Circadian effects of ionizing radiation on reproductive function and clock genes expression in male mouse

BACKGROUND@#Exposure to the ionizing radiation (IR) encountered outside the magnetic field of the Earth poses a persistent threat to the reproductive functions of astronauts. The potential effects of space IR on the circadian rhythms of male reproductive functions have not been well characterized so far.@*METHODS@#Here, we investigated the circadian effects of IR exposure (3 Gy X-rays) on reproductive functional markers in mouse testicular tissue and epididymis at regular intervals over a 24-h day. For each animal, epididymis was tested for sperm motility, and the testis tissue was used for daily sperm production (DSP), testosterone levels, and activities of testicular enzymes (glucose-6-phosphate dehydrogenase (G6PDH), sorbitol dehydrogenase (SDH), lactic dehydrogenase (LDH), and acid phosphatase (ACP)), and the clock genes mRNA expression such as Clock, Bmal1, Ror-α, Ror-β, or Ror-γ.@*RESULTS@#Mice exposed to IR exhibited a disruption in circadian rhythms of reproductive markers, as indicated by decreased sperm motility, increased daily sperm production (DSP), and reduced activities of testis enzymes such as G6PDH, SDH, LDH, and ACP. Moreover, IR exposure also decreased mRNA expression of five clock genes (Clock, Bmal1, Ror-α, Ror-β, or Ror-γ) in testis, with alteration in the rhythm parameters.@*CONCLUSION@#These findings suggested potential health effects of IR exposure on reproductive functions of male astronauts, in terms of both the daily overall level as well as the circadian rhythmicity.

Photoperiodic effects on activity behaviour in the spiny eel (Macrognathus pancalus).

The study focused on the characteristics of circadian locomotor activity in the spiny eel, M. pancalus, kept under different photoperiodic conditions. Two experiments were conducted. Experiment 1 tested the light intensity dependent effect on circadian rhythmicity of the locomotor activity in spiny eel. Three groups of fish were entrained to 12L:12D conditions for 10 days. Thereafter, they were released to constant conditions for 15 days as indicated below: group 1-DD (0 lux), group 2- LLdim (~1 lux) and group 3-LLbright (~500 lux). The locomotor activity of the fish, housed singly in an aquarium, was recorded continuously with infrared sensors connected to a computer. More than 90% activity of the eels was confined to the dark hours suggesting nocturnal habit. Under constant conditions, the activity in 7/9 fish in group 1, 4/8 in group 2 and 3/8 in group 3, started free running with a mean circadian period of 24.48 ± 0.17 h, 23.21 ± 0.47 h and 25.54 ± 1.13 h in respective groups. Remaining fish in each group became arrhythmic. This suggests that spiny eel can be synchronised to LD cycle and under constant conditions they free run with a circadian period. However, their activity under LL is light intensity dependent; higher the intensity, more disruption in circadian locomotor activity. Experiment 2 was conducted to study the effect of decreasing night length (increasing photoperiod) on circadian locomotor activity. The fish were sequentially exposed to 16D (8L:16D), 12D (12L:12D), 8D (16L:8D), 4D (20L:4D) and 2D (22L:2D) for 10 days in each condition, thereafter, they were released in constant dark (DD= 0lux). The results showed that the duration of night length affects both, the amplitude and duration of locomotor activity. It can be concluded that the spiny eels are nocturnal and that their locomotor activity is under the circadian control and may be influenced by the photoperiod.

Effects of light intensity on circadian activity behaviour in the Indian weaverbird (Ploceus philippinus).

Circadian (locomotor activity/perching) behaviour of the weaverbird (Ploceus philippinus) under different light intensities was studied. Six groups of birds were subjected to 12L:12D (L = 1000 and 10 lux and D = 0.3 lux) for two weeks, and thereafter released into constant dim illumination (LLdim = 0.3 lux). After two weeks of LLdim, birds were given a 2 h light pulse of 1000 lux at circadian time (CT) 12, 17 and 20, and exposure of LLdim was continued for another two weeks and the activity pattern was monitored. As expected, all birds were entrained under 12L:12D showing dense-activity in the group that was placed under light phase of 1000 lux. Under LLdim birds exhibited circadian activity rhythms with periods longer or shorter than 24 h. Light pulse at CT 12 caused small delay shift in the activity phase, but a larger delay in phase shift occurred when the pulse was given at CT 17. A pulse at CT 20 caused small advanced phase shift. Thus, photoperiodic weaverbird appears to show circadian system regulated behaviour as seen by activity-rest pattern under programmed light cycles.

Proposal of an experimental model for the study of polycystic ovaries

In view of the correlation of the circadian system with the estrous cycle in the rat, some investigators have proposed the induction of polycystic ovaries by exposing rats to continuous light. However, there is divergence with respect to time of exposure and light intensity. in the present paper we propose a simple and efficient experimental model for the study of polycystic ovarian physiopathology in rats. Twenty female Wistar rats weighing 200-220 g were initially submitted to a 14-h light/10-h dark cycle. of the animals with regular estrous cycles, 9 were exposed to continuous light (600 lux) for 74 days (group 1) and 6 remained under the initial lighting conditions. A daily vaginal smear was used as indirect evidence for the changes in the estrous cycle. Plasma gonadotropin measurement and histological ovarian analysis showed that 90% of the animals in group 1 developed cystic follicles with the absence of the corpus luteum, despite the lack of reduction in ovarian weight commonly observed under 24-h lghting. This observation may be explained by the reduced time of stress to which the animals were submitted, since polycystic ovarian development occurred within less than 75 days of continuous exposure to 600-lux light, a time relatively shorter than commonly reported in the literature