Hamster pineal noradrenaline: Levels over a regulated lighting period and the influence of superior cervical ganglionectomy

Adult male hamsters were sacrificed in groups at 4 hour intervals over a 24 hour period. In one Experiment adult male Sprague-Dawley rats were also sacrificed. No statistically significant daily changes in noradrenaline (NA) content were observed in the hamster pineal in three separate experiments. On the other hand, a very significant daily change in NA content was observed in the rat pineal. Bilateral superior cervical ganglionectomy depleted NA in the hamster pineal. Marked daily changes in pineal NA may be peculiar to the rat.     

Age-related changes in 24-hour rhythms of norepinephrine content and serotonin turnover in rat pineal gland: effect of melatonin treatment

The 24-hour rhythms of pineal norepinephrine (NE) content and serotonin (5-HT) turnover [estimated from the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to 5-HT] were studied in young (2 months) and aged (18-20 months) Wistar rats killed at 6 different time points throughout a 24-hour cycle. In the first study, significant changes dependent on the time of day were identified, with acrophases in the first half of the activity span for both parameters. Old rats showed significantly smaller mesor and amplitude of the 24-hour rhythm of pineal NE content. They also showed decreased amplitude of the pineal 5-HT turnover rhythm, in the absence of changes in mesor. In old rats, pineal 5-HT and 5-HIAA concentrations were 41-47% of those found in young rats. In a second study, young and old rats received daily intraperitoneal injections of melatonin (30 microg) or vehicle for 11 days at 19.00 h (i.e. 11 h after light on). Analyzed as a main factor in a factorial analysis of variance, both pineal NE content and 5-HT turnover decreased in old rats while pineal 5-HT turnover increased after melatonin treatment. Melatonin treatment augmented the amplitude of the 24-hour rhythm of pineal NE content by 120 and 52% in young and old rats, respectively. The amplitude of the 24-hour rhythm of pineal 5-HT turnover almost doubled after melatonin treatment in young rats and did not change in old rats. Melatonin injection did not modify the rhythm's acrophase. The results indicate that old rats had lower amplitude and lower mesor values of 24-hour variations in pineal NE content and 5-HT turnover. Melatonin treatment only partly restored pineal NE content and was devoid of activity on pineal 5-HT turnover and 5-HT and 5-HIAA concentration in old rats. Impairment of pineal melatonin synthesizing capacity and intrapineal responses to melatonin may underlie pineal aging in rats.     

Meal feeding schedule and ventromedial hypothalamic lesions do not affect rhythm of pineal serotonin N-acetyltransferase activity in rats

Effects of meal feeding schedule and bilateral lesions of the ventromedial hypothalamus (VMH) on the circadian rhythm of pineal serotonin N-acetyltransferase (SNAT) activity were examined in rats, under LD (12:12) condition. Neither meal feeding nor VMH lesions affected the phase of the circadian rhythm of pineal SNAT activity, but the VMH lesions reduced the level. Meal feeding caused a shift of the phases of the daily rhythms of phosphoenolpyruvate carboxykinase and tyrosine aminotransferase activities in the liver. These findings suggest that the circadian rhythm of pineal SNAT activity is not entrained by the food intake, and that the VMH does not function as a master oscillator of the rhythm.     

Suppression of circadian rhythms of pineal and testicular hormones following lithium treatment in normal and reversed light-dark cycles, constant light and constant dark in rats

The aim of the current investigation was to study the effect of lithium on circadian rhythms of pineal - testicular hormones by quantitations of pineal and serum serotonin, N-acetylserotonin and melatonin, and serum testosterone at four time points (06.00, 12.00, 18.00 and 24.00) of a 24-hr period under normal photoperiod (L:D), reversed photoperiod (D:L), constant light (L:L) and constant dark phase (D:D) in rats. Circadian rhythms were observed in pineal hormones in all the combinations of photoperiodic regimens, except in constant light, and in testosterone levels in all the photoperiodic combinations. Pineal and serum N-acetylserotonin and melatonin levels were higher than serotonin at night (24.00 hr), in natural L:D cycle, in reversed L:D cycle or similar to normal L:D cycle in constant dark phase, without any change in constant light. In contrast, testosterone level was higher in light phase (12.00 hr through 18.00 hr) than in the dark phase (24.00 hr through 06.00 hr) in normal L:D cycle, in reversed L:D cycle, similar to normal L:D cycle in constant dark (D:D), and reversed to that of the normal L:D cycle in constant light (L:L). Lithium treatment (2 mEq/kg body weight daily for 15 days) suppressed the magnitude of circadian rhythms of pineal and serum serotonin, N-acetylserotonin and melatonin, and testosterone levels by decreasing their levels at four time points of a 24-hr period in natural L:D or reversed D:L cycle and in constant dark (D:D). Pineal indoleamine levels were reduced after lithium treatment even in constant light (L:L). Moreover, lithium abolished the melatonin rhythms in rats exposed to normal (L:D) and reversed L:D (D:L) cycles, and sustained the rhythms in constant dark. But testosterone rhythm was abolished after lithium treatment in normal (L:D)/reversed L:D (D:L) cycle or even in constant light/dark. The findings indicate that the circadian rhythm exists in pineal hormones in alternate light - dark cycle (L:D/D:L) and in constant dark (D:D), but was absent in constant light phase (L:L) in rats. Lithium not only suppresses the circadian rhythms of pineal hormones, but abolishes the pineal melatonin rhythm only in alternate light - dark cycles, but sustains it in constant dark. The testosterone rhythm is abolished after lithium treatment in alternate light - dark cycle and constant light/dark. It is suggested that (a) normal circadian rhythms of pineal hormones are regulated by pulse dark phase in normal rats, (b) lithium abolishes pineal hormonal rhythm only in pulse light but sustains it in constant dark phase, and (c) circadian testosterone rhythm occurs in both pulse light or pulse dark phase in normal rats, and lithium abolishes the rhythm in all the combinations of the photoperiod. The differential responses of circadian rhythms of pineal and testicular hormones to pulse light or pulse dark in normal and lithium recipients are discussed.     

Effect of Lithium on the Rhythms of Melatonin in the Pineal Gland, Serum and Retina of Viscacha (Lagostomus maximus maximus)

The aim of this work was to describe the pineal, serum and retinal melatonin daily rhythms in viscacha (Lagostomus maximus maximus), a nocturnal and subterranean rodent. A daily rhythm with a nocturnal peak and an increase during the light phase was found in all cases, with the seric rhythm being delayed with respect to the pineal one. Chronic lithium administration to viscachas suppressed the diurnal increase of pineal melatonin, abolished the retinal rhythm and had no effect on seric melatonin.     

Daily rhythms of pituitary-ovarian function in the immature hamster are independent of adrenal and pineal influence

In female hamsters, the daily rhythm of LH appeared on the 15th or 16th day after birth with a peak occurring at about 16:00 h (14L:10D, lights on 06:00 h). Progesterone concentrations increased and became rhythmic a few days later. In serum samples collected at 14, 16, 18, 20, 25, 30, 40 and 60-62 days of age between 13:00 and 23:00 h, significant rhythms of serum cortisol and corticosterone concentrations were not detected before 25 days of age; furthermore, the phase of the rhythms did not stabilize to the adult pattern until about 40 days of age. As in the adult, significant rhythms were present in both sexes and the levels of cortisol were greater than those of corticosterone. Injection of pig ACTH (50 i.u./kg body wt, i.p.) significantly increased serum cortisol by 10 days of age, but corticosterone did not respond until 25 days of age. Thus, for cortisol at least, the appearance of 24-h rhythms in the serum is probably not dependent on the ability of the adrenal to respond to ACTH. Ovariectomy had no effect on the late afternoon surge of serum cortisol; similarly, adrenalectomy of immature females did not abolish the surge of LH. Ovariectomy did not alter the daily rhythm of pineal melatonin content and pinealectomy had no effect on the daily afternoon surge of LH. These results demonstrate functional independence of circadian rhythms in the pituitary-gonadal axis and the pituitary-adrenal axis of the immature hamster and also independence of daily rhythms of pineal melatonin and pituitary release of LH.     

Urinary melatonin rhythms during sleep deprivation in depressed patients and normals

Melatonin excretion was measured in 8 hour urine aliquots for eight healthy controls and six depressed patients. Both groups had similar diurnal rhythms, with increased melatonin excretion during the night. When subjects were sleep deprived, remaining awake and active in continuous light from 7 a.m. one morning until 11 p.m. the following day, the diurnal rhythm in melatonin excretion remained unchanged. These data in man appear to be inconsistent with previous studies in rats showing rapid light-induced suppression of the nocturnal rise in pineal melatonin synthesis.     

Circadian activity rhythms and sensitivity to noise in the Mongolian gerbil (Meriones unguiculatus)

Since consistent data on endogenous circadian rhythms of Mongolian gerbils are not available, the main aim of our study was to identify suitable conditions to receive stable and reproducible free-running rhythms of activity under different light intensities. Another objective was to determine the role of social cues as an exogenous zeitgeber in the absence of a light-dark (LD) cycle. We performed two long-term sets of experiments with adult male gerbils kept in climatic chambers under various photoperiods of at least 30 days each. In all cases, the time of lights on in the chambers differed from the daily starting hour of work in the animal house. Always, two animals per chamber were kept separately in cages with a running wheel while their activity was monitored continuously. During the first set, only three of eight animals developed intra- and interindividual variable free-running rhythms. The activity patterns seemed to be influenced by human activities outside, indicating high sensitivity to external factors. Subsequently, we damped the chambers and the room and restricted access to the room. In the following noise-reduced set, all gerbils developed comparable free-running rhythms of activity. We determined the mean of the free-running period tau, the activity-rest relationship alpha/theta and the amount of running wheel activity per day: tau = 23.7h +/- 0.08h under low light (5 lux) and 25.5h +/- 0.19h under high light intensities (450 lux); alpha/theta = 0.53 +/- 0.08 under 5 lux and 0.34 +/- 0.04 under 450 lux. The amount of daily activity was 12 times as high under 5 lux as under 450 lux. There was no indication that the two animals in one chamber socially synchronized each other. In conclusion, the pronounced rhythm changes in accordance with Aschoff's theory support the view that gerbils are mainly nocturnal animals.     

Malate Dehydrogenase Activity of Rat Testis: Circadian Rhythm and its Ontogeny

Malate dehydrogenase activity and soluble protein content in testes from rats exposed to a 14:00 h light:10:00 h dark photoperiod, have been determined every two or four hours over a 24 hour period in 5, 15, 25 and 120 day-old rats. By using the Cosinor method, the ontogeny of an unimodal rhythm was studied for MDH activity and soluble protein content in testis. In 5 and 15 day-old rats, the MDH acrophases were recorded around 19:00 h and 17:00 h, respectively. Rats aged 25 and 110 days showed the MDH acrophases during the dark period. An inversion of the MDH circadian rhythms was detected in 25 day-old compared to those of 5 and 15 day-old rats. An inversion of the protein circadian rhythm was also detected at 15 days compared to that at 5 days. These inversions persist in the adult rats. The amplitude of the MDH and protein rhythms reached the lowest value in adulthood. The mean daily value of testicular MDH increased between day 5 and 15, decreasing at day 35 and remaining unchanged until adulthood. The variation of malate dehydrogenase activity, soluble protein content levels, and the circadian rhythm parameters during the maturation process may be related to gonad development.     

Malate Dehydrogenase Activity of Rat Testis: Circadian Rhythm and its Ontogeny

Malate dehydrogenase activity and soluble protein content in testes from rats exposed to a 14:00 h light:10:00 h dark photoperiod, have been determined every two or four hours over a 24 hour period in 5, 15, 25 and 120 day-old rats. By using the Cosinor method, the ontogeny of an unimodal rhythm was studied for MDH activity and soluble protein content in testis. In 5 and 15 day-old rats, the MDH acrophases were recorded around 19:00 h and 17:00 h, respectively. Rats aged 25 and 110 days showed the MDH acrophases during the dark period. An inversion of the MDH circadian rhythms was detected in 25 day-old compared to those of 5 and 15 day-old rats. An inversion of the protein circadian rhythm was also detected at 15 days compared to that at 5 days. These inversions persist in the adult rats. The amplitude of the MDH and protein rhythms reached the lowest value in adulthood. The mean daily value of testicular MDH increased between day 5 and 15, decreasing at day 35 and remaining unchanged until adulthood. The variation of malate dehydrogenase activity, soluble protein content levels, and the circadian rhythm parameters during the maturation process may be related to gonad development.     

Circadian rhythms of indoleamines and serotonin N-acetyltransferase activity in the pineal gland

Conclusion The circadian rhythm of melatonin synthesis in the pineal glands of various species has been summarized. The night-time elevation of melatonin content is in most if not all cases regulated by the change of N-acetyltransferase activity. In mammals, the N-acetyltransferase rhythm is controlled by the central nervous system, presumably by suprachiasmatic nuclei in hypothalamus through the superior cervical ganglion. In birds, the circadian oscillator that regulates the N-acetyltransferase rhythm is located in the pineal glands. The avian pineal gland may play a biological clock function to control the circadian rhythms in physiological, endocrinological and biochemical processes via pineal hormone melatonin.     

A day/night rhythm of vasopressin and oxytocin in rat retina, pineal and harderian gland

Arginine vasopressin (AVP), oxytocin (OT) and neurophysins (Np) have been found in the pineal gland and the retina of the rat. Because the retina, pineal gland and Harderian gland (HG) serve analogous functions, we undertook a study to determine the presence of these peptides in these three organs of rats. They were detected by two specific methods: HPLC and specific radioimmunoassays. For Np, total neurophysins (NpT) were measured. To determine a 24 hr rhythm, the animals were maintained under a light/dark cycle of 12 hr/12 hr for 3 weeks. The pineal glands, retinae and HG were collected. Day/night rhythms of AVP, OT and NpT were demonstrated in the retina and HG; but the pineal gland had only AVP rhythm. A significant decrease in the rhythms at 4 a.m. was demonstrated in the retina and HG. The 24 hr variation of AVP in the retina seemed parallel to that of the HG.     

CIRCADIAN ACTIVITY RHYTHMS AND SENSITIVITY TO NOISE IN THE MONGOLIAN GERBIL (MERIONES UNGUICULATUS)

Since consistent data on endogenous circadian rhythms of Mongolian gerbils are not available, the main aim of our study was to identify suitable conditions to receive stable and reproducible free-running rhythms of activity under different light intensities. Another objective was to determine the role of social cues as an exogenous zeitgeber in the absence of a light-dark (LD) cycle. We performed two long-term sets of experiments with adult male gerbils kept in climatic chambers under various photoperiods of at least 30 days each. In all cases, the time of lights on in the chambers differed from the daily starting hour of work in the animal house. Always, two animals per chamber were kept separately in cages with a running wheel while their activity was monitored continuously. During the first set, only three of eight animals developed intra- and interindividual variable free-running rhythms. The activity patterns seemed to be influenced by human activities outside, indicating high sensitivity to external factors. Subsequently, we damped the chambers and the room and restricted access to the room. In the following noise-reduced set, all gerbils developed comparable free-running rhythms of activity. We determined the mean of the free-running period τ, the activity-rest relationship α/θ and the amount of running wheel activity per day: τ = 23.7h ± 0.08h under low light (5 lux) and 25.5h ± 0.19h under high light intensities (450 lux); α/θ = 0.53 ± 0.08 under 5 lux and 0.34 ± 0.04 under 450 lux. The amount of daily activity was 12 times as high under 5 lux as under 450 lux. There was no indication that the two animals in one chamber socially synchronized each other. In conclusion, the pronounced rhythm changes in accordance with Aschoff's theory support the view that gerbils are mainly nocturnal animals. (Chronobiology International, 17(2), 137–145, 2000)     

Sympathetic Regulation of Circadian Rhythm of Serotonin N-Acetyltransferase Activity in Pineal Gland of Infant Rat

Abstract: The circadian rhythms of serotonin N -acetyltransferase activity in the pineal glands of infant and adult rats were compared. The nighttime increase of N -acetyltransferase activity in the pineals of infant rats was blocked by removal of superior cervical ganglion or by pretreatment with reserpine, l -propranolol, and cycloheximide. Injection of isoproterenol to infant rats markedly elevated pineal N -acetyltransferase activity. When the pineal glands of infant rats were organ-cultured, N -acetyltransferase activity spontaneously increased 7–12 h after the rats were killed. When infant rats were previously denervated or pretreated with reserpine and their pineals were cultured, this spontaneous elevation of N -acetyltransferase activity was abolished, indicating that the transient increase of the enzyme activity in organ culture was due to a liberation of catecholamine from degenerating nerve endings. Additional illumination until midnight prevented the nighttime increase of N -acetyltransferase activity in intact infant rats but not in blinded infant rats. These observations are taken to indicate that N -acetyltransferase rhythm in immature rat pineals is regulated by the sympathetic nerves in the same manner as in adult rat pineals, that the immature rat pineal does not contain a time-keeping system, and that there is no extraretinal light perception in infant rats as far as N -acetyltransferase rhythm is concerned.     

Role of pineal in the regulation of some aspects of circadian rhythmicity in the catfish, Heteropneustes fossilis (Bloch)

The findings reported here indicate that the pineal organ in catfish is involved in the regulation of locomotor activity rhythms and in some aspects of osmoregulation. Under LD 12:12 regimen, catfish is nocturnally active, with the maximum activity just before dawn. However, under conditions of continuous darkness (DD), the locomotor rhythm became free-running. Pinealectomy abolished the activity rhythm under DD and resulted in arrhythmicity. Circadian rhythms in plasma cortisol, osmolality and electrolytes (Na+ and K+) were also observed. Pinealectomy, though, increased the amplitudes of the rhythm; however the differences were not statistically significant. Removal of pineal significantly increased the mesor values of plasma osmolality and electrolytes, but there were no significant differences in the mesor values of plasma cortisol.     

Daily rhythm in rat pineal catecholamines.

A daily rhythm in the oscillations of pineal dopamine, norepinephrine and epinephrine content was found in male Wistar: Han rats. The acrophases of the oscillations were localized in the first half of the dark period and generally higher values were found in the dark part of the day.     

Circadian Rhythm of the Liver of Male Rats Pre-Treated with Phenobarbital—ii. Hexobarbital Sleeping Time and Lipids Content in Liver and Serum

The circadian rhythm of hexobarbital sleeping time and lipids content in liver and serum were studied in 226 male Sprague-Dawley rats pretreated daily at 0800-0900 with 70 mg/kg (study 1 or 3) or 50 mg/kg (study 2) phenobarbital (PB) orally for 7 days. Thereafter, eight (study 1) or five (study 2 and 3) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through the following day. The lighting schedule in the colony was 12:12 ± light:dark (light from 0600 to 1800). The hexobarbital sleeping times of PB-pretreated rats were generally shortened compared to the controls and no circadian rhythm was observed. PB-treatment increased slightly the liver content of cholesterol, and significantly that of triglycerides and phospholipids. Liver cholesterol and phospholipids showed circadian rhythms with peaks during the dark phase. No circadian rhythm of liver triglycerides existed. In serum, levels of triglycerides and phospholipids were slightly lowered by PB-treatment, while levels of cholesterol and beta-lipoprotein were not influenced. Serum values did not exhibit circadian rhythms.     

Effects of short-term cold exposure on pineal biosynthetic function in rats

In light of recent studies demonstrating stress-induced changes in pineal indoleamine metabolism, we tested the effect of acute cold stress on pineal biosynthetic function. Adult male rats were subjected to 30, 60, or 120 min of cold exposure (Ta = 2 degrees C) during either the light or dark phase of the daily photoperiodic cycle. Controls were kept at room temperature (22 +/- 2 degrees C). Animals were killed by decapitation and pineals were analyzed by radioimmunoassay for melatonin content and by radioenzymeassay for the activity of N-acetyltransferase (NAT). Cold exposure during the day elicited no significant changes in pineal indoleamine metabolism. Exposure to cold for 1 hr during the second hour after lights off slightly increased pineal melatonin content, without a concomitant change in NAT activity. Rats exposed to 2 hr of cold beginning 2 hr after lights off, however, displayed a 50% reduction in NAT activity, whereas pineal melatonin content remained unchanged. The paradoxical response of pineal NAT activity and melatonin content are not uncommon when rats are exposed to adverse stimuli.     

Rhythms of ghrelin, leptin, and sleep in rats: effects of the normal diurnal cycle, restricted feeding, and sleep deprivation

To determine the relationships among plasma ghrelin and leptin concentrations and hypothalamic ghrelin contents, and sleep, cortical brain temperature (Tcrt), and feeding, we determined these parameters in rats in three experimental conditions: in free-feeding rats with normal diurnal rhythms, in rats with feeding restricted to the 12-h light period (RF), and in rats subjected to 5-h of sleep deprivation (SD) at the beginning of the light cycle. Plasma ghrelin and leptin displayed diurnal rhythms with the ghrelin peak preceding and the leptin peak following the major daily feeding peak in hour 1 after dark onset. RF reversed the diurnal rhythm of these hormones and the rhythm of rapid-eye-movement sleep (REMS) and significantly altered the rhythm of Tcrt. In contrast, the duration and intensity of non-REMS (NREMS) were hardly responsive to RF. SD failed to change leptin concentrations, but it promptly stimulated plasma ghrelin and induced eating. SD elicited biphasic variations in the hypothalamic ghrelin contents. SD increased plasma corticosterone, but corticosterone did not seem to influence either leptin or ghrelin. The results suggest a strong relationship between feeding and the diurnal rhythm of leptin and that feeding also fundamentally modulates the diurnal rhythm of ghrelin. The variations in hypothalamic ghrelin contents might be associated with sleep-wake activity in rats, but, unlike the previous observations in humans, obvious links could not be detected between sleep and the diurnal rhythms of plasma concentrations of either ghrelin or leptin in the rat.     

Pineal peptides in the regulation of milk-ejection reflex in lactating rats

The effects of pineal peptides (mol. mass 1-4 kDa) intranasal infusions on some parameters of milk-ejection reflex were investigated. Peptides were extracted from dairy-cattle pineal glands. Pineal peptides increase body weight, levels of water intake, plasma prolactin concentration and milk yield in rats when infusing daily in dose 1 microgram/kg from the third day of lactation. On 9th and 12th days of lactation during 1-hour nursing seance the significantly greater number of reflective milk ejections were found. When 1 hour before the peptides infusion rats were intraperitoneally injected by rabbit antiserum to oxytocin (200 microliters at dilution of 1:20) the effects of pineal peptides were significantly less expressive or were absent at all. Using enzymimmunoassay it was demonstrated that there were greater increasing of oxytocin content in pineal gland in suckling-induced oxytocin release from neurohypophysial system in the chronic pineal peptides-treated female rats compared with control. This effect was absent when rats were injected by oxytocin antibodies. These data suggest that pineal peptides can participate in forming of reflect oxytocin release pattern. This pattern is initiated by suckling and is limited by oxytocin content in blood.