似，被认为是IFS MNs固有的特性。局部分支直径也与远端树突分支数量共同变化，但在这种情况下，随着产后年龄的增加，这种关系存在系统变化。看来IFS MN树突中的局部直径是远端树突分支大小的关键指标。
