Supplementation of corn seed with regular diet modulates immune function and antioxidant status in Capra hircus.

Melatonin modulates the functional activation of antioxidative enzymes to maintain the oxidant-antioxidant balance in the physiological system. Melatonin administration via subcutaneous injection increases endogenous melatonin concentration that has been used to modulate the immune function in rodents and reproductive activity in small ruminant like goats. However, to date, no report exist which could suggest the effect of corn seed supplementation on the endogenous melatonin concentration and its impact on cellular-immune function and antioxidative enzymes activity in any small ruminant like goats. Therefore, in this study, Zea mays (corn seeds), as source of melatonin, were supplemented with regular diet to explore its impact on endogenous melatonin concentration in goat, Capra hircus. Zea mays supplementation with regular diet for 40 days significantly elevated the endogenous melatonin concentration, proliferative response of peripheral blood mononuclear cells and antioxidative enzymes activity along with total antioxidant capacity of the plasma. An increase in circulatory IL-2 and IL-6 level along with declined TNF-α, malondialdehyde and nitric oxide was noted with elevated endogenous melatonin concentration. In conclusion, it might be suggested that corn seed could be used as supplement to modulate endogenous melatonin concentration that may improve cellular-immune function and antioxidant status. The corn seed might also be included as nutraceutical in regular diet to maintain immune-antioxidant homoeostasis in other species.

Melatonin improves ultraviolet B-induced oxidative damage and inflammatory conditions in cutaneous tissue of a diurnal Indian palm squirrel Funambulus pennanti.

BACKGROUND: Skin is exposed to various abiotic and biotic factors. Solar radiation, of which ultraviolet (UV) rays are a principle component, increases the free radical load, and the accumulation of reactive oxygen species (ROS) causes lipid peroxidation, DNA damage and apoptosis, and is also associated with inflammatory responses recruiting molecules [nuclear factor (NF)-κB, interleukin (IL)-6] that can potentially further aggravate the damaged milieu of the cells. One of the potent causes of skin cancers is exposure to UV rays. UV radiation generates a wide range of biological responses such as adaptive, inflammatory and immunological reactions in the skin. OBJECTIVE: To examine the effects of pretreatment with melatonin on UVB (290-320 nm) radiation-mediated damage to the skin of a diurnal rodent Funambulus pennanti. RESULTS: The UVB radiation (1·5 J cm(-2) for 30 min daily on the shaved abdominal area) for 4 days caused a significant increase in the lipid peroxidation products (thiobarbituric acid reactive substances, TBARS) and decreased the activity of the antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) of the skin. Pretreatment with melatonin (100 µg 100 g(-1) bodyweight subcutaneously) improved the damage induced by UVB radiation on the skin and might act via a receptor-independent mechanism. No significant effect of melatonin pretreatment was found on the expression pattern of MT1 (melatonin membrane receptor) and RORα (nuclear retinoic orphan receptor alpha), which suggests a receptor-independent action. However, NF-κB and inflammatory cytokine IL-6 levels were downregulated in the squirrels pretreated with melatonin before the UVB radiation. CONCLUSION: UVB radiation induced oxidative stress in the skin culminating in an inflammatory response. The action of melatonin in protecting the skin from oxidative damage occurs in a receptor-independent manner by lowering the oxidative damage and inflammatory response. On the other hand, melatonin decreased the expression of NF-κB and the circulating proinflammatory cytokine IL-6, suggesting an anti-inflammatory action in protecting the skin from UVB radiation.

Reciprocal interaction between melatonin receptors (Mel(1a), Mel(1b), and Mel(1c)) and androgen receptor (AR) expression in immunoregulation of a seasonally breeding bird, Perdicula asiatica: role of photoperiod.

Light is the major environmental stimulus affecting behaviour and physiology of avian species. Our study elaborates the photoperiodic regulation of melatonin (Mel1a, Mel1b, and Mel1c) and androgen receptor (AR) to elucidate its reciprocal interaction in regulation of general immunity in tropical wild bird, Perdicula asiatica. Effect of different photoperiodic exposures such as continuous light (LL), continuous dark (DD), long days (LD; 16 h light/day), short days (SD; 10h light/day) and normal day length (NDL) was accessed both on cellular and humoral immune parameters like per cent stimulation ratio (%SR), total leukocyte count (TLC), leukocyte count (LC), plasma interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-α), spleen and gonad weight, plasma melatonin, and testosterone level as well as their receptor expression on spleen and testis. Expression of melatonin receptor, Mel1a and Mel1b in spleen was high in SD experiencing bird as compared to LD birds. In all photoperiodic groups, AR expression was upregulated in spleen. In addition, our reverse transcription polymerase chain reaction (RT-PCR) results support differentially localized mRNA Mel1b and Mel1c expression in spleen and testis. In sum, photoperiodically modulated level of melatonin via reciprocal regulation of Mel1a, Mel1b, and Mel1c, and AR in spleen as well as in testis modulates immunity, suggesting a compensatory mechanism between reproduction and immunity in a seasonally breeding bird, P. asiatica.

Daily variation in antioxidant enzymes and lipid peroxidation in lungs of a tropical bird Perdicula asiatica: role of melatonin and nuclear receptor RORα.

The wild animals are exposed in nature to more oxidative stress than any laboratory animals. Studies on oxidative stress of brain, liver and kidney are quite common while very less reports are available on respiratory system when it is the most susceptible organ to various stressors. We checked the oxidative stress of lung tissue of a wild seasonally breeding bird Perdicula asiatica by noting down the daily variation in antioxidant enzymes (superoxide dismutase and catalase) levels, lipid peroxidation in terms of malondialdehyde level and total antioxidant status during reproductively active (RAP) and inactive phase (RIP). On the other hand melatonin has been accepted as free radical scavenger acting via receptor (nuclear receptor) or non receptor pathway. To pin point the role of melatonin in regulation of antioxidant enzymes via non receptor mediated pathway in lungs of bird, we checked variation in the nuclear melatonin receptor RORα. Antioxidant enzymes (superoxide dismutase and catalase) exhibited a marked 24h rhythm in lungs being high during night time and coincided almost with the peak of melatonin and total antioxidant status where as malondialdehyde level and nuclear receptor RORα showed inverse relationship with all the above mentioned parameters. These findings suggest that melatonin might be acting as an antioxidant for the free radical load of lung tissue of a tropical bird P. asiatica and its action might be via nuclear receptor RORα.

Variation in melatonin receptors (Mel(1a) and Mel(1b)) and androgen receptor (AR) expression in the spleen of a seasonally breeding bird, Perdicula asiatica.

Daily variation in the peripheral level of melatonin plays a major role in integrating reproduction and environmental information for seasonally breeding birds. However, the variation in immunity and reproduction has never been assessed in any avian species on a 24 h time scale. Therefore, to understand the relationship between immune function and reproductive phases in a seasonally breeding bird, Perdicula asiatica, the Indian jungle bush quail, we studied the daily variation of melatonin and testosterone levels along with expression of their receptors Mel(1a), Mel(1b), and androgen receptor in the spleen during the reproductively active phase. Immunocytochemistry for the melatonin receptors Mel(1a) and Mel(1b) presented a differential distribution pattern. Western blot of splenic protein suggested a daily rhythm of melatonin receptors, while acrophases for the two melatonin receptors Mel(1a) and Mel(1b) differed by 4 h, suggesting that the expression of the receptors may peak at different times, causing more of either Mel(1a) or Mel(1b) to be available at a particular time to mediate function. The circulatory melatonin level correlated with percentage stimulation ratio of splenocytes and plasma interleukin-2 level, but did not correlate with testosterone or androgen receptor, suggesting that melatonin could be a major hormone imparting a time-of-day effect on the modulation of immune function in a seasonally breeding bird during the reproductively active phase.

Reproductive phase dependent daily variation in melatonin receptors (Mel(1a) and Mel(1b)), androgen receptor (AR) and lung associated immunity of Perdicula asiatica.

Our knowledge about the involvement of melatonin in the regulation of lung associated immune system (LAIS) is still poor though the melatonin receptor types (Mel(1a) and Mel(1b)) have been localized in lungs of some wild birds. We thought to explore the correlation between daily variation (within a 24h time scale) in peripheral melatonin and testosterone along with expression of melatonin receptors (Mel(1a) and Mel(1b)) and androgen receptor (AR) in lungs during reproductively active and inactive phases. Receptor expression of Mel(1b) was more prominent than Mel(1a) at all the time points during both the reproductive phases. The expression of AR was inversely related to both the melatonin and its receptor expression at the 24h time scale during both the reproductive phases. Results also reflected a parallel relationship of melatonin, melatonin receptors and all the immune parameters (total leukocyte count, lymphocyte count, % stimulation ratio) suggesting that peripheral melatonin might be responsible for daily periodicity of LAIS. The presence of androgen receptors in lung led us to propose that gonadal steroid does influence the LAIS. Therefore melatonin along with testosterone might be acting as a temporal synchronizer for daily rhythms in lung associated immunity in Perdicula asiatica during different reproductive phases.

Melatonin and androgen receptor expression interplay modulates cell-mediated immunity in tropical rodent Funambulus pennanti: an in-vivo and in-vitro study.

An inverse relation exists between melatonin and androgen in most of the seasonally breeding rodents, but the regulation of their receptors in modulation of immune function has never been reported. The present study accessed the expression pattern of melatonin receptor types (mt1R & mt2R), immune parameters (lymphoid organs weight, leucocyte count, delayed type hypersensitivity and lymphocyte proliferation) in spleen and thymus whereas androgen receptor (AR) expression in thymus of Funambulus pennanti during reproductively active phase. In-vivo melatonin treatment (Mel) and castration (Cx) significantly increased mt1R expression, immune parameters in spleen and thymus but decreased AR expression in thymus only when compared with sham control (Con) squirrels as AR expression was not observed in spleen. Mel alone or in combination with testosterone (T) to Cx squirrels significantly increased mt1R expression, immune parameters in spleen and thymus but decreased AR expression in thymus. T alone in Cx squirrels significantly decreased mt1R expression, immune parameters in spleen and thymus but increased thymic AR expression significantly. In-vitro thymocyte culture supported our in-vivo findings. Mel significantly increased mt1R expression, lymphocyte proliferation, IL-2 secretion but decreased AR expression. T alone significantly decreased aforementioned three parameters but increased AR expression. Combined treatment of Mel and T bring back all parameters to control level. Though we found high mt2R expression, but no significant change has been observed. Thus, present study suggests a clear-cut trade-off relation between mt1R and AR expression that might be acting as an important mediator in seasonal adjustment of immune function in tropical rodents.

Long-term melatonin administration attenuates low-LET gamma-radiation-induced lymphatic tissue injury during the reproductively active and inactive phases of Indian palm squirrels (Funambulus pennanti).

A comparative analysis of low linear energy transfer (LET) gamma-radiation-induced damage in the lymphatic tissue of a tropical seasonal breeder, Indian palm squirrel (Funambulus pennanti), during its reproductively active phase (RAP) and inactive phase (RIP) was performed with simultaneous investigation of the effects of long-term melatonin pre-treatment (100 microg/100 g body weight). A total of 120 squirrels (60 during RAP and 60 during RIP) were divided into 12 groups and sacrificed at 4, 24, 48, 72 and 168 h following 5 Gy gamma-radiation exposure; control groups were excluded from exposure. Total leukocyte count and absolute lymphocyte count (ALC) and melatonin only of peripheral blood, stimulation index, thiobarbituric-acid-reactive substances (TBARS) level, superoxide dismutase (SOD) activity, and the apoptotic index of spleen as analysed by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labelling (TUNEL) noted at observed time-points were significantly reduced in melatonin pre-treated groups during RAP and RIP. Long-term melatonin pre-treatment mitigated radiation-induced alterations more prominently during RIP, as assessed by ALC, TBARS, SOD, TUNEL and caspase-3 activity, at some time-points. Our results demonstrate an inhibitory role of melatonin on caspase-3 activity in splenocytes during RAP and RIP following gamma-radiation-induced caspase-mediated apoptosis. Hence, we propose that melatonin might preserve the viability of immune cells of a seasonal breeder against background radiation, which is constantly present in the environment.

Photoimmunomodulation and melatonin.

The seasons, and daily physical rhythms can have a profound effect on the physiology of the living organism, which includes immune status. The immune system can be influenced by a variety of signals and one of them is photic stimulus. Light may regulate the immunity through the neuroendocrine system leading to the most recent branch of research the "Photoimmunomodulation". Mammals perceive visible light (400-700 nm) through some specialized photoreceptors located in retina like retinal ganglion cells (RGC). This photic signal is then delivered to the visual cortex from there to the suprachiasmatic nucleus (SCN) of the hypothalamic region. Melatonin--one of the universally accepted chronobiotic molecule secreted by the pineal gland is now emerging as one of the most effective immunostimulatory compound in rodents and as oncostatic molecule at least in human. Its synthesis decreases with light activation along with norepinephrine and acetylcholine. The changes in level of melatonin may lead to alterations (stimulatory/inhibitory) in immune system. The evidences for the presence of melatonin receptor subtypes on lymphoid tissues heralded the research area about mechanism of action for melatonin. Further, melatonin receptor subtypes-MT1 and MT2 was noted on pars tuberalis, SCN and on lymphatic tissues suggesting a direct action of melatonin in modulation of immunity by photoperiod as well. The nuclear receptors (ROR, RZR etc.) of melatonin are known for its free radical scavenging actions and might be indirectly controlling the immune function.

Photoperiod-testicular-immune interaction in a seasonal breeder Indian palm squirrel Funambulus pennanti during the reproductively inactive and active phases.

The differential effect of long (LD; 16 : 8 h light/dark), short (SD; 10 : 14 h light/dark) and natural day length (NDL; 12 : 12 h light/dark) during the reproductively inactive (RIP) and active (RAP) phases was assessed in relation to immunity and reproductive function of a tropical rodent Funambulus pennanti. They presented high immunity and low testicular activity during RIP and an opposite during RAP. SD increased spleen and thymus weight, leukocyte and lymphocyte counts, cell mediated immunity [i.e. blastogenic response in terms of percentage stimulation ratio of splenocytes and thymocytes (when challenged with concanavalin A)] and delayed type hypersensitivity to oxazolone. SD during RIP increased the above mentioned parameters and reduced testes weight compared to NDL groups. During RAP, LD reduced all the immunological parameters when compared with NDL and SD experiencing groups of RIP and RAP phases. The LD group reduced the immunological parameters compared to RAP, suggesting that LD had always an inhibitory effect on immune status being independent of reproductive phases. The intensity of the stimulatory effects of SD and inhibitory effects of LD during both reproductive phases was significantly different. We exposed another set of squirrels to the above photoperiodic schedule for prolonged period (30 weeks) during RAP. A clear testicular refractoriness followed by immunorefractoriness was observed in the group experiencing SD and LD for 30 weeks. The photorefractoriness presented by the testes was inversely related to the immunorefractoriness. The peripheral melatonin level of those squirrels reflected the photoperiodic signal perceived by squirrels for immunomodulation and gonadal function, suggesting that immune system and gonadal function might have coevolved.

Pineal control of immune status and hematological changes in blood and bone marrow of male squirrels (Funambulus pennanti) during their reproductively active phase.

In addition to pineal control of reproduction in seasonal breeders, melatonin is also known to influence various immune parameters. In the present experiment, we assessed the effect of exogenous melatonin treatment on different hematological parameters of peripheral blood and bone marrow cells, together with histological observations of spleen and thymus blastogenic response and stimulation ratio, and hormonal assays (melatonin and testosterone) of Indian palm squirrel (Funambulus pennanti) during their reproductively active phase when endogenous melatonin levels are low. Daily subcutaneous injection of melatonin (25 microg/100 g body mass.) at 17.30-18.00 h to adult male squirrels for 60 consecutive days during May-June significantly increased the lymphocyte count of blood and bone marrow and the blastogenic response/percent stimulation ratio of spleen and thymus. Histological observation showed densely packed thymocytes and splenocytes. During this period, peripheral testosterone level was high and melatonin was low establishing an inverse relationship as noted earlier for this squirrel. In pinealectomized squirrels, decreased total leukocyte count and percent lymphocyte count in peripheral blood and bone marrow, along with a decreased cell density in spleen and thymus was observed histologically. Further, melatonin treatment of pinealectomized squirrels resulted in restoration of the immune parameters in line with a normal control level. We suggest that during the reproductively active period of male Indian palm squirrels the lymphoid organs were sensitive to melatonin; hence, the exogenous melatonin treatment had an immuno-enhancing effect.

Maternal transfer of melatonin alters the growth and sexual maturation of young Indian palm squirrel Funambulus pennanti.

To date, the phenomenon of maternal transfer of hormones to the young is an enigma. The present study explains for the first time the maternal transfer of melatonin (MEL) to the young, affecting neonatal growth and sexual maturation. The suckling pups of MEL-treated mothers exhibited significant decreases in body, testicular, vas deferens (male pups), ovarian and uterine (female pups) weights and increases in pineal gland activity along with high plasma MEL levels. The plasma level of testosterone decreased significantly in male pups, while estradiol increased and progesterone decreased in female pups of MEL-treated mothers. These results clearly suggest that MEL could be transported from the mothers to their young postnatally via the milk in order to influence neonatal growth and sexual maturation. Our results support the earlier concept and show for the first time that MEL can be transported from the mother to the young either prenatally through the placenta or postnatally via the milk. Therefore, maternal MEL can act as a biological signal for neonatal growth and sexual maturation.

A reproductive phase-dependent effect of dietary L-tryptophan on pineal gland and gonad of a nocturnal bird, Indian spotted owlet Athene brama.

Unlike other temperate owls, Indian spotted owlet Athene brama possesses a well-developed pineal gland that secrets moderate amount of hydroxy- (serotonin) and methoxy- (melatonin) indoles in circulation. However, in this study, we have reported the response of this endocrine gland to exogenous L-Tryptophan (precursor of the above indoles), and also its effect on gonads of this nocturnal bird. During breeding phase or pineal inactive phase (March), oral treatment of L-Trp (0.5 mg/100 g Bwt/day) significantly increased the pineal gland wt and plasma melatonin (MEL) level, while decreased the gonadal wt and plasma sex steroids levels (estradiol and progesterone in female and testosterone in male). Interestingly, during reproductively quiescent phase or pineal active phase (August), similar amount of L-Trp significantly decreased the plasma MEL level, while increased the above sex steroid levels in plasma. Finally, the results show a clear reproductive phase-dependent inverse effect of L-Trp on pineal gland and gonads for both sexes of the spotted owlets, and suggest that the therapeutic use of this amino acid would be a great advantage for controlling the reproduction of these economically important birds.

Pineal organ-like organization of the retina in megachiroptean bats.

Phylogenetically originated from photoreceptive structures, the pineal organ adapts the organism to circadian and circannual light periodicity of the environment, while the retina develops to a light-based locator. Bats have a nocturnal life and an echolocator orientation presumably modifying the task of photoreception. Looking for morphological basis of the special functions, in the present work we compared the fine structure and immunocytochemistry of the retina and pineal organ in micro- and megacrochiroptean bats. We found that there is a high similarity between the retina and pineal organ in megachiropterans when compared to other species investigated so far. Besides of photoreceptor derived pinealocytes, the pineal organ of both micro- and megachiropterans contain intrapineal neurons and/or ganglionic cells as well as glial cells. Like spherules and pedicles of retinal photoreceptors, axon-type processes of pinealocytes form synaptic ribbon containig terminals. Similar to retinal photoreceptors and neurons, pinealocytes and pineal neurons contain immunoreactive glutamate and aspartate. In addition, excitatory amino acids accumulate in the pineal neurohormonal endings and might have a role in the hormonal (serotonin?) release of the organ. Concerning the structure of the retina the highest similarity to the organization of the pineal organ was found in the megachiroptean fruit eating bats Cynopterus sphinx and Rusettus niloticus. The retina of these species forms folds and crypts in its photoreceptor layer. This organization is similar to the folds of the pineal wall successively developed during evolution. Since a folded photoreceptor layer is not viable for a photolocator screen in decoding two-dimensional images, we suppose that this peculiar organization of the megachiropteran retina is connected to a "pineal-like" photometer task of the eye needed by these species active at night.

Reproductive phase depedent circadian variation in the pineal biochemical constituents of Indian palm squirrel, Funambulus pennanti.

In mammals, pineal gland is intimately concerned with the co-ordination of rhythm physiology. Biochemical characteristics of pineal gland in man and other mammals may provide strong, yet sometimes elusive support for the belief in functional individuality and probable importance of this tiny gland. In seasonal breeding animals, pineal gland function is very much dependent on the reproductive status. Therefore, the aim of this experiment is to note the circadian rhythmicity of different biochemical constituents of pineal gland during active and inactive phases of reproductive cycle of a seasonally breeding rodent, F. pennanti. In the present study, pineal biochemical constituents i.e. protein and cholesterol showed higher values during daytime (1400 h). The plasma melatonin level presented two peaks during active (April; at 1800 h and 0200 h) and inactive (December; at 1400 h and 0200 h) phases of reproductive cycle. The pineal protein, cholesterol and plasma melatonin values in term of basal and peak levels were higher during the reproductive inactive/pineal active phase. Therefore, pineal--also known to have antigonadotropic properties and cholesterol which appears conjugated with pineal serotonin, presented circadian rhythmicity along with the plasma level of melatonin. This rhythmicity noted in present study was dependent on the reproductive and pineal activity status, and might be regulated by the sex steroid receptor present on the pineal gland.

Comparative view of pineal gland morphology of nocturnal and diurnal birds of tropical origin.

Although having a similar developmental pattern, the pineal gland of tropical birds varies in shape, size, and morphology, probably more than any other part of the avian brain. Following the old classification, we noted a solid follicular (transitional) type of the pineal gland in the nocturnal bird Athene brama, and a tubulo-follicular and elongated tubular types of pineal gland in diurnal birds Perdicula asiatica and Euroloncha punchulata, respectively. Detailed light (LM) and electron microscopic (EM) studies of the pineal gland from these tropical birds revealed the presence of a well-developed, functionally active gland in nocturnal birds (contrary to reports available until now). Unlike diurnal birds, the nocturnal bird A. brama has no deep pineal in the posterior region (near the habenular commissure). It could be that the deep encephalic receptors have no/fewer functions in nocturnal birds. At present, we were unable to define the significance of deep pineal in these tropical avian species. A notable difference in the proximodistal orientation of intrapineal follicles and parenchymatous cells was noted among these birds due to different habitats. Ultrastructurally, the pinealocytes exhibited great similarities in terms of secretory organelles, except for the presence of some peculiar membranous structure in E. punchulata. The pinealocytes have rudimentary photoreceptive features (e.g., outer segment) along with cytoplasmic organelles for secretory activity, suggesting both photosensory and photosecretory types of function. The present study also suggests more heterogenicity in pineal gland morphology (cellular architecture) among diurnal birds than the nocturnal one.

Seasonal changes in adrenal and gonadal activity in the quail, Perdicula asiatica: involvement of the pineal gland.

The present study assessed annual adrenal gland activity in the Indian tropical Jungle bush quail, Perdicula asiatica. We also elucidated the role of the annual variations in gonadal steroids and melatonin in the regulation of its activity. Increasing day length (photoperiod), ambient temperature and rainfall are positively correlated with adrenal and gonadal functions, and inversely related to pineal gland activity. Pineal, adrenal and gonadal weights showed cyclical patterns relative to environmental factors, which were also correlated with plasma melatonin, corticosterone and gonadal steroids, respectively. In both sexes of P. asiatica, pineal gland weight and/or plasma melatonin levels were inversely related to adrenal lipids, (e.g. phospholipids, free and esterified cholesterol) and plasma corticosterone levels. Melatonin levels also showed an inverse relationship with plasma testosterone and estradiol levels. These studies indicate that changes in environmental factors promote annual variations in adrenal and gonadal activity probably by modulating the pineal gland. Melatonin receptors have been localized in the pars tuberalis, adrenal gland and gonads of birds, the pineal gland may, therefore, mediate environmental stimuli indirectly and directly to down regulate adrenal and gonadal activity, which run in parallel in this species.

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/100 g 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.

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 gland of a nocturnal bird, Indian spotted owlet, Athene brama: morphological and endocrine observations.

It has been reported that owls (Strigiformes) do not have a pineal gland. However, our light microscopy study revealed an intermediate form of tubulofollicular and solid-type large pineal gland in a tropical owlet, Athene brama. The epithelial cells forming follicles (6-8) in the distal region and the solid cluster of parenchymal cells of different diameters in the proximal region anteriorly tapered with a long cylindrical stalk and continued into commissural organs and choroid plexus. The intrapineal localization of perivascular nerve fibers and blood vessels clearly explained the sympathetic innervation as well as vascularization of this neuroendocrine gland. Further, electron microscopy revealed a developed intracellular structure of the pinealocytes with a large number of mitochondria, Golgi bodies, and granular as well as clear vesicles in the process terminals. The evidence of intrapinealocyte lipid droplets and dense bodies and a moderate amount of melatonin in plasma (ranging from 100-365 pg/mL) during different reproductive phases finally proved a defined secretory activity of the gland in this tropical, nocturnal bird.