Neuroscience
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Diphtheria toxin (DT) administration into transgenic mice that express the DT receptor (DTR) under control of specific promoters is often used for cell ablation studies in vivo. Because DTR is not expressed in mice, DT injection has been assumed to be nontoxic to cells in vivo. In this study, we demonstrated that DT application during the juvenile stage leads to hearing loss in wild-type mice. ⋯ Histological studies demonstrated that hearing loss was accompanied by significant degeneration of inner and outer hair cells (HCs), as well as spiral ganglion neurons. Scanning electron microscopy showed quick degeneration of inner HCs within 3days and gradual degeneration of outer HCs within 1week. These results demonstrated that DT has ototoxic action on C57BL/6 mice during the juvenile period, but not thereafter, and the hearing loss was due to degeneration of inner and outer HCs by unknown DT-related mechanisms.
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Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain and plays an important role in regulating neuronal excitability. GABA reuptake from the synapse is dependent on specific transporters - mainly GAT-1, GAT-3 and BGT-1 (GATs). This study is the first to show alterations in the expression of the GATs in the Alzheimer's disease (AD) hippocampus, entorhinal cortex and superior temporal gyrus. ⋯ In AD there was a significant decrease in GAT-1 expression in the entorhinal cortex and superior temporal gyrus. We also found a significant decrease in GAT-3 immunoreactivity in the stratum pyramidale of the CA1 and CA3, the subiculum and entorhinal cortex. These observations indicate that the expression of the GATs shows brain-region- and layer-specific alterations in AD, suggesting a complex activation pattern of different GATs during the course of the disease.
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The prefrontal cortex and the amygdala are critical for the emotional guidance of behavior and are believed to be a site of action for many anxiolytics and anxiogenics. Despite extensive studies examining how these drugs affect behavior, there is little information regarding their effects on neuronal activity. Additionally, with recent recognition of anxiety as a non-motor symptom of Parkinson's disease, it is unknown if activity in the cortex and the amygdala is altered. ⋯ On the other hand, yohimbine treatment (5mg/kg, SubQ) coincided with lower neuronal spiking activity compared to controls in the BLA of sham-lesioned rats, but was unchanged from controls in hemiparkinsonian rats. Yohimbine did not affect ACC neuronal spiking activity in either group. Overall, the lack of ACC responsiveness to diazepam in hemiparkinsonian, but not sham-lesioned rats underscores a plausible fundamental difference in anxiety-related neural signaling between animal groups.
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Sodium-activated potassium (KNa) channels contribute to firing frequency adaptation and slow after hyperpolarization. The KCNT1 gene (also known as SLACK) encodes a KNa subunit that is expressed throughout the central and peripheral nervous systems. Missense mutations of the SLACK C-terminus have been reported in several patients with rare forms of early onset epilepsy and in some cases severely delayed myelination. ⋯ Loxapine exhibited no effect, indicating that this mutation either caused the channel to be insensitive to this established opener or proper translation and trafficking to the membrane was disrupted. Protein analysis confirmed that while total mutant protein did not differ from wild type, membrane expression of the mutant channel was substantially reduced. Although gain-of-function mutations to the Slack channel are linked to epileptic phenotypes, this is the first reported loss-of-function mutation linked to severe epilepsy and delayed myelination.
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The stimuli that commonly activate the catecholaminergic C1 neurons (nociception, hypotension, and hypoxia) also increase breathing. Pharmacogenetic evidence suggests that catecholaminergic neurons regulate breathing. Therefore, we evaluated whether the loss of C1 cells affects cardiorespiratory control during resting, hypoxic (8% O2) and hypercapnic (7% CO2) conditions. ⋯ Bilateral depletion of C1 neurons did not alter cardiorespiratory variables during rest and hypercapnia (7% CO2), but it did affect the response to hypoxia. Specifically, the increase in ventilation, the number of sighs, and the tachycardia were reduced, but unexpectedly, the mean arterial pressure increased during hypoxia (8% O2). The present study indicates that C1 neurons contribute to cardiorespiratory control during hypoxia rather than at rest or during hypercapnia.