Synaptic connections in a dissociated mixed culture of rat dorsal root ganglion and spinal cord neurons

Postsynaptic currents and action potentials recorded from neurons in a mixed culture of rat dorsal root ganglion and spinal cord cells are described. The existence of mutual synaptic connections between the above two types of neurons is demonstrated. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 358–360, July–August, 2006.     

Assessment of the Reliability of Amplitude Histograms for Inhibitory Synaptic Currents in Rat Cortex Culture

We analyzed in detail the quantum parameters of evoked inhibitory postsynaptic currents (eIPSC) recorded from synaptically connected cultured cortex neurons using a whole-cell patch-clamp technique. The IPSC were evoked using minimum extracellular stimulation of a presynaptic unit with a frequency of 0.2 sec^-1 at the holding potential of -80 mV. Amplitude histograms for eIPSC demonstrated clearly detectable equally spaced peaks. For each histogram, we used a method based on autocorrelation analysis and Monte Carlo simulation to determine whether peaks in the amplitude histograms can result due to finite sampling from the sum of the Gaussian distributions. The autocorrelation function allowed us to measure the peak spacing (and, hence, the mean quantum size) for each histogram; this parameter was found to be 10 pA.     

Differentiation of potassium currents in cultured inhibitory interneurons of the rat hippocampus (identification of the potassium M-type current)

Using a patch-clamp technique in the whole-cell configuration, we identified the potassium M-type current and estimated its contribution to the integral depolarization-induced potassium current evoked in cultured hippocampal inhibitory interneurons of the rat. With the help of immunocytochemical labeling, we checked the presence of the KCNQ-family channels responsible for generation of M current in these neurons. It was demonstrated that non-inactivated potassium channels and channels with slow kinetics play the main role in the processes of repolarization of the membrane of inhibitory interneurons. In all studied cells, a potassium current non-inactivated with time and possessing kinetic parameters close to those of the M current developed in response to depolarization. In all cells, positive immunocytochemical labeling with respect to KCNQ2 channels was observed; however, its intensity varied significantly from neuron to neuron. The level of suppression of non-inactivated potassium currents by a blocker of KCNQ channels, linopirdine, varied noticeably in different cells; therefore, the level of expression of these channels in the interneurons under study is probably considerably dissimilar. The reason for incomplete suppression of the M current is perhaps the involvement of other potassium channels (e.g., those of Kv1 family) in the formation of this current. Neirofiziologiya/Neurophysiology, Vol. 38, No. 3, pp. 198–204, May–June, 2006.     

Effects of extracellular concentration of calcium and intensity of stimulation on short-term plasticity in single inhibitory synapses between cultured hippocampal neurons

We studied the characteristics of short-term plasticity in inhibitory synapses of cultured neurons of the rat hippocampus. In our experiments, we used techniques of voltage clamp in the whole-cell configuration and of local electrical stimulation (pairs of stimuli were applied to a single synaptic terminal of the GABA-ergic neuron under conditions of the blockade of spreading excitation). We demonstrated that an increase or a decrease in the extracellular concentration of calcium ions ([Ca²⁺]_o) results in modifications of the pattern of this plasticity. Depression of the second postsynaptic response under conditions of normal [Ca²⁺]_o was characterized by a paired-pulse ratio (PPR) equal, on average, to 0.78 ± 0.04 (n = 5). With a decrease in the [Ca²⁺]_o to 0.5 mM, depression was changed to facilitation (PPR = 1.17 ± 0.08, n = 5), while with a rise in the [Ca²⁺]_o to 5.0 mM, depression became more clearly pronounced (PPR = 0.48 ± 0.03, n = 5). Alterations of responses, which were determined by a decrease or an increase in the [Ca²⁺]_o, differed significantly from those related to a decrease or an increase in the amplitude of presynaptic stimulation. Analysis of the parameters of the pairs of evoked inhibitory postsynaptic currents under conditions of various [Ca²⁺]_o and different intensities of stimulation of the presynaptic terminal allows us to conclude that in these terminals calcium-dependent (and, probably, also voltage-dependent) mechanisms underlying control of short-term synaptic plasticity are present. Neirofiziologiya/Neurophysiology, Vol. 38, No. 2, pp. 103–112, March–April, 2006.     

Quantum Properties of GABA Release in Cultured Neurons from the Rat Cortex

We analyzed the properties of inhibitory synaptic transmission between neurons in low-density cultures of cortical cells. Miniature, spontaneous, and evoked inhibitory postsynaptic currents were studied using a whole-cell path-clamp technique at a holding potential of -80 mV. These postsynaptic currents were identified as GABA release-activated Cl^- currents mediated by GABA_A receptors. Fitting amplitude histograms of these currents with Gaussian curves and an autocorrelation technique revealed the presence of equidistant peaks corresponding to a mean quantum size of 10 pA.