Neuroscience
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The apical dendrite of hippocampal CA1 pyramidal cells receives information from the entorhinal cortex via the dentate gyrus and CA3 (Schaffer-collateral (SC) input) proximally within the stratum radiatum (SR) and directly from the entorhinal cortex/thalamus distally within the stratum lacunosum-moleculare (SLM). During the early postnatal development, very low/low frequency (0.033-1Hz) activation of previously non-stimulated (naïve) SC synapses (SR-CA1 synapses) results in a stimulus-, but not frequency-, dependent depression which is explained by postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) silencing. This lability of AMPA signaling has been suggested to play a role in the activity-dependent organization of the SR synaptic input. ⋯ The SLM-CA1 synapses did also exhibit less long-term depression than the SR-CA1 synapses. We conclude that in the developing hippocampus the labile glutamate signaling onto CA1 pyramidal cell depends mechanistically on input pathway. The labile AMPA signaling at SLM-CA1 synapses is most likely explained by a presynaptic mechanism with limited amount of postsynaptic AMPA silencing.
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Attentional deficits including difficulty in switching attention between tasks or rules, sustaining attention, and selectively attending to specific stimuli are commonly seen in patients with Parkinson's disease (PD). While these deficits are frequently reported, it is unclear how traditional dopamine replacement therapy such as l-dopa affects these deficits. In a rat model of PD in which dopamine is unilaterally depleted with a 6-hydroxydopamine infusion to the medial forebrain bundle, we first examined the impact of acute and chronic l-dopa treatment on attention switching as modeled by disengagement behavior (i.e. the ability to disengage from an on-going behavior such as eating or drinking to attend to perioral stimulation). ⋯ Our data suggest that the l-dopa dose necessary to recover motor function can successfully restore attention switching behavior (i.e. disengagement behavior), but further worsens performance in the selective and sustained attention task. Furthermore, this same dose was responsible for inducing dyskinesias in rats given chronic daily injections. Taken together, these findings demonstrate that dopamine replacement therapy may not be sufficient for treating all types of attentional dysfunction occurring in PD.
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Unexpected presentation of a startling auditory stimulus (SAS>120 decibels) in a reaction time (RT) paradigm results in the startle reflex and an early release (<100ms) of the preplanned motor response (StartReact effect). Mechanical perturbations applied to the upper limbs elicit short- (M1) and long-latency (M2) stretch reflexes and have also been shown to initiate intended motor responses early (<100ms). Ravichandran et al. (2013) recently proposed that unexpected delivery of a perturbation could also elicit a startle response and therefore the StartReact effect may be responsible for the early trigger of a preplanned response. ⋯ On unexpected trials we probed startle circuitry with a large perturbation or SAS. The SAS consistently elicited a startle response in both ACT and DNI conditions, but startle-like activity was only observed on 17.4% of ACT perturbation probe trials. Our findings suggest that while unexpected upper limb perturbations can be startling, startle triggering of the preplanned voluntary response is not the primary mechanism responsible for goal-dependent modulation of the M2 response.
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Neuroglobin (Ngb) is a respiratory protein that is almost exclusively expressed in the vertebrate nervous system. Despite many years of research, the exact function and even the expression sites of Ngb are still a matter of debate. However, to investigate hypotheses surrounding the potential roles of Ngb, a detailed knowledge of its major and minor expression sites is indispensable. ⋯ Thus, Ngb mRNA is expressed at a basal level in many mammalian brain regions, but shows distinctive regional peaks. RNA-Seq analysis further revealed only low levels of Ngb mRNA in retina and testes and no signal in standard tumor cell lines, thus raising questions concerning previous studies and functional hypotheses. In conclusion, this broad-scale expression study may point to distinct Ngb functions for high- and low-expressing cells and tissues and argues against a single, generic role of Ngb as an oxygen supplier or as an endogenous protectant in all nerve cells.
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Diffusion tensor imaging (DTI) provides a unique contrast based on the restricted directionality of water movement in an anisotropic environment. As such, DTI-based tractography can be used to characterize and quantify the structural connectivity within neural tissue. Here, DTI-based connectivity within isolated abdominal ganglia of Aplysia californica (ABG) is analyzed using network theory. ⋯ Both small-worldness and novel small-world metrics were used as tools to verify the small-world properties for the experimental results. The aim of this manuscript is to categorize the properties exhibited by structural networks in a model neural tissue to derive unique mean field information that quantitatively describe macroscopic connectivity. For ABG, findings demonstrate a default structural network with preferential specific small-world properties when compared to simulated lattice and random networks that are equivalent in order and degree.