Uncoupling axon guidance and neuronal migration in Robo3-deficient inferior olivary neurons

Cerebellum Lecture: the Cerebellar Nuclei-Core of the Cerebellum

The cerebellum is a key player in many brain functions and a major topic of neuroscience research. However, the cerebellar nuclei (CN), the main output structures of the cerebellum, are often overlooked. This neglect is because research on the cerebellum typically focuses on the cortex and tends to treat the CN as relatively simple output nuclei conveying an inverted signal from the cerebellar cortex to the rest of the brain. In this review, by adopting a nucleocentric perspective we aim to rectify this impression. First, we describe CN anatomy and modularity and comprehensively integrate CN architecture with its highly organized but complex afferent and efferent connectivity. This is followed by a novel classification of the specific neuronal classes the CN comprise and speculate on the implications of CN structure and physiology for our understanding of adult cerebellar function. Based on this thorough review of the adult literature we provide a comprehensive overview of CN embryonic development and, by comparing cerebellar structures in various chordate clades, propose an interpretation of CN evolution. Despite their critical importance in cerebellar function, from a clinical perspective intriguingly few, if any, neurological disorders appear to primarily affect the CN. To highlight this curious anomaly, and encourage future nucleocentric interpretations, we build on our review to provide a brief overview of the various syndromes in which the CN are currently implicated. Finally, we summarize the specific perspectives that a nucleocentric view of the cerebellum brings, move major outstanding issues in CN biology to the limelight, and provide a roadmap to the key questions that need to be answered in order to create a comprehensive integrated model of CN structure, function, development, and evolution.

Neurogenic timing of the inferior olive subdivisions is related to the olivocerebellar projection topography

The olivocerebellar projection is organized into an intricate topographical connection from the inferior olive (IO) subdivisions to the longitudinally-striped compartments of cerebellar Purkinje Cells (PCs), to play an essential role in cerebellar coordination and learning. However, the central mechanisms for forming topography need to be clarified. IO neurons and PCs are generated during overlapping periods of a few days in embryonic development. Therefore, we examined whether their neurogenic timing is specifically involved in the olivocerebellar topographic projection relationship. First, we mapped neurogenic timing in the entire IO by using the neurogenic-tagging system of neurog2-CreER (G2A) mice and specific labeling of IO neurons with FoxP2. IO subdivisions were classified into three groups depending on their neurogenic timing range. Then, we examined the relationships in the neurogenic-timing gradient between IO neurons and PCs by labeling topographic olivocerebellar projection patterns and PC neurogenic timing. Early, intermediate, and late groups of IO subdivisions projected to late, intermediate, and early groups of the cortical compartments, respectively, except for a few particular areas. The results indicated that the olivocerebellar topographic relationship is essentially arranged according to the reverse neurogenic-timing gradients of the origin and target.