The previous studies on the anxiety-like behaviour in rats by using elevated plus maze and open field have provided rather unequivocal results because they obtained data at different times of the day. These studies have never investigated the effects of the different times of day in a single research paradigm even though the results of such studies are generally attributed to the different measurement times. Thus, we aimed to examine the effects of the time of the day and the pinealectomy on anxiety-like behaviour in male Wistar albino rats by using elevated plus maze and open field in this study. Experiments were performed with control and pinealectomy groups at the four different time points (6:00, 12:00, 18:00 and 24:00 hr; LD 12:12, lights on at 6:00 h and off at 18:00 h). In open field, the main effect of the measurement time was significant on the total distance travelled, the mobility and the velocity. In elevated plus maze, the main effect of the measurement time was significant on the total distance travelled, the total entry to closed arms and mobility. The main effect of the pinealectomy was insignificant on all of the measured parameters in both open field and elevated plus maze except for the total entry to closed arms in elevated plus maze. The results of the present study showed for the first time that the time of the day when the measurements are performed is important on the anxiety-like behaviour of the Wistar albino rats.
Many people regularly wake up early in the morning on week days; however, during weekends, they stay awake late into the night and wake up late, thus representing a phase delay in their locomotor activity and sleeping pattern. We suggest that these phase delays on weekends may affect the spatial memory performance at the first couple of days in the following week. In the present study, we aimed to investigate the effects of the weekend phase delays on spatial memory performance of the Wistar albino rats at the beginning of the coming week by using Morris water maze. Control and phase delay groups were performed for both juvenile and adult rats in males and females. After eight weeks of the experimental phase delays, Morris water maze experiments were performed. Locomotor activity rhythms of the rats were also examined. The adult rats showed better learning performances in the total distance travelled and latency than the juvenile ones. However, juvenile rats entered and spent more time in the correct quadrant than adult ones. Phase delays reduced the velocity of the rats. The interaction effects among the phase delays, generation and sex were also significant. The findings of the present study showed that the phase delays at the weekends as well as their interaction with sex and generation are important on the learning performances of the Wistar albino rats.
We studied the effects of melatonin and leptin hormones on ovarian follicular development in intact and pinealectomized female Syrian hamsters. We first monitored the oestrous cycle of the hamsters by the vaginal smear samples throughout a ten day period to start the injections simultaneously in all groups and performed saline, melatonin and leptin hormone injection groups for both control and pinealectomized hamsters. Then the injections were applied for four days starting the oestrus phase of the cycle and the ovaries were removed for preparation of histological analysis. We measured the diameters and the numbers of the follicles and we classified the follicles according to the number of the granulosa cell layer. Leptin hormone injection increased melatonin hormone injection decreased the number and the diameter of the follicles. The stimulating effect of the leptin hormone was more pronounced in the pinealectomized group. The results of the present study indicate that the removal of the pineal gland and leptin hormone administration are playing a stimulatory while melatonin hormone administration is playing an inhibitory role on the follicular development in female Syrian hamsters.
Melatonin is the main hormone of the pineal gland that informs the body about the environmental light and darkness regimen and is considered to regulate many important physiological and behavioural activities. In the present study, we examined the effects of pinealectomy, constant-release melatonin implants and timed melatonin injections on spatial memory in male Wistar rats by using Morris water maze. Pinealectomy, melatonin injection and melatonin implantation were performed on groups, including controls for all groups. After a week of the pinealectomy and melatonin implantation surgeries, we applied the injections and made the training trials throughout 4 days. At the fifth day, experiments were performed and recorded. Spatial memory performance of the rats was impaired by the pinealectomy and melatonin injections, since they elongated the latency and shortened the time passed in the correct quadrant. Melatonin implantation did not affect the spatial memory performance of the rats. The latency and the time passed in correct quadrant were not statistically different from their controls. The results suggest that while the removal of the pineal gland and exogenous administration of melatonin via injections are causing impairment, constantrelease melatonin administration via implantation does not affect the spatial memory in Wistar albino rats.
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