Contribution of postsynaptic GluD2 to presynaptic R-type Ca(2+) channel function, glutamate release and long-term potentiation at parallel fiber to Purkinje cell synapses.

Glutamate-receptor-like molecule delta2 (GluD2) is selectively expressed on the postsynaptic membranes at parallel fiber to Purkinje cell (PF-PC) synapses in the cerebellum. GluD2 plays critical roles not only in postsynaptic long-term depression but also in the induction of presynaptic differentiation through trans-synaptic interaction with neurexin. However, how GluD2 influences the presynaptic function remains unknown. Here, effects of the deletion of postsynaptic GluD2 on the presynaptic properties were studied focusing on the paired pulse ratio (PPR) of two consecutive EPSC amplitudes, which was larger in GluD2 knockout mice. The PPR difference remained even if saturation of glutamate binding to postsynaptic receptors was suppressed, confirming the presynaptic difference between the genotypes. We then explored the possibility that presynaptic voltage-gated Ca(2+) channels (VGCCs) are affected in GluD2 knockout mice. Application of selective blockers for specific VGCCs indicated that R-type but not P/Q- or N-type VGCC, was affected in the mutant mice. Furthermore, presynaptic long-term potentiation (LTP) at PF-PC synapses, which requires R-type VGCC, was impaired in GluD2 knockout mice. These results suggest that GluD2 deletion impairs presynaptic R-type VGCC, resulting in decreased release of synaptic vesicles, and also in the impairment of presynaptic LTP at PF-PC synapses.

Characteristics of Persistent Symptoms Manifested after SARS-CoV-2 Vaccination: An Observational Retrospective Study in a Specialized Clinic for Vaccination-Related Adverse Events.

Background: Although many adverse reactions after SARS-CoV-2 vaccination have been reported, there have been few comprehensive studies on persistent symptoms after SARS-CoV-2 vaccination. The aim of this study was to determine the clinical characteristics of patients with various persistent symptoms after SARS-CoV-2 vaccination. Methods: A retrospective descriptive study was performed for patients who visited a specialized clinic established at Okayama University Hospital to evaluate adverse events after SARS-CoV-2 vaccination during the period from April 2021 to March 2023. Results: Descriptive analysis was performed for 121 of 127 patients who visited the clinic during the study period, and separate analysis was performed for the other 6 patients who had serious complications, who required treatment with prednisolone, and who had persistent symptoms. The median [interquartile range] age of the patients was 48 years [31-64 years], and the patients included 44 males (36.4%) and 77 females (63.6%). The most frequent symptoms were sensory impairment (34 patients, 28.1%), general fatigue (30 patients, 24.8%), fever/low-grade fever (21 patients, 17.4%), and headache (21 patients, 17.4%). Serious complications included myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), sarcoidosis, aseptic meningitis, neuromyelitis optica spectrum disorders (NMOSDs), tendon adhesions, and idiopathic thrombocytopenia. Conclusions: Although causal relationships were not determined, 15 persistent symptoms after SARS-CoV-2 vaccination were characterized. All of the symptoms had onset from 12 hours to one week after vaccination, with 10 symptoms persisting for 6 months or longer. The most frequent symptom was sensory impairment.

Induction of excitatory and inhibitory presynaptic differentiation by GluD1.

The δ subfamily of ionotropic glutamate receptor subunits consists of GluD1 and GluD2. GluD2, which is selectively expressed in cerebellar Purkinje neurons, has been shown to contribute to the formation of synapses between granule neurons and Purkinje neurons through interaction with Cbln1 (cerebellin precursor protein1) and presynaptic Neurexin. On the other hand, the synaptogenic activity of GluD1, which is expressed not in the cerebellum but in the hippocampus, remains to be characterized. Here, we report that GluD1 expressed in non-neuronal HEK cells, induced presynaptic differentiation of granule neurons through its N-terminal domain in co-cultures with cerebellar neurons, similarly to GluD2. We also show that GluD1 rescued the defect of synapse formation in GluD2-knockout Purkinje neurons, indicating the functional similarity of GluD1 and GluD2. In contrast, GluD1 expression alone did not induce presynaptic differentiation in co-cultures of HEK cells with hippocampal neurons. However, when Cbln1 was exogenously added to the culture medium, GluD1 induced presynaptic differentiation of not only glutamatergic presynaptic terminals but also GABAergic ones. Cbln1 is not expressed in hippocampal neurons but is expressed in entorhinal cortical neurons projecting to the hippocampus. In co-cultures of HEK cells expressing GluD1 and entorhinal cortical neurons, both glutamatergic and GABAergic presynaptic terminals were formed on the HEK cells without exogenous application of Cbln1. These results suggest that GluD1 might contribute to the formation of specific synapses in the hippocampus such as those formed by the projecting neurons of the entorhinal cortex.

A Novel Method to Monitor GABA Loading into Synaptic Vesicles by Combining Patch Pipette Perfusion and Intracellular, Caged-GABA Photolysis in Brain Slice Preparations.

A given concentration of GABA can be introduced into a presynaptic terminal by patch clamping the soma of a presynaptic neuron, if the neuron has a relatively short axon. By combining patch pipette perfusion or intracellular, caged-GABA photolysis, it is possible to measure various parameters related to synaptic vesicle filling with GABA.

Receptor subunit compositions underly distinct potencies of a muscle relaxant in fast and slow muscle fibers.

A line of studies in the 1960s-1980s suggested that muscle relaxants do not work uniformly on all skeletal muscles, though its mechanism has not been clarified. We showed here that a classical non-depolarizing muscle relaxant pancuronium inhibits fast muscle fibers at lower concentration compared to slow muscle fibers in zebrafish. The difference of effective concentration was observed in locomotion caused by tactile stimulation as well as in synaptic currents of the neuromuscular junction induced by motor neuron excitation. We further showed that this difference arises from the different composition of acetylcholine receptors between slow and fast muscle fibers in the neuromuscular junction of zebrafish. It will be interesting to examine the difference of subunit composition and sensitivity to muscle relaxants in other species.

Gender-Dependent Characteristics of Serum 1,25-Dihydroxyvitamin D/25-Hydroxyvitamin D Ratio for the Assessment of Bone Metabolism.

Objectives Vitamin D deficiency, which is common worldwide, increases the risks of falls and fractures and can lead to increased morbidity and mortality. However, the clinical utility and relevance of vitamin D activation remain unknown. The aim of the present study was to clarify the clinical usefulness of serum 1,25-dihydroxyvitamin D (1,25D)/25-hydroxyvitamin D (25D) ratio for assessment of the extent of bone metabolism. Methods We retrospectively screened data for 87 patients whose serum 1,25D and 25D levels were measured. Eight patients who were taking vitamin D preparations were excluded, and data for 79 patients (33 males and 46 females) were analyzed. Since menopausal status can be associated with serum vitamin D level, we divided the patients by gender and divided the female patients into two groups at the age of 50 years. Results The median serum 1,25D/25D ratio was significantly lower in males than in females, with the most considerable difference in all males [4.1 (interquartile range: 2.3-5.8) × 10-3] versus elderly females (aged ≧50 years) [7.9 (3.3-10.1) × 10-3). Main disorders were endocrine (30.6%), inflammatory (18.5%), and bone-related (16.7%) disorders. The ratios of serum 1,25D/25D had significant negative correlations with femoral dual-energy X-ray absorptiometry % young adult mean (DEXA %YAM) (R=-0.35) and lumbar DEXA %YAM (R=-0.32). Significant correlations were found between the 1,25D/25D ratio and serum levels of inorganic phosphate (iP), parathyroid hormone, and alkaline phosphatase (ALP). The 1,25D/25D ratio had gender-specific characteristics: the ratio was significantly correlated with age in males (R=-0.49), while it was significantly correlated with BMI in females (R=0.34). Conclusions The results of this study suggested that vitamin D activity is negatively correlated with bone mineral density, being reduced in aged males but enhanced in obese females.

Vesicular GABA Uptake Can Be Rate Limiting for Recovery of IPSCs from Synaptic Depression.

Synaptic efficacy plays crucial roles in neuronal circuit operation and synaptic plasticity. Presynaptic determinants of synaptic efficacy are neurotransmitter content in synaptic vesicles and the number of vesicles undergoing exocytosis at a time. Bursts of presynaptic firings depress synaptic efficacy, mainly due to depletion of releasable vesicles, whereas recovery from strong depression is initiated by endocytic vesicle retrieval followed by refilling of vesicles with neurotransmitter. We washed out presynaptic cytosolic GABA to induce a rundown of IPSCs at cerebellar inhibitory cell pairs in slices from rats and then allowed fast recovery by elevating GABA concentration using photo-uncaging. The time course of this recovery coincided with that of IPSCs from activity-dependent depression induced by a train of high-frequency stimulation. We conclude that vesicular GABA uptake can be a limiting step for the recovery of inhibitory neurotransmission from synaptic depression.

Enhancement of both long-term depression induction and optokinetic response adaptation in mice lacking delphilin.

In the cerebellum, Delphilin is expressed selectively in Purkinje cells (PCs) and is localized exclusively at parallel fiber (PF) synapses, where it interacts with glutamate receptor (GluR) delta2 that is essential for long-term depression (LTD), motor learning and cerebellar wiring. Delphilin ablation exerted little effect on the synaptic localization of GluRdelta2. There were no detectable abnormalities in cerebellar histology, PC cytology and PC synapse formation in contrast to GluRdelta2 mutant mice. However, LTD induction was facilitated at PF-PC synapses in Delphilin mutant mice. Intracellular Ca(2+) required for the induction of LTD appeared to be reduced in the mutant mice, while Ca(2+) influx through voltage-gated Ca(2+) channels and metabotropic GluR1-mediated slow synaptic response were similar between wild-type and mutant mice. We further showed that the gain-increase adaptation of the optokinetic response (OKR) was enhanced in the mutant mice. These findings are compatible with the idea that LTD induction at PF-PC synapses is a crucial rate-limiting step in OKR gain-increase adaptation, a simple form of motor learning. As exemplified in this study, enhancing synaptic plasticity at a specific synaptic site of a neural network is a useful approach to understanding the roles of multiple plasticity mechanisms at various cerebellar synapses in motor control and learning.