Rossi F, van der Want J J, Wiklund L, Strata P
Department of Human Anatomy and Physiology, University of Turin, Italy.
J Comp Neurol. 1991 Jun 22;308(4):536-54. doi: 10.1002/cne.903080404.
A salient feature of the cerebellar Purkinje cells is the highly ordered distribution of their excitatory afferents on the dendritic tree. Climbing fibres synapse exclusively on the proximal dendrites, whereas parallel fibres articulate with the distal branches, the so-called spiny branchlets. This input organization is lost following the removal of climbing fibres. Such denervation results in the formation of a large number of new spines on the proximal dendrites, and these become contacted by sprouting parallel fibres, which thereby extend their domain of innervation. We have previously shown that the climbing fibres surviving a subtotal lesion of the inferior olive sprout and reinnervate neighbouring Purkinje cells. In the present ultrastructural study, we have investigated the features of Purkinje cells reinnervated by sprouting climbing fibres. The objectives were to examine the fine morphology of the newly formed synapses and to determine whether the modifications of Purkinje cell morphology and afferent organization are reversed by this reinnervation. Surviving climbing fibres were labelled by the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) and immunohistochemically visualized by means of the gold-substituted silver peroxidase technique, 2 and 6 months after 3-acetylpyridine lesions of the inferior olive in adult rats. Sprouting climbing fibres and newly formed arborizations were identified in the light microscope, isolated, and cut in serial ultrathin sections for electron microscopic analysis. The labelled boutons belonging to newly formed terminal plexuses exhibited the typical morphological features of climbing fibre terminals, i.e., a high number of round synaptic vesicles and a few small mitochondria. Most frequently they formed asymmetric synapses on stubby thorns protruding from the proximal Purkinje cell dendrites. In some instances, however, the postsynaptic element consisted of long slender spines or spines showing an atypical morphology. A number of labelled boutons was also in contact with the perikarya of reinnervated Purkinje cells, either articulating with spines or synapsing directly on the smooth somatic surface. The proximal dendrites of denervated Purkinje cells were characterized by large numbers of spines, which were frequently postsynaptic to parallel fibres. By contrast, Purkinje cells reinnervated by the sprouting climbing fibres generally showed a lower number of spines on their proximal dendrites, indicating a reversal of this morphological change. The aberrant parallel fibre input was also decreased on reinnervated dendrites or had completely disappeared. Nevertheless, some reinnervated Purkinje cells showed the persistence of some parallel fibre synapses on their proximal dendrites. On occasion, climbing fibre and parallel fibre boutons synapsed on the same spine.
小脑浦肯野细胞的一个显著特征是其兴奋性传入纤维在树突树上高度有序分布。攀缘纤维仅与近端树突形成突触，而平行纤维则与远端分支即所谓的棘状小分支相连。去除攀缘纤维后，这种输入组织会丧失。这种去神经支配导致近端树突上形成大量新的棘突，并且这些棘突会被发芽的平行纤维接触，从而扩大其支配区域。我们之前已经表明，在橄榄下核次全损伤后存活的攀缘纤维会发芽并重新支配邻近的浦肯野细胞。在本超微结构研究中，我们研究了由发芽的攀缘纤维重新支配的浦肯野细胞的特征。目的是检查新形成突触的精细形态，并确定浦肯野细胞形态和传入组织的改变是否会因这种重新支配而逆转。在成年大鼠橄榄下核经3 - 乙酰吡啶损伤后2个月和6个月，通过顺行示踪剂菜豆白细胞凝集素（PHA - L）标记存活的攀缘纤维，并采用金取代银过氧化物酶技术进行免疫组织化学可视化。在光学显微镜下识别出发芽的攀缘纤维和新形成的分支，分离后切成连续超薄切片进行电子显微镜分析。属于新形成终末丛的标记终扣表现出攀缘纤维终末的典型形态特征，即大量圆形突触小泡和少量小线粒体。它们最常与从近端浦肯野细胞树突伸出的粗短棘突形成不对称突触。然而，在某些情况下，突触后成分由细长的棘突或形态异常的棘突组成。一些标记终扣也与重新支配的浦肯野细胞的胞体接触，要么与棘突相连，要么直接在光滑的胞体表面形成突触。去神经支配的浦肯野细胞的近端树突以大量棘突为特征，这些棘突经常是平行纤维的突触后成分。相比之下，由发芽的攀缘纤维重新支配的浦肯野细胞的近端树突上通常棘突数量较少，表明这种形态变化发生了逆转。重新支配的树突上异常的平行纤维输入也减少或完全消失。然而，一些重新支配的浦肯野细胞在其近端树突上仍存在一些平行纤维突触。偶尔，攀缘纤维和平行纤维终扣会在同一棘突上形成突触。
