Seiichi Nohara

Activation of cerebral dopaminergic systems by noise and whole-body vibration

To clarify the involvement of the central nervous system in responses of organisms to noise and whole-body vibration, the activity of dopamine (DA) neuron systems was estimated by examining DA turnover rates in various discrete regions of the brains of rats exposed to noise (broad band, 102 dB) or whole-body vibration (20 Hz, 4G) for 90 min. Plasma corticosterone level (COR) was determined simultaneously as an index of stress-induced autonomic-nervous and endocrine functions. Noise and whole-body vibration increased both COR and DA turnover rates (shown by an increase of homovanillic acid (HVA) and/or HVA/DA ratio) in the frontal cortex (FC) and the nucleus accumbens (NAc). Only noise increased the DA turnover rate in the amygdala (AMY). Furthermore, strong positive correlations of the HVA/DA ratios in the FC and the NAc with COR were observed in rats exposed to noise or vibration. These results suggest that the responses of organisms to noise and whole-body vibration may be critically mediated by cerebral DA systems, in particular by the mesocortical DA system, indicating that change of DA in the AMY can be considered a specific response to noise.

Effects of whole-body vibration stress on substance P- and neurotensin-like immunoreactivity in the rat brain

In order to clarify the involvement of substance P (SP) and neurotensin (NT) neurons in the response of organisms to stress, SP-like immunoreactivity (SP-LI) and NT-like immunoreactivity (NT-LI) were determined in various regions of the rat brain following exposure to the whole-body vibration (20 Hz, 4 G, 90 min). SP-LI and NT-LI in the rat brain were measured by means of a sensitive and specific double-antibody solid-phase enzyme immunoassay. SP-LI in the frontal cortex was significantly reduced following whole-body vibration, while that in the nucleus accumbens and amygdala was significantly increased. NT-LI in both the frontal cortex and the hypothalamus of rats exposed to the whole-body vibration was significantly increased. However, striatal SP-LI and NT-LI remained unchanged. The present findings indicate that the SP and NT neuronal systems in various brain areas are involved in the response to stress. The frontal and amygdalofugal SP and hypothalamic NT neuronal systems, in particular, may have an important role in mediating the response of organisms to the whole-body vibration-induced stress.

Experimental Studies on the Pathogenesis of the Gastric Mucosal Lesions Induced by Whole-Body Vibration

In order to determine the pathogenesis of gastric mucosal lesions induced by whole-body vibration (WBV), the effects of WBV (3.0 G, 10 Hz, 90 min) on gastric mucosal blood flow (GMBF), plasma corticosterone (COR) and catecholamines (CA), and gastric ulcer formation were investigated in relation to the effects of forced water-immersion stress (FWI) upon the same parameters. While WBV increased GMBF during the exposure, FWI decreased it both during and after the stress. No difference in the severity of ulcer formation between the WBV and the FWI groups was seen. Both WBV and FWI increased plasma COR and CA, although the degree of the increase in COR that accompanied WBV was less than that associated with FWI. Truncal vagotomy attenuated the reduction of GMBF and the extent of ulcer formation that occurred with FWI, but promoted a reduction of GMBF with WBV. These findings indicate that ulceration induced by WBV may be caused primarily by its direct and specific mechanical actions and not by indirect, central nervous system effects known to be important in the pathogenesis of ulcerations produced by mental stress.

Study on the perceptible level for infrasound

The human perception of infrasound was investigated by a field survey. Experiments on the perceptible level of infrasound were performed at various places, such as under a bridge, inside an automobile and around a cooling tower, where infrasounds were predominantly observed. The dose-response relationship was also evaluated under various levels of infrasound with a single predominant frequency. Examinees were asked whether they could feel infrasound as pressure on the ears and head, and/or as reverberation in the chest and abdomen. In the frequency range between 6 and 23 Hz, the 50% response level (threshold value) had a slope of −10 dB/octave, and at 10 Hz was about 93–94 dB. The 20% response level was nearly 6 dB lower than the 50% response level, and the 80% response level was nearly 6 dB higher than the 50% response level. The response level for the chest and abdomen was 6–9 dB higher than that of the total response for the ear, head, chest and abdomen.

Combined effect of whole‐body vibration and noise on the dopamine turnover in the rat brain

In order to clarify the combined effects of whole‐body vibration and noise on dopamine (DA) metabolism within the brain, which is known to regulate the response of the organism to various stimuli, the DA turnover rate in regions of the rat brain was determined. The rats were divided into five groups: (1) control; (2) wholebody vibration (4 G, 20 Hz, 90 min) exposure alone; (3) noise [70 dB(A), 90 min] exposure alone; (4) noise [100 dB(A), 90 min] exposure alone; and (5) combined exposure for 90 min to whole‐body vibration (4 G, 20 Hz) and noise [100 dB(A)]. Changes of plasma corticosterone levels were examined as indices of the pituitary‐adrenal function (PAF). The whole‐body vibration exposure alone caused increases in the DA turnover rate [an increase of homovanillic acid (HVA) or HVA/DA] in the frontal cortex and nucleus accumbens. Noise exposure alone caused metabolic increases in the amygdala. The combined effect of whole‐body vibration and noise on the DA neuron systems suggested that the response o...

System for monitoring peripheral circulation in the diagnosis of vibration hazards

Peripheral circulatory disorders such as Raynauds phenomenon are thought to be basal symptoms of vibration hazards. The elucidation of their pathogenesis and their diagnosis between attacks is regarded as important. A system for monitoring the body surface circulation noninvasively and continuously has been developed, which enables the quantitative dynamic assessment of skin blood flow. This apparatus is based on the thermal diffusion method and uses a probe incorporating a Peltier stack. After fundamental studies on this system, the peripheral circulatory functions of workers using vibrating tools were studied. The workers were divided into three groups: group A, without any symptoms; group B, with numbness and/or pain but without Raynauds phenomenon; and group C, with Raynauds phenomenon. The finger blood flow (FBF) of group C at rest was significantly lower than that of group A (p < 0.01). In a handgrip test and with exposure to local vibration (60 Hz, 50 m/s2), the FBF of group A significantly changed compared to its value at rest, but that of group C showed no significant change.