A current project in the Welsh lab is to use optogenetics to probe the function of the cerebellar systems in movement control. Here, we use a variety of optical stimulation methods in combination with multisite patch clamp and in vivo multielectrode recording to determine how cerebellar circuits provide temporal precision to movement. We use the Ai27 and Ai32 mouse lines and breed them to ptf1a-cre mouse line in order to get uniform expression of ChR2 in inferior olive neurons. A novel paradigm developed with the use of this mouse line is an ability to assay electrotonic coupling by combining optical stimulation of single neurons with paired whole-cell recordings in vitro. This allows for an optical approach for assaying modulatory effects of chemical synaptic transmission on electrical synapse function.
Figure to left: Optical interrogation of electrical synapses using transgenic ChR2 mice in the Welsh lab. In the top, two neighboring neurons that express ChR2 are whole-cell patched using dual recording. The neuron on the left (cell I) is selectively stimulated using multibeam two-photon excitation at 920 nm while voltage recordings are obtained from both neurons. Below shows the voltage responses of neurons tested as above from a wild-type mouse (left) and from a ptf1a-Ai32 mouse, which expressed ChR2 in both neurons. Single neuron optical stimulation depolarized the membrane of Cell I, and drives a coupled response in the neighboring neuron (Cell II). This is a novel paradigm to address electrotonic coupling and the mechanisms whereby it can be modulated in health and disease.