摘要:

Abstract:The effect on nocturnal melatonin secretion of acute administration of the indirectly acting serotonin (5‐HT) receptor agonists d‐fenfluramine (30 mg) and paroxetine (20 mg) and a partial 5‐HT1Areceptor agonist ipsapirone (20 mg) was investigated in healthy male volunteers and compared to a placebo condition. Each subject (n=8) received each drug on one occasion over a 4 week study period, with drug administration separated by 1 week. A randomized, counter‐balanced design was used. Drugs or placebo were administered at 2,000 hours in the light, and all blood samples were collected throughout the night in the dark at regular intervals until 0600 hours. Neither d‐fenfluramine, paroxetine, or ipsapirone following acute dosage had a statistically significant effect on nocturnal melatonin synthesis. The lack of effect seen with d‐fenfluramine, paroxetine, and ipsapirone may be due to limitations imposed by the dose r

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00271.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Second order neurons within intact isolated pineal glands of the rainbow trout were explored by extracellular recordings to investigate modulatory effects of putative intrapineal neurotransmitters. Acetylcholine, dopamine, and norepinephrine were found to increase ganglion cell activity in a majority of cells tested. The excitatory effects of acetylcholine, dopamine, and norepinephrine were mimicked by muscarinic, dopamine D2, and β‐adrenergic receptor agonists and significantly increased with the applied light intensity, resulting in an attenuation of the ganglion cell response to light. GABA decreased discharge activity in most cells tested. This effect, which could be mimicked with the GABAAreceptor agonist piperidine, was independent from the adaptive status. Acetylcholine and GABA were still active if applied during synaptic blockade with low Ca++high Mg++‐perfusion medium, whereas dopamine and norepinephrine exhibited no effects if applied during synaptic blockade, suggesting a differential cellular distribution of neurotransmitter receptors in the trout pineal gland. These data demonstrate that ganglion cell activity in the trout pineal gland is under the influence of several neurotransmitters, including acetylcholine, dopamine, norepinephrine, and GABA, which is in contrast to the originally proposed simple bineuronal transduction pathway from photoreceptors onto ganglion cells. Since the above‐mentioned neurotransmitters are believed to be released from pineal interneurons, we may conclude that ganglion cell activity in the teleost pineal gland is, similarly to the retina, the product of photoreceptor signals and a modulatory active interneuronal

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00272.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:It seems clear that the pineal hormone, melatonin (N‐acetyl‐5‐methoxytryptamine), is involved in the reproductive behavior of several animal species including humans. Moreover, several data also support a role for 5‐methoxytryptophol (ML), another pineal hormone, in the control of sexual processes. To test the role of ML in human reproductive axis, 128 healthy children, 68 boys and 60 girls, were studied. Each of these groups was divided in three age subgroups of 6, 11, and 14 years. A single blood sample (0900 hours) was obtained from each subject to determine melatonin, ML, FSH, LH, estradiol (girls), and testoterone (boys) by RIA. Statistical analysis of the data included ANOVA‐II (factor I: age, factor II: sex) and an analysis of covariance with age as covariate. A similar plasma melatonin concentration, with a significant decrease between 6 and 11 years, was found in boys and girls. Melatonin concentrations correlate well with initiation of the pubertal development in these children, although no sex differences were found. Concentrations of ML are approximately 50% of those of melatonin. In contrast to melatonin, ML levels show significant age and sex differences. Plasma ML concentration significantly increased in boys (P<0.001) and decreased in girls(P<0.001) after 8 years of age. These results support the hypothesis that, besides melatonin, other pineal compounds such as ML may be involved in the maturation process in humans. The pineal indole ML may also be used as a marker of the different chronobiology in the pubertal development in boys

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00273.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Melatonin production by isolated pineal glands from guinea pigs was examined under conditions that affect membrane potential or the firing of action potential‐like spikes. In glands from superior cervical ganglionectomized animals, depolarization resulting from increasing extracellular potassium concentration to 100 mM did not initiate melatonin production, and it delayed the response to the β‐adrenoceptor agonist orciprenaline. In glands from intact animals, melatonin production was initiated by exposure to 100 mM potassium with a time‐course similar to the response to orciprenaline. A proportion of this response was propanol resistant, suggesting that the normal control of melatonin production may involve a neurotransmitter in addition to norepinephrine. Exposure to verapamil or nifedipine, or removal of extracellular calcium, previously shown to eliminate action potential‐like spikes, did not substantially affect the increase in melatonin production induced by orciprenaline. Phenylephrine, which stimulates spiking, produced only a slight increase in melatonin production. It is concluded that the depolarization and the spiking are not closely related to the stimulation of melatonin production, but may relate principally to the secretion of a substance other than m

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00274.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:The aim of our study was to examine the effects of 16.7 Hz electromagnetic‐field exposure on pineal melatonin production in healthy humans. The study was based on comparing urinary 6‐hydroxymelatonin sulfate (6‐OHMS) levels of 108 male railway workers between leisure periods and days following the start of service on electrically powered engines (66 engineers) or working beneath transmission lines (42 railway employees such as train attendants and station managers; controls). A repeated measures design was used, i.e., each volunteer served as his own control. The exposure averaged 20 μTesla in the most exposed workers and around 1 μTesla in the least exposed. Apart from magnetic exposure the workers were subject to a shift work schedule with daily advances between 15 min and 1 hr. Melatonin was assessed by sampling urinary 6‐OHMS both in the morning and the early evening.Evening 6‐OHMS values appeared to be lowered by a factor of 0.81 (95%CI: 0.73–0.90) during work days compared to leisure days among engine drivers, but not in the controls. The lowering was not confined to certain types of shift work such as early, normal, or late shifts. During subsequent leisure periods evening values recovered significantly, mean ratio=1.27 (95%CI: 1.03–1.56), i.e., the effects appeared to be reversible. In contrast, morning 6‐OHMS samples of engineers and controls did not differ much between work and leisure days. There was, however, a tendency for a rebound of morning values in a leisure period following a work period both for engineers and controls. The observed pattern appears to be in line with predictions of the “phase response curve.” No evidence for a dose‐response relation was found. The results support the hypothesis that 16.7 Hz magnetic fields alter 6‐OHMS excretion in humans exposed to magnetic fields. An alternative explanation that cannot be excluded in this study is that the difference between engineers and controls is due to differential expo

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00275.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Melatonin has been shown to regulate gene transcription through RZR/ROR nuclear receptors in mammalian cells. Thiazolidine dione CGP 52608 is a selective agonist of RZR/ROR receptors with little or no affinity for the cell surface G protein‐coupled melatonin receptors. In this study, we addressed whether nuclear signaling may be involved in indoleamine‐induced encystment of the unicellular dinoflagellates by examining their responses to CGP 52608. Three species of dinoflagellates (Alexandrium catenella, Amphidinium carterae, andCrypthecodinium cohnii) encysted in the presence of CGP 52608 and the responses were reversible and dose‐dependent. Since a previous study has implicated the involvement of G proteins in mediating indoleamine‐induced encystment of dinoflagellates, we explored the possibility of cross‐talks between G protein‐dependent and nuclear signaling pathways. The responses ofA. catenellato either mastoparan (a direct activator of mammalian G proteins) or indoleamines were assessed in the presence or absence of CGP 52608. Interestingly, CGP 52608 synergized with either indoleamines or mastoparan to produce a more rapid encystment response. These findings suggest that nuclear signaling may be involved in the indoleamine‐induced encystment of di

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00276.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:The effect of melatonin, a potent free radical scavenger, on L‐cysteine‐induced seizures and lipid peroxidation was investigated in mice. When L‐cysteine (1.25, or 5.0 μmol/animal) was injected intracerebroventricularly (i.c.v.) into mice, severe tonic seizures were observed for over 20 sec in 75% and 100% of the treated mice, respectively. However, when melatonin (20 or 100 mg/kg) was injected subcutaneously (sc) into mice 15 min before L‐cysteine injection (1.25 umol/animal, i.c.v.), the incidence of seizures was observed in only 35% and 20% of the treated mice, respectively. Furthermore, when L‐cysteine (1.25 or 5.0 (amol/animal, i.c.v.) was injected into mice, lipid peroxidation in whole brain 20 min after injection was significantly increased by 56% or 67% as compared to that of the control. However, when the seizures induced by L‐cysteine (1.25 μmol/animal) were abolished by preadminstration of melatonin, the increased lipid peroxidation induced by L‐cysteine was prevented. These results suggest that there may be a positive correlation between free radical formation and seizures induced by L‐cysteine and that melatonin affords protection against the seizures as well as against the associated l

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00277.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Two experiments were designed to determine whether gonadal steroids during the estrous cycle may modify the characteristics of the plasma melatonin rhythm. In the first experiment, 12 ovariectomized estradiol‐treated ewes were used and exposed to constant short days. The experimental design was a latin square to distinguish between steroid treatments and individual effects on melatonin secretion. Twenty four hours before the bleeding period (hourly during 20 hr) and with a 1 week interval, animals were treated with a) additional subcutaneous estradiol implants, b) progesterone devices, or c) control. In the second experiment, nine ewes received a treatment combining fluorogestone acetate devices and pregnant mare serum gonadotrophin to induce synchronous ovulations. Samples for melatonin determination were obtained hourly for 13 hr at three stages of estrous cycle: follicular phase, early luteal phase, and late luteal phase. Ovarian activity was monitored by taking daily samples for progesterone analysis and ovulation rate was determined by laparoscopy. Duration and mean melatonin plasma concentrations of the elevation were calculated for each ewe and each night and analysed by latin square test (experiment 1) or ANOVA (experiment 2). Melatonin concentrations of elevation and duration of elevation were not significantly affected by hormonal treatments or by phase of estrous cycle. A strong individual effect was detected (P<0.01) for both parameters in both experiments. It was concluded that melatonin secretion is unaffected by steroid administration or by phase of estrous cycle. The existence of very high inter‐individual variation suggest that both parameters are individual characteristics of each animal which may have a strong genetic ba

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1996.tb00278.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY