• Text in Japanese

Professor Shoichi Shimada

Neuroscience and Cell Biology

The lab has a long history and has passed through the leadership of many professors before coming under the direction of Professor Shimada.

Mechanisms through which exercise and experience regulate brain plasticity, memory and emotion

1) Influence of exercise on emotion and memory

It is well known that exercise is an excellent preventative measure for many diseases including cardiovascular diseases, diabetes, osteoporosis and the like. Exercise also has profound effects on many brain functions including emotion and memory. Even in adult brains, new neurons are born in the hippocampus of the brain, an event known as neurogenesis. Exercise enhances hippocampal neurogenesis, produces antidepressant effects and promotes memory and learning. However, the molecular mechanism of this effect is not well understood. We found that serotonin released in the brain by exercise activates the ligand-gated ion channel receptor for serotonin (5-HT3 receptor), which has positive effects on neurogenesis in the hippocampus and antidepressant behavior in mouse models [1]. We are studying the detailed mechanism of these processes [2].

(Photo 1, Neurogenesis in the hippocampus increases with exercise)

2) Fear memory and Post-Traumatic Stress Disorder (PTSD)

Dangerous experiences are stored in the brain as fear memory. The purpose of fear memory is to quickly detect and avoid dangers when encountering similar situations again. However, if the individual is assured that new encounter of the same situation is not dangerous, then fear memory will be attenuated and eventually eliminated. Fear memory consists of a series of processes including acquisition, consolidation, and extinction. Dysfunction in the fear memory mechanism, in particular the extinction process, is associated with disorders such as Post-Traumatic Stress Disorder (PTSD). We found 5-HT3 receptor knockout mice showed no abnormalities in the acquisition and retention of fear memories, but that extinction was dysfunctional [3]. We are using this model to study the fear mechanism and the pathogenesis of PTSD.

3) Effects of emotion on sensory systems

Sensory organs express characteristic genes, the abnormalities of which are associated with diseases inflicting the specific organ. We have studied sensory functions such as hearing, pain, bladder control and taste using knockout mice [4]. There is a strong association between emotion and sensory systems. We are therefore researching how emotions can affect on sensory perceptions.

(Photo 2, Left, bladder pressure in P2X3 receptor KO mouse. Right, localization of ASIC1b in inner ear hair cells)

References

1. Kondo et al. Molecular Psychiatry, 20:1428-37, 2015.
2. Kondo et al. Molecular Psychiatry, in press.
3. Kondo et al. Learning & Memory, 21: 1–4, 2014.
4. Takezawa et al. Scientific Reports, 6: 19585, 2016.