Neuroscience
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Stains for acetylcholinesterase (AChE) and retrograde labeling with Fluorogold (FG) were used to study olivocochlear neurons and their dendritic patterns in mice. The two methods gave similar results for location and number of somata. The total number of medial olivocochlear (MOC) neurons in the ventral nucleus of the trapezoid body (VNTB) is about 170 per side. ⋯ DPO neurons, however, had more symmetric dendrites that projected into more dorsal parts of the trapezoid body, suggesting that this small group of olivocochlear neurons has very different physiological properties. Dendrites of both types of neurons were somewhat elongated rostrally, about 20% longer than those directed caudally. These results can be interpreted as extensions of dendrites of olivocochlear neurons toward their synaptic inputs: medially to meet crossing fibers from the cochlear nucleus that are part of the MOC reflex pathway, and rostrally to meet descending inputs from higher centers.
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Genes that are highly expressed in the inner ear, as revealed by cDNA microarray analysis, may have a crucial functional role there. Those that are expressed specifically in auditory tissues are likely to be good candidates to screen for genetic alterations in patients with deafness, and several genes have been successfully identified as responsible for hereditary hearing loss. To understand the detailed mechanisms of the hearing loss caused by the mutations in these genes, the present study examined the immunocytochemical localization of the proteins encoded by Crym, KIAA1199 homolog, Uba52, Col9a3, and Col9a1 in the cochlea of rats and mice. ⋯ Uba52 protein was restrictedly localized within the surface of the marginal cells of the stria vascularis. Collagen type IX was found within the tectorial membrane as well as fibrocytes in the spiral ligament. The present results showed cell-specific localization of the encoded proteins of these highly expressed genes, indicating that the coordinated actions of various molecules distributed in different parts of the cochlea are essential for maintenance of auditory processing in the cochlea.
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Dissociated cortical neurons from rat embryos cultured onto micro-electrode arrays exhibit characteristic patterns of electrophysiological activity, ranging from isolated spikes in the first days of development to highly synchronized bursts after 3-4 weeks in vitro. In this work we analyzed these features by considering the approach proposed by the self-organized criticality theory: we found that networks of dissociated cortical neurons also generate spontaneous events of spreading activity, previously observed in cortical slices, in the form of neuronal avalanches. Choosing an appropriate time scale of observation to detect such neuronal avalanches, we studied the dynamics by considering the spontaneous activity during acute recordings in mature cultures and following the development of the network. ⋯ Finally, a computational model of neuronal network was developed in order to interpret the experimental results and understand which parameters (e.g. connectivity, excitability) influence the distribution of avalanches. In summary, cortical neurons preserve their capability to self-organize in an effective network even when dissociated and cultured in vitro. The distribution of avalanche features seems to be critical in those cultures displaying medium synchronization among bursts and poor random spiking activity, as confirmed by chemical manipulation experiments and modeling studies.
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A continuous supply of fusion-competent synaptic vesicles is essential for sustainable neurotransmission. Drosophila mutations of the dicistronic stoned locus disrupt normal vesicle cycling and cause functional deficits in synaptic transmission. Although both Stoned A and B proteins putatively participate in reconstituting synaptic vesicles, their precise function is still unclear. ⋯ Therefore, we conclude that STNB not only functions as an essential component of the endocytic complex for vesicle reconstitution, as previously proposed, but also regulates the competence of recycled vesicles to undergo fusion. In support of such role of STNB, synaptic levels of the vesicular glutamate transporter (vGLUT) and synaptotagmin-1 are strongly reduced with diminishing STNB function, while other synaptic proteins are largely unaffected. We conclude that STNB organizes the endocytic sorting of a subset of integral synaptic vesicle proteins thereby regulating the fusion-competence of the recycled vesicle.
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Both mu- and delta-opioid agonists selectively inhibit nociception but have little effect on other sensory modalities. Voltage-activated Ca(2+) channels in the primary sensory neurons are important for the regulation of nociceptive transmission. In this study, we determined the effect of delta-opioid agonists on voltage-activated Ca(2+) channel currents (I(Ca)) in small-diameter rat dorsal root ganglion (DRG) neurons that do and do not bind isolectin B(4) (IB(4)). ⋯ Additionally, DPDPE significantly inhibited high voltage-activated I(Ca) in Tyrode's or N-methyl-d-glucamine solution but not in tetraethylammonium solution. This study provides new information that delta-opioid agonists have a distinct effect on voltage-activated Ca(2+) channels in different phenotypes of primary sensory neurons. High voltage-activated Ca(2+) channels are more sensitive to inhibition by delta-opioid agonists in IB(4)-negative than IB(4)-positive neurons, and this opioid effect is restricted to DRG neurons devoid of functional T-type Ca(2+) currents.