[Neurobiology of physical environmental stress]

Although effects of physical environmental stress, including noise and whole-body vibration, on human psychological activities and emotion are not negligible for environmental and occupational hygiene, attempts to elucidate their physiological and biomedical mechanisms have been not made until recently. Neurobiological researches on the effects of the physical environment, e.g., noise and whole-body vibration on organisms were reviewed. It has been well accepted that such effects can be classified into specific and nonspecific reactions to the stressor. Activations of the mesofrontal and the meso-accumbens dopaminergic (DA) systems and changes of frontal substance P (SP) have been reported to play a part in emotional changes and to be induced by acute physical environmental stressors as a nonspecific reaction. On the basis of data demonstrating that these three systems do not show the same changes with the chronic exposure, it is assumed that emotional changes may account for the differences among the systems. Specific responses of amygdaline DA and SP to noise suggest that the psychopharmacological mechanisms by which actions of DA and SP in the cortical association areas for the sensory systems of hearing, as well as in the amygdala and the mesencephalon together, cause the specific sensation of noise, and furthermore lead to psychological and physical nonspecific reactions. In these mechanisms, descending amygdalofugal neural systems of SP, neurotensin (NT) and somatostatin are activated as a common pathway, and subsequently relayed to the hypothalamus-pituitary system responsible for several endocrinological hormones. The involvements of the hippocampal VIP in whole-body vibration and of the DA and NT in cold exposure have been pointed out. Further researches to elucidate the roles of central neurotransmitters in physical environmental stress will be important in the study of human high-level mental activity.