Abstract
The cerebellum has a long history in terms of research on its network structures and motor functions, yet our understanding of them has further advanced in recent years owing to technical developments, such as viral tracers, optogenetic and chemogenetic manipulation, and single cell gene expression analyses. Specifically, it is now widely accepted that the cerebellum is also involved in non-motor functions, such as cognitive and psychological functions, mainly from studies that have clarified neuronal pathways from the cerebellum to other brain regions that are relevant to these functions. The techniques to manipulate specific neuronal pathways were effectively utilized to demonstrate the involvement of the cerebellum and its pathways in specific brain functions, without altering motor activity. In particular, the cerebellar efferent pathways that have recently gained attention are not only monosynaptic connections to other brain regions, including the periaqueductal gray and ventral tegmental area, but also polysynaptic connections to other brain regions, including the non-primary motor cortex and hippocampus. Besides these efferent pathways associated with non-motor functions, recent studies using sophisticated experimental techniques further characterized the historically studied efferent pathways that are primarily associated with motor functions. Nevertheless, to our knowledge, there are no articles that comprehensively describe various cerebellar efferent pathways, although there are many interesting review articles focusing on specific functions or pathways. Here, we summarize the recent findings on neuronal networks projecting from the cerebellum to several brain regions. We also introduce various techniques that have enabled us to advance our understanding of the cerebellar efferent pathways, and further discuss possible directions for future research regarding these efferent pathways and their functions.
Highlights
The cerebellum is a region of the brain that is anatomically separated from the other regions, and is morphologically unique in several aspects
The abovementioned rAAV-retro or CAV2 expressing Cre was injected into target brain regions, and associated virus (AAV) triggering Cre-dependent expression of chemogenetic or optogenetic molecules were injected into the deep cerebellar nuclei (DCN), which resulted in the specific expression of molecules in the DCN neurons projecting to the target brain regions
Disynaptically connected cerebellar efferent pathways were investigated, as follows: AAV serotype 1 expressing Cre, or AAV expressing wheat germ agglutinin (WGA)-Cre was injected into the DCN, and AAV triggering the Cre-dependent expression of chemogenetic or optogenetic molecules was injected into the intermediate regions, which resulted in the expression of these molecules in neurons of the intermediate regions receiving inputs from the DCN
Summary
The cerebellum is a region of the brain that is anatomically separated from the other regions, and is morphologically unique in several aspects. One of the two major cerebellar inputs comes from mossy fibers, which originate from several regions of the brainstem and spinal cord, and indirectly innervates Purkinje cells (PCs) through granule cells Another type of major inputs, from climbing fibers, directly innervates PCs. PCs are inhibitory output neurons from the cerebellar cortex, and their axons mainly project to the deep cerebellar nuclei (DCN), from where cerebellar efferent projections are sent to other brain regions. Unlike relatively uniform network structures in the cerebellar cortex, efferent projections mostly from DCN neurons and occasionally from PCs are highly heterogeneous, and the investigation of efferent pathways is essential toward understanding the multifunctionality of the cerebellum. Novelty-suppressed feeding test, sucrose preference test (rat) Three-chamber social behavior task, social olfaction, self-grooming behavior (mouse)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
