Melatonin ameliorates oxidative stress and induces cellular proliferation of lymphoid tissues of a tropical rodent, Funambulus pennanti, during reproductively active phase

Effect of melatonin treatment on free radical production was assessed with simultaneous investigation of hormonal level (melatonin and testosterone), blastogenic response, stimulation index, and histological observation of lymphoid organs (spleen, thymus, and bone marrow) in male Indian palm squirrel (Funambulus pennanti) during reproductively active phase (RAP). Low endogenous melatonin and high testosterone level were noted during RAP. Daily subcutaneous injection of melatonin (25 μg/100 g B wt.) at 17.30–18.00 h to squirrels for 60 consecutive days during May–June significantly decreased the thiobarbituric acid reactive substances (TBARS) level compared to control squirrels. Melatonin treatment significantly increased % stimulation ratio (%SR) of splenocytes and thymocytes against T cell mitogen concanavalin A. Pinealectomy (Px) led to a significant increase in TBARS level whereas a significant decrease was observed in blastogenic response and stimulation index was noted. Melatonin injection to Px squirrels showed restoration in %SR of thymocytes and splenocytes with a significant decrease in the TBARS level of the lymphoid tissues. Further, free radical load was induced by lipopolysaccharide (LPS; 400 μg/ml) in lymphatic tissue homogenates and noted that melatonin supplementation (2 mM/ml) led to a significant decrease in TBARS level compared to the control and LPS-supplemented groups. Histological observation showed dense cellularity of thymocytes and splenocytes. Acridine orange staining technique shows a significant increase in thymocyte apoptosis Px squirrels when compared with melatonin-treated squirrels. These findings suggest that endogenous and exogenous melatonin might be responsible for the maintenance of immune system to adapt this seasonal breeder for the rigors of the environmental changes.     

Pineal modulation of thymus and immune function in a seasonally breeding tropical rodent, Funambulus pennanti

The immune system driven by cytokines is now known to be influenced by various other endocrine glands and its hormones. Results of the present study indicate a bidirectional relation between the pineal-thymus axis and the immune system status of an Indian tropical rodent, Funambulus pennanti, during winter months (reproductive inactive phase), when it faces maximum challenges from nature. Pinealectomy during the reproductive inactive phase inhibited thymus and spleen functions, which resulted in significant changes in leukocyte and lymphocyte counts and T-cell-mediated immune function (measured in terms of delayed-type hypersensitivity response to oxazolone). Blastogenic responses of lymphoid cells (thymocytes, splenocytes, and lymph node cells) also decreased following ablation of the pineal gland. To check the definite role of the pineal gland we injected melatonin into pinealectomized squirrels, and the suppressed immune function was significantly restored. Neuroendocrine control of the pineal gland on the histocompatible tissues in this seasonal breeder, F. pennanti, suggests an adaptive mechanism of the immune system for survival in the tropical zone. J. Exp. Zool. 289:90-98, 2001.     

Pineal sensitivity to nighttime swimming stress changes during the active season in Richardson's ground squirrels (Spermophilus richardsonii)

Melatonin synthesis in the pineal gland, which is primarily regulated by the environmental lighting regime, can also be influenced by other factors that elicit modifications in sympathetic tone. The objectives of this study were to determine if forced swimming alters the normal pattern of melatonin production in the pineal gland of the Richardson's ground squirrel (Spermophilus richardsonii). In early June, the squirrels were forced to swim for 10 min during the photophase or during the scotophase. In mid-July squirrels swam only during the scotophase. Animals were sacrificed 15, 30, or 60 min after the onset of swimming. Activities of pineal N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) were assessed by radioenzyme assay, and pineal melatonin content was measured by radioimmunoassay. Daytime swimming elicited no major changes in enzyme activity or pineal melatonin. In June, swimming at night prevented the normal rises in NAT activity and pineal melatonin seen in nonswimming controls. In contrast, the pineals of squirrels that were tested 6 weeks later in mid-July did not appear to be as sensitive to nighttime swimming, as there were only minor differences in both NAT activity and melatonin content compared to controls. These results demonstrate that forced nighttime swimming, unlike several other aversive stimuli, can evoke changes in the normal pattern of pineal melatonin production in this species. Furthermore, the pineal's response to such stimuli may not be stable over the course of the active season.     

Effect of metopirone on pituitary gland of male squirrel, Funambulus pennanti (Wroughton)

1. The ACTH cell type has been demonstrated for the first time in the hypophysis of the squirrels. These are large cells with homogenous cytoplasm and are more abundant in the anteromedian zone and in the peripheral portion than elsewhere. 2. A great hypertrophy and hyperplasia of the pituitary corticotrophs were observed in the experimental group at all the intervals. 3. Metopirone treated animals showed a moderate hypertrophy and degranulation of pituitary thyrotrophs. 4. By effect of metopirone, a marked regression of pituitary interstitiotrophs and total degranulation took place by 30 days treatment. The folliculotrophs did not show alterations.     

Relationship between the annual rhythms in melatonin and immune system status in the tropical palm squirrel, Funambulus pennanti

Melatonin (MEL) regulation of seasonal variation in immunity has been studied extensively in temperate mammals. This report is the first on a tropical mammal, the Indian palm squirrel, F. pennanti. In response to the annual environmental cycle, we studied the rhythms of plasma MEL and the immune parameters of total blood leucocytes, absolute blood lymphocytes and blastogenic responses of blood, thymus and spleen lymphocytes. We found that in parallel with MEL all the immune parameters increased during the month of April onward, when natural day length, temperature, humidity and rainfall were increasing. Maximum values occurred during November (reproductively inactive phase) when the values of all the physical factors were comparatively low. Lowest values occurred during January-March (reproductively active phase) when the values of the physical factors were lowest. In order to establish a clear interrelationship between the pineal MEL and the immune system function, we manipulated these squirrels with exogenous MEL (25mg/100g B wt/day) at 1730 h during their pineal inactive phase (March) while another group was pinealectomized (Px) during November when their pineal was active. The MEL injection significantly increased all the immune parameters, while Px decreased them significantly. Hence, we suggest that MEL is immuno-enhancing for this tropical squirrel, and plays an important role in the maintenance of its immunity in accordance with the seasonal changes in environmental factors and gonadal status. (Chronobiology International, 18(1), 61-69, 2001)     

Seasonal metabolic changes in a year-round reproductively active subtropical tree-frog (Hypsiboas prasinus)

Although seasonal metabolic variation in ectothermic tetrapods has been investigated primarily in the context of species showing some level of metabolic depression during winter, but several species of anurans maintain their activity patterns throughout the year in tropical and subtropical areas. The tree-frog Hypsiboas prasinus occurs in the subtropical Atlantic Forest and remains reproductively active during winter, at temperatures below 10 degrees C. We compared males calling in summer and winter, and found that males of H. prasinus exhibit seasonal adjustments in metabolic and morphometric variables. Individuals calling during winter were larger and showed higher resting metabolic rates than those calling during summer. Calling rates were not affected by season. Winter animals showed lower liver and heart activity level of citrate synthase (CS), partially compensated by larger liver mass. Winter individuals also showed higher activity of pyruvate kinase (PK) and lower activity of CS in trunk muscles, and higher activity of CS in leg muscles. Winter metabolic adjustments seem to be achieved by both compensatory mechanisms to the lower environmental temperature and a seasonally oriented aerobic depression of several organs. The impact of seasonal metabolic changes on calling performance and the capacity of subtropical anurans for metabolic thermal acclimatization are also discussed.     

Reproductive phase dependent circadian variations of plasma melatonin, testosterone, thyroxine and corticosterone in Indian palm squirrel, Funambulus pennanti

To explain the complex mechanism of environmental influence along with internal hormonal (factors) milieu on daily variations in the circulating levels of melatonin, testosterone, thyroxine and corticosterone were analyzed with the help of inferential statistics (Cosinor rhythmometry) in a seasonally breeding tropical rodent, F. pennanti during the reproductively active (RAP) and inactive phases (RIP). Plasma melatonin, thyroxine and corticosterone levels exhibited a significant circadian oscillation during both the active and inactive phases of the annual reproductive cycle. Melatonin showed higher amplitude during RIP in the circulating plasma. Testosterone presented a peak level during evening hours (16:00 - 18:00 h) during RAP only. The phase of thyroxine was noted ∼09:76 h and ∼10.35 h during active and inactive phases, respectively. Corticosterone showed a peak level at ∼12.00 h during both phases of the reproductive cycle. Further, in this tropical rodent, the minimum difference in photoperiod (∼3 - 4 hours) and maximum variation in temperature (max. 18°C - min. 10°C during RIP and max. 45°C - min. 32°C during RAP) and humidity (85% during RIP and 35% during RAP) regulated the diurnal rhythm of circulating melatonin circadian rhythm by ∼1 hour phase advance during RIP. In conclusion, the studied hormonal rhythms may be part of an integrative system to coordinate reproduction and physiological processes successfully with environmental factors.     

Photoperiod-related changes in hormonal and immune status of male Siberian hamsters,Phodopus sungorus

Previously we have demonstrated that in Siberian hamsters some immune measures, especially the development of experimentally evoked peritonitis, varied in a photoperiod- and gender-dependent manner. The aim of the present study was to investigate whether the photoperiod-related differences in the activity of inflammation-involved immune cells are in this species attributed to the changes in the pineal gland function and/or hormonal status. Male hamsters housed in short day (SD), compared with those from long day (LD) conditions, exhibited significantly reduced plasma testosterone concentration and elevated cortisol and melatonin levels, the latter resulting from increased activity of hydroxyindole-O-methyltransferase (HIOMT). In LD hamsters but not in those from SD, an intraperitoneal (i.p.) injection of zymosan evoked a well-pronounced peritonitis expressed by increased free radical (ROS) production by peritoneal leukocytes (PTLs) stimulated in vitro with PMA. ROS production by these cells was additionally stimulated by both in vivo and in vitro treatment with melatonin and the latter was partially reversed by melatonin receptor antagonist luzindole. To conclude, in Siberian hamsters melatonin seems to exert rather immunostimulatory than anti-inflammatory effect, therefore other mechanisms, e.g. immunosuppressive effect of glucocorticoids, may underlay the compromised immune status observed in SD in this species.     

达乌尔黄鼠冬眠期间体温的变化和冬眠模式

用植入式半导体温度记录元件iButton 记录了达乌尔黄鼠冬眠季节及其前后的体温,分析了其冬眠模式和体温调节特点。结果显示:1)实验室条件下,达乌尔黄鼠冬眠季节长短的个体差异较大,可以分成深冬眠型、
少冬眠型和不冬眠型三种类型;2)达乌尔黄鼠在冬季表现出深冬眠阵(最低体温Tbm in <20℃ ,冬眠阵的持续时间BD >24 h)、短冬眠阵(T_bmin < 20℃ , BD≤24h)和日眠阵(T_bmin ≥20℃ , BD≤24 h)3 种类型,最低体温分别
为2.54℃ ± 0.35℃ 、10.05℃ ± 1.97℃ 和23.09℃ ± 0.40℃ ,彼此之间差异显著。日眠阵阵间产热阶段的最高体温为38.09℃ ±0.17℃ ,高于深冬眠阵(37.31℃ ±0.15℃ )和短冬眠阵(37.22℃ ±0.31℃ ); 3)深冬眠阵和日
眠阵中最低体温均与环境温度显著相关,冬眠过程中的最低体温为-2.43℃ ;4)深冬眠过程中,多数个体可以短时(≤3 h)耐受- 2℃ ～ 0℃ 的低温,激醒或继续维持深冬眠,无致死效应,但长时间(15 h)或过度低温
(- 5℃ 以下)的条件下,深冬眠的达乌尔黄鼠被激醒(70% )或死亡(30% ),不能持续冬眠; 5)入眠前10 d体温日波动幅度显著增加,高于出眠后的日体温波动,且多数个体入眠前出现体温的“试降”。表明,冬眠前
入眠的准备阶段,动物的体温调节已开始发生变化;冬季日眠的调节机制可能与冬眠不同;短时- 2℃ ～ 0℃ 的体温对深冬眠的达乌尔黄鼠无致死效应。     

Cytosolic progesterone receptors in the oviducts of reproductively active and quiescent turkeys (Meleagris gallopavo)

Cytosolic progesterone receptors (PRcs) from the reproductive tract of the female turkey were analyzed by high-performance liquid chromatography using a diethylaminoethyl (DEAE) ion-exchange column. PRcs from oviduct tissue of laying, incubating, photorefractory and short-day turkey hens were compared. In general, three types of PRcs were identified: Receptor I, a partially displaceable species that was eluted at a 0.13 M salt concentration; and Receptors II and III, which were two specific binding species eluting at 0.23 M and 0.26 M, respectively. In the subdivided tissue from the laying hen oviduct, Receptor I was the major PRc species of the isthmus and Receptor III was the only receptor present in the uterus. The infundibulum and magnum each contained a small amount of Receptor II and a substantial amount of Receptor III. The whole oviduct of incubating hens contained a greater proportion of Receptor I than Receptor II or III, and these last two receptor types were present in equal quantity. The whole oviduct of the short-day hens had an equal distribution of the three receptor types. In the presence of sodium molybdate, an inhibitor of phosphatase and protease, only one sharp Receptor II species was seen in the magnum and uterus of the laying hen oviduct and in the whole oviducts of incubating and short-day hens. The transformation of Receptor II to Receptor III in the absence of sodium molybdate was facilitated by the aging of cytosol at 0-4 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum ACTH and adrenal histology in reproductively inhibited male prairie deermice (Peromyscus maniculatus bairdi)

Exogenous ACTH will cause adrenal hypertrophy and gonad dysfunction in reproductively capable male deermice. The ultrastructure of the zona fasciculata of inhibited animals is substantially different from ACTH stimulated animals which suggests that ACTH alone does not produce the inhibition. Although ACTH concentrations were variable, there was no clear demonstration that any differences existed between reproductively capable vs inhibited animals at the time when corticosterone is known to be elevated in the inhibited animals. A contributory role for ACTH in promoting inhibition is not ruled out, but neither is it likely that elevated ACTH alone accounts for the observed reproductive inhibition in animals taken from populations.     

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)