Neonatal pinealectomy impairs murine antibody-dependent cellular cytotoxicity

The pineal gland, through its principal hormone melatonin, is able to modulate different immune functions. We have previously demonstrated that exogenous melatonin induces a significant enhancement of murine antibody-dependent cellular cytotoxicity (ADCC). In order to determine whether the pineal gland plays a physiological role in ADCC regulation, we studied the influence of neonatal pinealectomy on this activity. The results presented here indicate that ablation of the pineal gland during the first week of life significantly reduces ADCC levels in adult mice. This impairment appears around 60 days of age, suggesting that sexual hormones may be involved in the pineal effect. Moreover, the administration of melatonin to pinealectomized mice restores ADCC levels regardless of the hour and seasonal time of injection. On the basis of the data reported here, a physiological regulation of ADCC by the pineal gland can be assumed.     

Investigations of the regulation of specific 2-[I]iodomelatonin binding sites in Siberian hamsters by endogenous and exogenous melatonin

These studies used quantitative in vitro autoradiography to investigate whether endogenous or exogenous melatonin modulate specific 2-[¹²⁵I]iodomelatonin binding sites in the pars tuberalis or suprachiasmatic nuclei of Siberian hamsters. Saturation analyses were conducted on tissue sections from hamsters that were pinealectomized, exposed to constant illumination (72 h), or injected with melatonin, and from hamsters that were treated as controls. High affinity (K_d approximately 20–75 pM) specific 2-[¹²⁵I]iodomelatonin binding sites were detected in the suprachiasmatic nuclei and pars tuberalis of all animals. Neither pinealectomy nor constant illumination significantly affected either the affinity or the density of the specific 2-[¹²⁵I]iodomelatonin binding sites in either region. Melatonin injections led to a decrease in specific 2-[¹²⁵I]iodomelatonin binding to the pars tuberalis at 3–4 h after the last injection. However, washing the sections before incubation with 2-[¹²⁵I]iodomelatonin eliminated this effect, suggesting that melatonin was occupying the binding sites rather than decreasing their actual number. Furthermore, when hamsters were sacrificed 18 h after the last melatonin injection, no effect of melatonin on either the affinity or density of specific 2-[¹²⁵I]iodomelatonin sites was observed. These data suggest that 2-[¹²⁵I]iodomelatonin binding sites in Siberian hamsters are not regulated by changes in circulating melatonin levels.     

Daily variations in melatonin receptor density of rat pars tuberalis and suprachiasmatic nuclei are distinctly regulated

Suprachiasmatic nuclei (SCN) and pars tuberalis (PT) are two structures in the rat exhibiting high affinity receptors for melatonin. Melatonin receptor density in these two structures was previously shown to be inversely related to endogenous ligand concentration, thus elevated at daytime. We now demonstrate that, in the PT, these daily variations are directly induced by the circadian rhythm of plasma melatonin concentration. Variations persist in constant darkness and can only be blocked by pinealectomy. Thus, autoregulation loop of melatonin receptors determines the circadian rhythm in PT melatonin receptor de density. However, this process of densensitization does not determine the daily variations in SCN melatonin receptor density. Indeed, in the SCN, the light/dark cycle is the regulatory factor: melatonin receptor density was shown to be specifically reduced during the night even in pinealectomized animals, while one h light was shown to reverse this nocturnal decrease in the SCN. Moreover, this darkness-induced down-regulation of SCN melatonin receptors has a masking effect on the earlier shown ligand-dependent desensitization process in this structure. This explain why, in constant darkness, SCN melatonin receptor density did not show any variation throughout the 24 h subjective day and night, although the circadian rhythm of melatonin persisted. These results thus clearly show that although daily rhythms in the density of melatonin receptors are identical in the PT and in the SCN, their regulation is totally different in each of these two structures.     

Effect of pinealectomy and a constant high level of circulating melatonin or of 5-methoxytryptamine on the vasopressinergic innervation in the brain of the European hamster (Cricetus cricetus,L)

Summary In the European hamster (Cricetus cricetus, L.) pinealectomy as well as a constant high level of either circulating melatonin or 5-methoxytryptamine induce marked changes in the immunocytochemically demonstrable central vasopressinergic innervation. When compared to control animals, a drastic decrease of AVP-immunoreaction was observed in the diagonal band of Broca, the lateral septum, the medial amygdala and the ventral hypothalamus.The results obtained suggest that part of the central vasopressinergic innervation is involved in pineal dependent seasonal functioning of the animal.This work is supported by ATP-CNRS Europe, Fondation de Recherche en Hormonologie n° 6786007 and Commission of the European Communities n° ST2J-0271-C.     

Pinealectomy and two-way avoidance in the guinea pig (Cavia porcellus)

The effects of pinealectomy on two-way avoidance learning in the guinea pig were investigated. Results showed no difference between pinealectomized and normal guinea pigs on any of the performance measures taken. This suggests that blindness-induced facilitation of two-way avoidance in guinea pigs is not a result of the hormonal changes in the pineal known to accompany variations in visual input.     

A rapid and reliable technique for pinealectomizing rats

Rats may be quickly and easily pinealectomized by first removing a small area of skull between the saggital and lambdoid sutures, and then extracting the unexposed pineal gland with iridectomy forceps. Little cortical or epithalamic damage results from this procedure and loss of blood is extremely slight. Operate mortality is quite low and comparable to that of animals given sham operations.     

The effects of pineal gland transplantation on the production of spinal deformity and serum melatonin level following pinealectomy in the chicken

Pinealectomy frequently produces spinal deformity in some animal models, but the precise biological mechanism of this phenomenon remains obscure. The current study investigated the effects of an autograft pineal body on the development of spinal deformity and serum melatonin (MLT) concentration after pinealectomy in the chicken. Thirty-six chickens (2 days of age) were divided into three equal groups. While the removal of the pineal gland was performed in groups B and C, a pineal body autograft was surgically implanted into the body wall musculature only in the pineal transplantation group (group C). Chickens in which no surgical intervention was performed served as intact controls (group A). Posteroanterior radiographs of the spines of the chickens were taken at the age of 8 weeks. These were used to determine Cobb angles and to measure the rib-vertebra angles (RVA) on the concave and convex sides of the curves, from which data the difference between the convex and concave RVA (the RVAD) was calculated. At the end of the study, serum MLT levels were determined using the enzyme-linked immunosorbent assay method, and histopathological examination of specimens from all the groups was performed. The results were compared using one-way analysis of variance followed by Duncan's test for pairwise comparisons or by the Kruskal-Wallis test followed by the Mann-Whitney U tests for comparisons between two groups. In this study, the serum MLT levels in groups B and C were significantly lower than those in group A ( P<0.05). However, scoliosis developed in only 7 of 12 (58%) in group B and 6 of 12 (50%) in group C. The average Cobb angle and RVAD in groups B and C were significantly larger than those found in group A ( P=0.000 and P=0.001, respectively). Interestingly, there were no significant differences in either serum MLT levels or development of scoliosis between groups B and C. From the results of the current study, it is evident that the intramuscular pineal gland transplantation following pinealectomy in young Hybro Broiler chickens has no significant effect on the development of spinal deformity and serum MLT level. In the light of this result, the role of MLT in the development of spinal deformity in chickens after pinealectomy remains controversial, and further investigations are warranted.     

去卵巢、去松果体对大鼠学习记忆及海马胆碱能神经的影响

目的 探讨雌激素（E)、褪黑素（MT）缺乏对大鼠学习记忆及海马胆碱能纤维密度的影响。方法 用Y型迷宫测试淘汰学习记忆障碍大鼠,将学习正常大鼠分为正常、假去卵巢（假OVX）、OVX、假去松果体（假PX）、PX、假OVX＋假PX、OVX＋PX7组。90d后再行Y型迷宫测试,乙酰胆碱酯酶（AChE)组织化学检测海马CA1－4区AChE。结果 大鼠学习记忆能力及AchE阳性纤维密度在正常、假手术各组间无显著差别,在OVX、PX、OVX＋PX组间依次显著降低,三组均比正常及假手术各组显著降低。结论 OVX、PX可使大鼠学习记忆及海马胆碱能纤维密度降低。PX作用大于OVX,联合作用大于单独作用。     

Pinealectomy in ground squirrels: effect on behavioral and physiological responses to heat stress

Richardson's ground squirrels, 1 year after pinealectomy, showed altered behavioral and physiological responses to heat stress when compared to an intact group. Pinealectomized squirrels bar-pressed more often for a cool temperature reward in a hot environment. When deprived of behavioral control of the hot environment, pinealectomized squirrels increased their oxygen consumption, had a higher body temperature, and displayed signs of greater thermal stress, including death, as compared to intact animals. When the intact group was pinealectomized and the experiments were repeated, the difference in behavioral and physiological responses to heat stress were not as great as with the 1 year pinealectomized group. A speculative explanation of the pineal gland's influence on central and peripheral control of evaporative water loss and peripheral blood circulation are offered. The pineal gland may exert a subtle influence on heat transfer mechanisms and adaptations to thermal stress.