Effect of naloxone administration upon the diurnal concentrations of oxytocin in the cerebrospinal fluid of rhesus and cynomolgus monkeys.

A diurnal pattern in oxytocin concentrations is present in cerebrospinal fluid (CSF) removed from the spinal subarachnoid space of monkeys, with elevated levels occurring in the early light hours. In order to investigate the possible role of endogenous opioid peptides in the generation of this oxytocin rhythm, we administered naloxone (0.4 mg/kg/h x 48 h) to rhesus and cynomolgus monkeys and examined the effects on the diurnal pattern of oxytocin in CSF collected from the lumbar subarachnoid spinal space. Monkeys maintained on jacket/tether/swivel systems and in a 12 h light: 12 h dark cycle (lights on 07.00-19.00 h) were implanted with temporary spinal subarachnoid catheters. CSF was continuously collected from the lumbar subarachnoid space and assayed for oxytocin. Oxytocin concentrations in CSF showed a diurnal variation with peak and nadir concentrations during light and dark hours, respectively. The lumbar CSF concentrations of oxytocin were not significantly different during naloxone vs. saline infusion. Plasma oxytocin concentrations, measured in the same animals, displayed no diurnal variation and were not significantly different during naloxone vs. saline infusion. We conclude that naloxone administration for 48 h does not perturb the diurnal variation in oxytocin concentrations in the CSF of monkeys. Mu opioid receptors are unlikely to be involved in modulating the diurnal rhythm of oxytocin in the CSF of monkeys.     

Circadian variation in the CSF cortisol concentration of the rhesus monkey

Cortisol concentrations in the cerebrospinal fluid (CSF) of the rhesus monkey were found to undergo a marked diurnal variation. Hourly samples of CSF from 4 adult male rhesus monkeys showed a mean peak cortisol concentration of 1.56 ± .29 μg% occuring between 0800–0900 hrs and a mean minimum concentration between 2200-0000 hrs of 0.21 ± .06 μg%. The mean daily CSF cortisol concentration increase was 900%, a greater variation than has been reported for plasma cortisol diurnal changes.     

Comparative Study of the Activity/Rest Rhythms in Young and Old Ringdove (Streptopelia Risoria): Correlation with Serum Levels of Melatonin and Serotonin

Aging is characterized by changes in the circadian rhythms of melatonin, serotonin, and sleep/wakefulness, alterations that affect sleep quality. The authors studied the circadian rhythms of serotonin and melatonin in young and old ringdoves (Streptopelia risoria) (2–3 and 10–12 yrs old, respectively), animals that are characterized by being monophasic and active by day, like humans. The aim was to correlate the indole rhythms with the animals' activity/rest periods. The animals were kept under a 12∶12 h light/dark cycle, fed ad libitum, and housed in separate cages equipped for activity recording. Activity pulses were recorded with one actometer per animal (two perpendicular infrared transmitters) and were logged every 15 min by a computer program (DAS 16) throughout the experiment. Melatonin was measured by radioimmunoassay and serotonin by ELISA at intervals of 3 h (from 09∶00 to 18∶00 h) and 1 h (from 21∶00 to 06∶00 h), respectively. The results showed a reduction in nocturnal vs. diurnal activity of 89% and 61% in the young and old animals, respectively, with 100% considered to be the diurnal activity of each group. The amplitude of a cosine function fit to the melatonin concentrations of the old animals was half that of the young birds. The acrophase and nadir were at 02∶00 and 14∶00 h in the young and 01∶00 and 13∶00 h in the old animals, respectively. The amplitude of the corresponding cosine function fit to the serotonin concentrations in the old birds was one‐third that of the young animals. The acrophase and nadir were at 15∶00 and 03∶00 h in the young and 16∶00 and 04∶00 h in the old animals, respectively. For both melatonin and serotonin, the concentrations in the young animals were significantly higher than in the old at most of the measurement times. There was a clear negative correlation between the circadian rhythms of activity and the serum melatonin levels in both young and old animals. The equivalent correlation for serotonin was positive, and stronger in the case of the young animals. The results suggest a possible relationship between the observed decline in the amplitude of the old animals' melatonin and serotonin rhythms and the lower percentage reduction in their nocturnal relative to diurnal activity pulses compared to the young animals. In conclusion, the circadian rhythms of melatonin and serotonin undergo alterations with age that could be involved in the changes in age‐associated sleep.     

Comparative study of the activity/rest rhythms in young and old ringdove (Streptopelia risoria): correlation with serum levels of melatonin and serotonin

Aging is characterized by changes in the circadian rhythms of melatonin, serotonin, and sleep/wakefulness, alterations that affect sleep quality. The authors studied the circadian rhythms of serotonin and melatonin in young and old ringdoves (Streptopelia risoria) (2-3 and 10-12 yrs old, respectively), animals that are characterized by being monophasic and active by day, like humans. The aim was to correlate the indole rhythms with the animals' activity/rest periods. The animals were kept under a 12:12 h light/dark cycle, fed ad libitum, and housed in separate cages equipped for activity recording. Activity pulses were recorded with one actometer per animal (two perpendicular infrared transmitters) and were logged every 15 min by a computer program (DAS 16) throughout the experiment. Melatonin was measured by radioimmunoassay and serotonin by ELISA at intervals of 3 h (from 09:00 to 18:00 h) and 1 h (from 21:00 to 06:00 h), respectively. The results showed a reduction in nocturnal vs. diurnal activity of 89% and 61% in the young and old animals, respectively, with 100% considered to be the diurnal activity of each group. The amplitude of a cosine function fit to the melatonin concentrations of the old animals was half that of the young birds. The acrophase and nadir were at 02:00 and 14:00 h in the young and 01:00 and 13:00 h in the old animals, respectively. The amplitude of the corresponding cosine function fit to the serotonin concentrations in the old birds was one-third that of the young animals. The acrophase and nadir were at 15:00 and 03:00 h in the young and 16:00 and 04:00 h in the old animals, respectively. For both melatonin and serotonin, the concentrations in the young animals were significantly higher than in the old at most of the measurement times. There was a clear negative correlation between the circadian rhythms of activity and the serum melatonin levels in both young and old animals. The equivalent correlation for serotonin was positive, and stronger in the case of the young animals. The results suggest a possible relationship between the observed decline in the amplitude of the old animals' melatonin and serotonin rhythms and the lower percentage reduction in their nocturnal relative to diurnal activity pulses compared to the young animals. In conclusion, the circadian rhythms of melatonin and serotonin undergo alterations with age that could be involved in the changes in age-associated sleep.     

Cerebrospinal Fluid Concentrations of Tryptophan and 5-Hydroxyindoleacetic Acid in Macaca Mulatta: Diurnal Variations and Response to Chronic Changes in Dietary Protein Intake

In rats, dietary protein is known to influence brain tryptophan (TRP) concentrations and serotonin (5HT) synthesis. However, few studies have examined this relationship in primates (including humans). We therefore studied the effect in monkeys of changes in chronic protein intake on plasma and cerebrospinal fluid (CSF) concentrations of TRP and 5-hydroxyindoleacetic acid (5HIAA), the principal 5HT metabolite. Juvenile male monkeys (Macacca mulatta) consumed for sequential 4-week periods diets differing in protein content (~23% ~ 16% ~10% ~6% protein [%-energy/day]). Each day, food was presented as a morning meal of fruit, and an afternoon meal consisting of a pelleted, commercial diet and fruit. During week 4 on each diet, blood and CSF were sampled diurnally via indwelling catheters. Plasma and CSF TRP varied diurnally and with dietary protein content. On all diets, CSF TRP declined modestly in the morning, and increased in the afternoon; the magnitude of the increments varied directly with dietary protein content. Diurnal variations were absent for CSF 5HIAA; however, CSF 5HIAA varied directly with chronic dietary protein content. We conclude that dietary protein content can chronically influence CSF TRP concentrations in monkeys. The variation in CSF 5HIAA suggests chronic protein intake may influence serotonin synthesis and turnover, perhaps via changes in TRP concentrations.     

Pulses of oxytocin in the cerebrospinal fluid of rhesus monkeys.

Cerebrospinal fluid (CSF) samples were collected at frequent intervals (every 10-15 min) to determine if oxytocin pulses were present in the CSF of monkeys. Temporary indwelling subarachnoid catheters, with the tip of the catheter at the T12-L1 subarachnoid space, were placed in 4 nonlactating and 3 lactating (4 months post partum) female monkeys. Monkeys were maintained on jacket/tether/swivel systems in a constant photoperiod (07.00-19.00 h). CSF was continuously withdrawn at a rate of 1.2 ml/h by peristaltic pump, and CSF was collected in 15-min fractions (from 3 lactating monkeys and 1 nonlactating monkey) or in 10-min fractions (from the other 3 nonlactating monkeys) using a fraction collector. CSF oxytocin was measured by radioimmunoassay. Pulses of oxytocin were analyzed using the computerized Pulsar pulse detection algorithm. A pulsatile pattern of oxytocin concentrations was found in the CSF of lactating and nonlactating monkeys. The ultradian pulses of oxytocin were superimposed upon the diurnal rhythm of oxytocin in CSF. We conclude that frequent sampling of CSF provides a way to monitor moment-to-moment changes in central nervous system concentrations of oxytocin in primates.     

The diurnal variation of immunoreactive adrenocorticotropin in rhesus monkey plasma and cerebrospinal fluid

ACTH immunoreactivity (ACTH-IR) in the plasma and cerebrospinal fluid (CSF) collected simultaneously from rhesus monkeys was found to undergo significant diurnal variations. In plasma, the mean peak ACTH-IR was 15.4 +/- 1.95 pg/ml at 0500 h, and the mean minimum concentration was 9.05 +/- 1.80 pg/ml at 1800 h. In CSF, the mean peak ACTH-IR concentration occurred at 1900 h and was 4.64 +/- 0.41 pg/ml. The mean minimum CSF ACTH-IR concentration was 2.93 +/- 0.26 pg/ml, occurring at 0500 h. This is the first report of a diurnal variation in CSF ACTH-IR concentration and is consistent with other work suggesting that plasma ACTH and CSF ACTH originate from different sources.     

Simultaneous determination of N-acetyltransferase activity, hydroxyindole-O-methyl-transferase activity, and melatonin content in the pineal gland of the Syrian hamster

The activities of serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) and the melatonin content were measured in Syrian hamster pineal glands at 2-hr intervals over a period of 24 hr. NAT and HIOMT are the two enzymes which catalyze the formation of melatonin from serotonin. The use of micromethods for determination of the enzyme activities allowed concurrent measurement of NAT and melatonin or HIOMT and melatonin in the same gland. HIOMT activity showed no significant diurnal rhythm whereas NAT activity and melatonin content exhibited distinct peak values late in the dark phase as described previously. Despite an apparent parallelism between the NAT activity rhythm and melatonin content, no correlation exists between these parameters in single pineal glands.     

Opposite effects of tryptophan intake on motor activity in ring doves (diurnal) and rats (nocturnal)

The role of l-tryptophan as precursor of serotonin and melatonin synthesis on activity-rest rhythm was studied in ring doves, Streptopelia risoria, as a representative of diurnal animals and rats, Rattus norvegicus, as a typical nocturnal one. The animals were housed in cages equipped for horizontal activity recording in a thermostatized chamber and submitted to a 12/12h light/dark photoperiod (lights on at 08:00 h). After acclimatization, the animals received vehicle (methylcellulose) and l-tryptophan (240 mg/kg) by esophagic cannula 2h before the onset of either light or dark phase. Also, oral melatonin (2.5mg/kg) was tested for comparative purposes. After nocturnal l-tryptophan administration, rats showed increased activity (149%), while the opposite occurred in ring doves (39% decrease). No significant changes were found after diurnal l-tryptophan intake in either species. Melatonin produced effects similar to those of l-tryptophan. These results suggest that the effects of l-tryptophan administration are dependent on the nocturnal/diurnal habits of the studied species and, most probably, are mediated by increased melatonin synthesis.     

The relationship between blood and cerebrospinal fluid prolactin in nonhuman primates

We studied the relationship between plasma and cerebrospinal fluid (CSF) concentrations of prolactin (PRL) in repeated and simultaneous samples of blood and CSF from chair-restrained rhesus monkeys. Following administration of thyrotropin releasing hormone (TRH), each of 4 monkeys showed increased plasma and lumbar CSF PRL concentrations. Increases in CSF PRL concentrations were muted and delayed until 60 min after peak plasma concentrations were attained. In 3 other monkeys we compared PRL concentrations in simultaneous lateral ventricular and lumbar CSF samples. Although we found no difference in PRL concentrations under baseline conditions, a ventricular-lumbar PRL concentration gradient became apparent after TRH stimulation. These studies demonstrate that changes in plasma PRL concentrations are reflected in CSF concentrations. They suggest that a significant blood-CSF barrier exists for PRL and that PRL may enter the the CSF selectively via the ventricles.     

Diurnal Variations in Cyclic AMP and Melatonin Content of Golden Hamster Retina

Abstract: The diurnal variations and photic regulation of cyclic AMP and melatonin content in golden hamster retina were studied. Both parameters showed significant diurnal variations with maximal values at night. Light exposure during the night inhibited retinal cyclic AMP and melatonin levels, whereas exposure to darkness during the day significantly increased cyclic AMP and melatonin content. Incubation with melatonin of retinas excised at different intervals indicated that the methoxyindole inhibited cyclic AMP accumulation in a time-dependent manner. The inhibitory effect of melatonin at 2400 h and at noon showed a threshold concentration of 1 and 10 pM, respectively. At 0400 h melatonin did not affect cyclic AMP accumulation. The results indicate a diurnal variability of retinal cyclic AMP and melatonin content in hamsters, mainly influenced by a photic stimulus. Cyclic AMP could be a putative second messenger for melatonin action in golden hamster retina.     

Melatonin in psychiatric disorders - subtyping affective disorder

Altered diurnal secretory patterns, i.e. altered phase and/or amplitude of melatonin have been reported in sleep and affective disorders. The alteration may depend on environmental factors which in vulnerable individuals may cause sleep and/or affective disorders. Early stress in conjunction with development of resistance to corticotropin-releasing hormone may be linked to the low melatonin syndrome in subgroups of depressed patients. Also the seasonal variation in melatonin as well as serotonin may be linked to the seasonal pattern seen in subgroups of affective disorders. Melatonin may be used as a combined marker for proneness to develop affective disorders especially in latent carriers of bipolar disorders.     

Food availability but not melatonin affects nocturnal restlessness in a wild migrating passerine

A large number of passerine species migrate at night, although most of them are diurnal outside the migratory seasons. This diurnal-to-nocturnal transition is a major life-history event, yet little is known about its physiological control. Previous work showed that during the migratory periods captive birds showing nocturnal migratory restlessness (Zugunruhe) have reduced concentrations of circulating melatonin at night compared to non-migratory periods. This suggested that the hormone melatonin, a main component of the avian circadian system, is involved in the expression of Zugunruhe. Other studies demonstrated that the relationship between low melatonin levels and Zugunruhe is not a seasonal correlation. When Zugunruhe was interrupted by exposing birds to a fasting-and-refeeding protocol, melatonin levels increased. Here we studied whether melatonin and food availability influence the intensity of Zugunruhe in wild migrating garden warblers (Sylvia borin) at a stopover site. Birds were held in recording cages overnight, with or without food available, and either bled to determine melatonin concentrations or treated transdermally with melatonin. We found that melatonin levels at night were correlated with the intensity of diurnal locomotor activity and with condition, but were not correlated with Zugunruhe. Similarly, the melatonin treatment did not have effects on Zugunruhe, whereas food availability increased it. Our study shows that the nocturnal melatonin levels in migrating warblers depend on food availability and are correlated with condition. In addition, it suggests that melatonin does not control Zugunruhe and might rather be involved in energy conservation and/or clock synchronization during migration.     

Diurnal rhythms of pinealocyte ultrastructure, pineal serotonin content and plasma melatonin level in the domestic pig

The study was conducted to investigate diurnal changes in pinealocyte ultrastructure, pineal serotonin content and plasma melatonin concentration in the domestic pig. The immature pigs (n=24) were kept under a cycle of 12 h light : 12 h dark, with a photophase between 0800 and 2000. During the photophase the animals were exposed to direct sunlight. After four weeks the gilts were slaughtered at 0900, 1400, 2100 and 0200. The pineals were removed and divided into two parts - one for quantitative ultrastructural study (by a point count method) and one for serotonin assay. Simultaneously, blood samples were taken for melatonin assay. The relative volume of mitochondria in pinealocyte perikarya was significantly higher at 1400 than at 0200 and 0900 as well as at 2100 than at 0200. The relative volume of Golgi apparatus was higher at 0900 and 1400 than at 0200. The relative volume of dense bodies of the MBB-1 type in pinealocyte perikarya was significantly lower at 1400 and 2100 than at 0900. In contrast, the relative volume of MBB-2 was higher at 1400 than at 0900 and 0200. The numerical density of DCV in perikarya was significantly higher at 0200 than at 1400. No significant differences were found in rough endoplasmic reticulum, lysosomes and multivesicular bodies. The pineal serotonin content showed a prominent rhythm with the maximum at 1400. The plasma melatonin concentration was significantly higher at 0200 than at 0900, 1400 and 2100. The obtained results demonstrate that both pinealocyte ultrastructure and pineal biochemistry in the pig undergo significant changes in the course of the diurnal rhythm.     

Melatonin concentrations in the two jugular veins, and relationship with the seasonal reproductive activity in goats

The authors investigated whether melatonin concentrations vary between the two jugular veins and whether absolute (nocturnal) or relative (nocturnal/diurnal ratio) plasma melatonin concentrations are associated with seasonal reproductive activity measured by oestrus or ovulatory activity in Payoya goats. Thirty-two adult Payoya goats were penned under natural photoperiod. Oestrus activity was tested daily using aproned males—twice a week plasma was sampled for progesterone. Melatonin plasma concentrations were studied at each equinox and solstice of the year in jugular samples taken simultaneously by venipuncture. Nocturnal and diurnal plasma melatonin concentrations from each jugular vein were assessed in 3 and 2 plasma samples per goat, respectively, taken at hourly intervals in each period. No differences in melatonin concentrations between the two veins were observed, but there was a significant interaction (P < 0.001) between jugular vein and animal in nocturnal melatonin concentrations. There was no effect of sampling period on melatonin concentrations and the coefficient of correlation between sampling periods was very high. The analyses performed indicated that neither absolute nor relative melatonin concentrations were related with the dates of onset or end of ovulatory/oestrus activity. Therefore, we concluded that in goats (1) melatonin concentrations are highly variable between jugular veins in the same individual but not in the general population, (2) melatonin concentrations are highly repeatable for each individual, and (3) absolute and relative amplitudes of melatonin concentrations are not linked to the seasonal breeding activity in Mediterranean goats.     

Melatonin: A potential regulator of plant growth and development?

Summary Recent research has reported the presence of melatonin (N-acetyl-5-methoxytryptamine), a mammalian indoleamine neurohormone, in higher plants, indicating that melatonin may be an important metabolic regulator that has been highly conserved across biological kingdoms. Melatonin is synthesized from tryptophan in the mammalian pineal gland and a similar biosynthetic pathway was recently described in St. John's wort shoot tissues, wherein radiolabel from tryptophan was recovered in serotonin and melatonin as well as indoleacetic acid. There is growing information describing melatonin control of physiological processes in mammals, yeast, and bacteria, including diurnal responses, detoxification of free radicals, and environmental adaptations. However, at the current time, there is no known specific role for melatonin in plant physiology. Alterations in melatonin concentrations in plant tissues have been shown to affect root development, mitosis, and mitotic spindle formation. The recent advancements in melatonin research in plants and some directions for important areas of future research are reviewed in this article.     

Negative correlation of age and the levels of pineal melatonin, pineal N-acetylserotonin, and serum melatonin in male rats

Pineal concentrations of N-acetylserotonin and melatonin and serum levels of melatonin were studied in 3-wk-old (prepubertal), 8-wk-old (adult), and 17-mo-old (senile) male rats. They were adapted to a photoperiod of 12 h light/12 h darkness for a minimum of 1 wk and killed at mid-light and mid-dark. Melatonin and N-acetylserotonin were determined by radioimmunoassay. The concentrations of pineal N-acetylserotonin and melatonin were high in the dark period and low in the light period. Statistical analysis indicated that pineal N-acetylserotonin and melatonin levels per 100 gm body weight declined with age. Similarly, serum melatonin demonstrated diurnal changes in all the age groups studied. In addition, there was a significant reduction in the levels of serum melatonin with age. The parallel patterns of decrease in pineal and serum melatonin levels with age suggest a decline in pineal secretion of melatonin in the older animals.     

New approach to model effects of darkness, melatonin and serotonin on Tetrahymena thermophila growth and production of hydrolytic enzymes

Central composite design was used to quantify the relationship between darkness, melatonin and serotonin with growth ofTetrahymena thermophila and hydrolytic enzyme activities. Circadian variation was the most important factor to optimise the maximal population without a long generation time; i.e. light at the beginning of culture for 640 min followed by darkness for 800 min. In addition, the medium should be supplemented with serotonin and melatonin (0.1 mM each). Supplemental melatonin and serotonin increased lipase, phosphatase and protease activities but without a circadian variation.     

Diurnal and circadian variations in indole contents in the goose pineal gland

ABSTRACT

The diurnal and circadian profiles of pineal indoles, except melatonin, are poorly characterized in birds. Moreover, there are no data on the effect of sudden changes in the light–dark cycle on these profiles. Therefore, we investigated the diurnal (Experiment I) and circadian variation (Experiment II) of nine pineal indoles (tryptophan, 5-hydroxytryptophan, serotonin, N-acetylserotonin, melatonin, 5-hydroxyindole acetic acid, 5-methoxytryptophol, 5-methoxyindole acetic acid, 5-methoxytryptamine) in geese, as well as the changes in the profiles of these substances in geese subjected to a reversed light–dark cycle (Experiment III). For the first 12 weeks of life, all geese were kept under a diurnal cycle of 12 h of light and 12 h of darkness (12L:12D). In Experiment I (n = 48), they were kept under these conditions for another 14 days before being sacrificed at 2-h intervals for sampling of the pineal glands. In Experiment II, the geese (n = 48) were divided into three groups (12L:12D, 24L:0D, 0L:24D) for 10 days before sampling at 6-h intervals. In Experiment III, 24 geese were exposed to a reversed light–dark cycle before sampling at 14:00 and 02:00 on the first, second and third days after light–dark cycle reversal. To determine the content of the indoles in the goose pineals, HPLC with fluorescence detection was used. We found that, with the exception of tryptophan, all the investigated indoles showed statistically significant diurnal variation. When geese were kept in constant darkness, most of the indoles continued to show this variation, but when geese were kept in constant light, the indoles did not show significant variation. When the light–dark cycle was reversed (12L:12D to 12D:12L), the profiles of NAS, melatonin, 5-MTAM and 5-MTOL reflected the new cycle within 2 days. The content of serotonin in geese in 12L:12D was higher than that observed in other birds under these conditions, which suggests that this compound may play a special role in the pineal physiology of this species. In conclusion, our results show that the daily variations in the metabolism of melatonin-synthesis–related indoles in the goose pineal gland are generated endogenously and controlled by environmental light conditions, as in other birds. However, comparison of the results obtained with the goose to those obtained with other species (chicken, duck) unambiguously shows that the profiles of pineal indoles differ markedly between species, in both the quantitative proportions of the compounds and the characteristics of the diurnal changes. These findings provide strong arguments for the need for comparative studies.     

Episodic secretion of opioid activity in human plasma and monkey CSF: Evidence for a diurnal rhythm

Using a radioreceptor assay, opioiod activity has been determined in human plasma and monkey CSF at two-hour intervals across a 24-hour period. In both human plasma and monkey CSF, opioid activity showed an episodic secretion and a significant variation over time, suggesting a diurnal rhythm with increased levels in the morning. This rhythm is similar to those of adrenocorticotropin and beta-lipotropin (LPH) and reciprocal to the diurnal rhythm of pain sensitivity.