Bülent Gündüz - Academia.edu (original) (raw)

Papers by Bülent Gündüz

Turkish Journal of Biology, 2014

Turkish Journal of Biology, Apr 1, 2003

Photoperiod is an important environmental cue in the regulation of reproductive activity in Mongo... more Photoperiod is an important environmental cue in the regulation of reproductive activity in Mongolian gerbils. Photoperiodic information is ultimately transduced into a hormonal signal by the pineal gland. We examined the effect of constantrelease melatonin capsules on the testicular size and body weights of male Mongolian gerbils exposed to a long (14L: 10D) photoperiod. Three groups were formed: control (n = 10), intact + melatonin implant (n = 10) and pinealectomy + melatonin implant (n = 10). The testes and body weights of the gerbils were recorded every week for 8 weeks. Body weights (76 ± 2.0 g intact + melatonin implant; 79 ± 3.0 g pinealectomy + melatonin implant) and testes weights (1.54 ± 0.21 g intact + melatonin implant; 1.47 ± 0.19 g pinealectomy + melatonin implant) of intact + melatonin implanted and pinealectomy + melatonin implanted groups were not statistically different from those of the control group (80 ± 3.1 g body weight; 1.55 ± 0.20 g testes weight) (P > 0.05) at the end of the study. Regardless of treatment, the animals fully reflected the characteristics of a long photoperiod. These results indicate that masking the endogenous melatonin rhythm via constant-release melatonin implants has no effect on the testis volume or body weight of Mongolian gerbils when the animals are kept in a long photoperiod.

Türk Tarım ve Doğa Bilimleri Dergisi

The complex neuronal and hormonal interaction between the brain and gonads controls the neuroendo... more The complex neuronal and hormonal interaction between the brain and gonads controls the neuroendocrine reproductive axis. GnRH, GnIH, and kisspeptin are important neuropeptides in this relationship. Although seasonal variations of these neuropeptides have been demonstrated in photoperiodic animals, there is no clear evidence in their daily rhythms. Melatonin and leptin hormones are also two important hormones in reproductive regulation. In our study, the relationship of melatonin and leptin hormones with daily rhythm with GnIH, GnRH, and kisspeptin gene expressions and protein oscillations was examined. Adult male Syrian hamsters were exposed to the long photoperiod and at the end of the 30-day experimental period, blood and tissue samples from each group were collected at 04:00 h, 12:00 h, 20:00 h, and 00:00 h. Daily rhythms of melatonin and leptin hormones were determined by ELISA. Quantitative analysis of GnRH, GnIH, Kisspeptin, and β-actin genes was performed with the correspond...

Türk Tarım ve Doğa Bilimleri Dergisi, 2021

Immune responses play a key role in the survival of all living things. Intake of inorganic materi... more Immune responses play a key role in the survival of all living things. Intake of inorganic materials is of critical importance in living organisms because of their participation in metabolism and some component of cells. Iron (Fe), magnesium (Mg) and selenium (Se) were selected for this study because of their participation in critical constituents of cells, such as nucleic acids and enzymes in living organisms, and their indirect and direct effects on immunity. Although the separate effects of these inorganic materials are known, there is no study on their combined effects. Galleria mellonella, which is used as a model organism, is frequently used in evaluating of effects of human pathogens due to its various properties. Total hemocyte counts and encapsulation-melanization responses are the most commonly observed parameters when examining the immune responses of this model organism. In our study, the effects of the selected inorganic materials added in the ratio of 0.1%, 0.25%, 0.5%...

Biology of Reproduction, Dec 1, 1994

When transferred from a long to short photoperiod, Siberian hamsters (Phodopus sungorus) undergo ... more When transferred from a long to short photoperiod, Siberian hamsters (Phodopus sungorus) undergo a number of physiological and morphological changes including suppression of gonadal activity, a change in pelage color, a decrease in body weight, and, in response to a simultaneous decrease in ambient temperature, physiological changes associated with the induction of daily torpor. All these functions can be affected by photoperiod and melatonin treatment. To investigate the interactive effects of photoperiod, pinealectomy, and melatonin on gonadal development, two experiments were performed using juvenile Siberian hamsters. In experiment 1, animals born in a long photoperiod (16L:8D) either remained in a long photoperiod or were transferred to a short photoperiod (8L:16D) from 15 days of age, when surgeries (pinealectomy and/or melatonin implantation) were performed. Testicular development was inhibited in all animals bearing melatonin implants irrespective of the presence or absence of the pineal gland. Pinealectomy blocked the inhibitory effect of short photoperiod on maturation of the reproductive system. Therefore, the pineal gland must be involved in the short photoperiod-induced inhibition of testicular maturation of juvenile Siberian hamsters. In experiment 2, a similar experimental design was employed except that the hamsters were born and raised to 15 days of age in 8L:16D. Exogenous melatonin, pinealectomy, or both retarded gonadal development in hamsters born in 8L:16D and transferred on Day 15 of age to 16L:8D. All hamsters maintained in a short photoperiod had small testes irrespective of the presence or absence of the pineal gland or of melatonin implants. Hamsters transferred to a long photoperiod after pinealectomy and/or melatonin implantation had small testes compared to those of the control group. These results suggest that melatonin implants inhibit prepubertal testicular development irrespective of ambient photoperiod.

The Journal of Spinal Cord Medicine, 2009

Background/Objective: Spinal cord injury influences many hormones that are known to be involved i... more Background/Objective: Spinal cord injury influences many hormones that are known to be involved in the modulation of neurotrophic, neurogenic, and neuroprotective events. Recent studies showed that leptin could be neuroprotective, enhancing neuronal survival in vitro and in vivo. The objective of this study was to evaluate the pattern of the serum leptin levels in rats during acute traumatic SCI. Methods: Forty male Sprague-Dawley rats were divided randomly into 4 groups. In the control group, neither laminectomy nor SCI was performed; only laminectomy was performed without SCI in the sham group. In the cervical and thoracic spinal trauma groups, laminectomies were performed following the same trauma procedure. Blood samples were drawn 2, 6, 12, and 24 hours after the procedures and assayed immediately. Results: In the first 2 hours, levels of leptin were similar in control and sham-operated groups and higher in neurotrauma groups (P , 0.05). At the sixth hour, leptin levels increased in the sham-operated group, decreased in the neurotrauma groups (P , 0.05), and did not change in the control group (P. 0.05). At the 12th hour, the levels of leptin increased in all groups (P. 0.05). At the 24th hour, they decreased in the control, sham-operated, and cervical groups (P , 0.05); levels did not change in the thoracic group (P. 0.05). The decrease was higher in the control group than in the other groups (P , 0.05). Conclusions: Activation of endogenous leptin secretion started immediately after the SCI. The level of neurologic lesion (either cervical or thoracic regions) affected the levels of serum leptin differently, but with the exception of the first 12-hour period, this difference did not reach a statistically significant level.

Biology of Reproduction, 1994

Journal of Animal Physiology and Animal Nutrition, 2021

A pregnant hamster's exposure to changes in environmental factors, such as light, temperature... more A pregnant hamster's exposure to changes in environmental factors, such as light, temperature and nutrition, may influence behavioural and physiological changes in offspring. In this study, dietary methyl donor supplementation was employed to examine the role of maternal diet on appetite, body weight, serum leptin levels and locomotor activity in male Syrian hamster offspring. Dams were fed a standard control (SC) or methyl donor-supplemented (MDSD) diet through pregnancy and lactation. At birth, offspring were cross-fostered to dams fed an SC or MDSD diet (SC-MDSD and MDSD-SC) or remained with their birth mothers (SC-SC and MDSD-MDSD). At weaning, offspring were fed a SC or MDSD diet until 60 days of age. Food intake, serum leptin levels and locomotor activity were measured from 30-60 days of age. Offspring fed a MDSD diet post-weaning (MDSD-MDSD and SC-MDSD) consumed more than double the amount of food daily compared with offspring fed a SC diet post-weaning (SC-SC, MDSD-SC). Interestingly, there were no observed differences in body weight among all four groups. Serum leptin levels at 60 days of age were depressed in offspring fed a MDSD diet post-weaning (MDSD-MDSD and SC-MDSD). There were no observed differences in wheel running activity between the SC-SC and MDSC-SC groups. Wheel running activity was at least twice the amount in offspring fed a MDSD diet post-weaning (SC-MDSD and MDSD-MDSD). Taken together, these results indicate that the timing of methyl donor supplementation appears to be an important factor during the development of offspring.

Turk J Biol, 2003

Animals exposed to long or short photoperiods show a number of physiological and morphological ch... more Animals exposed to long or short photoperiods show a number of physiological and morphological changes that presumably increase the animal's probability of overwintering, such as a molt to a winter pelage, a change in body mass and the ability to enter torpor. Many animals use ...

Spinal Cord, 2009

Objective: To evaluate the serum melatonin levels in acute period of the spinal cord injury (SCI)... more Objective: To evaluate the serum melatonin levels in acute period of the spinal cord injury (SCI) caused by trauma in the rats. Background: Traumatic SCI induces many types of physiological and pathological damage, including hormonal level variations. Methods: 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. Results: 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. Conclusions: 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.

Objectives: In this study the aim was to evaluate the effects of on biochemical markers and histo... more Objectives: In this study the aim was to evaluate the effects of on biochemical markers and histopathological findings of pancreas tissue of decreeasing and increasing serum melatonin levels in rats with had experimental acute pancreatitis. Materials and methods: This study was conducted three groups of Winstar Albino rats (ten animals in every group) that have experimental acute pancreatitis. First group was evaluated as control group. Surgical pinealectomy was applied in the second group and the source of endogen melatonin was (low melatonin levels group). Third group of rats injected with 0.1 ml daily intraperitoneal injection of 20 mg/ml melatonin solution for one week was high melatonin levels group. The effects of melatonin levels on acute pancreatitis were evaluated by comparing these group according to histopathologial results of polimorphonuclear leukocytes. infiltration, oedema, haemorrhagie, apoptosis, aciner cellular degeneration in pancreatic tissue and the levels of ma...

Turk. J. Biol, 2003

Like many temperate zone rodent species, Siberian hamsters (Phodopus sungorus) display marked phy... more Like many temperate zone rodent species, Siberian hamsters (Phodopus sungorus) display marked physiological and behavioral adaptations in response to annual changes in the ambient photoperiod. While Siberian hamsters are reproductively active in long photoperiods, they ...

Turkish Journal of Biology, 2011

Th e suprachiasmatic nucleus (SCN) generates and controls the circadian rhythms in mammals includ... more Th e 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 eff ects of 3 diff erent 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 aff ected the level of phase-shift s in an administration method-dependent manner. Th e biggest phase advance was observed in intra-SCN infusion (P = 0.001), and th...

Turkish Journal of Biology, 2007

We investigated whether photoperiodic information is transferred from mother to young and whether... more 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 mothe...

Rates of growth and sexual maturation of Mongolian gerbils vary in response to photoperiod. Previ... more Rates of growth and sexual maturation of Mongolian gerbils vary in response to photoperiod. Previous work has shown that the responses of the testes and body weight of juvenile and adult gerbils are influenced not only by the photoperiods but also by other factors. The present work sought to determine if Mongolian gerbils alter body mass, body composition and/or reproductive organ mass in response to different photoperiods and temperatures. Male Mongolian gerbils were raised under long (14L) or short (10L) photoperiods from 26 days of age. Photoperiods did not affect body mass and body length. Temperature affected body mass only under 10L with animals housed at 10oC being significantly ligter than gerbils housed at 20oC. Temperature did not affect the length of the body. Changes in body mass in response to photoperiod and/or temperature exposure were primarily due to the deposition or loss of fat-free dry mass and water. The mass of the reproductive organs (testes and seminal vesicl...

Gündüz B, Stetson M.H. The impact of photoperiods and melatonin on gonadal development in juvenil... more 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

Gereç ve yöntem: Bu çalışma deneysel akut pankreatit oluşturulan ve her grupta 10 hayvan bulunan ... more Gereç ve yöntem: Bu çalışma deneysel akut pankreatit oluşturulan ve her grupta 10 hayvan bulunan 3 grup Winstar Albino cinsi sıçan üzerinde yürütüldü. Birinci grup denekler kontrol grubu olarak değerlendirildi. İkinci grup deneklerde pinealektomi yapılarak temel endojen melatonin ...

TURKISH JOURNAL OF BIOLOGY, 2014

We have shown that circadian changes in leptin concentrations are inversely linked to circulating... more 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 melatoninimplanted 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.

Zoological Science, 2002

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Zoological Science, 2005

Reproductive activity of Mongolian gerbils is regulated by photoperiod nevertheless body weight r... more 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.