Micronucleated polychromatic (mn-PCE) and normochromatic erythrocytes (nm-NCE) were enumerated in the bone marrow and peripheral blood of Swiss male mice at different time intervals following whole-body (1.0 Gy) gamma-irradiation. Polychromatic cells migrated to the peripheral blood soon after their formation in the bone marrow and mn-PCE achieved a frequency close to that of the bone marrow with a delay of about 12 h. The optimal time for peripheral sampling was found to be about 36 h after radiation exposure. The frequency of mn-NCE in bone marrow and peripheral blood showed only a moderate and gradual increase till 60 h, and was much lower in the latter. In another experiment, mice irradiated with 0.42 Gy gamma-rays (0.21 Gy/h) once a day for 5, 10 or 15 days (5 days per week) showed a cumulative dose-dependent increase in the levels of mn-NCE in the peripheral blood, sampled at 7 or 21 days after the last exposure. These observations demonstrate persistence and accumulation of mn-PCE in the peripheral blood of mice during repeated exposure to ionizing radiation, and the sampling could be delayed up to several days after the last exposure. Thus, peripheral mn-PCE, scored between 24-48 h following irradiation, can be conveniently used to measure acute chromosomal damage induced by ionizing radiation in the bone marrow erythroblasts of mice, while peripheral mn-NCE are suited to monitor accumulated damage during chronic/repeated exposure.
Adult male Syrian hamsters maintained under 6-h light, 18-h dark cycles (lights out daily from 1200-0600 h) were exposed to either 1 or 5 sec light either 8 h (at 2000 h) or 12 h (at 2400 h) into the dark phase. The light had an irradiance of 32,000 microW/cm2. With both light pulse durations and at both times, melatonin levels were depressed to daytime values 30 min after the onset of the light pulse. Whereas pineal melatonin production eventually increased to high nighttime values in hamsters exposed to 1 sec light at either 2000 or 2400 h and in animals receiving a 5-sec light pulse at 2000 h, when the 5-sec light occurred at 2400 h, pineal melatonin levels remained low for the remainder of the night. Thus, both the placement and the duration of light exposure appear to be important in determining the ability of light to depress melatonin production in the Syrian hamster.
Pineal N-acetyl-transferase activity and radioimmunoassayable melatonin levels were determined in adult male gerbils subjected to aggressive encounters using the intruder-model. In the first experiment, a single encounter of 3 min was applied in the afternoon to intact and to animals with sympathetically denervated pineal organs. Compared with controls, both stressed groups demonstrated a drastic decrease in N-acetyl-transferase activity followed by a slow recovery. In both groups there also occurred a marked change in pineal melatonin content: in intact animals pineal melatonin levels were elevated immediately after the encounter; thereafter, melatonin values decreased. In animals bearing denervated pineal organs melatonin levels fell as a consequence of the encounter. In a second experiment, intact gerbils experienced four daily encounters of 1 min for one week. Thereafter the nocturnal formation of melatonin was studied. In comparison with untreated controls, the repeatedly stressed animals demonstrated a temporal delay in the rise of both N-acetyl-transferase activity and melatonin. Since the pineal organ is able to transduce events of the social environment into an endocrine message--as set forth by both our experiments--the pineal organ might play an important role within central processing of social stress.
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