PhotoMEA: A new step towards total optical analisys of in vitro neuronal networks

Light stimulation of neurons is a promising approach for investigating the molecular mechanisms at the basis of neuronal physiology and plasticity. In particular, flash photolysis of caged compounds offers the unique advantage of allowing to quickly change the concentration of either intracellular or extracellular bioactive molecules, such as neurotransmitters or second messengers, for the stimulation or modulation of neuronal activity. In this field of research, we describe a simple laser-based set-up for the local activation of caged compounds. The coupling of a UV laser diode to a small-core optical fibre allows to reduce the uncaging area and to quickly change the stimulation point. The actual localisation of the light stimulation is determined using a caged fluorescent compound (dextran, DMNB-caged fluorescein). The efficiency of our set up for neuronal stimulation is tested with a caged neurotransmitter (MNI-caged-L-glutamate). Activation of caged glutamate evokes neuronal responses that are recorded using a MicroElectrode Array system and/or following the variations in the concentrations of the Ca _i ²⁺. This work shows that our laser-based set-up is a powerful tool for local activation of caged compound allowing a unique opportunity to follow the effects of local neuronal pathways on neuronal network activity, for instance during pharmacological and toxicological treatments.