bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship of Putative Nicotinic Cholinergic Receptors in the Suprachiasmatic Nucleus to Levels of Pineal Serotonin N‐Acetyltransferase Activity in the Normally Cycling Female, the Male, and the Ovariectomized Rat
Authors: Miller M. M. , Billiar R. B.
Published: February 2007

We have examined the nocturnal increase in pineal serotonin N‐acetyltransferase (SNAT) activity in the rat and the decrease in activity of this enzyme as a result of exposure of the rats to light during the nocturnal period. In females with normal ovulatory cycles and ovariectomized females, levels of the enzyme were similar during the dark (695 ± 70 pmol/min/gland vs. 590 ± 68) or after 20 min of lights on at night (107 ± 5 vs. 105 ± 8). Carbachol, a cholinergic agonist, was injected at 2400 hr (EST) into the lateral ventricle of orbitally enucleated rats. The agonist simulated the lights on effect in both intact and ovariectomized rats. Highly purified fractions of α‐bungarotoxin, a nicotinic cholinergic antagonist were injected into either the third ventricle or bilaterally adjacent to the SCN in intact females, intact males, or ovariectomized rats. These injections had no effect on either the nighttime increase or the lights on inhibition of SNAT. This study makes the following observations: 1) As was previously demonstrated [Illnerova, H. Endocrinol. Exp. 9:141–148, 1975], ovariectomy affects neither the daytime (light period) nor nighttime (dark period) activity of pineal SNAT. This study extends previous work by demonstrating that ovariectomy also has no effect on the lights on at night decrease of SNAT activity. 2) This study confirms that intraventricular infusion of carbachol decreases the nocturnal pineal SNAT activity [Zatz, M., and Brownstein, M. J. Brain Res. 213: 438–442, 1981]. 3) This study does not confirm the report that the nicotinic cholinergic antagonist α‐bungarotoxin prevents the loss of nocturnal SNAT activity induced by turning lights on at night [Zatz, M., and Brownstein, M. J. Brain Res. 213: 438–442, 1981].
Melatonin Suppression of the Colloid Droplet Formation in the Thyroid Is Not Related to the Alteration of Prostacyclin Synthesis
Authors: Lewiński Andrzej , Pawlikowski Marek
Published: February 2007

The goal of the present investigation has been to compare the effect of melatonin on the early secretory event in the thyroid follicular cells (thyroglobulin endocytosis; colloid droplet [CD] formation) and the effect of this pineal indoleamine on the release of a stable prostacyclin (PGI2) metabolite, 6‐keto‐PGF1α from the thyroid. 6‐keto‐PGF1α is believed to be a good index of PGI2 synthesis, since PGI2 is not stored within the tissue, but is continuously formed and released. We found that melatonin, administered to rats as daily subcutaneous injections at a dose of 25 μg and/or 250 μg for a total of 3 days, inhibited the CD formation. Moreover, melatonin partially suppressed the stimulatory effect of TSH on the CD formation. In turn, melatonin did not affect 6‐keto‐PGF1α release in basal conditions, but blocked the stimulatory effect of TSH.

It is concluded that melatonin decreases the thyroid secretion acting by a mechanism that is independent of the effect of this hormone on PGI2, synthesis.
The Effect of Orally Administered Melatonin on the Seasonality of Deer Pelage Exchange, Antler Development, LH, FSH, Prolactin, Testosterone, T3, T4, Cortisol, and Alkaline Phosphatase
Authors: Bubenik G. A. , Smith P. S. , Schams D.
Published: February 2007

Five milligrams of melatonin (M) per day was administered orally to four male white‐tailed deer on a schedule that mimicked first decreasing and then increasing lengths of natural photoperiod. The following seasonal phenotypic and hormonal responses were observed: 1) Pelage exchange, antler mineralization, velvet shedding, and rutting behavior of experimental animals were advanced by 50–55 days. 2) Prolactin (PRL) levels exhibited a bimodal curve with peaks in May and August, as compared to a monomodal curve of controls (peak in June). 3) Peak FSH levels of M‐fed deer were advanced 2 months as compared to controls (June vs August). 4) LH concentrations of both groups reached maxima in July; however, in the experimental group, LH levels declined much faster than in controls and then rose again in October‐November. 5) Testosterone (T) concentrations of M‐fed bucks were elevated 2 months ahead of controls. 6) Melatonin treatment had no significant effect on seasonal variation of T3, or T4. 7) No seasonal rhythm of cortisol was seen in either group and no detectable effect of M was evident. 8) No statistical differences in levels of alkaline phosphatase were seen between groups, although concentrations in experimental bucks sharply dropped to basal levels two months ahead of controls.
Production of Methoxyindoles In Vitro From Methoxytryptophan by Rat Pineal Gland
Authors: Morton Dougal J.
Published: February 2007

Pineal glands were incubated in the presence of [3H] methoxytryptophan with and without methoxamine, epinephrine, and norepinephrine. The beta‐adrenoceptor‐stimulated pineal glands were capable of converting methoxytryptophan to methoxytryptamine, melatonin, methoxyindole acetic acid, and methoxytryptophol, albeit in small quantities. Only methoxyindole acetic acid was detectable after incubation of unstimulated and alpha‐adrenergic‐agonist‐treated pineal glands. These results support the proposal that melatonin can be formed from methoxytryptophan although this is a minor synthetic pathway, and the classic pathway from serotonin via N‐acetylserotonin should be considered to be responsible for the majority of pineal melatonin production.
Morphology of the Pineal Glin Pregnant Nursing Sows
Authors: Wyrzykowski Zygmunt , Przybylska Barbara , Wyrzykowska Krystyna
Published: February 2007

The pineal glands of pregnant nursing sows were studied by light electron microscopy. Similar structural changes in the pineal glduring pregnancy lactation were noted as follows, 1) a proliferation of glial cells concurrent with a decrease in the number of pinealocytes, 2) a relative increase in the number of pinealocytes with cytoplasmic accumulation of dense bodies, 3) an increase in number of presumptive microglia. It appears that pregnancy lactation exert a complex influence on pineal function, with a predominantly stimulating effect.
Immunohistochemical Characterization of Rat Pineal Dopamine β‐Hydroxylase‐Containing Structures: Use of a Homologous Monoclonal Antibody
Authors: Schröder Hannsjörg , Fujisawa Hitoshi , Vollrath Lutz
Published: February 2007

Previous immunohistochemical studies using a polyclonal heterologous antibody to dopamine‐β‐hydroxylase (DBH) (EC 1.14.17.1) have shown that only a few of the many sympathetic nerve fibers in the rat pineal display DBH‐like immunoreactivity. This is in contrast to other sympathetically innervated organs. To ascertain this observation and to rule out antibody‐or method‐related artifacts, in the present study a well‐characterized, monospecific, homologous monoclonal antibody to DBH was used in combination with the biotin‐streptavidin‐fluorescein‐mediated detection system. As in a previous study, immunoreactive fibers were only rarely encountered in the rat pineal gland, with an identical distribution pattern. The present findings indicate that the sympathetic nerve fibers in the rat pineal gland appear to have a low capacity for de novo synthesis of noradrenaline and that most of the noradrenaline present may be taken up from the general circulation. In addition to nerve fibers, perikarya‐like cells and endbulb‐like structures were seen in the pineal gland similar to those demonstrated by the polyclonal antibody. It is suggested that both structures may be part of an as yet unknown intrapineal regulatory system.
Age‐Related Incidence of Pineal Gland Calcification in Children: A Roentgenological Study of 1,044 Skull Films and a Review of the Literature
Authors: Winkler Peter , Helmke Knut
Published: February 2007

Anterior‐posterior and lateral skull roentgenograms of 1,044 children aged 0–18 yr were examined for pineal gland calcification. Eighty children with pineal calcification were identified. Cranial computed tomograms (CCT) existing for half of the 80 cases provided confirmation. In contrast to existing reports on pineal calcification in the first decade of life, we found a significant percentage of “physiological” calcification even between 0 and 6 yr of age (range 2.9–4.2%). Contrary to current opinion we were not able to detect any signs of pineal gland tumors in these cases. We were able to confirm other reports which note a steep rise of the incidence of pineal calcification during the second decade of life.
Short‐Term Variations of Circulating Melatonin in the Ewe
Authors: English Judie , Arendt Josephine , Poulton Anthony , Symons Andrew M.
Published: February 2007

Melantonin levels have been studied in venous blood sampled at different frequencies (0.5‐, 2‐, 60‐min intervals) from intact ewes. All samples were taken during the dark phase of either natural or artificial photoperiods. In one experiment samples were taken simultaneously from both jugular veins to investigate the possible effects of “streaming” on the levels measured. Plasma cortisol was measured to ascertain whether or not the frequent removal of blood activated the ACTH stress axis. Plasma melantonin levels showed considerable variation with peaks of up to 365 pg/ml on a baseline of between 30 60 pg/ml. There was consistent evidence of intermittent peaks, the frequency of which increased with an increase in sampling frequency. Plasma cortisol showed no correlation with either the frequency or the amplitude of the melatonin peaks. When plasma samples were taken from both jugular veins a similar melatonin pattern was seen in the samples from both sides, but samples taken from the left jugular vein invariably showed higher levels than those taken from the right vein. This may be due to differential vascular drainage of the pineal to the two sides.
Suppression of Melatonin Secretion in Île‐de‐France Rams by Different Light Intensities
Authors: Arendt Josephine , Ravault Jean‐Paul
Published: February 2007

The intensity of cool, white, fluorescent light required to suppress melatonin secretion in Île‐de‐France rams was investigated. Animals were conditioned to 12L:12D, lights on 0600 hours, 104 μW/cm2 (350 lux) at eye level and subjected to a 1‐hour light pulse beginning 3 hours after lights off. Plasma melatonin measurements indicated that secretion was significantly suppressed by 0.30, 7.46, and 26.32 μW/cm2 (1.02, 25.10, and 88.60 lux, respectively) but not by 0.043 μW/cm2 (0.15 lux). A clear dose‐response relationship was apparent between light intensity and degree of melatonin suppression.
Local Glucose Utilization of the Brain and Pineal Gland During Stimulation of the Cervical Sympathetic Trunk
Authors: Ito Masanori , Kadekaro Massako , Sokoloff Louis
Published: February 2007

The quantitative autoradiographic 2‐[14C]deoxyglucose method was employed to map the metabolic activity of the superior cervical ganglion and the entire brain during unilateral electrical stimulation of the cervical sympathetic trunk in the urethane‐anesthetized rat. Stimulation of the cervical sympathetic trunk increased glucose utilization in the ipsilateral superior cervical ganglion (+95%) but did not produce side‐to‐side differences in glucose utilization in any of the brain structures examined in this study. Compared to the control nonstimulated animals, the rate of glucose metabolism in the pineal gland was increased 71% following stimulation of the cervical sympathetic trunk. The pineal gland was the only brain region out of 87 structures examined in which glucose utilization was increased by electrical stimulation of its sympathetic innervation.
Effect of Pinealectomy on Testosterone, Estradiol‐17β, Esterone, and 17α‐ Hydroxyprogesterone Levels During the Annual Reproductive Cycle in the Freshwater Catfish, Clarias batrachus
Authors: Nayak P. K. , Singh T. P.
Published: February 2007

The present study examines the relationship of the pincal gland to gonadal activity during the annual reproductive cycle in the freshwater catfish Clarias batracbus. The hormonal profiles of testosterone, estradiol‐17β, estrone, and 17α‐hydroxyprogesterone along with the gonadosomatic index (GSI) were monitored to assess the effect of pinealectomy. Pinealectomy appeared to accelerate the gonadal development from January to May. Removal of pineal prior to the start of gonadal recrudescence (January and February), induced initiation of ovarian recrudescence earlier than scheduled in nature. On the other hand pinealectomy during the vitellogenic phase (May to June) reduced the gonadal activity, suggesting the stimulatory role of pineal on gonads. During the remaining period of July to December (postvitellogenic and early resting phase) pinealectomy had no effect on gonadal activity. Thus, in this species the pineal gland during the annual reproductive cycle appears to have either inhibitory, stimulatory, or no effect on gonadal physiology depending upon the sexual conditions.
Corpus Luteum Progesterone Secretion in Rats Undergoing Pineal‐Mediated Reproductive Regression
Authors: Sánchez‐Criado José E. , Guisado R.
Published: February 2007

In nonseasonal breeders, such as the laboratory rat, the potentiation of the antigonadal action of light deprivation by olfactory bulbectomy is manifested, among other things, by a diminished secretion of testosterone in males and estradiol in females. Little is known about the actions of the pineal gland on progesterone secretion. Since secretion of the luteotrophic hormones (LH and PRL) decreases in blind‐anosmic rats and because the rat corups luteum exhibits different degrees of LH and/or PRL dependency, the purpose of these experiments was to study the corpus luteum progesterone secretion in both pseudopregnant and pregnant blinded‐bulbectomized rats. Female rats blinded and bulbectomized at the age of 25 d showed at adulthood (75 d old) (1) estrous cycles longer than the regular 4–5 d in length exhibited by intact rats: 82.3 vs. 9.0% (P < .01); (2) a decreased paired ovarian weight, 24.1 ± 3.7 (nine) vs. 37.3 ± 2.2 (ten) mg/100 gm BW (P <.05), and lower plasma levels of LH on metestrus: 15.9 ± 1.7 vs. 26.2 ± 3.4 ng/ml (P < .01). Pinealectomy, as previously reported, completely reversed the effects of dual sensory deprivation. In contrast to the clear antigonadal action of the pineal gland, which seems to affect the follicular component of the ovary through modifications in the rate of LH secretion, the production of progesterone by the corpus luteum remained almost unaffected. Although the duration of the diestrous phase in both pseudopregnancy and pregnancy was significantly longer in blind‐anosmic rats than in intact ones (P < .01), the serum levels of progesterone throughout both corpus luteum phases were identical. In summary, this study shows that even in spite of strong antigonadal actions, the corpus luteum, once formed, expresses its autonomy and independence of pituitary by maintaining normal capacity for the secretion of progesterone.
Cyclic Nucleotide Metabolism in Pineal Homogenates
Authors: Sweat B. F. W. , Carmack C. F. , Jewell L. S.
Published: February 2007

Adenylate cyclase (AC) in pineal paniculate fractions from rabbit, rat, cow, and the vole Microtus montanus was stimulated by L‐norepinephrine (NE) and L‐isopro‐terenol (ISO). NE stimulation of rabbit and bovine pineal AC was biphasic, with a plateau between 0.01 μM and 1.0 μM and additional stimulation by NE above 1.0 μM. Stimulation by different ISO concentrations gave a typical hyperbolic curve, and optimal stimulation by ISO exceeded that by NE.

Melatonin decreased ISO and NE stimulation of AC 10–20%. Although α‐ad‐renergic agonists increase β‐agonist‐mediated adenosine‐3′, 5′‐cyclic monophosphate (cyclic AMP) accumulation in intact pinealocytes, similar amplification of AC stimulation was not seen with broken‐cell preparations.

Most (60–70%) pineal guanylate cyclase (GC) was recovered in supernatant fractions after centrifugation of homogenates at 110,000 × g; this soluble GC was unaffected by potential agonists. Low concentrations (0.01–1 nM) of NE, ISO, and phenylephrine (PE) stimulated GC in impure and purified membrane fractions, but each inhibited at concentrations above 10 μM. All concentrations of ISO and NE inhibited GC in the presence of the a‐agonist PE. Melatonin alone did not affect particulate GC, but L‐ISO stimulation was not seen in the presence of equivalent concentrations of melatonin.

The in vitro data are consistent with both α‐ and β‐receptor regulation of cyclic nucleotide metabolism in pinealocytes. Endogenous NE may differentially regulate cyclic AMP and guanosine‐3′, 5′‐cyclic monophosphate (cyclic GMP) in pineal; low NE concentrations that stimulate GC have only a slight effect on AC, but higher NE concentrations that inhibit GC maximally stimulate AC. Particulate GC and AC also were resolved by equilibrium centrifugation, to give several discrete peaks of enzyme activity. The results support the existence of several forms of AC and GC, which have different responses to adrenergic agonists.
Influence of Age on August Levels of Pineal Immunoreactive Arginine Vasotocin in Rats
Authors: Prechel M. Margaret , Audhya Tapan K. , Simmons William H.
Published: February 2007

The present study was undertaken to evaluate carefully the influence of age on physiological levels of arginine vasotocin‐like peptide in rat pineal glands. Glands were collected from male and female rats aged 13, 33, 53, and 73 days on August 4, 12, and 19, 1984. Individual extracts were assayed for arginine vasotocin (AVT) by radioimmunoassay. The results confirm our previous observation that rat pineal AVT immunoactivity (iAVT) increases significantly during August each year; and in this study, each group of rats reached the same peak level of iAVT (700–750 pg/gland) regardless of age or gender. Thus we do not confirm a previously reported decrease in AVT activity with age. In our studies thus far, season of the year is the physiological variable with the most significant influence on pineal AVT activity levels.
Changes in Immunoreactivity in S‐Antigen‐Induced Pinealitis
Authors: Das Noveen D. , Yoshioka Toru , Shichi Hitoshi
Published: February 2007

Changes in immunoreactivity in rat pineal gland were investigated in S‐antigen (S‐Ag)‐induced pinealitis. Anti‐S antibodies were used to study the accessibility of pathogenic epitopes in the organ, and phosphatidyl inositol 4, 5‐bisphospate (PI[4,5]P2) antibodies were chosen to study changes in functional phospholipid in membranes. Control pineal gland (without inflammation) did not show much reactivity toward these antibodies. Immunoreactivity toward both antibodies was markedly increased throughout the organ at the peak of inflammation and decreased almost to control level in the postinflammatory stage. The rise and fall of immunoreactivity were attributed to changes in the accessibility of antigenic sites rather than changes in the amounts of S‐Ag and P(4, 5)P2 The transient enhancement in immunoreactivity, probably consequential to tissue damage, suggests that the pineal gland, unlike the retinal photoreceptors, is capable of quick repair of tissue.
Cytochemical Demonstration of Lysosomes in the Chicken Pineal Gland: Changes Induced by Light‐Dark Cycle
Authors: Matsuo Shinichi , Ohshima Koji
Published: February 2007

Light and electron microscopic demonstrations for acid phosphatase (AcPase) activity in the chicken pineal gland were studied with special reference to the changes induced by the light—dark cycle. AcPase‐positive lysosomes and Golgi cisternae and vesicles located in the pinealocyte in the light period are well developed and more numerous than in the dark period. In a few cases, a type of lysosome wrapping mechanism is present in the pinealocyte during the light period. Therefore, the lysosomes in the chicken pinealocyte appear active during the light period. In addition, the lysosomes may have functional relationships with the lipid‐like inclusions seen in the dark period.
Melatonin, Serotonin, 5‐Hydroxyindole‐3‐Acetic Acid and N‐Acetyltransferase in the Pineal of the European Hamster (Cricetus cricetus) Kept Under Natural Environmental Conditions: Lack of a Day/Night Rhythm in Melatonin Formation in Spring and Early Summer
Authors: Pévet P. , Vivien‐Roels B. , Masson‐Pévet M. , Steinlechner S. , Skene D. , Canguilhem B.
Published: February 2007

In female European hamsters killed in spring and early summer, pineal melatonin content exhibited no day/night rhythm. Absolute levels measured were relatively low, being on the order of daytime levels detected in other hamster species. An absence of day/night changes in the activity of N‐acetyltransferase was also observed. However, a marked rhythm in pineal serotonin (5‐HT) was found, an abrupt large increase being observed at the beginning of the light period. The day /night rhythm of pineal 5‐HIAA content is similar to that of 5‐HT. This absence of rhythm in pineal melatonin formation might mean that in the European hamster it is not melatonin but another substance that is of importance in photoperiodism. An absence of melatonin rhythm, however, could also be simply a peculiar pattern of melatonin production observed at a given period of the year. In this case, melatonin would be able to transduce photoperiodic information in the European hamster, as in other photope riodic species.
Measurement of Tryptophan Hydroxylase Activity in Rat Pineal Glands and Pinealocytes Using an HPLC Assay With Electrochemical Detection
Authors: Sugden David , Grady Richard , Mefford Ivan N.
Published: February 2007

A method for measuring tryptophan hydroxylase activity by assaying the product 5‐HTP using high‐performance liquid chromatography (HPLC) with electrochemical detection is described. A nocturnal elevation (80%) in rat pineal gland tryptophan hydroxylase activity was detected. Experiments on isolated rat pinealocytes with the protein synthesis inhibitor cycloheximide indicate that tryptophan hydroxylase turns over rapidly in these cells. This method will be valuable in studies of the adrenergic mechanisms regulating pineal tryptophan hydroxylase activity.
Effects of Melatonin and Hypothyroidism on Somatomedin Levels of Female Syrian Hamsters
Authors: Vriend Jerry , Sheppard M. Suzanne , Bala R. Marvin
Published: February 2007

Female Syrian hamsters maintained on a 14 h light, 10 h dark photoperiod were injected once daily (1–2 h before lights out) with melatonin (25 μg), alone or in combination with thiourea, or with thiourea plus thyroxine. Serum levels of the somatomedin, Insulin‐like growth factor‐I (IGF‐I), were significantly reduced by thiourea as well as by melatonin administration. These data suggest that in the female hamster melatonin‐induced reduction of circulating IGF‐I depends largely on a reduction in circulating levels of thyroid hormones. However, melatonin‐induced changes in secretion of thyroid hormones, gonadal hormones, and hypothalamic hormones could contribute to decreased growth hormone (GH)‐stimulated somatomedin secretion.
Melatonin‐Induced Suppression of Human Lymphocyte Natural Killer Activity in Vitro
Authors: Lewiński A. , Zelazowski P. , Sewerynek E. , Zerek‐Mełeń G. , Szkudliński M. , Zelazowska E.
Published: February 2007

One of the important immune functions influenced by neuroendocrine factors is natural killer (NK) activity, which is directed against neoplastic and virus‐infected cells. The effects of melatonin (Mel) and N‐acetylserotonin (NAc‐5HT) on NK activity of human peripheral blood lymphocytes were investigated. Leukocytes of healthy human subjects were used in the experiment. NK activity was estimated by measurement of radioactive chromium (51Cr) release from human leukemia cells K 562 (target cells). The previous exposure of human lymphocytes (effector cells) to Mel in concentrations of 10−6 M and 10l0 M resulted in an inhibition of NK activity (P < 0.01) for all the examined effector‐target cell ratios (10:1; 20:1, 40:1). NK activity was also suppressed by Mel (108 M), but only if effector‐target ratio equal to 20:1 was used (P < 0.02), and by Mel (10−12 M) for effector‐target ratio equal to 40:1 (P < 0.05). In none of the examined concentrations did NAc‐5HT inhibit NK activity of human lymphocytes. On the basis of the data reported above, a direct suppressive effect of Mel (but not of NAc‐5HT) on NK activity of human peripheral blood lymphocytes can be assumed.
Retracted: 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.
Diurnal Changes in Serum Melatonin Concentrations Under Indoor and Outdoor Environments and Light Suppression of Nighttime Melatonin Secretion in the Female Japanese Monkey
Authors: Nozaki Masumi , Tsushima Mikako , Mori Yuji
Published: February 2007

To examine whether artificial light with the intensity commonly used for animal experimentation can mimic natural sunlight with respect to diurnal changes in serum melatonin, and to determine the minimum light intensity required to suppress nocturnal melatonin, serum melatonin profiles were examined in groups of female Japanese monkeys (Macaca fuscata fuscata). Under outdoor environment, light intensities at the level of the monkey's eyes varied during daytime (0900–1500 h) depending on weather conditions (minimum and maximum on particular experimental days: 170 lux at 0900 h on a rainy day and 9500 lux at 0900 h on a slightly cloudy day); under indoor environment, light was provided by ordinary fluorescent bulbs that resulted in intensities of 400–500 lux at the level of monkey's eyes. No difference was found in diurnal changes in serum melatonin concentrations regardless of weather or housing conditions: Serum melatonin remained low during daytime and increased during nighttime. Following exposure to light, irradiances of 10,000, 400‐500, 100‐140, 50‐100, and 10‐30 lux at midnight resulted in a rapid decrease in serum melatonin to daytime levels within 1 to 2 h. After the onset of dark, serum melatonin reverted to previous nighttime levels within 2 h. Exposure to a light irradiance of 2–5 lux, however, did not suppress nocturnal melatonin secretion. It is concluded that artificial light can mimic natural sunlight with respect to melatonin secretion in the female Japanese monkey, and that light of 10‐30 lux irradiance was sufficient to suppress serum melatonin to near daytime levels.
Determination of Pineal Melatonin by High‐Performance Liquid Chromatography With Electrochemical Detection: Application for Rhythm Studies and Tissue Explants
Authors: Hernandez Guadalberto , Abreu Pedro , Alonso Rafael , Calzadilla Carlos H.
Published: February 2007

High‐pressure liquid chromatography with electrochemical detection has been used for the determination of melatonin in rat pineal glands and tissue explants. Rat pineal melatonin content was measured at 2‐hr intervals during a 2.t‐hr period by direct injection of supernatants from centrifuged pineal homogenates into a reversed‐phase C18 column. The lower limit of sensitivity was 32 pg per gland for a 2:1 signal‐to‐noise ratio, which allows melatonin measurements during daytime. Both absolute values and circadian rhythmicity obtained with the present method are in agreement with previously validated rddioimmunoassays. In addition, isoproterenolinduced release of melatonin from individual rat pineal explants was measured after chloroform extraction of the incubation medium.
Sex‐ and Age‐Dependent Nature of the Cytoplasmic 5 α‐Dihydrotestosterone (DHT) Binding Site/Receptor in Bovine Pineal Gland
Authors: Haldar Chandana , Gupta Derek
Published: February 2007

Recent research has justified the presumption that the pineal gland plays a role in the regulation of the gonadal system in mammals. Evidence also exists for androgen receptors in pinealocytes. In the current study, our approach has been to assess the age‐ and sex‐dependent nature of 5α‐DHT receptors in bovine pineal. Although no significant difference was noted between various groups of bulls, cows, peripuberal cows, and calves (male) for pineal weight, the cytoplasmic 5α‐DHT binding site/receptor content in the pineal gland differed significantly. While the males had a low androgen receptor concentration in the pineal (46 fmol/pineal), the females showed the highest (442 fmol/pineal). The peripuberal females without calves and calves (male) presented a 5α‐DHT receptor content in between (225 fmol/pineal; 138 fmol/pineal). When the data were related to unit weight of pineal tissue, the difference still existed. It is suggested that the concentration of cytoplasmic 5α‐DHT receptors reflects the cellular activity and they are inversely related. Further, low cytoplasmic receptors also indicate that most of it is confined to the nuclear sites, as generally suggested for other androgen‐dependent tissues. In the light of these suggestions, it is possible that lowest cytosolic 5α‐DHT receptor concentration in the males, in reality, reflects a higher degree of cellular function and a high concentration of the receptors in the nuclear site. Similarly, the peripuberal cows and calves perhaps have more cellular activity in the pincal than the mature cows. The current investigation, for the first time, by directly estimating the androgen receptors/binding site in the bovine pineal gland, demonstrates the sex‐ and age‐dependent nature.
Development of day‐night rhythmicity in “synaptic” ribbon numbers in the pinealocytes of posthatch chicks kept under either natural photoperiodic conditions or continuous illumination
Authors: Maitra S.K. , Vollrath L.
Published: February 2007

Abstract: Pineal synaptic ribbons (SR) undergo characteristic changes over a period of 24 hr under natural photoperiodic conditions in various vertebrates, being low in number during daytime and elevated at night. During posthatch development of chicks, the rhythmicity of SR numbers is reported to appear at the age of about 2 weeks. Because the influence of external light during the growth phase of chicks on the development of day‐night rhythmicity in SR numbers is unknown, we studied day‐night differences in SR numbers in the pinealocytes of chicks at the posthatch ages of 15, 17, and 19 days; chicks had previously been kept under natural photoperiodic conditions or continuous illumination. Under natural photoperiodic conditions a statistically significant nocturnal (midnight) rise in SR numbers over the value of midday was seen in the pineal of 17‐ and 19‐day‐old chicks, but not in 15‐day‐old chicks. SR numbers in the pinealocytes of continuously illuminated chicks did not show any day‐night rhythmicity on days either 15 or 17, but exhibited significant day‐night differences on day 19 posthatch. These findings suggest that continuous illumination, which is known to dampen circadian rhythmicity of melatonin secretion in the chick pineal, causes a delay, but not a total suppression of the mechanism involved in the ontogenic development of diurnal rhythmicity in SR numbers in the pinealocytes of chicks.
Melatonin and the coding of day length in male Syrian hamsters
Authors: Karp Jonathan D. , Hastings Michael H. , Powers J. Bradley
Published: February 2007

Abstract: Two experiments investigated the response of the pituitary‐gonadal axis of pinealectomized male Syrian hamsters to programmed systemic administration of melatonin. In the first experiment, castrated male Syrian hamsters were housed in a short photoperiod (8L:16D) and maintained on subcutaneous testosterone implants for 7 weeks. These males were then pinealectomized or sham‐pinealectomized and their testosterone capsules removed. Daily infusions of melatonin 250 ng/infusion) or its vehicle were administered for 3 weeks; infusion duration was long (11 or 12 hr) or short (6 hr). Measurement of serum luteinizing hormone (LH) following this 3‐week period indicated that long‐duration melatonin infusions mimicked short‐day conditions (LH levels were low), but short‐duration infusions did not (LH levels were significantly elevated). In the second experiment, pinealectomized, gonadally intact males were housed in a 12L:12D photoperiod and injected once daily with melatonin or its vehicle, either 3 or 5 hr after dark onset for 11 weeks. These times were chosen to coincide with the light: dark cycle phase that according to published reports is optimally responsive to exogenous melatonin for the induction of short‐photoperiodic effects. Melatonin injections did not induce gonadal regression in pinealectomized hamsters. Melatonin and vehicle‐treated males responded similarly; their testis widths and serum testosterone levels were not significantly different at the end of the experiment. These results support the hypothesis that the duration of melatonin secretion each night is an important variable in conveying photoperiodic information, but that the circadian phase during which melatonin is present is not.
Pineal‐gonadal relationship in the teleost Channa punctatus (Bloch): Evidence for possible involvement of hypothalamic serotonergic system
Authors: Joy K.P. , Khan I.A.
Published: February 2007

Abstract: In Channa punctatus, pinealectomy results in an accelerated growth (stimulatory effect) of the ovary in preparatory phase (March), but had no significant effect in prespawning (May‐June) or postspawning (September) phases. Administration of melatonin (25 (μg/fish or 0.4 mg/kg BW at 2‐day intervals for 30 days) inhibits the stimulatory effect of a long photoperiod and high temperature (16L:8D; 22 ± 1°C) on the ovary in the early preparatory phase (February). In the late preparatory phase (April), the administration of both melatonin (0.5 mg/kg BW at 2‐day intervals) and parachlorophenylalanine (pCPA, a serotonin synthesis blocker; 100 mg/kg BW at 3‐day intervals) for 30 days inhibits ovarian activity in comparison to that of the saline‐treated control group. In the dose‐response study, ≥0.5 mg/kg BW of melatonin induced a significant increase in hypothalamic 5‐HT content and ≥10 mg/kg BW of pCPA decreased it significantly. In the time‐course study, melatonin (2.0 mg/kg BW) elevates the 5‐HT content significantly after an hr of the injection and maintained it up to 48 hrs. The administration of pCPA (200 mg/kg BW) had significantly inhibited the 5‐HT content which was sustained for 72 hr. In another study, a single injection of melatonin (0.5 mg/kg BW) increased the 5‐HT content significantly. A single injection of pCPA (100 mg/kg BW) decreased significantly both the content and activity of 5‐HT. It is inferred that hypothalamic 5‐HT may play a central role in photosexual mechanisms and mediate long photoperiodic effects on neuroendocrinereproductive axis.
A phase‐dependent delay of the chick pineal rhythm in rate of thymidine incorporation by brief exposure to aphidicolin
Authors: Wainwright S.D. , Wainwright Lillian K.
Published: February 2007

Abstract: Cultured chick pineal glands show a persistent rhythm in the rate of cumulative incorporation of thymidine into DNA. In this study we have examined the effects of pulse‐exposure to aphidicolin in the dark on the first day of culture on thymidine incorporation during the second and third days of culture in the dark with aphidicolin‐free medium. The phase of the rhythm in the rate of thymidine incorporation was delayed in a concentration‐dependent manner by a 4‐hr exposure to aphidicolin, commencing in the final hour of the photoperiod. This effect was phase‐dependent and not seen when exposure to aphidicolin began earlier in the photoperiod.
The effect of exogenous melatonin on the hypothalamic‐pituitary‐adrenal axis in intact and pinealectomized rats under basal and stressed conditions
Authors: Weidenfeld Y. , Schmidt U. , Nir I.
Published: February 2007

Abstract: The effect of exogenous melatonin on the adrenocortical axis was studied by determining serum corticosteroid and adrenocorticotrophic hormone (ACTH) levels under basal and stressed conditions in intact, pinealectomized, and adrenalectomized mature male rats. A direct interrelationship between pineal/melatonin and the adrenal cortex, dissociated from the hypothalamic‐pituitary axis, was established. Intraperitoneal injection of 100 μg melatonin brought about an elevated adrenocortical response recorded in the serum corticosteroid levels 15 hr afterwards. This effect could be demonstrated only at the beginning of the photophase, when physiological levels of corticosteroids and ACTH are at their lowest daily levels. The pattern of this reaction is different from those caused by stressors such as ether or hypoglycemic reagents, and did not occur in pinealectomized animals although the daily rhythm of corticosteroids and ACTH persisted. No effect on ACTH was evident in intact or adrenalectomized rats, where the serum levels remained unchanged. Moreover, the corticotrophin releasing factor (CRF) content of the median eminence was not affected by melatonin.
Unusual responses of nocturnal pineal melatonin synthesis and secretion to swimming: Attempts to define mechanisms
Authors: Yaga Ken , Tan Dun‐xian , Reiter Russel J. , Manchester Lucien C. , Hattori Atsuhiko
Published: February 2007

Abstract: The effect of swimming at night on rat pineal melatonin synthesis was compared with that of light exposure at night. Rats were forced to swim at 0030 hr (lights out at 2000 hr) and sacrificed by decapitation 15 and 30 min later, immediately after swimming. Other groups of animals were exposed to white light (650μW/cm2) for 15 and 30 min at same time. Swimming caused a rapid and highly significant drop in the melatonin content in the pineal gland; however, the activity of N‐acetyltransferase (NAT), the supposed rate limiting enzyme in the melatonin production, was not changed. Despite the drop in pineal melatonin levels, serum concentrations of the indole remained elevated in the rats that swam. In contrast, melatonin levels in the pineal and serum of light exposed rats fell precipitously, accompanied by a significant suppression of NAT activity. Since we anticipated that the strenuous exercise associated with swimming may induce release of artrial natriuretic peptide (ANP) from the heart, which in turn could cause the release of pineal melatonin, in a second study we injected physiological saline intravenously to stretch the cardiac muscle and release ANP. Three milliliters of normal saline was injected during the day into the jugular vein of anesthetized rats that were pretreated with isoproterenol to stimulate pineal melatonin production. Animals were killed 15 min after the saline injection, and pineal NAT activity and pineal melatonin levels were measured. The saline injections caused no alteration in the elevated levels of either NAT or melatonin. These data suggest that the disparity in pineal NAT activity (which was high) and pineal melatonin (which was low), in animals swum at night, may not be caused by ANP which is released during strenuous exercise such as swimming.
Effects of nightbreak, T‐cycle, and resonance lighting schedules on the pineal melatonin rhythm of the lizard Anolis carolinensis: Correlations with the reproductive response
Authors: Hyde Linda L. , Underwood Herbert
Published: February 2007

Abstract: Experiments were conducted to determine if a correlation exists between any aspect of the pineal melatonin rhythm (such as its duration or phase) in the lizard Anolis carolinensis and the reproductive response to photoperiod. The rhythm of pineal melatonin content was determined in anoles exposed to nightbreak lighting protocols (10L:5D:1L:8D, 10L:10D:1L:3D), resonance lighting cycles (LD 11:13, LD 11:25), and T‐cycle lighting protocols (LD 11:7, LD 11:9, LD 11:13, LD 11:15, LD 11:19) and compared with the testicular response to these lighting protocols as determined previously [Underwood and Hyde, (1990) J. Comp. Physiol. (A) 167:231–243]. Different T‐cycles and nightbreak cycles elicited changes in both the duration of the melatonin peak and the phase of the melatonin peak relative to these light cycles. The response to the resonance cycle (LD 11:25) was complex, probably due to the overlapping patterns of two groups whose pineal melatonin rhythms were entrained approximately 12 hr out of phase with each other. No correlation was observed between the duration, or the amplitude, of the nocturnal melatonin peaks seen on the various light cycles and the reproductive response to these cycles. A correlation was observed between the phase of the pineal melatonin rhythm and the reproductive response. Light cycles were inductive (stimulated testicular growth) when the entrained melatonin rhythm peaked near the light‐to‐dark or the dark‐to‐light transition, but they were not inductive when the melatonin rhythm peaked during the middle third of the night. These results suggest that if melatonin is involved in the transduction of photoperiodic information in Anolis, neither the duration nor amplitude of the nocturnal melatonin pulse is involved in the measurement of day length. Instead, the phase‐relationship of the melatonin rhythm to the rest of the circadian system may determine photoperiodic responsiveness.
Effects of melatonin treatment on the gonadotropin‐releasing hormone neuronal system and on gonadotropin secretion in male mink, Mustela vison, in the presence or absence of testosterone feedback
Authors: NToumi F. , Martinet L. , Mondain‐Monval M.
Published: February 2007

NToumi F, Martinet L, Mondain‐Monval M. Effects of melatonin treatment on the gonadotropin‐releasing hormone neuronal system and on gonadotropin secretion in male mink, Mustela vison, in the presence or absence of testosterone feedback. J. Pineal Res. 1994: 16: 18–25.

The effects of subcutaneous melatonin capsules on the gonadotropin‐releasing hormone (GnRH) immunoreactive (ir) system and the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) have been tested in intact, castrated, and castrated adult male mink supplemented with testosterone. Animals were transferred in July, i.e., during the period of sexual rest, under a daily light: dark cycle of 16‐hr light and 8‐hr darkness and studied over 13 weeks. GnRH (ir) perikarya, visualized by immunocytochemistry, were counted on serial coronal sections from the diagonal band of Broca to the infundibulum. Serum FSH and LH concentrations were measured by radioimmunoassay. In intact mink, melatonin induced a significant increase in the number of (ir) perikarya and in FSH and LH concentrations 3 and 8 weeks, respectively, after melatonin capsule implantation. In castrated mink, the number of perikarya and the concentrations of FSH, which had increased within 2 weeks after castration, did not change during melatonin treatment. In contrast, the concentrations of LH, which were not altered by castration, increased 3–6 weeks after the onset of melatonin administration, suggesting a stimulation of GnRH release. In castrated testosterone‐treated mink, the number of perikarya was increased as in castrated males, but the elevation of FSH in response to castration was prevented. Within 2 weeks after melatonin capsule implantation, the concentrations of FSH decreased while those of LH remained low, indicating an inhibition of GnRH release. These results show that testosterone modulates the effect of melatonin on the activity of the GnRH–gonadotropin system.
Different patterns of light exposure in relation to melatonin and Cortisol rhythms and sleep of night workers
Authors: Koller Margit , Härma Mikko , Laitinen Jarmo T. , Kundi Michael , Piegler Brigitte , Haider Manfred
Published: February 2007

Koller M, Harma M, Laitinen JT, Kundi M, Piegler B, Haider M. Different patterns of light exposure in relation to melatonin and Cortisol rhythms and sleep of night workers. J. Pineal Res. 1994: 16: 127–135.

There is strong evidence to suggest that circadian psychophysiological adaptation processes are modified by light, depending on its intensity and timing. To characterize such modifications and determine whether they are associated with an alteration in the day/night pattern of melatonin excretion, measurements were obtained around the clock in 14 permanent night workers, each studied over a 48 hr period in the field. The light exposure behavior of these workers was studied with a newly developed light dosimetry by measuring light intensity at eye level. Physical activity was continuously registered and sleep indices were obtained by sleep logs and activity markings. Circadian rhythms of melatonin and Cortisol were analysed from salivary samples collected for 24 hr at 2 hr intervals. The inter individual variation of melatonin acrophase determined by cosinor analysis was greater than 180 degrees (from around midnight to noon) and that of Cortisol was about 135 degrees (from early morning to afternoon). Hormonal phase positions coincided significantly with light exposure: the more bright light pulses in the morning (maximum lux between 0600 and 0900), the less were the melatonin and Cortisol acrophases shifted into the day. There was also a negative correlation between melatonin acrophase shift and duration of the overall light exposure above 1500 lux. Morning light maximum and sleep onset correlated highly significantly. Night workers were divided into those with less than (‘non‐shifters’, n = 9) and more than 6 hr deviation from midnight (‘shifters’, n = 5) of the melatonin acrophase. The group comparison revealed a marked difference of the mean melatonin concentrations at night, and at 0700. Shifters did not experience bright light exposure in the morning and showed a tendency towards shorter overall exposure of light above 1500 lux. In conclusion, light avoidance behavior during morning hours, as observed in 5 out of 14 night workers, coincided significantly with a phase delay of melatonin acrophase. Light avoidance also correlated with an earlier sleep onset and a tendency to longer sleep hours. Thus our data suggest that the interaction of a phase shifted activity cycle and the light/dark exposure leads in the field situation to different degrees of adaptation to the prevailing activity/rest requirements, depending on dose and phase position of bright light exposure.