Heterologous expression of ion channels that can be directly gated by light has made it possible to stimulate almost any excitable cell with light. Optogenetic stimulation has been particularly powerful in the neurosciences, as it allows the activation of specific, genetically defined neurons with precise timing. Organotypic hippocampal slice cultures are a favored preparation for optogenetic experiments. They can be cultured for many weeks and, after transfection with optogenetic actuators and sensors, allow the study of individual synapses or small networks. The absence of any electrodes allows multiple imaging sessions over the course of several days and even chronic stimulation inside the incubator. These timescales are not accessible in electrophysiological experiments. Here, we introduce the production of organotypic hippocampal slice cultures and their transduction or transfection with optogenetic tools. We then discuss the options for light stimulation.
