Chandana Haldar

Annual pineal and testicular cycle in the indian jungle bush quail, Perdicula asiatica, with reference to the effect of pinealectomy

The annual testicular cycle of Perdicula asiatica has a single peak which appears to be under the dual influence of the environment and the pineal gland. An inverse relationship was noted between pineal gland and testicular weight cycle. Pinealectomy, after 60 days, retarded testicular growth in the progressive phase, inhibited activity of the gonad in the active phase, and accelerated gonadal regression in the regressive phase. This complete study of short-term pinealectomy effects on the annual testicular cycle of a tropical bird for the first time reflects both the essentialness of the pineal gland to the maintenance of proper testicular cyclicity under natural environment conditions and the progonadotropic nature of the pineal gland.

Improvement of oxidative stress and immunity by melatonin: An age dependent study in golden hamster

Reactive oxygen species (ROS) have been proposed to play an important role in balancing the pro- and antioxidant homeostasis during aging. Melatonin has been suggested as an effective free radical scavenger that might have a role during the process of aging. We observed, that melatonin administration (25 μg/100 g body weight for 30 days) significantly augments the activity of anti-oxidative enzymes like superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) in the plasma, spleen and bone marrow (BM) of young (6 weeks), adult (30 weeks) and old aged (2.5 years) male golden hamster, Mesocricetus auratus. A sharp decline in generation of ROS was observed in peripheral blood mononuclear cells (PBMC) and splenocytes upon melatonin administration in different age group of hamsters. Reduction in the level of thiobarbituric acid-reactive substances (TBARS) and total nitrite and nitrate concentration as metabolites and indicators of nitric oxide (NO) in plasma, spleen and BM were observed along with night time (22:00 h) melatonin concentration in different age group of hamsters after administration of melatonin and compared to the control group (treated with 0.9% saline). General immune parameters like proliferation of splenocytes, PBMC and colony forming ability of GM-CFU were observed following melatonin treatment in different age group, although it was low only in aged hamsters compared to the young and adult. Our data indicates that the age related increase of oxidative load and simultaneously augments the general immunity in aged hamsters.

PHOTOPERIODIC REGULATION OF MT1 AND MT2 MELATONIN RECEPTOR EXPRESSION IN SPLEEN AND THYMUS OF A TROPICAL RODENT FUNAMBULUS PENNANTI DURING REPRODUCTIVELY ACTIVE AND INACTIVE PHASES

Photoperiodic regulation of melatonin receptor types on target tissues, such as lymphatic organs, has never been explored for any seasonal breeder. In the present study, we accessed the high affinity membrane melatonin receptors MT1 and MT2 expression dynamics in lymphoid organs (i.e., spleen and thymus) of a seasonally breeding rodent Funambulus pennanti during two major reproductive phases (i.e., active and inactive), when the internal hormonal (melatonin and gonadal steroid) as well as the ecological conditions were entirely different. Photoperiod regulates circulatory melatonin level; hence, we noted the effect of different photoperiodic regimes (long; 16L:8D and short; 10L:14D photoperiod) equivalent to summer and winter daylength on membrane melatonin receptor MT1 and MT2 expression in spleen and thymus. We have correlated the melatonin receptor expression with two major hormones varying seasonally (i.e., melatonin and testosterone) also being responsible for modulation of immunity of a seasonal breeder. Differential immunoreactivity of MT1 and MT2 receptor in spleen and thymus of F. pennanti suggests an involvement of both the receptor types in signal transduction of photoperiod for seasonal immunomodulation, because in the tropical zone, a slight difference (1:45–2 h) in daylength may change reproductive physiology and immunity of animals for adaptation. Our above suggestion receives strong support from the experiment of photoperiodic exposure on MT1 and MT2 expression at the translational level, where long daylength decreased the circulatory melatonin level and melatonin receptor expression in both lymphatic tissues. On the other hand, under short daylength, expression of MT1 and MT2 receptor increased in both spleen and thymus along with concomitant increase in circulatory melatonin level. Differential hormonal level of melatonin and gonadal hormones during reproductively active and inactive phase and its direct relation with melatonin receptor expression dynamics in lymphoid organs could be responsible for seasonal adjustment of immunity and reproduction. (Author correspondence: chaldar2001@yahoo.com)

Physiological crosstalk between melatonin and glucocorticoid receptor modulates T-cell mediated immune responses in a wild tropical rodent, Funambulus pennanti

Immunoenhancing attributes of melatonin (Mel) on the immunocompromised state induced by glucocorticoid is well known, but the involvement of their receptors in the modulation of immunity has never been studied in any rodent. The present study explores the role of Mel and its receptors (MT1 and MT2) in amelioration of immunocompromised state induced by a synthetic glucocorticoid, dexamethasone (Dex) in a tropical rodent Funambulus pennanti. Immune parameters viz. DTH response, Lymphocyte proliferation, cytokine (IL-2) and antibody production were assessed following pretreatment of Mel and Dex alone or in combination. Mel enhanced the IL-2 production, thymic and splenic lymphocyte proliferation thereby increasing T helper cell associated immune responses and anti-KLH-IgG production. MT1 and MT2 receptor expression was downregulated following Dex treatment while glucocorticoid receptors (GR) expression was downregulated in Mel treated groups suggesting that the immunomodulatory effects of glucocorticoids and Mel are mediated via their receptors. To gain further insights on the role of Mel receptors, we used nonselective melatonin receptor antagonist luzindole which resulted in reversal of most of the immunomodulatory actions of Mel. Therefore, it may be suggested that a physiological cross talk exist between Mel and GR which is of high adaptive significance in wild animals for balancing the immunity during ecologically stressful conditions.

Effect of exogenous melatonin on X-ray induced cellular toxicity in lymphatic tissue of Indian tropical male squirrel, Funambulus pennanti.

Purpose: The radioprotective ability of melatonin was investigated in the Indian tropical rodent, Funambulus pennanti during its reproductively inactive phase (RIP) when peripheral melatonin is high and the animal is under the influence of environmental stresses. Materials and methods: Fifty male squirrels were divided into two sets of 25 each; with set 1 receiving 0.9% saline and set 2 receiving 25 μg melatonin/100 g body weight/day for four weeks during evening hours. Five saline-treated and five-melatonin treated squirrels were sacrificed at times of 4, 24, 48 and 72 hours following 2.06 Gy X-ray radiation. Remaining squirrels that were not exposed to X-ray were used as control and melatonin treated, respectively. Total leukocyte count (TLC) and lymphocyte count (LC) in peripheral blood and lipid peroxidation (LPO) status, superoxide dismutase (SOD) activity, total antioxidant status (TAS), apoptotic percentage on the basis of morphological changes and DNA fragmentation and caspase-3 activity were measured in the spleens of squirrels. Results: Peripheral blood and spleens with higher intrinsic levels of environmental and X-radiation induced free radical generation had inhibited TLC, LC, SOD activity and TAS and increased LPO and apoptosis. Melatonin pre-treatment significantly reduced and altered the changes brought on by X-radiation. Conclusion: Exogenous melatonin with its anti-apoptotic and antioxidant properties additively increased the immunity of the squirrels, by protecting their hematopoietic system and lymphoid organs against X-ray radiation induced cellular toxicity.

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)

Melatonin blocks dexamethasone-induced immunosuppression in a seasonally breeding rodent Indian palm squirrel, Funambulus pennanti.

In vivo effect of dexamethasone and melatonin on immunomodulation has been investigated by studying the lymphocyte proliferation to the mitogen Con A from various lymphoid tissues including bone marrow cells of a seasonally breeding rodent adult male F. pennanti during reproductively inactive phase (October to December). During this phase, animal faces the maximum challenges of the nature (hypothermic stress, scarcity of food and shelter). Dexamethasone treatment (60 microg/day/squirrel) for 60 consecutive days significantly decreased the thymus and spleen activity. The lymphoid tissues mass, total leukocyte, lymphocyte count of peripheral blood, bone marrow and T-cell mediated immune function was also significantly suppressed following the dexamethasone treatment but treatment of melatonin (25 microg/squirrel/day) along with dexamethasone significantly restored the suppressed immune status in squirrels. Further, histological study of the thymus showed profound changes in the cellularity with a depletion of thymocytes in the cortex region of thymic lobules and increased in connective tissues and spindle cells. Melatonin treatment alone increased thymocytes density in thymic cortex, clearly suggesting that melatonin counteracted the experimentally induced immune stress by dexamethasone. Therefore, in nature during reproductively inactive phase of the squirrel a high level of melatonin was noted, that is required to combat natures stress, which might have increased the internal level of corticoids.

Pineal gland and humidity effects on testicular function of the Indian palm squirrel, Funambulus pennanti.

The effect of two different conditions of humidity (80 ± 5% and 40 ± 5%) under stimulatory photoperiod (14L/10D) and high temperature (38 ± 2°C) was studied on the testes and accessory sex organs of the Indian palm squirrel, Funambulus pennanti, during the sexually active phase. High humidity (80 ± 5%) reduced significantly the testes weight of the sham‐operated animals as compared to the controls under natural environmental conditions but had no effect on that of pinealectomized animals. Moderate humidity (40 ± 5%) did not affect the testes of sham‐operated as well as pinealectomized animals, as compared to the respective controls. The seminal and prostatic weights showed no significant difference in high or moderate humidity conditions. However, the epididymal weight of the animals exposed to high humidity was significantly reduced in sham‐operated animals only. Thus, these results indicate that the pineal gland may be implicated in mediating the humdity information to control the male gonadal function in the Indian palm squirrel, Funambulus pennanti.

Effect of pinealectomy on the annual testicular cycle of Calotes versicolor

Abstract Pinealectomy resulted in an earlier recrudescence and a later regression of the annual gonadal cycle of the lizard Calotes versicolor . Spermatozoa appeared early and were present throughout the course of the experiment, namely, for 11 months. In control lizards (sham-operated, intact), on the other hand, spermatozoa appeared in late April and were observed only until August, a period of 5 months. The sex segments of the kidneys showed a cycle similar to the cycle of the testes in both groups.

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.