Bülent Gündüz

Çanakkale Onsekiz Mart Üniversitesi, Kale-Sultanie, Çanakkale, Turkey

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Publications (19)59.18 Total impact

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    Bülent GÜNDÜZ
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    ABSTRACT: We have shown that circadian changes in leptin concentrations are inversely linked to circulating melatonin levels in the Syrian hamster. The present study aimed to assess the effects of subcutaneous melatonin implants under different photoperiodic conditions: did the implants affect serum leptin levels, body weight, food consumption, and/or testicular weight? Male hamsters were exposed to long and short photoperiods for 10 weeks and received subcutaneous melatonin implants (1 mg in 24 mg beeswax) every 2 weeks. Blood samples were collected every week at midday (1200 hours) or midnight (0000 hours) to assess leptin and melatonin concentrations. Testes were measured to calculate weight. Body weight and food intake were determined every week. Melatonin implants blocked the testicular regression produced by short photoperiods. No differences in body weight were observed among any of the groups. Food consumption increased only with the melatonin implant in the short photoperiod. Serum leptin levels in both photoperiods remained constant. Differences were apparent between noon and night leptin profiles. Noon leptin levels were high (16-18 ng/mL) compared to night leptin levels (8-11 ng/mL) in untreated controls. On the other hand, serum leptin concentrations declined in melatonin-implanted hamsters in both photoperiods. The effects of melatonin on leptin hormone profiles are very pronounced, and melatonin seems to have both physiologically and pharmacologically suppressive effects on leptin production by direct or indirect mechanisms.
    Preview · Article · Jan 2014 · Turkish Journal of Biology
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    ABSTRACT: In the present study, the effects of intraamygdalar administrations of melatonin (1 and 100μg/kg), saline and diazepam on the anxiety-like behavior and spatial memory performance in pinealectomized and sham-pinealectomized Wistar rats were investigated. The animals were tested by open field and elevated plus maze tests for anxiety-like behavior, and Morris water maze test for spatial memory. In open field, (a) diazepam was more effective in reducing the anxiety, (b) control subjects were more mobile than pinealectomized subjects and (c) 100μg/kg melatonin administrations reduced the velocity of the animals. In elevated plus maze, (a) 100μg/kg melatonin administrations increased the distance totally travelled and (b) enhanced the time spent in open arms, however, after the pinealectomy, 1μg/kg melatonin administrations decreased it and (c) control animals were less mobile than pinealectomized ones. In Morris water maze, (a) diazepam group travelled more distance than the others in control condition whereas, in pinealectomy condition high dose of melatonin and saline groups travelled more distance than the others, (b) in pinealectomy condition subjects who received 100μg/kg melatonin also travelled more distance than those who received 1μg/kg melatonin and diazepam, (c) the subjects who received 1μg/kg spent less time than those who received other treatments, and (d) in control condition subjects who received 100μg/kg melatonin were slower than those who received the other treatments. In conclusion, melatonin administration to amygdala decreased the anxiety; however, spatial memory performance of the rats was impaired by the pinealectomy and melatonin administrations.
    No preview · Article · Mar 2011 · Behavioural brain research
  • B. Gündüz · Alper Karakas
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    ABSTRACT: The suprachiasmatic nucleus (SCN) generates and controls the circadian rhythms in mammals including the rhythm of locomotor activity. Leptin is a hormone secreted by adipose tissue that informs the brain about the fat stores. SCN neurons express leptin receptors. Here we investigated the effects of 3 different leptin administrations on the locomotor activity of the Syrian hamsters maintained in constant darkness. Animals were intraperitoneally (ip) injected (4 μg/kg), subcutaneously (sc) infused (4 μg/kg), or intra-SCN infused (0.4 μg/kg) with leptin for 3 days at circadian time 10 whereas the controls received saline (0.9% NaCl) at the same time in order to eliminate stress factors. Our results demonstrate that the locomotor activity of the hamsters can be phase advanced by the external leptin administrations. Leptin affected the level of phase-shift s in an administration method-dependent manner. The biggest phase advance was observed in intra-SCN infusion (P = 0.001), and the smallest was in the ip injection (P = 0.041) group. The wheel-turn amounts did not change significantly in the groups before and after the leptin administrations (P = 0.233); however, the period lengths increased (P = 0.011) significantly after leptin administrations. These results suggest for the first time that in vivo leptin administrations may change the rhythm of locomotor activity in adult male Syrian hamsters.
    No preview · Article · Jan 2011 · Turkish Journal of Biology
  • A Karakaş · Aliye Kaya · B Gündüz
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    ABSTRACT: 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.
    No preview · Article · Dec 2010 · Acta Biologica Hungarica
  • A R Gezici · A Karakaş · R Ergün · B Gündüz
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    ABSTRACT: To evaluate the serum melatonin levels in acute period of the spinal cord injury (SCI) caused by trauma in the rats. Traumatic SCI induces many types of physiological and pathological damage, including hormonal level variations. Forty male Sprague-Dawley rats were divided randomly into four groups. In the control group, neither laminectomy nor SCI were performed; only a large laminectomy was performed without SCI in the sham group. In the cervical and thoracic spinal trauma groups, laminectomies at C5-6 and a T6-7 were performed, respectively, followed by clip compression of the spinal cord. Blood samples were drawn 2, 6, 12 and 24 h after the procedures and assayed immediately. The levels of melatonin in the neurotrauma groups were high in the first 2 h, but at the end of sixth hour, melatonin levels increased in sham-operated group, decreased in neurotrauma groups and did not change in control group. At the 12th hour, melatonin levels continued to decrease in thoracic group significantly. At the 24th hour, the melatonin levels decreased in the cervical, control and sham groups, whereas melatonin levels increased in the thoracic group. The present study revealed that (1) activation of endogen melatonin secretion of the organism starts immediately after the SCI, but it shows a great lowering trend between 2 and 6 h post-SCI, (2) the tetraplegic rats, which had complete injuries at the lower cervical spinal cord, could not produce enough melatonin secretion; on the contrary, the paraplegic rats, which had complete injury at the upper thoracic spinal cord, showed normal melatonin secretion.
    No preview · Article · Jul 2009 · Spinal Cord
  • Alper Karakas · Erdinc Serin · Buelent Guenduez · Arzu Ucar Tuerker
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    ABSTRACT: Throughout history folk medicine has served as an alternative or complimentary method of treating disorders like intestinal colic. Mistletoe is a common name for many species of semi-parasitic plants that grow on trees throughout the world, and has been used widely to treat intestinal colic. We conducted a study to evaluate the effect of freeze-dried (group 1) and heat-treated (group 2) extracts of Viscum album subsp. album leaves on contractions induced by acetylcholine in isolated hamster intestinal segments (duodenum, jejunum, and ileum). Freeze-dried extracts decreased intestinal contractions in all the intestinal segments (P < 0.05). The strongest relaxant effect was observed in the jejunum and the weakest was seen in the duodenum. Higher doses of heat-treated extracts were required to affect segmental contractions than that of freeze-dried extracts (P < 0.05); heat-treated extracts had the greatest effect on reducing contractions in the jejunum and the least effect in the duodenum. Mistletoe extracts affected the level of contractions in a dose- and extraction preparation-dependent manner. The results of this study show that mistletoe extracts could be effective against intestinal motility problems and that they have potential use as a therapeutic remedy for intestinal colic.
    No preview · Article · Nov 2008 · Turkish Journal of Biology
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    ABSTRACT: The effects of pinealectomy and leptin hormone on proliferative and apoptotic processes in the epithelia of testicular seminiferous tubules of Syrian hamsters have been investigated. Proliferative and apoptotic processes were assessed semi-quantitatively by proliferating cell nuclear antigen (PCNA) and caspase-3 immune stainings. Animals used in the study were divided into four groups; control, pinealectomy (PinX), leptin-treated (10 microg/mL/day/kg body weight, intraperitoneally) and pinealectomy + leptin groups. Half of the hamsters in each group were exposed to short and the other half to long photoperiods for 8 weeks. In short photoperiod, PCNA activity especially in spermatogonia was significantly higher in the pinealectomy and leptin-treated groups compared with the control group. Histological score (HSCORE) value of PCNA in the PinX + leptin group was lower than those of PinX and leptin-treated groups. HSCORE value of caspase-3 in PinX and PinX + leptin groups was increased. In the long photoperiod, PCNA activation in the PinX group was significantly lower than the control group while the differences between the controls and other groups were not significant. The difference between the increases in caspase-3 activity in the PinX and control groups was significant. Thus, it was observed that photoperiods had no effect on the proliferation activity in the control groups. The inhibiting effect of short photoperiod on testis was not observed throughout 8 weeks. PinX eliminated the inhibiting effect of short photoperiod but did not alter the stimulating effect of long photoperiod. Leptin did not show any effect in long photoperiod but decreased proliferation by stimulating melatonin in short photoperiod.
    No preview · Article · Feb 2008 · International Journal of Andrology
  • A. Karakaş · Bülent GÜNDÜZ
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    ABSTRACT: We investigated whether photoperiodic information is transferred from mother to young and whether the pineal gland and its hormone, melatonin, are involved in this transfer in Mongolian gerbils. Adult female gerbils were paired with males and housed in photoperiods of 12L:12D or 8L:16D. Three groups of pregnant gerbils in each photoperiod were prepared: one group was the sham-operated control, one group consisted of pinealectomized gerbils, and one group consisted of pinealectomized gerbils that were treated with melatonin. Pinealectomy was performed before pairing the animals and melatonin injections were applied to the pinealectomized group from day 8 of gestation until parturition. On the day of parturition, the mother and young were transferred to an intermediate photoperiod (10L:14D). After weaning, body weight gain and gonadal development of the male young were measured every week over 8 weeks. Animals gestated and born to control and pinealectomized + melatonin injected mothers exposed to 12L:12D responded to 10L:14D as a short day; they had significantly (P < 0.05) smaller testes than animals born to pinealectomized mothers. Animals gestated and born to control mothers exposed to 8L:16D responded to 10L:14D as a long day, they had significantly (P < 0.05) larger testes than animals born to pinealectomized and pinealectomized + melatonin injected mothers. Body weights of the gerbils did not vary significantly among the groups (P > 0.05). These results are the first evidence that the photoperiod to which the mother is exposed during gestation affects the postnatal gonadal development of the young and the pineal gland and melatonin play an important role in the transmission of photoperiodic information in the Mongolian gerbil.
    No preview · Article · Jan 2007
  • Alper Karakas · Bülent Gündüz
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    ABSTRACT: The suprachiasmatic nuclei (SCN) generate the circadian rhythm of many hormones. The hormone leptin is a metabolic signal that informs the brain about fat and energy stores of the body. We investigated whether the rhythm of leptin hormone release in Syrian hamsters is directly controlled by the SCN. Three experiments were performed: in the first, hamsters were SCN-lesioned; in the second, hamsters were exposed to different feeding regimes; and in the third, hamsters were adrenalectomized and implanted with cortisol capsules to maintain constant glucocorticoid release. Blood samples were collected before and after the experiments at different clock times and examined for leptin levels by enzyme-linked immunosorbant assay (ELISA). Different feeding regimes and constant glucocorticoid release did not alter the rhythm of leptin release; whereas, SCN lesions abolished the rhythm. The results of the present study suggest the rhythm in leptin release in Syrian hamsters may be controlled by the SCN.
    No preview · Article · Feb 2006 · Chronobiology International
  • A. Karakaş · E. Serin · Bülent GÜNDÜZ
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    ABSTRACT: The circadian rhythm of the locomotor activity is regulated by at least 2 external pacemakers, environmental photoperiod and food availability. In the present study, the effects of short-term (2 weeks) food restriction on locomotor activity rhythm in adult male and female Mongolian gerbils were investigated. Animals were fed ad libitum with no restriction during the first week of the experiment and their daily ad libitum food consumptions were determined. Then the food was restricted 40% of ad libitum for the next 2 weeks. At constant temperature, locomotor activity was monitored by running wheel in animals exposed to a long photoperiod (14L) for 3 weeks. A significant phase advance was recorded in the locomotor activity rhythm in both male and female animals. The shift was bigger in males (12 ± 1.1 h) than in females (6 ± 0.5 h) (P < 0.05). Activity levels and body weights decreased in males (P < 0.01) and females (P < 0.012) compared with the first week values. The gerbils' locomotor activity was significantly affected by the food restriction. These results indicate that the rhythm and the level of the locomotor activity in the Mongolian gerbil can be entrained by food restriction.
    No preview · Article · Jan 2006
  • Alper Karakaş · Cağri Camsari · Erdinç Serin · Bülent Gündüz
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    ABSTRACT: Reproductive activity of Mongolian gerbils is regulated by photoperiod nevertheless body weight regulation is controlled without ambient photoperiod. Food intake is a major factor affecting rodent reproductive efficiency. Leptin is a hormone secreted by adipose tissue and modulates food intake, energy expenditure and body fat stores. In this study we studied the interaction of photoperiod and food availability on growth, sexual maturation and leptin concentration in the male and female gerbils. Gerbils were gestated and reared in either 14L:10D or 2L:22D. At weaning, gerbils were housed individually and divided into three groups: fed ad libitum, fed 80% of ad libitum or fed 60% of ad libitum. Body weights were recorded at weaning and every week thereafter. After twelve weeks of treatment, animals were sacrificed and testes and uterine weights were determined and blood was collected for leptin measurement. Food restriction reduced body weight and inhibited reproductive development. Absolute paired testis weights were similar in ad lib and 80% of ad lib groups but significantly different compared with the 60% of ad lib group in both photoperiods. Body weights were also directly dependent upon the level of food restriction. Uterine mass was only affected in the 60% of ad lib group in 14L but both food restriction levels significantly affected the uterine weights in 2L. Significant variations were found in leptin profiles. Leptin concentration was highest in ad lib and 80% of ad lib groups and lowest in 60% of ad lib groups. These results suggest that the reproductive activity of Mongolian gerbils is sensitive to food intake and multiple potential environmental cues (e.g., food availability, temperature) can be utilized.
    No preview · Article · Jul 2005 · ZOOLOGICAL SCIENCE
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    Bülent Gündüz · Milton H Stetson
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    ABSTRACT: We tested in Siberian hamsters the nature of the maternal signal that relays photoperiodic information to the developing fetuses. As previous investigations have identified maternal hormonal and circadian components in this process, the specific goal of this presentation is to determine quality of the signal that connotes daylength when it is imparted to the fetus. Does the function of the signal received by the fetus best support the coincidence or duration hypotheses of photoperiodic induction? Pregnant hamsters received 1 or 8 hr melatonin or vehicle infusions everyday. Juveniles of intact mothers gestated on 16 hr of light per day (16L) experienced maximal suppression of testicular development when reared on 14L. However, when intact mothers gestated on 10L received a 1-hr melatonin infusion daily at 20:00-21:00 hr, their young responded to 14L with greatly accelerated testicular development. In the absence of the maternal pineal gland (and, therefore, the maternal melatonin signal), the effects of maternal melatonin infusions were reversed. Here, only the juveniles of 16L-gestated females infused at 20:00-21:00 hr daily responded to 14L with enhanced testicular development. All other groups showed the same extent of gonadal development, independent of the time or type of infusion their mothers received. Testicular development on 14L of all juveniles from pinealectomized mothers gestated on 10L was of the same magnitude, regardless of the type and time of infusion their mothers received during pregnancy. The results suggest that the maternal signal transferred to the fetuses during gestation consists not only of the daily melatonin signal, but also some circadian-based component that greatly affects the effect of the former. The timing, and not the duration, of the maternal melatonin signal with respect to the animals' (mother and fetus) circadian day is of crucial importance in the transfer of photoperiodic information from mother to fetus.
    Preview · Article · May 2003 · Journal of Pineal Research
  • Bülent Gündüz
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    ABSTRACT: Melatonin is produced and secreted by the pineal gland in a rhythmic manner; circulating levels are high at night and low in the day. Leptin is a hormone secreted by adipocytes as a product of the obese gene and plays an important role in regulating body energy homeostasis and reproductive function in rodents and humans. The present study was conducted to examine daily fluctuations in serum levels of melatonin and leptin in Syrian hamster. We measured serum leptin and melatonin levels by ELISA in (a) intact and pinealectomized (pinx) male hamsters kept under long daylight conditions [14 h of light (14L)]; (b) intact and pinx hamsters under short daylight (10L); and (c) intact hamsters in constant light (24L). Blood samples were obtained every 2 h throughout a 24-h period. Statistically significant circadian variations were found in both melatonin and leptin profiles. Their relationship was inverse, i.e. when melatonin was high in the serum, leptin was comparably low. These results suggest that there is a rhythm in leptin levels in the adult male Syrian hamster and this rhythm is pineal gland (melatonin) and/or photoperiod dependent.
    No preview · Article · Jul 2002 · Comparative Biochemistry and Physiology - Part A Molecular & Integrative Physiology
  • Alper Karakaş · Bülent Gündüz
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    ABSTRACT: The role of photoperiod in adult testicular maintenance and body weight and juvenile development was assessed in male Mongolian gerbils (Meriones unguiculatus). Gerbils were raised on a 14L (14 hr of light) photoperiod. In the first study, adult gerbils with functional testes were transferred to thirteen different photoperiods (0L, 2L, 4L, 6L, 8L, 10L, 12L, 14L, 16L, 18L, 20L, 22L, or 24L) and body weights and testicular size were measured every week for 10 weeks. Body weights were similar in all groups. Testicular regression had occurred in animals housed on 0L, 2L, 4L, 6L, 8L, and 24L by week 10. In the second study, 14L-born prepubertal gerbils were transferred to thirteen different photoperiods as in the first study. Body weights and testicular development were examined for 10 weeks. At the end of 10 weeks the body weights of animals in all groups except 24L were similar to those of adults. Animals in 24L had a lower body weight gain. Exposure to 0L, 2L, and 24L inhibited testicular development and testes weights were significantly different from those of the other groups. These results demonstrate that maintenance of body weight in adult gerbils appears to be independent of photoperiodic signal. Exposure to very long (24L) and short photoperiods (< 10 hr) causes testicular regression in adult gerbils. Moreover, different photoperiods experienced in early life can influence prepubertal testis growth and body weight gain.
    No preview · Article · Feb 2002 · ZOOLOGICAL SCIENCE
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    ABSTRACT: We examined the effects of the absence of the pineal gland on testicular maintenance and regression in adult male Mongolian gerbils. Pineal-ectomized and control gerbils were maintained in different photoperiods (0 L, 8 L, 14 L, or 24 L), and body weights and testicular maintenances were investigated. Testes sizes and body weights were measured every week for ten weeks. Body weight did not change during the course of the experiment in all photoperiods. In testes weights, there was no difference between pinealectomized and control groups in the 14 L photoperiod (p > 0.05), while there was a significant difference between pinealectomized and control groups in 0 L, 8 L, and 24 L photoperiods; in control groups there was a regression in testes weights. These results demonstrate that photoperiod does not affect the regulation of body weight, but it does affect the reproductive system of Mongolian gerbils. Thus, the pineal gland plays an important role in the transduction of photoperiodic information.
    No preview · Article · Jan 2002 · Israel Journal of Zoology
  • Bülent Gündüz · Milton H. Stetson
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    ABSTRACT: The pineal hormone melatonin is known to play an important role in mediating photoperiodic messages to the reproductive system in seasonal breeding animals. Our goal was to test, in a single experimental paradigm, two hypotheses that have been forwarded to describe how the circadian rhythm of pineal melatonin transmits photoperiodic information to the reproductive system: 1) induction, i.e., a short-day effect, occurs when secreted melatonin and a circadian rhythm of sensitivity to melatonin coincide in time; 2) induction occurs following exposure to elevated circulating melatonin levels for a prescribed duration. In order to determine the relative validity of these hypotheses, we investigated the testicular maturation response to 1-hr daily infusions of 10, 25, and 50 ng of melatonin in pinealectomized intact and prepubertal Siberian hamsters (Phodopus sungorus). Animals received, beginning on day 15 of life, programmed subcutaneous infusions of melatonin or vehicle at one of five time points (19:00-20:00, 20:00-21:00, 21:00-22:00, 24:00-01:00, and 03:00-04:00 hr) for 15 days. In animals gestated and raised in a long photoperiod (LD16:8 = 16L, where L is the duration of light in hours, and D that of dark), melatonin infusion right after lights off (20:00-21:00 hr) significantly retarded gonadal maturation; this dose was ineffective at other times tested. Doses of 10 and 25 ng melatonin were ineffective at all time points. Identical results were obtained in prepubertal hamsters gestated in a short photoperiod (LD10:14 = 10L) and raised in 16L; these results were independent of the presence or absence of the pineal gland. In animals gestated and raised in 10L, melatonin infusions failed to suppress testicular development beyond that induced by the photoperiod; testicular development was maximally suppressed in all groups. The results of these investigations are best explained under the experimental conditions employed here: 1) the photoperiodic gonadal response in juvenile Siberian hamsters is regulated by the coincidence in time of exogenously administered melatonin with an intrinsic rhythm of sensitivity to melatonin, which, under the constraints imposed by our experimental design, occurred at 20:00-21:00 hr; and 2) the duration of the melatonin signal alone, equal in all groups, cannot explain the results.
    No preview · Article · Apr 2001 · Journal of Pineal Research
  • Bülent Gündüz · Milton H. Stetson
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    ABSTRACT: In a previous paper we demonstrated that properly timed 1-hr infusions of 50 ng melatonin effectively suppressed testicular development in juvenile Siberian hamsters. Only melatonin infused between 20:00 and 21:00 hr was effective in animals exposed to 16L (lights off 20:00 hr). In this paper we further investigate the importance of the coincidence and duration hypotheses of daily exposure of melatonin. Prepubertal Siberian hamsters received either 4- or 8-hr melatonin infusions at various times either on long photoperiod (LD 16:8 = 16L) or on short photoperiod (LD 10:14 = 10L). Daily 8-hr melatonin infusions suppressed testicular development in both photoperiods. Daily 4-hr, 50 ng/hr, melatonin infusions at 17:00-21:00 hr inhibited testicular growth in 16L and daily 4-hr melatonin infusions (either 50 ng/h or 50 ng/day) inhibited testicular growth at 17:00-21:00 hr in 10L. We also tested the efficacy of an interrupted melatonin infusion of long duration (8 hr). Pinealectomized prepubertal male Siberian hamsters, born on 16L, were infused with two signals of 4 hr separated by an interval of 2 hr. Melatonin-infused groups had significantly inhibited testicular growth compared to vehicle-infused animals. Testicular development was maximally inhibited only in those groups in which the period of melatonin sensitivity identified in the previous paper (20:00-21:00 hr) overlapped or immediately followed a period of melatonin infusion. Considering the restrictions of the experimental design employed in these studies, the results are best explained by the hypothesis that the photoperiodic gonadal response in juvenile Siberian hamsters is regulated by the coincidence in time of exogenously administered melatonin with an intrinsic rhythm of sensitivity to melatonin, which occurred at 20:00-21:00 hr. The duration of the melatonin signal alone can not explain the results.
    No preview · Article · Feb 2001 · Journal of Pineal Research
  • Bülent GÜNDÜZ
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    ABSTRACT: We examined the effects of daily melatonin (Mel) infusions in pinealectomized prepubertal male Siberian hamsters in three different conditions. In one study we investigated the body weight maturation response to one hour daily infusions of 10 ng, 25 ng, or 50 ng of Mel in pinealectomized hamsters. Animals received, at day 15 of life, programmed subcutaneous infusions of Mel or vehicle at one of five time points (1900-2000, 2000-2100, 2100-2200, 2400-0100, and 0300-0400 hours) for 30 days. In long-day-born (16L) animals, Mel infusion right after lights off (2000-2100 hours) significantly inhibited body growth; this dose was ineffective at other times. Doses of 10 ng and 25 ng Mel were ineffective at all time points. In a second study, hamsters received either 4-or 8-h infusions of Mel (either 50 ng/h or 50 ng/day) at various times throughout the day and night of a 16L or 10L photoperiod. Daily 4-h, 50 ng/h, Mel infusions at 1700-2100 hours inhibited body weight growth in 16L and daily 4-h Mel infusions (either 50 ng/h or 50 ng/day) inhibited body weight growth at 1700-2100 hours in 10L. In all cases, daily 8-h infusions suppressed body weight development. In a third study, long-day-born pinealectomized hamsters were infused with two signals of four hours separated by an interval of two hours. Mel infused groups had significantly inhibited body growth compared to vehicle infused animals. Body weight development was maximally inhibited only in those groups in which the period of Mel sensitivity was identified in the first study (2000-2100 hours) overlapped or immediately followed a period of Mel infusion These results show that the photoperiodic body weight response in juvenile Siberian hamsters is regulated by the coincidence in time of exogenously administered Mel with an intrinsic rhythm of sensitivity to Mel, and the duration of the Mel signal alone cannot explain the results.
    No preview · Article · Jan 2001
  • Bülent Gündüz · Milton H. Stetson
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    ABSTRACT: Gündüz B, Stetson M.H. The impact of photoperiods and melatonin on gonadal development in juvenile Turkish hamsters (Mesocricetus brandti). J. Pineal Res. 1998; 25:193–200. © Munksgaard, Copenhagen The reproductive response of both intact adult and juvenile Turkish hamsters has been thoroughly studied and shown to be similar, unlike the golden hamster where juveniles remain aphotoperiodic until approximately 8 weeks of age. Unstudied to date, however, is the role of the pineal and its hormone melatonin in generating the testicular response to photoperiod in juvenile Turkish hamsters. Therefore, in this study we examined the reproductive response of prepubertal male Turkish hamsters, subjected to four different photoperiods (8L: 16D, 16L: 8D, 20L: 4D, and 24L: 0D) with altered pineal gland function. At 15 days of age, long-day-born (16L: 8D) hamsters were either pinealectomized, received melatonin implants, or remained untreated. Testes sizes were measured every 2 weeks. Testicular growth occurred only in untreated and beeswax implanted groups in 16L: 8D. Exposure to other photoperiods inhibited testicular development in untreated and beeswax implanted animals. Removal of the pineal gland, masking of the daily melatonin rhythm with constant release subcutaneous melatonin implants, or eliminating the daily rhythm of melatonin by continuous light exposure resulted in inhibition of gonadal development. These results demonstrate that juvenile Turkish hamsters respond similarly to adults on all photoperiods and under all conditions of pineal function tested.
    No preview · Article · Jan 1999 · Journal of Pineal Research

Publication Stats

181 Citations
59.18 Total Impact Points


  • 2010-2014
    • Çanakkale Onsekiz Mart Üniversitesi
      • Department of Biology
      Kale-Sultanie, Çanakkale, Turkey
  • 2002-2008
    • Abant İzzet Baysal Üniversitesi
      • Department of Biology
      Claudiopolis, Bolu, Turkey
  • 1999-2001
    • University of Delaware
      • Department of Biological Sciences
      Delaware, United States