Neuroscience
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Niches are specialized microenvironments that regulate stem cells' activity. The neural stem cell (NSC) niche defines a zone in which NSCs are retained and produce new cells of the nervous system throughout life. ⋯ Strikingly, depletion of APP increased NSC proliferation in the subventricular zone, indicating that endothelial cells negatively regulate NSCs' growth. The emerging knowledge from this research will be important for the treatment of several neurological diseases.
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Behavioral effects of transcranial magnetic stimulation (TMS) have been shown to depend on various factors, such as neural activation state, stimulation intensity, and timing of stimulation. Here we examined whether these factors interact, by applying TMS at either sub- or suprathreshold intensity (relative to phosphene threshold, PT) and at different time points during a state-dependent TMS paradigm. The state manipulation involved a behavioral task in which a visual prime (color grating) was followed by a target stimulus which could be either congruent, incongruent or partially congruent with the color and orientation of the prime. ⋯ Only TMS applied at suprathreshold intensity facilitated the detection of incongruent stimuli, with no effect with subthreshold stimulation. The need for higher stimulation intensity is likely to reflect reduced susceptibility to TMS of neurons responding to visual stimulation. Furthermore, the finding that in Experiment 2 only suprathreshold TMS induced a behavioral facilitation on incongruent targets (whereas facilitations in the absence of priming have been reported with subthreshold TMS) indicates that priming, by reducing neural excitability to incongruent targets, shifts the facilitatory/inhibitory range of TMS effects.
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Ectopic transgene expression in the retina has been reported in various transgenic mice, indicating the importance of characterizing retinal phenotypes. We examined transgene expression in the VGAT-ChR2-EYFP mouse retina by fluorescent immunohistochemistry and electrophysiology, with special emphasis on enhanced yellow fluorescent protein (EYFP) localization in retinal neuronal subtypes identified by specific markers. Strong EYFP signals were detected in both the inner and outer plexiform layers. ⋯ In contrast, no EYFP signal was detected in the somata of retinal excitatory neurons: photoreceptors, bipolar and ganglion cells, as well as Müller glial cells. When glutamatergic transmission was blocked, bright blue light stimulation elicited inward photocurrents from amacrine cells, as well as post-synaptic inhibitory currents from ganglion cells, suggesting a functional ChR2 expression. The VGAT-ChR2-EYFP mouse therefore could be a useful animal model for dissecting retinal microcircuits when targeted labeling and/or optogenetic manipulation of retinal inhibitory neurons are required.
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The brain oscillations may play a critical role in synchronizing neuronal assemblies in order to establish appropriate sensory-motor integration. In fact, studies have demonstrated phase-amplitude coupling of distinct oscillatory rhythms during cognitive processes. Here we investigated whether olfacto-hippocampal coupling occurs when mice are detecting familiar odors located in a spatially restricted area of a new context. ⋯ Furthermore, mice were able to discriminate odors from a different cage and avoided the quadrant with predator odor 2,4,5-trimethylthiazoline (TMT), reinforcing the specificity of the SOT. The local field potential (LFP) analysis of non-lesioned mice revealed higher gamma activity (35-100Hz) in the main olfactory bulb (MOB) and a significant theta phase/gamma amplitude coupling between MOB and dorsal hippocampus, only during exploration of home-cage odors (i.e. in the target quadrant). Our results suggest that exploration of familiar odors in a new context involves dynamic coupling between the olfactory bulb and dorsal hippocampus.