摘要:

“Synaptic” ribbons and spherules are typical organelles of the mammalian pinealocytes, that present quantitative day‐night variations parallel to pineal melatonin levels. The European hamster is a wild photoperiodic mammal whose pineal melatonin concentrations do not vary during the 24 hr light‐dark cycle. The aim of this study was thus to see if a rhythmic variation in synaptic structures was nevertheless present in this species. It was found that, in contrast to all of the photoperiodic species studied to date, the European hamster pinealocyte contains no ribbons, and virtually no spherules. Moreover, constant administration of melatonin does not result in the occurrence of these organelles; nevertheless, the pinealocytes have the potentiality to produce spherules and, to a lesser extent, ribbons, as they are observed in ganglionectomized animals and in the deep pineal of some hamsters after ablation of the superficial part of the gland. The formation of pineal synaptic structures, normally lacking in the European hamster, thus seems directly related to the noradrenergic innervation of th

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00801.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

High‐pressure liquid chromatography with electrochemical detection has been used for the determination of melatonin in rat pineal glands and tissue explants. Rat pineal melatonin content was measured at 2‐hr intervals during a 2.t‐hr period by direct injection of supernatants from centrifuged pineal homogenates into a reversed‐phase C18 column. The lower limit of sensitivity was 32 pg per gland for a 2:1 signal‐to‐noise ratio, which allows melatonin measurements during daytime. Both absolute values and circadian rhythmicity obtained with the present method are in agreement with previously validated rddioimmunoassays. In addition, isoproterenolinduced release of melatonin from individual rat pineal explants was measured after chloroform extraction of the incuba

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00802.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The frequency of mitoses of adrenaline (A) cells and noradrenaline (N) cells in the adrenal medulla of nonoperated (NO), sham‐operated (SPX), and pinealectomized (PX) male, 53‐day‐old Holtzman rats (n = 133) was investigated by means of light microscopy. Animals were killed at eight time points during a standardized 24‐h light‐dark (12:12) cycle 14 days after surgery. Mitotic indices (n/1,000) were determined in sections of adrenal medulla fixed with glutaraldehyde and OsO4. Overall frequency of mitoses was extremely low (mitotic index: 0.73 = 115/157,223). Daily mean mitotic index was maximum in A cells (0.83) and minimum in N cells (0.52) of PX group but did not show statistically significant differences between cell types or experimental groups. Neither cell type in NO animals showed 24‐h changes in mitotic index, but cells in SPX animals did, with highest value in the late dark phase and lowest in the late light phase, when values of two cell types were combined (P<0.01–0.001). In PX animals, mitotic index followed a similar but more distinct 24‐h change in A cells (P<0.009), but not in N cells, resulting in different time‐of‐day changes between two types of cells (P<0.01–0.05). The mitotic index was higher in PX than in control (NO and SPX) animals in the middark phase (P<0.05) and lower in operated (SPX and PX) than in nonoperated (NO) animals from late light to the early dark phase, suggesting that the latter was possibly due to a residual effect of the surgery. These results are consistent with the interpretation that the pineal has an inhibitory action on A cells and may coordinate the two types of cells in their mitotic activity, especially in the middark pha

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Pineal glands were obtained from two young female black rhinoceri that had died as a result of postcapture trauma during a translocation exercise. Hydroxyindole‐O‐methyltransferase (HIOMT) from these pineal glands showed a peak activity at pH 8.2, although high activity extended over a fairly wide pH range (7.8–8.4). N‐acetylserotonin was the best hydroxyindolic substrate for the enzyme, although other hydroxyindoles were methylated, the relative affinities being similar to values previously reported for bovine HIOMT. Kinetic analyses revealed that black rhinoceros HIOMT was subject to substrate inhibition by both substrates at high concentration; this observation is unlikely to have physiological significance. The catalytic mechanism was found to be ordered Bi‐Bi, in which S‐adenosylmethionine is the obligatory first substrate to bind to the enzyme, such binding allowing for binding of the hydroxyindolic substrate followed by catalysis, products again leaving the catalytic site in a sequent

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Vasoactive intestinal peptide (VIP)‐like immunoreactive nerve fibers were demonstrated by peroxidase antiperoxidase (PAP) inmmunohistochemistry to be distributed throughout the entire pineal gland of the sheep. VIP‐containing fibers were observed along the blood vessels, penetrating into the gland from the pial capsule and also in the capsule itself. Some fibers left the perivascular position and entered the pineal parenchyma, where they were located among pinealocytes. This suggested that the VIPergic fibers might influence both pinealocytes and blood vessels of the gland. The location of VIP‐containing fibers in the capsule of the pineal gland indicates that the fibers originate from perikarya located in a peripheral gan

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Melatonin secretion was investigated in ewes maintained in continuous darkness for 6 days and following an acute delay of lights off as part of a study offactors controlling the melatonin rhythm. In continuous darkness, the interval between successive offsets in circulating melatonin was always greater than 24 hr, indicating that the decline in melatonin secretion in sheep is controlled by endogenous mechanisms having a period longer than 24 hr. In ewes placed under extended darkness with no delay in the time of lights off, the decline in circulating melatonin was delayed by 2.5 ± 0.2 hr. Animals that had dusk delayed by 4 hr continued to secrete melatonin for at least 4 hr after subjective lights on. Under these conditions, it is proposed that the offset of melatonin secretion is influenced by the timing of lights off and the onset of melatonin secretion. The brain centers controlling melatonin secretion in sheep appear to operate in a manner similar to several species, and thus the sheep may prove to be a useful experimental animal for further studies of circadian mechanisms

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A naturally occurring compound, 6‐methoxybenzoxazolinone (6‐MBOA), present in grasses, has been shown to induce sexual maturation in a number of rodent species. The structural similarity of 6‐MBOA and melatonin has led researchers to suspect that 6‐MBOA might induce its progonadal effects by directly altering pineal function. Previous studies have shown that 6‐MBOA has the properties of a weak β‐adrenergic agonist capable of stimulating rat pineal N‐acetyltransferase (NAT) activity at pharmacological concentrations of 10−3M. In the present study we have examined the effect of 6‐MBOA on both the pineal melatonin synthesizing enzymes, namely. NAT and hydroxyindole‐O‐methyltransferase (HIOMT) as well as on melatonin production, in organ cultured rat pineal glands. In addition, we have also examined the ability of 6‐MBOA to displace a ligand from rat brain α‐and β‐adrenoceptors. Our results confirm that 6‐MBOA stimulates NAT activity and melatonin production at the high concentration of 10−3M. It appears to have no effect on HIOMT activity. A competition study shows that 6‐MBOA is able of displacing ligands at the α‐and β‐adrenoceptors but only at concentrations greater that 10−4M. Whether such high concentrations of 6‐MBOA reach the pineal of rodent in their natural habitat is unknown. However, if 6‐MBOA does mediate progonadal effects by altering pineal function it would be expected that 6‐MBOA would ultimately inhibit the effects of melatonin. The possibilities are that the high melatonin levels induced by 6‐MBOA cause desensitization of melatonin receptors or that 6‐MBOA is an antagonist at the level of the melatonin receptor, thus restricting the inhi

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effects of exogenous melatonin (subcutaneous implants containing 0.031 ± 0.006 mg/gm body mass melatonin) or long photoperiod (18L:6D) on wild‐caught adult male hedgehogs were studied. Hedgehogs were implanted with melatonin‐filled or empty capsules in May, August, or September, or maintained under long photoperiod from August. Blood samples collected at monthly intervals were assayed for testosterone, melatonin, and thyroxin. Melatonin‐filled capsules elevated plasma melatonin concentrations for 4–6 months. Although melatonin administration in May depressed plasma testosterone levels, testicular reactivation was advanced by 1 month the following year, and the characteristic prehibernal gain in body mass was abolished. Melatonin administration in August had no effect on plasma testosterone concentrations but reduced body mass fluctuations before and during hibernation. Hedgehogs receiving melatonin in September recovered early from hibernal body mass loss and showed a 2 month advance in testicular reactivation the following year. Maintaining hedgehogs at 18L:6D photoperiod, however, elevated plasma melatonin concentrations. Testicular reactivation the following spring was delayed by 1 month, ended 3 months early, and testosterone concentrations were depressed. All treatments depressed plasma thyroxin levels. These results suggest that elevated melatonin levels during winter are important in the regulation of endogenous endocrine cycles in the hedgehog. Hedgehogs do not respond positively to melatonin at the end of the breeding season, but are again responsive to melatonin as early as S

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effect of melatonin treatment on the Gonosomatic Index (GSI), ovarian germinal epithelium, plasma estradiol and testosterone levels was studied inRana perezifemales in December. No significant changes were observed in GSI, estradiol, and testosterone levels in melatonin treated animals when compared with saline injected controls, but the percentage of previtellogenic follicles decreased in animals treated with melatonin (100 μg). The effect of melatonin treatment on glucose level was studied inRana perezifemales in December andRana temporariamales in February. InRana perezino significant differences were observed between melatonin treated and control animals; however, significant reductions by melatonin treatment were obtained inRana temporaria. The possibility that the inhibitory effect of melatonin can be observed only when gonadal function and metabolism are stimulated by temperature is discussed

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00810.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY