Effects of acute cold exposure at night on pineal N-acetyltransferase activity and melatonin content in white-footed mice, Peromyscus leucopus

1. Pineal N-acetyltransferase (NAT) activity in long-day white-footed mice (Peromyscus leucopus) exposed to cold soon after onset of darkness was depressed relative to controls, whereas mice exposed to cold later at night had slightly elevated enzyme activity. 2. NAT activity in short-day mice exposed to cold soon after lights off did not differ from controls. Pineal melatonin in these mice, however, did not rise, as it did in controls. 3. These results suggest that acute cold exposure may modulate NAT activity, which is controlled primarily by the L:D cycle.

Effect of photoperiod on pineal gland volume and pinealocyte size in the Chinese hamster, Cricetulus griseus

Male adult (200-day-old) Chinese hamsters (Cricetulus griseus) raised from weaning under either LD 16:8 or LD 8:16 were used. The pineal gland of the Chinese hamster consists of superficial (major) and deep (minor) components and a continuous, or interrupted, narrow parenchymal stalk interposed between them. The volume of the superficial pineal including the parenchymal stalk is greater under LD 16:8 than under LD 8:16. Under both photoperiods, pinealocytes in the superficial pineal have larger nuclei and more abundant cytoplasm than those in the deep pineal. Nuclei in the superficial pineal appear pale and usually have irregular profiles, whereas those in the deep pineal appear dark and have round profiles. In the superficial pineal, pinealocyte nuclei are larger, paler, and more irregular; and, in addition, nuclear density is lower under LD 16:8 than under LD 8:16. Similar, but less prominent, photoperiod-induced changes occur in the volume of the deep pineal, the size of pinealocytes, and pinealocyte nuclear morphology in the deep pineal. The results indicate that the development and differentiation of pinealocytes in both pineal portions may be advanced under long photoperiods and delayed under short photoperiods, although pinealocytes in the deep pineal may remain not fully differentiated even in adults. Since testicular weights and body weights are similar under both photoperiods, the photoperiod may exert marked influences on the development of the pineal gland without affecting reproductive activity and growth rates of animals.

Reproductive responses of male Microtus montanus to photoperiod, melatonin, and 6-MBOA

Juvenile male Microtus montanus were examined for the effects of photoperiod, melatonin, and the naturally occurring reproductive stimulant 6-MBOA on growth and sexual maturation. 6-MBOA, present in sprouting grass, is an important environmental cue used for the initiation of reproduction in natural populations of this species. Long photoperiod (16:8) was stimulatory to body, testes, and seminal vesicle growth, while short photoperiod (8:16) inhibited these parameters. The pineal hormone melatonin, administered via daily afternoon injections (5 micrograms), was also inhibitory to all of the above parameters as well as to serum testosterone. 6-MBOA, administered via injection (0.0001-100 micrograms) or dietary means (0.1 or 1.0 microgram/gm unsifted chow), appeared unable to augment the rate of maturation in long-photoperiod-stimulated animals. When short-photoperiod animals were treated with high doses of the compound (100 micrograms injected or 1.0 micrograms/gm sifted chow), body and gonadal growth was inhibited to a greater extent than when animals were exposed to short photoperiod alone, and serum LH was reduced. Lower doses of the compound had no effect. Melatonin-treated animals experienced less maturational inhibition when simultaneously given a low dose of 6-MBOA-coated chow (1.0 micrograms/gm unsifted chow). A higher dose of 6-MBOA (1.0 micrograms/gm sifted chow) was ineffective in preventing the response to melatonin. These results indicate that 1) male M. montanus utilize photoperiod, rather than 6-MBOA, as a primary environmental cue, 2) high doses of 6-MBOA can be inhibitory under short photoperiod, 3) juvenile male voles are highly sensitive to the inhibitory effects of exogenously administered melatonin, and 4) 6-MBOA can partially prevent the inhibitory effects of melatonin on growth and sexual maturation.

Influence of melatonin on the sleep-independent component of prolactin secretion

Sleep has a stimulatory effect on prolactin secretion. Recent studies in the human suggest the hypothesis that prolactin has also an endogenous sleep-independent rhythm, which can be influenced by endogenous melatonin. To investigate this hypothesis, the prolactin response to nighttime exposure to bright light was studied in eight women in detail. Light exposure induces a decrease in nocturnal melatonin secretion. It was demonstrated that exposure to bright light for 2 h at night caused a decrease in prolactin secretion, which surpassed significantly the decline one would expect by sleep deprivation only (P less than 0.01). This was associated with a similar decline in melatonin secretion. Fall and rise of prolactin secretion under these conditions were always preceded by decrease and rise in melatonin levels in all eight women studied. Based on these observations, it is concluded that melatonin is associated with an endogenous circadian component of prolactin secretion. As specific melatonin receptors have been identified in the human nucleus suprachiasmaticus, which is the "master" circadian pacemaker, the observed phenomenon might be mediated through this structure. An alternative explanation of our findings could be based on the fact that melatonin influences dopamine metabolism, which in turn alters prolactin secretion. It can also not be ruled out that melatonin might act via the opioid system, which then could affect prolactin secretion. The total secretory activity for both hormones (area under the curve) did not change under experimental conditions, when compared to a control group. This suggests that acute light exposure and sleep deprivation influence the secretory process rather than the synthesis of these two hormones. This is in agreement with the observation that changes in natural light exposure throughout the year do alter the amplitude, but not the total amount of melatonin secreted. Further studies are needed to answer the question of melatonin storage definitively, as it is commonly believed that melatonin is immediately released after synthesis. It is concluded that melatonin through its external modulator light might entrain the circadian sleep-independent component of prolactin secretion and via its action on prolactin could modulate reproductive processes.

Tumor-inhibiting activity in the rat pineal gland displays a circannual rhythm

The aim of this study was to investigate whether the tumor-inhibiting activity present in the rat pineal gland undergoes seasonal fluctuations as do other pineal substances. Crude ethanol extracts of rat pineal glands were tested for tumor-inhibiting activity in an in vitro microbioassay using human erythroleukemia cells which could not be inhibited by melatonin. Highest activity was detected in summer and least inhibition and even stimulation were observed in winter. There were no differences in activity between animals of different age, sex, or strain. Therefore, season seems to be the factor that exerts the most important influence on the content of tumor-inhibiting activity in the rat pineal gland. Correlation with seasonality in the occurrence of cancer is discussed.

Effects of season, pinealectomy, and blinding, alone and in combination, on hypothalamic monoaminergic activity in the teleost Channa punctatus (Bloch)

In Channa punctatus, day-night variations in hypothalamic 5-HT (serotonin) and monoamine oxidase (MAO) activity were noticed in preparatory but not other phases (prespawning and postspawning) of the annual reproductive cycle. Hypothalamic MAO, 5-HT, and norepinephrine (NE) activity was found to be high in the prespawning phase and low in the postspawning phase. Dopamine (DA) activity, on the other hand, was high in the postspawning season and low in the prespawning phase. Pinealectomy caused season-dependent effects on hypothalamic monoaminergic activity, with a significant increase in serotonergic activity and a significant reduction in MAO activity at midscotophase during the preparatory phase (March) but not in the prespawning (May-June) or postspawning (September) phases. Hypothalamic catecholaminergic (CA) activity was not influenced by pinealectomy during any of the seasons. To determine whether or not the photoperiodic influences on daily variations of 5-HT and MAO in the preparatory phase are mediated via pineal and/or lateral eyes, fish were pinealectomized and/or blinded in January, when there is no rhythm, and sacrificed in February, when a day-night variation normally sets in. The day-night difference in 5-HT content and activity and MAO activity was not abolished by pinealectomy or blinding alone; but the combination (pinealectomy + blinding) obliterated the daily variation only in 5-HT content and in MAO activity. However, pinealectomy and blinding, alone or in combination, caused a significant elevation of 5-HT activity (not its level) and a significant decrease in MAO activity at midscotophase, with the combination having an additive effect. Hypothalamic CA content or activity was not affected by these regimes. The results show that photoperiodic influence on the daily pattern of 5-HT and MAO activity is mediated through and by the interaction of the pineal and lateral eyes.

Alteration of plasma cation levels in rats kept in constant light

A variety of reports indicate that some kind of interaction may exist between the pineal gland and cations. Of particular interest are the reports that indicate comparatively high levels of copper, manganese, and zinc in the pineal gland and that the pineal gland exhibits a circadian rhythm in calcium, magnesium, potassium, and sodium. There are, unfortunately, no reports suggesting a functional role for these findings. This study investigated circadian rhythms in circulating plasma cations in rats under 12/12 h light-dark cycle and in rats whose pineal function had been suppressed by exposure to constant light for 1 and 7 days. Neither of the treatments affected circulating potassium levels but had some significant effects on sodium concentration at a number of time points without affecting the total amount of sodium circulating in a 24 h period. Calcium, magnesium, and zinc plasma concentrations were little affected by 1 day of constant light, while 7 days of constant light caused a dramatic and highly significant increase in the circulating levels of the three cations. The plasma levels of copper, on the other hand, while also being unaffected by 1 day were significantly depressed by 7 days of constant light. It is apparent, therefore, that the pineal gland may be involved in regulation of circulating levels of the cations measured. The functional significance of these observations is not clear at this stage but warrants further investigation.

Binding characteristics, regional distribution and diurnal variation of [125I]-iodomelatonin binding sites in the chicken brain

The [125I]-iodomelatonin binding sites in chicken brain membrane preparations were studied. The binding of [125I]-iodomelatonin to the membrane preparations of chicken brain was rapid, stable, saturable, and reversible. The order of pharmacological affinities of [125I]-iodomelatonin binding sites in the chicken brain membrane preparations was: melatonin greater than 6-chloromelatonin greater than N-acetylserotonin greater than 5-hydroxytryptamine greater than tryptamine greater than 5-methoxytryptophol, much greater than 1-acetylindole-3-carboxaldehyde, 5-hydroxyindole-3-acetic acid, L-tryptophan, 5-hydroxytryptophan, 3-acetylindole. Compounds known to act on the receptor of norepinephrine or acetylcholine were inactive as compared to melatonin. Among the various brain regions studied, melatonin binding had maximal level in the hypothalamus, intermediate levels in the mid-brain, ponsmedulla, and telencephalon, and minimum level in the cerebellum. Subcellular fraction studies indicated that 40% of the binding was located in the mitochondrial fraction, 27% in the nuclear, 26% in the microsomal, and 6% in the cytosol fraction. Scatchard analysis of the membrane preparations revealed a dissociation constant (Kd) of 199.6 +/- 17 pM and a total number of binding sites (Bmax) of 16.6 +/- 0.75 fmol/mg protein at midlight. Thus, our results showed the presence of specific melatonin binding sites in the chicken brain membrane preparations. Saturation studies demonstrated that [125I]-iodomelatonin binding capacity in chicken brain membrane preparations were 40% greater at midlight (16.6 +/- 0.75 fmol/mg protein) than at middark (10.6 +/- 0.56 fmol/mg protein), with no significant variation in their binding affinities.

Changes in indole metabolism in organ cultured rat pineal glands induced by interferon-gamma

The purpose of this study was to test the effects of recombinant rat interferon-gamma (IFN-gamma) on rat pineal function in organ culture. The glands were pre-incubated with IFN-gamma (50, 100, and 1,000 antiviral units/ml) for two hours, followed by a stimulation with isoproterenol (ISO, 10(-6) M) (in the presence of IFN-gamma) for an additional three hours. The effect of IFN-gamma alone on the pineal function was also tested by adding another group incubated with IFN-gamma (1,000 antiviral units/ml) without ISO stimulation. The following parameters were estimated at the end of the incubation: the activities of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT), the levels of melatonin, 5-hydroxytryptophan (5HTP), 5-hydroxytryptamine (5HT), and 5-hydroxyindole acetic acid (5HIAA), and the 5HT/5HIAA ratio. IFN-gamma had no effect on either NAT or HIOMT activities in the pineal glands. At 50 units/ml, IFN-gamma increased the melatonin content over the ISO-stimulated level in the pineal but not in the media. IFN-gamma alone, at 1,000 units/ml, also increased the melatonin content significantly over the control level. The levels of 5HTP and 5HIAA were significantly suppressed by IFN-gamma, either alone or in combination with ISO. The level of 5HT was not altered by any of the treatments. The 5HT/5HIAA ratio was significantly increased by IFN-gamma, either when given alone or when given in combination with ISO. The results suggest that IFN-gamma enhances melatonin production in the pineal gland by suppressing the oxidative deamination of 5HT to 5HIAA and shunting the biosynthetic pathway toward melatonin production.

Influence of pinealectomy on sexual behavior of normal and monosodium L-glutamate-treated rats

Subcutaneous injections of monosodium L-glutamate (MSG) were administered, as a neurotoxin, at a dose of 4 mg/g body weight to rat pups on days 1 and 3 postnatally. Pinealectomy was performed at 6 weeks of age, and animals were allowed to mature. The intact MSG-treated rats showed a decrease of lordosis quotient in females and a reduction of ejaculation frequency and an increase in mount frequency in males. Pinealectomy caused no significant improvement on sexual behavior of the saline-treated normal rats, but it caused a marked improvement of the sexual receptivity in MSG-treated female rats and reinstated ejaculation in MSG-treated males. The circulatory sex steroid levels, estrogen in females and androgen in males, were not significantly different between the intact and pinealectomized MSG-treated groups in the respective sexes, whereas the progesterone level in females was significantly elevated in the pinealectomized MSG-treated group compared with the intact MSG-treated group. These findings suggest that the pineal gland plays an inhibitory role on the sexual behavior of MSG-treated rats and the improvement of sexual behavior following pinealectomy may be dependent on certain mechanisms other than the actions of circulatory androgens or estrogens.

"Synaptic" ribbons in the pineal gland of the horse

Previous studies on the ultrastructure of the horse pineal gland did not report the presence of "synaptic" ribbons, functionally enigmatic pinealocyte organelles regularly occurring in other mammalian species. The aim of the present study was to reinvestigate the horse pinealocyte in this respect. Careful investigations here reported allowed detection of "synaptic" ribbons in the pinealocytes of all the examined animals, although in a relatively low number (5.4 +/- 2.0 per 20,000 microns 2 of pineal tissue; mean +/- SD). The ultrastructure of "synaptic" ribbons in pinealocytes of the horse resembles closely that observed in other mammalian species.

6-sulphatoxymelatonin production in breast cancer patients

The daily pattern of the major urinary metabolite of melatonin, 6-sulphatoxymelatonin (aMT6s), was determined in women prior to having a breast biopsy. Women with malignant tumors appeared to have significantly lower 24 h concentrations of aMT6s with a decrease in the amplitude of the rhythm compared to women with benign tumors. The amount of urinary aMT6s was dependent upon the age of the subject but was not affected by either menopausal status or body mass index. However, when the women with malignant tumors were compared with a large group of normal women of the same age their aMT6s levels were not outside the normal range. The results show that a large control group and very accurate age matching are essential when investigating melatonin production in different groups of subjects.

Effect of pineal indoles on testicular histology of mice

The effect of late afternoon injections of melatonin, 5-methoxytryptamine, 5-methoxytryptophol, and 5-methoxyindole-3-acetic acid on testicular histology in mice were examined. Melatonin and 5-methoxytryptophol injections caused a reduction in the diameters of seminiferous tubules. The tests of melatonin-treated animals underwent some detectable regressive changes in the seminiferous tubules, whereas administration of 5-methoxytryptamine or 5-methoxytryptophol appeared to cause atrophy in some tubules. The percentage of aspermic tubules in melatonin-treated and methoxytryptamine-treated mice was significantly higher than that of the control. In involuted testes, some seminiferous tubules contained only Sertoli cells together with spermatogonia and spermatocytes, but no discernible spermatids and spermatozoa. Regressing spermatids and cell debris were frequently observed in the tubules. The tested of mice that received daily injections of 5-hydroxytryptophol and 5-methoxyindole-3-acetic acid were indistinguishable from those of the controls.

Choline acetyltransferase in bovine pineal gland

Recent studies from our laboratories have shown that the bovine pineal gland contains a muscarinic cholinergic receptor with a Kd value of 0.423 +/- 0.010 nM and a Bmax value of 69.75 +/- 20.91 fmol/mg protein. In order to substantiate further the possible existence of a pineal cholinergic transmission, we have measured the activity of choline acetyltransferase and delineated its kinetic properties in the bovine pineal gland. This enzyme exhibited an activity of 0.0339 +/- 0.0042 nmol/mg protein/min. Furthermore, the bovine pineal choline acetyltransferase possessed a Km value of 124.86 +/- 24.06 microM and a Vmax value of 0.0598 +/- 0.0034 nmol/mg protein/min for acetyl CoA, and a Km value of 3.11 +/- 0.94 mM and a Vmax value of 0.0155 +/- 0.0016 nmol/mg protein/min for choline. The presence of muscarinic cholinergic receptors along with a specific choline acetyltransferase are supportive evidences that the bovine pineal gland may receive cholinergic innervation.

Postnatal development of the dog pineal gland: electron microscopy

The ultrastructure of the dog pineal gland from the first postnatal day to the seventh month is described. In the first postnatal stages, pineal parenchyma only shows immature proliferative cells with abundant cytoplasmic glycogen. Nerve fibers are seen in the pineal connective tissue spaces. The differentiation of the dog pineal cell types begins in the first postnatal week. Both pinealocytes and pigmented cells are first seen on the fourth postnatal day. The pineal astrocytes are observed on the tenth day. Immature cells are still found in the pineal gland of 1 mo-old dogs. The differentiation of the dog pineal cell types is completed by the second postnatal month.

The influence of acute or chronic nicotine treatment on ethanol-induced gastric mucosal damage in rats

The influences of acute or chronic nicotine pretreatment on ethanol-induced changes on gastric secretion, mucosal blood flow (GMBF), and glandular mucosal damage were studied in anesthetized rats. Ethanol administration decreased gastric acid secretion and GMBF, which were accompanied by a marked increase in gastric mucosal damage. Acute nicotine incubation 2 or 4 mg dose-dependently elevated both the titratable acid in the luminal solution and the gastric secretory volume; it also prevented the depressive action on GMBF and gastric mucosal damage in ethanol-treated animals. Chronic nicotine treatment for 10 days reduced the inhibitory action of ethanol on gastric acid secretion; the higher dose (25 micrograms/ml drinking water) potentiated the decrease of GMBF and the ulcerogenic property of ethanol. However, chronic treatment with the lower dose (5 micrograms/ml drinking water) had the opposite effects; it also markedly increased the gastric secretory volume. It is concluded that acute nicotine pretreatment elevates, whereas chronic nicotine pretreatment differentially affects GMBF. These effects could account for their protective or preventive actions on ethanol ulceration. The increase in nonacid gastric secretory volume by nicotine could partially explain its antiulcer effect. Furthermore, the acid secretory state of the stomach appears unrelated to the ulcerogenic property of ethanol.

Annual pineal and testicular cycle in the Indian jungle bush quail, Perdicula asiatica, with reference to the effect of pinealectomy

The annual testicular cycle of Perdicula asiatica has a single peak which appears to be under the dual influence of the environment and the pineal gland. An inverse relationship was noted between pineal gland and testicular weight cycle. Pinealectomy, after 60 days, retarded testicular growth in the progressive phase, inhibited activity of the gonad in the active phase, and accelerated gonadal regression in the regressive phase. This complete study of short-term pinealectomy effects on the annual testicular cycle of a tropical bird for the first time reflects both the essentialness of the pineal gland to the maintenance of proper testicular cyclicity under natural environment conditions and the progonadotropic nature of the pineal gland.

Type II thyroxine 5'-deiodinase activity in the rat brown adipose tissue, pineal gland, Harderian gland, and cerebral cortex: effect of acute cold exposure and lack of relationship to pineal melatonin synthesis

The effect of acute cold exposure for 6 hours on nocturnal type II thyroxine 5'-deiodinase (5'-D) activity was studied in brown adipose tissue (BAT), Harderian gland, cerebral cortex, and pineal gland of the rat. Moreover, the effect of iopanoic acid (IOP), a potent inhibitor of 5'-D activity, on both pineal N-acetyltransferase (NAT) activity and melatonin content in rats maintained in a cold environment was also examined. Results show that acute cold exposure significantly increases 5'-D activity in BAT but not in either the pineal gland, Harderian gland, or cerebral cortex. In all tissues, the injection of IOP reduced dramatically 5'-D activity, while exposure of the animals to light at night reduced 5'-D activity in pineal gland but not in either the Harderian gland or BAT while light exposure at night increased cerebrocortical 5'-D activity. Cold exposure did not change either pineal NAT activity or the melatonin content of the gland. Finally, when pineal 5'-D activity was inhibited by IOP treatment, neither nocturnal pineal NAT activity nor melatonin content was affected.

Entrainment of the rhythm in thymidine incorporation by cultured chick pineal glands

Young chicks were raised under a standard cycle of illumination and their pineal glands were cultured in organ culture. We have already reported a rhythmic daily cycle in the cumulative incorporation of thymidine into DNA when the glands were incubated under the cycle of illumination to which they were entrained in vivo. Incorporation ceased shortly after the end of the photoperiod and resumed again at, or shortly after, start of the following photoperiod. We have now shown that this cycle was entrained to other lighting schedules and largely unaffected by the time of explanting into culture. The rhythm also persisted in glands cultured in constant darkness. However, when the cycle was maintained by daily renewal of the culture medium it was markedly affected by changes in the time of day at which medium was renewed. Results for glands cultured under constant illumination were inconsistent.

Time-dependent effect of melatonin on actin mRNA levels and incorporation of 35S-methionine into actin and proteins by the rat hypothalamus

The synthesis of the cytoskeletal protein actin exhibits, in the rat hypothalamus, a diurnal variation with maxima during morning hours. The objective of the present study was to assess whether melatonin injection could affect the in vitro incorporation of 35S-methionine into actin, as well as the levels of actin mRNA, in the hypothalamus of adult male rats treated either acutely or chronically with the hormone at 10:00 or 18:00. Injection of 100 micrograms/kg of melatonin for ten days at either time induced a significant depression in the incorporation of 35S-methionine into a 43 kDa protein with the electrophoretic mobility of actin. The specific activity of total soluble proteins after labeled methionine incubations decreased only after evening melatonin administration (100 micrograms/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot-blot analysis, decreased only after the injection of 100 micrograms/kg melatonin for ten days at 10:00. Neither a 10-micrograms/kg dose of melatonin, nor a single injection of 100 micrograms/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 micrograms/kg for ten days) did not modify hypothalamic somatostatin or H-Ras mRNA concentration. These results suggest the existence of an inhibitory effect of melatonin on hypothalamic actin synthesis.

Effect of melatonin administration and long day-length on endocrine cycles in the hedgehog Erinaceus europaeus

The effects of exogenous melatonin (subcutaneous implants containing 0.031 +/- 0.006 mg/gm body mass melatonin) or long photoperiod (18L:6D) on wild-caught adult male hedgehogs were studied. Hedgehogs were implanted with melatonin-filled or empty capsules in May, August, or September, or maintained under long photoperiod from August. Blood samples collected at monthly intervals were assayed for testosterone, melatonin, and thyroxin. Melatonin-filled capsules elevated plasma melatonin concentrations for 4-6 months. Although melatonin administration in May depressed plasma testosterone levels, testicular reactivation was advanced by 1 month the following year, and the characteristic prehibernal gain in body mass was abolished. Melatonin administration in August had no effect on plasma testosterone concentrations but reduced body mass fluctuations before and during hibernation. Hedgehogs receiving melatonin in September recovered early from hibernal body mass loss and showed a 2 month advance in testicular reactivation the following year. Maintaining hedgehogs at 18L:6D photoperiod, however, elevated plasma melatonin concentrations. Testicular reactivation the following spring was delayed by 1 month, ended 3 months early, and testosterone concentrations were depressed. All treatments depressed plasma thyroxin levels. These results suggest that elevated melatonin levels during winter are important in the regulation of endogenous endocrine cycles in the hedgehog. Hedgehogs do not respond positively to melatonin at the end of the breeding season, but are again responsive to melatonin as early as September.

Temporal changes in the pattern of melatonin secretion in sheep held in constant darkness

The pattern of melatonin secretion was investigated in six 2 yr-old Suffolk ewes transferred from a long-day lighting regime (14L:10D) to continuous darkness. During the 9 d in continuous darkness, five of the ewes maintained a characteristic diurnal rhythm in melatonin secretion. However, there was a systematic change in the duration of each episode of melatonin secretion with the result that it extended from 10 h under the entraining lighting regime to about 19 h by the fourth cycle and then contracted to about 14 h by the eighth cycle under continuous darkness. The pattern of individual ewes varied, but overall the time of offset showed a consistent delay each successive day of about 1 h, indicative of control by a pacemaker with a period of greater than 24 h. By contrast, the time of onset tended to occur earlier each day during the first 4 d of continuous darkness, then changed so that after 8 d, it was delayed in all animals compared to the time of onset on d 4. If, as previously postulated, onset is controlled by a separate pacemaker, then this change is accounted for by interaction with the dominant offset control pacemaker; however, control of both onset and offset through a single pacemaker cannot be excluded. The study confirms that the patterns of melatonin secretion developed in sheep held in continuous darkness may be used to gain insight into the activity of the light-sensitive pacemaker centre(s) controlling the offset and onset of pineal function. Further experimentation is required to differentiate whether control is being exerted by one or two or more independent but interacting pacemaker centres.

Physical exercise at night blunts the nocturnal increase of plasma melatonin levels in healthy humans

The effects of physical exercise on nighttime melatonin secretion have never been investigated in humans. For this purpose, plasma melatonin levels were measured at different times during the day and the night in seven healthy men (aged 26-33 yrs), both in resting condition and before and after a physical exercise performed between 10.40 and 11.00 p.m.. The exercise consisted in bicycling on a bicycle ergometer at 50% of the personal maximal work capacity (MWC) for 10 min, followed by other 10 min of bicycling at 80% of the MWC. The results clearly showed that physical stress at night significantly blunts the nocturnal increase in plasma melatonin levels (group X time interaction: p less than 0.00001; two-way ANOVA with repeated measures). These findings, taken together with the data of the literature, suggest that the response of the pineal gland to provocative stimuli may depend on its level of activity when the stimulus is applied.

Thymidine incorporation by chick pineal glands as studied by pulse-labelling in vitro

We have studied the pattern of variations in extent of thymidine incorporation during pulse-labelling in cultured chick pineal glands. During the first 24-30 h in culture the extent of pulse-labelling varied in parallel with the cycle in cumulative incorporation. Pulse-labelling was seen during the period of apparent arrest of cumulative incorporation. However, it was probably "masked" by the SD of assays of cumulative incorporation and represented a minor, but distinct, process of thymidine incorporation. The pattern of variation in extent of pulse-labelling was qualitatively consistent under a wide variety of conditions. Control of this pattern appeared to be different from that of the circadian rhythm in cumulative thymidine incorporation.

Mechanisms of action of ECT in Parkinson's disease: possible role of pineal melatonin

Recent clinical studies have suggested that electroconvulsive therapy (ECT) may be efficacious in the therapy of Parkinson's disease (PD). However, the mechanisms of action of ECT in PD are largely unknown. PD may be associated with reduction in the secretory activity of pineal melatonin, and the therapeutic efficacy of ECT in PD may be associated with an effect on the secretory activity of pineal melatonin. Further studies involving analysis of plasma melatonin levels and circadian release prior to and following ECT are needed more precisely to determine the role of pineal melatonin in PD and in the therapeutic efficacy of ETC in PD.

The effect of sleep/wake state on nocturnal melatonin excretion

Twenty-four hour patterns of urinary 6-sulphatoxymelatonin excretion were monitored in eight healthy adult subjects in two bed rest constant routines, one with normal nocturnal sleep and one with continuous wakefulness. The implementation of dim light "constant routines" enabled the effect of the sleep wake/state on melatonin to be tested without the confounding effects of body activity and normal room lighting. In both conditions 6-sulphatoxymelatonin excretion was significantly higher during the nighttime hours (2200-1000) than during the daytime hours (1000-2200) producing averages of 80% and 78.5% of the total 24 hour output in the sleep and wakeful conditions, respectively. The large differences between subjects in nocturnal melatonin excretion (38 to 150 nmol) were highly consistent between the two conditions. There were no differences between the nocturnal wakeful and sleep conditions in total nighttime melatonin excretion nor in the nighttime percentage of the 24 hour total melatonin excretions. Therefore, the sleep/wake state alone had no effect on nocturnal melatonin excretion. On the other hand, a significant correlation between the nighttime melatonin percentage and sleep length suggested the need to investigate further the relation between the amplitude of the melatonin circadian rhythm and sleep length and quality.

Does moclobemide stimulate melatonin synthesis as the other selective MAO-A inhibitors do?

It has been reported that selective MAO-A inhibitors, clorgyline and brofaromine, but not the MAO-B inhibitors, deprenyl and pargyline, stimulated rat pineal melatonin synthesis in humans and animals. Recent studies, however, found no effect of moclobemide, a selective MAO-A inhibitor, on human plasma melatonin levels. Present study found that in vitro moclobemide produced very weak stimulation of rat pineal NAT activity. However, in vivo moclobemide induced a significant increase of rat pineal NAS and melatonin content, and a dramatic decrease of 5-HIAA content (HPLC-fluorimetric procedure). Moclobemide's effect on melatonin and related indoles could be detected as early as 30 min after the injection and lasted, at least, for 2 h. The possible reasons for discrepancies between human and animal data are discussed.

Melatonin effects on the cytoskeletal organization of MDCK and neuroblastoma N1E-115 cells

Despite the fact that many physiological and pharmacological actions of melatonin (MEL) have been described, its mechanism of action at the subcellular level remains unclear. It has been suggested that MEL has effects on cellular processes that involve microfilaments and microtubules. In the present study MEL effects on the cytoskeleton were evaluated in MDCK and N1E-115 cells in which the microfilaments have been shown to participate in cell morphology and dome formation (MDCK) and the microtubules in neurite outgrowths. After one day of culture with 10(-11)-10(-7) M MEL MDCK cells showed an increase in the number of elongated cells. After four days with the hormone, an increase in the incidence of MDCK cells contacting neighboring cells through long cytoplasmic elongations was observed. Actin antibody stain showed the appearance of thicker fluorescent fibres beneath the cell membrane and over the nucleus in the MEL treated cells. An increase in dome formation in confluent cells was also observed. In N1E-115 cells MEL (10(-13)-10(-5) M) induced an increase in cell with neurite processes. Neurite outgrowth is clearly seen at 24 h after plating. MEL-treated cells grow in clusters with neurites forming intricate networks. Antitubulin antibody stain showed long fluorescent neurites in the N1E-115 MEL-treated cells. A decrease in N1E-115 neurite formation was observed with either serotonin or 6-hydroxymelatonin (6OH-MEL). However, the number of MDCK cells with cytoplasmic elongations was decreased only after 6OH-MEL. We conclude that MEL action at the cellular level involves a modification of the cytoskeletal organization.

Effects of melatonin on gonadal steroids and glucose plasma levels in frogs (Rana perezi and Rana temporaria)

The effect of melatonin treatment on the Gonosomatic Index (GSI), ovarian germinal epithelium, plasma estradiol and testosterone levels was studied in Rana perezi females in December. No significant changes were observed in GSI, estradiol, and testosterone levels in melatonin treated animals when compared with saline injected controls, but the percentage of previtellogenic follicles decreased in animals treated with melatonin (100 micrograms). The effect of melatonin treatment on glucose level was studied in Rana perezi females in December and Rana temporaria males in February. In Rana perezi no significant differences were observed between melatonin treated and control animals; however, significant reductions by melatonin treatment were obtained in Rana temporaria. The possibility that the inhibitory effect of melatonin can be observed only when gonadal function and metabolism are stimulated by temperature is discussed.

Melatonin receptors: current status, facts, and hypotheses

Great progress has been made in the identification of melatonin binding sites, commonly identified as melatonin receptors by many authors, in recent years. The bulk of these studies have investigated the sites using either autoradiographic and biochemical techniques with the majority of the experiments being done on the rat, Djungarian and Syrian hamster, and sheep, although human tissue has also been employed. Many of the studies have identified melatonin binding in the central nervous system with either tritium- or iodine-labelled ligands. The latter ligand seems to provide the most reproducible and consistent data. Of the central neural tissues examined, the suprachiasmatic nuclei are most frequently mentioned as a location for melatonin binding sites although binding seems to be widespread in the brain. The other tissue that has been prominently mentioned as a site for melatonin binding is the pars tuberalis of the anterior pituitary gland. There may be time-dependent variations in melatonin binding densities in both neural and pituitary gland tissue. Very few attempts have been made to identify melatonin binding outside of the central nervous system despite the widespread actions of melatonin. Preliminary experiments have been carried out on the intracellular second messengers which mediate the actions of melatonin.

Effect of melatonin administration and long day-length on endocrine cycles in the hedgehog Erinaceus europaeus

The effects of exogenous melatonin (subcutaneous implants containing 0.031 +/- 0.006 mg/gm body mass melatonin) or long photoperiod (18L:6D) on wild-caught adult male hedgehogs were studied. Hedgehogs were implanted with melatonin-filled or empty capsules in May, August, or September, or maintained under long photoperiod from August. Blood samples collected at monthly intervals were assayed for testosterone, melatonin, and thyroxin. Melatonin-filled capsules elevated plasma melatonin concentrations for 4-6 months. Although melatonin administration in May depressed plasma testosterone levels, testicular reactivation was advanced by 1 month the following year, and the characteristic prehibernal gain in body mass was abolished. Melatonin administration in August had no effect on plasma testosterone concentrations but reduced body mass fluctuations before and during hibernation. Hedgehogs receiving melatonin in September recovered early from hibernal body mass loss and showed a 2 month advance in testicular reactivation the following year. Maintaining hedgehogs at 18L:6D photoperiod, however, elevated plasma melatonin concentrations. Testicular reactivation the following spring was delayed by 1 month, ended 3 months early, and testosterone concentrations were depressed. All treatments depressed plasma thyroxin levels. These results suggest that elevated melatonin levels during winter are important in the regulation of endogenous endocrine cycles in the hedgehog. Hedgehogs do not respond positively to melatonin at the end of the breeding season, but are again responsive to melatonin as early as September.

Failure of prazosin to mimic the effects of melatonin under in vivo and in vitro conditions

The gonads of male hamsters exposed to short photoperiod (LD, 10:14) or treated with melatonin in the late afternoon under long photoperiod (LD, 14:10) had undergone complete regression by the end of the treatments (8 weeks). Animals treated for the same period of time with prazosin (a putative melatonin analogue) under the same conditions failed to show a difference in their gonadal status as compared to the long photoperiod controls. Prazosin was unable to prevent melatonin-induced gonadal atrophy when injected either in the morning or 30 min before melatonin. Moreover, prazosin was without any effect on (and unable to prevent the melatonin-stimulated) progesterone production by rat adrenals under in vitro conditions. These data demonstrate that prazosin, which reportedly inhibits 2-[125I]iodomelatonin binding in the hamster brain in an affinity-related manner, does not possess properties of a biological melatonin analogue under conditions of two different model systems in two species.

Immunoreactive levels of pineal arginine vasopressin change during the rat estrous cycle

It has been reported that mammalian pineal activity is influenced by reproductive hormones. However, even though a relationship between serum estrogen levels and pineal indole metabolism is well documented, little is known about other pineal components. Among peptides, arginine vasopressin (AVP) has been identified in the pineal gland of several species. In the present work, variations of immunoreactive (IR)-AVP in the rat pineal during the estrous cycle were studied by radioimmunoassay. Pineal IR-AVP levels increased significantly at the proestrus afternoon, and returned to basal levels by the end of estrus. These variations were partially related to those of serum estradiol concentration. Although the functional role of AVP in the rat pineal has not been clearly elucidated, these findings provide an additional indication that it might be involved in the reproductive function of the female rat.

Permeability of the pineal gland of the viscacha (Lagostomus maximus maximus) to the lanthanum hydroxide

Lanthanum hydroxide together with a fixative solution was injected into the third ventricle of the viscacha. The tracer penetrated freely into the pineal gland demonstrating an extensive network of intercommunicating intercellular spaces. Numerous gap junctions were observed indicating that they are the predominant interparenchymal contacts. The capillaries were characterized by non-fenestrated endothelial cells lining a moderate-sized perivascular space. Precipitates of lanthanum hydroxide were found in the basal membranes of the perivascular and interendothelial spaces, but not in the vascular lumina. The tracer stopped at tight junctions; these constitute a barrier between the pinealocytes and the blood compartment. Active micropinocytosis observed in the capillary walls suggest a transendothelial transport.

Correlation between salivary and serum melatonin: dependence on serum melatonin levels

Saliva and serum samples were collected from eight healthy volunteers every two hours during a 26-hour period. Melatonin concentrations were measured by radioimmunoassay after chloroform extraction using radioiodinated melatonin as a tracer. Five of the subjects had high serum melatonin levels at night (peak levels higher than 75 pg/ml); in three subjects the highest serum melatonin concentration was 20-40 pg/ml. All subjects had low levels (less than 10 pg/ml) during the day. The correlations between salivary and serum levels were calculated. The regression line y = 0.33x + 3.7 pg/ml, r = 0.95, P less than 0.001, was obtained for all detectable value pairs (n = 73). The regression and correlation coefficients were almost equal for the peak values of melatonin and during the rising and descending phases of the secretion patterns. However, no significant correlation was found between low daytime salivary and serum concentrations when calculated separately. In the five high-secretors the melatonin levels in saliva reflected reliably the changes in serum, but in the three low-secretors the correlation between salivary and serum melatonin was not significant. The proportion of melatonin found in saliva decreased with increasing serum melatonin levels. Circadian rhythm parameters were estimated by single cosinor analysis. The acrophases did not differ significantly within a subject in the concomitant measurements of serum and salivary melatonin. The measurements of salivary melatonin levels seem valid for studies on melatonin rhythms, but the melatonin concentrations measured in saliva do not always consistently reflect the absolute concentrations in blood.

A study of heart-pineal interactions: atrial natriuretic peptide response to melatonin administration in healthy humans

It is known that the pineal hormone melatonin plays a role in the regulation of several biological functions. In an attempt to investigate interactions between the pineal and the cardiac endocrine activity, in this preliminary study we have evaluated the effect of melatonin on the secretion of the cardiac hormone, atrial natriuretic peptide (ANP). The study included five healthy volunteers, and melatonin was given orally at a dose of 30 mg at 17:00. The results of the study show that the administration of melatonin does not influence ANP plasma concentrations. Further studies will be required to better define the cardiac-pineal interaction.

Effects of short-day photoperiods and of N-(2,4-dinitrophenyl)-5-methoxytryptamine, a putative melatonin antagonist, on melatonin synthesis in the Harderian gland of the Syrian hamster, Mesocricetus auratus

The Harderian glands of Syrian hamsters contain melatonin and the enzymes N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) which synthesize melatonin from serotonin. Because the Harderian glands share this metabolic pathway with the pineal gland, we examined the effects of short-day photoperiods, which stimulate pineal-mediated gonadal regression, and N-(2,4-dinitrophenyl)-5-methoxytryptamine (ML-23), which has been described as a melatonin antagonist, on melatonin synthesis in the Harderian glands of the hamster. Harderian glands of male hamsters kept in short days had reduced NAT activity and melatonin concentration, but HIOMT activity was unchanged from that of long-day controls. In males kept in short days, ML-23 restored melatonin concentrations to levels seen in long days but did not affect the short-day induced reduction in NAT activity. ML-23 had no effect upon NAT or HIOMT activity or melatonin concentration in male hamsters kept on long days. Harderian glands of female hamsters kept on short days had reduced melatonin concentrations, but NAT and HIOMT activities similar to those of long-day controls. ML-23 had no effect on Harderian NAT or HIOMT activities or melatonin concentration in females kept in short days. However, in females kept in long days, ML-23 treatment led to increased NAT activity and decreased melatonin concentrations. We conclude from these results that short-day photoperiods alter some aspects of melatonin synthesis in hamster Harderian glands and that these effects differ in males and females. ML-23 does not usually prevent the effects of short days on Harderian melatonin synthesis, suggesting that it is not a melatonin antagonist in the Syrian hamster.

Sensitivity of goats to a light pulse during the night as assessed by suppression of melatonin concentrations in the plasma

This study investigates the ability of a 1 h light pulse of different intensities at night to suppress plasma melatonin in goats. Six female Saanen dairy goats, about 2 yr old, were housed in a light-tight shed. The goats were habituated for 1 wk to an 8L:16D photoperiod (40.70 +/- 4.16 microW/cm2; 137 +/- 14 lux), lights on 0800 h. A 1 h light pulse, of different intensity on each occasion, was given from 1900 to 2000 h. Light intensity was measured by using a lux meter (mean of 36 measurements at goat's eye level). Five different light intensities were given during December in the order 4.22 +/- 0.62 microW/cm2 (14.2 +/- 2.1 lux), 0.68 +/- 0.09 microW/cm2 (2.3 +/- 0.3 lux), 0.26 +/- 0.004 microW/cm2 (0.87 +/- 0.14 lux), darkness, 40.70 +/- 4.16 microW/cm2 (137 +/- 14 lux), with 1-3 d between treatments. The goats were bled hourly from 1500 to 1900 h and every 15 min from 1900 to 2100 h, and a last bleed occurred at 2200 h. Dark-phase samples were taken in dim red light (less than 0.03 microW/cm2; 0.1 lux). Plasma was assayed for melatonin by radioimmunoassay. Suppression of melatonin concentrations increased as light intensity increased as follows: Darkness, 0%; 0.26 +/- 0.004 microW/cm2; 0%; 0.68 +/- 0.09 microW/cm2; 43.1%; 4.22 +/- 0.62 microW/cm2, 71.1%; 40.70 +/- 4.16 microW/cm2, 81.2%. Suppression was significant (P less than 0.05) at light intensities greater than 0.68 microW/cm2, 2.3 lux. A hyperbolic relationship existed between percent suppression and light intensities.

Light-induced plasma melatonin suppression in seasonal affective disorder

1. Subjects with seasonal affective disorder were exposed to 0, 500 and 1000 lux of white light for one hour beginning at 0300 hours. 2. Plasma samples were taken periodically and analysed for melatonin. 3. Plasma melatonin levels were suppressed by exposure to both 500 and 1000 lux light levels, suggesting that SAD patients show no neuroendocrine insensitivity to light but may show supersensitive responses to light.

Continuous darkness stimulates body growth of the juvenile giant freshwater prawn, Macrobrachium rosenbergii de Man

The effect of photoperiod on growth of juvenile giant freshwater prawns, Macrobrachium rosenbergii de Man, was tested. The prawns were divided into four groups and each group was reared under one of the following light-dark conditions: continuous darkness (L0:D24), 12 hr light: 12 hr dark (L12:D12), 16 hr light: 8 hr dark (L16:D8), and 20 hr light: 4 hr dark (L20:D4). Body size was determined at the age of 45, 75, and 110 days by measuring total length, orbital length, and carapace length; body weight was determined at the age of 110 days. At 110 days of age, the prawns reared under L0:D24 photoperiod were significantly longer and heavier than those reared under other light-dark conditions. The survival rate of the prawns reared under L0:D24 photoperiod was also higher than that of other groups. This study indicates a positive effect of continuous darkness on growth and survival rate of juvenile giant freshwater prawns, M. rosenbergii.

Circadian variations in plasma melatonin, FSH, LH, and prolactin and testosterone levels in infertile men

Circadian patterns of plasma melatonin, FSH, LH, prolactin, and testosterone were studied in 10 healthy men, 20 men with oligozoospermia, and 8 men with azoospermia. Circadian rhythms were found in concentrations of melatonin and prolactin, with higher values at night in comparison with daytime levels. In patients with oligozoospermia and azoospermia an elevation in melatonin levels was observed, and an increase in melatonin concentrations occurred before onset of darkness (i.e., at 2000 h). Levels of FSH, LH, and prolactin were elevated in infertile patients. The possibilities that an increase in melatonin concentrations is either the primary feature that leads to the regression of the seminiferous epithelium or is secondary and depends on elevated gonadotropins and/or prolactin levels are discussed.

Prenatal development of "synaptic" ribbons in the guinea pig pineal gland

Pineal "synaptic" ribbons are a heterogeneous population of organelles. "Synaptic" ribbons (SR) sensu stricto, "synaptic" spherules (SS), and intermediate forms (IMF) are present. Their function and origin are unknown, and a knowledge of their prenatal development is lacking. Thus the pineal glands of prenatal, neonatal, and adult guinea pigs were prepared for electron microscopy. "Synaptic" ribbons were studied morphologically and quantitatively. The three categories of "synaptic" ribbons reported in adult pineal glands were also present in prenatal pineal glands. Their structural features, distribution, grouping, and composition patterns are similar to those in adults. "Synaptic" ribbons were first detected in pinealocytes of the distal region of a 42-day postcoitus (PC) pineal gland and were comparable with those in adults. They increased in number with age and reached a peak at 63 days PC, followed by a steep decline at 66 and 67 days PC. By day 69 PC, the numbers increased again and showed a dramatic increase after birth. Several true ribbon synapses were seen at day 63 PC between pinealocyte cell processes or between pinealocyte cell process and pinealocyte cell body. Since true ribbon synapses have not been found in adult guinea pig pinealocytes, their synaptic nature could have been lost during development. No precursors for the "synaptic" ribbons were found. The endoplasmic reticulum cisternae may be the origin for the ribbon vesicles because of their close association with the "synaptic" ribbons.

Ontogeny of N-acetyltransferase activity rhythm in pineal gland of chick embryo

1. N-acetyltransferase was present in pineal glands of 14-day-old chick embryos though no rhythm either in LL, DD or LD 12:12 was observed in this age. 2. Daily rhythm in pineal NAT activity was found in 18-day-old embryos incubated under LD 12:12 and LD 16:8 but no NAT rhythm was detected in DD or LL. 3. NAT rhythm persists for 2 days in constant darkness and it may be circadian in nature. 4. Presence of melatonin (85 +/- 8 pg/mg tissue) was detected in pineals of 18-day-old chick embryos.

Diurnal changes in serum melatonin concentrations under indoor and outdoor environments and light suppression of nighttime melatonin secretion in the female Japanese monkey

To examine whether artificial light with the intensity commonly used for animal experimentation can mimic natural sunlight with respect to diurnal changes in serum melatonin, and to determine the minimum light intensity required to suppress nocturnal melatonin, serum melatonin profiles were examined in groups of female Japanese monkeys (Macaca fuscata fuscata). Under outdoor environment, light intensities at the level of the monkey's eyes varied during daytime (0900-1500 h) depending on weather conditions (minimum and maximum on particular experimental days: 170 lux at 0900 h on a rainy day and 9500 lux at 0900 h on a slightly cloudy day); under indoor environment, light was provided by ordinary fluorescent bulbs that resulted in intensities of 400-500 lux at the level of monkey's eyes. No difference was found in diurnal changes in serum melatonin concentrations regardless of weather or housing conditions: Serum melatonin remained low during daytime and increased during nighttime. Following exposure to light, irradiances of 10,000, 400-500, 100-140, 50-100, and 10-30 lux at midnight resulted in a rapid decrease in serum melatonin to daytime levels within 1 to 2 h. After the onset of dark, serum melatonin reverted to previous nighttime levels within 2 h. Exposure to a light irradiance of 2-5 lux, however, did not suppress nocturnal melatonin secretion. It is concluded that artificial light can mimic natural sunlight with respect to melatonin secretion in the female Japanese monkey, and that light of 10-30 lux irradiance was sufficient to suppress serum melatonin to near daytime levels.

Pineal gland free amino acids and indoles during postnatal development of the rat: correlations in individual glands

Free amino acids and indoles were measured by HPLC in single pineal glands of 5-, 10- and 20-day-old rats sacrificed during mid-light and mid-dark at each age. Melatonin was detectable in neonates (5-day-old), but day vs night differences in indole constituents did not occur until 10 days of age. Free amino acid steady state levels were high in neonates and there was a tendency for reversal of day vs night differences coinciding with the onset of circadian rhythmicity in indole biosynthesis. High correlations (r greater than 0.85) existed for taurine vs. glutamate in individual glands regardless of age and time of sacrifice. These findings suggest that taurine and glutamate are biochemically interrelated and that developmental changes in amino acid metabolic pools reflect functional innervation of the gland.

Nocturnal melatonin and cortisol secretion in newly admitted psychiatric inpatients. Implications for affective disorders

Melatonin secretion has been suggested as a marker of both circadian and noradrenergic dysfunction in affective disorders. Seventy-two newly admitted psychiatric inpatients [49 with major depressive disorder (MDD), 12 with schizophrenia, and 11 with intermittent depressive disorder (IDD)] underwent neuroendocrine screening at 0200, 0800, 1600 and 2300 hours prior to and the day following dexamethasone administration. All groups showed a drop in cortisol following dexamethasone. Dexamethasone nonsuppression was found in 20 of 49 patients with MDD, in none of the schizophrenics and in none of those with intermittent depressive disorder. Mean melatonin levels decreased significantly after the administration of dexamethasone across all four groups. Overall, the schizophrenic group had a significantly greater mean melatonin level than each of the other three groups, whereas the three depressive groups did not differ significantly from one another. Only at 2300 hours did both the schizophrenic group and the MDD patients with normal dexamethasone suppression show significantly greater melatonin levels than the MDD patients with dexamethasone nonsuppression or the IDD group. The observed trend for a low circadian melatonin profile in IDD patients with superimposed personality disorders is puzzling.

"Synaptic" ribbons and spherules lacking in the pineal gland of the European hamster appear after ganglionectomy

"Synaptic" ribbons and spherules are typical organelles of the mammalian pinealocytes, that present quantitative day-night variations parallel to pineal melatonin levels. The European hamster is a wild photoperiodic mammal whose pineal melatonin concentrations do not vary during the 24 hr light-dark cycle. The aim of this study was thus to see if a rhythmic variation in synaptic structures was nevertheless present in this species. It was found that, in contrast to all of the photoperiodic species studied to date, the European hamster pinealocyte contains no ribbons, and virtually no spherules. Moreover, constant administration of melatonin does not result in the occurrence of these organelles; nevertheless, the pinealocytes have the potentiality to produce spherules and, to a lesser extent, ribbons, as they are observed in ganglionectomized animals and in the deep pineal of some hamsters after ablation of the superficial part of the gland. The formation of pineal synaptic structures, normally lacking in the European hamster, thus seems directly related to the noradrenergic innervation of the gland.

Ontogeny of type II thyroxine 5'-deiodinase, N-acetyltransferase, and hydroxyindole-O-methyltransferase activities in the rat Harderian gland

The ontogeny and regulation by isoproterenol of type II thyroxine 5'-deiodinase, N-acetyltransferase, and hydroxyindole-O-methyltransferase activities were studied in the rat Harderian gland. Both 5'-deiodinase and N-acetyltransferase activities exhibited maximal values at the first week of age. These activities gradually decreased till the fourth week. However, hydroxyindole-O-methyltransferase activity did not change during the period of time studied. Neither the different killing times (1600 or 0200 h) nor the photoperiod regimens (darkness or light exposure at night) modified the enzyme activities. On the other hand, isoproterenol, a beta-adrenergic agonist, could not to stimulate 5'-deiodinase at first week of life. Nevertheless, while basal 5'-deiodinase activity was diminishing during development, the enzyme was becoming sensitive to the action of isoproterenol. Thus, isoproterenol elicited increases in Harderian gland 5'-deiodinase activity in rats older than two weeks. However, both N-acetyltransferase and hydroxyindole-O-methyltransferase activities were not affected by isoproterenol treatment in either week studied.

Retention and metabolic fate of [3H]-melatonin in the spotted skunk

Two experiments were designed to determine which tissues accumulate [3H]-melatonin and the metabolic fate of this hormone in the spotted skunk. Tritiated melatonin was injected into the jugular vein of 10 anesthetized skunks 1-3 h before the onset of darkness and allowed to circulate for 22 min before the vasculature was flushed with saline to clear radioactivity from the blood. Selected tissues were removed from five skunks and oxidized in a Packard Biological Oxidizer which yielded 95 +/- 5% recovery of radioactivity. Relatively high amounts of radioactivity were found in the pineal (367 +/- 304 dpm/mg tissue), ovary (69 +/- 38 dpm/mg), pituitary (89 +/- 56 dpm/mg), liver (107 +/- 29 dpm/mg), and kidney (63 +/- 15 dpm/mg). Relatively small amounts of [3H] were found in different brain regions (approximately 6-7 dpm/mg). The uterus, pancreas, and temporalis muscle also accumulated radioactivity (approximately 13 dpm/mg). The lung retained the least amount of radioactivity (4 +/- 1.3 dpm/mg). In the second experiment, hypothalami, pituitaries, and ovaries were removed from the remaining five females. Radioactivity from these tissues was extracted and subjected to thin-layer chromatography. Melatonin accounted for approximately 70% of the radioactivity recovered while 6-hydroxymelatonin and unidentified more polar compounds made up the majority of the melatonin metabolites. These data indicate that tissues other than the hypothalamus are able to accumulate [3H]-melatonin.