bluuebunny/crossref_metadata_2025 huggingface dataset:
Administration of melatonin into the mediobasal hypothalamus as a continuous or intermittent signal affects the secretion of follicle stimulating hormone and prolactin in the ram
Authors: Lincoln G.A.
Published: February 2007

Abstract: The biological effects of administering melatonin into the mediobasal hypothalamus (MBH) was documented in adult Soay rams using two delivery systems: (1) microimplants in the MBH delivering melatonin continuously and (2) microdialysis probes in the MBH delivering melatonin intermittently as a daily timed infusion. The experimental protocol was to precondition rams to long days (LD 16:8) for 10 to 12 weeks, and then introduce the exogenous source of melatonin by implantation or infusion. Sixteen rams were divided equally into four treatment groups: (a) microimplants in the MBH, (b) microdialysis probes in the MBH, (c) empty microimplants in the MBH to act as sham‐operated controls, and (d) no surgery to act as unoperated controls. The microimplants consisted of 22‐gauge stainless steel cannulae with melatonin fused inside the tip and were placed bilaterally in the brain for 14 weeks. These implants had previously been shown to release melatonin at a relatively constant rate when incubated in buffered saline at 37°C (3.42 ± 0.42 μg/24 hr, mean ± SEM, 1–10 weeks) and to produce a localised concentration of melatonin when implanted in the brain (localised to within 1 mm of the center of the implant). The microdialysis probes were also 22‐gauge cannulae with a 3 mm membrane (Biotech). They were placed bilaterally into the MBH, connected to two portable syringe drivers secured to a backpack. Melatonin was infused daily for 10 hr (estimated delivery: 0.5 μg/hr) starting in the mid‐light phase to produce a long‐duration intermittent melatonin signal. Technical problems limited the period of infusions to 8–10 weeks with minor interruptions. Animals from all groups were maintained on long days, and the observations extended for a period of 28 weeks. The melatonin implants placed in the MBH induced a premature increase in the blood concentrations of FSH and growth of the testes. This treatment also induced a marked decrease in the plasma concentrations of prolactin and the earlier development of the long winter pelage. These changes were reversed after the end of treatment with a decline in the plasma concentrations of FSH and regression of the testes, and an increase in the concentrations of prolactin and moult of the winter pelage. Daily infusions of melatonin from the microdialysis probes in the MBH produced qualitatively similar, but less marked responses. The overall results illustrate that the administration of melatonin into the MBH, either continuously or intermittently, to extend the duration of the daily melatonin signal, induces multiple short‐day responses. The dialysis technique provides a potential way to investigate the mechanism of action of melatonin since it is possible to simultaneously administer melatonin and sample dialysate from the brain.
Coexpression of vimentin and glial fibrillary acidic protein in glial cells of the adult rat pineal gland
Authors: López‐Munoz Francisco , Calvo Jose Luis , Boya Jesus , Carboneil Angel L.
Published: February 2007

Abstract: In the present work, coexpression of vimentin (VIM) and glial fibrillary acidic protein (GFAP) is demonstrated in the glial cells of the adult rat pineal gland. Serial consecutive Epon semithin sections (0.5 μm thick) were alternately immunostained for VIM and GFAP. GFAP positive cells and processes were found in the proximal region of the pineal gland, near the pineal stalk. Most of these cells were also immunostained for VIM in adjacent semithin sections. The significance of the coexpression VIM‐GFAP and the restricted location of GFAP positive cells is discussed in relation with the maturation of pineal glial cells.
High affinity specific binding of 2‐[125I]iodomelatonin by spleen membrane preparations of chicken
Authors: Pang C.S. , Pang S.F.
Published: February 2007

Abstract: The binding sites for 2‐[125I]iodomelatonin in chicken spleens were characterized. The binding was rapid, stable, saturable, reversible, and of high affinity. Both melatonin and 6‐chloromelatonin strongly inhibited the binding. The dissociation constant (Kd) obtained from the Scatchard analysis was 31.4 ± 5.19 pmol/1 (3‐weeks old, n = 4), which was in good agreement with the Kd (50.6 pmol/1) calculated from the kinetic study. The maximum number of binding sites (Bmax) was 1.09 ± 0.11 fmol/mg protein (3‐weeks old, n = 4). Twelve 11‐week‐old chicks were killed in two groups at mid‐light or mid‐dark. Saturation studies indicated no significant difference (P > 0.05) in the Kd between mid‐light (42.1 ± 3.9 pmol/1) and mid‐dark (31.6 ± 4.9 pmol/1). The maximum number of binding sites (Bmax) at mid‐light and mid‐dark were 1.52 ± 0.16 and 1.35 ± 0.08 fmol/mg protein, respectively, with no significant variation (P > 0.05) recorded. However, when the whole spleen was taken into consideration, the Bmax per spleen protein of the mid‐light samples (253 ± 36 fmol/spleen protein) was significantly greater than that (129 ± 16 fmol/spleen protein) of the mid‐dark samples (P < 0.05). This indicated that in our study a diurnal rhythm of the total number of 2‐[125I]iodomelatonin binding sites might exist in the chicken spleen.
Prolonged suppression of serum concentrations of melatonin in prepubertal heifers
Authors: Buchanan Brent A. , Chapin Larry T. , Tucker H. Allen
Published: February 2007

Abstract: Our objective was to suppress the daily surge of melatonin in serum of prepubertal dairy heifers by manipulating intensity of light (Experiment 1) and duration of exposure to light (Experiment 2). Heifers in Experiment 1 were exposed to either 12 hr of darkness (000 lux, control), or 400, 800, or 1,200 lux of light during the last 6 hr of their usual 12‐hr nocturnal period. During this 6‐hr exposure to various intensities of light, melatonin concentrations were similar to their respective daytime baseline values measured under 400 lux of light, but were 62% to 82% lower than melatonin concentrations during their nocturnal surge period. Suppression of melatonin concentrations was similar between 400 and 1,200 lux of light. In Experiment 2, heifers were exposed to LD 8:16, LD 16:8, LD 20:4, or LD 24:0 photoperiods (1,200 lux) for 4 months. Throughout treatment, concentrations and durations of the melatonin surge were suppressed in the LD 24:0 group and were greatest (during the nocturnal period) in the LD 8:16 group. Concentrations of prolactin in serum were elevated in animals under long days relative to LD 8:16 treatment and respective pretreatment periods. In conclusion, continuous light at an intensity of 1,200 lux suppressed the nocturnal surge of melatonin, but increased secretion of prolactin for at least 4 months in prepubertal heifers.
Effects of pinealectomy on wool growth and wool follicle density in Merino sheep
Authors: McCloghry Elizabeth , Foldes Andrew , Hollis David , Rintoul Allan , Maxwell Colin , Downing Jeff , Baker Peter , Kennedy John , Wynn Peter
Published: February 2007

Abstract: There is evidence to indicate that pinealectomy may enhance wool growth in the sheep. The aim of this study was to determine the effect of pinealectomy on wool growth and wool follicle density in Merino sheep.

Castrated Merino rams (4 months old) were either pinealectomized (P), sham‐pinealectomized (S) or not treated (C). Wool growth on mid‐side patches was measured every 4 weeks and follicle density was monitored in skin biopsies collected before treatment and at regular intervals for 60 weeks. Venous blood samples were taken on each of these occasions for prolactin analysis. Melatonin concentrations were determined in venous blood collected pre‐ and posttreatment from samples taken over a 24‐hr period during the winter solstice.

Pre‐ and posttreatment plasma melatonin levels (mean ± SEM) 65 ± 17 and < 13 pg/ml for P, 86 ± 21 and 69 ± 20 pg/ml for S, and 94 ± 41 and 122 ± 37 pg/ml for C, respectively, indicated that the pineal glands had been successfully removed. Wool growth, total follicle density and liveweight (mean ± SEM) did not differ between treatment groups. Measurements at week 60 were 3.9 ± 0.3, 4.1 ± 0.2, and 3.8 ± 0.3 gm clean wool/100 cm2; 66 ± 6, 69 ± 7, and 64 ± 3 follicles/mm2; and 50.4 ± 1.3, 50.8 ± 1.4, and 52.6 ± 1.1 kg liveweight for groups P, S, and C, respectively. There was no difference in plasma prolactin levels between the groups during the experiment (P:179 ± 37, S:183 ± 37, C.189 ± 37 ng/ml), but the expected seasonal prolactin rhythm was absent in all animals. These results indicate that the removal of endogenous pineal hormones by pinealectomy has no effect on wool growth and wool follicle density in Merino lambs.
Inhibitory influence of late afternoon melatonin injections and the counter‐inhibitory action of melatonin‐containing pellets on thyroid growth process in male Wistar rats: Comparison with effects of other indole substances
Authors: Wajs Ewa , Lewiski Andrzej
Published: February 2007

Abstract: Previous studies performed in our laboratory indicated that melatonin, when adminstered in late afternoon (1600–1800) as s.c. injections for 10 days, exerted an inhibitory effect on thyroid growth in mice and Sprague‐Dawley rats. The goal of the present study was to examine the effects of melatonin and other indole substances (5‐methoxytryptophol, N‐acetylserotonin, 6‐methoxytryptamine), administered for 10 days, for either 4, 8, or 10 weeks, on thyroid growth processes in adult male Wistar rats. We have also compared the action of melatonin administered in late afternoon as s.c. injections with effects of the melatonin‐released chronically from s.c. implanted beeswax pellets containing 1 mg of the hormone. Additionally, the effects of melatonin injections in animals with the pineal gland removed and in thyroid stimulating hormone (TSH)‐injected rats have been studied. We examined the mean mitotic activity rates (MMARs) of thyroid follicular cells (TFC) and the wet thyroid weights. We concluded that melatonin, of the examined substances, is the most potent inhibitor of thyroid growth; the hormone reduced the MMAR of TFC and the thyroid weight at all time‐points. 5‐Methoxytryptophol, like melatonin, exerted the inhibitory influence on the mitotic activity; however, it did not affect thyroid weight. The influence of other indole substances was much less pronounced. It was shown that melatonin‐pellets prevented the inhibitory effect of late afternoon melatonin injections on thyroid growth processes. This observation is consistent with results of other authors concerning the counter‐antithyroid effect of melatonin on thyroid hormone secretion. Pinealectomy revealed the stimulatory effect on thyroid growth processes, while melatonin treatment reversed the effect of the surgery. Melatonin suppressed the stimulatory effect of TSH on the thyroid growth.
Thyroxine 5'‐deiodinase type II activity in chick pineal and Harderian gland: Nyctohemeral rhythmicity and its regulation by noradrenergic input
Authors: Rubio A. , Menendez‐Pelaez A. , Reiter R.J.
Published: February 2007

Abstract: Circadian rhythmicity of type II thyroxine 5′‐deiodinase (5′‐D) activity was studied in the pineal gland and Harderian glands of chicks. Only Harderian 5′‐D activity showed a nyctohemeral rhythmicity with a maximal peak during the day time (1300), while no rhythm of enzyme activity was found in the pineal gland. Besides type II 5′‐D activity, we found high basal levels of the type I isoenzyme in both glands; this activity was specifically suppressed by the addition of 6‐n‐propyl‐thiouracil (PTU). However, day‐night differences in Harderian 5′‐D activity were maintained even after the addition of PTU. This activity was not affected for either continuous light exposure or darkness during the day. 5′‐D activity seems to be regulated by the noradrenergic input, since the enzymatic activity was stimulated by a β‐adrenergic agonist, isoproterenol, and by the α‐adrenergic agonist, phenylephrine, in both pineal and Harderian glands. Both drugs affected 5′‐D activity in the Harderian gland by stimulating the enzyme activity over basal levels.
Response of rat pineal melatonin to calcium, magnesium, and lithium is circadian stage dependent
Authors: Zhao Zi‐Yan , Touitou Yvan
Published: February 2007

Abstract: Herein we documented the response of pineal melatonin production to electrolytes known to be effective on pineal function in view of a possible circadian stage dependence. We studied the release of melatonin by perifused rat pineal glands at 2 different circadian stages corresponding to the middle of the light and dark periods, i.e., respectively, 7 and 19 HALO (Hours After Light Onset, L:D = 12:12). The initial efflux rates were, as expected, much higher in the perifusates of glands removed from rats sacrificed during the dark phase than of those removed during the light phase. After 3 hr of perifusion, melatonin release reached similar levels which were found constant up to the 8th hr of perifusion, whatever the circadian stage. Perifusion of the glands with physiological concentrations for the rat of calcium (5.2 mmol/1) and magnesium (1.34 mmol/1) resulted in a stimulatory effect on the pineal glands removed from rats sacrificed in the middle of the dark period (19 HALO), whereas no effects were observed on the pineal glands removed from rats sacrificed during the light (7 HALO). Lithium (0.28 and 0.55 mmol/1) was ineffective on melatonin release in pineal glands removed 7 and 19 HALO. Our results show differences in the initial efflux rates of melatonin and in the response of perifused pineal glands to calcium and magnesium according to the circadian stage.
Melatonin and photoperiodic time measurement: Seasonal breeding in the sheep
Authors: Matthews Colin D. , Guerin Michael V. , Deed Jim R.
Published: February 2007

Abstract: Well‐established circadian physiology supports the view that photoperiodic time measurement utilizes the coincidence between the presence of light and a photosensitive phase of a 'biological clock' to alter reproductive status—the so‐called external coincidence model of seasonal breeding. In this review, we examine the mechanism whereby photoperiod interacts with presumed suprachiasmatic nuclei activity to allow endogenous melatonin to normally synchronize reproductive activity to the optimal time of year. The Romney Marsh sheep is particularly explored as an experimental model. It is suggested that the on/off activity of seasonal reproduction may be a robust mechanism able to be predictably manipulated by the judicious use of the light/dark cycle and exogenous melatonin, but firmly based on circadian principles.
Effect of magnetic field on pineal gland volume and pinealocyte size in the rat
Authors: Matsushima Shoji , Sakai Yuko , Hira Yoshiki , Kato Masamichi , Shigemitsu Tsukasa , Shiga Yoichi
Published: February 2007

Abstract: Light microscopic observations on the superficial pineal gland of Wistar‐King rats were made to examine whether or not pineal volume and pinealocyte size, expressed as nuclear density, at daytime or nighttime are affected by long‐term exposure to 50 Hz rotating magnetic field (MF) at 5.0 μT. Determinations of pineal volume and pinealocyte size were repeated twice (April and October) during the year. Size of pinealocytes in MF‐exposed and sham‐exposed rats exhibited, in addition to the difference between peripheral and central regions, regional differences in a proximodistal direction; pinealocytes in the distal and middle‐peripheral regions were usually larger than those in the proximal and middle‐central regions at daytime or nighttime. In October, distal and proximal pinealocytes showed significant day‐night changes in size in sham‐exposed rats, but not in MF‐exposed animals. The situations in the two groups were almost reversed in April. Significant day‐night differences were scarcely found in pinealocyte size in the middle region in the two groups. Throughout the study, pineal volume and pinealocyte size in each region were generally the same between MF‐exposed and sham‐exposed rats at daytime or nighttime. The results suggest that pinealocytes in the distal and proximal regions, but not those in the middle region, are affected by MF‐exposure; day‐night differences in sizes of distal and proximal pinealocytes appear in April and disappear in October under the influence of MF. MF may exert an effect on mechanisms controlling day‐night rhythms of pinealocyte size in the rat.
One‐hour exposure to moderate illuminance (500 lux) shifts the human melatonin rhythm
Authors: Laakso Maija‐Liisa , Hätönen Taina , Stenberg Dag , Alila Aino , Smith Sabrina
Published: February 2007

Abstract: Salivary melatonin levels were measured in 12 healthy volunteers in order to determine whether a moderate light intensity, which suppresses the nocturnal rise of melatonin, was able to shift the melatonin rhythm. The samples were collected at 1‐hr intervals under lighting of < 100 lux (experiment 1) or < 10 lux (experiment 2). The control melatonin profiles were determined during the first night. In the second night the subjects were exposed to light of 500 lux for 60 min during the rising phase of melatonin synthesis. The third series of samples was collected during the third night. The mean decrease of melatonin levels by the exposure to light was 56% of the prelight concentrations. The melatonin onset times were delayed significantly (about 30 min) the night after the exposure to light. The melatonin offset times tended to be delayed in experiment 2. The shifts of the melatonin offset correlated positively with the amount of the melatonin suppression. The results suggest that a relatively small and short lasting light‐induced interruption of melatonin synthesis may affect the melatonin rhythm in humans.
An immunohistochemical study of neuropeptide Y in the bovine pineal gland
Authors: Phansuwan‐Pujito Pansiri , Pramaulkijja Sarita , Govitrapong Piyarat , Møller Morten
Published: February 2007

Abstract: An immunohistochemical study of the bovine pineal gland was performed using rabbit polyclonal antibodies raised against neuropeptide Y (NPY) or against the C‐terminal flanking peptide of proNPY (CPON). A large number of NPY/CPON‐immunoreactive (IR) nerve fibers were demonstrated throughout bovine pineal gland. The IR‐fibers were located in the capsule of the gland, usually piercing into the gland together with blood vessels. In the gland itself, the fibers wen also located intraparenchymally between the pinealocytes. Within the rostral and caudal areas of the pineal stalk, NPY‐IR fibers were also observed, and these fibers could be followed not only into the gland bul also to the habenular and posterior commissures. The morphological localization of the NPY‐IR nerve fibers in the bovine pineal gland indicate that the majority of fibers originate from the superior cervical ganglion. However, some fibers probably originate from the brain itself.
Pharmacological profile and diurnal rhythmicity of 2‐[125I]‐iodomelatonin binding sites in murine mammary tissue
Authors: Recio J. , Mediavilla M. D. , Cardinali D. P. , Sánchez‐Barceló E. J.
Published: February 2007

Recio J, Mediavilla MD, Cardinali DP, Sánchez‐Barceló EJ. Pharmacological profile and diurnal rhythmicity of 2‐[125I]‐iodomelatonin binding sites in murine mammary tissue. J. Pineal Res. 1994: 16: 10–17.

Recent studies demonstrated that melatonin treatment decreased the growth of mammary glands in pubertal and pregnant mice. In vitro, melatonin inhibited murine mammary gland growth at μM concentrations and increased it at pM concentrations. Melatonin‐induced changes of cyclic nucleotide synthesis was also demonstrated in mammary gland slices in vitro. The objective of the present study was to assess the possible existence of specific binding sites for melatonin in murine mammary gland by using 2‐[125I]‐iodomelatonin as a probe. The specific binding of 2‐[125I]‐iodomelatonin to murine mammary gland membranes was rapid, saturable, and reversible, showed an affinity in the low nM range, and displayed time, temperature, and pH dependence. Scatchard analysis indicated the existence of a single class of binding sites that exhibited a diurnal rhythmicity in affinity (Kd) and receptor density (Bmax). A maximum in Bmax (267 ± 42 fmol/mg protein) was found at the light period, while affinity was maximal during darkness (Kd= 1.33 ± 0.22 nM). In competition studies dopamine and dopamine‐related agents, as well as 6‐hydroxymelatonin and serotonin, but not melatonin, effectively displaced 2‐[125I]‐iodomelatonin from mammary binding sites. The results demonstrated a specific binding of 2‐[125I]‐iodomelatonin to murine mammary glands, with affinity in the low nM range, and a pharmacological profile that differed from that reported for 2‐[125I]‐iodomelatonin acceptor sites in other tissues.
Melatonin rhythms in Arctic urban residents
Authors: Stokkan K.‐A. , Reiter R. J.
Published: February 2007

Stokkan K‐A, Reiter RJ. Melatonin rhythms in Arctic urban residents. J. Pineal Res. 1994: 16: 33–36.

The 24‐hr rhythm of salivary melatonin was measured in persons living in the city of Tromsø (70°N) at the following times of the year: in January at a day length of 2 hr of twilight, in June under continuous sunshine, and in March and September at about 12 hr light and 12 hr darkness. The hormone patterns varied widely between individuals, but, in general, they were consistent within most individuals between the seasons. Highest peak values occurred in January when the mean level was also significantly higher than at any other time of year. The lowest mean levels occurred in June. Although individual rhythms were not always apparent, the mean patterns showed significantly elevated melatonin concentrations during the night at all seasons. The June melatonin peak was similar to that in March and September, but appeared to be phase‐delayed with increased melatonin concentrations from midnight until 0900. It is assumed that the delayed melatonin peak in June may be associated with a tendency among people to shift their activity/rest rhythm and that the pineal sensitivity to light is reduced in the morning in summer.
Distribution of cholinergic and dopaminergic receptors in rainbow trout pineal gland
Authors: Samejima Michikazu , Happe H. Kevin , Murrin L. Charles , Pfeiffer Ronald F. , Ebadi Manuchair
Published: February 2007

Samejima M, Happe HK, Murrin LC, Pfeiffer RE, Ebadi M. Distribution of cholinergic and dopaminergic receptors in rainbow trout pineal gland. J. Pineal Res. 1994: 16: 37–43.

The involvement of multiple receptors in modulating the function of the pineal gland was investigated by searching for dopaminergic and cholinergic receptors in trout pineal gland. Dopamine D1 and D2 receptors were measured using [3H]SCH23390 and [3H]spiperone, respectively. Muscarinic and nicotinic cholinergic receptors were measured using quinuclidinyl benzilate ([3H]QNB) and [3H]methylcarbamyl choline, respectively. High‐affinity choline uptake sites were measured using [3H]hemicholinium‐3. The distribution of dopaminergic receptors varied throughout the pineal gland in that the density of D2 receptors, which was higher than that of D1 receptors, was most abundant in the distal region, exhibiting a value of 112 ± 17 fmol/mg tissue. The distribution of both muscarinic and nicotinic receptors was uniform throughout the pineal gland. However, the highest value for the high‐affinity choline transporter (106 ± 17 fmol/mg tissue) occurred in the proximal portion of the trout pineal gland. The results of these studies indicate that the pineal gland should not be viewed as a homogenous tissue possessing identical density of various receptors. Furthermore, these results, along with previous data, are interpreted to suggest that different regions of pineal gland may indeed possess unique functions.
Immunocytochemical localization of basic fibroblast growth factor in the rat pineal gland
Authors: Marin Fernando , Boya Jesús , Calvo José Luis , López‐Muñoz Francisco , Garcia‐Mauriño José Enrique
Published: February 2007

Marín F, Boya J, Calvo JL, López‐Muñoz F, García‐Mauriño JE. Immunocytochemical localization of basic fibroblast growth factor in the rat pineal gland. J. Pineal Res. 1994: 16: 44–49.

The immunocytochemical localization of basic fibroblast growth factor (b‐FGF) during the postnatal development of the rat pineal gland was studied using a polyclonal antibody against the fraction 1–24 of bovine recombinant b‐FGF. Basic FGF immunoreactivity was evident from day 20 after birth in the endothelial cells and perivascular spaces of the gland. Although b‐FGF immunostaining showed its maximal expression at 30–45 days, it was maintained throughout the entire study period (up to 6 months), mainly in the distal zone of the gland. Pinealocytes did not show b‐FGF immunoreactivity at any time. There were no differences in the localization patterns or the intensity of b‐FGF immunostaining after the prenatal denervation with DSP‐4, a neurotoxic amine. The physiological role of b‐FGF in the adult pineal gland remains unknown; however, it does not seem to play a major role during the cytodifferentiation period of the parenchymal cells, or during the neovascularization in the early postnatal days. Furthermore, its immunocytochemical expression is not affected by the prenatal sympathetic denervation with DSP‐4, in contrast with other neutrophic factors.
Multiple circadian oscillators in the photosensitive pike pineal gland: A study using organ and cell culture
Authors: Bolliet Valérie , Bégay Valérie , Ravault Jean‐Paul , Ali Mohamed A. , Collin Jean‐Pierre , Falcón Jack
Published: February 2007

Bolliet V, Bégay V, Ravault J‐P, Ali MA, Collin J‐P, Falcón J. Multiple circadian oscillators in the photosensitive pike pineal gland: A study using organ and cell culture. J. Pineal Res. 1994: 16: 77–84.

The fish pineal organ contains typical and, in some species, modified photoreceptor cells involved in the photoperiodic control of melatonin production. In the majority of species studied, the rhythm in melatonin production is driven by an intra‐pineal circadian oscillator synchronized by the light: dark cycle. In the present study, it is shown that the endogenous rhythm in melatonin release of super fused pike pineals maintained under constant darkness is expressed at temperatures of 19°C, 20°C, 25°C, and 30°C (period > 24 hr), but not at temperatures of 10°C and 15°C. Under constant darkness, pineal fractions containing either typical photoreceptors, modified photoreceptors, or both behaved like total organs. Dissociated pike pineal cells, cultured statically at 20°C, expressed a high amplitude rhythm in melatonin secretion under a light: dark cycle. Under constant darkness, circadian oscillations, which appeared better sustained than in organ culture, were also observed. This study provides the first evidence that the rhythmic production of melatonin, by a fish pineal, is driven by a population of circadian oscillators or clocks. It is hypothesized that each typical and modified photoreceptor might be the locus of a circadian clock. Damping of the overall rhythm under constant darkness might reflect the resynchronization (uncoupling) between these clocks and/or damping of individual oscillators.
Effect of pinealectomy upon the nonspecific immune response of the ring‐dove (Streptopelia risoria)
Authors: Rodriguez Ana B. , Lea Robert W.
Published: February 2007

Rodriguez AB, Lea RW. Effect of pinealectomy upon the nonspecific immune response of the ring‐dove (Streptopelia risoria). J. Pineal Res. 1994; 16: 159–166.

The different stages of the phagocytic process by granulocytes of pinealectomized or sham‐pinealectomized ring doves (Streptopelia risoria) as well as hematological parameters (total white blood cells, smear, and total protein) and serum hormone levels (triiodothyronine (T3), thyroxine (T4), and corticosterone) were studied. A number of immunological parameters of the phagocytosis process, including adherence capacity, mobility rate, the phagocytosis capacity for inert particles and the digestion capacity of ingested material, were studied. Adult male ring doves were injected intravenously with either 0. 1 ml of normal sheep serum (NSS) or saline (SS). Blood samples were collected before injection, and 1 hr, 3 hr, 24 hr, and 4 days afterwards. The results indicate that pinealectomy produces a significant increase in the number of total white blood cells and total protein concentration in plasma in addition to altering different stages of the phagocytic process. During the immunization study, a decrease in the percentage of leukocytes and lymphocytes and an increase in the percentage of heterophils accompanied by an increase in the concentration of serum corticosterone were observed 3 hr following treatment. For the immunological parameters, adherence capacity and latex bead ingestion were increased 3 hr after NSS injection and the NBT reduction test 3 and 24 hr after NSS treatment. In addition, the administration of NSS produced a significant increase in serum T3 and T4 concentrations 4 days following injection. These results show that pinealectomy has a marked effect on both the number and function of immune cells.
Photoperiod and the pineal gland regulate the male phenotype of the Harderian glands of male Syrian hamsters after androgen withdrawal
Authors: Coto‐Montes Ana M. , Rodríguez‐Colunga Maria J. , Uria Higinio , Antolin Isaac , Tolivia Delio , Buzzell Gerald R. , Menendez‐Pelaez Armando
Published: February 2007

Coto‐Montes AM, Rodriguez‐Colunga MJ, Una H, Antolin I, Tolivia D, Buzzell GR, Menendez‐Pelaez A. Photoperiod and the pineal gland regulate the male phenotype of the Haderian glands of male Syrian hamsters after androgen withdrawal. J. Pineal Res. 1994: 17: 48–54.

The Harderian glands of Syrian hamsters exhibit a marked sexual dimorphism in cell types and porphyrin production. The glands of male hamsters have two secretory cell types (Type I and II) while the glands of females consist of a single secretory cell type (female Type I) and large intraluminal deposits of porphyrins. Besides androgens, there is evidence that the pineal gland, through the secretion of melatonin, contributes to the maintenance of the “male” and “female” phenotypes. In this study, we investigated the effects of castration, short photoperiods, and pinealectomy on the distribution of secretory cells and porphyrin deposits in the Harderian glands of male Syrian hamsters. Two groups of animals were maintained in long days (14 hr light/day). Hamsters in one group were left intact and those in the other were castrated. Another three groups were maintained in short days (8 hr light/day); these animals were either left intact, castrated, or both castrated and pinealectomized. The duration of the experiment was 5 weeks. Castration of long photoperiod‐exposed animals resulted in a significant drop in the number of Type II cells and a large increase in the porphyrin deposits (P < 0. 01). However, castrated animals exposed to short photoperiod showed a significant smaller change in both parameters compared with those exposed to long days (P < 0. 05). Pinealectomy prevented the effects of short days in castrated animals. No significant changes were observed in the relative number of mitotic figures or in the number of cell nuclei, indicating that the changes observed were due in part to a transformation of Type II into Type I cells. In a second experiment, male hamsters were injected daily either with 25 μg of melatonin late in the afternoon or with the saline for 8 weeks. The administration of melatonin resulted in a significant (P < 0. 05) increase in the percentage of Type II cells. We conclude that when circulating androgens are very low or absent, pineal melatonin maintains the male phenotype in the Syrian hamster Harderian gland.
Effects of melatonin on microtubule assembly depend on hormone concentration: Role of melatonin as a calmodulin antagonist
Authors: Huerto‐Delgadillo Lourdes , Antón‐Tay Fernando , Benitez‐King Gloria
Published: February 2007

Huerto‐Delgadillo L, Antón‐Tay F, Benítez‐King G. Effects of melatonin on microtubule assembly depend on hormone concentration: rate of melatonin as a calmodulin antagonist. J. Pineal Res. 1994: 17: 55–62. ©Munksgaard, 1994

Melatonin may play a key role in cytoskeletal rearrangements through its calmodulin antagonism. In the present work, we tested this hypothesis by studying melatonin effects on both microtubule polymerization in vitro and cytoskeletons in situ. Microtubule assembly is a dynamic process inhibited by Ca2+/calmodulin. Calmodulin antagonists prevent the inhibition by binding to Ca2+‐activated calmodulin, thus causing microtubule enlargement. In the presence of calmodulin (5 μM) and CaCl2 (1 mM), polymerization at equilibrium was inhibited by 40%. Complete reversal of the Ca2+/calmodulin effect on microtubules was observed with 10‐9 M melatonin or with 10‐5 M trifluoperazine or 1 μg/ml of compound 48/80. In the absence of Ca2+/calmodulin, melatonin at 10‐5 M inhibited tubulin polymerization like 10‐4 M trifluoperazine does. Melatonin effects on microtubule assembly at both nanomolar and micromolar ranges were corroborated in cytoskeletons in situ. Therefore, it is suggested that at a low concentration (10‐9 M), cytoskeletal melatonin effects are mediated by its antagonism to Ca2+/calmodulin. At a higher concentration (10‐5 M), non‐specific binding of melatonin to tubulin occurs, thus overcoming the melatonin antgonism to Ca2+/calmodulin. The results support the hypothesis that under physiological conditions, melatonin synchronizes different body rhythms through cytoskeletal rearrangements mediated by its calmodulin antagonism.
Clonidine in vivo mimics the acute suppressive but not the phase‐shifting effects of light on circadian rhythm of serotonin N‐acetyltransferase activity in chick pineal gland
Authors: Zawilska Jolanta B.
Published: February 2007

Zawilska JB. Clonidine in vivo mimics the acute suppressive but not the phase‐shifting effects of light on circadian rhythm of serotonin N‐acetyltransferase activity in chick pineal gland. J. Pineal Res. 1994; 17: 63–68. ©Munksgaard, 1994

Comparative in vivo studies on effects of pulses of light and clonidine, a selective agonist of α2‐adrenergic receptors, on the circadian rhythm of serotonin N‐acetyltransferase (NAT) activity in chick pineal gland were performed. Six‐hour pulses of white light caused an acute suppression of the nocturnal NAT activity and phase‐dependent phase shifts of the circadian rhythm of the enzyme activity relative to controls. Systemic administration of clonidine acutely suppressed NAT activity of chick pineal gland, but did not affect the phase of subsequent cycles in constant darkness. These results give further support to the concept based on in vitro studies that α2‐adrenergic receptors are involved in regulation of melatonin biosynthesis in chick pineal gland by a mechanism distal to the pacemaker that generates the circadian melatonin rhythm.
Benzodiazepines influence melatonin secretion of the pineal organ of the trout in vitro
Authors: Meissl Hilmar , Yáñez Julián , Ekström Peter , Grossmann Eberhard
Published: February 2007

Meissl H, Yáñez J, Ekström P, Grossman E. Benzodiazepines influence melatonin secretion of the pineal organ of the trout in vitro. J. Pineal Res. 1994; 17: 69–78. ©Munksgaard, 1994

The effect of benzodiazepines (BZP) on melatonin release was investigated in the pineal gland of the rainbow trout, Oncorhynchus mykiss, maintained under in vitro perifusion culture conditions. Melatonin and the methoxyindoles 5‐methoxytryptophol (5‐MTOL), 5‐methoxyindoleacetic acid (5‐MIAA), and 5‐methoxytryptamine (5‐MT) were determined directly in samples of the supervision medium by HPLC with electrochemical detection. Melatonin release was significantly increased by addition of diazepam and clonazepam in a dose‐related and reversible manner. The effects of benzodiazepines were more pronounced in light‐adapted pineal organs, when melatonin secretion is low, than under scotopic conditions. When the perifusion medium was replaced by a medium containing low calcium, high magnesium concentrations, melatonin release was considerably decreased by 70% in light‐adapted and 20% in dark‐adapted pineal organs. Addition of diazepam to low Ca2+, high Mg2+‐medium reversed the decrease of melatonin release and produced a clear rise in its secretion rate. Addition of the BZP antagonist flumazenil to the perifusion medium slightly decreased melatonin release in the light‐ and dark‐adapted state, whereas the peripheral receptor antagonist PK 11195 did not alter melatonin release. The effect of diazepam is reduced by simultaneous addition of flumazenil to the superfusion medium, suggesting that the effects of diazepam are receptor‐mediated. The methoxyindoles 5‐MTOL, 5‐MIAA, and 5‐MT showed no significant changes of their release pattern after diazepam application in light‐ and dark‐adapted pineal organs. These results suggest that BZP can influence melatonin production and release by an intrapineal action possibly on the melatonin synthesizing photoreceptor cell.
Calbindin‐D28k, calretinin, and recovering immunoreactivities in developing chick pineal gland
Authors: Bastianelli E. , Pochet R.
Published: February 2007

Bastianelli E, Pochet R. Calbindin‐D28k, calretinin, and recover in immunoreactivities in developing chick pineal gland. J. Pineal Res. 1994: 17: 103–111.

Calbindin‐D28k, calretinin, and recoverin, three intracellular calcium‐binding proteins belonging to the troponin C/calmodulin superfamily, were immunohistochemically localized in chick pineal during development [from embryonic day 16 (E16) to postnatal day 14 (P14)]. At E18, only calretinin immunoreactivity could be detected in nuclei from follicular pinealocytes. With development, calretinin immunoreactivity expanded from nucleus to cytoplasm, and calretinin immuno‐positive cell number increased. At P14 almost all pinealocytes were calretinin positive. Calbindin‐D28k immunoreactivity was not detected before E20. During development, many follicular and parafollicular pinealocytes became strongly calbindin‐D28k positive, reaching a peak both in intensity and in number at P7; thereafter their number decreased. In addition to pinealocytes, neuron‐like cells appeared calbindin‐D28k positive at E20 and calretinin positive at P7. Recoverin, a myristoylated protein isolated from vertebrate photoreceptor and which might participate in the inactivation of the phototransduction cascade, was transiently expressed in follicular and parafollicular pinealocytes from P1 to P14 with a maximal expression at P7. This transitory expression may coincide with a transitory light sensitivity period in chick pinealocytes, before complete maturity of the pineal gland.
Response of collared lemmings to melatonin: I. Implants and photoperiod
Authors: Nagy Tim R. , Gower Barbara A. , Stetson Milton H.
Published: February 2007

Nagy TR, Gower BA, Stetson MH. Response of collared lemmings to melatonin: I. Implants and photoperiod. J. Pineal Res. 1994:17:177–184.

We examined the effect of constant‐release melatonin capsules on the physiology and morphology of female collared lemmings exposed to either chronic long (22L:2D) or short (8L:16D) photoperiod, or to a change in photoperiod. When animals were maintained on unchanging long or short photoperiod, subcutaneous melatonin implants were without effect. However, when animals were reared on either 22L:2D or 8L:16D and transferred to the alternate photoperiod at weaning, melatonin (implanted at weaning) prevented most photoperiod‐related responses. At sacrifice (after 8 weeks of treatment), melatonin‐implanted animals exposed to a change in photoperiod did not differ from animals remaining in the original photoperiod with respect to pelage color, bifid claw size, uterine mass, or serum prolactin (PRL). In contrast, regardless of treatment, animals exposed to a photoperiod transfer developed a body mass that partially or fully reflected that characteristic of the secondary photoperiod; i. e., both control‐ and melatonin‐implanted animals transferred from long to short photoperiod developed a large body mass. These results indicate that masking the endogenous melatonin rhythm via constant‐release melatonin implants renders collared lemmings unable to respond to a change in photoperiod with respect to most physiological parameters. However, the striking seasonal change in body mass experienced by collared lemmings appears to be at least partially independent of a melatonin signal.
Urinary 6‐sulphatoxymelatonin excretion reflects pineal melatonin secretion in the Djungarian hamster (Phodopus sungorus)
Authors: Stieglitz Ariane , Spiegelhalter Frank , Klante Gabriela , Heldmaier Gerhard
Published: February 2007

Abstract: To monitor pineal function in the Djungarian hamster (Phodopus sun‐gorus), we measured the urinary excretion of the melatonin metabolite 6‐sulpha‐toxymelatonin (aMT6s) at 3‐hr intervals by radioimmunoassay. Hamsters maintained in either long photoperiod (LP, LD 16: 8) or short photoperiod (SP, LD 8: 16) showed marked daily rhythms in aMT6s excretion, with elevated levels during the dark phase. In both photoperiods, we found large interindividual differ‐ences, mainly in the amplitude of the signal. However, the amplitude as well as the duration of nocturnal aMT6s excretion was higher in SP than in LP. Light ex‐posure at night (180 mW/m2, 30 min) caused a decrease in aMT6s excretion, indicating that the pineal gland is the major source of urinary aMT6s. Moreover, there was a significant correlation between nocturnal pineal/plasma melatonin contents and 24‐hr aMT6s excretion. We conclude that, measurements of aMT6s provide a valid and quantitative index of pineal melatonin synthesis in this hamster species. As an advantage in determining pineal melatonin contents, this approach will al‐low noninvasive long‐term studies of individual animals under varying environ‐mental conditions.
Seasonal changes in the levels of antidiuretic hormone and melatonin in the elderly
Authors: Asplund Ragnar , Åberg Hans , Wetterberg Lennart
Published: February 2007

Abstract: Antidiuretic hormone (ADH) and melatonin in plasma were measured every 4 hr during a 24‐hr period in 69 elderly volunteers (42 males and 27 females) aged 75.6 ± 8.8 years (± SD) and 73.5 ± 9.5 years, respectively. The population was divided into three groups, which were examined February 27–28, April 25–26, and November 14–15. For the males, the mean ADH level during 24 hr was lowest in April and highest in November with a level five times higher than in April. The ADH level in February was about three times higher that in April. Females did not show any seasonal variation in the ADH system. The melatonin levels were lowest in November, higher in February, and even higher in April in both male and female volunteers. The ADH increased with age in males (R2= 0.13; P < 0.05) but not in females (R2= 0.07; NS). The melatonin concentration decreased with age for the whole group, aged 60–98 years.
Day‐night changes in melatonin levels in different organs of the cricket (Gryllus bimaculatus)
Authors: Itoh Masanori T. , Hattori Atsuhiko , Sumi Yawara , Suzuki Takuro
Published: February 2007

Abstract: Day‐night levels of melatonin (N‐acetyl‐5‐methoxytryptamine) were determined in different organs of adult female crickets (Gryllus bimaculatus) exposed to a 12/12 light/dark cycle, using reversed‐phase high performance liquid chromatography coupled with fluorometric detection. Melatonin levels in the compound eye, brain, and palp were significantly higher during the dark period than during the light period, suggesting that a diurnal rhythm of melatonin levels exists in these organs of crickets, with a peak during the dark period. Conversely, melatonin levels were significantly higher during the light period than the dark period in the cercus, ovipositor, antenna, hind‐leg and ovary. No significant day‐night difference was found in the fore‐ and mid‐legs, Malpighian tube, and digestive tube. Thus, these organs may have different melatonin‐metabolizing systems compared to those found in the compound eye, brain, and palp. Differences in the phasing of the melatonin rhythm in various organs of the cricket suggest possible differences in melatonin function in these organs.
Distribution and characterization of the melatonin receptors in the hypothalamus and pituitary gland of three domestic ungulates
Authors: Nonno Romolo , Capsoni Simona , Lucini Valeria , Møller Morten , Fraschini Franco , Stankov Bojidar
Published: February 2007

Abstract: With some exceptions, in most of the mammals the pituitary pars tuber‐alis and the hypothalamic suprachiasmatic nuclei are reportedly the main targets for the pineal hormone melatonin. However, it is not known if the conspicuous diversity in the distribution pattern of melatonin binding sites in these areas depicts differences in reproductive behavior observed in the seasonally breeding species in the temperate zones. We explored the distribution and the characteristics of melatonin binding sites in the hypothalamus and pituitary of three species (bovine, horse, and donkey) different in terms of seasonal reproductive competence. The topographical localization, investigated by in vitro autoradiography, revealed 2‐[125I]iodomelatonin binding sites only in the pituitary gland in all three species, primarily in the pars tuberalis (PT), but also in the pars distalis (PD) and pars intermedia (PI). Kinetic, inhibition, and saturation studies, performed by means of in vitro binding, revealed presence of a single class high affinity binding sites. The Kd values, melatonin, and 2‐iodomelatonin Kj values were in the low picomo‐lar range. Coincubation with GTP7S inhibited 2‐[125 I]iodomelatonin binding, demonstrating that these putative receptors are linked to a G protein in their signal‐transduction pathway. The hypothalamus was devoid of specific binding. In conclusion, the results suggest that in these species, the hypophysis may be a principal target for the melatonin action on the reproductive system.
N‐Acetyltransferase, hydroxyindole‐O‐methyltransferase and melatonin in the optic lobes of the giant tiger shrimp Penaeus monodon
Authors: Withyachumnarnkul Boonsirm , Pongtippatee Pattira , Ajpru Supaporn
Published: February 2007

Abstract: The activities of the enzymes N‐acetyltransferase (NAT) and hydroxyin‐dole‐O‐methyltransferase (HIOMT) and the hormone melatonin were studied in the optic lobe of the subadult giant tiger shrimp Penaeus monodon. Compared with the level in other species, a relatively high level of NAT activity that was temperature‐ and pH‐dependent were observed. The NAT enzyme had a relatively high maximum velocity (Vmax, 100 pmol/hr/μg protein) and low Michaelis constant (Km, 22 μM), when tryptamine is used as substrate. In contrast to the high level of NAT activity, HIOMT activity and melatonin levels were low in the optic lobe of the giant tiger shrimp. Sex differences in the levels of NAT activity and melatonin, which are observed in a freshwater species Macrobrachium rosenber‐gii, were not noticeable in the saltwater species P. monodon, at least not when they were in their subadult stage.
Light‐induced suppression of nocturnal serotonin N‐acetyltransferase activity in chick pineal gland and retina: A wavelength comparison
Authors: Zawilska Jolanta B. , Jarmak Adam , Woldan‐Tambor Agata , Nowak Jerzy Z.
Published: February 2007

Abstract: Effects of white and monochromatic (blue—434 nm, green—548 nm, and red—614 nm) lights on the nighttime retinal and pineal NAT activity were examined in chicks. The potency of the tested lights to suppress NAT activity was similar for the retina and pineal gland, with a following rank order: white > green > blue > red. The studied tissues of chick were far less sensitive to pulses of monochromatic light than the rat pineal gland. The potency of light to decrease pineal NAT activity of rat was: white > green >> blue > red. In chicks, the suppression of the nocturnal NAT activity produced by a short 5‐min pulse of monochromatic light was completely reversible in the pineal gland, and partially reversible in the retina. Our data suggest the existence of some differences between birds and mammals in terms of sensitivity and mechanisms involved in the light‐induced suppression of melatonin biosynthesis.