Neuroscience
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Studies of major depressive disorder (MDD) in postmortem brain tissue report enhanced binding to inhibitory serotonin-1A autoreceptors in midbrain dorsal raphe and reductions in length of axons expressing the serotonin transporter (SERT) in dorsolateral prefrontal cortex. The length density of axons expressing SERT in the orbitofrontal cortex (OFC) was determined in 18 subjects with MDD and 17 age-matched control subjects. A monoclonal antibody was used to immunohistochemically label the SERT in fixed sections of OFC. ⋯ Neither gender, tissue pH, postmortem interval, 5-HTTLPR genotype, time in fixative, nor death by suicide had a significant effect on axon length. The age-related decrease in SERT-ir axon length in MDD may reflect pathology of ascending axons passing through deep white matter hyperintensities. Greater length of axons expressing SERT in younger subjects with MDD may result in a significant deficit in serotonin availability in OFC.
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The superior temporal gyrus (STG) is involved in speech recognition against informational masking under cocktail-party-listening conditions. Compared to healthy listeners, people with schizophrenia perform worse in speech recognition under informational speech-on-speech masking conditions. It is not clear whether the schizophrenia-related vulnerability to informational masking is associated with certain changes in FC of the STG with some critical brain regions. ⋯ The results showed that in healthy participants, but not participants with schizophrenia, the contrast of either the PSS or PSC condition against the masker-only condition induced an enhancement of functional connectivity (FC) of the STG with the left superior parietal lobule and the right precuneus. Compared to healthy participants, participants with schizophrenia showed declined FC of the STG with the bilateral precuneus, right SPL, and right supplementary motor area. Thus, FC of the STG with the parietal areas is normally involved in speech listening against informational masking under either the PSS or PSC conditions, and declined FC of the STG in people with schizophrenia with the parietal areas may be associated with the increased vulnerability to informational masking.
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The plasticity of nervous systems allows animals to quickly adapt to a changing environment. In particular, seasonal plasticity of brain structure and behavior is often critical to survival or mating in seasonal climates. Songbirds provide striking examples of seasonal changes in neural circuits and vocal behavior and have emerged as a leading model for adult brain plasticity. ⋯ On the contrary, lesions did not affect singing behavior during the breeding season. Our results therefore indicate that the BG-forebrain pathway introduces acoustic and syntactic variability in song when canaries resume singing in early fall. We propose that BG-forebrain circuits actively participate in seasonal plasticity by injecting variability in behavior during non-breeding season.
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Prolonged low-level noise exposure alters loudness perception in humans, presumably by decreasing the gain of the central auditory system. Here we test the central gain hypothesis by measuring the acute and chronic physiologic changes at the level of the cochlea and inferior colliculus (IC) after a 75-dB SPL, 10-20-kHz noise exposure for 5weeks. The compound action potential (CAP) and summating potential (SP) were used to assess the functional status of the cochlea and 16 channel electrodes were used to measure the local field potentials (LFP) and multi-unit spike discharge rates (SDR) from the IC immediately after and one-week post-exposure. ⋯ Surprisingly, one-week post-exposure supra-threshold responses from the cochlea had not only recovered, but were significantly larger than normal, and thresholds were significantly better than controls. Moreover, sound-evoked hyperactivity in the IC was sustained within the noise exposure frequency band but suppressed at higher frequencies. When response amplitudes representing the neural output of the cochlea and IC activity at one-week post exposure were compared with control animal responses, a central attenuation phenomenon becomes evident, which may play a key role in understanding why low-level noise can sometimes ameliorate tinnitus and hyperacusis percepts.
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Aquaporin-4 (AQP4) is the predominant water channel in mammalian CNS where it is localized at the perivascular astrocytic foot processes abutting brain microvessels. Several lines of evidence suggest that AQP4 is involved in important homeostatic functions and that mislocalization of the perivascular pool of AQP4 is implicated in several different brain disorders. A recent study suggests that the differential susceptibility of midbrain dopaminergic neurons to the parkinsonogenic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) depends on the expression of AQP4. ⋯ Treatment with MPTP further increased (by >30%) the perivascular AQP4 density in SN, but also increased AQP4 labeling in the neocortex. Our data indicate that the perivascular AQP4 pool in SN is high in normal animals and even higher after treatment with MPTP. This would leave the SN more prone to water accumulation and supports the idea that AQP4 could be involved in the pathogenesis of PD.