Controladores del tiempo y el envejecimiento: núcleo supraquiasmático y glándula pineal / Aging process entrainment: suprachiasmatic nucleus and pineal gland

El núcleo supraquiasmático (NSQ) es el principal reloj biológico de los mamíferos y sincroniza la actividad de la glándula pineal al ciclo luz-oscuridad a través de una vía polisináptica. El efecto de asa de retroalimentación neuroendocrina se lleva a cabo por la melatonina. El presente trabajo pretende demostrar que la glándula pineal modula la sensibilidad a la luz en el NSQ. Se utilizaron ratas Wistar, y se asignaron a 3 grupos: grupo A (falsa pinealectomía -sham-, sin luz), grupo B (falsa pinealectomía -sham- + luz) y grupo C al cual se le realizó la pinealectomía + luz, después de la manipulación se sacrifican para realizar inmunohistoquímica para c-Fos y al final conteo celular por técnica de estereología. Se obtuvo una reducción del 46,8% del promedio de células inmunorreactivas a c-Fos en el grupo C en comparación del grupo B. Este trabajo muestra que la sensibilidad a la luz está modulada por la actividad de la glándula pineal.

The suprachiasmatic nucleus (SCN) is the main and major biological clock in mammals and is responsible for the synchronization of the pineal gland to the light/darkness cycle through a polysynaptic pathway. The neuroendocrine feedback loop effect is carried out by melatonin. This study was carried out to demonstrate that the pineal gland adjusts the sensibility to light in the suprachiasmatic nucleus. Wistar rats were allocated in 3 groups: Group A (sham pinalectomy, without light), group B (sham pinealectomy + light) and group C which underwent real pinalectomy + light. After the intervention the animals were slain to perform immunohistochemistry for c-Fos and cell counting by stereology technique. A 46.8% average reduction in c-Fos immunoreactive cells was achieved in-group C as compared with group B. The present work shows that sensibility to the light is modulate by the activity of the pineal gland.

Modulation of pineal activity during the 23rd sunspot cycle: Melatonin rise during the ascending phase of the cycle is accompanied by an increase of the sympathetic tone.

In two groups of female CD-rats nocturnal urine (19-23 h, 23-3 h, 3-7 h) was collected at monthly intervals over 658 days (I: 1997-1999) and 494 days (II: 1999-2000) coinciding with the ascending limb (1996-2000) of the 23rd sunspot cycle (1996-2008). The excretion of 6-sulfatoxymelatonin (aMT6s: I, II) was determined as well as the ratio of noradrenaline/adrenaline (NA/A: I) reflecting the activity of the sympathetic nervous system. AMT6s was higher in II than I (19-7 h: +24%; P<0.001; 23-3 h: +30% and 3-7 h: +17%, P<0.001), and progressively increased (19-23 h) showing linear regressions (I: R=+0.737, P=0.003; II: R=+0.633, 0.008) which correlated (I) with the Planetary Index (Ap: R=+0.598, P=0.020), an established estimate of geomagnetic disturbances due to solar activity. NA/A rose at all intervals (I: 46-143%) correlating with Ap (R=+0.554-0.768; P=0.0399-0.0013). These results indicate that melatonin secretion rises as solar activity increases during the ascending limb of a sunspot cycle accompanied by growing geomagnetic disturbances (Ap) which elevate the sympathetic tone and thus affect the pineal gland, initially stimulating the activity of arylalkylamine N-acetyltransferase and subsequently fostering the expression of N-acetylserotonin O-methyltransferase (rate-limiting enzyme for melatonin biosynthesis) if Ap increases further. The potential (patho) physiological significance of these findings is discussed and the need for a systematic continuation of such studies is emphasized.

Critical time delay of the pineal melatonin rhythm in humans due to weak electromagnetic exposure.

Electromagnetic fields (EMFs) can increase free radicals, activate the stress response and alter enzyme reactions. Intracellular signalling is mediated by free radicals and enzyme kinetics is affected by radical pair recombination rates. The magnetic field component of an external EMF can delay the "recombination rate" of free radical pairs. Magnetic fields thus increase radical life-times in biological systems. Although measured in nanoseconds, this extra time increases the potential to do more damage. Melatonin regulates the body's sleep-wake cycle or circadian rhythm. The World Health Organization (WHO) has confirmed that prolonged alterations in sleep patterns suppress the body's ability to make melatonin. Considerable cancer rates have been attributed to the reduction of melatonin production as a result of jet lag and night shift work. In this study, changes in circadian rhythm and melatonin concentration are observed due to the external perturbation of chemical reaction rates. We further analyze the pineal melatonin rhythm and investigate the critical time delay or maturation time of radical pair recombination rates, exploring the impact of the mRNA degradation rate on the critical time delay. The results show that significant melatonin interruption and changes to the circadian rhythm occur due to the perturbation of chemical reaction rates, as also reported in previous studies. The results also show the influence of the mRNA degradation rate on the circadian rhythm’s critical time delay or maturation time. The results support the hypothesis that exposure to weak EMFs via melatonin disruption can adversely affect human health.

Melatonin: fifty years of scientific journey from the discovery in bovine pineal gland to delineation of functions in human.

Melatonin (N-acetyl-5-methoxytryptamine) was first purified and characterized from the bovine pineal gland extract by Aron Lerner and co-workers in 1958. Since then, a plethora of information has piled up on its biosynthesis, metabolism, time-bound periodicity, physiological and patho-physiological functions, as well as its interactions with other endocrine or neuro-endocrine organs and tissues in the body. Melatonin has wide range of applications in physiology and biomedical fields. In recent years, a significant progress has been made in the understanding mechanism of its actions at the cellular and molecular levels. Consistent efforts have uncovered the mystery of this indoleamine, and demonstrated its role in regulation of a large as well as diverse body functions in different groups of animals in general, and in humans in particular. Current review, in commemoration of 50 years of discovery of melatonin, while revisiting the established dogmas, summarizes current information on biosynthesis, secretion, metabolism and molecular mechanism of action of melatonin at cellular level and highlights the recent research on its role in human physiology and clinical biology.

Morphologic changes in rat's pineal gland after eliminating retinal photic stimulation / Cambios morfológicos en la glándula pineal de ratas luego de la eliminación de la estimulación fótica retiniana

Melatonin secretion from mammalian pineal glands is regulated by light stimulation by means of a complex neuroanatomical pathway that includes the retina, hypothalamic suprachiasmatic nucleus, intermediolateral nucleus of the thoracic spinal cord, and finally, the superior cervical ganglia. The purpose of this study was to analyze the changes in the pinealocytes and the blood vessel density of the pineal gland after eliminating photic stimulation in rats. Thirteen adult Sprague-Dawley rats were divided into 2 groups, Group I acted as control, and Group II was subjected to a retinal lesion, by means of alcohol injected bilaterally to both ocular bulbs. After 3 weeks, the glands of both groups were processed with hematoxilin-eosin (HE) and observed with an optic microscope. Group II results presented higher values in the number of pinealocytes and in the blood vessels observed. The differences with Group I was significant at p <0.01. These results give an indirect evidence of the effect that photic stimulation suppression has in the pineal gland in rats.

La secreción de melatonina por parte de glándula pineal de los mamíferos es regulada por la estimulación luminosa mediante complejas vías neuro anatómicas que incluyen la retina, el núcleo supraquiasmático hipotalámico, el núcleo intermediolateral de la médula torácica y finalmente el ganglio cervical superior. El propósito de este estudio fue analizar los cambios en la densidad de pinealocitos y vasos sanguíneos de la glándula pineal, luego de eliminar la estimulación fótica en ratas. Se utilizaron 13 ratas adultas Sprague Dawley divididas en 2 grupos, Grupo I actuó como control, y el Grupo II fue sometido a una lesión retiniana, por medio de alcoholización bilateral de ambos bulbos oculares. Luego de tres semanas las glándulas de ambos grupos fueron procesadas para hematoxilina-eosina y observadas al microscopio óptico. El grupo II presentó valores mayores en el número de pinealocitos y de vasos sanguíneos observados, las diferencias con el Grupo I fueron significativas con p<0.01. Estos resultados entregan una evidencia indirecta del efecto que la supresión de la estimulación fótica tiene en la glándula pineal en ratas.

Triiodothyronine and melatonin influence antioxidant defense mechanism in a teleost Anabas testudineus (Bloch): in vitro study.

The effect of the hormones triiodothyronine (T3) and melatonin on antioxidant defense system was studied in 6-propyl thiouracil (6-PTU)-treated or photoperiod-exposed teleost Anabas testudineus. 6-PTU (2 microg/g) treatment or photoperiod exposure (24 h) increased malondialdehyde (MDA) and conjugated dienes (CD) concentrations, indicating increased lipid peroxidation (LPO) in the experimental conditions. T3 or melatonin (10(-6) M) treatment for 15 min in vitro in PTU-treated fish reversed the activity of superoxide dismutase (SOD), catalase and glutathione content. T3-treated group showed no change in glutathione peroxidase (GPx) activity, whereas melatonin treatment decreased its activity. T3 inhibited glutathione reductase (GR) activity. Photoperiod exposure (physiological pinealotomy) induced a stressful situation in this teleost, as evidenced by LPO products and antioxidant enzyme activities. Melatonin and T3 treatment for 15 min in vitro also reversed the effect of photoperiod on peroxidation products and the SOD and catalase activities. GR activity decreased in photoperiod-exposed group and melatonin and T3 treatment reversed the activities. The antioxidant enzymes responded to the stress situation after 6-PTU treatment and photoperiod exposure by altering their activities. The study suggested an independent effect of T3 and melatonin on antioxidant defence mechanism in different physiological situations in fish.

O tecido adiposo como centro regulador do metabolismo / The adipose tissue as a regulatory center of the metabolism

Os avanços da pesquisa sobre as propriedades metabólicas do tecido adiposo e as recentes descobertas sobre sua capacidade em produzir hormônios atuantes em processos fisiológicos e fisiopatológicos, estão revolucionando conceitos sobre a sua biologia. O seu envolvimento em processos como obesidade, diabetes mellitus tipo 2, hipertensão arterial, arteriosclerose, dislipidemias, processos inflamatórios agudos e crônicos, entre outros, indicam que a compreensão das suas propriedades funcionais contribuirão para melhorar o prognóstico daquelas doenças, cuja prevalência vem crescendo de forma preocupante. Nesta revisão, abordamos aspectos funcionais dos adipócitos, como o metabolismo, a participação na homeostase energética, a sua habilidade endócrina e a adipogênese, entendida como a capacidade de pré-adipócitos, presentes no parênquima do tecido, de se diferenciarem em novos adipócitos e reconstituírem o tecido. Além disso, estamos incluindo estudos sobre as relações entre o tecido adiposo e a glândula pineal, aspecto novo e pouco conhecido, mas, como será visto, muito promissor da fisiologia do adipócito com possíveis repercussões favoráveis para a terapêutica das moléstias relacionadas com a obesidade.

The recent progress in the research about the metabolic properties of the adipose tissue and the discovery of its ability to produce hormones that are very active in pathophysiologic as well as physiologic processes is rebuilding the concepts about its biology. Its involvement in conditions like obesity, type 2 diabetes mellitus, arterial hypertension, arteriosclerosis, dislipidemias and chronic and acute inflammatory processes indicate that the understanding of its functional capacities may contribute to improve the prognosis of those diseases whose prevalence increased in a preoccupying manner. Here we review some functional aspects of adipocytes, such as the metabolism, its influence on energy homeostasis, its endocrine ability and the adipogenesis, i.e., the potential of pre-adipocytes present in adipose tissue stroma to differentiate into new adipocytes and regenerate the tissue. In addition, we are including some studies on the relationship between the adipose tissue and the pineal gland, a new and poorly known, although, as will be seen, very promising aspect of adipocyte physiology together with its possible favorable repercussions to the therapy of the obesity related diseases.

Immunohistochemical demonstration of opioids and tachykinins in human pineal gland.

The human pineal gland secretes melatonin in a circadian rhythm manner. The rhythm of melatonin synthesis is primarily controlled by the noradrenergic sympathetic system originating from the superior cervical ganglion. Several neurotransmitters/neuropeptides have been reported to influence the production of melatonin in the pineal glands of many mammalian species. Both opioid peptide, a pain suppressing peptide and substance P, a pain inducing peptide were also reported to be present in the pineal gland of several kinds of mammals. However, few studies have been demonstrated in humans. Therefore, in the present study, the immunohistochemical investigation was performed in the human pineal gland by using antisera raised against leu-enkephalin, met-enkephalin and beta-endorphin to demonstrate an opioidergic system; and antisera raised against substance P, neurokinin A, and neurokinin B to study a tachykinin system. A high amount of leu- and met-enkephalin immunoreactivities were observed in intrapineal neuronal-like cells while very few were presented in nerve fibers. This result suggests a local regulatory function or paracrine opioidergic control in human pineal. Substance P- and neurokinin A-immunoreactivities, but not neurokinin B were observed in the human pineal gland. They are located mostly in nerve fibers but a few in neuronal-like cells. The tachykininergic control of human pineal is mainly from the nerve fibers which have their perikaryal origin outside the gland. Some of the nerve fibers might originate from neurons in the brain and/or from a peripheral ganglion.

Influence of continuous light and darkness on the secretory pinealocytes of Heteropneustes fossilis.

In an earlier study on Heteropneustes fossilis, evidence of secretory activity in the pinealocytes had been demonstrated at the electron microscopic (EM) level and it was found to exist in two phases: a secretory phase (light cells) and a storage phase (dark cells). In the present investigation, H. fossilis was subjected to artificial photoperiods of continuous illumination and continuous darkness for a period of ten days and the effect on the secretory pinealocytes was studied at the EM level. Marked results were observed within the short period of ten days emphasizing the role of environmental photoperiod on the secretory activity of the pinealocytes. During continuous illuminated phase, both light and dark cells were observed: the light cells showed intense secretory activity and dark cells a storage one. During the dark phase both types of cells were present but in different metabolic states and neither of the cells demonstrated synthetic nor storage activity. Light cells were metabolically active but not secretory active and dark cells showed a necrotic condition. Phagocytotic activity of the dark cells was also seen. Intense neural activity was also observed during exposure to both the artificial photoperiods. The results highlight the role of light on the secretory activities of the pinealocytes of the catfish pineal organ.

Influence of the pineal gland on the physiology, morphometry and morphology of pancreatic islets in rats

To investigate the influence of the pineal gland through melatonin secretion on the physiological and morphological parameters of pancreatic islets, we studied the plasma biochemistry and morphological and morphometric characteristics of the endocrine pancreas of male Wistar rats. The animals were distributed into five groups of ten rats each: NC - normal control group; NS - sham-operated group; Px (25) - pinealectomised group, studied 15-25 days after surgery; Px (70) - pinealectomised group, studied 60-70 days after surgery; ALX - alloxan monohydrate-treated group. Data are analyzed statistically by ANOVA and by the Kruskal-Wallis test. Although there was no significant difference in plasma glucose or insulin levels between the Px (25), Px (70) and NC groups, Px (25) animals showed a tendency to increased glucose and reduced insulin levels. The ALX group showed a clear elevation of plasma glucose and a reduction of plasma insulin compared to the other groups. Morphometric analysis showed a larger pancreatic islet area and a lower pancreatic islet density in the pancreas of Px (70) animals and an increase in degenerative pathological processes in the pancreatic islets of the Px (25) and ALX groups. The present results suggest that melatonin, in addition to acting on tissue sensitivity to insulin (as reported in other studies), affects the secretory action of beta cells, as demonstrated by the morphological and morphometric changes observed in pinealectomised animals

Caffeine injection in the dark phase prolongs the nocturnal rise in serotonin N-acetyltransferase activity and melatonin content in the pineal gland of male rats

Caffeine, an important member of methylxanthines, induced a prolonged nocturnal rise in pineal melatonin content and an increase in its rate-limiting enzyme serotonin N-acetyltransferase [NAT] activity. The highest levels were reached five hours after subcutaneous caffeine injection to male rats in the dark phase, where the NAT activity increased from 920 +/- 70 pM pineal-1h-1 in the control group to 1190 +/- 120 pM pineal-1h-1 [p<0.001] in the treated group. The pineal melatonin content, as well, was elevated from 520 +/- 40 pg pineal-1 in the control group to 1120 +/- 80 pg pineal-1 [p<0.001] in caffeine treated group. These changes could be attributed to the depressive effect of caffeine on the activity of phosphodiesterase [PDE], the enzyme responsible for the hydrolysis of the intracellular second messenger cyclic adenosine monophosphate [cAMP]

A melatonina e o sono em criancas / Melatonin and sleep in children

A melatonina foi isolada e caracterizada como um hormonio produzido pela glandula pineal no final da decada de 50. A partir dai inumeros estudos trataram das funcoes da pineal e da melatonina, que surpreendentemente parece agir em praticamente todos os sistemas fisiologicos. Por ser sintetizada e secretada apenas durante o periodo de escuro, funciona como um sinalizador, para o meio interno, do dia e da noite. A producao de melatonina diminui com o envelhecimento. Devido a sua potente acao indutora de sono, a melatonina tem sido utilizada na terapeutica das perturbacoes do sono, principalmente nas insonias, nos transtornos decorrentes da mudanca de fusos horarios e nos trabalhadores com jornada noturna. Os estudos da melatonina nos disturbios do sono na infancia, sao ainda raros...

The effects of castration on the dense-core vesicles and lysosomes of pinelacoytes in male adult mice: a quantitative study

The dense-core vesicles and lysosomes of the adult mice pinealocytes has been studied during normal and experimental (castrated) conditions. Twelve male animals were studied and divided into two groups of six animals: a control group and a castrated one. In all the specimens the dense-core vesicles and lysosomes were counted in a total area of 2,764.80 µm2 of pineal tissue. In adult mice the pineal gland shows dense clusters of light and dark pinealocytes in a distinct rosette-like arrangement. The perinuclear region and cytoplasmic processes of these cells have a moderate distribution of lysosomes and dense-core vesicles. The castrated animals showed a decrease in the number of lysosomes and an increase in the number of dense-core vesicles. Thus, it appears from the present results that the testicular androgens play an inhibitory function on the secretory activity of pinealocytes.

Melatonina / Melatonin

Se revisan las principales acciones fisiológicas de la melatonina, destacando sus efectos metabólicos y endocrinológicos y sus influencias sobre el sistema nervioso y el inmunológico. Se señalan los factores que estimulan la secreción de la melatonina en la glándula pineal. Entre ellos destaca la oscuridad, por lo que la melatonina ha sido considerada como el mensajero de la noche y la reguladora de los ritmos circadianos. Se señalan igualmente los posibles usos terapéuticos de la melatonina, de los cuales el más importante hasta ahora es la regulación del ciclo vigilia-sueño y la prevención del jet-lag. Por el momento se discuten sus eventuales proyecciones terapéuticas derivadas de efectos antioxidantes; inmunomoduladores y cardioprotectores. Los efectos laterales indeseables son muy escasos con la dosis habituales de 3 a 10 mg

La melatonina en el sistema inmunoneuroendocrino / Melatonin in the immuno-neuro-endocrine system

El conocimiento actual de las relaciones neuroendocrinas e inmunológicas confiere un rol importante a la melatonina (MT) en la regulación de los ritmos circadianos de los mamíferos. La función de la glándulapinela en todas las especies es traducir información del ciclo luz/oscuridad a los ritmos fisiológicos del organismo. La MT es producida casi exclusivamente en la oscuridad. En los humanos la secreción ocurre en correspondencia a la edad, disminuyendo en la vejez; guarda relación inversa con la temperatura del cuerpo; evidencia un efecto anti-estrés, posiblemente a través del sistema opioide; favorece la respuesta inmunológica y protege frente al daño tisular que provocan los radicales libres, por su fuerte acción antioxidante. La MT ha sido usada con éxito en la inducción del sueño en personas que ven perturbado su ritmo habitual de sueño por trabajos nocturnos, el síndrome de jet-lag u otras causas. No se ha logrado beneficio en el tratamiento de trastornos mayores del sueño, ni en la depresión ni en otros trastornos psiquiátricos. La presencia de receptores para la MT en múltiples órganos y sistemas estimula actualmente la investigación clínica sobre estas funciones posibles de la melatonina

Alterações metabólicas e da bioquímica plasmática após pinealectomia em ratos / Metabolic and biochemical changes after pialectomy in rats

A pineal, pela secreção de melatonina (MLT), está envolvida no controle do eixo hipotálamo-hipófise-gônadas, regulação de ritmos biológicos e sensibilidade tecidual à insulina. O presente estudo foi realizado para verificar a influência da pineal sobre parâmetros metabólicos e bioquímica plasmática em ratos. Ratos wistar machos (180- 200g) foram mantidos em gaiolas metabólicas por 10 dias para avaliação diária da ingestão de água e alimento, volume urinário e peso corporal. Ao final deste período, os animais foram anestesiados e submetidos à pinealectomia (n=10) ou cirurgia fictícia (n=10) e coleta de sangue para dosagens de glicose, colesterol, triglicérides, proteínas totais e eletrólitos (Na+, K+, Ca++, Cl-). Após 20 e 50 dias da cirurgia, os animais foram recolocados em gaiolas metabólicas para observação por 10 dias e coleta de sangue. Os resultados obtidos demonstram nos animais pinealectomizados: a) aumento da ingestão de alimento e do volume urinário; b) maior ganho de peso após 60 dias da cirurgia; c) elevação plasmática de glicose e colesterol e redução das proteínas totais. Os resultados indicam que a pinealectomia induz alterações metabólicas nos ratos gerando quadro que se assemelha ao diabetes mellitus tipo II que, provavelmente, ocorre pela ausência de melatonina e conseqüente diminuição da sensibilidade celular à insulina.

Pineal gland, through secretion of melatonin (MLT), is envolved in the control of hypothalamus-hypophisis-gonadas axis, regulation of biological rhythms and tissue sensibility to insulin. The present work was made in order to verify pineal influence on metabolic and plasmatic conditions in rats. Wistar male rats were kept in metabolic cages for daily registration of food and water ingestion and urinary output, during 10 days. At the end of this period blood sample was collected for plasmatic determination of glucosis, cholesterol, triglicerides, total protein and electrolytes (Na, K, Ca, Cl). The animals were then pinealectomized (n=10) or sham operated (n=10), and observed again after 20 and 50 days of surgery, during 10 days. Results obtained show that pinealectomized animals present: a) greater food ingestion and urinary output; b) increased body weight after 60 days of surgery; c) increase in plasmatic glucosis and cholesterol, and decrease in total protein concentrations. Data obtained suggest that pinealectomy induces metabolic alterations similar to diabetes mellitus type II, which probably occurs because the absence of MLT reduces tissue sensibility to insulin.

Induction of the c-fos proto-oncogene in the rat pineal gland during stress

To investigate the effects of stressful stimuli on pineal gland activity, male Wistar albino rats (200-250 g, 2-4 per group) were submitted to 30 min of forced immobilization or to unilateral vibrissotomy 30 min before sacrifice. In situ hybridization was performed with a 35S-labelled 50-base oligonucleotide probe complementary to nucleotides 270-319 of rat c-fos on sections containing the pineal gland. Autoradiograms were quantified using a JAVA microdensitometer. Stressful stimuli induced a significant increase in the expression of c-fos mRNA in the pineal gland (restraint = 144.3 +/- 14.4 cpm/mm2; hemivibrissotomy = 206.7 +/- 29.5 cpm/mm2) as compared to no restraint animals (30.6 +/- 5.1 cpm/mm2), animals displaying tonic-clonic seizures after an ip (64 mg/kg) injection of pentylenetetrazole (34.0 +/- 4.7 cpm/mm2), or competition (70.6 +/- 11.4 cpm/mm2) and RNAase-treated (52.7 +/- 9.1 cpm/mm2) controls. These results raise the possibility that stressful stimuli may interfere with pineal gland function

Influence of the pineal extract and melatonin on the estrous cycle of the mice

This work was undertaken to study the effects of daily injections of pineal extract of camel and melatonin for 21 days on the estrous cycle in mice. Daily injections of either 1.5 ml pineal extract or 100 micro g. melatonin -significantly reduced the number of the estrous cycles per animal and the length of these cycles were significantly prologed. Days in proestrus and estrus were significantly decreased. Days in metestrus were not affected. All animals injected with either pineal extract or melatonin spend proportionately more significant time in diestrus phase. When the animals were paired with fertile males, mice seemingly mated as soon as they came into estrus. However, both pineal extract and melatonin treatment inhibited fertile matings. Pineal extract and melatonin showed no effect on the induced estrous cycles when oestradiol and progesterone were given with these agents in ovariectomized mice. Both pineal extract and melatonin significantly increased the release of oestradiol and progesterone. Histological examination of the ovaries of pineal extract and melatonin treated animals revealed the presence of several graafian follicles in different stages of maturation. The interstitial tissue dominate the ovary. The results showed that the estrous cycles of mice were interrupted and ovulation decreased after daily injections of either pineal extract or melatonin for 21 days. It is concluded that pineal gland plays an important physiological role in the regulation of ovarian function as well as estrous cyclicity in female mice. Also, melatonin may be one of the factors modulating the effect of pineal gland on estrous cycle

Time-dependency for the effect of different stressors on rat pineal melatonin content

Este estudio describe el efecto de la forzada durante 15 min o la inyección i.p. de ß-carboline (ß-CCE) sobre el contenido pineal de melatonina. Ambos agentes estresantes fueron aplicados al final del período de luz (1800 h) o en el momento del máximo nocturno de melatonina (2200 h). A las 1800 h, ninguno de los procedimientos modificó los niveles de melatonina pineal, mientras que a las 2200 h ambos fueron efectivos. Sólo ß-CCE aumentó, y en forma no significativa, los niveles nocturnos de melatonina pineal cuando se la inyectó a las 1800 h. Ninguno de los dos agentes estresantes fue efectivo en revertir la inhibición del aumento nocturno de melatonina producido por la luz continua. En cambio, la privación de agua durante 2 días produjo un incremento de los niveles diurnos de melatonina a valores semejantes a los de la oscuridad, sin modificar los niveles nocturnos. La privación de alimentos durante 2 días no efectó los níveles de melatonina. Los presentes resultados indican que existen efectos diferenciales de los distintos tipos de estrés sobre la producción de melatonina pineal