Effects of melatonin treatment and environmental lighting on the ultrastructural appearence, melatonin synthesis, norepinephrine turnover and microtubule protein content of the rat pineal gland

Molecular Mechanisms of Melatonin-Mediated Cell Protection and Signaling in Health and Disease

Melatonin, an endogenously synthesized indolamine, is a powerful antioxidant exerting beneficial action in many pathological conditions. Melatonin protects from oxidative stress in ischemic/reperfusion injury, neurodegenerative diseases, and aging, decreases inflammation, modulates the immune system, inhibits proliferation, counteracts the Warburg effect, and promotes apoptosis in various cancer models. Melatonin stimulates antioxidant enzymes in the cells, protects mitochondrial membrane phospholipids, especially cardiolipin, from oxidation thus preserving integrity of the membranes, affects mitochondrial membrane potential, stimulates activity of respiratory chain enzymes, and decreases the opening of mitochondrial permeability transition pore and cytochrome c release. This review will focus on the molecular mechanisms of melatonin effects in the cells during normal and pathological conditions and possible melatonin clinical applications.

Melatonin modulates cytoskeletal organization in the rat brain hippocampus

Melatonin concentration in plasma reaches high levels during the night and synchronizes body rhythms with the photoperiod. Previous evidence obtained in cultured cells suggests that melatonin synchronizes cytoskeletal re-arrangements at nocturnal plasma concentration. In this study, we determined the amount of microtubules and microfilaments in the rat hippocampus as an index of cytoskeletal organization in rats submitted to a photoperiodic regime. Additionally, these parameters were determined in control rats, sham rats, pinealectomized rats, and rats that were pinealectomized and treated with melatonin for 1 week. The results showed an increase in both the amount of microfilaments in the hippocampus of rats sacrificed in the dark phase, and in melatonin levels. In addition, a decrease in both microfilament and microtubule amounts occurred in pinealectomized rats. In contrast, melatonin treatment partially reestablished actin and tubulin proportions organized in microfilaments and microtubules, respectively. The results indicate that actin organization in microfilaments was associated with both the photoperiod and with melatonin levels. Together, the data support that cytoskeletal organization is regulated rhythmically by melatonin in synchrony with the photoperiod.

The microtubule cytoskeleton acts as a key downstream effector of neurotransmitter signaling

Microtubules are well known to play a key role in the trafficking of neurotransmitters to the synapse. However, less attention has been paid to their role as downstream effectors of neurotransmitter signaling in the target neuron. Here, we show that neurotransmitter-based signaling to the microtubule cytoskeleton regulates downstream microtubule function through several mechanisms. These include tubulin posttranslational modification, binding of microtubule-associated proteins, release of microtubule-interacting second messenger molecules, and regulation of tubulin expression levels. We review the evidence for neurotransmitter regulation of the microtubule cytoskeleton, focusing on the neurotransmitters serotonin, melatonin, dopamine, glutamate, glycine, and acetylcholine. Some evidence suggests that microtubules may even play a more direct role in propagating action potentials through conductance of electric current. In turn, there is evidence for the regulation of neurotransmission by the microtubule cytoskeleton.

Serum serotonin levels determine the magnitude and type of bystander effects in medium transfer experiments

Serotonin has been shown to be involved in the production of bystander signals by irradiated cells. In this study we examined the levels of serotonin in 10 different batches of commercially available fetal calf serum and correlated the serotonin levels with the toxicity of medium harvested from irradiated cells (ICCM) using a standard medium transfer colony-forming assay. The serotonin levels in the serum varied widely between batches, and the levels correlated directly with the toxicity of the harvested ICCM. Three serum samples had levels of serotonin below 25 ng/ml, and these did not show medium transfer bystander effects. Exposure of serum samples to normal daylight reduced serotonin levels significantly. We suggest that serum batch variability may underlie much of the observed interlaboratory variation in the ability to produce bystander effects and further suggest that serum batches should be protected from light and prescreened for their ability to produce a bystander effect using a positive control cell line.

Antioxidative effects of melatonin administration in elderly primary essential hypertension patients

The imbalance of the redox state of the aging organism may be involved in the development of primary essential hypertension. Melatonin, a potent antioxidant agent, was found to exert a hypotensive effect and improve the function of the cardiovascular system. The aim of this study was to determine the influence of melatonin supplementation on oxidative stress parameters in elderly primary essential hypertensive (EH) patients, controlled by a diuretic (indapamide) monotherapy. The levels of malondialdehyde (MDA) and reduced glutathione (GSH), activities of Cu-Zn superoxide dismutase (SOD-1), catalase (CAT) and glutathione peroxidase (GSH-Px) in erythrocytes, the plasma level of nitrate/nitrite, the content of carbonyl groups of plasma proteins and morning melatonin levels in the serum of 17 elderly EH patients were determined at the baseline and after the 15th and 30th days of melatonin supplementation (5 mg daily). Melatonin administration resulted in a significant increase in the morning melatonin concentration, SOD-1 and CAT activities, and a reduction in the MDA level. Statistically significant alterations in the levels of GSH, nitrate/nitrite and carbonyl groups and the activity of GSH-Px were not observed. These results indicate an improvement in the antioxidative defense of the organism by melatonin supplementation in the examined group and may suggest melatonin supplementation as an additional treatment supporting hypotensive therapy in elderly EH patients.

Generation of the melatonin endocrine message in mammals: a review of the complex regulation of melatonin synthesis by norepinephrine, peptides, and other pineal transmitters

Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

The effect of treatment with melatonin upon the ultrastructure of the mouse pineal gland: a quantitative study

In order to evaluate melatonin implication in the regulating of its own secretory process by pinealocytes, we used morphometric techniques for transmission electron microscopy. In mice treated with 100 mg of melatonin (N-acetyl-5-methoxy-tryptamine) by daily subcutaneous injection, we observed a decrease in number and volumetric density of lysosomes. Our results showed that melatonin influences the secretory activity of pinealocytes and participates in a complex secretory regulating mechanism.

Effect of melatonin on beta-tubulin and MAP2 expression in NIE-115 cells

Physiological concentrations of the pineal hormone melatonin induce an increase of microtubules in neuroblastoma NIE-115 cells. This effect is due to an increase in the polymerization state of tubulin. Concomitantly, higher levels of soluble beta-tubulin are present in the treated cells. Unexpectedly, no significant changes in the levels of beta-tubulin or its mRNA occur in the presence of melatonin reflecting perhaps a strict control of its steady state in a physiological context. In contrast, higher amounts of microtubule-associated-protein 2 are found when the cells are exposed to melatonin. These findings support the idea that tubulin polymerization process is one of the targets of melatonin action. Furthermore, our results might explain the increase in the length and number of neurites present in these cells when they are treated with this hormone.

Evidence for a regulatory role of melatonin on serotonin release and uptake in the pineal gland

Melatonin has been proposed to exert some regulatory actions within the pineal gland itself. The present study examined the effect of melatonin on the release of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) from rat pineal glands by using an in vitro perifusion system. Melatonin induced a concentration-dependent stimulatory effect on 5-HT secretion from 10(-6) M to 10(-3) M. Maximal effects were obtained with melatonin 10(-3) M and concentrations lower than 10(-6) M were without effect. The secretion of 5-HIAA was inhibited by melatonin 10(-3) and 10(-4) M, but it was increased when pineals were incubated with 10(-5) and 10(-6) M of melatonin. The indoleamine secretion was also studied on peripherally denervated rat pineal glands. Basal output of 5-HT from these glands was increased when compared with those from control rats. In contrast, the secretion of 5-HIAA was strongly reduced after removal of the sympathetic input to the pineal gland. Melatonin 10(-3) M failed to stimulate 5-HT release from denervated pineal glands, although it inhibited 5-HIAA secretion. In contrast, melatonin 10(-5) M enhanced 5-HT release without altering 5-HIAA output. Fluoxetine, a 5-HT uptake inhibitor, produced similar effects than mM concentrations of melatonin on the indoleamine secretion from control pineal glands, but it had no effect on glands taken from peripherally denervated rats. These data suggest that mM concentrations of the pineal hormone are able to stimulate 5-HT release from the pinealocyte, while mM concentrations of melatonin increase extracellular 5-HT by inhibiting its reuptake in the adrenergic nerve endings. These findings are discussed in relation to the possible role of melatonin regulating the intra- and extracellular availability of 5-HT in the pineal gland and its significance as an autocrine factor.

Melatonin desensitizing effects on the in vitro responses to MCH, alpha-MSH, isoproterenol and melatonin in pigment cells of a fish (S. marmoratus), a toad (B. ictericus), a frog (R. pipiens), and a lizard (A. carolinensis), exposed to varying photoperiodic regimens

Melatonin is a weak dose-independent lightening agonist in fish skin, a moderate dose-dependent lightening agonist in toad skin and a potent lightening agent in frog and lizard skins (reversing in a dose-dependent manner the darkening caused by alpha-melanocyte-stimulating hormone). In frog skins, previous exposure to melatonin reduced further lightening actions of the indoleamine, and in toad skins, increasing concentrations of melatonin elicited decreasing lightening responses, suggesting an autodesensitizing action of the hormone. Various concentrations of melatonin diminished the responses to the lightening agonist melanin-concentrating hormone (MCH) in fish skins and to the darkening agonists alpha-MSH in toad, frog and lizard skins and isoproterenol in frog skins. In vitro inhibitory actions of melatonin are mimicked in the absence of the hormone in skin preparations from toads kept in continuous darkness for 48 hr. The lipophylic nature of the indoleamine associated with the results herein described suggests intracellular actions of melatonin on vertebrate pigment cells.

Calmodulin mediates melatonin cytoskeletal effects

In this article, we review the data concerning melatonin interactions with calmodulin. The kinetics of melatonin-calmodulin binding suggest that the hormone modulates cell activity through intracellular binding to the protein at physiological concentration ranges. Melatonin interaction with calmodulin may allow the hormone to modulate rhythmically many cellular functions. Melatonin's effect on tubulin polymerization, and cytoskeletal changes in MDCK and N1E-115 cells cultured with melatonin, suggest that at low concentrations (10(-9) M) cytoskeletal effects are mediated by its antagonism to Ca2+-calmodulin. At higher concentrations (10(-5)M) non-specific binding of melatonin to tubulin occurs thus overcoming the specific melatonin antagonism to Ca2+-calmodulin. Since the structures of melatonin and calmodulin are phylogenetically well preserved, calmodulin-melatonin interaction probably represents a major mechanism for regulation and synchronization of cell physiology.

The contribution of extrapineal sites of melatonin synthesis to circulating melatonin levels in higher vertebrates

While the production of melatonin in higher vertebrates occurs in other organs and tissues besides the pineal, the contribution of extrapineal sites of melatonin synthesis such as the retina, the Harderian glands and the gut to circulating melatonin levels is still a matter of debate. The amount of melatonin found in the gastrointestinal tract is much higher than in any other organ including the pineal and the gut appears to make a significant contribution to circulating melatonin at least under certain conditions. The gut has been identified to be the major source of the elevated plasma concentrations of melatonin seen after tryptophan administration and of the changes of circulating melatonin level induced by the feeding regimen. Whereas the circadian and circannual fluctuations of the concentration of melatonin in the blood seem to be triggered by changes of the photoenvironment and its effect of pineal melatonin formation, basal daytime melatonin levels and the extent of their elevation at nighttime appear to be additionally controlled by nutritional factors, such as the amount and the composition of ingested food and therefore availability of tryptophan as a rate-limiting precursor of melatonin formation by the enterochromaffin cells of the gastrointestinal tract.

Melatonin effect on serotonin uptake and release in rat platelets: diurnal variation in responsiveness

The present study was conducted to examine whether melatonin impairs serotonin (5HT) release and uptake in rat platelets. Exposure of platelet-rich plasma samples (PRP) to melatonin induced a concentration-dependent inhibition of 5HT uptake and the value of IC50 was 1.3 x 10(-3) M. We have also investigated the melatonin effect on the kinetic parameters of platelet 5HT uptake. Transport capacity was inhibited (Vmax;

CONTROL

2.28 +/- 0.52, Melatonin: 0.74 +/- 0.13 pmol/10(7) platelet.min; p < 0.05) while the affinity of 5HT for its uptake carriers remained unaltered, thus indicating a non-competitive effect. Studies carried out to determine the existence of a differential morning (8:00h)-evening (21:00h) melatonin effect showed a higher platelet uptake sensitivity at 8:00h (two-way ANOVA, p < 0.001). Spontaneous 5HT release was not impared by the hormone and no daily variation in sensitivity was detected. The possible mechanism of action of melatonin on platelet transport is discussed, and the results support the suitability of the platelet model for studying sensitivity changes in target cells to the hormone.

Presynaptic effects of melatonin on norepinephrine release and uptake in rat pineal gland

The effect of melatonin injection on norepinephrine (NE) turnover rate in rat pineal gland was estimated from the decline of tissue NE levels after the injection of the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine. The administration of a single injection of 300 micrograms/Kg of melatonin at the beginning of the scotophase induced, 3 hr later, a significant decrease of pineal NE turnover. The possible direct effect of melatonin on pineal NE release was examined in vitro. Exposure of rat pineal explants previously loaded with 3H-NE to 10(-8)-10(-6) M melatonin decreased significantly 3H-NE release triggered by 60 mM K+. This activity of melatonin was revealed only in pineals excised at night (0000 and 0400, i.e., at the fourth or eighth hours of darkness) and not in those excised in the middle (1400) or late light phase of the daily photoperiod (2000). Melatonin did not modify the spontaneous pineal 3H-NE efflux. Melatonin decreased 3H-NE uptake at a low NE concentration (0.5 microM) in a dose-dependent manner (IC50 identical to 10(-10) M). A kinetic analysis of the pineal NE uptake process indicated that melatonin augmented both Vmax and Km of transmitter uptake. These results suggest that endogenously released melatonin may be a regulatory signal for rat pineal sympathetic synapses.

Neuronal markers in the rodent pineal gland--an immunohistochemical investigation

Although some embryological and morphological features speak in favour of a neuronal character of rodent pinealocytes, histochemistry and ultrastructure let this issue appear controversial. Using antibodies to different neurofilaments, the neural adhesion molecule L1, synaptophysin and tubulin as neuronal markers, the pineal glands of rat and guinea-pig were studied by means of immunofluorescence. Neurofilament-immunoreactivity was present in some rat pineal nerve fibers and in the majority of guinea-pig pinealocytes, L1 decorated rat intrapineal nerve fibers, synaptophysin was almost ubiquitously distributed in the pineal of both species, while tubulin-immunofluorescence was seen in nerve fibers of rat and guinea-pig pineal and in some pinealocytes of the latter. These findings speak in favour of the neuronal character of guinea-pig pinealocytes. The lack of neurofilament- and tubulin-immunoreactivity in rat pinealocytes might be attributable to very low concentrations of these proteins or species differences as to their expression. Further studies including in situ-hybridisation of relevant mRNAs will be necessary to answer these questions definitely.

Melatonin effects on prolactin secretion in pituitary-grafted male rats

Melatonin influences prolactin (PRL) secretion through unknown mechanisms. This work was undertaken to study the effects of melatonin administration on PRL secretion in pituitary-grafted male rats. Melatonin administration 5 hours before dark resulted in a marked decrease of previously high basal plasma PRL levels in pituitary-grafted rats, whereas a marked increase was detected in sham-operated animals. Vehicle treatment did not modify basal PRL values in grafted or sham-operated animals. Luteinizing hormone-releasing hormone (LHRH) administration resulted in a marked decrease of plasma PRL levels in vehicle-treated, sham-operated or grafted rats, as well as in melatonin-treated sham-operated rats. An increase in PRL levels was shown in grafted rats treated with melatonin. Estradiol benzoate (EB) administration resulted in an increase in plasma PRL levels both in sham-operated and grafted vehicle-treated rats. No PRL response could be detected in sham-operated, melatonin-treated animals after EB administration. In pituitary-grafted animals given melatonin, PRL response to EB administration was slight and delayed. From these data, melatonin appears to modify PRL secretion through multiple complex mechanisms that may depend on the physiological status (hormonal and neurotransmitter) of the animals. A direct effect at the pituitary level altering lactotroph sensitivity seems to be one plausible explanation for the current findings, although an hypothalamic site of action cannot be excluded.

Unusual configurations of endoplasmic reticulum in pinealocytes of the Djungarian hamster (Phodopus sungorus)

Ultrastructural observations of the pineal gland of Phodopus sungorus revealed different morphological forms of endoplasmic reticulum. These included crystalloids composed of 200A-wide tubules with an intervening space of 200A and connected at right angles to form a rectangular lattice; complexes of undulating 500A-wide tubules in an electron-dense cytoplasmic matrix; and stacks of flattened cisternae covered with granular electron-dense material. All these structures are continuous with the surrounding endoplasmic reticulum. Frequently one structure is directly connected with another. The exact function of these structures derived from the endoplasmic reticulum is still unclear, but they can be assumed to be morphological features of augmented secretory activity.

Comparison of the effects of short photoperiod exposure and melatonin treatment in ovariectomized LSH/SsLaK hamsters

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 E2 replacement, 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 E2 implants, whereas MEL effectively suppressed them. SP or MEL reduced serum LH levels to a similar extent in the absence of E2 replacement, yet in animals with E2 implants 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 E2 replacement. 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 micrograms 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 LHRH system.

The annulate lamellae--from obscurity to spotlight

This review aims to provide a comprehensive and in-depth survey of a cell organelle, the annulate lamellae, that is widely distributed and especially prevalent in both female and male sex cells as well as tumor and cancer cells. The organelle is also present in many somatic cells and plant cells. Emphasis is placed on the contributions that electron microscopy and associated experimental approaches have made in providing information about the distribution, ultrastructure, morphogenesis and relationships of annulate lamellae to other cellular organelles, especially the nuclear envelope and endoplasmic reticulum, as well as cell product. An increasing number of experimental manipulations have recently been shown to alter, either increase or decrease, the amount of annulate lamellae and these studies are explored in depth. Information about the origin and morphogenesis of annulate lamellae in different cells is summarized and extensive coverage is given to several hypotheses about possible annulate lamellae function. A detailed bibliography provides a thorough compilation of research dealing with annulate lamellae. A major goal of this extensive review is to generate increased awareness of, and interest in, this cell organelle for students and investigators of the cell who, by bringing current techniques in cell and molecular biology to bear, might focus and intensify studies on the function of an organelle whose precise role in the cell is presently enigmatic.

Annulate lamellae in the pineal organ of a tinamid bird

This study reports the occurrence of annulate lamellae in the rudimentary photoreceptor cells of the pineal organ of a tinamid bird Crypturellus parvirostris. The annulate lamellae observed in these cells are located in the cell body and are comprised of 1 to 8 parallel lamellae, symmetrically aligned and regularly spaced. Each lamella consists of pairs of parallel membranes interrupted by regularly spaced pores or annuli. These observations are discussed and compared with the structure and distribution of these organelles referred in the literature.

The pineal gland: anatomy, physiology, and clinical significance

Since the discovery of melatonin approximately 25 years ago, there has been intense study regarding the details of the structure and function of the pineal gland. This work is reviewed, with particular emphasis on those aspects of importance to human physiology and disease.

Morphometric analysis of the pineal complex of the golden hamster over a 24-hour light:dark cycle: I. The superficial pineal in untreated and optically enucleated animals

Morphometric analysis of the superficial pineal gland of intact and blinded golden hamsters was conducted at both the light and electron microscopic level. The volume of the superficial gland was estimated to be 151 X 10(6) micron 3, comprising 90-94% of the total pineal parenchymal tissue. Analysis of structural rhythms in animals maintained under a 14:10 L:D cycle showed significant 24-hr variations in values for pinealocyte nuclei, nucleoli, rough and smooth endoplasmic reticulum, Golgi bodies, dense bodies, and dense-cored vesicles. Peak values for these structures generally occurred at the light:dark interface. These results provide morphological correlates for known rhythmic variations in the synthesis of pineal-gland products. Superficial pineals examined 8 weeks following optic enucleation exhibited a decrease in the volume of pinealocyte nuclei and cytoplasm, while nucleolar size and the amounts of smooth and rough endoplasmic reticulum, Golgi bodies, dense bodies and dense-cored vesicles were enhanced. The latter changes are interpreted as indications of increased synthetic activity by the superficial pineal gland in response to light deprivation.

No correlation of pineal "synaptic" ribbon numbers and melatonin formation in individual rat pineal glands

As previous circadian studies of pineal "synaptic" ribbon numbers and melatonin formation suggested that a positive correlation of the two variables exists, in the present investigation this problem was examined in individual pineal glands of rats killed at 1200 h and 2400 h, respectively. For this purpose, one half of the gland was processed for electron microscopy and the ribbons were counted in an area of 20,000 micron2 tissue; in the other half serotonin N-acetyltransferase (NAT) activity and melatonin content were determined. No correlation was found to exist between ribbon numbers and pineal NAT activity, pineal melatonin levels and serum melatonin levels, either at day- or at nighttime. It is concluded that the ribbons may perhaps be more closely related to the innervation of the pineal gland than to melatonin formation.

Effects of melatonin and control injections on pineal serotonin and norepinephrine: afternoon injections lower serotonin levels thirty-six percent at light-dark transition

Pineal weight and serotonin (5-HT) and norepinephrine (NE) contents were studied in male Sprague-Dawley rats that were maintained under controlled light:dark conditions (LD 14:10; lights on 0700-2100) and that received daily subcutaneous injections of either melatonin (20 micrograms in 0.1 ml per animal) or the same volume (0.1 ml) of vehicle alone, at one of two times (0800-0900 or 1800-1900). Animals were sacrificied at four times (1000, 1400, 2000, or 2300) on the day after the last of the 7 consecutive d of injection. Pineal glands were quickly weighed and then frozen for 5-HT and NE assay by the Maickel and Miller extraction and fluorescence methods. Pineal NE content showed differences related to time of day, in confirmation of early work. But no effects attributable specifically to melatonin were found. Melatonin also failed to affect pineal 5-HT content significantly. But injection of either melatonin or vehicle at 1800-1900 led to a reduction in 5-HT content averaging 36% when sampled at either 2000 or 2300, and in comparison with animals injected at 0800-0900. It is suggested that a stresslike or zeitgeberlike effect of injections within a critical period at the end of the daily light phase can cause an earlier-than-normal daily fall in pineal 5-HT content.

The pineal gland of the mole (Talpa europaea L.). VII. Activity of hydroxyindole-O-methyltransferase (HIOMT) in the formation of 5-methoxytryptophan, 5-methoxytryptamine, 5-methoxyindole-3-acetic acid, 5-methoxytryptophol and melantonin in the eyes and the pineal gland

Using a method in which no substrate is added to the incubation medium, the capacity of HIOMT to synthesize 5-methoxytryptophan, 5-methoxytryptamine, 5-methoxyindole-3-acetic acid, 5-methoxytryptophol and melatonin has been determined in the pineal and the eyes of the mole, a mammal having an atrophied visual system. The results demonstrate that the indoleamine metabolism in the retina is similar to the indoleamine metabolism in the pineal. Moreover, in all animals studied both eyes together synthesize 2 to 30 times more of 5-methoxyindoles than the pineal, a result which proves again that the pineal is not the only and not always the most important source of 5-methoxyindoles. With the exception of 5-methoxyindole-3-acetic acid, the synthesis of which is practically neglectable, the production of all other 5-methoxyindoles in the pineal as well as in the retinae is always larger than that of melatonin. In the pineal, 5-methoxytryptophan, for example, is synthesized in a quantity which is 60 to 170 times larger than that of melatonin, while in the retinae the synthesized amount of 5-methoxytryptophan is even 60 to 1000 times larger than that of melatonin.

Hypothalamic cuts suggest a brain site for the antigonadotrophic action of melatonin in the Syrian hamster

Thrice daily melatonin injections inhibit reproductive functions in pinealectomized male hamsters, as measured by sex organ weights and plasma testosterone levels. Total or anterior, but not posterior, hypothalamic deafferentation prevented the antigonadotrophic effect of melatonin. The findings suggest a site of action of melatonin within the central nervous system.

The independency of an intact pineal gland of the inhibition by 5-methoxytryptamine of the reproductive organs in the male hamster

Subcutaneous injections fo 25 micrograms of 5-methoxytryptamine (5-MT) in oil into intact and pinealectomized male hamsters given between 4.30 p.m. and 5 p.m. (light on from 5 a.m. to 7 p.m.; 14 L/10 D) for 54 consecutive days caused involution of the testes. 5-MT, however, is more effective when the pineal is present. These results indicate that melatonin is not the only pineal factor inducing gonadal atrophy in the hamster. 5-MT seems even more effective than melatonin in so far as it is, contrary to melatonin under the same experimental conditions, also effective in the absence of the pineal. Like melatonin, 5-MT appears to be implicated in the control of the reproductive function.

Circadian rhythmicity of the activity of hydroxyindole-O-methyl transferase (HIOMT) in the formation of melatonin and 5-methoxytryptophol in the pineal, retina, and harderian gland of the golden hamster

The day and night rhythms in the activity of HIOMT in the formation of melatonin of 5-methoxytryptophol have been determined in the pineal, retina and Harderian gland of the adult male golden hamster. In all hamsters used there was no detectable HIOMT activity in the deep pineal. In the superficial pineal HIOMT activity, involved in the synthesis of melatonin (Mel), was observed to be high at the end of the dark period and at the middle of the light period. Considering the HIOMT activity involved in the production of 5-methoxytryptophol (5-MTL), an increase in 5-MTL synthesis was observed only during the light period. Comparing the peak of Mel-production with that of 5-MTL it appears that during the light period the pineal produces more 5-MTL than Mel. In the Harderian glands, the circadian course of HIOMT activity involved in the synthesis of Mel seems to run parallel to that of the enzyme implicated in 5-MTL synthesis, both being stimulated at the end of the dark period. The activity of HIOMT in 5-MTL production is, however, always approximately 2 times higher than for Mel synthesis. In the retina the synthesis of Mel and 5-MTL is not significantly higher during the dark period than during the light period. However, the production of 5-MTL is larger than that of Mel. It appears that (1) with the exception of the end of the dark period, the extra-pineal synthesis of Mel and 5-MTL is always higher than that in the pineal; (2) the carcadian synthesis of 5-methoxyindoles is different in each organ, and (3) in the pineal the carcadian activity of HIOMT involved in 5-MTL formation is different from that of the same enzyme involved in the formation of Mel. The results are discussed.

Ultrastructural evidence for seasonal changes in pinealocytes of the 13-lined ground squirrel, Spermophilus tridecemlineatus: a qualitative and quantitative study

The fine structure of pinealocytes in the hibernating ground squirrel, Spermophilus tridecemlineatus, was found to vary both qualitatively and quantitatively according to the season in which the animals were sacrificed. Ultrastructural features of pinealocytes from fall (prehibernation) and winter (hibernation) periods, when the animals were sexually quiescent, included: 1) arrangement of the endoplasmic reticulum into flattened stacks or concentric rings (formations which have been implicated in antigonadotropic activity of the pineal); 2) condensations of a fine granular material; and 3) dilation of the cisternae of the endoplasmic reticulum and Golgi bodies with an increased number of Golgi associated vesicles. Moreover, there was an apparent increase in the number of dense-cored vesicles and microtubules in pinealocytes of winter animals. These findings indicate that a circannual rhythm in pinealocyte ultrastructure occurs in this species and further suggest that cellular activity is seasonal.

Norepinephrine turnover in pineal gland and superior cervical ganglia. Changes after gonadotrophin administration to castrated rats

The effects of FSH and LH on norepinephrine (NE) turnover in pineal gland and superior cervical ganglia of castrated female rats were examined by measuring the decline of [3H]NE concentration in the organ 30--120 min after a single i.v. injection of the labeled amine. Both FSH and LH treatment significantly decreased [3H]NE turnover in the pineal gland whereas only FSH accelerated it in the ganglia. As compared to controls, the initial uptake of [3H]NE was lower in the pineal gland of FSH- and LH-treated animals, and higher in the superior cervical ganglia of rats injected with FSH. Neither FSH nor LH modified [3H]NE turnover in heart or adrenal gland, nor changed their endogenous catecholamine content. Pineal monoamine oxidase (MAO) activity type B (assaying by using beta-phenylethylamine as substrate) was decreased by FSH or LH injection. Only FSH modified MAO activity in the ganglia by increasing significantly type A enzyme (assaying by using serotonin as substrate). These results suggest that FSH and LH affect significantly NE metabolism in pineal gland and superior cervical ganglia of spayed rats.

Fast axonal transport in rat sciatic nerve. Inhibition by pineal indoles

The effect of pineal indoles on fast axoplasmic transport of proteins in the sciatic nerve was examined in rats injected with [3H]leucine in the sixth lumbar dorsal root ganglion. Melatonin (350-1100 nmol) applied locally in the sciatic nerve impaired significantly axonal transport. At a 350-nmol dose all other indoles tested (i.e., 5-hydroxyindoleacetic acid, 5-methoxyindoleacetic acid, serotonin, N-acetylserotonin, tryptamine, 5-methoxytryptamine) were less potent than melatonin to impair fast axonal flow. Vinblastine injected either into the ganglion or in the sciatic nerve markedly inhibited axonal transport.

Influence of agents which modulate thromboxane A2 synthesis or action on R3230AC mammary carcinoma

The effects of agents which modulate thromboxane A2 synthesis or action, were tested in the R3230AC transplanted mammary tumour. Three different inhibitors of thromboxane A2 synthesis or action (copper, dipyridamole and diazepam) all caused an increase in tumour growth. Colchicine and melatonin, both stimulators of thromboxane A2 synthesis, inhibited the growth of the tumour significantly.

Membranous structures in pinealocytes of the infertile diabetic mutant mouse (C 57 BL/Ks-db/db)

The fine structure of the pineal gland of the infertile, diabetic mutant mouse (C 57 BL/Ks-db/db) has been studied. Light and dark parenchymal cells were observed. The major population of pinealocytes in these animals is characterized by an abundance of highly organized membranes located in both the cell body and cell processes. Pinealocytes containing these membranous structures have low electron density (light pinealocytes) and large amounts of perinuclear cytoplasm containing granular vesicles and extensive Golgi. Dilated cisternae of the membranous structures may indicate secretory activity or selective aggregations or raw material. Changes in granule and vesicle content of the central core of cytoplasm of the concentric-shaped membranes and their apparent migration from the cell body to terminal process suggest a synthetic or secretory role. It is not known whether the membranous structures are related to the infertile condition or to the hyperglycemic syndrome; however, the presence of comparable membranes in subterranaen mammals lends support to the theory that the structures may be involved in the synthesis of pineal compounds.