Foreword

We experience diverse types of stresses from environmental and internal situations. These environmental and internal stresses include physical stresses (e.g., temperature and noises), chemical stresses (e.g., food chemicals and pollution), and biological stresses (e.g., mental stresses and pain caused by diseases or injuries). Our body has tolerance to these stresses to maintain our health. However, when stress level exceeds the tolerable limit, the body dysfunctions and needs a long time to recover. To maintain our health, it is necessary to understand how stress-induced health problems occur.

This special issue provides two informative review articles and three novel original regular articles on the phenomena and mechanisms of biological responsiveness to various stresses. Dr. Yo Shinoda, Dr. Masahiro Akiyama, and Dr. Takashi Toyama present a review about the association between inflammatory responses and neurodegeneration caused by methylmercury which is an environmental toxic chemical. They introduce numerous in vivo and in vitro studies to summarize the regulation of inflammatory responses to methylmercury by various nervous system cell types. Dr. Keiichi Ishihara, Dr. Eri Kawashita, and Dr. Satoshi Akiba present a review about genes and mechanisms related to the pathophysiology of Down syndrome and the significance of copper, an essential trace element, in the accelerated aging and cognitive impairment of patients with Down syndrome. Dr. Eri Segi-Nishida and her colleagues provide valuable information regarding the association between hippocampal inflammation and anxiety-like behavior. Interestingly, the temporal change of inflammatory gene expression and the maturation of dentate gyrus neurons show good correlation with sickness and emotional changes. Dr. Yasuhiro Ishihara and his colleagues describe their findings on the mechanisms and medical approaches for febrile seizure–related epilepsy. They demonstrate that docosahexaenoic acid intake after febrile seizure attenuates increased seizure susceptibility in adulthood by suppressing microglial activation and neuroinflammation. The final article authored by us describes the different responses of hindbrain astrocytes to excess ethanol intake. We also found that estrogen plays a critical role in ethanol-induced astrocytic responses.

These articles deal with different stressors to disclose the physiological responses to stresses. However, the mechanisms of stress responses should be common to some stressors at least in part. Hence, it would be valuable to understand such common mechanisms to aid the treatment and care of our stress-induced health problems. Furthermore, revealing the stress response mechanisms to different types of stressors will contribute toward understanding the responses to multiple stresses. As we are constantly exposed to multiple stresses simultaneously in our daily life, we must consider the combined effect of multiple stresses for maintaining our health. I hope that this issue of Current Topics will contribute toward developing subsequent studies on the understanding of biological stress responses and novel care and treatments to maintain our health in stressful environments. Finally, I thank all authors for their kind contribution to this special issue.