[Mechanisms of neural circuit remodeling in the primary somatosensory cortex in mouse models of chronic pain].

Chronic pain is caused by injury or inflammation of the peripheral tissues and by abnormal activities in the central nervous system including the spinal cord area related to generation and maintenance of chronic pain. In the cerebral cortex, several areas respond to noxious stimulation. Since activities of these cortical areas are enhanced in chronic pain conditions, not only a single cortical area, but also the interaction between multiple cortical areas seems to contribute to chronic pain. The primary somatosensory cortex (S1), which is one of the pain-related cortical areas, plays a role in recognition of strength, location, and duration of pain. Since activities of the S1 are enhanced in chronic pain conditions, this area is likely to have an important role in the generation or maintenance of chronic pain. The S1 consists of 6 layers and has both excitatory and inhibitory neurons. The excitatory neurons integrate pain information from the peripheral nerves and send it to other excitatory neurons in the S1 and other cortical areas. On the other hand, the inhibitory neurons modulate activities of the excitatory neurons and contribute to sensory processing. However, how these neuronal structures and functions alter in chronic pain and contribute to chronic pain behavior is unknown. In this review, we highlight recent two-photon microscopy studies that elucidate the mechanisms of neuronal circuit remodeling in the S1 under chronic pain conditions.