Optogenetic Stimulation of the Axons of Visual Cortex and Hippocampus Pyramidal Neurons in Living Brain Slices

Widening and deepening our understanding of how the brain works requires constant improvements not only in methods of recording neuron activity, but also improvements in experimental approaches to activating individual cells and their compartments. Optogenetic stimulation methods using finely focused light to trigger the opening of the light-activated depolarizing cation channel rhodopsin-2 (ChR2) have become widely used in recent years. Current molecular biological methods provide for the genetic expression of ChR2 in different cell types, which, along with the ability to carry out electrophysiological experiments with reproducible patterns of activation and stable levels of ChR2 expression, have developed optogenetics into an effective method for gathering physiological data previously unavailable to conventional methods. We report here the use of local activation of axons using an optogenetic stimulation method. Experiments were performed in combination with recording the electrical activity of neurons using the patch-clamp method, as well as laser scanning confocal microscopy. Experiments used the transgenic mouse strain Thy1-ChR2-YFP, in which ChR2 is expressed in only a small proportion of pyramidal cells. Direct studies of the effects of functional activity in the proximal branches of pyramidal neuron axons in layer 5 of the visual cortex and hippocampal field CA1 on the shape and generation of action potentials were carried out. We also describe methodological advances and means of solving problems encountered in the optogenetic stimulation of the axons of pyramidal neurons in the central nervous system of mammals.