Ryoichi Inaba

Effects of whole body microwave exposure on the rat brain contents of biogenic amines.

SummaryThe effects of whole body microwave exposure on the central nervous system (CNS) of the rat were investigated. Rats weighing from 250 to 320 g were exposed for 1 h to whole body microwave with a frequency of 2450 MHz at power densities of 5 and 10 mW·cm−2 at an ambient temperature of 21–23°C. The rectal temperatures of the rats were measured just before and after microwave exposure and mono-amines and their metabolites in various discrete brain regions were determined after microwave exposure. Microwave exposure at power densities of 5 and 10 mW·cm−2 increased the mean rectal temperature by 2.3°C and 3.4°C, respectively. The noradrenaline content in the hypothalamus was significantly reduced after microwave exposure at a power density of 10 mW·cm−2. There were no differences in the dopamine (DA) content of any region of the brain between microwave exposed rats and control rats. The dihydroxyphenyl acetic acid (DOPAC) content, the main metabolite of DA, was significantly increased in the pons plus medulla oblongata only at a power density of 10 mW·cm−2. The DA turnover rates, the DOPAC:DA ratio, in the striatum and cerebral cortex were significantly increased only at a power density of 10 mW·cm−2 The serotonin (5-hydroxytryptamine, 5-HT) content in all regions of the brain of microwave exposed rats was not different from that of the control rats. The 5-hydroxyindoleacetic acid (5-HIAA) content in the cerebral cortex of microwave exposed rats was significantly increased at power densities of 5 and 10 mW·cm−2. The 5-HT turnover rates and the 5-HIAA:5-HT ratio were significantly increased in the cerebral cortex at a power density of 5 mW·cm−2. Significant increases in the 5-HT turnover rate were observed in the pons plus medulla oblongata and hypopthalamus at a power density of 10 mW·cm−2. These results indicated that whole body microwave exposure with a frequency of 2450 MHz at power densities of 5 and 10 mW·cm−2 affected the function of mono-aminergic neurons in the rat brain. It would seem that the effects of whole body microwave exposure on the CNS can be attributed to the hyperthermia characteristic of microwave exposure, although the direct effects of microwave irradiation on the CNS cannot be completely discarded.

Experimental studies on the effects of vibration and noise on sympathetic nerve activity in skin

SummaryMulti-unit sympathetic activity was recorded at elbow level from median nerve fascicles supplying glabrous skin of the left hand in five healthy subjects. The resultant vasomotor responses accompanying the neural activity were monitored by simultaneous recordings of skin blood flow using the laser doppler method and skin temperature in the innervation zones. No significant change in sympathetic activity was observed during handgrip exercise of the right hand under a constant gripping force of 2 kg. Subjects maintained the same gripping force of the right hand during exposure in random order to local vibration and/or noise, each type of exposure lasting 5 min with intervals of 20 min. A two-peaked significant increase in outflow from sympathetic nerves was observed during local exposure of the right hand to vibration with a frequency of 60 Hz and an acceleration of 50 m·s−2, followed by a postexposure period which revealed a relative suppression of sympathetic nerve activity and a significant increase in blood flow. Noise at 100 dB(A) showed only an initial effect on skin sympathetic nerve activity (SSA), whereas when combined with local vibration at 60 Hz, a pronounced increase in neural activity was noticed, indicating a combined effect of vibration and noise. These results from direct recordings of SSA suggest a sympathetic vasomotor reflex mechanism triggered by local vibration stimuli to the hand.