Different types of multiple‐synapse boutons in the cerebellar cortex between physically enriched and ataxic mutant mice

• Published in: Microscopy research and technique 2019-01, Vol.82 (1), p.25-32
• Main Authors: Kim, Hyun‐Wook, Oh, Seunghak, Lee, Seung Hwan, Lee, Sanghoon, Na, Ji‐Eun, Lee, Kea Joo, Rhyu, Im Joo
• Format: Article
• Language: English
• Subjects: Animals; Ataxia - genetics; Ataxia - pathology; Cerebellar Cortex - pathology; Cerebellum; Cognitive ability; Dendrites; Dendrites - physiology; dendritic spine; Dendritic spines; Dendritic structure; Dimensional analysis; Enrichment; environmental enrichment; Information storage; Mice; Mice, Inbred C57BL; Mice, Transgenic; Motors; Mutants; Nervous system; Neural networks; Neurological diseases; parallel fiber; Presynapse; Presynaptic Terminals - pathology; Presynaptic Terminals - ultrastructure; Purkinje cell; Purkinje cells; Purkinje Cells - pathology; Structure-function relationships; synapse; Synapses; Synaptic transmission; Synaptogenesis
• ISSN: 1059-910X; 1097-0029
• DOI: 10.1002/jemt.23054

Experience‐dependent synapse remodeling is associated with information storage in the nervous system. Neuronal synapses show alteration in various neurological and cognitive disorders in their structure and function. At the ultrastructural level, parallel fiber boutons contacting multiple spines of Purkinje cells in the cerebellar cortex are commonly observed in physiologically enriched animals as well as pathological ataxic mutants. However, the dendritic origin of those spines on parallel fiber multiple‐synapse boutons (MSBs) has been poorly understood. Here, we investigated this issue by 3‐dimensional ultrastructural analysis to determine synaptic connectivity of MSBs in both mice housed in physically enriched environment and cerebellar ataxic mutants. Our results demonstrated that environmental enrichment selectively induced MSBs to contact spines from the same parent dendrite, indicating focal strengthening of synapse through the simultaneous activation of two adjacent spines. In contrast, ataxic mutants displaying impaired motor coordination had significantly more MSBs involving spines originating from different neighboring dendrites compared to both wild‐type and environmentally enriched animals, suggesting that compromising multiple synapse formation may lead to abnormal motor behavior in the mutant mice. These findings propose that environmental stimulation in normal animals mainly involves the refinement of preexisting synaptic networks, whereas pathological ataxic conditions may results from less‐selective but compromising multiple synaptic formation. This study underscores that different types of multiple synapse boutons may have disparate effects on cerebellar synaptic transmission. Multiple‐synapse boutons (MSB) are observed in the cerebellum of both environmentally enriched (EE) and tottering ataxic mutant mice. MSBs from EE mice contact two spines originating from the same dendritic segments, but MSBs from ataxic mutants contact two spines of different dendritic origins.