Effect of pinealectomy on the circadian clock of the chick retina under different monochromatic lights

The avian circadian rhythm pacemaker is composed of the retina, pineal gland and suprachiasmatic nucleus. As an intact input-pacemaker-output system, each of these structures is linked within a neuroendocrine loop to influence downstream processes and peripheral oscillations. While our previous study found that monochromatic light affected the circadian rhythms of clock genes in the chick retina, the effect of the pineal gland on the response of the retinal circadian clock under monochromatic light still remains unclear. In this study, a total of 144 chicks, including sham-operated and pinealectomized groups, were exposed to white, red, green or blue light. After 2 weeks of light illumination, the circadian expression of six core clock genes (cClock, cBmal1, cCry1, cCry2, cPer2 and cPer3), melanopsin (cOpn4-1, cOpn4-2), Arylalkylamine N-acetyltransferase (cAanat) and melatonin was examined in the retina. The cBmal1, cCry1, cPer2, cPer3, cOpn4-1, cOpn4-2 and cAanat genes as well as melatonin had circadian rhythmic expression in both the sham-operated and pinealectomized groups under different monochromatic lights, while cClock and cCry2 had arrhythmic 24 h profiles in all of the light-treated groups. After pinealectomy, the rhythmicity of the clock genes, melanopsins, cAanat and melatonin in the chick retina did not change, especially the mesors, amplitudes and phases of cBmal1, cOpn4-1, cOpn4-2, cAanat and melatonin. Compared to the white light group, however, green light increased the mRNA expression of the positive-regulating clock genes cBmal1, cAanat, cOpn4-1 and cOpn4-2 as well as the melatonin content in pinealectomized chicks, whereas red light decreased their expression. These results suggest that the chick retina is a relatively independent circadian oscillator from the pineal gland, whose circadian rhythmicity (including photoreception, molecular clock and melatonin output) is not altered after pinealectomization. Moreover, green light increases ocular cAanat expression and melatonin synthesis by accelerating the expression of melanopsin and positive-regulating clock genes cBmal1 and cClock.     

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.     

Thermoregulatory behaviour in two species of iguanid lizards (Crotaphytus collaris andSauromalus obesus): diel variation and the effect of pinealectomy

Summary Thermal selection by collared lizards (Crotaphytus collaris) and chuckawallas (Sauromalus obesus) was studied in continuously operating laboratory thermal gradients in a 12L12D photoperiod in spring-summer. In both species, selected temperatures above the median were higher during the day than at night. Below the median selected temperature, however, nighttime temperature significantly exceeded daytime temperature in chuckawallas but not in collared lizards. Pinealectomized collared lizards selected significantly lower temperatures than sham-operated or intact controls. This effect was most pronounced at night. Pinealectomy had no effect on the temperatures selected by chuckawallas. The significance of these results is discussed in relation to the seasonal life-history strategy of these two species.     

Increased REM sleep associated with melatonin deficiency after pinealectomy: a case study

The objectives of the investigation were to assess hypersomnia, which progressively appeared in a young patient after a pinealectomy, chemotherapy, and radiotherapy for a typical germinoma, as well as the potential benefit of melatonin administration in the absence of its endogenous secretion. 24 h ambulatory polysomnography and the Multiple Sleep Latency Test (MSLT) were performed; in addition, daily plasma melatonin, cortisol, growth hormone, prolactin, and rectal temperature profiles were determined before and during melatonin treatment (one 2 mg capsule given nightly at 21:00 h for 4 weeks). MSLT showed abnormal sleep latency and two REM sleep onsets. Nighttime total sleep duration was lengthened, mainly as a consequence of an increased REM sleep duration. These parameters were slightly modified by melatonin replacement. Plasma melatonin levels, which were constantly nil in the basal condition, were increased to supraphysiological values with melatonin treatment. The plasma cortisol profile showed nycthemeral variation within the normal range, and the growth hormone profile showed supplementary diurnal peaks. Melatonin treatment did not modify the secretion of either hormone. The plasma prolactin profile did not display a physiological nocturnal increase in the basal condition; however, it did during melatonin treatment, with the rise coinciding with the nocturnal peak of melatonin concentration. A 24 h temperature rhythm of normal amplitude was persistent, though the mean level was decreased and the rhythm was dampened during melatonin treatment. The role of radiotherapy on the studied parameters cannot be excluded; the findings of this case study suggest that the observed hypersomnia is not the result of melatonin deficiency alone. Overall, melatonin treatment was well tolerated, but the benefit on the sleep abnormality, especially on daytime REM sleep, was minor, requiring the re-introduction of modafinil treatment.     

Pineal mediation of the thermoregulatory and behavioral activating effects of beta-endorphin

Intraventricular administration of the opioid peptide, beta-endorphin to goldfish altered their body temperatures and activity levels. Low doses (0.5-5.0 pg g-1 body weight) of beta-endorphin significantly increased behaviorally selected body temperatures while higher doses (15 pg g-1) decreased the preferred temperatures selected in horizontal thermal gradients. There was a significant day-night rhythm in the extent of these effects. These thermoregulatory effects could be blocked and reversed by systemic administration of the opiate antagonist, naloxone, supporting mediation of the thermoregulatory effects at opioid receptors. In addition, administration of naloxone by itself significantly decreased preferred temperature. Removal of the pineal gland significantly increased the preferred temperatures selected by goldfish and eliminated the thermoregulatory effects of beta-endorphin administration in both the day and the night. The behavioral activity effects of beta-endorphin were dependent on the thermal conditions. In fish held at a constant temperature (20 degrees C) beta-endorphin caused a dose-dependent increase in activity, while in individuals held in thermal gradients administration of beta-endorphin had no effects on activity. In both situations naloxone caused a decrease in activity levels. Pinealectomy also eliminated the behavioral activating effects of beta-endorphin, though it had no apparent effects on the actions of naloxone. These results indicate that the pineal gland is involved in the mediation of the thermoregulatory and behavioral activating effects of beta-endorphin. Speculations are made as to the possible mechanisms of action of the pineal gland in mediating the effects of opioid neuropeptides.     

Increased REM Sleep Associated with Melatonin Deficiency after Pinealectomy: A Case Study

The objectives of the investigation were to assess hypersomnia, which progressively appeared in a young patient after a pinealectomy, chemotherapy, and radiotherapy for a typical germinoma, as well as the potential benefit of melatonin administration in the absence of its endogenous secretion. 24 h ambulatory polysomnography and the Multiple Sleep Latency Test (MSLT) were performed; in addition, daily plasma melatonin, cortisol, growth hormone, prolactin, and rectal temperature profiles were determined before and during melatonin treatment (one 2 mg capsule given nightly at 21:00 h for 4 weeks). MSLT showed abnormal sleep latency and two REM sleep onsets. Nighttime total sleep duration was lengthened, mainly as a consequence of an increased REM sleep duration. These parameters were slightly modified by melatonin replacement. Plasma melatonin levels, which were constantly nil in the basal condition, were increased to supraphysiological values with melatonin treatment. The plasma cortisol profile showed nycthemeral variation within the normal range, and the growth hormone profile showed supplementary diurnal peaks. Melatonin treatment did not modify the secretion of either hormone. The plasma prolactin profile did not display a physiological nocturnal increase in the basal condition; however, it did during melatonin treatment, with the rise coinciding with the nocturnal peak of melatonin concentration. A 24 h temperature rhythm of normal amplitude was persistent, though the mean level was decreased and the rhythm was dampened during melatonin treatment. The role of radiotherapy on the studied parameters cannot be excluded; the findings of this case study suggest that the observed hypersomnia is not the result of melatonin deficiency alone. Overall, melatonin treatment was well tolerated, but the benefit on the sleep abnormality, especially on daytime REM sleep, was minor, requiring the re‐introduction of modafinil treatment.     

PINEAL INFLUENCE ON ANNUAL NUCLEAR VOLUME CHANGES IN VENTROMEDIAL HYPOTHALAMIC NUCLEUS (VMH) NEURONS OF THE MALE WISTAR RAT

The ventromedial hypothalamic nucleus (VMH) regulates various autonomic, endocrine, and behavioral activities. These activities show annual changes, and the pineal gland is involved in their adjustment to environmental cues. Therefore, this study investigated whether the VMH belongs to the effector structures of the pineal gland. To abolish the rhythmic melatonin release, male Wistar rats were subjected to pinealectomy (PX) or ganglionectomy (sympathetic denervation of the pineal gland, GX) regularly at the beginning of any of the four seasons. Brains from animals of PX-, GX-, and sham-operated control groups were prepared 3 months later for measurement of the nuclear volume, which changes according to the general gene activity. At each of the four seasons, 2000 nuclei of VMH neurons stemming from 18 animals per group were measured to obtain both seasonal daily mean values and annual mean values,respectively, as well as to calculate annual curves of the nuclear volume using empirical regression and locally adjusted polynomial approximation. The major findings are the following. First,inactivation of the pineal function influences the nuclear activity of VMH neurons. (2) PX and GX mainly depress the nuclear activity, indicating that the pineal influence on the VMH may predominantly be a stimulatory one. Third, size and direction of the changes caused by PX and GX vary in a seasonally dependent manner. Fourth, the annual rhythm of the nuclear activity of the VMH is modified by PX and GX.To explain how the pineal effects on the VMH may be mediated, a possible inhibitory influence of the suprachiasmatic nucleus (SCN),which has been activated in the same animals following both PX and GX, is discussed. In conclusion, the results confirm that the nuclear activity of VMH neurons underlies pineal influences. This also indicates an involvement of the pineal gland in many VMH-regulated functions.(Chronobiology International,17(1),15–28, 2000)     

Arginine vasotocin and aggression in rats

Pinealectomized (PX) and sham animals were administered either AVT (1 ng/kg) or vehicle (1 ml H₂O). Boxing-kicking-biting episodes were significantly reduced by administration of AVT, F(1,21)=8.09,p<0.009. Crawling under behavior was increased in PXH₂O animals (p<0.05). Non-aggressive rearing was decreased by administration of AVT, F(1,21)=4.75, p<0.04. These results are in agreement with previous findings that AVT lowers emotionality-arousal. Results are discussed in terms of vasotonergic effects on central monoamines.     

Pineal influence on annual nuclear volume changes in ventromedial hypothalamic nucleus (VMH) neurons of the male Wistar rat

The ventromedial hypothalamic nucleus (VMH) regulates various autonomic, endocrine, and behavioral activities. These activities show annual changes, and the pineal gland is involved in their adjustment to environmental cues. Therefore, this study investigated whether the VMH belongs to the effector structures of the pineal gland. To abolish the rhythmic melatonin release, male Wistar rats were subjected to pinealectomy (PX) or ganglionectomy (sympathetic denervation of the pineal gland, GX) regularly at the beginning of any of the four seasons. Brains from animals of PX-, GX-, and sham-operated control groups were prepared 3 months later for measurement of the nuclear volume, which changes according to the general gene activity. At each of the four seasons, 2000 nuclei of VMH neurons stemming from 18 animals per group were measured to obtain both seasonal daily mean values and annual mean values,respectively, as well as to calculate annual curves of the nuclear volume using empirical regression and locally adjusted polynomial approximation. The major findings are the following. First,inactivation of the pineal function influences the nuclear activity of VMH neurons. (2) PX and GX mainly depress the nuclear activity, indicating that the pineal influence on the VMH may predominantly be a stimulatory one. Third, size and direction of the changes caused by PX and GX vary in a seasonally dependent manner. Fourth, the annual rhythm of the nuclear activity of the VMH is modified by PX and GX.To explain how the pineal effects on the VMH may be mediated, a possible inhibitory influence of the suprachiasmatic nucleus (SCN),which has been activated in the same animals following both PX and GX, is discussed. In conclusion, the results confirm that the nuclear activity of VMH neurons underlies pineal influences. This also indicates an involvement of the pineal gland in many VMH-regulated functions.(Chronobiology International,17(1),15-28, 2000)