Endocrine effects of pineal gland and of melatonin

Effects of lighting patterns in pubertal development and metabolism of female wistar rats

Modern lifestyle is characterized by constant exposure to artificial light, which is associated with alterations in biological rhythms, abnormalities to reproductive cycles and metabolic changes. In this study, we aimed to evaluate the effects of four different lighting patterns on puberty timing and on possible metabolic changes in female Wistar rats. Additionally, we developed a machine learning algorithm to automatically classify the stages of the estrous cycle. Adult Wistar rats mated during a week at a photoperiod station where they were exposed to combined red-green-blue lights (RGB) during the photoperiod that varied its spectral composition (i.e., variable color temperature) during the day (RGB-v; N = 14), RGB during the photoperiod with a fixed light color temperature (RGB-f; N = 13) during the whole photoperiod; constant darkness (DD; N = 13) and constant fixed light (LL; N = 15). Experiments were performed only on female litters from postnatal day (PND) 22 to 50. Body weight, puberty onset, estrous cyclicity and serum metabolic parameters were measured. We also collected pictures of vaginal smears to create a dataset of 15,936 images to construct an automatic classifier based on convolutional neural networks. No significant differences were found in the age of vaginal opening; however, the RGB-v group showed a significantly lower number of complete and consecutives cycles. Also, the RGB-f group showed the first complete estrous cycle significantly earlier than the RGB-v group. Female rats housed in LL condition presented significantly lower mean body weight from PND 33 to PDN 47 compared to the other groups. Furthermore, higher levels of plasma triglycerides were found in the DD group compared to RGB-f and RGB-v. HDL levels were significantly lower in RGB-v compared to RGB-f and LL groups. Total cholesterol was significantly lower in RGB-v compared to all groups. Visceral fat was significantly higher in RGB-f compared to the LL group. These results suggest that both changes in photoperiod and lighting quality affect pubertal development and alter lipid profiles and visceral fat accumulation.

Developmental expression patterns of six6: A gene linked with spawning ecotypes in Atlantic salmon

The Atlantic salmon has been studied extensively, particularly as a model for understanding the genetic and environmental contributions to the evolution and development of life history traits. Expression pattern analysis in situ, however, is mostly lacking in salmon. We examine the embryonic developmental expression of six6, a candidate gene previously identified to be associated with spawning ecotypes and age at sexual maturity, in Atlantic salmon. Six6 is a member of the sine oculis homeobox family of transcription factors and is known to regulate eye and brain development in other vertebrates. We assay the expression of this gene in embryonic Atlantic salmon Salmo salar by whole-mount in situ hybridization. In line with earlier studies in other vertebrate species, we find conserved expression in the developing brain and sensory organs, including optic and olfactory primordia. However, we also find previously unreported domains of expression that suggest additional roles in axial and appendicular development, cardiovascular, intestinal, and sensory organogenesis. Each of these systems are important in the sensory ecology of Atlantic salmon, suggesting it is plausible that six6 may have pleiotropic roles in this complex phenotype.

Effects of photoperiod on brain corticosteroid receptors and the stress response in the golden hamster (Mesocricetus auratus)

Following exposure to short daylengths, in golden hamsters, changes in basal adrenal glucocorticoid secretion are associated with a significant increase in Type I receptor binding, and are preceded by alterations in the stress-induced release of glucocorticoids, which is one of the major modes of operation of the hypothalamo-pituitary-adrenocortical axis (HPA). These results lend support to the hypothesis that corticosteroid receptors, and in particular the Type I receptor subtype, play a central role in the regulation of circadian and circannual rhythms of the HPA.

The Pineal Gland Mediates the Inhibition of Proestrous Luteinizing Hormone Surge and Ovulation in Rats Resulting from Stimulation of the Medial Raphe Nucleus or Injection of 5-HT into the Third Ventricle

Abstract In cycling rats, electrochemical stimulation of the medial raphe nucleus or injection of 5-HT into the third ventricle on the day of proestrus blocked the preovulatory surge of luteinizing hormone and inhibited ovulation. The inhibitory effect of these procedures on gonadotropin secretion failed to occur in rats that had been pinealectomized a few weeks earlier. In contrast, sham-pinealectomized rats exhibited a response similar to that of intact rats. Luteinizing hormone release and ovulation in pinealectomized rats were not different from that in the controls. The results of the present work indicate that inhibition of gonadotropin secretion induced by activation of the serotonergic system requires the presence of the pineal gland.

Bovine pineal tripeptide threonylseryllysine retards puberty in female rats

When injected into rodents, the bovine pineal tripeptide threonylseryllysine (TSL) elicits diverse antireproductive effects in a number of animal models. Extensive studies of its effects on pubertal development have not been carried out, however. In the present study, 1.0 microgram of T-S-L was administered daily to female Charles River CD rats throughout the peripubertal period, and effects on vaginal opening time, ovarian histology, and serum luteinizing hormone (LH) levels were observed. Since TSL is known to alter the action of luteinizing hormone releasing hormone (LHRH), it was postulated that this antireproductive tripeptide would delay the time of vaginal opening associated with first ovulation. Two hundred eighty-seven weanling females were housed at 22 degrees C under a 14L:10D photoperiod. They were divided into three groups for daily intraperitonal injections of either saline (SAL), 1.0 micrograms TSL, or 5.0 micrograms melatonin (aMT) beginning on the 23rd day of life. Subgroups of nine to ten rats from each treatment group were sacrificed on days 28, 30, 32, 33, 34, 35, 36, 37, 38, and 40. Although the body weights of all animals increased significantly during the course of the study, no significant differences were observed in this parameter among rats treated with saline, aMT, or TSL. Vaginal opening time was significantly delayed by TSL between days 32 and 40, and uterine weights were significantly lower in this group. Prepubertal increases in serum levels of LH were also significantly reduced. At the dose utilized, aMT was without significant effects on these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereological changes in rat ventral prostate induced by melatonin

Effects of melatonin on the ventral prostate of castrated rats supplemented with testosterone were studied using light microscopy. Stereological measurements were made of volume fractions of acini and stroma and surface fractions of glandular epithelium. From these figures and the weights of the glands, the volumes and surface areas were calculated, as well as the mean epithelial heights, mean acinar diameters, and mean distances between glandular acini. Doses of melatonin were varied, to verify its physiological and pharmacological effects. Castration without hormonal treatments produced atrophic changes, with decreases in acinar and stromal volume and widenings in the mean distances between the acini. None of these measurements differed among intact controls, sham-operated controls, and testosterone-supplemented castrated rats. In the castrated rats receiving both testosterone and melatonin, however, there were changes according to the doses of melatonin given. The animals receiving low doses of melatonin (50 and 400 micrograms daily) showed significant decreases in the volumes of the stroma and epithelium and the height of the epithelium. These stereological changes occurred without a significant reduction in the prostatic weights. The animals receiving the higher dose (800 micrograms daily) of melatonin showed no difference in any measurement compared with those of the testosterone-supplemented castrated rats. In rats receiving 2,000 micrograms of melatonin daily, there were significant reductions in the weights of the prostates and the volumes of the acini. These results suggest a direct action of melatonin on the ventral prostate, and the effects depend on the dose given.

Inhibitory actions of pineal indoles on steroidogenesis in isolated rat Leydig cells

The inhibition elicited by pineal indoles on testosterone production by isolated rat Leydig cells could not be overcome by a maximally active dose of luteinizing hormone (LH), and dibutyryl-cAMP-induced steroidogenesis was also suppressed, suggesting that the indoles did not exert their effect through an interaction with LH receptors on Leydig cells. Pregnenolone-induced progesterone secretion was unaffected, indicating that the activity of 3 beta-dehydrogenase was not altered. Methoxytryptamine (MTN) at a dose of 1 mM decreased progesterone-induced 17 alpha-hydroxyprogesterone secretion by 50%, suggesting that the enzyme 17 alpha-hydroxylase was inhibited. The inhibition caused by other pineal indoles was either very slight or absent. MTN reduced 17 alpha-hydroxyprogesterone-induced androstenedione production by 65%, methoxytryptophol (MTOL) and melatonin (MEL) by 35%, and methoxyindoleacetic acid (MIAA) and hydroxyindoleacetic acid (HIAA) by 10%, revealing an inhibition of 17-20 desmolase. The reduction of androstenedione-induced testosterone production by MTN infers inhibition of 17-ketoreductase activity. However, testosterone production induced by either dehydroepiandrosterone or androstenedione was unaffected by other indoles. The data suggest that MTN inhibited 17 alpha-hydroxylase, 17-20 desmolase, and 17-ketoreductase while MEL, MTOL, MIAA, and HIAA inhibited only 17-20 desmolase. The highest potency of MTN in inhibiting enzymes on the testosterone biosynthestic pathway was reflected in its greatest inhibition of testosterone production. On the other hand, MIAA and HIAA had the lowest potency in inhibiting the enzymes and testosterone production while MEL and MTOL had intermediate potencies.

Influence of subcutaneous melatonin implantation on gonadal development and on plasma levels of luteinizing hormone, testosterone, estradiol, and corticosterone in the pigeon

Subcutaneous implantation of melatonin for a period of 12 weeks with reinforcement of implants every fortnight had no significant influence on photoinduced gonadal development in the pigeon. Neither the weight of the gonads or the oviduct nor the gonadal size was affected by melatonin. Pinealectomy also was found to have no significant influence on gonadal weight when examined 20 weeks after the surgery. The plasma levels of luteinizing hormone and testosterone were not significantly influenced by a 10-week implantation of melatonin, although a trend toward an increase (statistically insignificant) in testosterone concentration was apparent in melatonin-implanted male pigeons. Plasma concentration of estradiol was found to increase significantly in both male and female pigeons following the 10-week melatonin implantation. A trend toward an increase in plasma corticosterone level was also apparent in these melatonin-implanted birds, but the increase was statistically insignificant.

The role of the pineal gland in stress

A short survey of the results of our previous research into the protective role of the pineal gland against stress is given. The neuroendocrine aspect of a chronic auditory stress and the neuroendocrine aspect of ulcer disease in man were studied. Auditory stress: hypertrophy and hyperplasia of pinealocytes, hyperplasia of the STH, FSH, LTH and TSH cells, hypertrophy of the nuclei and nucleoli of the neuroglandular cells of the supraoptic and paraventricular nuclei, pronounced hyperplasia of the cells of the reticular zone of the adrenal gland, involution of the seminal epithelium, hyperplasia of the Leydig cells. Ulcer disease: numerous glial plates, cavities and acervuli in the pineal gland, numerous granules and vacuoles in the FSH cells, large and eccentrical nuclei in the LH cells, hyperplasia of the cells of the reticular zone of the adrenal gland, presence of the seminal tubules marked by signs of involution, hyperplasia of the Leydig cells. The results obtained point to the secretion of androgens and the insufficiency of the antiandrogenic function of the pineal gland both in auditory stress and ulcer disease. The anticancerogenic effect of the pineal gland would be based on its antiandrogenic function.

Effects of precocious pinealectomy and hemicastration on pituitary and plasma LH levels in immature male rats

In the immature male rat (7 to 28 days of age) precocious hemicastration provokes a marked compensatory testicular hypertrophy accompanied by a significant increase in pituitary LH content, and a non-significant increase in plasma LH level. In pinealectomized and sham-pinealectomized animals, hemicastration had the same effect with some exceptions at certain ages. Pinealectomy alone causes less evident changes in pituitary LH content than hemicastration. Only a transient effect was found, which was more evident in the hemicastrated rats. Plasma LH was only increased in the pinealectomized hemicastrated rats at days 16 and 18. It is concluded that pinealectomy in immature male rats seems to have only a transient stimulatory effect on pituitary and plasma LH levels, which is more striking in hemicastrated rats. So, hemicastration seems to sensitize the animals to the effect of pinealectomy.

DNA synthesis in the anterior pituitary of the male rat: effect of castration and photoperiod

Castration increased incorporation of tritiated thymidine into total DNA in the anterior pituitary gland. Furthermore, there was a threefold increase in the percentage of labeled basophils 1 month after castration. Exposure of rats to constant light or dark also changed DNA synthesis; these changes depended on age of the animal and on exposure length. The results reflect physiologically induced mitotic activity in specific classes of pituitary cells and further suggest that neuroendocrine mechanisms may be involved in control of cell turnover in the gland.

Brain serotonin concentration: elevation following intraperitoneal administration of melatonin

The intraperitoneal administration of melatonin to rats caused an increase in brain serotonin concentration, especially in the midbrain. This effect could be demonstrated within 20 minutes of melatonin administration and was not associated with changes in norepinephrine concentration.

Brain receptors sensitive to indole compounds: function in control of luteinizing hormone secretion

The placement of melatonin and of 5-hydroxytryptophol in the median eminence of castrated male rats is followed 5 days later by a significant decrease in pituitary stores of luteinizing hormone. Pituitary reserve of this hormone is also depleted after the implantation of melatonin, 5-hydroxytryptophol, and 5-methoxytryptophol in the reticular formation of the midbrain. It is suggested that these indole compounds, which are normally synthesized in the pineal gland, may intervene in the control of the secretion of luteinizing hormone, possibly by acting on specific receptors localized in the median eminence and in the midbrain.