Response of pineal serotonin N-acetyltransferase activity in male guinea pigs exposed to light pulses at night (original) (raw)
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Journal of Pineal Research, 1985
In three separate experiments, the effect of acute exposure to either artificial o r natural light during darkness of pineal N-acetyltransferase (NAT) activity and melatonin content was studied in the cotton rat (Szgmodon hispidus). The exposure of animals to an artificial-light irradiance of 160,000 pW/cm2 during darkness for either 1 s, 5 s, or 30 min was followed by a precipitous decline in pineal NAT activity and melatonin content when measured at either 15 or 30 min after light onset. When cotton rats were acutely exposed to light at night for 5 s, irradiances of either 3.2, 32, 320, and 3,200 did not suppress either pineal NAT or melatonin 30 min later; however, if the 5-s exposure had an irradiance of either 32,000 or 160,000 pWlcm2, the pineal enzyme activity and indole content were depressed. Moonlight, which had a maximal irradiance of 0.32 pW/cm2, was unable to suppress pineal NAT activity and melatonin content even when the animals were exposed to the moonlight for 30 min. The treatment of cotton rats with either norepinephrine or its agonist, isoproterenol, before their exposure to light at night retarded slightly the suppressive effect of light on the pineal constituents measured. Also, these drug treatments suppressed the pre-exposure levels of both NAT activity and melatonin content in the cotton rat pineal gland.
Cell and Tissue Research, 1986
To characterize further the functionally enigmatic "synaptic" ribbons (SR) of the mammalian pineal gland and to study possible relationships to melatonin synthesis, in the present investigation rats were exposed to short pulses of light at night when both SR numbers and serotonin N-acetyltransferase (NAT) activity are high in comparison to day-time values. Male Sprague-Dawley rats were killed at 13:00 and 01:00 h, respectively, and at 01:10 and 02:00 h after exposure to light for 10 and 60 rain, respectively. The pineals were rapidly taken out and cut sagittally in half. One half was processed for electron-microscopic quantitation of SR numbers and the other half for NAT determinations. It was found that both SR numbers and NAT activity decreased significantly when the animals were exposed to light at night. Although both parameters showed corresponding changes, there was no clear-cut correlation between SR numbers and NAT activity in individual animals within a group, except after exposure to light for 60 rain when a positive correlation (R--0.939; p < 0.05) existed. After exposure to light the electron-lucent vesicles of the SR decreased in number, but the length of the SR was unchanged. These results show that numbers of pineal SR can be easily and quickly manipulated and that the presently used model may be ideal in studying the poorly understood mode in which degradation of SR occurs.
Brain Research, 1983
When Richardson's ground squirrels were kept under light:dark cycles of 14:10 h there was no nocturnal rise in pineal hydroxyindole-O-methyltransferase (HIOMT) activity. Conversely, the 10 h dark period was associated with large nocturnal rises in both pineal serotonin-N-acetyltransferase (NAT) activity and radioimmunoassayable melatonin levels. The nighttime rises in pineal NAT and melatonin were not suppressed by the exposure of the animals to a light irradiance of 925 ~W/cm 2 during the normal dark period. On the other hand, when the light irradiance was increased to 1850 ~W/cm 2 the rise in pineal NAT activity was eliminated while the melatonin rise was greatly reduced. When ground squirrels were acutely exposed to a light irradiance of 1850juW/cm 2 for 30 min beginning at 5.5 h after lights out, pineal NAT activity and melatonin levels were reduced to daytime values within 30 rain. The half-time (tv2) for each constituent was less than 10 min. Exposure to a light irradiance of either 5 s or 5 min (beginning at 5.5 h into dark period) was equally as effective as 30 min light exposure in inhibiting pineal NAT activity and melatonin levels. When animals were returned to darkness after a 30 rain exposure to a light irradiance of 1850/~W/cm 2 at night, both pineal NAT activity and melatonin levels were restored to high nighttime levels within 2 h of their return to darkness. The results indicate that the pineal gland of the wild-captured, diurnal Richardson's ground squirrel is 9000x less sensitive to light at night than is the pineal gland of the laboratory raised, nocturnal Syrian hamster.
2000
OBJECTIVES: Results of the majority of studies have revealed that diurnal changes in circulating melatonin level in the domestic pig differ from the typical patterns observed in other species. The aim of the present investigation was to study the effect of continuous darkness and continuous illumination on plasma melatonin in the pig. MATERIAL AND METHODS: The study was performed on three groups of immature gilts. The first group was kept under 14hrs light:10hrs dark cycle (500 lx of fluorescent light during photophase), the second group-under continuous illumination (500 lx of fluorescent light) and the third group-under red light with intensity below 1 lx, which was considered as darkness. The pigs were maintained nine days under above reported conditions and then plasma melatonin was monitored during five consecutive days. RESULTS: The diurnal changes in plasma melatonin concentration with increased levels during scotophases were observed in gilts kept under light:dark cycle, but...
Journal of Pineal Research, 1984
The purpose of the present studies using artificial light was to determine how the timing and duration of exposure influence the light-induced suppression of pineal melatonin levels in hamsters. An 8;min exposure to 0.186 pWlcm2 of cool white fluorescent light caused a continued depression of pineal melatonin even when animals were returned to darkness. In addition, the pineal gland does not appear to change its sensitivity to light throughout the night. A 20-min exposure to 0.019 pW/cm* of cool white fluorescent light did not significantly suppress pineal melatonin during any time of the melatonin peak, whereas a 20-min exposure to 0.186 pWlcm2 was capable of always suppressing melatonin. Furthermore, increasing the duration of 0.019-pW/cm2 exposure to 30, 60, 120, or 180 min does not increase the capacity of this irradiance to depress melatonin. Similar to artifical light, natural light has a variable capacity for suppressing nocturnal levels of pineal melatonin. Twilight irradiances of 0.138 pW/cm2 or less did not suppress nocturnal melatonin whereas twilight irradiances of 3.0 pW/ cm2 or greater did suppress pineal melatonin. A few animals did have lower melatonin after a 40-min exposure to full moonlight during July (0.045 pW/cm2) or January (0.240 pW/cm2). However, pineal melatonin levels remained high in the majority of animals exposed to full moonlight.
Neuroscience Letters, 1987
Castrated male and intact female pigs were kept under natural photoperiodic and temperature condi tions and were killed over a 24 h period in either May (under long days) or in December (under short days). Neither the pineal norepinephrine (NE) concentration nor the melatonin content rose at night: like wise, neither the activities of N-acetyltransferase (NAT) nor hydroxyindole-O-methyltransferasc (HIOMT) increased during darkness. In May pineal melatonin content actually decreased (P<0.05) at night while in December NAT activity fell (P < 0.05) at night. Daytime levels of each of these variables were equivalent to those measured in other species. The absence of a nocturnal increase in pineal melato nin production in either Mayor December raises the possibility that pineal melatonin may be involved in regulating seasonal breeding in the pig in a manner different from other mammals. Alternatively, pineal melatonin production may be unrelated to seasonal reproduction in the pig. Few reports have examined levels of melatonin in the blood of the wild boar and domestic pig. Kennaway et al. [8] measured melatonin in the plasma of one boar and found that the midnight level was about 3 times higher than the midday value. The photoperiodic conditions under which the boar was kept were not specified. Accord ing to McConnell and Ellendorff [10], the plasma melatonin profile in domestic adult German Landrace sows is determined by the photoperiod environment to which the animals are exposed. Thus, under photoperiodic conditions of LD 12: 12 they found that 3 of 4 sows exhibited a nighttime rise in plasma melatonin (the increase ranged from 2 to 5-fold). However, when the animals were shifted to a summer photoperiod,
Neuroscience Letters, 1992
Effects of light on the pineal and plasma melatonin were examined in Wistar and Long-Evans rats at two different times in the dark phase (light off from 18.00 h to 06.00 h) using lights of two different monochromatic wavelengths but with the same irradiance. The green light pulse (520 nm) given at 24.00 h suppressed the pineal and plasma melatonin to the daytime level for at least 2 h, while the red light (660 nm) pulse given at the same time of the day suppressed pineal melatonin only transiently and did not suppress the plasma melatonin at all. Both green and red lights given at 4.00 h suppressed the pineal and plasma melatonin to a similar extent. The results demonstrated that the suppression of melatonin by light depends on the wavelength of light and the circadian phase.
Response of the Pineal Gland in the Rats Exposed to Three Different Light Spectra of Short Periods
Turkish Journal of Veterinary & Animal Sciences, 2006
The pineal gland is a part of the photo-endocrine system. Photon energy is important for the function of this system, and affects the level of nocturnal melatonin. In mammals light-induced suppression of melatonin production is dependent on the intensity and wavelength of the light used. We studied the chronic effects of light wavelengths on the pineal gland in rats after exposure to a short photoperiod using 3 different light spectra with the same irradiance. Male Sprague-Dawley rats were used. The animals were divided into 5 groups. They were exposed 8/16 L:D periods in rooms under automatically regulated light and climate. Lee filters were used for the light spectra application. From animals at the age of 6 months blood samples were taken over a week at the third hour of the dark period under dim red light. The pineal glands were processed for electron microscopy. Melatonin levels in the blood were analyzed by ELISA. Melatonin levels were the higher in control group and group 5 (...