Eisaku Maeda

The mechanisms of generation and propagation of synchronized bursting in developing networks of cortical neurons

The characteristics and mechanisms of synchronized firing in developing networks of cultured cortical neurons were studied using multisite recording through planar electrode arrays (PEAs). With maturation of the network (from 3 to 40 d after plating), the frequency and propagation velocity of bursts increased markedly (approximately from 0.01 to 0.5 Hz and from 5 to 100 mm/sec, respectively), and the sensitivity to extracellular magnesium concentration (0–10 mM) decreased. The source of spontaneous bursts, estimated from the relative delay of onset of activity between electrodes, varied randomly with each burst. Physical separation of synchronously bursting networks into several parts using an ultraviolet laser, divided synchronous bursting into different frequencies and phases in each part. Focal stimulation through the PEA was effective at multiple sites in eliciting bursts, which propagated over the network from the site of stimulation. Stimulated bursts exhibited both an absolute refractory period and a relative refractory period, in which partially propagating bursts could be elicited. Periodic electrical stimulation (at 1 to 30 sec intervals) produced slower propagation velocities and smaller numbers of spikes per burst at shorter stimulation intervals. These results suggest that the generation and propagation of spontaneous synchronous bursts in cultured cortical neurons is governed by the level of spontaneous presynaptic firing, by the degree of connectivity of the network, and by a distributed balance between excitation and recovery processes.

Spontaneous periodic synchronized bursting during formation of mature patterns of connections in cortical cultures.

Long-term recording of spontaneous activity in cultured cortical neuronal networks was carried out using substrates containing multi-electrode arrays. Spontaneous uncorrelated firing appeared within the first 3 days and transformed progressively into synchronized bursting within a week. By 30 days from the establishment of the culture, the network exhibited a complicated non-periodic, synchronized activity pattern which showed no changes for more than 2 months and thus represented the mature state of the network. Pharmacological inhibition of activity only during the period when regular synchronized bursting was observed was capable of producing a different mature activity pattern from the control. These results suggest that periodic synchronized bursting plays a critical role in the development of synaptic connections.

Modification of parallel activity elicited by propagating bursts in developing networks of rat cortical neurones

Networks of cultured cortical neurones exhibit regular, synchronized, propagating bursts which are synaptically mediated, and which are hypothesized to play a part in activity‐dependent formation of connections during development in vivo. The relationship between the strength of synaptic connections and the characteristics of synchronized propagating bursting, however, is unclear. Modification of synchronized activity in cortical cultures in response to electrical stimulation was examined using multisite electrode array recording. By measuring the response of the network to weak, localized, test stimulation (TS), we observed a potentiation of activity following a relatively stronger inducing stimulation (IS). This potentiation was evident as an increased probability of eliciting bursts by TS, an increased frequency of spontaneous bursts and number of spikes per burst, and increased speed of burst propagation, and it lasted for at least 20 min. Changing the parameters of IS revealed that high frequency tetanic stimulation is not necessary to induce potentiation, while it is essential for IS to produce a regeneratively propagating burst. The results provide a direct demonstration of modification of both the spatial and temporal characteristics of synchronized network activity, and suggest an important physiological role for propagating synchronized bursting, as a mechanism for inducing plastic modifications in the developing cortex.

Experimental analysis of neuronal dynamics in cultured cortical networks and transitions between different patterns of activity

Abstract. Experimental investigation of the dynamics of biological networks is a fundamental step towards understanding how the nervous system works. Spontaneous activity in cultured networks of cortical neurons has been investigated by using a multisite recording technique with planar electrode arrays. In these networks, the spatiotemporal firing patterns were studied in the presence of different extracellular solutions. Transitions from asynchronous firing dynamics to synchronous firing dynamics were observed when the extracellular Ca2+ concentration was increased from 0.1 mM to 1 mM. Addition of extracellular Mg2+ reduced the spontaneous activity at any Ca2+ concentration, and an increase in the extracellular K+ concentration enhanced the frequency of periodical synchronous bursts. N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor antagonists inhibited synchronous activity. A spatiotemporal analysis of the data has been performed, and the properties of the network such as the synchronization and the periodicity have been quantified in order to clarify how variations of intrinsic parameters of the network can induce structural transitions in the neural dynamics. This experimental study is a possible approach to investigate the computational properties of a neuronal network.

1317 Effect of BNDF on synchronous and asynchronous activity in cultured networks of cortical neurons

Sheng-Tian Li’ , Kunio Kato3, Katsuhiko Mikoshiba’ Long-term depression (LTD) in the CA1 area of rat hippocampal slices was studied. We employed a special perfusion solution composed of variable concentrations of Ca 2+ Mg2+ and K+ to substitute for low frequency , stimulation in order to induce LTD without electrical stimulation. LTD was successfully induced with this conditioning solution (Ca 2f: 4 mM; Mg2+: 0.1 mM; Kf: 5mM) applied for 20min (-28.5h8.8’30; N=12). The advantage of this protocol is that the whole slice is exposed to conditioning solution, and therefore LTD should be induced in all of the synapses, possibly yielding clearer results in biochemical studies than electrical stimulation-induced LTD. We tested the effect of protein phosphatase inhibitors, such as FK-506 and cyclosporine A on the LTD induced by the conditioning solution. We also investigated phosphatase activity during LTD induction by biochemical methods, and compared protein phosphatase activity before and after the induction of LTD.

Synchronous bursting and asynchronous firing activity in cultured cortical neurons

Spontaneous activity in cultured networks of cortical neurons was investigated by extracellular recordings of their spatiotemporal firing patterns, using planar electrode arrays which comprised 64 microelectrodes. In the cultured cortical networks synchronous bursts states, asynchronous bursts states and non-burst firings states were observed by changing the Ca/sup 2+/, Mg/sup 2+/ and K/sup +/ concentration of the extracellular solution and by adding NMDA and non-NMDA receptor antagonists. Observed phenomena, such as burst generation and asynchronous firing activity as a function of the activation of random synaptic inputs, could be simulated by using a simplified single neuron model.