Contrary to previous presumption, accumulated evidence indicates that far-infrared rays are biologically active. A small ceramic disk that emits far-infrared rays (4-16 microns) has commonly been applied to a local spot or a whole part of the body for exposure. Pioneering attempts to experimentally analyze an effect of acute and chronic radiation of far-infrared rays on living organisms have detected a growth-promoting effect in growing rats, a sleep-modulatory effect in freely behaving rats and an insomiac patient, and a blood circulation-enhancing effect in human skin. Questionnaires to 542 users of far-infrared radiator disks embedded in bedclothes revealed that the majority of the users subjectively evaluated an improvement of their health. These effects on living organisms appear to be non-specifically triggered by an exposure to far-infrared rays, which eventually induce an increase in temperature of the body tissues or, more basically, an elevated motility of body fluids due to decrease in size of water clusters.
We continuously monitored the circadian sleep patterns of unrestrained rats for more than 96 hr and infused various prostaglandins into their third ventricles for 10 hr to study the effects on inducing sleep. Prostaglandin D2 at 6 fmol/min had no effect on either slow wave sleep or paradoxical sleep. However, prostaglandin D2 at as little as 60 fmol/min caused a significant amount of excess slow wave sleep as compared with the control level during saline infusion. Paradoxical sleep was induced by prostaglandin D2 at doses greater than 600 fmol/min. Prostaglandin D2 (600 fmol/min) increased slow wave sleep by 33% and paradoxical sleep by 56%. Although prostaglandin F2a (600 fmol/min) increased the amount of slow wave sleep, its activity was less than that of the same amount of prostaglandin D2. Prostaglandin E2 (600 fmol/min) had no effect on increasing the amounts of both slow wave sleep and paradoxical sleep. During the infusion of prostaglandin D2, rats were easily aroused by clap sound stimulation and their sleeping and waking postures remained normal. Further, their sleep was episodic, as observed in the physiological sleep of rats.Prostaglandin D2 (PGD2) has been identified as a natural constituent in brains of various mammals (1-4) and its synthesis and degradation in brain have been investigated in detail (2, 5, 6). Recently, Ueno et aL (4,7,8) reported that the use of the intracerebral microinjection technique to administer nmol doses of PGD2 elicits several central actions. One of the prominent actions of PGD2 was the induction of sleep (7,8). A site of action of PGD2 on inducing sleep was the preoptic area and 0.3 nmol of PGD2 induced excess slow wave sleep (SWS) (7). However, the PGD2 content in the preoptic/hypothalamic area in rat brain was 4-6 pmol/g (wet weight) of tissue (3, 4), indicating that even the doses we used before were not physiologically feasible. In the present study, we continuously infused small amounts of various PGs into the third ventricles of conscious rats and found that PGD2 at as little as 60 fmol/min induced excess sleep.MATERIALS AND METHODS Experimental Animals. Male Sprague-Dawley rats, 300-350 g, 70-80 days old were used. Rats were housed in a 12-hr light (08:00-20:00)/dark (20:00-08:00) cycle for at least 2 wk prior to surgery. Under pentobarbital anesthesia (50 mg/kg), rats were mounted on a stereotaxic instrument with the head fixed according to the coordinate system of Pellegrino et aL (9). For electroencephalogram (EEG) recordings, three silver ball electrodes were placed on the cortex and a silver plate over the frontal skull served as the indifferent electrode. The electromyogram (EMG) electrodes were inserted into the neck muscle. For intracerebral infusion to the third ventricle, a stainless steel cannula (o.d., 0.35 mm) was placed 3.4 mm lateral and 0.6 mm anterior from the bregma and inserted about 9 mm from the surface of the cortex at an angle of 20°from the midsagittal plane. The position of the cannula was determined by x-ray photographs. The ele...
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