Excitatory and inhibitory receptors utilize distinct post- and trans-synaptic mechanisms in vivo

Preferential Localization of STIM1 to dendritic subsurface ER structures in Mouse Purkinje Cells

The endoplasmic reticulum (ER) is the largest intracellular Ca2+ store, serving as the source and sink of intracellular Ca2+ The ER Ca2+ store is continuous yet organized into distinct subcompartments with spatial and functional heterogeneity. In cerebellar Purkinje cells (PCs), glutamatergic inputs trigger Ca2+ release from specific ER domains via inositol 1,4,5-trisphosphate receptors (IP3Rs) or ryanodine receptors (RyRs). Upon ER store depletion, refilling occurs through store-operated Ca2+ entry mediated by stromal interaction molecule-1 (STIM1). Although the significance of STIM1-mediated Ca2+ regulation within PCs is established, STIM1 localization in ER subcompartments in PCs for Ca2+ release and refilling remains elusive. Using validated antibodies, we demonstrated that STIM1 was predominantly localized as intense puncta along dendritic shafts in male and female mice, colocalizing with IP3R1 but not with RyR1. Immunoelectron microscopy revealed that STIM1 was accumulated in the subsurface ER in the dendritic shaft but excluded from those in the dendritic spine, the primary site of metabotropic glutamate receptor 1 (mGluR1)-IP3R-mediated Ca²⁺ signaling. Ca²⁺ imaging from control and STIM1-knockdown (STIM1-KD) PCs demonstrated that mGluR1-mediated Ca²⁺ release is more critically dependent on STIM1 than RyR-mediated Ca²⁺ release. These findings reveal a spatially organized ER network in PCs, where specialized ER subcompartments differentially regulate Ca²⁺ release and refilling. These findings suggest that STIM1 preferentially regulates Ca²⁺ dynamics associated with mGluR1-IP3R signaling, supporting specialized ER subcompartments for Ca²⁺ release and refilling. These findings highlight the intricate molecular-anatomical organization of dendritic ER Ca2+ signaling in PCs, which is crucial for synaptic plasticity and motor learning.Significance statement Intracellular calcium (Ca²⁺) signaling is essential for neuronal function, yet the organization of endoplasmic reticulum (ER) subcompartments that coordinate Ca²⁺ release and refilling remains unclear. This study demonstrates that stromal interaction molecule-1 (STIM1), a key regulator of store-operated Ca²⁺ entry, is predominantly localized to the subsurface ER in Purkinje cell dendrites, which had not been previously identified. STIM1 colocalizes with inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) and sarco/endoplasmic reticulum Ca²⁺-ATPase 2 (SERCA2) but is segregated from ryanodine receptor 1 (RyR1), highlighting specialized ER subdomains for Ca²⁺ release and refilling. These findings provide new insights into the molecular-anatomical organization of Ca²⁺ signaling in Purkinje cells, which plays key roles in synaptic plasticity, motor learning, and the pathophysiology of neurodegenerative diseases.

Loss of Elp1 in cerebellar granule cell progenitors models ataxia phenotype of Familial Dysautonomia

Familial Dysautonomia (FD) is an autosomal recessive disorder caused by a splice site mutation in the gene ELP1, which disproportionally affects neurons. While classically characterized by deficits in sensory and autonomic neurons, neuronal defects in the central nervous system have also been described. Although ELP1 expression remains high in the normal developing and adult cerebellum, its role in cerebellar development is unknown. To explore the role of Elp1 in the cerebellum, we knocked out Elp1 in cerebellar granule cell progenitors (GCPs) and examined the outcome on animal behavior and cellular composition. We found that GCP-specific conditional knockout of Elp1 (Elp1cKO) resulted in ataxia by 8 weeks of age. Cellular characterization showed that the animals had smaller cerebella with fewer granule cells. This defect was already apparent as early as 7 days after birth, when Elp1cKO animals also had fewer mitotic GCPs and shorter Purkinje dendrites. Through molecular characterization, we found that loss of Elp1 was associated with an increase in apoptotic cell death and cell stress pathways in GCPs. Our study demonstrates the importance of ELP1 in the developing cerebellum, and suggests that loss of Elp1 in the GC lineage may also play a role in the progressive ataxia phenotypes of FD patients.

Immunohistochemical Analysis of the Drosophila Larval Neuromuscular Junction

Synapses are specialized junctions between cells that mediate neurotransmission to modify brain activity and body function. Studies on synapse structure and function play an important role in understanding how neurons communicate and the consequences of their dysfunction in neurological disorders. The Drosophila larval neuromuscular junction is an excellent model for dissecting the cellular and molecular mechanisms of the synapse, with its large size, accessibility, and well-characterized genetics. This protocol describes the steps required for morphological and immunohistochemical analysis of the Drosophila larval neuromuscular junction including its dissection and multiplex labeling of synaptic proteins. This technique can be used to assess the impact of genetic manipulations on synaptic development, integrity, and plasticity, thus providing a valuable tool for probing complex neurological processes in a whole animal system.

Structure, function, and pathology of Neurexin-3

Neurexin-3 is primarily localized in the presynaptic membrane and forms complexes with various ligands located in the postsynaptic membrane. Neurexin-3 has important roles in synapse development and synapse functions. Neurexin-3 mediates excitatory presynaptic differentiation by interacting with leucine-rich-repeat transmembrane neuronal proteins. Meanwhile, neurexin-3 modulates the expression of presynaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors and γ-aminobutyric acid A receptors by interacting with neuroligins at excitatory and inhibitory synapses. Numerous studies have documented the potential contribution of neurexin-3 to neurodegenerative and neuropsychiatric disorders, such as Alzheimer's disease, addiction behaviors, and other diseases, which raises hopes that understanding the mechanisms of neurexin-3 may hold the key to developing new strategies for related illnesses. This review comprehensively covers the literature to provide current knowledge of the structure, function, and clinical role of neurexin-3.

Cerebellar granule cell signaling is indispensable for normal motor performance

Within the cerebellar cortex, mossy fibers (MFs) excite granule cells (GCs) that excite Purkinje cells (PCs), which provide outputs to the deep cerebellar nuclei (DCNs). It is well established that PC disruption produces motor deficits such as ataxia. This could arise from either decreases in ongoing PC-DCN inhibition, increases in the variability of PC firing, or disruption of the flow of MF-evoked signals. Remarkably, it is not known whether GCs are essential for normal motor function. Here we address this issue by selectively eliminating calcium channels that mediate transmission (CaV2.1, CaV2.2, and CaV2.3) in a combinatorial manner. We observe profound motor deficits but only when all CaV2 channels are eliminated. In these mice, the baseline rate and variability of PC firing are unaltered, and locomotion-dependent increases in PC firing are eliminated. We conclude that GCs are indispensable for normal motor performance and that disruption of MF-induced signals impairs motor performance.

Modulation of Trans-Synaptic Neurexin-Neuroligin Interaction in Pathological Pain

Synapses serve as the interface for the transmission of information between neurons in the central nervous system. The structural and functional characteristics of synapses are highly dynamic, exhibiting extensive plasticity that is shaped by neural activity and regulated primarily by trans-synaptic cell-adhesion molecules (CAMs). Prototypical trans-synaptic CAMs, such as neurexins (Nrxs) and neuroligins (Nlgs), directly regulate the assembly of presynaptic and postsynaptic molecules, including synaptic vesicles, active zone proteins, and receptors. Therefore, the trans-synaptic adhesion mechanisms mediated by Nrx-Nlg interaction can contribute to a range of synaptopathies in the context of pathological pain and other neurological disorders. The present review provides an overview of the current understanding of the roles of Nrx-Nlg interaction in the regulation of trans-synaptic connections, with a specific focus on Nrx and Nlg structures, the dynamic shaping of synaptic function, and the dysregulation of Nrx-Nlg in pathological pain. Additionally, we discuss a range of proteins capable of modulating Nrx-Nlg interactions at the synaptic cleft, with the objective of providing a foundation to guide the future development of novel therapeutic agents for managing pathological pain.