摘要:

Nocturnal light‐induced changes in pineal glandN‐acetyltransferase activity were investigated in intact or enucleated 4‐, 6‐, or 8‐day‐old maternally isolated rats maintained at different ambient temperatures. Nighttime enzyme activity was increased markedly in rats maintained in 23°C compared to 35°C environments. Four hours of nocturnal light significantly reducedN‐acetyltransferase activity in intact rats at all ages studied when the animals were maintained at 35°C. Shorter duration (1 min) nocturnal light reducedN‐acetyltransferase activity in intact rats 6 days of age. However, the enzyme activity suppression observed after the 4 hr of nocturnal light was still present in 4‐day‐old rats (but not older animals) even when the younger animals had been made blind by bilateral orbital enucleation. Taken together, these data suggest that an extraretinal mechanism may mediate light‐induced changes in some aspects of pineal gland indoleamine bioc

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00445.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The purpose of this study was to determine and compare the effects of chronic melatonin treatment in vivo on several aspects of prolactin (PRL) cell activity (PRL synthesis, storage, and release) in vitro in male and female Syrian hamsters. Adult male and female hamsters were maintained on long photoperiod and treated with daily late afternoon injections of melatonin (25 μg) or vehicle for 11 weeks. Melatonin treatment resulted in an 85% and 65% decrease in serum PRL levels in male and female hamsters, respectively. There was a similar 79% and 64% decrease in PRL release in vitro from pituitaries of male and female hamsters, respectively, treated with melatonin in vivo. Total stored PRL was 75% lower in male hamsters and 62% lower in female hamsters receiving melatonin. The synthesis of PRL by pituitaries from melatonin‐treated male hamsters was reduced by 65%, whereas in melatonin‐treated females it was decreased by 58%. Both nanomolar and micromolar doses of melatonin in vitro caused a modest but significant decrease (14–19%) in the amount of PRL stored in and released from normal male pituitaries without affecting synthesis. The inhibitory effects of melatonin on PRL cell function appear to be more pronounced in male than in female hamsters suggesting a sexually dimorphic response to this pineal hormone. While melatonin's PRL‐inhibitory effects appear to be exerted primarily via indirect neuroendocrine mechanisms, a secondary component of its overall regulation of PRL processing may involve direct pituitary mechanisms

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00446.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Anestrus brought about after 2–4 weeks of short photoperiod (SP) exposure in LSH/SsLak hamsters is preceded by impaired follicular development. Since the latter is critically dependent on adequate FSH levels, this study tested the hypothesis that SP might alter baseline or compensatory FSH levels prior to the onset of anestrus. Regularly cycling females in 14L:10D (LP) were transferred to SP (8L: 16D). Between 0800 and 0900 h on days 20 through 24 of SP exposure, half of the animals in diestrus II were unilaterally ovariectomized (UO), and the remaining animals were sham‐operated (Sham‐UO). Seven hours after surgery, blood samples were taken via cardiac puncture. All animals were killed the following morning at 0900 h. Uterine weights were significantly reduced in SP‐exposed hamsters, yet the compensatory increase in FSH following unilateral ovariectomy was not affected; a tendency for higher levels was noted. On proestrus, serum and pituitary FSH levels of SP‐exposed Sham‐UO animals were significantly elevated over similarly treated LP‐exposed hamsters. Interestingly, in animals with severe follicular impairment, the highest FSH levels correlated with the lowest uterine weights. The data suggest that SP exposure does not impair compensatory FSH release or the ability of the ovaries to respond to UO. SP‐induced elevations in FSH levels may result from reduced follicular secretion and reduced inhibin and/or

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00447.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

We tested whether juvenile males ofMicrotus pennsylvanicuswere more sensitive than adults to the suppressive effects of short photoperiods. Voles were transferred to short photoperiods (10L:14D) at 20 or 80 d of age, and 60 d later (i.e., at 80 or 140 d) the animals were killed at intervals throughout the day and night. Pineal glands were collected for measurement of melatonin, and the testes were weighed. There were no differences in paired testicular weights of 80 and 140 d old animals held on long days (median testicular weights: 1,953 and 1,843 mg). In contrast, median testicular weights of voles held on short days were 504 and 1,112 mg, respectively, at 80 and 140 d of age; the testicular weights of both groups were significantly different from their age‐matched controls (P.001, two‐sample t‐tests on log transformed data). The responses of the two age groups were compared by normalizing the individual values by the mean and variance of the respective long‐day controls. This comparison suggests that the responsiveness to photoperiod decreases as the animals age (t‐test,P= .01). Duration and amplitude of the nocturnal rise in pineal melatonin content were similar in differently aged animals. In two experiments, voles were injected daily with melatonin from 20 to 80 or 80 to 140 d of age. Melatonin‐injected animals had smaller testes than did saline‐injected controls (ANOVA:P= .01), and injections were more effective in the afternoon than in the morning (P= .01). Comparison of the effectiveness of short day and melatonin injections in juvenile and adult voles suggests that while short days inhibited testicular development of young animals more than it induced regression of adults, this decrease in responsiveness may involve factors other than alterations in the nocturnal pattern of melaton

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00448.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Cultured chick pineal glands showed a cycle in the cumulative incorporation of thymidine into DNA. In undisturbed cultures the rate of thymidine incorporation, amount of thymidine incorporated per 1 ‐day cycle, and persistence of the incorporation process were all markedly affected by the concentration of exogenous precursor. However, more than two full cycles of incorporation were found when culture medium of low thymidine content was renewed daily, or when medium of intermediate concentration was replaced on the 3rd day of culture. At a high thymidine concentration the second cycle of incorporation sometimes appeared to be impaired. At all concentrations tested, less than2%of the available thymidine was incorporate

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00449.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A recent review of the pineal literature revealed that when hamsters are exposed to 24‐hour light:dark (LD) cycles with<12 hours of darkness (summerlike, SLD), the nightly period of pineal melatonin synthesis (PPMS) begins close to the midpoint of the dark period (“midnight”) and ends at lights‐on irrespective of the length of the dark period or time of day presented. New evidence based on the onset of behavioral estrus every 4 days indicated that the 24‐hour hamster clock controlling timing of estrus (4:30 PM) and the PPMS has a 12‐hour light‐sensitive period (LSP) set to 6 PM‐6 AM in LD 16:8 (dark 8 PM‐4 AM, SLD) by a balance in opposing actions of evening and morning light [Alleva:Pineal Research Reviews, Volume 5, Alan R. Liss, Inc., New York, 1987]. Present experiments focus on how this balance is maintained. When lights‐off was advanced to 6 PM in SLDs ranging from LD 12.5:11.5 (dark 6:15 PM‐5:45 AM) to 18:6 (dark 9 PM‐3 AM), the onset of estrus later that day was advanced in every SLD. However, when lights‐on was delayed to or beyond 6 AM, the onset of estrus was unaffected. Thus, the balance is maintained by a resistive force (blocking without a delaying action) of evening light and an advancing action of morning light. In this balancing process all evening light from 6 PM to lights‐off but only the first 5 minutes or less of morning light were involved. The advancing action of morning light was characterized in LD 13:11 and 18:6 by imposing on the night before estrus a 5:30 PM‐6:30 AM dark period scanned with a 15‐minute light pulse. Shifts in onset of estrus later that day were plotted vs. time of the light pulse. The resulting phase response curves (PRCs) were similar and comprised only an advancing curve, which rose about 10 PM, peaked at 2 AM, and returned gradually to normal at 6 AM. In contrast, a PRC obtained from LD 12:12 (dark 6 PM‐6 AM) was sinelike, comprising a 6 PM‐9 PM delaying curve followed by an advancing curve similar to those from SLD. An hypothesis based on these findings is presented to explain how hamsters would keep co

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00450.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Pinealectomy ofHeteropneustes fossilisheld under normal photoperiod and ambient temperature produced season‐dependent effects on ovarian activity. When the fish were pinealectomized in the preparatory phase (early light‐responsive period) and maintained until the early prespawning phase, there was an accelerated growth of the ovary, as adjudged from increased gonado‐somatic index (GSI), ovarian histology, elevated ovarian total protein and ascorbic acid levels, and an increased level of serum alkali‐labile protein phosphorus (vitellogenin). Pinealectomy was ineffective in the prespawning and spawning (late light‐responsive phase) and postspawning (light refractory) phases. The results suggest that the pineal exerts an inhibitory effect on the hypothalamo‐hypophysial‐ovarian axis and synchronizes temporally ovarian activity in response to increasing photothermal conditions such that spawning takes place at a time most suitable for the survival

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00451.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The object of this study was to compare the effects of short photoperiod (SP) and melatonin (MEL) treatment on the reproductive axis in ovariectomized LSH/SsLak hamsters. Animals acclimatized in long photoperiods (LP) (14L:10D) and showing regular estrous cycles were ovariectomized. Half of the operated hamsters received Silastic capsules containing 17‐beta estradiol (E2). On the following day the animals were further subdivided into three groups: the animals in one group received daily afternoon injects of melatonin (MEL), those in a second group were given the vehicle, and animals in the third group were transferred from LP to SP (8L:16D). All animals were killed after 30 days. In hamsters without E2replacement, MEL or SP exposure significantly suppressed serum and pituitary FSH levels, although MEL was more effective in this regard. On the other hand, SP exposure did not change serum FSH levels in animals with E2implants, whereas MEL effectively suppressed them. SP or MEL reduced serum LH levels to a similar extent in the absence of E2replacement, yet in animals with E2implants only MEL significantly lowered LH levels below LP E2‐treated controls. This was in contrast to effects on the pituitary where both treatments were equally effective in the depression of LH content. Serum PRL levels were similarly suppressed by MEL or SP exposure in E2‐treated hamsters. On the other hand, pituitary PRL levels were not affected by either treatment in animals with E2‐containing capsules, whereas SP or MEL treatment both significantly depressed pituitary PRL contents in hamsters without E2replacement. SP treatment lowered MBH LHRH contents in animals with E2‐containing capsules; no other significant changes in hypothalamic LHRH were noted. The data suggest that daily treatment with 25 μg of MEL is generally more effective in the suppression of gonadotropin levels than SP exposure. It is suspected that the mode of administration of MEL, and its quantity, may interact with estrogen differently than SP in the induction of physiological changes and regulation of the L

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00452.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Synaptic ribbons (SR) in melatonin‐deficient pinealocytes of the C57BIV6J mouse were quantitatively compared to SR in pinealocytes of the rat after β‐adrenergic receptor activation by isoproterenol. Two populations of SR comprising synaptic spherules (SRsp) and synaptic rods (SRr) were described in both the mouse and the rat, but species differences existed in the ratio of SRr to SRsp. Isoproterenol caused a significant increase in frequency of SR of the rat but had little or no effect on SR populations in the mouse. It is unlikely that β‐adrenergic receptors are absent on mouse pinealocytes or were not activated since isoproterenol elevated plasma renin concentrations indicating activation of β‐adrenergic receptors. Furthermore the pineal of both species receives heavy sympathetic input. These findings indicate that the role and regulation of pinealocyte SR are complex and are functionally linked to β‐adrenergic receptors as well as other mechanisms related to the production

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00453.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1989.tb00454.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY