Influence of extracellular matrix proteins on membrane potentials and excitability in NG108-15 cells

Methamphetamine inhibits voltage-gated potassium currents in NG108-15 cells: possible contribution of large-conductance calcium-activated potassium channels

Methamphetamine (MA), a highly abused amphetamine-like psychostimulant, has surged in popularity worldwide in the last decade. Repeated MA exposure has been shown to affect the alternative splice variant expression of large conductance Ca(2+)-activated K(+) (BK) channels. It remains unclear whether MA affects BK channel activity. The present study investigated the effects of MA on BK channels in NG108-15 mouse neuroblastoma×rat glioma hybrid cells using whole-cell and cell-attached patch clamp techniques. In whole-cell recordings, the macroscopic K(+) outward currents were inhibited by MA with an EC50 of 146μM, but not affected by dopamine (DA). It implies that DA is not involved in the effects of MA on K(+) outward currents. In cell-attached patches, MA significantly decreased BK channel activity. Moreover, MA significantly decreased the BK channel opener NS1619-evoked whole-cell K(+) outward currents and BK channel activity. Finally, the effect of MA on membrane potential was examined by current-clamp configuration. MA caused membrane depolarization and application of NS1619 returned the depolarized potential to resting value. These findings suggest that MA might act as an inhibitor of BK channels, and thereby increase the neuronal excitability and enhance neurotransmitter release.

Engineering the morphology and electrophysiological parameters of cultured neurons by microfluidic surface patterning

The ability to control the orientation, morphology, and electrophysiological characteristics of neurons in culture allows the construction of neural circuits with defined physiological properties. Using microfluidic protein deposition onto chemically modified glass, we achieve the controlled growth of Aplysia neurons on geometrical patterns of poly-L-lysine and collagen IV, surrounded by nonadhesive regions of bovine albumin. We investigate the parameters essential for forming functional neuronal networks, the morphology, biochemistry, and electrophysiology under engineered cell culture conditions. We demonstrate that not only the orientation of neurite extension but also the number of primary neurites originating from the cell soma, their length, and branching pattern depend on the spatial constraints presented by the size and shape of the adhesion region on the patterned substrate. In addition, the physicochemical properties of the support layer influence the electrical activity of the cultured neurons. Substrate-dependent changes in the amplitude and in the dynamic parameters of the action potential cause decreased spike broadening in patterned neurons, which reflects changes in the number or functioning of active membrane ion channels. In contrast to morphology and electrophysiology, the neuropeptide content, as determined by mass spectrometry of individual patterned neurons, is not affected by the growth on patterned surfaces. Our results suggest that the morphological and electrophysiological parameters of neurons can be predictably altered/engineered by modulation of the chemical, physical, and topographical features of culture substrates. We also demonstrate that a full suite of techniques is required for functional characterization of neurons on engineered substrates.

Mice deficient for the extracellular matrix glycoprotein tenascin-r show physiological and structural hallmarks of increased hippocampal excitability, but no increased susceptibility to seizures in the pilocarpine model of epilepsy

Recognition molecules provide important cues for neuronal survival, axonal fasciculation, axonal pathfinding, synaptogenesis, synaptic plasticity, and regeneration. Our previous studies revealed a link between perisomatic inhibition and the extracellular matrix glycoprotein tenascin-R (TN-R). Therefore, we here studied neuronal excitability and epileptic susceptibility in mice constitutively deficient in TN-R. In vitro analysis of populational spikes in hippocampal slices of TN-R-deficient mice revealed a significant increase in multiple spikes in the CA1 region, as compared with wild-type mice. This difference between genotypes was only partially reduced after blockade of GABA(A) receptors with picrotoxin, indicating a deficit in GABAergic inhibition and an increase in intrinsic excitability of CA1 pyramidal cells in TN-R-deficient mice. Using a battery of immunohistochemical markers and histological stainings, we were able to identify two abnormalities in the hippocampus of TN-R-deficient mice possibly related to increased excitability: the high number of glial fibrillary acidic protein-positive astrocytes and low number of calretinin-positive interneurons in the CA1 and CA3 regions. In order to test whether the revealed abnormalities give rise to increased susceptibility to seizures in TN-R-deficient mice, we used the pilocarpine model of epilepsy. No genotype-specific differences were found with regard to the time-course of pilocarpine-induced and spontaneous seizures, neuronal cell loss, aberrant sprouting and distribution of synaptic and inhibitory interneuron markers. However, pilocarpine-induced astrogliosis and reduction in calretinin-positive interneurons were less pronounced in TN-R mutants, thereby resulting in an occlusion of effects induced by TN-R deficiency and pilocarpine. Thus, TN-R-deficient mutants show several electrophysiological and morphological hallmarks of increased neuronal excitability, which, however, do not give rise to more accelerated or severe epileptogenesis in the pilocarpine model of epilepsy.