Restoration of fertility in light-deprived female hamsters by chronic melatonin treatment

Summary Blinding young adult female hamsters was followed by functional involution of the ovaries and uteri and by the cessation of cyclic vaginal phenomena. Light deprivation was also accompanied by elevated plasma and pituitary levels of luteinizing hormone and depressed levels of prolactin in both the blood and the pituitary gland. Only one of 15 blinded hamsters became pregnant when they were exposed to fertile males for 30 days. Both pinealectomy or chronic melatonin treatment (1 mg melatonin implanted subcutaneously per week in beeswax) prevented the changes in the reproductive organs and in pituitary hormone levels attendant on light-deprivation. Both treatment also returned vaginal cycles to normal and restored plasma prolactin titers. Unlike hamsters that were blinded only, light deprived hamsters that were either pinealectomized or melatonin treated were capable of reproducing when they were caged with fertile males. The reproductive capability (i.e., percent of animals that become pregnant and the sizes of their litters) of these animals was equivalent to that of the untreated control hamsters. This is the first report that chronic melatonin treatment restores fertility in blinded female hamsters.Supported by Grant GB-43233X from the National Science Foundation     

Antigonadal effects of blinding in the presence of antibody against circulating melatonin

The effect of melatonin on reproductive function in the rat was studied. Reproductive organ weights and sex hormone levels were compared between sighted controls and animals which were either blinded, blinded and pinealectomized or blinded and immunized against circulating melatonin. Circulating androgens as measured by accessory sexual organ weights were significantly reduced by blinding. This effect was reversed by pinealectomy but not by immunization. Blinding also increased pineal melatonin levels but there were no differences in the plasma levels of luteinizing hormone. Circulating testosterone levels and pineal melatonin levels of immunized animals did not differ from those of blinded controls. These findings confirm reports that pineal stimulation by blinding enhances pineal melatonin content and inhibits accessory sex organ development. Circulating melatonin does not appear to be the mediator of the stimulated pineal's antigonadal effects in the rat since, in contrast to pinealectomy, neutralization of circulating melatonin failed to reverse accessory organ regression.     

Effects of photoperiod, melatonin, and the pineal gland on compensatory gonadal hypertrophy during postnatal development in the marsh rice rat (Oryzomys palustris)

The roles of photoperiod, melatonin, and the pineal gland in regulating the magnitude of compensatory gonadal hypertrophy (CGH) and other reproductive and non-reproductive organ growth during post-weaning development were examined in the marsh rice rat Oryzomys palustris. Juvenile rice rats of both sexes were left gonadally intact (control group) or unilaterally castrated (ULC) and housed on 12L:12D, 14L:10D, or 16L:8D. Within a photoperiod (14L:10D and 16L:8D, but not 12L:12D), growth of the remaining testis, but not the remaining ovary, as well as several additional organs in both sexes were significantly affected, suggesting that the compensatory hypertrophy of the testis is photoperiod-dependent. There was no effect of testis asymmetry on CGH as ULC of either testis in rice rats housed on 14L:10D resulted in a comparable increase of CGH. Melatonin implants in rice rats maintained on 16L:8D had little to no effect (CGH included) on most parameters examined. Both melatonin implants and pinealectomy (separate experiments) in rice rats transferred to 12L:12D prevented short photoperiod-induced effects on CGH, the growth of the reproductive organs and the Harderian glands. Evening melatonin injections had a significant inhibitory effect on the growth of the remaining testis (no CGH was observed) and all other parameters measured. Lastly, ULC did not alter the percentage of males which successfully mated compared to intact animals. Taken together, these data suggest that photoperiod, melatonin, and the pineal gland can affect and regulate reproductive (e.g., CGH in some cases) and non-reproductive growth during postnatal development in the marsh rice rat.     

Annual testicular cycle of the lizard Anolis carolinensis: effects of pinealectomy and melatonin

The effects of pinealectomy and exogenous melatonin treatment on the reproductive system of male anoles were examined at several different times of year. In September pinealectomy of anoles exposed to either a stimulatory LD 14:10 light cycle or a nonstimulatory LD 10:14 light cycle induced significant testicular growth and development over that observed in sham-operated anoles. At a nonphotosensitive time of year (December) pinealectomy also had a significant progonadal effect but no effect of pinealectomy was seen in February-March. Daily melatonin injections given either in the morning or afternoon (or both) failed to block gonadal growth either (1) in sham-operated or pinealectomized anoles exposed to LD 14:10 in the fall or (2) in pinealectomized lizards exposed to LD 10:14 in the fall. Continuous melatonin administration via subcutaneous silastic implants blocked the progonadal effects of pinealectomy in the winter (December). The results show that pinealectomy can have significant progonadal effects; these effects are seasonal but can encompass phases of the annual testicular cycle which are either photoperiod-dependent or temperature-dependent; and melatonin may be a reproductively active factor involved.     

Effects of pinealectomy and exogenous melatonin on ghrelin and peptide YY in gastrointestinal system and neuropeptide Y in hypothalamic arcuate nucleus: immunohistochemical studies in male rats

It is reported that the pineal gland and its main hormone melatonin may have a role in the regulation of ghrelin synthesis in the brain. Stomach is the place where ghrelin is predominantly expressed and secreted. One aim of this study was to investigate possible effects of pinealectomy and melatonin treatment on gastric ghrelin amount. The studies on the effects of the pineal gland on leptin and ghrelin arises the question whether the pineal gland has also effects on the other energy-regulatory peptides such as peptide YY (PYY) and neuropeptide Y (NPY). Therefore, we also aimed to investigate the changes in the immunohistochemical staining of intestinal PYY and hypothalamic NPY following pinealectomy and melatonin treatment. Serum PYY levels were also investigated. Sprague-Dawley rats were divided into four groups as sham-operated (SHAM), sham-operated with melatonin treatment (SHAM-MT), pinealectomised (PNX) and melatonin-treated PNX (PNX-MT) groups. The cells immunostained for ghrelin were abundant throughout the gastric mucosa in all the groups. Neither pinealectomy nor exogenous melatonin affected significantly immunohistochemical staining of ghrelin in stomach. Pinealectomy resulted in a significant increase in immunohistochemical staining of PYY in ileum. The results of serum PYY measurement corresponded closely to the data obtained by immunohistochemical analysis of PYY in ileum, being significantly lower and higher in SHAM and PNX groups, respectively. Pinealectomy caused a decrease in NPY synthesis in ARC as understood from low immunohistochemical staining of NPY. Melatonin treatment increased NPY synthesis in SHAM rats and restored reduction in NPY synthesis caused by pinealectomy. In conclusion, the pineal gland and its main hormone melatonin can be suggested to have a role in the regulation of NPY synthesis in ARC and PYY in gastrointestinal system.     

Seasonal variations of gonadotropins and prolactin in the laboratory rat. Role of maternal pineal gland

The laboratory rat, a non-photoperiodic rodent, exhibits seasonal fluctuations of melatonin. Melatonin has been found to be readily transferred from the maternal to the fetal circulation. No data exist on the possible influence of maternal pineal gland upon seasonal variations of the offspring. The aim of the present study was to asses the influence of the maternal melatonin rhythm on the offspring postnatal development of the reproductive hormones LH, FSH and prolactin. Male offspring from control, pinealectomized (PIN-X) and PIN-X + melatonin (PIN-X+MEL) mother Wistar rats were studied at 21, 31, and 60 days of age. Seasonal age-dependent variations were found for all hormones studied in control offspring but PIN-X offspring showed a tendency to have reduced duration or altered seasonal variations. Maternal melatonin treatment to PIN-X mothers partially restored the effect of pinealectomy. The chronological study of LH, FSH, and prolactin in PIN-X offspring also showed an altered pattern as compared to control-offspring. Melatonin treatment to the mothers partially restored the developmental pattern of reproductive hormones. Results of this study indicate that maternal pineal gland of the laboratory rat is involved in the seasonal postnatal development variations of reproductive hormones of the offspring.     

A melatonin-independent seasonal timer induces neuroendocrine refractoriness to short day lengths.

The duration of nocturnal pineal melatonin secretion transduces effects of day length (DL) on the neuroendocrine axis of photoperiodic rodents. Long DLs support reproduction, and short DLs induce testicular regression, followed several months later by spontaneous recrudescence; gonadal regrowth is thought to reflect development of tissue refractoriness to melatonin. In most photoperiodic species, pinealectomy does not diminish reproductive competence in long DLs. Turkish hamsters (Mesocricetus brandti) deviate from this norm: elimination of melatonin secretion in long-day males by pinealectomy or constant light treatment induces testicular regression and subsequently recrudescence; the time course of these gonadal transitions is similar to that observed in males transferred from long to short DLs. In the present study, long-day Turkish hamsters that underwent testicular regression and recrudescence in constant light subsequently were completely unresponsive to the antigonadal effects of short DLs. Other hamsters that manifested testicular regression and recrudescence in short DLs were unresponsive to the antigonadal effects of pinealectomy or constant light. Long-term suppression of melatonin secretion induces a physiological state in Turkish hamsters similar or identical to the neuroendocrine refractoriness produced by short-day melatonin signals (i.e., neural refractoriness to melatonin develops in the absence of circulating melatonin secretion). A melatonin-independent interval timer, which would remain operative in the absence of melatonin during hibernation, may determine the onset of testicular recrudescence in the spring. In this respect, Turkish hamsters differ from most other photoperiodic rodents.     

What photoperiodic signal is provided by a continuous-release melatonin implant?

The purpose of this study was to evaluate whether the insertion of a continuous-release melatonin implant into ewes provides a short-day photoperiodic signal or acts as a functional pinealectomy (provides no specific photoperiodic signal but renders ewes incapable of responding to changes in photoperiod). Ewes primed with 60 long days (18L:6D) during the spring were moved to intermediate day length (13L:11D) for 66 days and then given one of five treatments: 1) short-day control, second drop in photoperiod to 8L:16D; 2) intermediate-photoperiod control, kept on 13L:11D; 3) pinealectomy and kept on 13L:11D; 4) melatonin implant and kept on 13L:11D; 5) melatonin implant and moved to 8L:16D. Mean number of estrous cycles per group and total duration of reproductive activity were determined. Ewes in all groups began to exhibit estrous cycles after the initial reduction in photoperiod. The number of estrous cycles and duration of reproductive activity differed among groups. The number of estrous cycles and duration of reproductive activity was extended in ewes receiving the second drop in photoperiod compared to that of the intermediate-photoperiod controls. Pinealectomized ewes had a number of estrous cycles and duration of reproductive activity similar to those of ewes maintained on the intermediate photoperiod. Melatonin implants increased the number of estrous cycles and prolonged reproductive activity in ewes maintained on the intermediate photoperiod; melatonin implants did not prevent the extension of reproductive activity in ewes receiving the second photoperiodic drop to the short daylength.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of melatonin on rat thyroid, adrenals and testis secretion during the day.

The effect of pinealectomy and exogenous melatonin on circadian rhythm of triiodothyronine (T3), thyroxin (T4), corticosterone and testosterone in sham-operated and pinealectomized rats were investigated. The hormones concentration were RIA-measured and the circadian rhythm secretion were analysed by cosinor method. The findings suggest that pinealectomy abolishes the rhythmical character of corticosterone secretion and disturbs the circadian rhythm of T3, T4 and testosterone. Exogenous melatonin has the suppressive effect of diurnal secretion of T3, T4 and testosterone in pinealectomized rats but stimulates the rhythmical corticosterone secretion.     

Evaluation of the Role of Chronic Daily Melatonin Administration and Pinealectomy on Penicillin-Induced Focal Epileptiform Activity and Spectral Analysis of ECoG in Rats: An In Vivo Electrophysiological Study

In the present study, we aimed to investigate the effects of pinealectomy and chronic melatonin administration on focal epileptiform activity induced by penicillin in the rat cortex and to determine the relation between melatonin levels and electrocorticogram (ECoG) power spectrum. For this purpose, male Sprague-Dawley rats were divided into six groups: control, sham operated, ethanol, melatonin, pinealectomy and pinealectomy + melatonin group. Melatonin-treated rats was intraperitoneally injected with a daily single dose of 10 mg/kg melatonin for 14 days, but the last dose was given 30 min after local application of penicillin as a convulsant agent. Focal epileptiform activity was produced by intracortical administration of penicillin (200 units/1 μl). While chronic melatonin application did not affect either the onset latency or the spike frequency of epileptiform activity, pinealectomy significantly reduced latency to onset of initial epileptiform discharges and increased cortical epileptiform activity. However, acute melatonin administration decreased the epileptiform activity. The results also indicated that exogenously applied melatonin did not change the spectral analysis of ECoG, but pinealectomy led to a reduction in the power of the fast bands (gamma) power in ECoG. We conclude that endogenous melatonin signaling seem to have a tonic inhibitory action on neuronal excitability and epileptiform activity, and also a certain concentration of melatonin required for normal cortical excitability.     

松果体及其褪黑素对大鼠胸腺细胞凋亡的影响

目的探讨松果体及其褪黑素对胸腺细胞凋亡的影响以及Caspase-3的表达。方法选用清洁级SD大鼠,分为正常对照组、假手术对照组、松果体摘除组、松果体摘除 褪黑素腹腔注射7.5mg/kg/d组和松果体摘除 褪黑素腹腔注射15mg/kg/d组。术后4、8周取材。运用TUNEL法检测胸腺细胞的凋亡程度,用ABC法染胸腺Caspase-3阳性细胞,计算机图像分析仪测量阳性细胞面积及其染色强度。以RT-PCR法检测褪黑素干预原代培养胸腺细胞Caspase-3的表达。结果松果体摘除后8周时胸腺细胞凋亡显著增加,补充褪黑素则能明显减少胸腺细胞的凋亡。Caspase-3阳性细胞主要见于胸腺皮质,松果体摘除后胸腺皮质Caspase-3阳性细胞面积增加明显,补充褪黑素则使其下降。褪黑素能上调培养胸腺细胞Caspase-3的表达水平。结论松果体能调控大鼠胸腺细胞的凋亡,松果体摘除促进胸腺细胞的凋亡,补充褪黑素能缓解相关影响。     

The influence of pinealectomy and single dose of melatonin administered at different times of day on serum T3 and T4 concentrations in rats

The influence of pinealectomy and melatonin administration on the levels of total T3 and T4 plasma levels were determined by RIA method. The results of hormonal measurements were evaluated by means of Student's t-test, and the diurnal rhythm by cosinor method. It has been established that pinealectomy disturbs the T3 diurnal rhythm and caused marked changes in T4 levels during the 24 hours. Exogenous melatonin does not influence the thyroid function during the light phase. During the dark phase, however, its inhibitory effect is prevalent in pinealectomized rats, and the stimulating in sham operated rats.     

CHANGES IN SEROTONIN LEVEL AND TURNOVER IN DISCRETE HYPOTHALAMIC NUCLEI AFTER PINEALECTOMY AND MELATONIN ADMINISTRATION TO RATS

The influence of the pineal gland on the hypothalamic serotonergic function was examined by studying the effects of long-term pinealectomy (1 month) and melatonin replacement (500 μg/kg; 10 days) on serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content as well as on the in vivo 5-HT synthesis rate in discrete hypothalamic nuclei. Pinealectomy was followed by a significant decrease of 5-HT content in the anterior hypothalamic nuclei (AHN) and the ventromedial hypothalamic nuclei (VMHN), and also in 5-HIAA content in lateral (LPON) and medial preoptic nuclei (MPON). The 5-HT synthesis rate, estimated from the accumulation of 5-hydroxytryptophan after blockade of the 1-amino acid decarboxylase activity, were also decreased in the AHN and the paraventricular hypothalamic nuclei (PVHN) of pinealectomized rats. In contrast, an enhanced 5-HT synthesis rate and basal 5-HIAA content were found in the suprachiasmatic nuclei (SCN) after pinealectomy. Daily treatment with melatonin for 10 days reversed most of the effects induced by pinealectomy. Thus, melatonin increased the levels of 5-HT in the AHN and VMHN, and slightly increased the 5-HIAA content in preoptic nuclei. In addition, melatonin increased the 5-HT synthesis rate in the AHN and VMHN, but also in the MPON, VMHN and dorsomedial hypothalamic nuclei (DMHN) where pinealectomy had no effect. By contrast, melatonin treatment did not affect SCN 5-HT synthesis rate, although it decreased 5-HIAA levels. The results demonstrate that melatonin is able to stimulate 5-HT metabolism in most of the hypothalamic areas, but inhibits SCN 5-HT function. Some of the effects of melatonin seems to be exerted by modulating the synthesis of the amine, although melatonin likely also interacts with other regulatory processes of 5-HT function (i.e. release/uptake). The well defined presence of melatonin receptors in the rat SCN, and its absence in other hypothalamic structures, suggest that this may be the mechanism mediating the differential response to endogenous melatonin. Moreover, the larger effect of exogenous melatonin in relation to pinealectomy suggests the presence of melatonin unespecific effects possibly owing to supraphysiological doses. The present findings may be relevant for the mode of action of melatonin and its implication in several endocrine and behavioral functions mediated by serotonergic neurons. Copyright © 1996 Elsevier Science Ltd     

Melatonin-pineal relationships in female golden hamsters.

Light deprivation by blinding in female hamsters was followed by a regression of the reproductive organs, an elevation of pituitary LH concentration and a depression of pituitary prolactin levels. Pinealectomy negated almost completely the effects of light deprivation on the neuroendocrine-reproductive axis. Weekly subcutaneous implants of a melatonin:beeswax pellet completely prevented the pineal gland from inhibiting reproductive physiology in blinded hamsters. The findings suggest that melatonin is not pineal antigonadotrophic factor in female golden hamsters. Melatonin implanted hamsters also had higher than normal levels of plasma prolactin.     

Synchronization of the circannual reproductive rhythm of the ewe by discrete photoperiodic signals

Although many species display endogenous circannual rhythms of biological activity that are synchronized by day length, the specific photoperiodic requirements for synchronizing such rhythms are not established for any species. We tested the hypothesis that the circannual reproductive rhythm of sheep can be synchronized by exposure to just one or two discrete blocks of photoperiodic information each year. Ewes were pinealectomized to prevent their ability to transduce photoperiodic information into altered reproductive neuroendocrine activity. During the 53/4 yr following pinealectomy, specific photoperiodic signals were restored for discrete periods of time via replacement of 24-h patterns of melatonin, the pineal hormone that transmits photic information to the reproductive neuroendocrine axis. The ewes were kept in a 12-mo photoycycle that alternated between short (8L:16D) and long (16L:8D) days every 6 mo and that was 6 mo out of phase with the geophysical year. Pineal-intact control ewes exhibited synchronous annual reproductive cycles. Noninfused pinealectomized control ewes did not exhibit synchronous cycles. Pinealectomized ewes infused with alternating 70-day blocks of short- and long-day patterns of melatonin every 6 mo for the first 21/2 yr of the experiment exhibited synchronous annual reproductive cycles that were 6 mo out of phase with those of ewes maintained outdoors. This synchrony persisted when the frequency of the melatonin treatment was reduced to just one 70-day block of a long-day pattern of melatonin each 365 days. Cycle period was 368 +/- 3 days; standard deviation of the date of onset of reproductive induction averaged only 3 days. Our study provides the first direct evidence that a single block of photoperiodic information a year can synchronize a circannual rhythm.     

Pinealectomy Decelerates the Circadian Food Intake Rhythm of Cervically Sympathectomized Rabbits

Long-term records of the free-running food intake rhythms were obtained from 26 young adult blinded rabbits that were subjected in the course of recording to bilateral superior cervical ganglionectomy (sympathectomy). This always resulted in acceleration of the rhythm (mean λ r= - 0.35 h). Some 4 months afterwards, 12 rabbits were pinealectomized and after another 4 months sham pinealectomized also. In the other 14 animals, these operations were performed in the reverse order. It appeared that suctioning away part of the ventricular walls during sham pinealectomy was followed by a slight reduction in r (mean = - 0.07 h) that could be largely attributed to the spontaneous gradual reduction of r that occurred throughout all experiments. On the other hand, total pinealectomy in these already sympathectomized blinded rabbits always resulted in a substantial deceleration of the rhythms (mean λ r = + 0.23 h). These observations on blinded rabbits suggest that a sympathetically denervated pineal gland releases appreciable amounts of melatonin or of another hormone with a melatonin-like accelerating effect on the circadian pacemaker (SCN).     

Diurnal Variations in [125I]Melatonin Binding by Rat Thymus Membranes: Effects of Continuous Light Exposure and Pinealectomy

Binding of melatonin by rat thymus membranes exhibited diurnal changes. Binding increased during the daytime and reached maximal values before entering the dark period. Then, binding decreased rapidly during the dark phase. In rats kept in light at night, binding of [¹²⁵I]melatonin by membranes was significantly higher than in animals that entered the normal dark period. Neonatal pinealectomy, which suppresses the circadian rhythm of melatonin, led to an increase in melatonin binding of 106%. Moreover, in animals maintained under continuous light exposure, which corresponds to functional pinealectomy, binding of melatonin by thymus membranes also increased in a time-dependent manner. The results support the hypothesis of a regulatory role of melatonin in the thymus in which melatonin downregulates its own binding sites.     

Melatonin and the synthesis of vasopressin in pinealectomized male rats

The pineal hormone, melatonin, is known to modify, under different experimental conditions, neurohypophysial hormone secretion in the rat. The aim of this study was to investigate the effect of melatonin on the vasopressin biosynthesis rate in the hypothalamus of either pinealectomized or sham-operated rats, using the colchicine method. To estimate whether colchicine affects the function of the neurohypophysis in these animals, the neurohypophysial and plasma vasopressin levels were also measured. The vasopressin synthesis rate was increased after pineal removal, when compared with sham-operated animals, and melatonin strongly inhibited the rise in the hormone synthesis due to pinealectomy. After pineal removal plasma vasopressin concentration was significantly elevated, and melatonin attenuated this effect. On the contrary, the neurohypophysial vasopressin content was significantly decreased after pinealectomy, but it was not further modified by melatonin.Thus, melatonin suppresses the synthesis and secretion of vasopressin in pinealectomized rats. The present results confirm our previous reports as to the inhibitory impact of the pineal on both vasopressin synthesis and release and suggest that melatonin may mediate the effect of the pineal gland on vasopressinergic neuron activity.     

Pinealectomy increases and exogenous melatonin decreases leptin production in rat anterior pituitary cells: an immunohistochemical study

Melatonin, the main hormone of the pineal gland, informs the body about the environmental light and darkness regimen, which in turn contributes to the photoperiodic adaptation of several physiological functions. Leptin, the hormone secreted mainly by adipocytes and some other tissues including the pituitary, informs the brain about the mass of adipose tissue, which plays an important role in energy homeostasis. Melatonin has been shown to decrease circulating leptin levels. It is currently not known whether melatonin has an effect on leptin synthesis in the pituitary. The aim of this study was to immunohistochemically examine the effects of pinealectomy and administration of melatonin on leptin production in the rat anterior pituitary. The pituitary samples obtained from 18 male Wistar rats including sham-pinealectomized, pinealectomized and melatonin-injected pinealectomized groups were immunohistochemically evaluated. Immunostaining of leptin was moderate (3+) in sham-pinealectomized rats, heavy (5+) in pinealectomized rats and low (1+) in melatonin-treated pinealectomized rats, respectively. The present results indicate that pinealectomy induces leptin secretion in anterior pituitary cells, and this increase of leptin synthesis can be prevented by administration of melatonin. Thus, melatonin seems to have both physiological and pharmacological effects on leptin production in the anterior pituitary of male rats.     

Functional relations of the adrenal cortex, thyroid and pineal body. II. Adrenal cortex reaction following epiphysectomy and administration of melatonin

Histologic-cytological and morphometrical changes were investigated in the adrenal cortex of male Wistar-rats following pinealectomy and application of melatonin in eu-, hypo-, and hyperthyroid situations. A rat experiment (at an average of 45 d) to find a possible functional connection between the pineal gland and the adrenal cortex was carried out. In the literature, there are only a few of informations about the role of the pineal in regulating ACTH secretion. The results are very contrarily. We found that pinealectomy is connected with a progressive transformation and melatonin with a little regressive transformation in the adrenal cortex. But, it is not evident, that the glomerular zone is activated after both pinealectomy and application of melatonin. In our opinion, the glomerular zone and the secretion of aldosterone increased after as well pinealectomy as melatonin. Application of melatonin diminishes the function of the pineal gland (see group 4-pinealectomy plus melatonin-where was found a progressive transformation). Under these experimental conditions, one can speak of a "pharmacological pinealectomy" after application of melatonin alone. However, the effect of melatonin on the fascicular zone and the glomerular zone is different. The effects of pinealectomy or application of melatonin in combination with methylthiouracil or thyroxin are relatively unimportant.