bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Melatonin on the Sleep‐Independent Component of Prolactin Secretion
Authors: Bispink Gerd , Zimmermann Ralf , Weise Hans Christoph , Leidenberger Freimut
Published: February 2007

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 < 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.
Temporal Changes in the Pattern of Melatonin Secretion in Sheep Held in Constant Darkness
Authors: Earl C. R. , D'Occhio M. J. , Kennaway D. J. , Seamark R. F.
Published: February 2007

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 19h 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 I 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 8d, 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.
Ontogeny of Light‐Induced Decrease of N‐Acetyltransferase Activity in Explanted Chick Pineal Glands
Authors: Rudeen P. Kevin , Creighton Julia , Bylund David B. , Petterborg Larry J. , Paredez Susan
Published: February 2007

The ontogeny of chick pineal serotonin N‐acetyltransferase (NAT) activity was investigated in explanted chick pineal glands at 4, 10 and 21 d of age. Nocturnal levels of the enzyme and the response of the enzyme to light exposure were determined in pineal glands maintained in short‐term culture at each age. The results indicate that nocturnal NAT activity was increased in the glands from older birds. Nocturnal levels of NAT activity at the time of the initiation of the experiment were threefold greater in glands from 21‐d‐old birds as compared to that in glands from 4‐day‐old chicks. The response to light was similar in all three ages examined; light induced a significant decrease in NAT activity within 60 min in explanted glands from 4‐d‐old chicks and within 180 min in the glands from the 10‐ and 21 ‐d‐old chicks. A paradoxical transient increase in enzyme activity occurred immediately (within 5 min) following light exposure which was significant in the glands from the youngest chicks, and present, but more variable, in the older chicks. These data indicate that the nocturnal enzyme activity is greater in glands from older birds, but that light exposure of explanted glands initiates a transient rise followed by a decrease in NAT activity at all three ages.
Time‐Dependent Effect of Melatonin on Actin mRNA Levels and Incorporation of 35S‐Methionine Into Actin and Proteins by the Rat Hypothalamus
Authors: Iovanna Juan , Dusetti Nelson , Cadenas Belen , Cardinali Daniel P.
Published: February 2007

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 μg/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 μg/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot‐blot analysis, decreased only after the injection of 100 μg/kg melatonin for ten days at 10:00. Neither a 10‐μg/kg dose of melatonin, nor a single injection of 100 μg/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 μg/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.
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
Authors: Guerrero J. M. , Santana C. , Reiter R. J.
Published: February 2007

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 cerebrocorticol 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.
Effect of Melatonin Administration and Long Day‐Length on Endocrine Cycles in the Hedgehog Erinaceus europaeus
Authors: Fowler Paul A. , Racey Paul A.
Published: February 2007

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.
Opsin Immunocytochemical Characterization of Different Types of Photoreceptors in the Frog Pineal Organ
Authors: Vigh‐Teichmann Ingeborg , Vigh Béla
Published: February 2007

The pineal organ of the frog, Rana esculenta and R. temporaria was studied by opsin immunocytochemistry using two polyclonal antibovine rhodopsin and the monoclonal antichicken opsin antibodies OS‐2 (detecting blue and green pigments) and COS‐1 (detecting green and red pigments). Four types of photoreceptor cells were distinguished. The large outer segments of the numcrous electron‐dense photoreceptor cells (“large pineal rods”) were immunoreactive with the rhodopsin and OS‐2 antibodies, but reacted weakly with antibody COS‐1. Some electron‐dense photoreceptors with smaller outer segments (“small pineal rods”) were found that were strongly OS‐2‐immunoreactive but moderately rhodopsin‐positive. The long outer segments of the oil droplet containing photoreceptors (“large pineal cones”) were only immunoreactive with the COS‐1 antibodies. The small electron‐lucent photoreceptors (“small pineal cones”) were immunonegative with all the opsin antisera used.

These results confirm the presence of the opsin of a (green‐sensitive) rhodopsin in the “large rod” photoreceptors. A blue‐sensitive pigment is supposed to be present in the “small rod” photoreceptors, and a red‐sensitive one in the oil droplet‐containing “large cones”. The opsin‐immunonegative “small cone” is discussed to contain a (UV‐blue?) photopigment that differs essentially in its antigenic sites from the other pigments. The presence of four types of photoreceptors equipped with the opsins of apparently different photopigments strengthens the view that the frog pineal organ is capable of measuring different ranges of the light spectrum.
Immunoreactive Levels of Pineal Arginine Vasopressin Change During the Rat Estrous Cycle
Authors: Moujir Fatima , Sanchez‐Franco Franco , Santana Celsa , Cacicedo Lucinda , Alonso Rafael
Published: February 2007

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.
Low temperature stimulates pineal activity in Syrian hamsters
Authors: Stokkan Karl‐Ame , Nonaka Keico O. , Lerchl Alexander , Vaughan Mary K. , Reiter Russel J.
Published: February 2007

Stokkan K‐A, Nonaka KO, Lerchl A, Vaughan MK, Reiter RJ. Low temperature stimulates pineal activity in Syrian hamsters. J Pineal Res 1991 : 10:4348.

The effect of 24‐hr exposure to cold (5°C) was studied in male Syrian hamsters adapted to short days (LD 8:16). Both pineal N‐acetyltransferase (NAT) activity and pineal and serum concentrations of melatonin showed a clear, diel rhythm with a moderate but significant increase late in the dark period. The nighttime peak levels of NAT activity and pineal and serum melatonin were significantly higher in the animals that had been exposed to cold than in those remaining in warm (22°C) conditions. The activity of type‐II 5'‐deiodinase (5'D) in the brown adipose tissue (BAT) was not different after 24 hr of cold exposure between cold‐ and warm‐exposed hamsters, and the enzyme did not show any diel rhythmicity. It has been speculated that some effects of cold exposure may be simulated by melatonin treatment; the present data further support this notion. The apparent lack of response in BAT 5'D activity remains enigmatic and needs further investigation.
Seasonal effects of administration of melatonin and 5‐methoxytryptophol on ovarian activity in the catfish Heteropneustes fossilis (Bloch)
Authors: Joy K.P. , Agha A.K.
Published: February 2007

k >y KP, Agha AK. Seasonal effects of administration of melatonin and 5‐methoxytryptophol on ovarian activity in the catfish Heteropneustes,ti,ssilis (Bloch). J Pineal Res 1991:10:65‐70.

In Heteropneustes fossilis, effects of intraperitoneal administration (25 fig/fish, alternate days for a month 1 hr before the onset of dark phase) of melatonin (MEL) and 5‐methoxytryptophol (5‐MTL) on ovarian activity were investigated during different seasons of the annual reproductive cycle under natural photothermal conditions. The gonadosomatic index (GSI) had decreased significantly by MEL during preparatory and prespawning seasons, and by 5‐MTL in all but the spawning season. Both MEL and 5‐MTL administrations arrested vitellogenesis during the gonadal recrudescence phase. As a result, stage I previtellogenic oocytes showed a significant increase in the MEL group in the preparatory and prespawning seasons, and in the 5‐MTL group only in the prespawning season. Almost the same trend was noticed in the percentage distribution of stage 2 and 3 oocytes. The percentage distribution of stage 4 postvitellogenic oocytes decreased significantly during the preparatory and prespawning seasons, but not in the spawning season. The indole treatment resulted in a highly significant increase in the percentage distribution of atretic oocytes during prespawning, spawning, and post‐spawning phases. Total protein content of the ovary was significantly lower in all seasons after MEL treatment, and only in the preparatory and prespawning seasons following 5‐MTL treatment. The ovarian glycogen level was significantly lower in the preparatory and prespawning seasons (MEL group), and in the 5‐MTL group only in the prespawning phase. Ascorbic acid level was inhibited by the indole treatment in all seasons except in the 5‐MTL group during the postspawning season. The results show that both MEL and 5‐MTL are effective in inhibiting ovarian vitellogenesis and inducing atresia in the catfish.
Melatonin effect on arachidonic acid metabolism to cyclooxygenase derivatives in human platelets
Authors: Martinuzzo Marta , Del Zar Maria de las M. , Cardinali Daniel P. , Carreras Luis O. , Vacas Maréa I.
Published: February 2007

Abstract: The effect of melatonin on thrombin‐induced [3H]‐arachidonic acid (AA) metabolism to cyclooxygenase derivatives was determined in platelets obtained from normal volunteers at 0830 and 2030 h. Percent conversion of radioactive AA was generally greater at 2030 h than at 0830 h for every cyclooxygenase derivative analyzed. Micromolar or greater concentrations of melatonin decreased significantly the conversion of [3H]‐AA to prostaglandin (PG) F2 and thromboxane (Tx) B2, and inhibited slightly the conversion to PGE2 and PGD2. After preincubation of platelets with 1 mM imidazole, the melatonin inhibitory effect was significant for PGF2 only. Melatonin (10−6 M) showed a significant inhibitory influence on platelet ATP release induced by phorbol‐12 myristate‐13 acetate (PMA) at 2030 h, an effect inhibited by 1 mM aspirin. These results indicate that at pharmacological concentrations melatonin inhibits human platelet cyclooxygenase.
The effect of intravenous administration of melatonin on cardiovascular parameters of the baboon (Papio ursinus)
Authors: Bosnian H. , Dormehl I.C. , Hugo N. , Redelinghuys I.F. , Theron J.J.
Published: February 2007

Abstract: Melatonin (0.3 to 0.4 mg/kg) dissolved in 0.5 ml dimethylsulphoxide (DMSO) was injected i.v. into six baboons, and their cardiovascular parameters were monitored. Left ventricular end‐diastolic and end‐systolic volumes, stroke volume, cardiac output, and left ventricular ejection fraction were measured, using conventional radionuclide ventriculography, and compared to normal values previously established. These parameters were also measured after an i.v. administration of only DMSO. The only statistical significant change due to melatonin was the increase in the cardiac output and left ventricular ejection fraction. With the reduced heart rate the increase in cardiac output implies a positive inotropic action on the heart by melatonin. There are indications that DMSO possibly suppresses cardiovascular actions of melatonin.
5‐Methoxypsoralen enhances plasma melatonin concentrations in the male rat: Non‐noradrenergic‐mediated stimulation and lack of effect in pinealectomized animals
Authors: Mauviard F. , Pévet P. , Forlot P.
Published: February 2007

Abstract: Previous studies have shown that 8‐methoxypsoralen (8‐MOP) is able to enhance melatonin secretion from rat pineal glands. The effect of another psoralen, 5‐methoxypsoralen (5‐MOP) on plasma melatonin concentrations alone or in combination with isoproterenol (Iso, 10 mg/kg BW, i.p.) or propranolol (Prop, 20 mg/kg BW, s.c.) was studied in the rat. An increase in plasma melatonin concentrations was observed 1 h after psoralen administration and lasted 8 h. The stimulatory effect of 5‐MOP on circulating melatonin concentrations was dose dependent above 5‐mg/kg, BW. 5‐MOP also potentiated the Iso‐induced rise in plasma melatonin levels. Furthermore, Prop did not block the effect of 5‐MOP, indicating that the psoralen acts independently of the noradrenergic system controlling pineal melatonin synthesis. No increase in plasma melatonin levels was observed in pinealectomized (Px) animals after injection of 5‐MOP (20 mg/kg BW) or 8‐MOP (20 mg/kg BW). This demonstrates that the rise in plasma melatonin concentrations observed after treatment requires the presence of the pineal gland, and that neither 5‐MOP nor 8‐MOP stimulates melatonin release from other structures such as the retina or Harderian gland.
The effects of benzodiazepines on basal and isoproterenol‐stimulated N‐acetyltransferase activity by the rat pineal gland, in vivo and in vitro
Authors: Winters W.D. , Yuwiler A. , Oxenkrug G.F.
Published: February 2007

Abstract: The present study examined the effects of “peripheral,”“central,” and “mixed” benzodiazepine agonists and antagonists on the nocturnal rise in rat pineal NAT activity in vivo and the isoproterenol‐ stimulated NAT activity of pineals in organ culture. Administration of the central agonist clonazepam or the mixed agonist‐antagonist diazepam, 4 hr after dark, at a dose of 25 mg/kg each, inhibited nocturnally elevated NAT 20 min later, while this same dose of the peripheral agonist RO 54864 elevated NAT activity. In a second study these agents were administered in vivo 1 hr before dark, at a dose of 3, 10, or 25 mg/kg i.p. and tested 4 hr after dark for in vitro rat pineal NAT activity. None of these agents affected NAT activity at the 3‐ or 10‐mg/kg dose, but RO 54864 25 mg/kg did induce elevated activity. In a third study, all of these agents prolonged the time period for NAT induction by isoproterenol in rat pineals cultured for 48 hr before stimuation. The data suggests that benzodiazepine stimulation of NAT activity in vitro is not specific to “central” or “peripheral” benzodiazepine receptors and that inhibition of melatonin production in vivo occurs either at some step before NAT induction or is involved with the inhibition of pineal HIOMT activity.
Melatonin, pinealectomy, and release of neurohypophysial hormones: In vitro studies
Authors: Juszczak Marlena , Stempniak Bozena , Guzek Jan W.
Published: February 2007

Abstract: The effect of melatonin as well as pinealectomy on the basal and K+‐evoked release of vasopressin and oxytocin from the neurointermediate lobes in vitro was determined. Pineal removal resulted in a diminution of vasopressin and oxytocin release from the neurointermediate lobes in vitro. Melatonin (10−3 or 10−6 M/1) increased vasopressin and oxytocin release from neurointermediate lobes of sham‐operated rats. Nevertheless, when pinealectomized rats served as donors of the neurointermediate lobes, melatonin (10−3 or 10−6 M/1) increased vasopressin release under basal conditions. For the same tissue, melatonin did not affect the oxytocin release either under basal conditions or during depolarization due to excess potassium. When 10−7 M/l melatonin was used, no changes in either vasopressin or oxytocin release were observed in vitro.
Permeability of the pineal gland of the rat to lanthanum: Significance of dark pinealocytes
Authors: Humbert Willy , Pévet Paul
Published: February 2007

Abstract: The permeability of the pineal gland to lanthanum was investigated by means of transmission electron microscopy and X‐ray microanalysis. Different pineal cell populations were studied. Light pinealocytes as well as glial cells were not permeated by the tracer lanthanum, which normally stays extracellularly. Dark pinealocytes showing different degrees of degenerative changes are permeated by lanthanum. The loss of plasma membrane integrity explains the entry of lanthanum into these cells. We conclude: (1) the lanthanum tracer can be used as an indicator of an alteration in membrane permeability, (2) dark pinealocytes appear as cells in the state of degeneration and represent a different physiological state than light pinealocytes.
The importance of timing in melatonin administration in a blind man
Authors: Tzischinsky Orna , Pal Itzhak , Epstein Rachel , Dagan Yaron , Lavie Peretz
Published: February 2007

Abstract: An 18‐year‐old blind man suffered from chronic sleep disturbances associated with daytime fatigue and excessive daytime somnolence. After two unsuccessful treatment regimens with 5 mg and 10 mg melatonin administered at bedtime (2200–2230), a third regimen of 5 mg melatonin administered at 2000 for 3 weeks resulted in a successful resolution of his sleep disturbances. We suggest that the efficacy of melatonin in ameliorating sleep disturbances because of alterations in circadian rhythmicity may be dependent on the time of administration.
Paradoxical effects of melatonin on spontaneous neuronal activity in the striatum of sham‐operated and pinealectomized rats
Authors: Romero J.L. Castillo , Montero F. Vives , Castroviejo D. Acuña
Published: February 2007

Abstract: The acute effects of intravenous melatonin on spontaneously active striatal neurons in sham‐operated and pinealectomized rats were studied. Extracellular recordings in a total of 76 neurons showed that only 19 did not modify their spontaneous activity after melatonin injection. In sham‐pinealectomized rats, neural firing decreased in most cells (80% of neurons), and increased in only 5.7% of the neurons after indole administration (100 ng/kg body weight). However, in the group of rats pinealectomized 7 days earlier, the injection of melatonin (at the same dose as above) significantly increased the excitatory response (44%), while the number of cells showing inhibitory response decreased (17%). Moreover, a small percentage (4.9%) of neurons in pinealectomized rats displayed a biphasic response (initial decrease followed by an increased firing). These results demonstrate that aMT can modulate the activity of striatal neurons, and suggest that other compounds of pineal origin (e.g., vasotocin) may change effects of aMT on basal ganglia neurons.
In vitro autoradiographical localization of melatonin binding sites in the caprine brain
Authors: Deveson Sharon , Howarth Julie A. , Arendt Josephine , Forsyth Isabel A.
Published: February 2007

Abstract: The recent development of a specific 2‐[125I]‐iodomelatonin ligand has led to the identification of I‐melatonin binding sites in the brains of numerous mammalian species. The present study reports the localization of 125I‐melatonin binding sites in the brain of the dairy goat. Six previously untreated female goats, aged 5–7 years, were culled under natural light between 0900 and 1100. Brains and pituitaries were immediately dissected out and frozen on dry ice. Both transverse and sagittal sections of frozen brain were cut 20 μm thick and thaw‐mounted onto gelatine‐coated slides. Three consecutive sections were cut at intervals throughout the brain, mounted onto three slides, labeled A, B, and C, and thusly treated: (A) incubated for 2 hr at room temperature in a 50 pM solution of 125I‐melatonin; (B) incubated for 2 hr at room temperature in a 50 pM solution of 125I‐melatonin plus 1 μM cold melatonin; (C) fixed in Clarke's fluid and stained with toluidine blue. After incubation, A (specific) and B (nonspecific) slides were washed three times in ice‐cold Tris‐HCl buffer (pH 7.7), air‐dried, exposed to an X‐ray film for 2 weeks at ‐20°C, and then fixed and stained. Specific 125I‐melatonin binding sites were found in the pars tuberalis (PT), the area of the suprachiasmatic nucleus (SCN), preoptic area (POA), fornix/mediolateral septal areas, hippocampus, and the cerebral cortex. 125I‐melatonin did not bind in the hindbrain, midbrain, neurohypophysis, pars intermedia or pars distalis of the adenohypophysis, or the pineal.
Interruption of nocturnal pineal melatonin synthesis in spontaneous recrudescent Djungarian hamsters (Phodopus sungorus)
Authors: Lerchl Alexander , Nieschlag Eberhard
Published: February 2007

Abstract: The duration of nighttime synthesis of the pineal hormone melatonin is believed to determine the breeding season in many mammalian species. Hamsters exposed to short days undergo gonadal involution followed by a return to normal function, suggesting a developed insensitivity to regressive photoperiods. This recrudescence may be due to either exhaustion of the pineal or to target‐desensitization. Both theories have been tested previously but failed to explain this phenomenon. We performed an experiment in the Djungarian hamster (Phodopus sungorus), a well‐characterized photosensitive species with a type C melatonin pattern (prolonged peak during majority of dark phase), in an attempt to resolve this issue. Among age‐matched male hamsters exposed to short days for either 16 weeks (involuted) or 38 weeks (spontaneous recrudescent), marked phase differences in diurnal pineal melatonin rhythms were observed. Furthermore, in recrudescent hamsters the melatonin pattern was divided into two parts, possibly no longer recognizable as a typical short‐day rhythm.
Binding sites for [3H]‐melatonin in human platelets
Authors: Vacas María I. , Del Zar María de las M. , Martinuzzo Marta , Cardinali Daniel P.
Published: February 2007

Abstract: A number of in vitro effects of melatonin on human platelets were revealed in previous studies. In order to examine whether high affinity binding sites for [3H]‐melatonin were present in membrane preparations of human platelets, a rapid filtration procedure through Whatman GFB paper was employed. Maximal melatonin binding was attained within 3 hr at 0°C. Scatchard analysis indicated a single population of binding sites with a dissociation constant (Kd) = 4.1 ± 0.5 nM and maximal number of binding sites (Bmax) = 24.2 ± 1.9 fmol/mg protein (mean ± SEM of five experiments). When various indole analogs were tested for their ability to inhibit [3H]‐melatonin binding, the following Ki (nM) were obtained: 6‐chloromelatonin (11.4), 2‐iodomelatonin (22.0), melatonin (24.7), 5‐methoxytryptophol (49.9), N‐acetylserotonin (68.9), 6‐hydroxymelatonin (78.2), 5‐methoxytryptamine (184). Serotonin was a potent inhibitor of [3H]‐melatonin binding with a Ki = 20.6 nM. Except for 2‐methylserotonin and α‐methylserotonin, a number of serotonin agonists and antagonists tested did not affect melatonin binding to platelet membranes. Binding experiments carried out at either 0800 or 2000 did not reveal time‐dependent differences in Kd or Bmax. The results suggest that high affinity melatonin acceptors are present in human platelets.
Androgenic function in adult rats: Influence of the pineal gland of the mother and of the offspring
Authors: Jarrige Jean‐François , Boucher Daniel
Published: February 2007

Abstract: Female rats exposed to long (LD 18:6) or short (LD 6:18) photoperiods from 21 days of age were mated when they reached 55 days of age. On day 2 of gestation animals of each group were either pinealectomized or sham‐operated. Lighting regimens were not changed during the course of the study. Male offspring of the four groups of dams were sacrificed on day 70 after birth. Rats that were maintained on long photoperiod had higher testicular testosterone, androstenedione, and dihydrotestosterone content than those raised on a LD 6:18 cycle. Whatever the breeding photoperiod used, maternal pinealectomy induced no modification of reproductive function. Among rats kept in short photoperiod, neonatal pinealectomy (on day 5 after birth) resulted in an enhanced testicular androgen content without any modification of plasma androgen concentration. These results indicate that (1) the previously reported effect of the mother's pineal on pubertal rat testicular function is not present in adulthood and (2) the pineal of the offspring is required to maintain normal testicular androgen content in the adult rat but exerts no influence on circulating androgens.
Inhibin‐like “antigonadotropic” activity in the ovine pineal
Authors: Bhagat Lakshmi , Duraiswami S.
Published: February 2007

Abstract: In an attempt to define the antigonadotropic activity associated with the protein/peptide extracts of ovine pineals, melatonin‐ and steroid‐free fractions obtained after subjecting crude ovine pineal acetone powder to soft gel chromatography were tested in three bioassay systems: (1) the conventional compensatory ovarian hypertrophy inhibition assay in rats, (2) the coupled bioassay in immature mice that enables one to distinguish factors acting at the level of the pituitary from those acting at the gonadal level, and (3) the classical in vitro pituitary cell culture assay for inhibin. The large molecular weight fraction, referred to as PI, behaved like a classical antigonadotropin as it suppressed compensatory ovarian hypertrophy following unilateral ovariectomy. Further, it not only lowered the basal and gonadotropin releasing hormone(GnRH)‐stimulated release of follicle stimulating hormone (FSH) by the cultured pituitary cells, but also inhibited the human chorionic gonadotropin(hCG)‐induced uterine weight gain in the coupled assay, thus acting like inhibin in these two assay systems. In addition, it showed immunological cross‐reactivity with ovine testicular inhibin. The present results strongly support the view that inhibin‐like activity may be the major player in what has so far been referred to as antigonadotropic activity.
Determination of kinetic properties of serotonin‐N‐acetyltransferase in bovine pineal gland using HPLC with fluorimetric detection
Authors: Fajardo Natalia , Abreu Pedro , Alonso Rafael
Published: February 2007

Abstract: The determination of serotonin‐N‐acetyltransferase (NAT) activity in the bovine pineal gland and other rat tissues was based upon the separation and detection of N‐acetyltryptamine formed from tryptamine and acetyl CoA by means of high performance liquid chromatography with fluorimetric detection. In the bovine pineal the enzyme exhibited a Km value of 31.45 ± 4.98 μM and a Vmax value of 30.90 ± 1.18 pmol N‐acetyltryptamine/min/mg protein for tryptamine, and a Km value of 28.72 ± 7.50 μM and a Vmax value of 25.90 μ 1.50 pmol N‐acetyltryptamine/min/mg protein for acetyl CoA. The present method is simple, allows the determination of NAT activity from a variety of enzyme sources, has application to pharmacological studies of NAT regulation in tissue cultures, and provides an alternative to current radioenzymatic assays.
Effect of immunization against melatonin on seasonal fleece growth in feral goats
Authors: Foldes A. , Hoskinson R.M. , Baker P. , McDonald B.J. , Maxwell C.A. , Restall B.J.
Published: February 2007

Abstract: Four vaccination protocols were utilized to investigate the effects of immunoneutralizing circulating melatonin on the annual cashmere growth cycle and cashmere production in Australian feral goats. A fluctuating anti‐melatonin antibody response, achieved by repeated booster vaccinations, resulted in an acceleration of the growth cycle in goats which exhibited a significant immune response, compared to sham‐immunized controls. Responding goats showed two cycles of cashmere length growth in the first 16 months and increased annual cashmere production in the first year. However, in the second year, these effects were no longer apparent, suggesting either some form of desensitization to melatonin, or a diminished response due to declining antibody titre. The effects of immunization were observed in both sexes; the effect on cashmere length was greater in wethers than in does. Cashmere fibre growth in response to a continuously declining plane of specific antibody showed increased cycle frequency, albeit with a decreased amplitude; guard hair growth cycles were affected to a much lesser extent. Small transient peaks of specific immunity at the summer or winter solstice were without significant effect on cashmere growth. Immunization to provoke a persistent anti‐melatonin antibody response at the winter solstice resulted in significantly increased greasy fleece weight, % cashmere yield, and mass of cashmere produced, but no change in fibre diameter in both sexes. Thus the timing of cashmere growth cycles in goats may be, at least transiently, altered by appropriately timed immunization against melatonin. The mechanism of pineal‐mediated regulation of cashmere growth cycles may involve (i) entrainment of an endogenous rhythm by melatonin, or (ii) seasonal alteration of cashmere follicle sensitivity to the effect of melatonin.
Influence of melatonin on the proliferation of hepatoma cells in the Syrian hamster: In vivo and in vitro study
Authors: Karasek M. , Liberski P. , Kunert‐Radek J. , Bartkowiak J.
Published: February 2007

Abstract: A study was carried out to determine the possible influence of melatonin on the proliferation of Kirkman‐Robbins hepatoma cells in Syrian hamsters, both in vivo and in vitro. A highly significant inhibition of the proliferation of transplanted hepatoma cells was observed in vivo following melatonin administration (proliferation index 10.3 ± 1.5; mean ± SD) in comparison with controls (proliferation index 23.3 ± 2.2), whereas in vitro melatonin (at concentrations of 10−5‐10−11M) was ineffective. These results indicate that inhibitory effect of melatonin on transplantable hepatoma cells in vivo may be indirect.
The presence and actions of opioid receptors in bovine pineal gland
Authors: Govitrapong P. , Pariyanonth M. , Ebadi M.
Published: February 2007

Abstract: The mammalian pineal gland and its main hormone, melatonin, working in conjunction with the hypothalamic suprachiasmatic nuclei, synchronize circadian rhythm and hence refine numerous physiological and biochemical parameters. An interaction among melatonin, opioids, and analgesia has been suspected for many years, since during nighttime, when the level of melatonin is high, the mammals are less sensitive to pain. In studying this phenomenon further, we have identified a single population of opioid receptors in the bovine pineal gland using [3H]‐diprenorphine and other ligands. The receptors have a dissociation equilibrium constant (Kd) of 1.36 ± 0.31 nM and a density (Bmax) of 17.93 ± 5.22 fmol/mg protein. In competitive experiments, the concentration of drugs required to inhibit 50% of the [3H]‐diprenorphine binding (IC50) in descending order of potency was found to be naltrexone > fentanyl > naloxone > nalbuphine > morphine > nalorphine > DAGO > dynorphin > metenkephalin. In order to delineate the function of the opioid system in the pineal gland, the effects of both opioid receptor agonists and antagonists on the basal activity of N‐acetyltransferase were examined in the bovine pineal expiants in culture. Morphine, an opioid receptor agonist, increased significantly the activity of N‐acetyltransferase in a dose‐dependent fashion. In addition, the stimulatory effect of morphine was inhibited by naloxone, an opioid receptor antagonist. The results of these studies indicate the existence of pineal opioid receptors, which play a pivotal role in the synthesis of melatonin and its action in synchronizing pineal events.
Entrainment of the circadian rhythm in the rat pineal N‐acetyltransferase activity by melatonin is photoperiod dependent
Authors: Humlová Martina , Lllnerová Helena
Published: February 2007

Abstract: Entraining effect of melatonin on the circadian rhythm in rat pineal N‐acetyltransferase (NAT) activity was studied under various photoperiods. Melatonin administration prior to dark onset for 5 successive days phase‐advanced the evening NAT rise under the light:dark (LD) cycle of either LD 10:14 or LD 8:16, but not under LD 12:12. It is assumed that under the latter regime, the end of a light period exhibited a phase‐delaying effect on the NAT rise. The light exposure appeared to be a stronger Zeitgeber than melatonin itself. Data show that melatonin applied in the late light period advances the evening NAT rise under a short photoperiod only; under a longer photoperiod, the phase‐advancing effect of melatonin may conflict with a phase‐delaying effect of the end of a light period, and the effect of light exposure overrides that of melatonin.
Immunoreactive somatostatin content in the pineal gland increases after lesion of the hypothalamic periventricular nucleus in male rats
Authors: Sabry I. , Suzuki M.
Published: February 2007

Abstract: Immunoreactive somatostatin (IRS) content in the pineal gland increased about two‐fold when the hypothalamic periventricular nucleus (Pe) of male rats, which contains many tuberoinfundibular somatostatin (SRIF) neuron cell bodies, was lesioned. However, the mechanism by which this increase takes place remains to be elucidated. Using 125I‐Tyr11‐SRIF‐14 as a ligand and autoradiography, specific binding was detected in several brain areas. However, we were unable to detect specific SRIF binding sites either in the pineals of control or lesioned animals. This undetectable binding of SRIF‐14 could be due to the localization of low‐affinity receptors that were not demonstrated by the present method. Another possibility for the undetectable binding of the radioligand to the pineal could be due to the fact that the majority of IRS may be within the nerve terminals and the receptors in a different location.
The circadian nature of melatonin secretion in Japanese quail (Coturnix coturnix japonica)
Authors: Kumar V. , Follett B.K.
Published: February 2007

Abstract: Plasma melatonin concentrations were measured in Japanese quail held under different photoperiods and constant darkness (<1 lux). When subjected to LD6:18 (6 hr light: 18 hr darkness), levels rose ∼2 hr after lights‐off, attained a peak level 8 hr after lights off, and subsequently declined to low daytime levels before the next lights‐on signal. This generated a distinct daily rhythm in melatonin secretion with a duration of ∼13 h. On exposing quail to a range of photoperiods, containing 6, 9, 11, 12, 13, 15, 18, or 20 hr of light per day, the onset of melatonin secretion remained essentially similar with the rise occurring soon after lights‐off. However, the offset of melatonin secretion was suppressed by the light of the next day and thus a much truncated rhythm was produced under long (> 12 hr) photoperiods. Importantly, between night lengths of 4 to 18 hr (i.e., LD 20:4 to LD 6:18) a linear relationship existed between the duration of night‐length and secretion of melatonin with the duration increasing by about 0.8 hr for each additional hour of darkness. If quail were released into darkness following a short (LD 6:18) or long (LD 20:4) day schedule, the rhythm persisted for at least two cycles with peaks occurring at about 24 hr intervals. In those quail coming into darkness from long days (LD 20:4), the rhythm of melatonin secretion decompressed rapidly on both sides of the peak, indicating that both the onset and offset of melatonin secretion were suppressed under long days. The endogenous nature of melatonin secretion was tested further by exposing birds to LD 6:30 for 4 cycles and then releasing into darkness. The rhythm in melatonin secretion persisted for at least three cycles before beginning to damp‐out. The circadian nature of the rhythm in melatonin secretion was also examined by subjecting quail to T‐cycles and then releasing into darkness. Both under the T‐cycles and darkness following T‐cycle treatments, the phase of the melatonin rhythm was advanced by > 3 hr under T = 27 hr cycles (LD 3:24) compared with T = 24 hr cycles (LD 3:21). This property is consistent with the melatonin oscillator being a circadian rhythm.
Commonalities in vasoactive intestinal peptide and peptide N‐terminal histidine C‐terminal isoleucine stimulation of N‐acetyltransferase activity in the rat pineal
Authors: Yuwiler A. , Brammer G.L. , Bennett B.L.
Published: February 2007

Abstract: Exposure of adult rat pineal glands in organ culture to the polypeptides vasoactive intestinal polypeptide (VIP), and peptide N‐terminal histidine C‐terminal isoleucine (PHI) increases pineal serotonin N‐acetyltransferase (NAT) activity and melatonin synthesis. The following research results are taken to indicate that VIP and PHI share common components of the NAT induction system: (1) The effects of the two peptides are additive at concentrations of 10 nM VIP and 100 nM PHI but not at higher peptide concentrations. (2) Pineals from newborns also respond to PHI with a dose dependent increase in NAT activity. NAT responses are additive at the same concentrations as seen with the adult pineals. (3) Light exposure affects the sensitivity of pineals to VIP and PHI stimulation in a similar manner; pineals taken after 3 hr of light are much less sensitive to PHI or VIP than those taken after 13 hr of light. (4) Pineals exposed for 48 hr to either PHI or VIP have a reduced NAT response to either agonist, which is reversible by culture in agonist‐free media. (5) Neither VIP nor PHI stimulation of NAT activity is affected by concentrations of the VIP antagonists (N‐Ac‐Tyr1, D‐Phe2)‐GRF(l‐29)‐NH2 (NAcTDGRF), L‐8‐K, VIP‐Neurotensin Hybrid (VIPNET), or (4Cl‐D‐Phe6, Leu17)‐VIP (4C1PLVIP), which affect VIP binding or function in other tissues.
New sensitive serum melatonin radioimmunoassay employing the Kennaway G280 antibody: Syrian hamster morning adrenergic response
Authors: Vaughan George M.
Published: February 2007

Abstract: A new procedure with the G280 antibody of Kennaway provides an assay for circulating melatonin (aMT) with a sample volume (200 μl), an analytic (0.33 pg/ml) and functional (0.62–0.80 pg/ml) detectability, a 50% displacement dose (6.4 pg/ml), a Kd (0.657 pM), and measured circulating daytime levels lower than reported for previous procedures, and 100% assay recovery. The normal daytime range in adult human and Syrian hamster serum was 0.4–4 pg/ml. The pattern of fall of the nocturnal surge of Syrian hamster serum aMT near the time of lights‐on was unaltered by extended darkness. Isoproterenol (ISO) injection 1 hr after lights‐on, when aMT had reached daytime levels, raised serum and pineal aMT dramatically 2 hr postinjection. The same dose of ISO injected 4 hr into light produced only a small detectable increase. Novel extension of nocturnal darkness did not affect the responses to ISO. Thus, when they are allowed to occur at the usual time on a 10‐hr dark schedule, both the fall from the nocturnal aMT surge and the subsequent loss of pineal beta‐adrenergic responsiveness in this species occur endogenously (probably entrained) rather than from gating by acute effects of morning light. Changes in daytime serum aMT consistent with concomitant changes in the pineal can be measured with a sufficiently sensitive radioimmunoassay.