In this paper, we study the modulation of low frequency closed-loop electric stimulation on spontaneous activity in cultured hippocampal neuronal networks. First, we plated monolayer cultures of hippocampal neurons from rat embryos (E18) on multi-electrode arrays and the experiments were performed in the networks from the second week to the sixth week continuously. During the experiments, we detected the spontaneous spikes of the networks firstly, and then stimulated the networks at low frequency (0.2 Hz or 1 Hz) stimulation respectively until a desired response was observed 20-80msec after a stimulus. The protocol was closed-loop. After that, we detected the spontaneous spikes of the networks. It is observed that the spontaneous activity in the developing networks is developing, which is oscillatory and periodic. Low frequency (0.2 Hz or 1 Hz) stimulation enhanced the spontaneous synchronous burst activity of the developing networks. These results implicated that activity-dependent mechanism in the modulation of plasticity of synaptic transmission in the cultured neuronal networks. Closed-loop stimulation will give a better view on the functional significance of networks activities. Besides, close-loop stimulation could set up the stimulus-reward system in the neuronal networks, which is of great benefit to the plasticity of synaptic transmission in the cultured neuronal networks.
Brain-derived neurotrophic factor (BDNF), like other neurotrophins, has long-term effects on neuronal survival and differentiation; furthermore, BDNF has been reported to exert an acute potentiation of synaptic activity and are critically involved in long-term potentiation (LTP). We found that BDNF rapidly induced potentiation of synaptic activity and an increase in the intracellular Ca<sup>2+</sup> concentration in cultured cortical neurons. Within minutes of BDNF application to cultured cortical neurons, spontaneous firing rate was dramatically increased as were the frequency and amplitude of excitatory spontaneous postsynaptic currents (EPSCs). Fura-2 recordings showed that BDNF acutely elicited an increase in intracellular calcium concentration ([Ca<sup>2+</sup>]<sub>c</sub>). This effect was partially dependent on [Ca<sup>2+</sup>]<sub>o</sub>; The BDNF-induced increase in [Ca<sup>2+</sup>]<sub>c</sub> can not be completely blocked by Ca<sup>2+</sup>-free solution. It was completely blocked by K252a and partially blocked by Cd<sup>2+</sup> and TTX. The results demonstrate that BDNF can enhances synaptic transmission and that this effect is accompanied by a rise in [Ca<sup>2+</sup>]<sub>c</sub> that requires two route: the release of Ca<sup>2+</sup> from intracellular calcium stores and influx of extracellular Ca<sup>2+</sup> through voltage-dependent Ca<sup>2+</sup> channels in cultured cortical neurons.