Regulation Of Slow Oscillation By Low Frequency Electrical Stimulations On Cultured Neuronal Networks

As an important category of phenomena in the neural system, synchronous oscillations are proved to play a role in varied brain activities. Oscillations synchronized at a slow frequency (<1 Hz), namely the slow oscillations, are correlated with learning and memory, but the detailed mechanism remains unclear. The present study has demonstrated the slow oscillation in dissociated hippocampal cultures with multi-electrode arrays, summarized the rule of low frequency stimulations on regulating slow oscillations, and proposed the possible mechanism underlying the regulation. The overall results and review of this dissertation are listed as follows.Slow oscillations with the frequency of 0.004 Hz were found during the mid-stage of in vitro development. In each period of the oscillation, there were two states:the'up'and the'down'state. In the'up'state, the network acted in synchronous superbursts. Both the mean firing rate and the synchrony of network were higher than those in the'down'state. A superburst was consisted of tight bursts, and immediately after a superburst the neuronal activity was almost silenced. In the'down'state, network activity was in a random spike firing pattern, and the spike firing was gradually regained from silence. In neuronal networks, the alternation of'up'and'down'states led the network to act in an slow oscillatory way. The slow oscillations had the characterization of precise time structure and synchronized network activity. They could be persisted in the network for more than two month, and supplied as a good modle for the mechanism study of slow oscillations.The results have proposed a method for regulating slow oscillations by low frequency electrical stimulation. When in the'down'state, low frequency stimulations (1,10 Hz) could induce the network into the'up'state, therefore shortened the period of slow oscillations.1 Hz stimulation did not change the duration of the'up'state, but 10 Hz increased the duration. The timing of starting delivering the 1 Hz stimulation and the number of pulses needed to induce superbursts were linearly correlated. The farther from the end of the'up'state, the less pulses were needed. The shortest duration of the'down' state induced by the 1 Hz stimulation was～60 s. The 10 Hz stimulation could make the duration shorter, and induce synchronous superbursts even when slow oscillations were diminished in the late-stage of in vitro development.The regulation of slow oscillation by low frequency stimulations was dependent on change of spike rate and GABA-A receptors. Low frequency stimulations delivered in 'down'states could induce a fixed quantity of response spikes which were linearly correlated with the spontaneous firing rate. Therefore, the 1 Hz stimulation increased the firing rate of all sites in the network with the same relative proportion (response spike number/mean spontaneous firing rate), and advanced the occurrence of the superbursts of all sites synchronously. After GABA-A receptors were blocked in the network, slow oscillations were replaced by 2 Hz synchronous bursting. During that time, the 10 Hz stimulation was not able to induce superbursts. Because the spontaneous network activity was increased while the precision timing of response spikes was decreased after blocking GABA-A receptors, therefore the GABA-A receptors may play a role in keeping the precise time structure of slow oscillations.To sum up, slow oscillations have precise time structure and synchronous activity in the'up'state. The low frequency electrical stimulation can advance the occurrence of synchronous superbursts and shorten the period of slow oscillations. The signaling pathway mediated by GABA-A receptors is supposed to keep the precise time structure of slow oscillations. When GABA-A receptors are blocked, the low frequency stimulation cannot induce slow oscillations.