Melatonin treatment decreases c-fos expression in a headache model induced by capsaicin

The aim of the present work was to analyze c-fos response within the trigeminal nucleus caudalis (TNC) of pinealectomized rats and animals that received intraperitoneal melatonin, after intracisternal infusion of capsaicin, used to induce intracranial trigeminovascular stimulation. Experimental groups consisted of animals that received vehicle solution (saline–ethanol–Tween 80, 8:1:1, diluted 1:50) only (VEI, n = 5); animals that received capsaicin solution (200 nM) only (CAP, n = 6); animals submitted to pinealectomy (PX, n = 5); sham-operated animals (SH, n = 5); animals submitted to pinealectomy followed by capsaicin stimulation (200 nM) after 15 days (PX + CAP, n = 7); and animals that received capsaicin solution (200 nM) and intraperitoneal melatonin (10 mg/kg) (CAP + MEL, n = 5). Control rats, receiving vehicle in the cisterna magna, showed a small number of c-fos-positive cells in the TNC (layer I/II) as well as the sham-operated and pinealectomized rats, when compared to animals stimulated by capsaicin. On the other hand, pinealectomized rats, which received capsaicin, presented the highest number of c-fos-positive cells. Animals receiving capsaicin and melatonin treatment had similar expression of the vehicle group. Our data provide experimental evidence to support the role of melatonin and pineal gland in the pathophysiology of neurovascular headaches.     

Involvement of the pineal gland in diurnal cocaine reward in mice

Contribution of circadian mechanisms to the psychostimulant-induced behaviors has been suggested. The pineal gland is important component of circadian mechanisms. Using pinealectomized mice and sham-operated controls, we tested the contribution of pineal gland to the rewarding effects of cocaine in conditioned place preference test. Experiments were performed both during the day and at night. Controls with intact pineal glands demonstrated significant decrease in cocaine-induced conditioned place preference at night compared to daytime, whereas pinealectomized mice did not show any diurnal differences. Circadian mechanisms regulated by the pineal gland thus appear critically involved in cocaine-induced reward.     

Efficacy of melatonin as protectant against oxidative stress and structural changes in liver tissue in pinealectomized rats

Previous observations demonstrated that physiological levels of melatonin, the pineal secretory product, are important in protecting against oxidative stress-induced tissue damage. We investigated the effects of pinealectomy and administration of exogenous melatonin on liver tissue in rats. Pinealectomized (Px) and sham-operated (non-Px) rats were used. We evaluated structural changes, reduced glutathione (GSH) levels and malondialdehyde (MDA) levels. Rats were divided into three groups (10 rats in each group): control (non-Px), Px+vehicle and Px+melatonin (4 mg/kg given daily intraperitoneally for 10 days). Liver GSH levels were significantly lower in Px rats than in the control group. Melatonin administration significantly increased GSH levels (p < 0.05). Px caused a significant increase in MDA levels as compared with the control group and melatonin administration to Px rats significantly reduced MDA levels in the liver (p < 0.05). Sinusoidal dilatation to a varying degree developed in all Px rats. Severity of mononuclear cell infiltration and sinusoidal congestion were lower in Px+melatonin group than in the Px group. These findings suggest that a significant increase in oxidative and structural changes occur in rat livers after pinealectomy, which can be diminished by melatonin treatment.     

Effect of pinealectomy and melatonin replacement on morphological and biochemical recovery after traumatic brain injury

Numerous studies showed that melatonin, a free radical scavenger, is neuroprotective. In this study, we investigated the effect of pinealectomy and administration of exogenous melatonin on oxidative stress and morphological changes after experimental brain injury. The animals were divided into six groups, each having 12 rats. Group 1 underwent craniotomy alone. Group 2 underwent craniotomy followed by brain trauma and received no medication. Group 3 underwent craniotomy followed by brain trauma and received melatonin. Group 4 underwent pinealectomy and craniotomy alone. Group 5 underwent pinealectomy and craniotomy followed by brain injury and received no medication. Group 6 underwent pinealectomy and craniotomy followed by brain trauma and received melatonin. Melatonin (100 mg/kg) was given intraperitoneally immediately after trauma to the rats in Groups 3 and 6. Pinealectomy caused a significant increase in the malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH), and xanthine oxidase (XO) levels, and a decrease in GSH levels as compared to the control group. Trauma to pinealectomized rats causes significantly higher oxidative stress. Exogeneous melatonin administration significantly reduced MDA, XO and NO levels, increased GSH levels, and attenuated tissue lesion area. These findings suggest that reduction in endogenous melatonin after pinealectomy makes the rats more vulnerable to trauma, and exogenous melatonin administration has an important neuroprotective effect.     

Both pineal and lateral eyes are needed to sustain daily circulating melatonin rhythms in sea bass

This study investigates the role of the pineal organ and lateral eyes (the two most important sources of melatonin in vertebrate species) on daily melatonin rhythms of sea bass, a fish exhibiting reversed melatonin profiles, as well as their contribution to circulating melatonin levels. To this aim, the pineal and/or the eyes were surgically removed (Exp. 1), the optic nerve sectioned and retinal dopaminergic neurons damaged with injections of 6-hydroxydopamine (Exp. 2), and the pineal or the eyes covered with aluminium foil (Exp. 3). The results show that plasma and ocular melatonin display opposing profiles. In Experiment 1, pinealectomized fish displayed lower nightly plasma melatonin levels (66+/-22 pg/ml) than intact or sham-operated groups (131+/-14 pg/ml), as it occurred in ophthalmectomized fish (64+/-12 pg/ml). Fish that were both pinealectomized and ophthalmectomized showed a further decrease in plasma melatonin levels (1.4+/-0.4 pg/ml), which approached daytime levels. In Experiment 2, plasma melatonin levels in both optic nerve-sectioned and ophthalmectomized fish were lower than control levels, while injection of 6-hydroxydopamine did not modify plasma melatonin concentrations. In Experiment 3, covering only the pineal made melatonin drop after a light pulse at MD, and covering only the eyes had a similar effect. In conclusion, these findings suggest that even though sea bass eyes do not directly contribute to plasma melatonin, the pineal organ, which unlike that of mammals is a direct photoreceptor in fish, requires light information from the lateral eyes to normally secrete melatonin into the bloodstream.     

Effects of pinealectomy on neurohypophysial hormones in the SFO and plasma of dehydrated rats exposed to 12 hours of light

Magnocellular neurons in the supraoptic and paraventricular nuclei synthesize and release vasopressin and oxytocin in response to dehydration. Pinealectomy has been observed to decrease the distribution in the supraoptic nuclei of thiamine diphosphate-phosphohydrolase, an enzyme specific for the Golgi apparatus that correlates positively with neurosecretory activity. Based upon these studies we postulated that pinealectomy would alter the concentration of neurohypohysial hormones in plasma elevated by 48 hr of water deprivation. In addition, we investigated the possibility that pinealectomy would affect vasopressin concentration in another circumventricular organ, the subfornical organ (SFO) and in a adjacent fiber tract of the limbic system, the hippocampal commissure-fornix (HC-F). Adult, male, Sprague-Dawley rats exposed to a 12 hr light/dark cycle were either unoperated (controls; C), sham-operated (Sham; S) or pinealectomized (PX) three weeks prior to testing. Food and water consumption and urinary excretion of Na and K were measured for 7 days. On the fifth day, half of the animals in each treatment group (C, S, PX) were deprived of water for 48 hr. Animals were decapitated on day 8. Vasopressin and oxytocin in plasma were extracted using bentonite and acetone-ether, respectively, then quantified by radioimmunoassay. The SFO and HC-F were microdissected from each brain. Like tissues from 4 rats were pooled, homogenized in 0.1 N HCl, and centrifuged. The supernatant was neutralized and vasopressin was quantified by radioimmunoassay. Dehydration resulted in antidiuresis, increased urine concentrations of Na and K, a decreased ratio of Na:K in urine, and reduced food consumption of similar magnitudes in all groups (C, S, PX; p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of propranolol on the blood pressure of normotensive and pinealectomized hypertensive rats

Summary The antihypertensive effect of propranolol on pinealectomy-induced hypertension was studied in male rats. Pinealectomized hypertensive and unoperated normotensive rats were treated with (±)-propranolol · HCl twice a day p.o. for 20 days, the total daily dose being 5 or 50 mg/kg. The blood pressure of unanaesthetized rats was measured by a tail cuff method about 3 h after the first half of the daily dose on the first, 6th and 16th day of treatment. In unoperated rats both doses of propranolol induced an elevation of blood pressure throughout the experimental period, the mean increase being 5–16 mm Hg. In pinealectomized rats propranolol did not affect the blood pressure on the first day of the treatment, but the higher dose lowered the blood pressure on the 6th day from 148±2 to 137±3 mm Hg, and on the 16th day from 144±2 to 127±3 mm Hg. The lower dose of propranolol lowered the blood pressure only on the 16th day of the treatment. In contrast to the delay in the onset of the antihypertensive action of propranolol, stress-induced tachycardia was antagonized as early as 1 h after the first administration of the drug.In pinealectomized rats plasma renin activity was slightly increased. On the 20th day of treatment plasma renin activity was not significantly affected by either dose of propranolol in unoperated or pinealectomized rats. In an acute experiment propranolol (50 mg/kg p.o.) clearly lowered plasma renin activity in both unoperated and pinealectomized rats within 1 h. A single dose of 5 mg/kg of propranolol influenced plasma renin activity in neither group of rats. Since there are beta-adrenoceptor antagonists which block cardiac beta-receptors and which lower plasma renin activity without exerting an antihypertensive effect, it is concluded that the antihypertensive effect of propranolol in pinealectomized rats is not attributable to a blockade of the cardiac beta-receptors or to a decrease of plasma renin activity.A preliminary report of this work was presented to the Fifth International Congress on Pharmacology, San Francisco, 1972 (Karppanen, 1972).     

Effect of pinealectomy on immune parameters in rats with Staphylococcus aureus infection

It is generally accepted that the pineal gland is a neuroendocrine organ. Several recent experiments have shown that the pineal gland has functional and anatomical connections, particularly with the immune system, and therefore the gland is now recognized as an important immunoneuroendocrine organ in both man and animals. The present study investigates the effect of pinealectomy on some immune parameters, including hematological alterations, and the response of the brain tissue against infection caused by Staphylococcus aureus. Experiments were performed on two different age groups of rats (neonatal and young). The results showed a significant reduction of the plasma zinc level in the third week following pinealectomy, impairment of the hematological parameters including lymphocyte, erythrocyte, and leucocyte, and the deficiency of the brain response to the infective agent, particularly in pinealectomized neonatal rats. In view of these data and as described previously, the pineal gland has a main regulatory function in immune physiology, but our study indicates that only neonatal immune functions are significantly affected by pinealectomy. Received: 8 June 1999 / Accepted: 27 December 1999     

Pathological mechanism of idiopathic scoliosis: experimental scoliosis in pinealectomized rats

The pathological mechanism of curve progression in idiopathic scoliosis is still obscure. In this study we investigated the pathological mechanism of idiopathic scoliosis in experimentally induced scoliosis in rats. A total 30 rats were divided into three groups: ten bipedal rats with a sham operation, which served as the control; ten quadrupedal rats with pinealectomy; and ten bipedal rats with pinealectomy. Scoliosis developed only in pinealectomized bipedal rats and not in pinealectomized quadrupedal rats. Cervicothoracic lordosis developed in bipedal rats with or without pinealectomy. These deformities of lordoscoliosis in pinealectomized bipedal rats were similar to human idiopathic scoliosis. Lordosis or lordotic tendency was sufficient to cause the spine to rotate to the side. Rotational instability of the spine with rotation of lordotic segment appears to produce a characteristic scoliotic deformity as a secondary phenomenon. Our findings suggest that lordosis may develop in bipedal rats, but pinealectomy is required for the development of lordoscoliosis. Balanced muscle tone controlled by the postural reflex is important to maintain normal posture with a straight spine in the bipedal condition. The disturbance of equilibrium and other postural mechanisms secondary to a deficiency of melatonin after pinealectomy may promote development of lordoscoliosis with vertebral rotation especially in the bipedal posture.     

松果体及其褪黑素影响胸腺T细胞发育周期

目的 探讨松果体对胸腺分化发育时细胞周期的影响。方法 选用清洁级SD大鼠,分为正常对照组、假手术对照组、松果体摘除、松果体摘除 褪黑素腹腔注射7．5mg／kg组和松果体摘除 褪黑素腹腔注射15mg／kg组。术后4、8周取材。用ABC法染胸腺cyclin A、cyclinE阳性细胞,计算机图像分析仪测量各阳性细胞面积及其染色强度。以碘化丙啶(PI)一步插入性DNA定量荧光染色法,流式细胞术测定胸腺T淋巴细胞不同细胞周期的分布状况。以Rrr-PCR法检测褪黑素对胸腺细胞周期依赖性激酶1β表达的影响。结果 松果体摘除对胸腺cyclin E表达的影响甚于对cyclin A的影响,促进cyclinE的合成,松果体摘除后胸腺细胞周期的变化表现为G1期减少,S期和G2 M期百分比增多。补充褪黑素后上述改变有所恢复,但与剂量不成线性关系,且对皮髓质影响有所不同。褪黑素能促进胸腺细胞表达细胞周期依赖性激酶1β。结论 松果体摘除能显著影响胸腺细胞分化发育,补充褪黑素能缓解相关影响。