Neuroscience
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Comparative Study
Developmental regulation of the A-type potassium-channel current in hippocampal neurons: role of the Kvbeta 1.1 subunit.
The rapidly inactivating A-type K+ current (IA) is prominent in hippocampal neurons; and the speed of its inactivation may regulate electrical excitability. The auxiliary K+ channel subunit Kvbeta 1.1 confers fast inactivation to Shaker-related channels and is postulated to affect IA. Whole-cell patch clamp recordings of rat hippocampal pyramidal neurons in primary culture showed a developmental decrease in the time constant of inactivation (tau(in)) of voltage-gated K+ currents: 17.9+/-1.5 ms in young neurons (5-7 days in vitro; n=53, mean+/-S. ⋯ This effect was most pronounced at -40 mV, where the ISI of the first pair of action potentials was nearly doubled. These data indicate that Kvbeta 1.1 contributes to the developmental control of IA in hippocampal neurons and that the magnitude of effect is sufficient to regulate electrical excitability. Viral-mediated antisense knockdown of Kvbeta 1.1 is capable of decreasing the electrical excitability of post-mitotic hippocampal neurons, suggesting this approach has applicability to gene therapy of neurological diseases associated with hyperexcitability.
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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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Comparative Study
Expression of auxiliary beta subunits of sodium channels in primary afferent neurons and the effect of nerve injury.
Multiple voltage-gated sodium channels are the primary mediators of cell excitability. They are multimers that consist of the pore-forming alpha subunit and auxiliary beta subunits. Although ion permeability and voltage sensing are primarily determined by the alpha subunit, beta subunits are important modulators of sodium channel function. ⋯ We also examined the expression of beta(3) mRNA in DRG neurons in the SNI model, a neuropathic pain model. We used activating transcription factor 3 to identify axotomized neurons, and found that beta(3) mRNA up-regulation occurred mainly in axotomized neurons in the neuropathic pain model. These data strongly suggest that beta(3) expression in injured DRG neurons following axotomy might be an important pathomechanism of post-nerve injury pain in primary sensory neurons.
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The metabolic events of neuronal energetics during functional activity are still partially unexplained. In particular, lactate (and not glucose) was recently proposed as the main substrate for neurons during activity. ⋯ In the present study we used a time-resolved proton magnetic resonance spectroscopy strategy in order to analyse the evolution of lactate during the early seconds following a brief visual stimulation (event-related design). A significant decrease in lactate concentration was observed 5 s after the stimulation, while a recovering of the baseline was observed at 12 s.
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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.