摘要:

Abstract:Well‐established circadian physiology supports the view that photoperiodic time measurement utilizes the coincidence between the presence of light and a photosensitive phase of a 'biological clock' to alter reproductive status—the so‐called external coincidence model of seasonal breeding. In this review, we examine the mechanism whereby photoperiod interacts with presumed suprachiasmatic nuclei activity to allow endogenous melatonin to normally synchronize reproductive activity to the optimal time of year. The Romney Marsh sheep is particularly explored as an experimental model. It is suggested that the on/off activity of seasonal reproduction may be a robust mechanism able to be predictably manipulated by the judicious use of the light/dark cycle and exogenous melatonin, but firmly based on circadian princ

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00493.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:In earlier studies from other laboratories it was shown that melatonin decreased ovarian weight in rats and inhibited compensatory hypertrophy of the remaining ovary after unilateral ovariectomy. This study was designed to examine the influence of melatonin on certain indices of ovarian hyperplasia and/or hypertrophy in adult female rats with both ovaries preserved and with either an intact pineal gland or with the pineal gland removed (pinealectomy, PX) or, finally, in sham‐PX animals. Similar studies were conducted on rats after unilateral ovariectomy, referring the examined parameters to the remaining intact ovary. The studies included mitotic activity of granulosa layer cells and corpus luteum cells, ovarian weight, ovarian cross‐sectional area, cross‐sectional area of the granulosa layer of all the Graafian follicles and the cross‐sectional areas of the corpora lutea, visible on the ovarian cross‐section. On the basis of results, we conclude that: 1) the effect of PX on the processes of ovarian hyperplasia and hypertrophy may vary; analogously, exogenous melatonin administration may influence ovarian hyperplasia and hypertrophy in different ways; 2) PX and exogenous melatonin may, under certain conditions, exert similar biological effects, even synergistic effects; 3) melatonin inhibits ovarian growth processes, while the effects of PX are variable; 4) the results indicate that in experiments performed on rats, with the use of two control groups, i.e., intact and sham‐PX, melatonin effects on these two groups

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00494.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:In vitropreparations of rat pinealocytes are widely used for biochemical analyses of signal transduction processes. This paper deals with morphological and immunocytochemical features of such preparations. Special attention was paid to the problems of whether pinealocytes represent a heterogeneous cell population and how such heterogeneity may develop during ontogeny. The investigations were performed with cells which were obtained from the pineal organ of one‐week‐and two‐month‐old rats, attached to synthetic peptide‐coated coverslips or tissue culture chamber slides, and maintained underin vitroconditions overnight. The attached cells were then fixed with paraformaldehyde. These preparations yielded monolayers of spherical cells of different sizes; most cells were isolated, but some of them were aggregated and formed small clusters. On the average, the cells from the one‐week‐old animals were smaller than the cells from the two‐month‐old animals. Immunocytochemical demonstration of S‐antigen, a pinealocyte‐specific marker, showed that the majority of the cells from two‐month‐old animals were intensely or moderately labelled. Pinealocytes from one‐week‐old animals were less S‐antigen immunoreactive. Only very few cells (less than 1% displayed glial fibrillary acidic protein (GFAP)‐immunoreactivity. Planimetric investigations of the cell size and semiquantitative densitometric investigations of the intensity of the S‐antigen immunoreaction revealed that (i) pinealocytes keptin vitroform a heterogeneous cell population, and that (ii) this heterogeneity increases during postnatal development from one‐week‐old to two‐month‐old animals. Two groups of pinealocytes can be distinguished based on their developmental fate: pinealocytes of one group grow dramatically, but show only a moderate increase in S‐antigen immunoreactivity, and pinealocytes of the other group retain their size, but display a dist

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00495.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:The purpose of this study was to determine whether the pineal gland of Turkish hamsters (Mesocricetus brandti) responds to adrenergic agonists with an increase in melatonin production, and, if it does, whether the sensitivity of the pineal gland to agonists would differ throughout the dark phase. Adult Turkish hamsters weighing 110–210 g received a subcutaneous injection of isoproterenol (ISO, 1 mg/kg B.W.) or norepinephrine (NE, 1 mg/kg B.W.) at different times of night. Animals exposed to LD 16:8 responded to ISO or NE with increased pineal melatonin content only when injected at dawn, when endogenous melatonin is at basal or near‐basal levels. When the 8 hr scotophase was entirely replaced with light, the responsiveness to ISO injections at dawn disappeared. In animals exposed to light from 30 min prior to injection to the time of sacrifice, ISO injections increased pineal melatonin content (P<0.005, three‐way ANOVA), which varied, depending on the specific time of injection (effect of time of night,P<0.05, three‐way ANOVA). These results demonstrate that (1) adrenergic agonists enhance the production of pineal melatonin in Turkish hamsters, (2) this stimulatory effect takes place late, but not early in the 8 hr scotophase, and (3) the adrenergic induction of pineal melatonin production in Turkish hamsters requires priming by darkness during the appropriate circadia

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00496.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Light microscopic observations on the superficial pineal gland of Wistar‐King rats were made to examine whether or not pineal volume and pinealocyte size, expressed as nuclear density, at daytime or nighttime are affected by long‐term exposure to 50 Hz rotating magnetic field (MF) at 5.0 μT. Determinations of pineal volume and pinealocyte size were repeated twice (April and October) during the year. Size of pinealocytes in MF‐exposed and sham‐exposed rats exhibited, in addition to the difference between peripheral and central regions, regional differences in a proximodistal direction; pinealocytes in the distal and middle‐peripheral regions were usually larger than those in the proximal and middle‐central regions at daytime or nighttime. In October, distal and proximal pinealocytes showed significant day‐night changes in size in sham‐exposed rats, but not in MF‐exposed animals. The situations in the two groups were almost reversed in April. Significant day‐night differences were scarcely found in pinealocyte size in the middle region in the two groups. Throughout the study, pineal volume and pinealocyte size in each region were generally the same between MF‐exposed and sham‐exposed rats at daytime or nighttime. The results suggest that pinealocytes in the distal and proximal regions, but not those in the middle region, are affected by MF‐exposure; day‐night differences in sizes of distal and proximal pinealocytes appear in April and disappear in October under the influence of MF. MF may exert an effect on mechanisms controlling day‐night rhythms

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00497.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY