Diego Ghezzi(a), Alessandra Pedrocchi(a), Andrea Menegon(b), Sara Mantero(a), Flavia Valtorta(b), and Giancarlo Ferrigno.(a)
(a)Bioengineering Department, Politecnico di Milano;
(b)Department of Neuroscience, San Raffaele Scientific Institute and "Vita-Salute" University.
Our ability in eliciting, modulating and recording this activity is fundamental for the understanding of the mechanisms that govern the central nervous system (CNS) functions.
In the last decade, a deluge of studies on neuronal physiology and plasticity have provided a highly detailed picture of the molecular mechanisms at the basis of these phenomena; on the contrary, molecular mechanisms which control the complex network properties remain still poorly understood, and they represent a new frontier in neuroscience.
In the field of research on neuronal functions two different approaches can be followed. On one hand, there is a large scale approach finalized at understanding a more or less synchronized activity of many neurons interacting in a complex neuronal network.
On the other hand, there is a micro scale approach finalized at providing detailed behavioural models, not only of the neuron, but also of complex molecular systems which, interacting with each other, actively contribute to the generation and modulation of the neuronal activity.
Neuronal long term potentiation (LTP) and long term depression (LTD) of the pre and postsynaptic sites are the most common examples of sub neuronal activity that actively contribute towards modulation of the network activity.
A new breakthrough into neuroscience would be the possibility to stimulate and modulate a single neuron, or selected parts of it, and study its influence over the functioning of the entire network.
This way, the micro scale meets the large scale approach, making possible the understanding of how the mechanisms able to influence the physiology of single neuronal units are able to alter the complex behaviour of the entire neuronal system.
In order to perform these studies, it will be necessary that the tools for the micro and large scale analysis are available in the same device.
Besides traditional electrophysiology or MEA techniques, optical methods for stimulating and recording neuronal activity have been used for a long time.
The ability to use light provides a tool for precise temporal and spatial activation of different regions of a neuronal network, which can be sized to single neurons as well as discrete portions of the neuron itself, and for monitoring the electrical activity of the sub neuronal compartments, the entire neuron and the whole network.
Combining local light stimulations and recordings with VSDs, it will be possible to reach the features required for a high detailed study into neuronal plasticity and physiology related at the network activity.
The combination of the two mentioned methods is not straightforward then, at the current state of the art, optical methods are not yet independent from electrical measurements, but they provide only a useful support for neurons stimulation, or alternatively for recording membrane electrical activity.
Recently, a new concept of device, named PhotoMEA, for neuronal cultures analysis has been proposed (Italian patent pending number MI2005A000114).
PhotoMEA is a biosensor useful for the analysis of an in vitro neuronal network, fully based on optical methods. Its function is based on the stimulation of neurons with caged glutamate and the recording of neuronal activity by fluorescence Voltage Sensitive Dyes.
The main advantage is that it will be possible to stimulate even at subâ€“single neuron level and to record with high resolution the activity of the entire network in the culture. A large scale view of neuronal intercommunications, combined with the micro scale view, offers a unique opportunity for testing the ability of drugs to affect neuronal properties as well as alterations in the behaviour of the entire network.
p.zza Leonardo da Vinci 32, 20133 Milano, Italy.
E-mail: diego DOT ghezzi AT polimi DOT it
E-mail: pedrocchi AT biomed DOT polimi DOT it
E-mail: ferrigno AT biomed DOT polimi DOT it
via Olgettina 60, 20132 Milano, Italy.
E-mail: menegon DOT andrea AT hsr DOT it
E-mail: valtorta DOT flavia AT hsr DOT it