One millisecond of light suffices to suppressnighttime pineal melatonin synthesis in rats

Q: What was the main experimental variable in the study?

The study used a single high-intensity light pulse with a duration of 1 ms delivered during the rats’ dark phase.

Q: How soon after light exposure were the pineal effects measured?

Pineal N-acetyltransferase activity and melatonin content were assessed 10 minutes after the light pulse.

Q: What conclusion does the study draw about the pineal’s sensitivity to light duration?

It concludes that the rat pineal can respond to extremely short light flashes, suggesting a required amount of radiation energy that is independent of exposure duration.

Oct 6, 2026

Uploaded by ahduag

A single 1 ms, high-intensity light pulse was tested to determine whether it can rapidly inhibit nighttime pineal function in male Sprague-Dawley rats. Ten minutes after exposure, pineal N-acetyltransferase activity and melatonin content were significantly reduced compared with untreated controls. The findings indicate that the rat pineal responds to extremely brief high-intensity flashes and support the idea that a threshold radiation energy is required regardless of exposure duration.

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# One millisecond of light suffices to suppressnighttime pineal melatonin synthesis in rats L.Vollrath¹,A.Seidel¹,A.Huesgen¹,B.Manz²,K.Pollow²and P.Leiderer³ Institute of Anatomy,2Department of Experimental Endocrinology and³/nstitute of Physics.JohannesGutenberg University,Mainz(F.R.G.(Received 7 December 1988;Accepted 7 December 1988) Key words:Rat:Pineal gland;Melatonin synthesis;Light exposurc The effect of a single high-intensity light pulse with a duration of 1 ms on nighttime pineal activity ofmale Sprague-Dawley rats was investigated.10 minutes after light exposure pineal N-actyltransferase ac-tivity and melatonin content were significantly reduced.These results show that the rat pineal is capableof responding to very short light flashes of high intensity. In numerous experiments it has been demonstrated that the biosynthetic activityof the mammalian pineal gland is controlled by environmental light.This environ-mental cue acts through the retinal-hypothalamic pathway and is mediated by thesympathetic innervation of the pineal gland [4].When rats or Syrian hamsters areexposed during the dark phase to artificial light for 1 min or less,both pineal N-ace-tyltransferase(NAT)activity and melatonin content are rapidly decreased [2,5,7,9].However.electrophysiological studies have shown that the mammalian retina re-sponds to light pulses much shorter than 1 s [10].This prompted us to investigatethe effect of a light flash of 1 ms on pineal activity in rats. Male Sprague-Dawley rats with a body weight between 365 and 465g wereobtaincd from a commercial breeder.After arrival the animals were kept under rou-tine laboratory conditions for 4 weeks(12 h light-12 h dark;lights on at 07.00 h;white fluorescent strip light;2001×at cage level).Six h after the onset of darkness7 rats were exposed to a light pulse produced by a commercial photographic flashlight.The duration of this flash was 1 ms as measured by a PIN-photodiode con-nccted to a storagc oscilloscope(GOULD 4035).Intensity was 2000 mWs/cm²atcage level.Ten min later the rats were sacrificed by decapitation.Six untreated ratskilled under dim red light(<1.5μW/cm²)served as controls.The pineal was rapidlyremoved and cut in half.One half of the gland was processed and reserved for futureelectronmicroscopic studies.The other half was frozen in liquid nitrogen and 8hlatersonicated in 60μl 50 mmol/l phosphate buffer pH 6.5.NAT activity was measured as described by Deguchi and Axelrod [2].Pineal melatonin levels were assessed byradioimmunoassay [1]and protein content was measured as described by Lowry etal.[6].Means were compared by Student's t-test. Means were compared by Student's t-test. Light exposure reduced the pineal NAT-activity significantly(P<0.01)from 84.6±18.9nmol·mg protein-¹·h-¹(mean±S.E.M.)to 6.4±1.6 nmol/mg protein-1.h-¹.Melatonin levels dropped from 18.0±1.7 to 0.21±0.07 ng mg protein-(P<0.01). The reduction of pineal melatonin synthesis found in our study was similar to thesuppression in response to much longer light pulses of 0.1 min in rats [5]and to a5-or l-s light pulse of very high intensity in Syrian hamsters [9].In a study by Minne-mann et al.[8]the minimum intensity which affected pineal melatonin content during30 min exposure was 0.11 μW/cm²,corresponding to a total radiation efflux ofapproximately 200 μWs/cm².In our study,the rats received about ten times as muchradiation within one millisecond.The suppression of NAT-activity and pineal mela-tonin content shows that the rat pineal is capable of responding to extremely shortlight flashes of high intensity.This supports earlier suggestions [11]that in rats a cer-tain amount of radiation energy is necessary to affect pineal function,independentof the duration of exposure. The technical assistance of R.Lieberth is gratefully acknowlegded.This study wassupported by the Deutsche Forschungsgemeinschaft Vo 135/8-5. I Althaus,U.,Manz,B.and Pollow,K.,Direct radioimmunoassay(125T)of free mcla

FAQs

What was the main experimental variable in the study?

The study used a single high-intensity light pulse with a duration of 1 ms delivered during the rats’ dark phase.

How soon after light exposure were the pineal effects measured?

Pineal N-acetyltransferase activity and melatonin content were assessed 10 minutes after the light pulse.

What conclusion does the study draw about the pineal’s sensitivity to light duration?

It concludes that the rat pineal can respond to extremely short light flashes, suggesting a required amount of radiation energy that is independent of exposure duration.

Oct 6, 2026

Uploaded by ahduag