Establishment of a neural activity recording method for unrestrained free-behavior mice

Abstract

When an animal is exposed to stress, it provokes an autonomic response, such as increased heart rate, respiration, blood pressure, or analgesia, called a stress defense response. Previous studies have shown that these responses are attenuated in orexin knockout mice, suggesting that orexin neurons are an essential factor in stress-induced autonomic responses. However, how orexin is involved in the stress-induced autonomic nervous response, especially whether the orexin nerve is active during stress loading, is still unclear. Therefore, in order to investigate the relationship between orexin neuronal activity and the stress-induced autonomic response, we established a fiber photometry system, which can be used as a neuronal activity recording method for unrestrained/free-moving mice. In this method, a highly sensitive calcium probe (GCaMP6) is expressed only in specific cell types of genetically modified animals and adeno-associated virus (AAV), and a single fiber is placed in the deep brain of consciously free-moving animals. This method is particularly useful for elucidating the neural circuits in the brain that control phenomena such as stress-induced autonomic responses, and physical responses that are observed only when the nervous system of the whole body including peripheral nerves is active. In this study, we generated mice that specifically expressed G-CaMP6 in orexin neurons, and attempted to simultaneously record heart rate variability and orexin neural activity in real-time. In this paper, we introduce the 2ch fiber photometry system we have created and consider the relationship between orexin neuronal activity and autonomic responses using the results obtained by this system.