Dual action of morphine on cold-stimulated thyrotropin secretion in male rats

The effect of morphine infused into 4 hypothalamic locations and the periaqueductal gray (PAG) on cold-stimulated thyrotropin (TSH) secretion was studied in male rats. Morphine decreased TSH cold-response when infused into the 3rd ventricle (1-20 micrograms/rat) or the median eminence (5 and 10 micrograms/rat). Infusions bilaterally into the anterior hypothalamus (1-10 micrograms/side) or PAG (1 and 10 micrograms/rat) were ineffective, while those given into the posterior hypothalamus (1 and 5 micrograms/side, but not 10 micrograms/side) significantly enhanced TSH cold-response. Naloxone pretreatment (2 or 5 mg/kg, s.c.) reversed the decreasing effect of morphine in the 3rd ventricle (1 microgram/rat) and the increasing effect of morphine in the posterior hypothalamus (1 microgram/side). We conclude that morphine has a dual hypothalamic action on cold-stimulated TSH secretion: an inhibition periventricularly, and a stimulation in the posterior hypothalamus.     

Melatonin Effects on Serotonin Synthesis and Metabolism in the Striatum,Nucleus Accumbens,and Dorsal and Median Raphe Nuclei of Rats

This work examined the influence of the pineal gland and its hormone melatonin on the metabolism of serotonin (5-HT) in discrete areas of the forebrain, such as the Striatum and the nucleus accumbens, and the midbrain raphe. The content of 5-HT and its major oxidative metabolite, the 5-hydroxyindoleacetic acid (5-HIAA), as well as the in-vivo tryptophan hydroxylation rate were examined after long-term pinealectomy (one month) and daily melatonin treatment (500 g/kg; twice daily for ten days) in pinealectomized rats. Pinealectomy did not alter 5-HT content in any of these brain areas, but it significantly increased the content of 5-HIAA in Striatum and the 5-HIAA/5-HT ratio in nucleus accumbens. The normal values of these parameters were recuperated after administration of exogenous melatonin, but it also increased the rate of tryptophan hydroxylation in both areas. In addition, melatonin treatment decreased the levels of 5-HIAA in dorsal raphe nucleus. These data suggest that the pineal gland, through the secretion of melatonin, modulates the local metabolism of 5-HT in forebrain areas by acting on the oxidative deamination. Moreover, melatonin injected in pinealectomized rats derives in a more extended effect than pinealectomy and induces a stimulation of 5-HT synthesis in the striatum, probably due to a pharmacological effect. These results point to the striatum as a target area for the interaction between pineal melatonin and the serotonergic function, and suggest a differential effect of the melatonin injected on areas containing serotonergic terminals and cell bodies, which may relevant for the mode of action of melatonin and its behavioral effects.     

松果体及其褪黑素对大鼠胸腺细胞凋亡的影响

目的探讨松果体及其褪黑素对胸腺细胞凋亡的影响以及Caspase-3的表达。方法选用清洁级SD大鼠,分为正常对照组、假手术对照组、松果体摘除组、松果体摘除 褪黑素腹腔注射7.5mg/kg/d组和松果体摘除 褪黑素腹腔注射15mg/kg/d组。术后4、8周取材。运用TUNEL法检测胸腺细胞的凋亡程度,用ABC法染胸腺Caspase-3阳性细胞,计算机图像分析仪测量阳性细胞面积及其染色强度。以RT-PCR法检测褪黑素干预原代培养胸腺细胞Caspase-3的表达。结果松果体摘除后8周时胸腺细胞凋亡显著增加,补充褪黑素则能明显减少胸腺细胞的凋亡。Caspase-3阳性细胞主要见于胸腺皮质,松果体摘除后胸腺皮质Caspase-3阳性细胞面积增加明显,补充褪黑素则使其下降。褪黑素能上调培养胸腺细胞Caspase-3的表达水平。结论松果体能调控大鼠胸腺细胞的凋亡,松果体摘除促进胸腺细胞的凋亡,补充褪黑素能缓解相关影响。     

Effects of pinealectomy and exogenous melatonin on ghrelin and peptide YY in gastrointestinal system and neuropeptide Y in hypothalamic arcuate nucleus: immunohistochemical studies in male rats

It is reported that the pineal gland and its main hormone melatonin may have a role in the regulation of ghrelin synthesis in the brain. Stomach is the place where ghrelin is predominantly expressed and secreted. One aim of this study was to investigate possible effects of pinealectomy and melatonin treatment on gastric ghrelin amount. The studies on the effects of the pineal gland on leptin and ghrelin arises the question whether the pineal gland has also effects on the other energy-regulatory peptides such as peptide YY (PYY) and neuropeptide Y (NPY). Therefore, we also aimed to investigate the changes in the immunohistochemical staining of intestinal PYY and hypothalamic NPY following pinealectomy and melatonin treatment. Serum PYY levels were also investigated. Sprague-Dawley rats were divided into four groups as sham-operated (SHAM), sham-operated with melatonin treatment (SHAM-MT), pinealectomised (PNX) and melatonin-treated PNX (PNX-MT) groups. The cells immunostained for ghrelin were abundant throughout the gastric mucosa in all the groups. Neither pinealectomy nor exogenous melatonin affected significantly immunohistochemical staining of ghrelin in stomach. Pinealectomy resulted in a significant increase in immunohistochemical staining of PYY in ileum. The results of serum PYY measurement corresponded closely to the data obtained by immunohistochemical analysis of PYY in ileum, being significantly lower and higher in SHAM and PNX groups, respectively. Pinealectomy caused a decrease in NPY synthesis in ARC as understood from low immunohistochemical staining of NPY. Melatonin treatment increased NPY synthesis in SHAM rats and restored reduction in NPY synthesis caused by pinealectomy. In conclusion, the pineal gland and its main hormone melatonin can be suggested to have a role in the regulation of NPY synthesis in ARC and PYY in gastrointestinal system.     

Melatonin and the synthesis of vasopressin in pinealectomized male rats

The pineal hormone, melatonin, is known to modify, under different experimental conditions, neurohypophysial hormone secretion in the rat. The aim of this study was to investigate the effect of melatonin on the vasopressin biosynthesis rate in the hypothalamus of either pinealectomized or sham-operated rats, using the colchicine method. To estimate whether colchicine affects the function of the neurohypophysis in these animals, the neurohypophysial and plasma vasopressin levels were also measured. The vasopressin synthesis rate was increased after pineal removal, when compared with sham-operated animals, and melatonin strongly inhibited the rise in the hormone synthesis due to pinealectomy. After pineal removal plasma vasopressin concentration was significantly elevated, and melatonin attenuated this effect. On the contrary, the neurohypophysial vasopressin content was significantly decreased after pinealectomy, but it was not further modified by melatonin.Thus, melatonin suppresses the synthesis and secretion of vasopressin in pinealectomized rats. The present results confirm our previous reports as to the inhibitory impact of the pineal on both vasopressin synthesis and release and suggest that melatonin may mediate the effect of the pineal gland on vasopressinergic neuron activity.     

The effects of blinding,pinealectomy and exposure to constant dark conditions on gonadal activity in the female goldfish,Carassius auratus

Synopsis The effects of pinealectomy, blinding, and exposure to constant darkness were examined in female goldfish during different seasons. Neither blinding nor pinealectomy under short or decreasing photoperiod conditions, nor exposure to constant darkness had an effect on ovarian activity in goldfish during fall and winter. In spring, constant darkness has an inhibitory effect on ovarian activity. Pinealectomy under increasing photoperiod conditions partially inhibits reproductive activity, but not to the extent of constant darkness. Blinding, under the same regime also inhibited to some extent the ovarian response to increasing photoperiod. Our data suggest that retinal pathways and the pineal organ are involved in the photosexual response to increasing day lengths.Address correspondence to: Dr. V. L. de Vlaming, Marquette University     

The pineal and oxytocin synthesis.

The aim of this study was to investigate the effect of pineal removal on oxytocin synthesis in the hypothalamus using the colchicine method. To this end, rats were injected intracerebroventricularly (i.c.v.) with colchicine solution (5 microg/5 microl) or normal saline and decapitated 20 h later. The animals were either pinealectomized or sham-operated two or eight weeks before i.c.v. injection. The oxytocin content in the hypothalamus was significantly higher in colchicine-treated rats whereas no significant differences were seen in the neurohypophysial hormone level between saline- or colchicine-injected animals. Thus, colchicine inhibited the hormonal transport but probably did not affect the function of the neurohypophysis. Two weeks after pinealectomy neither the oxytocin synthesis rate nor its neurohypophysial content were significantly different from control values. The oxytocin synthesis rate was increased markedly eight weeks after pineal removal. At that time, the neurohypophysial oxytocin content was reduced suggesting the increased secretion of the hormone. It is concluded that the pineal has an inhibitory impact on both oxytocin synthesis and release.     

Does pinealectomy,anopsia or exposure to constant darkness affect pituitary prolactin levels in the goldfish,Carassius auratus L.?

Synopsis The ef fects of exposure to constant darkness, anopsia and pinealectomy on pituitary prolactin levels in the goldfish were examined. Determination of prolactin was made in a polyacrylamide microelectrophoretic system coupled with densitometry. Neither pinealectomy nor anopsia had an effect on pituitary prolactin content in the fall. Exposure to constant darkness in the fall was without obvious effect, whereas such treatment in the spring resulted in significantly elevated pituitary prolactin content. Pinealectomy in the spring did not alter pituitary content, suggesting that the response to constant darkness is independent of the pineal organ, perhaps involving retinal or extra-retinal photoreception.     

Role of pineal gland in kidney-adrenal homeostasis

The effects of pineal gland on kidney-adrenal axis have been studied in male rats. Rats were pinealectomized and exposed to a photoperiod of 12 h light: 12 h dark. Plasma renin activity (PRA), corticosterone and corticotropin (ACTH) levels were measured at 10, 20 and 35 days postpinealectomy. Pinealectomy increased corticosterone and ACTH levels and decreased PRA in all age groups. A significant negative correlation was found between corticosterone and PRA, which suggest that changes in PRA were due to changes in circulating corticosterone, via feedback mechanism on renin secretion. On the other hand, melatonin administration prevents these effects of pinealectomy. It is suggested that the lack of this pineal indol is responsible for the pinealectomy-induced alterations in male rats.     

Effects of pinealectomy and melatonin or 5-methoxytryptamine on testicular LH and PRL receptors in Syrian hamsters (Mesocricetus auratus)

The pineal has been previously shown to be an important factor in the regulation of testicular function in photoperiodic mammals. The effects of lack or increase in pineal hormones on testicular hormonal receptors has, therefore, been examined. Pinealectomy decreased the concentration of testicular LH receptors in hamsters exposed to either a long or short photoperiod but had no effect on the concentration of testicular PRL receptors. In animals exposed to a short photoperiod, pinealectomy prevented testicular regression and the concomitant decreases in total LH and PRL receptor contents. Treatment for 12 weeks with either melatonin or 5-methoxytryptamine caused a decrease in testicular PRL receptor levels, whereas the only changes in LH receptor levels were due to melatonin-induced testicular regression. The present results indicate that some of the effects of pineal hormones on the testes are independent of the pineal-induced changes in testes mass and are the consequence of long-term action. Furthermore, testicular function appears to be affected by both the lack or the increase in pineal hormones.     

Light/dark cycle-dependent metabolic changes in adipose tissue of pinealectomized rats.

We investigated the effects of pinealectomy on adipose tissue metabolism at different times of day. Adult male Wistar rats were divided into two groups: pinealectomized and control (sham-operated). Eight weeks after surgery, the animals were killed at three different times (at 8.00 a.m., at 4.00 p.m. and 11.00 p.m.). We collected blood samples for glucose, insulin, corticosterone, and leptin determinations, and periepididymal adipocytes for in vitro insulin-stimulated glucose uptake, oxidation, and incorporation into lipids. Pinealectomy caused insulin resistance as measured by 2-deoxyglucose uptake (a fall of approximately 40 % in the maximally insulin-stimulated rates) accompanied by hypercorticosteronemia at the three time points investigated without changes in plasma insulin an or leptin levels. Furthermore, pinealectomy increased the insulin-induced glucose incorporation into lipids (77 %) at 4.00 p.m. and insulin-induced glucose oxidation in the morning and in the afternoon, while higher rates were observed in the evening and in the morning in control rats. In conclusion, cell responsiveness to insulin was differentially affected by pineal ablation and time of day, and persistent insulin resistance was obtained in pinealectomized rats. We hypothesize that pinealectomy exposes the animal to an inadequate match between energy requirements and fuel mobilization.     

Pineal and photoperiodic influences on fat deposition, pelage, and testicular activity in male meadow voles

Pinealectomy completely prevented gonadal regression as well as reduction in body weight and white adipose tissue content of the gonadal and retroperitoneal fat deposits in male meadow voles transferred from long to short day lengths. Pineal influences on pelage characteristics depended on which parameter was assessed. For instance, the increase in guard hair length observed in short-day control voles was blocked by pinealectomy; however, a similar increase in underhair length was unaffected by removal of the pineal gland. Photoperiod-dependent changes in fat deposition, testicular activity, and guard hair length presumably rely on altered pineal secretory activity to transduce the effects of day length on the neuroendocrine axis; however, mechanisms independent of pineal activity may be capable of mediating photoperiodic control of underhair growth.     

The effects of pinealectomy on pituitary and plasma gonadotropin levels in Carassius auratus exposed to various photoperiod–temperature regimes

The effects of pinealectomy on pituitary and plasma gonadotropin levels and gonadal development in female goldfish exposed to various photoperiod-temperature regimes during different seasons were examined. Pinealectomy during autumn had no effect on either pituitary or plasma hormone levels or gonadal development. When goldfish are pinealectomized in spring and exposed to long photoperiod conditions, the ovaries regress and plasma gonadotropin levels are significantly depressed compared to sham operated animals. Sham operated goldfish exposed to short photoperiod conditions in spring had regressing ovaries whereas pinealectomized animals under this regime either spawned or had ovaries in the late vitellogenic phase. Plasma gonadotropin titres in the pinealectomized group were significantly lower than those of sham operated animals. The pineal can be either stimulatory or inhibitory to gonadal development depending on the photoperiod regime to which the animals are exposed. The pineal apparently influences gonadal activity by modulating gonadotropin secretion. A diurnal variation in plasma gonadotropin levels was also observed in both sham operated and pinealectomized goldfish exposed to a long photoperiod warm-temperature regime in spring.     

Androgenic activity in 15-day-old male rats: role of the maternal pineal gland.

Female Sprague-Dawley rats, exposed to a long (18L:6D) or a short (6L:18D) photoperiod from 21 days of age, were mated when they reached 55 days of age. On Day 2 of gestation, dams were pinealectomized or sham-operated. Pre- and postnatal photoperiods were identical, and offspring were killed at 15 days of age. Maternal pinealectomy had no effect when rats were kept on 18L:6D. Rats born to sham-operated mothers and kept on 6L:18D had higher testicular testosterone and androstenedione content than offspring raised on the long photoperiod. This stimulatory effect of the short photoperiod was blocked by maternal pinealectomy and was not dependent on the offspring's own pineal since it was observed in both sham-operated and neonatally (on Day 5 after birth) pinealectomized rats. When sham-operated mothers housed on 18L:6D were treated daily during pregnancy and lactation by s.c. melatonin injection, there was an increase in the testicular testosterone content of offspring. It was concluded that when rats are maintained on a 6L:18D cycle the maternal pineal gland enhances the testicular testosterone and androstenedione content in 15-day-old offspring. This effect is probably mediated by maternally derived melatonin. At 15 days of age, the pineal of the offspring had no influence on testicular function.     

Effects of pinealectomy and melatonin treatments on serotonin uptake and release from synaptosomes of rat hypothalamic regions

This study examined the effects induced by long-term pinealectomy, daily melatonin treatment to pinealectomized and intact rats, and a single melatonin injection on [¹⁴C]-serotonin (5-HT) uptake and release from synaptosomes obtained of hypothalamic regions. Pinealectomy inhibited the accumulation of labeled 5-HT by synaptosomes of the preoptic area-anterior hypothalamus (POA-AH), but it failed to alter the [K⁺]-evoked 5-HT release. Melatonin treatment for 10 consecutive days to pinealectomized rats restored 5-HT uptake in POA-AH, and also increased 5-HT release in medial and posterior hypothalamus. These results suggest that pineal melatonin plays a stimulatory role on the serotoninergic terminals of the hypothalamus. Moreover, when daily melatonin treatment was administered to intact rats a significant increase in 5-HT uptake activity by synaptosomes of all the hypothalamic regions was observed, but 5-HT release was unaffected. In contrast, a single melatonin injection induced a significant decrease in 5-HT release from synaptosomes of the POA-AH was observed. The results suggest the existence of a differential sensitivity in the mechanisms mediating melatonin actions on 5-HT uptake/release, which depends on the presence of the pineal gland in the animals and on the frequency of the treatments with the pineal hormone.     

Influence of pinealectomy on the mitotic activity of regenerating adrenal cortex in rats

There is some evidence that the pineal gland may influence the proliferation of both normal and neoplastic cells. The adrenal cortex has very high capacity for regeneration. Therefore, the effects of pinealectomy on the mitotic activity of regenerating adrenal cortex of rats were studied on the second, seventh and twelfth days following the enucleation of adrenals. Pinealectomy caused a significant decrease in the mitotic index of regenerating adrenal cortex after 2 and 12 days in comparison to sham operated controls.     

Influence of the pineal gland on testicular function in offspring of pinealectomized rats

Female Sprague-Dawley rats exposed to a short (6L:18D) photoperiod from 21 days of age were mated when they reached 55 days of age. On Day 2 of gestation animals were pinealectomized or sham-operated. On Day 5 after birth male pups of the two groups of dams were either pinealectomized or sham-operated. They were killed at 42 and 49 days of age. In offspring born to sham-operated dams and in those born to pinealectomized mothers, neonatal pineal ablation resulted in increased testicular testosterone and androstenedione content. In sham-operated and neonatally pinealectomized rats removal of the maternal pineal gland induced a decrease in testicular testosterone and androstenedione content. In contrast, after maternal pinealectomy there was a decrease in plasma testosterone and dihydrotestosterone values and testicular dihydrotestosterone content in sham-operated rats but not in those neonatally pinealectomized. We conclude that (1) the pineal glands of the mother and offspring are required to maintain normal testicular testosterone and androstenedione content in the rat, and (2) the pineal of the offspring influences the inhibitory effects of maternal pinealectomy on testicular dihydrotestosterone content and on plasma testosterone and dihydrotestosterone concentration in the offspring.     

Functional relations of the adrenal cortex, thyroid and pineal body. II. Adrenal cortex reaction following epiphysectomy and administration of melatonin

Histologic-cytological and morphometrical changes were investigated in the adrenal cortex of male Wistar-rats following pinealectomy and application of melatonin in eu-, hypo-, and hyperthyroid situations. A rat experiment (at an average of 45 d) to find a possible functional connection between the pineal gland and the adrenal cortex was carried out. In the literature, there are only a few of informations about the role of the pineal in regulating ACTH secretion. The results are very contrarily. We found that pinealectomy is connected with a progressive transformation and melatonin with a little regressive transformation in the adrenal cortex. But, it is not evident, that the glomerular zone is activated after both pinealectomy and application of melatonin. In our opinion, the glomerular zone and the secretion of aldosterone increased after as well pinealectomy as melatonin. Application of melatonin diminishes the function of the pineal gland (see group 4-pinealectomy plus melatonin-where was found a progressive transformation). Under these experimental conditions, one can speak of a "pharmacological pinealectomy" after application of melatonin alone. However, the effect of melatonin on the fascicular zone and the glomerular zone is different. The effects of pinealectomy or application of melatonin in combination with methylthiouracil or thyroxin are relatively unimportant.     

The pineal gland influences rat circadian activity rhythms in constant light.

Mammalian circadian organization is believed to derive primarily from circadian oscillators within the hypothalamic suprachiasmatic nuclei (SCN). The SCN drives circadian rhythms of a wide array of functions (e.g., locomotion, body temperature, and several endocrine processes, including the circadian secretion of the pineal hormone melatonin). In contrast to the situation in several species of reptiles and birds, there is an extensive literature reporting little or no effect of pinealectomy on mammalian circadian rhythms. However, recent research has indicated that the SCN and circadian systems of several mammalian species are highly sensitive to exogenous melatonin, raising the possibility that endogenous pineal hormone may provide feedback in the control of overt circadian rhythms. To determine the role of the pineal gland in rat circadian rhythms, the effects of pinealectomy on locomotor rhythms in constant light (LL) and constant darkness (DD) were studied. The results indicated that the circadian rhythms of pinealectomized rats but not sham-operated controls dissociated into multiple ultradian components in LL and recoupled into circadian patterns only after 12-21 days in DD. The data suggest that pineal feedback may modulate sensitivity to light and/or provide coupling among multiple circadian oscillators within the SCN.     

Lipid peroxidation in liver tissue of ovariectomized and pinealectomized rats: effect of estradiol and progesterone supplementation

The present study aimed to determine the effect of estradiol-progesterone supplementation and pinealectomy on lipid peroxidation of liver tissue in ovariectomized rats. The study was carried out on 36 adult Sprague-Dawley female rats, which weighed 200-250 g. The rats were divided into 6 groups: Group 1: Sham Ovariectomy (Sham-Ovx), Group 2: Ovariectomy (Ovx), Group 3: Ovx + Estradiol-Progesterone supplementation (Ovx + H), Group 4: Sham Pinealectomy and Ovx (Sham Pnx -Ovx), Group 5: Ovx -Pnx, Group 6: Ovx -Pnx + H. Malondialdehyde (MDA), reduced form of glutathione (GSH) and glutathione peroxidase (GSH-Px) levels were determined in liver tissue of rats. The highest MDA levels and the lowest GSH-Px levels were determined in the ovariectomized-pinealectomized group, whereas the lowest MDA was in the Sham-Ovx group, and the highest GSH-Px levels were found in the Sham-Ovx and Ovx + Hormone supplemented group. Furthermore, the highest GSH levels were in group 1 and lowest levels were in group 5. The findings of this study demonstrate that ovariectomy led to lipid peroxidation in liver tissues of rats. Pinealectomy in addition to ovariectomy, increases lipid peroxidation, but, estradiol and progesterone supplementations to the ovariectomized-pinealectomized rats protect against lipid peroxidation to a significant extent.