Morphological study of cerebellar transplant cocultivated with cerebral cortical graft in the anterior eye chamber. II. Purkinje cells and molecular layer

Morphological study of organotypic cerebellar cultures

Organotypic cerebellar cultures from 8-days-old (P8) mouse pups were studied following 11 days of in vitro (I IDIV) culturing. The cerebellar cytoarchitectonic structure was maintained in most parasagittal cerebellar cortical slice cultures (also containing the deep cerebellar nuclei). The two main extrinsic excitatory inputs (the climbing and the mossy fibers) seem to be replaced by other axonal types: in the molecular layer mostly by parallel fibers (for climbing fibers) and in the granular layer by intrinsic mossy fiber collaterals of local excitatory interneurons, the unipolar brush cells. However, in a few organotypic cultures, which (although preserving the trilaminar cerebellar cortical structure) were "granuloprival" but also contained some of the deep cerebellar nuclei, the participation of extracortical axons from the deep cerebellar nuclei in the replacement of the missing afferents is suggested.

Intrinsic determinants of synaptic phenotype: an experimental study of abducens internuclear neurons connecting with anomalous targets

The present experiments investigate the role of postsynaptic neurons in the morphological differentiation of presynaptic terminals that are formed de novo in the adult CNS. Abducens internuclear neurons in the adult cat were chosen as the experimental model. These neurons project onto the contralateral medial rectus motoneurons of the oculomotor nucleus. Abducens internuclear axon terminals were identified by their anterograde labeling with biocytin and analyzed at the electron microscopic level. To promote the formation of new synapses, two different experimental approaches were used. First, after the selective ablation of medial rectus motoneurons with ricin, abducens internuclear neurons reinnervated the neighboring oculomotor internuclear neurons. Second, after axotomy followed by embryonic cerebellar grafting, abducens internuclear axons invaded the implanted tissue and established synaptic connections in both the molecular and granule cell layer. Boutons contacting the oculomotor internuclear neurons developed ultrastructural characteristics that resembled the control synapses on medial rectus motoneurons. In the grafted cerebellar tissue, abducens internuclear axons and terminals did not resemble climbing or mossy fibers but showed similarities with control boutons. However, labeled boutons analyzed in the granule cell layer established a higher number of synaptic contacts than controls. This could reflect a trend towards the mossy fiber phenotype, although labeled boutons significantly differed in every measured parameter with the mossy fiber rosettes found in the graft. We conclude that at least for the abducens internuclear neurons, the ultrastructural differentiation of axon terminals reinnervating novel targets in the adult brain seems to be mainly under intrinsic control, with little influence by postsynaptic cells.

The cerebellar model of neural grafting: structural integration and functional recovery

A synopsis is presented of the recent history of cerebellar tissue transplantation over the past 25 years. The properties of growth and differentiation of cerebellar grafts placed intraocularly or intracranially are reviewed, as well as the interaction of heterotopic and orthotopic grafts with the host brain. Particular emphasis is placed on the use of ataxic mouse mutants as recipients of donor cerebellar tissue for the correction of their structural deficits and the functional recovery of behavioural responses.

Cytoplasmic expression of the leu-4 (CD3) antigen in developing Purkinje cells in the rat cerebellum

Although commonly known to represent a T cell receptor (CD3) associated polypeptide, the leu-4 (CD3) antigen occurs in cerebellar Purkinje cells (PCs) of many species. The monoclonal pan T lymphocyte marker anti-leu-4 (CD3) recognizes both the lymphocytic and the Purkinje cell type of this antigen [22]. To obtain more information about the merit of anti-leu-4 (CD3) as an investigational tool, we evaluated the expression of leu-4 (CD3) in PCs of the developing rat cerebellum (in situ) by light microscopy. Positive anti-leu-4 (CD3) immunoreaction of PCs did not occur prior to post-natal day (D) 4. The analysis of immunostaining during cell differentiation revealed three major phases of post-natal PC maturation including antigenic development of cell somata (phase 1: until D6), dendrites (phase 2: D7-D11), and axons (phase 3: D12-D14). A massive post-weaning expansion of the dendritic arborization led then to the mature PC architecture. Additionally, the leu-4 (CD3) antigen was observed in ectopic PC dendrites (D10) and in ectopic (mature) PCs. Throughout post-natal development as well as in mature PCs, the leu-4 (CD3) antigen was found to be cytoplasmic. Due to its labile nature, neither an ultrastructural localization nor molecular characterization could be achieved. For the same reason, its application is basically restricted to cryo-fixed cerebellar tissue. However, at the level of light microscopy, the monoclonal human T cell marker anti-leu-4 (CD3) proved to be a useful tool for specific and sensitive labelling of differentiated cerebellar PCs in the rat.

Intrastriatal cerebellar grafts: differentiation of cerebellar anlage and sprouting of Purkinje cell axons

Pieces of cerebellar primordia were obtained from G16 (day 16 of gestation) rat fetuses and stereotaxically injected into the striatum of adult Wistar rats. The transplants were allowed to integrate with the host brain for 2 h up to 6 months after implantation. Ninety four out of 105 transplants perfectly integrated with the host brain (90%) and established the typical trilaminar histoarchitecture of cerebellar cortex. The transplants were sufficiently vascularized. Vessels seen within the grafts provided all ultrastructural elements of a blood-brain barrier. Light microscopic evaluation of graft development showed no considerable retardation of cerebellar histogenesis. Electron microscopic examination disclosed normal ultrastructure of cerebellar neurons, as well as elements of regular synaptic organization. The topic of efferent graft-to-host projections was investigated 2.5 months after transplantation using the monoclonal Purkinje cell marker anti-Leu-4 (CD3). This method allowed us to detect immunoreactive, morphologically intact axons of grafted Purkinje cells running over long distances (at least 500 microns) within the host striatum. Whilst afferent but in no case efferent connections of heterotopic cerebellar transplants had been demonstrated elsewhere, we could now prove the reciprocal modus of graft-host interaction with heterotopic cerebellar grafts.