Both neuroscience and nonlinear science have focused attention on the dynamics of the neural network. However, litter
is known concerning the electrical activity of the cultured neuronal network because of the high complexity and moment
change. Instead of traditional methods, we use chaotic time series analysis and temporal coding to analyze the
spontaneous firing spike train recorded from hippocampal neuronal network cultured on multi-electrode array. When
analyzing interspike interval series of different firing patterns, we found when single spike and burst alternate, the largest
Lyapunov exponent of interspike interval (ISI) series is positive. It suggests that chaos should exist. Furthermore, a
nonlinear phenomenon of bifurcation is found in the ISI vs. number histogram. It determined that this complex firing
pattern of neuron and the irregular ISI series were resulted from deterministic factors and chaos should exist in cultured
term.These results suggest that chaotic time series analysis and temporal coding provide us effective methods to
investigate the role played by deterministic and stochastic component in neuron information coding, but further research
should be carried out because of the high complexity and remarkable noise of the electric activity.
Intracellular calcium, as an important second messenger, plays a significant role in cell signaling transduction and metabolism. Glutamate can induce the intracellular calcium transient through triggering diverse signaling pathways. To test the effect of glutamate to neurons, we loaded Fluo-3/Am in cultured rat hippocampal neurons, and then acquired two-dimensional fluorescent image by confocal microscopy and the analyzed fluorescent intensity. In cultured neurons, we observed two types of neurons that have different morphology: bipolar-type and pyramidal-type. Inducing [Ca2+]i transient by glutamate, we found the amplitude and time constant of the response curves of bipolar neurons are larger than those of pyramidal neurons. Further, we induced [Ca2+]ii transient under different concentrations of glutamate. Two different types of kinetic of the [Ca2+]i transient have been found, corresponded to the two kinds of neuron. The amplitude of [Ca2+]i transient increased when applying higher concentration of glutamate in pyramidal neurons; while it decreased in bipolar ones. Responses of neurons bathing in calcium-free extracellular solution to glutamate were different from those bathing in normal solution. [Ca2+]i transient of pyramidal neurons caused by any concentration were totally blocked; while [Ca2+]i transient in bipolar neurons caused by high concentration of glutamate (500μM) were partly inhibited. All of the phenomena suggest that different types of cultured hippocampal neurons may have different mechanism of the response to glutamate.
Changes in the intracellular Ca2+ concentration ([Ca2+]i) play a crucial role involved in the modulation of signal transduction, development, and plasticity in the CNS. Glial cells can respond to various stimuli with an increase in [Ca2+]i. In this paper, we used confocal microscopy to study calcium transient induced by glutamate in cultured astrocytes. Firstly, 100 μM glutamate induced long-time intracellular calcium oscillations in astrocytes and only a single spike under calcium-free solution. When the concentration of glutamate decreased to 1 μM, only a single spike could be induced. It shows that intracellular calcium oscillations depend on agonist concentration and extracellular Ca2+. Secondly, we investigated amplitude of responses under different stimulation. The amplitude of initial peak induced by 100 μM glutamate decreased in Ca2+-free condition, whereas the duration of kinetics was prolonged. But both the amplitude and area of a single spike induced by 1 μM Glu decreased in Ca2+-free condition. The results show that areaof peak is more accurate than amplitude to display transients of [Ca2+]i. All results above suggest that astrocytes are not passive, they display diverse temporal and spatial increases in [Ca2+]i in response to a variety of stimuli. These [Ca2+]i increases provide a possible means for information coding.