bluuebunny/crossref_metadata_2025 huggingface dataset:
Elevated Environmental Temperature Alters the Responses of the Reproductive and Thyroid Axes of Female Syrian Hamsters to Afternoon Melatonin Injections
Authors: Reiter Russel J. , Li Kang , Gonzalez‐Brito Aldo , Tannenbaum Michael G. , Vaughan Mary K. , Vaughan George M. , Villanua Maria A.
Published: February 2007

Female Syrian hamsters were kept in a light (14: 10 h light: dark cycle, lights on 0600 h)‐ and temperature (22 or 30°C)‐controlled room; some groups were treated with an afternoon s. c. injection of melatonin (6.25, 12.5, or 25 μg/day) for 11 or 14 weeks. The melatonin‐induced suppression of the reproductive system in hamsters maintained at 22°C (as measured by vaginal cycles, uterine weights, ovarian histology, and plasma and pituitary prolactin levels) was delayed if hamsters were kept at 30°C. The dose‐related depression of thyroxine (T4) after melatonin injections for 14 weeks in 22°C was not seen at 30°C. Rather, the depression of plasma T4 and triiodothyronine (T3) seen at the end of 11 or 14 weeks of exposure to 30°C without melatonin injections (vs. control levels at 22°C) was offset by melatonin injections, raising T4 and T3 particularly at the lower doses. In contrast, there was no consistent effect of higher temperature alone on reproductive variables. The interactive effects of temperature and melatonin on the reproductive and thyroidal systems in female hamsters are apparently complex and probably provide a fine‐tuning mechanism for the environmental control of endocrine physiology.
Lack of “Synaptic” Ribbons in the Pineal Gland of BALB/c Mice
Authors: Satoh Y. , Vollrath L.
Published: February 2007

In mammalian pinealocytes “Synaptic” ribbons (SR) are regularly occurring organelles that are functionally poorly understood. Since in a number of studies on the mouse pineal gland the presence of SR has not been mentioned, it was the aim of this investigation to quantitate SR in mice. BALB/c mice were chosen, which have recently been shown to have a genetic defect for melatonin synthesis. The pineals of 15 mice killed at night, when SR numbers are normally high, were examined electron microscopically, scanning an area of >20,000 μm2 per gland. In none of these pineals were SR detected. It is concluded that the lack or extreme rarity of SR in laboratory mice may be related to the inability of the gland to synthesize melatonin, not to the absence of melatonin per se, as melatonin administration in mice does not result in the occurrence of SR.
Plasma, Cerebrospinal Fluid, and Brain Distribution of 14C‐Melatonin in Rat: A Biochemical and Autoradiographic Study
Authors: Vitte P. A. , Harthe C. , Lestage P. , Claustrat B. , Bobillier P.
Published: February 2007

The distribution of 14C‐Melatonin (14C‐MT) after systemic injection was studied in the plasma, cerebrospinal fluid (CSF), and brain of rats. Chromatographic analysis (thin‐layer chromatography and high‐performance liquid chromatography) indicated that the radioactivity from biological samples taken at various times following the injection of label was mainly associated with 14C‐MT. Computer analysis of plasma 14C‐MT kinetics showed a three‐compartment system with half‐lives of 0.21 ± 0.05, 5.97 ± 1.11, and 47.52 ± 8.86 min. The volume of distribution and the clearance were 1,736 ± 349 ml. kg−1 and 25.1 ± 1.7 ml. min−1. kg−1 respectively. The entry of 14C‐MT into the CSF was rapid and reached a maximum at 5 min. The decay followed a two‐compartment system with half‐lives of 16.5 ± 2.9 and 47.3 ± 8.6 min. The CSF/plasma concentration ratio was 0.38 at the steady state (30 min). At 2 min the level of 14C‐MT in the brain was 3.8 higher than in the CSF. Representative autoradiograms revealed an heterogeneous localization of 14C‐MT in the grey matter. The highest regional values, as evaluated by the permeability area product technique, were found in cortex, thalamic nuclei, medial geniculate nucleus, anterior pretectal area, paraventricular nucleus of the hypothalamus, choroid plexuses, and bulb‐pons. Thirty minutes later 14C‐MT was still detected in most of the brain regions analyzed.

These results point to a low but rapid penetration of circulating MT into the brain and the CSF. The heterogeneous distribution and the partial retention of 14C‐MT in the brain are compatible with the hypothesis of a central action of this hormone mediated via binding sites.
Melatonin Does Not Affect In Vitro Secretion of Testosterone in White‐Footed Mouse Testis
Authors: Knotts Lori K. , Bruot Brent C. , Glass J. David
Published: February 2007

There is evidence that melatonin may exert its antigonadal effect by acting in the gonad to inhibit steroidogenesis. To explore this possibility a hormonally sensitive in vitro system of dispersed Peromyscus leucopus testis was used to assess the effects of melatonin on human chorionic gonadotropin (hCG)‐ and dibutyryl‐cAMP (dbcAMP)‐ stimulated secretion of testosterone (T). At near‐maximally stimulating doses of hCG and dbcAMP, melatonin in concentrations of 2 × 10−12 M to 2 × 10−7 M did not affect the rate of secretion of T in cells from active or regressed testes. These results do not support the idea that melatonin helps to regulate seasonal reproduction by acting in the testes to inhibit steroidogenesis.
Melatonin Concentration in the Cerebral Vascular Sinuses of Sheep and Evidence for Its Episodic Release
Authors: Cozzi Bruno , Ravault Jean‐Paul , Ferrandi Bruno , Reiter Russel J.
Published: February 2007

Blood was collected from the cerebral sinuses and from the jugular vein of 5 ewes during both the day and night. Cerebral sinus samples were collected by means of a permanently indwelling cannula (roughly every 5 min) while jugular vein samples were collected by venipuncture (roughly every 10 min). In each of the 5 animals mean nighttime melatonin concentrations were greater at night than during the day. In 2 animals, cerebral sinus plasma melatonin concentrations were greater than in the jugular vein; in 2 animals the sinus and jugular plasma had similar melatonin levels; in 1 ewe jugular vein blood melatonin levels exceeded those in the cerebral sinus plasma. These differences among animals are presumably due to slight positional differences in the cerebral venous cannula placement. In several animals episodic release of melatonin was apparent. Whereas the episodes were most obvious in the cerebral venous blood at night, they were also apparent in 1 case in the jugular vein plasma and in 1 animal during the day. When episodes appeared they occurred about every 15–20 min.
Status of Dopamine in Bovine Pineal Glands and the Stimulation of N‐Acetyltransferase Activity by D2‐Dopaminergic Receptor Agonists in the Rat Pineal Glands in Culture
Authors: Govitrapong P. , Hama Y. , Pfeiffer R. , Ebadi M.
Published: February 2007

In a previous study, we identified in the bovine pineal gland two [H]spiroperidol‐binding sites with KD values of 0.18 and 2.1 nM and Bmax values of 37 and 630 fmol/mg protein, respectively. In this study, the status of dopamine in the bovine pineal glands was delineated further by measuring the relative concentrations of dopamine and norepinephrine and the relative concentrations of serotonin and melatonin. Furthermore, the presence of 4.0 ± 0.6 μg/dopamine/gm tissue encouraged us to delineate the effects of select dopaminergic receptor agonists and antagonists on the synthesis of melatonin in vivo and on the activity of N‐acetyltransferase in the rat pineal gland in culture. The acute1 administration of haloperidol (3 mg/kg intraperitoneally [ip]) or sulpiride (200 mg/kg ip) increased the concentration of melatonin in the pineal gland from 160.6 ± 8.18 to 327.6 ± 45.43 and 306.5 ± 40.53 pg/gland, respectively. Dopamine exhibited dual effects on the activity of N‐acetyltransferase, inhibiting the basal activity at 0.1 μM and stimulating it at 10 μM, and the later effect was blocked by propranolol. D2‐dopaminergic receptor agonists such as bromocriptine (4.0 μM) or LY‐171555 (10.0 μM) partially attenuated the norepinephrine‐induced stimulation of N‐acetyltransferase, and these attenuating effects were reversed by D2‐do‐paminergic antagonists such as haloperidol (10 μM) or domperidone (10 μM). The results of these studies are interpreted to indicate that for the synthesis of melatonin, the pineal D2‐dopaminergic receptors may function independently from those of the betai‐adrenergic receptor sites. Furthermore, the said D2‐dopaminergic receptors are amenable to down regulation since the activity of N‐acetyltransferase remained unaltered (0.0717 vs. 0.0729 nmol/gland/h) following chronic treatment (4 mg/kg ip/day for 30 days) with bromocriptine.
Catecholaminergic Mechanisms Mediate Hypothermia‐Induced Elevations in Pineal Gland N‐Acetyltransferase in Neonatal Rats
Authors: Torres German , Haak Katherine A. , Lytle Loy D.
Published: February 2007

The newly born of many mammalian species are ectothermic, and it is possible that biochemical processes important for the metabolism of endocrine hormones might vary with alterations in the environmental temperature. Temperature‐induced fluctuations in pineal gland N‐acetyltransferase activity were investigated in 4‐, 12‐, and 20‐day‐old rats placed for 4 hr in 23 or 34°C environments. Enzyme activity increased dramatically in ectothermic 4‐ and 12‐day‐old animals exposed to the 23°C environment, but not in endothermic 20‐day‐old rats. The elevations in daytime pineal gland NAT activity seen in cold‐exposed animals were absent in rats previously subjected to chemical sympathectomy induced by 6‐hydroxydopamine, or in animals treated with the beta‐noradrenoceptor antagonist drug propranolol. Catecholaminergic nerves and beta‐noradrenoceptors known to be important for light‐induced changes in mammalian pineal gland biochemistry also appear essential for environmental temperature‐dependent elevations in neonatal pineal N‐acetyltransferase activity.
Regulation of Melatonin in the Harderian Glands of Golden Hamsters
Authors: Hoffman Roger A. , Johnson Lucinda B. , Reiter Russel J.
Published: February 2007

A daily rhythm in melatonin concentration in Harderian glands (HG) of female golden hamsters is described and is characterized by significant reductions following lights‐on. Concentrations in HG of intact or pinealectomized males are low and consistent over a 24‐hour period. Castration of males is accompanied by increased levels of melatonin in the HG to approach those of females. When castrated males are exposed to short photoperiods, however, melatonin levels are typically low. Levels of serotonin (5‐HT), 5‐hydroxytryptophan (5‐HTP), and 5‐hydroxyindoleacetic acid (5‐HIAA) are extremely variable in HG of both males and females, precluding definitive conclusions. Melatonin concentrations in HG of females do not appear to be affected by light or stress per se, nor are the superior cervical ganglia the pathway by which concentrations are modified.
On Thymidine Incorporation by the Cultured Chick Pineal Gland
Authors: Wainwright S.D. , Wainwright Lillian K. , Lucarotti C J.
Published: February 2007

Explained chick pineal glands exhibited a cycle in thymidine incorporation when cultured either under a cycle of illumination or in constant darkness. This cycle appeared to be entrained to the light cycle under which the birds were maintained. The incorporation reflected gene replication in a small fraction of the cell population that was largely, but not entirely, located in the stroma of the gland. Glands cultured with colchicine for 28 h contained a very small number of cells showing metaphase chromosomes.
Preliminary Observations on the Suppression of Nocturnal Plasma Melatonin Levels by Short‐Term Administration of Diazepam in Humans
Authors: Monteleone Palmiero , Forziati Domenico , Orazzo Catello , Maj Mario
Published: February 2007

Several studies suggest that GABAergic mechanisms may be involved in the modulation of melatonin secretion. However, conflicting results have been reported in animal studies; in humans the issue has not been widely investigated. In the present study, using a double‐blind design, six healthy men received orally, at midnight, 10 mg of diazepam, a GABAergic agent, or placebo, on two different occasions 1 week apart. Blood samples were collected, in the dark, immediately before the drug administration, and at 12:30, 1, 2, 3, and 4 AM. Serum melatonin was measured by a radioimmunological method with [125I]melatonin as a tracer. Two‐way ANOVA with repeated measurements disclosed a significant effect for treatment (P < 0.01), for time (P < 0.0004), and for treatment X time interaction (P < 0.05). Following diazepam administration, serum melatonin levels observed at 2, 3, and 4 AM were significantly lower than the corresponding values following placebo (P < 0.02 at 2 and 4 AM; P < 0.03 at 3 AM [Students' paired t test]). These results show that nocturnal blood melatonin levels may be suppressed by the acute administration of a GABAergic agent, suggesting that GABA may be involved in the modulation of pineal activity in man.
Effects of Daily Afternoon Melatonin Administration on Body Weight and Thyroid Hormones in Female Hamsters
Authors: Petterborg Larry J. , Rudeen P. Kevin
Published: February 2007

Female hamsters were treated each afternoon for 8 weeks with subcutaneous injections of 25 μg of either melatonin or vehicle solution. Animals were sacrificed in either the morning or afternoon of diestrus and proestrus, along with their respective melatonin‐induced acyclic pairs. Melatonin‐treated hamsters had significantly greater mean body weights than did the vehicle‐treated hamsters (P < 0.05). Terminal mean serum T4 levels and free thyroxine index (FT41) were significantly reduced (P < 0.05) in melatonin‐treated hamsters compared with values obtained from animals subjected to the vehicle alone. In addition, T4 levels, FT41, T3 levels, and FT31 were significantly influenced by day and time of sacrifice independently of the melatonin treatment. T3 uptake was significantly lower on the morning of proestrus in melatonin‐treated animals. These results demonstrate that chronic afternoon melatonin administration in female hamsters results in the loss of estrous cyclicity, a significant gain in body weight, and the reduction of T4 levels and T3 uptake. Changes in serum T3 levels are a function of the time of sample collection and are not influenced by melatonin treatment. In addition, these data indicate that thyroid function in general changes during the estrous cycle in these animals.
Pineal Gland Hydroxyindole‐O‐Methyl Transferase (HIOMT) From Rainbow Trout (Salmo gairdneri) Subject to Temperature‐Dependent Substrate Inhibition by N‐Acetylserotonin
Authors: Morton Dougal J. , Forbes Heather J.
Published: February 2007

The effect of different incubation temperatures on the activity of trout hydroxy‐indole‐O‐methyltransferase (HIOMT) was determined in order to study the potential effects of changes in environmental temperature on production of melatonin. In the study, N‐acetylserotonin (NAS) was found to inhibit trout pineal HIOMT, inhibitory concentration decreasing with a decrease in incubation temperature. An increase in incubation temperature was accompanied by an increase in maximal velocity (Vm) and a decrease in affinity of the substrate NAS for the enzyme, while the affinity of the inhibitor NAS remained more or less constant with increase in temperature up to 30°C. It was interesting to note that at subinhibitory concentrations of NAS, possibly concentrations within the normal physiological range, there was a balance between increased velocity and decreased affinity for substrate, with increase in temperature resulting in a constant rate of melatonin production. On the basis of these results it is suggested that substrate inhibition might be involved in modulation of melatonin production and that trout pineal HIOMT can maintain a constant rate of melatonin production over a wide range of temperatures by a combination of compensatory changes in enzyme kinetic parameters.
Rhythmic Incorporation of Thymidine by Chick Pineal Glands In Vitro
Authors: Wainwright S. D. , Wainwright Lillian K.
Published: February 2007

Cultured chick pineal glands showed a cycle in the cumulative incorporation of thymidine into DNA. In undisturbed cultures the rate of thymidine incorporation, amount of thymidine incorporated per 1 ‐day cycle, and persistence of the incorporation process were all markedly affected by the concentration of exogenous precursor. However, more than two full cycles of incorporation were found when culture medium of low thymidine content was renewed daily, or when medium of intermediate concentration was replaced on the 3rd day of culture. At a high thymidine concentration the second cycle of incorporation sometimes appeared to be impaired. At all concentrations tested, less than 2% of the available thymidine was incorporated.
Comparison of the Effects of Short Photoperiod Exposure and Melatonin Treatment in Ovariectomized LSH/SsLak Hamsters
Authors: Hauser Ursula E. , Benson Bryant
Published: February 2007

The object of this study was to compare the effects of short photoperiod (SP) and melatonin (MEL) treatment on the reproductive axis in ovariectomized LSH/SsLak hamsters. Animals acclimatized in long photoperiods (LP) (14L:10D) and showing regular estrous cycles were ovariectomized. Half of the operated hamsters received Silastic capsules containing 17‐beta estradiol (E2). On the following day the animals were further subdivided into three groups: the animals in one group received daily afternoon injects of melatonin (MEL), those in a second group were given the vehicle, and animals in the third group were transferred from LP to SP (8L:16D). All animals were killed after 30 days. In hamsters without E2 replacement, MEL or SP exposure significantly suppressed serum and pituitary FSH levels, although MEL was more effective in this regard. On the other hand, SP exposure did not change serum FSH levels in animals with E2 implants, whereas MEL effectively suppressed them. SP or MEL reduced serum LH levels to a similar extent in the absence of E2 replacement, yet in animals with E2 implants only MEL significantly lowered LH levels below LP E2‐treated controls. This was in contrast to effects on the pituitary where both treatments were equally effective in the depression of LH content. Serum PRL levels were similarly suppressed by MEL or SP exposure in E2‐treated hamsters. On the other hand, pituitary PRL levels were not affected by either treatment in animals with E2‐containing capsules, whereas SP or MEL treatment both significantly depressed pituitary PRL contents in hamsters without E2 replacement. SP treatment lowered MBH LHRH contents in animals with E2‐containing capsules; no other significant changes in hypothalamic LHRH were noted. The data suggest that daily treatment with 25 μg of MEL is generally more effective in the suppression of gonadotropin levels than SP exposure. It is suspected that the mode of administration of MEL, and its quantity, may interact with estrogen differently than SP in the induction of physiological changes and regulation of the LHRH system.
Melatonin Profile in Marmots: The Influence of Catecholamines, Hibernation, and Light
Authors: Florant Gregory , Green Rahel , Abel Ted , Hartzell Scott , Tamarkin Lawrence , Brainard George
Published: February 2007

The aim of this study was to determine the effects of circulating catecholamines and light on the daily melatonin rhythm in the marmot. Endogenous levels of circulating catecholamines and plasma melatonin were measured during arousal from hibernation in light and stuthes were performed on the circadian melatonin rhythm in two photoperiods (LD 4:20 and LD 8:16). In addition, stuthes were done on the capacity of broad‐band white light at normal room intensities (32 μm2 or 108 lx) and of low‐intensity monochromatic green light (500 nm; 1.4 μm2 or 31 lx) to suppress high nocturnal melatonin levels. We conclude that high levels of plasma catecholamines that occur during arousal from hibernation do not influence the production and secretion of pineal melatonin. During the nocturnal portion of its light/dark cycle, the marmot plasma melatonin rhythm is suppressed by both white light and low‐intensity green light.
Plasma Melatonin Exhibits a Diurnal Secretion in the Common Marmoset (Callithrix jacchus): Relationship to the Rest‐Activity Cycle
Authors: Guerin Michael V. , Matthews Colin D.
Published: February 2007

The secretion of plasma melatonin exhibits a diurnal variation in the common marmoset (Callithrix jacchus jacchus) (n = 12) with mean values of 125.8 fmol/ml during darkness and below assay sensitivity (mean 70.5 fmol/ml) during the light period. Both melatonin secretion and the rest activity cycle appeared to be phase advanced with relation to the light dark cycle which is consistent with an endogenous circadian period (tau) of < 24 h in this species.
Propranolol Blockade of Short Photoperiod‐Induced Gonadal Regression: Modification by Melatonin Injections or Implants
Authors: Champney Thomas H.
Published: February 2007

Male Syrian hamsters were exposed to short photoperiods (10L: 14D) for ten weeks and received daily ethanolic saline (1:10), propranolol (125 μg, sc) or melatonin (25 μg, sc) injections at 16: 45. Some hamsters also received melatonin implants (1 mg in 24 mg beeswax, sc) every two weeks in addition to the above treatments. Testicular weights were determined at the beginning, every three weeks, and at the end of the experiment. Serum hormone levels, hypothalamic amine levels and cortical amine levels were also determined at the conclusion of the experiment. Propranolol prevented the decline in testes weight produced by short photoperiod (P<0.001 versus control). Propranolol was not able to prevent daily injections of melatonin from producing gonadal regression. Melatonin implants blocked testicular regression produced by both short photoperiod and melatonin injections. No differences in hypothalamic or cortical amine levels were observed between the treatment groups. These results add further support to the suggestion that propranolol is acting at the pineal gland preventing melatonin synthesis and not at a post‐pineal central site which would affect melatonin binding and action.
Thymidine Incorporation by Chick Pineal Glands as Studied by Pulse‐Labelling In Vitro
Authors: Wainwright S. D. , Wainwright Lillian K.
Published: February 2007

We have studied the pattern of variations in extent of thymidine incorporation during pulse‐labelling in cultured chick pineal glands. During the first 24‐30 h in culture the extent of pulse‐labelling varied in parallel with the cycle in cumulative incorporation. Pulse‐labelling was seen during the period of apparent arrest of cumulative incorporation. However, it was probably “masked” by the SD of assays of cumulative incorporation and represented a minor, but distinct, process of thymidine incorporation. The pattern of variation in extent of pulse‐labelling was qualitatively consistent under a wide variety of conditions. Control of this pattern appeared to be different from that of the circadian rhythm in cumulative thymidine incorporation.
Improved Method for the Measurement of Chicken and Rat Pineal Serotonin N‐Acetyltransferase Activity
Authors: Rodriguez‐Cabello J. C. , Arpa F. , Agapito M. T. , Garcia‐Herrero I. , Recio J. M.
Published: February 2007

EGTA, a nonspecific ion chelator, showed very good potential for preventing the loss of serotonin N‐acetyl transferase activity (arylamine: acetyl‐CoA: N‐acetyltransferase, EC 2. 3. 1. 5.) (SNAT) from rat and chicken pineal glands during preincubation at 37°C before substrate addition. SNAT activity was higher than that of the controls when EGTA was present in the homogenization buffer due to the prevention of the loss of activity probably not only during the preincubation period but also during incubation with its substrates. This characteristic of EGTA suggests that its use is suitable in the improved SNAT assay described in this paper since higher SNAT activities were found in both rat and chicken pineal glands than the activities recorded with the usual methods.
Failure of Prazosin to Mimic the Effects of Melatonin Under In Vivo and In Vitro Conditions
Authors: Stankov Bojidar , Lucini Valeria , Persengiev Stefan , Mariani Marco , Scaglione Francesco , Demartini Germana , Fraschini Franco
Published: February 2007

The gonads of male hamsters exposed to short photoperiod (LD, 10: 14) or treated with melatonin in the late afternoon under long photoperiod (LD, 14: 10) had undergone complete regression by the end of the treatments (8 weeks). Animals treated for the same period of time with prazosin (a putative melatonin analogue) under the same conditions failed to show a difference in their gonadal status as compared to the long photoperiod controls. Prazosin was unable to prevent melatonin‐induced gonadal atrophy when injected either in the morning or 30 min before melatonin. Moreover, prazosin was without any effect on (and unable to prevent the melatonin‐stimulated) progesterone production by rat adrenals under in vitro conditions. These data demonstrate that prazosin, which reportedly inhibits 2‐[1251]iodomelatonin binding in the hamster brain in an affinity‐related manner, does not possess properties of a biological melatonin analogue under conditions of two different model systems in two species.
Binding Characteristics, Regional Distribution and Diurnal Variation of [125I]‐Iodomelatonin Binding Sites in the Chicken Brain
Authors: Yuan He , Tang Fai , Pang Shiu Fun
Published: February 2007

The [125I]‐iodomelatonin binding sites in chicken brain membrane preparations were studied. The binding of [125I]‐iodomelatonin to the membrane preparations of chicken brain was rapid, stable, saturable, and reversible. The order of pharmacological affinities of [125I]‐iodomelatonin binding sites in the chicken brain membrane preparations was: melatonin > 6‐chloromelatonin > N‐acetylserotonin > 5‐hydroxytryptamine > tryptamine > 5‐methoxytryptophol, >> 1‐acetylindole‐3‐carboxaldehyde, 5‐hydroxyindole‐3‐acetic acid, L‐tryptophan, 5‐hydroxytryptophan, 3‐acetylindole. Compounds known to act on the receptor of norepinephrine or acetylcholine were inactive as compared to melatonin. Among the various brain regions studied, melatonin binding had maximal level in the hypothalamus, intermediate levels in the mid‐brain, ponsmedulla, and telencephalon, and minimum level in the cerebellum. Subcellular fraction studies indicated that 40% of the binding was located in the mitochondrial fraction, 27% in the nuclear, 26% in the microsomal, and 6% in the cytosol fraction. Scatchard analysis of the membrane preparations revealed a dissociation constant (Kd) of 199.6 ± 17 pM and a total number of binding sites (Bmax) of 16.6 ± 0.75 fmol/mg protein at midlight. Thus, our results showed the presence of specific melatonin binding sites in the chicken brain membrane preparations. Saturation studies demonstrated that [125I]‐iodomelatonin binding capacity in chicken brain membrane preparations were 40% greater at midlight (16.6 ± 0.75 fmol/mg protein) than at middark (10.6 ± 0.56 fmol/mg protein), with no significant variation in their binding affinities.
Opposite Effects of EGTA and Neutral Surfactants on the Loss of Chicken Pineal Serotonin N‐Acetyltransferase Activity
Authors: Rodriguez‐Cabello J. C. , Arpa F. , Agapito M. T. , Recio J. M.
Published: February 2007

The effects of some general purpose drugs on the deactivation and activity measurement of the chicken pineal gland enzyme serotonin N‐acetyl transferase (EC 2. 3. 1. 5.) were studied. The drugs used were EGTA and two neutral surfactants, Nonidet P40 and Triton X‐100. Enzyme activity showed significant variations ranging from 2.8 ± 1.3 nmol/gland/h when Nonidet P40 was added to the homogenate buffer, to 31.8 ± 1.7 nmol/gland/h when EGTA was present. This striking variation seemed to be caused by the ability of these compounds to modify the rate of NAT deactivation acting either as accelerating agents, as in the case of the detergents or as braking agent, as in the case of EGTA.
Thymidine kinase activity of the chick pineal gland
Authors: Wainwright Lillian K. , Wainwright S.D.
Published: February 2007

Wainwright LK, Wainwright SD. Thymidine kinase activity of the chick pineal gland. J. Pineal Res. 1991:J Pineal Res 1991:10:71‐73.

Pineal thymidine kinase activity of 1‐week‐old chicks in situvaried significantly throughout the day. However, the circadian rhythm of thymidine incorporation seen with cultured chick pineal glands was not accompanied by variations in level of thymidine kinase activity in vitro. Thus the circadian rhythm in rate of cumulative incorporation of thymidine by cultured chick pineal glands is not determined by a rhythm in rate of the first reaction of the complex series of reactions by which thymidine is incorporated into DNA.
Pinealocyte subsurface cisterns II: Influence of time of day, sympathectomy, and castration
Authors: Heinzeller Thomas , Tutter IIse
Published: February 2007

Heinzeller T, Tutter I. Pinealocyte subsurface cisterns 11: Influence of time of day, sympathectomy, and castration. J Pineal Res 199 1 : 10: 84‐90.

Subsurface cisterns (ssc) of the gerbil pinealocyte were studied by electron microscopic morphometry taking account of different external influences: time of day, sympathetic deafferentation, castration with or without substitution of testosterone. Male individuals of Meriones unguiculatus, aged 150 days, were used. Though ssc number is invariant with respect to the light‐dark cycle, ssc size follows a highly significant sinusoid curve. The largest ssc were found in the afternoon, the smallest ones in the early morning. Bilateral resection of the superior cervical ganglia reduces the density of pinealocyte ssc markedly, and their size is maximal or, in relation to the scaled‐down cell, unusually large. Castration with or without application of testosterone propionate does not alter pinealocyte ssc, neither with respect to density nor size. From these experimental data it is concluded that pinealocyte ssc may play a supportive role in the regulation of pinealocyte sensitivity, in so far as it depends on receptors located in the cell membrane.
Pinealocyte subsurface cisterns III: Storage of calcium ions and their probable role in cell stimulation
Authors: Tutter Use , Heinzeller Thomas , Seitz‐Tutter Dieter
Published: February 2007

Tutter I, Heinzeller T, Seitz‐Tutter D. Pinealocyte subsurface cisterns 111: Storage of calcium ions and their probable role in cell stimulation. J Pineal Res 1991:10:91‐99.

Different techniques for the ultrastructural demonstration of calcium have been applied to the pineal gland of Meriones unguiculatus, attention being focussed on the endoplasmic reticulum (ER) and its subsurface cisterns (ssc). By means of a “loading” method [Walz, 1982; Wakasugi et al, 1982] it is shown that the pinealocyte ER‐ssc system sequesters calcium with dependency on ATP. Furthermore, a modification of the method of Duce and Keen [1978] is presented which turned out a) to be sensitive enough to demonstrate the cell's own low amounts of calcium as fine granular precipitates, and b) to preserve ultrastructure sufficiently. This method rendered possible comparison of the calcium distribution inside pinealocytes of the following groups: animals fixed during daytime, animals fixed at night, animals fixed at night with prior exposure to bright white light, animals fixed at night but injected at the end of the preceding light period with a pharmacon known to prevent the release of calcium from the ER of muscle fibers (Dantrolen). In contrast to the daytime findings, the pinealocyte ER‐ssc system at night is free of precipitable calcium; nocturnal illumination induces reacquisition, Dantrolen hinders nocturnal depletion. From the nocturnal coincidence of pinealocyte activity and calcium release from ssc, and from other cytological and experimental data, it is concluded that the functional significance of ssc refers to the regulation of pinealocyte sensitivity. Vice versa, pinealocyte activity may influence ER expansion and ssc size via the calcium‐dependent stability of microtubules.
Crcadian patterns of melatonin, corticosterone, and progesterone in male rats subjected to chronic stress: Effect of constant illumination
Authors: Persengiev Stephen , Kanchev Lubomir , Vezenkova Gergana
Published: February 2007

Abstract: Plasma and pineal melatonin and plasma corticosterone and progesterone concentrations have been shown to be altered by several types of stressors. This study was designed to define the circadian patterns of the hormones mentioned above in rats subjected to chronic stress and to investigate the influence of constant illumination. The results revealed that melatonin and corticosterone circadian patterns deteriorated and their plasma concentrations were significantly elevated. The constant illumination (2,500 lux) during the dark period (from 2000 to 0600) was not able to suppress melatonin production in stressed animals, while the plasma content of corticosterone was decreased at the end of experimental period compared to control rats. Plasma levels of progesterone were increased in stressed animals as well. Constant illumination, however, provoked also an increase of progesterone secretion in controls. Statistical comparisons between hormonal secretory patterns showed that melatonin and corticosterone correlated negatively in controls (r =−0.58, P < 0.05) during the nighttime. However, in stressed animals correlation was observed only between melatonin and progesterone secretion during the light and dark period (r =−0.43, P < 0.05). Surprisingly, the correlation during the nighttime in rats subjected to constant illumination was negative (r =−0.60, P < 0.02) compared to positive correlation (r = 0.60, P < 0.02) in rats kept under normal lighting regimen. These results suggest that melatonin release is affected by stress and, possibly, under these circumstances, interacts with adrenal steroid secretion.
Circadian rhythms of plasma melatonin in the Adelie penguin (Pygoscelis adeliae) in constant dim light and artificial photoperiods
Authors: Cockrem J.F.
Published: February 2007

Abstract: The response of plasma melatonin in Adelie penguins (Pygoscelis adeliae) to constant dim light and to light/dark cycles was measured to determine the capacity of the pineal gland to secrete melatonin after exposure to continuous daylight for 2 months. Penguins were moved in mid‐summer from the natural photoperiod to either constant dim light (n = 10), to a 12L:12D light/dark cycle (n = 5), or to a 12L:12D light/dark cycle with a 30 min light pulse (50–155 lux) on the third (n = 4) or sixth (n = 5) “night.” Blood samples were collected regularly through cannulae for up to 33 h. The birds in dim light were sampled after 2 days, with samples obtained over at least 24 h from 7 birds. Three of these birds had melatonin rhythms (peak levels 66.7–130.2 pg/ml) whereas the other 4 birds had constant low levels (<44 pg/ml). The phase of the rhythm was similar for all 3 birds. This is consistent with the pacemaker that regulates the circadian rhythm of melatonin secretion being entrained to a period of 24 h when the penguins were exposed to the natural photoperiod. Mean melatonin levels (42.7 ± 2.5 pg/ml) were elevated compared to those previously reported in penguins under natural daylight. All penguins held under a 12L:12D light/dark cycle had melatonin rhythms. The phase and form of these rhythms were similar to those reported for other birds, and they appeared to be circadian rhythms entrained by the light/dark cycle. Melatonin levels after a 30 min light pulse increased to peak levels at 0700 h that were 131.9 ± 10.1% (third night) and 130.2 ± 21.5% (sixth night) of those at 0030 h, as compared to 93.5 ± 15.9% for birds without a pulse. This difference was not statistically significant, but it is consistent with data from other species where a light pulse at a similar time during the “night” reduces melatonin levels after the pulse and delays the time of nocturnal peak levels. These results indicate that the capacity of the Adelie penguin pineal gland to secrete melatonin rhythmically is not lost after exposure to 2 months of continuous daylight. Also, melatonin secretion in the Adelie penguin may respond to relative changes in light intensity, even when the lowest light intensities are much greater than those considered experimentally to be bright light.
Daily cycles of putrescine, sperrnidine, and spermine in the liver, pineal gland, Harderian gland, anterior pituitary, and testes of rats kept in LD 12:12
Authors: Sabry Ismail , Matsuzaki Shigeru
Published: February 2007

Abstract: A circadian rhythm in cellular polyamine levels was detected in the liver, pineal gland, anterior pituitary gland, Harderian gland, and testicular seminiferous tubules of male rats fed ad libitum and maintained in a light:dark cycle of LD 12:12 (lights on at 07:00). Liver putrescine content was highest at 24:00, showing a sixfold increase over 12:00 levels. Pineal sperrnidine and spermine contents reached a maximum at 06:00, late in the dark phase. A similar pattern was also detected in the Harderian gland. In the anterior pituitary, the polyamines putrescine, sperrnidine and spermine were highest at 18:00, late in the light phase. However, the increase in putrescine was not statistically significant. The three polyamine contents decreased late in the dark phase. In testicular seminiferous tubules putrescine, on the contrary, was highest (about a twofold increase) late in the dark phase.
Identification of a seasonal elevation in daytime melatonin levels associated with the rut in fallow bucks (Dama dama): The effect of day length and exogenous melatonin
Authors: Newman Ronald E. , Foldes Andrew , Maxwell Colin A. , Rigby Robin D. G. , Wynn Peter C.
Published: February 2007

Abstract: The timing of the seasonal reduction in voluntary food intake and hormonal changes associated with the rut were investigated in mature fallow bucks subjected to artificial long‐day exposure with and without superimposed melatonin‐releasing implants. Circulating testosterone profiles and the period of inappetence, signalling the onset of the period of reproductive activity in untreated bucks under natural photoperiod, were phase‐advanced in both treatment groups. In the long‐day treated group, these profiles were phase‐advanced by 1 week, while in the long‐day + melatonin group, the phase advance was 6 weeks compared to the controls. Circulating daytime melatonin, elevated in all three groups, corresponds with seasonal changes in circulating testosterone levels associated with the rut. Prolactin profiles followed ambient photoperiod, being high during natural or artificial long days and low during natural short days. Exogenous melatonin administered during long‐day exposure initiated a rapid and reversible decrease in circulating prolactin levels. The elevation in plasma melatonin could not be separated temporally from the seasonal testosterone peak by exposure to long days or to exogenous melatonin. However, this daytime melatonin profile was abolished by the ablation of circulating testosterone following immunization against luteinizing hormone releasing hormone (LHRH). The presence of this endogenous melatonin during daylight was observed only during the rut, as measured in two radioimmunoassays and confirmed by mass spectrometry. It is likely that both testosterone and melatonin influence the onset of the seasonal rut in fallow bucks.
Serotonin N‐acetyltransferase activity in chicken retina: In vivo effects of phosphodiesterase inhibitors, forskolin, and drugs affecting dopamine receptors
Authors: Zawilska Jolanta B. , Kazula Arkadiusz , Zurawska Ewa , Nowak Jerzy Z.
Published: February 2007

Abstract: A role of D2‐dopaminergic neurotransmission in the regulation of melatonin biosynthesis in retina was studied in vivo in chickens. The nighttime rise in serotonin N‐acetyltransferase (NAT)—the penultimate and key regulatory melatonin‐synthesizing enzyme—was potently inhibited by both acute light exposure and agonists of dopamine D2‐receptor (quinpirole, bromocriptine, and apomorphine). Spiroperidol, a selective dopamine D2‐receptor blocker, increased the enzyme activity in light‐exposed chickens, but had no effect in animals kept in darkness. Inhibitors of cyclic nucleotide phosphodiesterase, aminophylline, and 3‐isobutyl‐l‐methylxanthine given peripherally, along with a direct adenylate cyclase activator forskolin injected directly into the eye, mimicked the action of darkness, and markedly enhanced the retinal NAT activity when administered to animals maintained in an illuminated environment. Dopamine D2‐receptor agonists had no effect on aminophylline‐stimulated enzyme activity, whereas spiroperidol enhanced it. Forskolin‐driven NAT activity was suppressed by quinpirole. Spiroperidol and aminophylline given alone at different times of day under light conditions stimulated NAT activity, and their effects were mainly additive when given in combination. SCH 23390, a selective D1‐dopamine receptor antagonist, did not affect the rise in NAT activity of chicken retina produced by either darkness or by aminophylline. The results provide further evidence that dopamine, acting via D2‐receptors, mediates the inhibitory effects of light on the cyclic AMP‐dependent dark‐evoked induction of NAT activity in chicken retina.
Ultrastructure and opsin immunocytochemistry of the pineal complex of the larval Arctic charr Salvelinus alpinus: A comparison with the retina
Authors: Vigh‐Teichmann I. , Ali M.A. , Szél A. , Vigh B.
Published: February 2007

Abstract: The fine structure and opsin immunocytochemistry of the pineal and parapineal organs of the salmonid fish Salvelinus alpinus, the landlocked Arctic charr, were studied and compared with the retina in various developmental stages, from prehatching to two‐month‐old. For opsin immunocytochemistry two polyclonal antibovine rhodopsin and the monoclonal antichicken opsin antibodies OS‐2 (detecting blue and green pigments) and OS‐1 (detecting green and red pigments) were used.

Histologically, the pineal organ consists of nervous tissue like that of the retina. It is composed of photoreceptor pinealocytes, which formed axon terminals containing synaptic ribbons, on the dendrites and perikarya of secondary pineal neurons. Already in prehatching embryos, both the pineal and retinal photoreceptors display well‐developed outer segments and form synaptic terminals. The distal part of the pineal organ differentiates earlier than its proximal stalk. The differentiation of the retina starts centrally, but the caudal and dorsal retinae are differentiated earlier than the rostral and ventral ones. At the end of the larval period, the lateral retina is still undifferentiated.

In all stages studied, (rhod)opsin immunoreactivity was found in the outer segments of the pineal organ and rod‐type retinal photoreceptors, a finding speaking in favour of the presence of the opsin of a rhodopsin/porphyropsin. Cone‐type retinal photoreceptors identified morphologically in the pre‐ and posthatching stages were opsinimmunonegative with the four primary antisera used. This result suggests that in the charr the opsins of cone visual pigments differ in their chemical nature from those of rhodopsin/porphyropsin. The parapineal organ was opsin immunonegative. Using the monoclonal antibody OS‐2 opsin immunoreactivity was also detected in inner segments, perikarya, and pedicles of rod‐type photoreceptors of both retina and pineal organ of embryos and 1‐ to 4‐day‐old larvae. This may indicate a high level of opsin gene expression during photoreceptor growth around hatching. The well‐developed pineal organ and its opsin content are discussed in connection with the photonegative behaviour of the larval charr.
Melatonin‐induced relaxation of rat aorta: Interaction with adrenergic agonists
Authors: Weekley L. Bruce
Published: February 2007

Abstract: The influence of melatonin on alpha‐ and beta‐adrenergic responses of vascular smooth muscle ex vivo were examined in these experiments. Melatonin caused a dose‐dependent relaxation of precontracted (30 mM KCl) vascular smooth muscle. This response was not affected by the removal of vascular endothelium. Melatonin (10 nM) reduced the efficacy, but not potency, of the contractile responses to methoxamine and clonidine. Melatonin had no effect on the vascular beta‐adrenergic response to isoproterenol. Pretreatment of vascular rings with lithium sulfate (0.1 mM) completely blocked the relaxation in response to melatonin, suggesting that the inositol phosphate pathway may be involved in this relaxation. Furthermore, pretreatment of vascular rings with phorbol 12‐myristate‐13‐acetate, an activator of protein kinase C, antagonized the relaxation response to melatonin. Pharmacologic doses of melatonin (0.1 mM) slightly impaired the vascular smooth muscle response to calcium. These data indicate that melatonin per se is capable of relaxing vascular smooth muscle and that low doses of melatonin impair alpha‐1 and alpha‐2 adrenergic responses without changes in the beta adrenergic response of vascular smooth muscle.
β‐Adrenergic stimulation increases cAMP and melatonin production in ovine pinealocyte cultures
Authors: Howell H. Edward , Morgan Peter J.
Published: February 2007

Abstract: An ovine pinealocyte suspension culture method, using glands from young sheep as a source of cells, has been developed to study mechanisms of pineal regulation in this species. Cell suspensions are obtained by enzymatic digestion (preliminary trypsinization followed by collagenase/pronase treatment) of pineal glands and these cells may be usefully retained in culture for up to 48 hr. Initial characterization of cyclic adenosine monophosphate and melatonin production responses to adrenergic stimuli (norepinephrine, phenylephrine, isoproterenol) in the absence and presence of antagonists (propranolol, prazosin) by pinealocytes in suspension culture indicate that a β‐adrenergic receptor‐mediated mechanism is primarily involved in transduction of the adrenergic signal to melatonin synthesis. This is in agreement with data from earlier work on the sheep using short‐term tissue incubations but contrasts with in vivo evidence suggesting a predominant α1‐adrenergic receptor‐mediated mechanism.
Alpha‐methyltryptophan metabolism in rat pineal gland and brain
Authors: Montine T.J. , Missala K. , Sourkes T.L.
Published: February 2007

Abstract: Alpha‐methyltryptophan (AMTP), a synthetic amino acid, is metabolized by the rat in vivo to alpha‐methylserotonin (AM5HT), which appears in the pineal gland just as it does in the brain. Pineal AM5HT assumes the same diurnal rhythm as serotonin does in control animals. Administration of AMTP results in a decrease of the serotonin content of the pineal gland, but not of its melatonin content. Pharmacological evidence indicates that the uptake of AMTP into the gland is influenced by noradrenergic innervation. No evidence was obtained for formation in vivo of alpha‐methyl‐N‐acetylserotonin or the alpha‐methyl analogue of melatonin.