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Editorial for This Special Issue "Synaptic Transmission: From Molecular to Neural Network Levels"
No full textWe invited contributions reporting new evidence of synaptic mechanisms and their network-level impacts for this Special Issue. The six research articles published in this collection, from 33 authors, cover many aspects of synaptic function and plasticity, from single-cell mechanisms to neuronal network properties. These papers elucidate the physiological and pathological conditions underlying synaptic transmission, giving new perspectives for future applications and therapies
Expression and localization of ryanodine receptors in the frog semicircular canal.
Full text linkSeveral experiments suggest an important role for store-released Ca2+ in hair cell organs: drugs targeting IP3 and ryanodine (RyRs) receptors affect release from hair cells, and stores are thought to be involved in vesicle recycling at ribbon synapses. In this work we investigated the semicircular canal distribution of RyRs by immunofluorescence, using slice preparations of the sensory epithelium (to distinguish cell types) and flat mounts of the simpler nonsensory regions. RyRs were present in hair cells, mostly in supranuclear spots, but not in supporting cells; as regards nonsensory regions, they were also localized in dark cells and cells from the ductus. No labeling was found in nerve terminals, although nerve branches could be observed in proximity to hair cell RyR spots. The differential expression of RyR isoforms was studied by RT-PCR and immunoblotting, showing the presence of RyRα in both ampulla and canal arm and RyRβ in the ampulla only
Guanidine transport across the apical and basolateral membranes of human intestinal Caco-2 cells is mediated by two different mechanisms
No full textThe functional characteristics of the intestinal absorption and secretion of guanidine as a model
of a nutritionally and metabolically essential organic cation were examined in the Caco-2 human intestinal cell
line. Both apical and basolateral transport of [14C]-guanidine were studied using Caco-2 cells grown on polycarbonate
permeable membranes. The basolateral-to-apical flux of [14C]-guanidine (i.e., its secretion) was quantitatively
higher than the apical-to-basolateral transport (i.e., its absorption). When Na was replaced by K or Li,
both apical and basolateral accumulation were significantly inhibited. Studies using the cell monolayers and apical
membrane vesicles obtained from Caco-2 cells showed a potential-independent mechanism of guanidine apical
uptake and efflux. Conversely, basolateral uptake and efflux were membrane potential dependent. Kinetic analysis
revealed that both saturable and nonsaturable mechanisms accounted for the apical and basolateral accumulations.
The [14C]-guanidine efflux from cells through the apical and basolateral membranes was significantly
reduced at 4°C, suggesting carrier-mediated mechanisms. Moreover, the apical efflux was stimulated by an
inwardly directed H gradient. Influx and efflux of [14C]-guanidine were unaffected by the presence of tetraethylammonium,
cimetidine or decynium-22 in the donor compartment. Only quinine significantly reduced [14C]-
guanidine entrance through apical and basolateral membranes and its exit through the basolateral membrane. In
conclusion, our results suggest that the influx and the efflux through the apical membrane is mediated by different
transporters, whereas transport across the basolateral membrane is mediated by a member of the organic cation
transporter family with high affinity for guanidine
Theta-patterned tactile stimulation modifies deep cerebellar nuclei neurons responsiveness in vivo
No full textSeveral forms of synaptic plasticity have been described in the cerebellar network in vitro, but how plasticity may be induced in vivo remains poorly explored. Sensory tactile stimuli organized in theta patterns have been reported to induce long-term changes in cerebellar granule cells (Roggeri et al., 2008), Purkinje cells and molecular layer interneurons (Ramakrishnan et al., 2016) in vivo. Deep cerebellar nuclei (DCN) neurons are known to respond to low frequency sensory stimulation through typical discharge patterns reflecting the inhibitory and excitatory inputs converging onto these nuclei, provided by Purkinje cells and mossy fibers respectively (Rowland and Jaeger, 2008). Nevertheless, whether and how DCN are able to modify their discharges following theta-patterned sensory stimulation remains unexplored. Herein, we addressed this issue performing single-unit recordings in vivo, from the medial nucleus of anesthetized mice. Our results provide the first evidence that DCN neurons are indeed able to modify their discharge properties following sensory stimulation in vivo, completing the picture of the theta sensory stimulation (TSS) impact on cerebellar neurons discharge in viv
Aquaporin-6 expression in rat gastrointestinal tract is upregulated by feeding
No full textBackground: Some aquaporins have been identified and partially
characterized in the gastrointestinal tract suggesting their
involvement in fluid and small solutes movements. Here we
studied the presence and localization of aquaporin-6 in some
regions of the rat gastrointestinal tract, given its peculiar function
as an ion selective channel.
Materials and methods: The aquaporin-6 expression along the
gastrointestinal tract was investigated by RT-PCR and immunoblotting,
while its localization by in situ hybridization and
immunohistochemistry. The effect of feeding on the aquaporin-
6 mRNA expression was investigated by quantitative real
time RT-PCR.
Results: RT-PCR and immunoblotting experiments showed
that aquaporin-6 was expressed in all the investigated portions
of the rat gastrointestinal tract. Immunoblotting analysis of
brush border membrane vesicle preparations showed an intense
signal for aquaporin-6 protein. The results of in situ hybridization
experiments demonstrate that aquaporin-6 transcript is
present in the isthmus, neck and basal regions of the stomach
lining, and throughout the crypt-villus axis in both small and
large intestine. In the latter regions, immunohistochemistry
revealed strong aquaporin-6 labelling in the apical membrane of
the surface epithelial cells, while weak or no labelling was
observed in the crypt cells. In the stomach, an intense staining
was observed in mucous neck cells and lower signal in principal
cells and some parietal cells. In addition, jejunal mRNA expression
was specifically stimulated by feeding.
Conclusions: This study provides evidence for the aquaporin-
6 distribution throughout the gastrointestinal tract. Aquaporin-
6 localization at the apical membranes of the superficial epithelial
cells and its upregulation by feeding in the small intestine
suggest its direct involvement in the absorption of water and
anions
Histamine type 3 receptor expression in mouse Scarpa's ganglia
No full textOBJECTIVE: Histamine-related drugs such as betahistine are commonly used in the treatment of vertigo and related vestibular disorders. Their site and mechanism of action however deserve further investigation. We recently showed that the frog and mouse semicircular canal sensory epithelia, but not the vestibular (Scarpa’s) ganglia, express H1 histamine receptor subtype (Botta et al. 2008). Since it has been reported in the axolotl that H3 antagonists may act at the primary vestibular nerve afferents (Chavez et al. 2005), we have investigated the expression of H3 histamine receptor (H3R) subtype in the mouse vestibular ganglion.
METHODS: H3 receptor mRNA expression was investigated by RT-PCR. For each of three total RNA extractions the vestibular ganglia were isolated from ~ 50 Swiss CD1 mice, and subsequent cDNA amplification was performed by using specific primers for H3 receptors designed in accordance with the published sequence. H3R location in the tissue was investigated by immunolabelling, using anti-H3R antibodies (Alpha Diagnostic International) on cryostat slices of the Scarpa’s ganglia and on paraffin embedded sections of the whole labyrinth (section thickness: 10 mm).
RESULTS: RT-PCR experiments showed a band of 407 bp corresponding to H3R in the Scarpa’s ganglia. The immunolabelling study showed a clear signal for H3R in a subpopulation of Scarpa’s ganglia neurons, characterized by a large and roundish soma. Conversely, no clear staining for H3R was found in the vestibular sensory epithelia (cristae and maculae).
CONCLUSIONS: This study shows that a subpopulation of mouse vestibular ganglia neurons express the histamine H3 receptor subtype, thus providing a molecular substrate for the postsynaptic action of histamine-related drugs reported in the literature
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