Neuroscience
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Comparative Study
Synaptic background noise controls the input/output characteristics of single cells in an in vitro model of in vivo activity.
In vivo, in vitro and computational studies were used to investigate the impact of the synaptic background activity observed in neocortical neurons in vivo. We simulated background activity in vitro using two stochastic Ornstein-Uhlenbeck processes describing glutamatergic and GABAergic synaptic conductances, which were injected into a cell in real time using the dynamic clamp technique. With parameters chosen to mimic in vivo conditions, layer 5 rat prefrontal cortex cells recorded in vitro were depolarized by about 15 mV, their membrane fluctuated with a S. ⋯ Background activity was highly effective in modulating the firing-rate/current curve of the cell: the variance of the simulated gamma-aminobutyric acid (GABA) and AMPA conductances individually set the input/output gain, the mean excitatory and inhibitory conductances set the working point, and the mean inhibitory conductance controlled the input resistance. An average ratio of inhibitory to excitatory mean conductances close to 4 was optimal in generating membrane potential fluctuations with high coefficients of variation. We conclude that background synaptic activity can dynamically modulate the input/output properties of individual neocortical neurons in vivo.
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Activation of muscarinic receptors leads to proliferation of astroglial cells and this effect is inhibited by ethanol. Among the intracellular pathways involved in the mitogenic action of muscarinic agonists, activation of the atypical protein kinase C zeta (PKC zeta) appears to be of most importance, and is also affected by low ethanol concentrations. PKC zeta has been reported to activate nuclear factor kappaB (NF-kappaB), a transcription factor that has been shown to play an important role in cell proliferation. ⋯ Increased DNA synthesis was also antagonized by the IkappaBalpha kinase inhibitor BAY 11-7082. Ethanol (25-100 mM) inhibited the translocation of p65 and the binding of NF-kappaB to DNA in both 1321N1 astrocytoma cells and primary rat cortical astrocytes. Together, these results suggest that activation of NF-kappaB by muscarinic receptors in astroglial cells is important for carbachol-induced DNA synthesis and that ethanol-mediated inhibition of cell proliferation may be due in part to inhibition of NF-kappaB activation.
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Ionotropic glutamate receptors are ligand-gated ion channels that help mediate rapid excitatory neurotransmission in the CNS. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors are critical for synaptic plasticity in central nociceptive transmission. The current study was designed to investigate the role of the AMPA receptor subunit, GluR1, and its phosphorylated forms (at Ser-831 and Ser-845) in central sensitization in rat spinal cord. Western blots and immunohistochemistry were performed to examine the expression and localization of GluR1 and the phosphorylated forms of GluR1 (phospho-GluR1) at Ser-831 and Ser-845 with specific antibodies. ⋯ A significant upregulation of phospho-GluR1 both at Ser-831 and Ser-845 was found by 5 min after capsaicin treatment, and this increase lasted at least 60 min. Immunostaining showed that GluR1 and its phosphorylated forms were localized in the superficial laminae of dorsal horn and quantitative image analysis supported the immunoblotting results. Our findings are consistent with the suggestions that AMPA receptors show increased responsiveness because of their phosphorylation and that this may contribute to central sensitization following intradermal injection of capsaicin.
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In the present study, the expression of the HuC/D RNA-binding proteins, a marker of neurons that have left the mitotic cycle, in cells migrating from the olfactory neuroepithelium toward the telencephalon in the chick embryo was investigated by means of immunofluorescence and confocal laser microscopy. Results showed that this migratory cell population is early and massively labeled by the a-HuC/D antibody starting from the first olfactory pit stage. At this developmental stage, olfactory migratory cells appeared to be the only neuronal population that expressed the HuC/D antigens in the whole embryo. ⋯ HuC/D immunopositivity persisted until stage 30 HH (about 6.5 days), the later developmental stage investigated in this study, when colocalization with GnRH was detected. Negativity to the anti-proliferating cell nuclear antigen (anti-PCNA) immunostaining, a marker of S-phase, showed that migratory olfactory cells have left the mitotic cycle. Altogether, these results suggest that we have identified the first population of post-mitotic neurons in the developing nervous system of the chick embryo.
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Comparative Study
Brain afferents to the lateral caudal ventrolateral medulla: a retrograde and anterograde tracing study in the rat.
The ventrolateral medulla (VLM) modulates autonomic functions, motor reactions and pain responses. The lateralmost part of the caudal VLM (VLMlat) was recently shown to be the VLM area responsible for pain modulation. In the present study, the brain sources of VLMlat afferent fibers were determined by tract-tracing techniques. ⋯ The present study gives an account of the brain regions putatively involved in triggering the modulatory actions elicited from the VLMlat. These include areas committed to somatosensory processing, autonomic control, somatic and visceral motor activity and affective reactions. The findings suggest that the VLMlat may play a major homeostatic role in the integration of nociception with other brain functions.