Neural activity analysis of depressive disorder model mice using the Toyohashi probe

Abstract Major depressive disorder (MDD) is one of the most chronic diseases and life-threatening illnesses globally. However, mainstay medications do not provide sufficient relief for depressive patients with MDD. Thus, there is an urgent need for the development of analysis methods that allow drug screening and observation of phenotypes. We developed a tiny microneedle electrode block module called the Toyohashi probe, which can be inserted into a mouse brain with minimal invasiveness using the vapor–liquid–solid method. Photo-response was measured in the primary visual cortex of Nrf2 knockout (KO) mice using the Toyohashi probe. We then successfully identified characteristic electrophysiological phenotypes, such as abnormal excitability of neurons and a tendency to show higher firing frequency and spikes, in Nrf2 KO mice. In conclusion, our new microneedle electrode can be used in vulnerable disease model mice to record neuronal activity and observe characteristic phenotypes as indicators for drug efficacy.