Neuroscience
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Comparative Study
Afferent regulation of cytochrome-c and active caspase-9 in the avian cochlear nucleus.
During development, a subpopulation (approximately 30%) of neurons in the avian cochlear nucleus, nucleus magnocellularis (NM), dies following removal of the cochlea. It is clear that neuronal activity coming from the auditory nerve provides trophic support critical for cell survival in the NM. Several aspects of the intracellular signaling cascades that regulate apoptosis have been defined for naturally occurring, or programmed cell death, in neurons. ⋯ In addition, immunoreactivity for downstream active caspase-9 did increase following cochlea ablation. This increase was observed within 3 h following cochlea removal, but was not observed 4 days following surgery, a time point after the dying population of NM neurons have already degenerated. Together, these findings suggest that deafferentation of NM neurons results in caspase activation, but this activation may be cytochrome-c independent.
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Comparative Study
Neuronal activity regulates GABAA receptor subunit expression in organotypic hippocampal slice cultures.
The postnatal expression of GABA(A) receptor subunit mRNAs in the rat brain, including the hippocampus, exhibits a unique temporal and regional developmental profile in vivo, which may be altered by external stimuli. Using the in situ hybridization technique we have now studied the in vitro expression of alpha1,alpha2, alpha 4, alpha 5, beta 1, beta 3, gamma 2, and gamma 3 subunit mRNAs of GABA(A) receptors in organotypic hippocampal slices cultured for 7 days. To find out whether neuronal activity regulates the subunit expression, a subset of cultures was chronically treated either with a GABA(A) receptor antagonist picrotoxin, or by a non-N-methyl-D-aspartate (non-NMDA)-receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). ⋯ In picrotoxin-treated cultures, the expression of alpha1, alpha 5 and gamma 2 mRNAs was significantly increased in pyramidal cell layers, and in DNQX-treated cultures the expression of alpha2 mRNA in CA3c and DG, and that of beta1 in DG. Changes in the expression of GABA(A) receptor subunit mRNAs in treated cultures suggest that neuronal activity can regulate their regional expression in vitro. Since the expression profile in untreated control cultures closely resembled that observed earlier in vivo, organotypic hippocampal slice cultures could serve as a good model system to study the regulatory mechanisms of receptor expression under well-controlled experimental conditions in the developing hippocampus.
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Comparative Study
A combined blockade of glycine and calcium-dependent potassium channels abolishes the respiratory rhythm.
In order to test whether glycinergic inhibition is essential for the in vivo respiratory rhythm, we analysed the discharge properties of neurones in the medullary respiratory network after blockade of glycine receptors in the in situ perfused brainstem preparation of mature wild type and oscillator mice with a deficient glycine receptor. In wild type mice, selective blockade of glycine receptors with low concentrations of strychnine (0.03-0.3 microM) provoked considerable changes in neuronal discharge characteristics: The cycle phase relationship of inspiratory, post-inspiratory and expiratory specific patterns of membrane potential changes was altered profoundly. Inspiratory, post-inspiratory and expiratory neurones developed a propensity for fast voltage oscillations that were accompanied by multiple burst discharges. ⋯ In contrast, rhythmic activity was only weakened, but preserved after the "small" Ca2+-dependent activated K+ conductance was blocked with apamin (8 nM). Also low concentrations of pentobarbital sodium (6 mg/kg) abolished rhythmic respiratory activity after blockade of glycine receptors in the wild type mice and in glycine receptor deficient oscillator mice. The data imply that failure of glycine receptors provokes enhanced bursting behaviour of respiratory neurones, whilst the additional blockade of BKCa channels by charybdotoxin or with pentobarbital abolishes the respiratory rhythm.
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Calcitonin gene-related peptide (CGRP) is widely distributed in the central and peripheral nervous system. Its highly diverse biological activities are mediated via the G protein-coupled receptor that uniquely requires two accessory proteins for optimal function. CGRP receptor component protein (RCP) is a coupling protein necessary for CGRP-receptor signaling. ⋯ Our data suggest that the distribution of RCP immunoreactivity is closely matched with CGRP immunoreactivity in most of central and peripheral nervous systems. The co-localization of RCP and CGRP in motoneurons and primary sensory neurons suggests that CGRP has an autocrine or paracrine effect on these neurons. Moreover, our data also suggest that RCP expression in DRG and spinal cord can be modulated during CGRP receptor blockade, inflammation or neuropathic pain and this CGRP receptor-associated protein is dynamically regulated.
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Comparative Study
The differentiation potential of precursor cells from the mouse lateral ganglionic eminence is restricted by in vitro expansion.
We have investigated whether the differentiation potential of attached cultures derived from the mouse lateral ganglionic eminence (LGE) is influenced by in vitro expansion. Primary neuronal cultures derived from the LGE give rise to neurons expressing the striatal projection neuron markers Islet1 (ISL1) and dopamine and cAMP-regulated phosphoprotein of 32 kilodaltons (DARPP-32) as well as the olfactory bulb interneuron marker Er81. Our previous results showed that after expansion in vitro, LGE precursor cells can be induced to differentiate into neurons which exhibit molecular characteristics of the LGE, such as the homeobox transcription factors DLX and MEIS2. ⋯ This indicates that the expansion of LGE precursor cells restricts their differentiation potential in vitro. Interestingly, the undifferentiated LGE cultures retain the expression of both the Isl1 and Er81 genes, suggesting that precursor cells for both striatal projection neurons and olfactory bulb interneurons are present in these cultures. Thus the restriction in differentiation potential of the expanded LGE cultures likely reflects deficiencies in the differentiation conditions used.