MELATONIN, GESTATION and FETAL DEVELOPMENT Haldar C and Yadav R Pineal Research Lab, Department of Zoology, Banaras Hindu University, Varanasi – 221005, India

JER : 2006 (1) : 1 - 12 1

MELATONIN, GESTATION AND FETAL DEVELOPMENT Haldar C and Yadav R Pineal Research Lab, Department of Zoology, Banaras Hindu University, Varanasi – 221005, India.

SUMMARY

The pineal gland, the transducer of several environmental cues through its hormone, melatonin, is known to play a critical role in the reproduction of several seasonally breeding mammals. The role of pineal gland in the control of male reproduction is already established beyond doubt. The logical hypothesis that the pineal gland would be involved in the aspects of female reproduction, particularly gestation, embryonic development and fetal growth, has been tested in a few seasonally breeding mammals and this paper reviews the outcome as of now. Evidence for establishment of an inverse relationship before pregnancy followed by moderately high activity with a positive correlation during pregnancy and a sudden increase in pineal activity during parturition has been produced, which suggests that high melatonin level has something to do with parturition or early abortion. The pineal gland perhaps maintains the normal physiology during gestation and post-parturition periods. This is further reflected in the prolactin levels of fetal sheep which is modulated by the photoperiod experienced by the mother during gestation. Maternal photoperiodic exposures during gestation and lactation periods alter the neonatal growth and sexual maturation of the Indian palm squirrel via the maternal transfer of photoperiodic information through the pineal gland, as aspect known as “pineal programming”. The primary source of melatonin for the fetus is the maternal pineal gland, which is transferred across the placenta during conception and, later after parturition, through the milk, which suggests that a maternally generated melatonin rhythm would be expressed in fetal cerebrospinal fluid as well as in the circulation. Further, maternal melatonin is necessary for normal somatic growth and postnatal development of reproductive organs of the offspring. Melatonin ultimately affects reproductive activity by modulating hypothalamic neuroendocrine circuits whose activity is necessary for gonadal function. The influence of melatonin on reproductive development begins during the prenatal period and extends into the postnatal life. Photoperiodic information, mediated via the pineal gland may be important for maintaining gestational physiology as well as postpartum recovery in female rodents. Further, melatonin has been shown to play adaptive role in the maintenance of delayed embryonic development in bats. Correlation between a developmental decline in melatonin levels and the timing of puberty in humans led to the speculation that melatonin regulates the timing of puberty in the human. These studies on the influence of melatonin on gestation indicate two major inferences viz., melatonin could be one of the major hormones establishing homeostasis during gestation since any disturbance in the level of melatonin causes abortion, and melatonin is one of the hormones of great adaptive significance for embryonic diapause.

Key words: Embryonic growth, gestation, melatonon, photoperiod, pineal gland, puberty.

INTRODUCTION enabling the offspring to be born under the most favor- Reproductive function in mammals consists of able environmental conditions. an intricate interplay of hormonal events that are respon- The role of pineal gland in the control of male sible for the development and maturation of gametes, reproduction has been quite clearly established. However, puberty, major events of the reproductive cycle (i.e., ovu- its role in female reproduction, especially during gesta- lation and sexual receptivity) and preparation of the uterus tion, is not clear, although the females allocate the maxi- for the possible implantation of embryos. mum energy towards the begetting and bear most of the The pineal gland is known to play a critical role in cost of reproduction. The pineal gland of the female pro- the reproduction of several seasonally breeding mam- vides indications of higher activity, with a higher circulat- malian species (1). The seasonality of reproduction is ing level of melatonin during the reproductive period (6). usually enforced by a dependence on the day length per- Therefore, it is conceivable that the pineal gland is in- ceived, which in turn regulates the synthesis of melato- volved in the aspects of female reproduction, particularly nin, the pineal hormone. The daily duration and the level gestation, embryonic development and fetal growth. Un- of melatonin regulate the secretion of gonadotropins / til a little more than a decade ago there was no informa- gonadal steroids. They regulate the breeding in long day tion on i) the influence of pineal gland on gestation, ii) the breeders such as squirrels, ferrets, voles, hamsters etc. influence of pregnancy on the metabolism and function (2-5). In the broadest sense, then, melatonin influences of pineal, and iii) the interrelationship between maternal reproduction by restricting the season of conception and fetal pineal glands.

Correspondence to be addressed to: Prof. C. Haldar, Ph.D. Email - [email protected], [email protected] 2 Haldar C and Yadav R et al

The influence of melatonin may begin during suggest some morphological and hormonal changes dur- gestation i.e., the prenatal period, and could extend into ing pregnancy in relation to the physiological conditions the postnatal period (7). The earliest report on such a of the reproductive organs (6). relationship, published in 1965, was decrease in the weight Ultra-morphometric variation of the pinealocytes of pineal during the later part of pregnancy in rats bear- of a pregnant female rodent, the Indian palm squirrel, ing 10 or more fetuses, suggesting the involvement of correlating with the functional state, was studied in our pineal in gestation and fertility (8). In the present review lab (9). The pinealocytes of the pregnant females pos- we analyze the data so far generated by us on the role of sess two variants of mitochondria, based on size, which pineal gland during gestation and fetal development us- form mitochondrial clouds (Fig. I D). The Golgi zone ap- ing tropical mammals (squirrel and bat) and by others in pears to be hyperactive. A large number of granular laboratory animals (rat and mouse) and humans. vesicles are noticed in the pinealocyte cytoplasm and in MATERNAL PINEAL MORPHOLOGY AND the bulbous ending processes of the pinealocytes (Fig I MELATONIN A-D). A few dense bodies of unknown function are also noticed. The increased abundance of synaptic vesicles Systematic and detailed studies on pineal gland in the cytoplasm and the ending processes of the structure and function in pregnant females are lacking. pinealocytes of pregnant females indicate better cellular The cursorial reports on sheep, cattle and rat pineal gland Melatonin, gestation and fetal development 3 communications and transmission than in the non-pregnant females. Such a comprehensive study is not available for any other mammal. Name of Gestation Effect of Effect of melatonin animal period pinealectomy injection/ The pineal gland weight and melatonin level, (days) on gestation implantation which were high in the non-pregnant female rodents, de- clined sharply during the beginning of conception, fol- Rat 21 Spontaneous abortion Post natal ontogeny lowed by a gradual increase up to the end of gestation, of the neuroendocrine and then a sharp increase during parturition (10). This reproductive axis suggests the establishment of an inverse relationship before pregnancy followed by moderately high activity Hamster 16 - Delayed sexual with a positive correlation during pregnancy and sudden maturation in increase in pineal activity during parturition. This may offspring mean that the very high melatonin level has something to do with parturition or early abortion. Skunk 31 - Delays implantation PINEAL GLAND, MELATONIN AND GESTATION and long term suppression of Pregnancy is the period during which an animal prolactin levels carries one or more developing embryos. The sequence Indian Palm of events leading to pregnancy is complex and multidi- Squirrel 45 - May disrupt the mensional. Maintenance of pregnancy is largely depen- mother’s endogenous dent on a proper balance between the levels of various melatonin rhythm and hormones, which are maintained by interactions between delay the post-partum the mother, the placenta and the fetus. recovery process. Whether pregnancy would affect the pineal gland structure and function is not clear but some preliminary Bat 90-120 Abortion Delayed embryonic studies suggest that the pineal gland is involved in the development regulation of certain aspects of gestation (6, 8). An elabo- rate study on the weight of organs and plasma levels of Sheep 150 - Delayed sexual melatonin, estradiol and progesterone during the gesta- maturation tion period was made in the Indian palm squirrel. The outcome suggested a possible role for pineal gland in Prolactin levels of fetal sheep can be modulated maintaining the normal physiology during gestation and by the photoperiod experienced by the mother during post-parturition periods (10). In spite of the inverse rela- gestation. Long days resulted in higher prolactin levels tionship between the pineal gland and the gonad in the (12), while melatonin implants reduced prolactin levels non-pregnant adult females, the study indicated a direct (13, 14) acting via the pars tuberalis (15, 16). In skunks, relationship between the pineal gland activity and the melatonin treatment delays implantation by several ovarian steroids and uterine function, especially during months and a long-term suppression of prolactin levels. the gestation period. The inverse relationship between Ablation of the suprachiasmatic nuclei (SCN) does not melatonin and ovarian steroids is re-established after block the effect of exogenous melatonin (17). In contrast, parturition and maintained till the next pregnancy (10). anterior hypothalamic lesions cause precocious termination of diapause, regardless of the melatonin milieu (18, In order to assess the role of melatonin during 19). It is not clear whether melatonin acts within or through pregnancy, the hormone was infused at regular intervals the anterior hypothalamus. The anterior hypothalamus into pinealectomized dams (Table 1). Melatonin infusion may be a leg in the final common pathway in prolactin during the night hours determined the rate of pubertal regulation downstream of the melatonin target sites. Con- development. A single gestational melatonin infusion did sidering that high affinity melatonin receptor binding is not influence postnatal reproductive development, but two limited to the pars tuberalis in skunks (20), these data infusions on consecutive nights provided a sufficient sig- suggest a model in which melatonin regulates production nal. A period of maximum sensitivity to melatonin infu- of a factor from the pars-tuberalis that influences prolac- sions occurs during late gestation. Outcome of studies tin secretion. A similar suggestion has been made to ex- using timed injection of melatonin (rather than infusions) plain the influence of melatonin, mediated by the pars supports the conclusion that melatonin is a critical cue tuberalis on prolactin secretion in sheep (21). for transfer of day length information to the fetus (11). 4 Haldar C and Yadav R et al

MELATONIN, PHOTOPERIOD AND GESTATION training her circadian rhythm. But, some questions re- In spite of the extensive research on female garding the maternal transfer of photoperiodic / hormonal reproduction, it is not clear how information about the information still remain unsolved. Photoperiodic informa- factors of the environment (photoperiod, temperature, tion reaches the fetus during prenatal life and can have a humidity etc.) and the others (hormonal and metabolic) dramatic impact on reproductive development. Stetson are transferred from mother to the fetuses. Only a few et al. (23) opined that the photoperiodic condition experi- reports are available suggesting the phenomenon of maternal transfer of photic information to young ones via enced by the mother, especially during gestation is com- the pineal gland (Fig. II). However, the impact of mater- municated to the fetuses either in a stimulatory or in an nal photoperiodic exposures on the growth, pineal inhibitory manner for their pineal gland activity. functions and sexual development of neonates is lacking. During gestation, the mother provides protects The pineal gland is known to play an intermedi- the fetus from the external environment and generates ary role between the environment and the endocrine sys- signals which allow the fetus to perceive the length of the tem (Fig. III) (24, 25). Therefore, a direct influence of the day as well as the phase (timing) of the light-dark cycle. It maternal pineal gland on the growth and sexual develop- is remarkable that the mother is actively involved in ment of the offspring is conceivable. Horton (26), Stetson transferring environmental cues to the fetus during the et al. (27) and Horton et al. (28), working with Montane prenatal period. voles and Siberian hamsters, have suggested that the information transfer from the mother to the fetuses occurs during the prenatal period and not during lactation. Maternal photoperiodic exposures during gestation and lactation periods alter the neonatal growth and sexual maturation of the Indian palm squirrel via the maternal transfer of photoperiodic information through the pineal gland (10). Our several papers established the above relation in a diurnal rodent, the Indian palm squirrel. The results suggest that prenatal photoperiod has critical impact on postnatal reproductive development. Pups reared in an “intermediate” postnatal photoperiod differ in their rate of reproductive development if the prenatal photoperiods experienced by their mothers differed (23, 29, 30). At more extreme photoperiods, the postnatal photoperiod “overrides” the influence of the prenatal photoperiod (27, 29). Several groups of researchers have shown that the maternal pineal gland is necessary for prenatal Fig. II Diagrammatic representation of transfer of communication of day length information and this infor- photoperiodic information from mother to fetus mation profoundly influences postnatal reproductive and somatic development (28, 30). Studies using timed in- As pregnancy nears the term, the fetuses race to jection of melatonin to pregnant mothers support the con- prepare themselves for life outside the uterus with the clusion that melatonin is a critical cue for the transfer of development and maturation of various neuronal and day length information to the fetuses (27, 31). Consider- humoral systems in a protected intrauterine environment. ing the role of pineal gland in photoperiodic regulation, it Studies in several mammalian species show that during appeared likely that removal of the maternal pineal gland fetal life a biological clock in SCN is oscillating in phase would prevent prenatal perception of day length. Lee and (time) with the environmental light-dark cycle and this his colleagues (32-34) have shown that the prenatal de- fetal clock is entrained by reluctant circadian signals (22). velopment of meadow vole pups (Microtus pennsylvanicus) is influenced by the prenatal photoperi- Light-induced neural signals are conveyed to SCN ods and prenatal melatonin treatment (32-34). by the mother’s retino-hypothalamic pathway (RHP) en- Melatonin, gestation and fetal development 5

1200 80 NP NP 70 P 1000 P 60 800 50

600 40

400 30 20 200 10 Progesterone conc. (ng/ml) Conc. of hormone (pg/ml) 0 0 Melatonin Estradiol Progesterone Fig. III. Hormonal levels in pregnant (P) and non-pregnant (NP) in Indian palm squirrel, Funambulus pennanti.

Maternal transfer of photoperiodic information has that the maternal melatonin can affect the fetal SCN with been referred to as “prenatal programming” of postnatal consequences for the prenatal and postnatal expression reproductive development (27, 31). The developing ani- and entrainment of circadian rhythms. mal takes a reading of the day length (melatonin dura- Some possible role of melatonin in the fetal de- tion) during the late fetal life and compares this with the velopment of Indian palm squirrel, Funambulus pennanti, melatonin signal derived from the developing pineal has been proposed by Bishnupuri and Haldar (9). The around 15-20 days of age (2). This model suggests that a inability of the fetal and neonatal rat to synthesize mela- postnatal melatonin pattern is interpreted differently de- tonin does not necessarily mean that the developing rat pending on an animal’s prenatal photoperiodic history. lacks melatonin. Indeed, evidence is available which in- Melatonin is, thus, an important component of the per- dicates that the mother is an important source of melato- ceptual world of the fetus. In this context, it may be worth nin for the developing fetus and neonate. Melatonin can considering melatonin as a pheromone (a chemical sub- be transferred from mother to fetus in two ways: stance from one member of a species which communicates information to another) rather than as a hormone. 1. Placental transfer of melatonin has been demonstrated. First, it was shown that a small amount of (3H) - SOURCES OF MELATONIN FOR THE FETUS melatonin injected intravenously into pregnant animals The primary source of melatonin for the fetus is during the later stages of gestation promptly appear in the maternal pineal gland. Robust rhythms in melatonin the fetal circulation and that the rates of disappearance have been measured in pregnant mammals (35, 36) and of radiolabelled melatonin in the maternal and fetal cir- although the fetus may have some capacity for melato- culation are parallel. In another experiment, a diurnal nin production, any secretion would be low and without change in maternal melatonin, experimentally simulated rhythmicity. The melatonin rhythm in the maternal circu- on a reduced time scale, results in a rapid reflection of lation is accurately reflected in the fetus. Melatonin lev- the rhythm in the fetal circulation. Rapid placental trans- els in the fetal plasma are closely parallel to those in the fer of melatonin is quite predictable in view of the lipo- maternal plasma. Rapid transfer of maternal melatonin philic, non-ionized properties of this small molecule (9). across the placenta has been demonstrated in several Another important finding of the placental transfer study rodents, sheep and non-human primates (14, 36-40). was maternally derived (3H)-melatonin rhythm in fetus. Furthermore, maternal pinealectomy abolishes the rhythm This indicates that a maternally generated melatonin of melatonin in the fetal circulation (36, 41). It is likely rhythm would be expressed in fetal cerebrospinal fluid that the fetus has a functional circadian pacemaker in (CSF) as well as in the circulation, since it has been shown the SCN through out the gestation. Since the fetal pace- that in the adult mammal the rhythm in circulating levels maker expresses melatonin-binding sites, it is also likely is precisely reflected in the CSF. Both the routes may to be a target of maternal melatonin. Thus, it is possible deliver the hormone on a daily basis to the fetal brain where melatonin would potentially exert its effects. 6 Haldar C and Yadav R et al

2. The second pathway is via mother’s milk. A part of MELATONIN AND PUBERTY (3H) melatonin injected intravenously to lactating female Melatonin ultimately affects reproductive activ- was also found in the mammary gland and in the stom- ity by modulating hypothalamic neuroendocrine circuits ach of suckling pups. This is because the melatonin whose activity is necessary for gonadal function. The in- rhythm in the fetus is established after 1 week or 10 days fluence of melatonin on reproductive development be- postnatally. The melatonin rhythm in the fetus is driven gins during the prenatal period and extends into the post- up to one week by the maternal melatonin present in the natal life. Melatonin influences the other neuroendocrine milk (42). parameters in the developing animals prior to puberty. MELATONIN IN EMBRYONIC GROWTH AND In many seasonally breeding species, the timing SURVIVAL of initial reproductive development (sexual maturity or Melatonin is generally viewed as remarkably non- puberty) is strongly influenced by day lengths experienced toxic (43, 44) and this also appears to be the case during during the postnatal period. The most well studied spe- fetal life. Melatonin is without effects on the develop- cies include Siberian hamsters, Indian palm squirrel and ment of mouse embryos in vitro (45). Another study re- sheep. Administration of melatonin in the appropriate tem- ports that melatonin does produce toxicity to embryos poral (durational) patterns can influence the timing of (46). An influence of melatonin injection on embryonic puberty in these species. Exposure to long days stimu- survival has been reported in meadow voles (47). Mela- lated postnatal reproductive development. Infusion of long tonin injections (10µg) reduced survival rates of female day patterns of melatonin, similarly, stimulates gonadal (but not male) pups when given prior to blastocyst im- growth, while short day patterns of melatonin suppress plantation. Injections later in gestation were without ef- puberty. While the details are species-specific, the same fect. This effect of melatonin may underlie seasonal general phenomenon exists in the other photoperiodic changes in litter size and, perhaps, seasonal changes in species. Specific photoperiodic requirements must be met sex ratios. The mechanism by which melatonin modu- to allow rapid pubertal development, and these photope- lates prenatal mortality in a sex-specific manner is not riodic requirements are transduced to the neuroendocrine known. However, the melatonin binding and the density axis by melatonin. In general, puberty occurs at about of melatonin binding sites are more in the fetal than the the same time of the adult maturing season and, there- adult brain. fore, is also a photoperiodic reproductive phenomenon. In species with rapid development (e.g. rodents), animals Pinealectomy of the mother produced an altered born early in the year mature rapidly and reproduce within developmental pattern in the offspring of rat. During the the same season, while in animals born at the end of infantile period when pups are lacking maternal melato- breeding season, puberty is delayed until the beginning nin due to pinealectomy and their own melatonin rhythm of the next season. is yet to be established, a delayed growth of body was observed. Significantly greater growth rate was observed The photoperiod experienced by females during in pinealectomized offspring during the pubertal period their gestation period may influence the pineal physiol- than in the control offspring, which could be due to the ogy of fetus but nothing has been reported about the increase in LH secretion up to normal values observed in growth and sexual development of the young ones. Stud- the pinealectomized offspring. Melatonin treatment dur- ies on the maternal transfer of photoperiodic information ing pregnancy produced minor alterations in postnatal in mammals indicate that the daily photoperiod perceived development of the reproductive tract. Maternal melato- by the mother during the gestation and lactation periods nin is necessary for normal somatic growth and postnatal is communicated to the fetus either through the placenta development of reproductive organs of the offspring (48). or via the milk. In a seasonally breeding Indian tropical Melatonin, gestation and fetal development 7 rodent Funambulus pennanti, constant light (LL: 24L: 0D) centration, showing statistically significant differences with and long day length (LDL; 14L: 10D) exposure to gestat- the control levels and with the pin-x group. The percent- ing females conveyed opposite information to the fetuses age of rats in proestrus was higher in the offspring of and inhibited fetal pineal function. Short photoperiod (SDL; pinealectomy (78.6%) compared to control offspring (30%) 10L: 14D) exposure to gravid females stimulated pineal and offspring of melatonin-treated rats (11.8%). The function of the pups. Altered pineal functions of the pups pituitary weight was significantly lower in the offspring of ultimately interfered with their growth and sexual matu- pin-x rats than in the other two groups (50). ration. We, therefore, suggested that photic information Menstrual cyclicity is associated with fluctuations perceived by the mother during gestation alters her own in melatonin production but whether they are related to normal melatonin level, which passing through placenta ovulation or menstruation is not established. Menopause or through milk influences sexual maturation of the young is associated with a reduction in melatonin, which may ones (10). The maternal pineal gland can affect fetal de- relate to the changing gonadotropin levels. In males of velopment because the main pineal hormone, melato- the same age melatonin levels also drop with no signifi- nin, can cross the placental barrier. Melatonin treatment cant alteration in reproductive physiology (51). during gestation in the rat produced delayed sexual maturation of the female offspring (49). The maternal pineal MELATONIN AND EMBRYONIC DEVELOPMENT IN gland participates in the cellular and nuclear volumes of BATS prepubertal oocyte development. Melatonin treatment A fascinating and ecologically important role for during pregnancy resulted in a redirected postnatal oo- melatonin in regulating reproduction during early fetal life cyte development (49). is in the initiation and maintenance of seasonal embry-

Alterations in photoperiodic condition during late onic diapause (52). The period of delayed implantation gestation and lactation altered the postpartum recovery (embryonic diapause) is regulated by the environmental process. Pineal gland activity, as assessed by pineal mass, light cycle via melatonin. Seasonal embryonic diapause protein content and plasma melatonin, was the lowest occurs in many different mammalian species, including during the breeding phase, but increased gradually after mustelids (eg., skunks, ferrets, badgers, weasels, mink), parturition until the next breeding phase. During gesta- pinipeds (e.g. Australian sea lions and Antarctic fur seals, tion and lactation, constant light, long day length and short harbor seals), insectivores (several bat species), canids day length conditions were less effective, while constant (wolves and coyotes), bears, and marsupials. Western dark condition had a profound effect in depressing pineal spotted skunks, tammar wallabies and mink have been gland activity, which subsequently advanced postpartum studied most extensively with respect to the role of the recovery. Hence, lactating females under constant dark- pineal and melatonin. In each of these three species, ness prepared themselves for the next mating much ear- pinealectomy or denervation of the pineal prevents sea- lier than females under natural day length (12h light: 12h sonal embryonic diapause, and melatonin treatment in- dark) conditions. Therefore, photoperiodic information, fluences the length of diapause (17, 18, 53-56). The data mediated via the pineal gland may be important for main- from all these species are consistent with the interpreta- taining gestational physiology as well as postpartum re- tion that melatonin acts in the pregnant female to influ- covery in female rodents. ence neuroendocrine function, particularly prolactin secretion and that diapause is caused by alterations in the The offspring of melatonin-treated rats showed uterine environment. Melatonin does not appear to affect later vaginal opening than did control and pinealectomized the embryo directly. offspring, which was accompanied by a lower LH con- 8 Haldar C and Yadav R et al

The flying mammalian group, Chiroptera, is It could be suggested that high maternal melatonin flow known for its various reproductive delays. There may be via the placenta reached the fetus and retarded the growth stressfull situations in the wild (for example, lack of sup- and development of the fetus since melatonin is having port food or roosting sites) in which case the ability to an inverse relationship with growth hormone. Therefore, delay pregnancies would be of considerable adaptive melatonin may play an adaptive role in the maintenance value. The delayed embryonic development (DED) has of DED. been described by various workers as a phenomenon of The target of melatonin on the uterus is the myo- adaptation to unfavorable environmental conditions. Since metrium, where we found receivers for the MT1 and MT2 pineal gland is the mediator between the environmental melatonin receptors, through which they can modulate changes and adaptation to seasonal reproduction, a role myometrial operation, inhibiting the spontaneous contrac- for pineal gland was suspected in delayed embryonic tions induced by the oxytocin (63-65). However, Zhao et development of chiropterans. According to Sandyk et al. al. (66) reported the presence of the MT1 receptor in the (57) melatonin stimulates progesterone secretion that endometrial stroma, which decreases progressively dur- prevents the immunological rejection of the trophoblast. ing the decidualization, staying in this state until the end It has been demonstrated that melatonin levels of the gestation. in the plasma increase during gestation, reaching high MELATONIN IN HUMAN GESTATION AND FETAL values at the end of this period, suggesting that the hor- DEVELOPMENT mone plays an important role in the maintenance of the gestation (10, 35, 57-60). However, little is known about Correlation between a developmental decline in the importance of the melatonin on the implantation pro- melatonin levels and the timing of puberty in humans led cess. to the speculation that melatonin regulates the timing of puberty. Subsequent investigation indicated that this de- We found a high melatonin and estrogen ratio velopmental decline in melatonin levels is due at least in during DED beside the high androgen, as reported ear- part to developmental changes in body mass (and thus lier in fruit bats (61). Any disturbance in this ratio (follow- volume of distribution) and is without a strict relationship ing pinealectomy (Px), melatonin injection or photoperi- to pubertal development. While endogenous melatonin odic exposure, which may disturb internal melatonin level, does not appear to play a role in timing human puberty, leads to termination of DED either as immature delivery data are not available to draw a conclusion with respect or abortion. Furthermore, Sandyk et al. (57) suggested a to the effects of exogenous melatonin on puberty in hu- functional deficiency in the melatonin production at the mans. In the case of humans (pregnant women), pineal beginning of the gestation may cause spontaneous abor- concretions were found in a much higher percentage than tion in cases where chromosomal anomalies and struc- in women who had never been pregnant. tural abnormalities of the uterus were excluded. The pinealectomy, the constant illumination or association of Serum melatonin levels during the third trimes- these factors induce a reduction of the blastocysts num- ter of pregnancy (76.5+/- 38.3pmol/l) were significantly ber implanted in female rats besides stimulating the de- higher than those during the first (29.7+/-9.9 pmol/l) and velopment of the implantation sites .This would indicate the second trimesters (39.1+/-11.2 pmol/l) and those of that the melatonin can have an important function in the non-pregnant control women (41.7+/-15.5 pmol/l). There viability of implantation of the blastocyst and in the pro- was a positive correlation between the week of gestation cess of formation of the placenta in these animals. and serum melatonin at 11.00 h with a clear diurnal rhythm Pinealectomy followed by immediate high dose of mela- in serum melatonin concentrations both in early and late tonin maintains pregnancy in short-nosed fruit bats (62). pregnancies. The amplitude and duration of the noctur- Melatonin, gestation and fetal development 9 nal rise of melatonin were higher during late pregnancy, (UGC) and the Council of Scientific and Industrial Re- but there was no clear phase shift. Increased serum con- search (CSIR), New Delhi, for financial support and centration of melatonin in late pregnancy may be due to Alexander von Humboldt foundation, Bonn, Germany for increased synthesis and secretion or retarded metabo- equipments. lism of melatonin during late pregnancy (35). REFERENCES

In the case of human newborns, melatonin lev- 1. Bartness TJ, Powers JB, Hastings MH, Bittman EL, els in the umbilical artery and veins were no different Goldman BD (1993) The timed infusion paradigm from maternal serum melatonin (67, 68). Children with for melatonin delivery: what has it taught us about precocious puberty have lower nocturnal serum concen- the melatonin signal, its reception, and the photope- trations of melatonin than age-matched prepubertal chil- riodic control of seasonal responses? J Pineal Res dren (69), whereas children with delayed puberty present 15:161-190. higher nocturnal melatonin concentrations than age- 2. Tamarkin L, Reppert SM, Orloff DJ, Klein DC, Yellon matched normal children. SM, Goldman BD (1980) Ontogeny of the pineal melatonin rhythm in the Syrian (Mesocricetus auratus) It is likely that melatonin may exert an inhibitory and Siberian (Phodopus sungorus) hamsters and in effect on hypothalamic GnRH secretion in humans. It has the rat. Endocrinology 107: 321-326. been postulated that, before puberty, even if they progres- 3. Reiter RJ (1986) Pineal melatonin production: sively decrease, melatonin concentrations are too elevated photoperiodic and hormonal influences. In: Reiter RJ to allow hypothalamic activation; however, at 9 or 10 years and Karasek M (eds) Advances in Pineal Research, of age the decline of serum melatonin below a threshold pp 77-87, John Libbey, London. value (500 pmol/l -115 pg/ml) represents the activating sig- 4. Haldar C, Saxena N (1989) Antigonadotropic activity nal for the hypothalamic pulsatile secretion of GnRH and of pineal gland of the Indian palm squirrel, hereafter the onset of pubertal changes (70). Funambulus pennanti. Indian J. Exp Biol 27: 421. CONCLUSIONS 5. Haldar C (1996) In: Haldar C (ed) The Pineal Gland: Studies on melatonin influence on gestation indicate two Its Molecular Signals, pp 94-117, HPLC, New Delhi. major observations: 6. Lew GM (1987) Morphological and biochemical changes in the pineal gland during pregnancy. Life i) Melatonin could be one of the major hormones Sci 41: 2581-2596. establishing homeostasis during gestation since any disturbance in the level of melatonin causes 7 Attanasio A, Borelli P, Gupta D (1985) Circadian abortion. rhythms in serum melatonin from infancy to adoles- cence. J Clin Endocrinol Metab 61: 388-390. ii) Melatonin is one of the hormones of great adap- 8 Huang CY, Everitt AV (1965) The effect of pregnancy tive significance for embryonic diapause. on pineal weight in the rat. J Endocrinol 32: 261-262. Both the results/effects of melatonin are of high clinical 9 Bishnupuri KS, Haldar C (1999) In: Gpupta PD and value for treatment of frequent abortion or maintenance Yamamoto H (eds) Electron Microscopy in Biology, of gestation. This is one of the novel branch offs of mela- pp 33-40. Oxford and IBH Publishing Co. Pvt. Ltd., tonin physiology that warrants attention of researchers New Delhi. and clinicians. 10 Bishnupuri KS, Haldar C (2000) Profile of organ Acknowledgement: weights and plasma concentrations of melatonin, estradiol and progesterone during gestation and post- We thank the University Grants Commission 10 Haldar C and Yadav R et al

parturition periods in female Indian palm squirrel 21 Lincoln GA, Clark IJ (1994) Photoperiodically-induced Funambulus pennanti. Indian J Exp Biol 38: 974-981. cycles in the secretion of prolactin in hypothalamo- pituitary disconnected rams: evidence for translation 11 Thomas L, Drew JE, Abramovich DR, Williams LM of the melatonin signal in the pituitary gland. J (1998) The role of melatonin in the human fetus. Int Neuroendocrinol 6: 251-260. J Mol Med 1: 539-543. 22 Viswanathan N, Davis, FC (1993) The fetal circa- 12 Ebling FJ, Wood RI, Suttie JM, Adel TE, Foster DL dian pacemaker is not involved in the timing of birth (1989) Prenatal photoperiod influences neonatal pro- in hamsters. Biol Reprod 48: 530-537. lactin secretion in the sheep. Endocrinology 125: 384- 391. 23 Stetson MH, Elliot JA, Goldman BD (1986) Maternal transfer of photoperiodic information influences the 13 Bassett JM, Curtis N, Hanson C, Weeding C (1989) photoperiodic response of prepubertal Djungarian Effects of altered photoperiod or maternal melatonin hamsters (Phodopus sungorus sungorus). Biol administration on plasma prolactin concentrations in Reprod 34: 664-669. fetal lambs. J Endocrinol 122 633-643. 24 Carter DS, Goldman BD (1983) Anti-gonadal effect 14 Serone-Ferre M, Vergara M, Parraguez VH, Riquelme of timed melatonin infusion in pinealectomized male R, Llanos AJ (1989) The circadian variation of pro- Djungarian hamsters (Phodopus sungorus sungorus): lactin in fetal sheep is affected by the seasons. En- Duration is the critical parameter. Endocrinology 113: docrinology 125: 1613-1616. 1261-1267. 15 Houghton DC, Young IR, McMillen IC (1997) Photo- 25 Reiter RJ (1991) Pineal metabolism: Cell biology of periodic history and hypothalamic control of prolac- its synthesis and its physiological interactions. tin secretion before birth. Endocrinology 138: 1506- Endocrine Rev 12: 151-180. 1511. 26 Horton TH (1985) Cross-fostering of voles demon- 16 McMillen IC, Houghton DC, Young IR (1995) Mela- strates in utero effect of photoperiod. Biol Reprod tonin and the development of circadian and seasonal 33: 934-939. rhythmicity. J Reprod Ferti Suppl 49: 137-146. 27 Stetson MH, Ray SL, Creyaufmiller N, Horton TH 17 Berria M, DeSantis M, Mead RA (1988) Effects of (1989) Maternal transfer of photoperiodic informa- suprachiasmatic nuclear ablation and melatonin on tion in Siberian hamsters. II. The nature of the ma- delayed implantation in the spotted skunk. Neuroen- ternal signal, time of signal transfer, and the effect of docrinology 48: 371-375. the maternal signal on peri-pubertal reproductive 18 Berria M, DeSantis M, Mead RA (1989) Lesions to development in the absence of photoperiodic input. the anterior hypothalamus prevent the melatonin-in- Biol Reprod 40: 458-465. duced lengthening of delayed implantation. Endocri- 28 Horton TH, Stachecki SA, Stetson MH (1990) nology 125: 2897-2904. Maternal transfer of photoperiodic information in 19 Kaplan JB, Berria M, Mead RA (1991) Prolactin lev- Siberian hamsters. IV. Peripubertal reproductive els in the western spotted skunk: changes during pre- development in the absence of maternal photoperi- and peri-implantation and effects of melatonin and odic signals during gestation. Biol Reprod 42: 441- lesions to the anterior hypothalamus. Biol Reprod 44: 449. 991-997. 29 Shaw D, Goldman BD (1995) Influence of prenatal 20 Duncan MJ, Mead RA (1992) Autoradiographic lo- and postnatal photoperiods on postnatal testis de- calization of binding sites for 2-[125I] iodo-melatonin velopment in the Siberian hamster (Phodopus in the pars tuberalis of the Western spotted skunk sungorus). Biol Reprod 52: 833-838. (Spilogale putorius latifrons). Brain Res 569: 152-155. 30 Weaver DR, Reppert SM (1986) Maternal melatonin communicates day length to the fetus in Djungarian Melatonin, gestation and fetal development 11

hamsters. Endocrinology 119: 2861-2863. 42 Reppert SM, Klein DC (1978) Transport of maternal [3H] melatonin to suckling rats and fate of [3H] mela- 31 Horton TH, Ray SL, Stetson MH (1989) Maternal tonin in the neonatal rat. Endocrinology 102: 582- transfer of photoperiodic information in Siberian ham- 588. sters: Melatonin injection programs post-natal reproductive development expressed in constant light. Biol 43 Sugden D, (1983) Psychopharmacological effects of Reprod 41: 34-39. melatonin in mouse and rat. J Pharmacol Exp Ther 227: 587-591. 32 Lee TM, Zucker I (1988) Vole infant development is influenced perinatally by maternal photoperiodic his- 44 Weaver DR (1997) Reproductive safety of melato- tory. Am J Physiol 255: R 831-838. nin: a “wonder drug” to wonder about. J Biol Rhythms 12: 682-689. 33 Lee TM, Smale L, Zucker I, Dark JD (1987) Influ- ence of day length experienced by dams on post- 45 McElhinny AS, Davis FC, Warner CM (1996) The natal development of young meadow voles (Micro- effect of melatonin on cleavage rate of C57BL/6 and tus pennsylvanicus). J Reprod Fertil 81: 337-342. CBA/Ca preimplantation embryos cultured in vitro. J Pineal Res 21: 44-48. 34 Lee TM, Spears N, Tuthill CR, Zucker I (1989) Ma- ternal melatonin treatment influences rates of neo- 46 Chan WY, Ng TB (1995) Changes induced by pineal natal development of meadow vole pups. Biol Reprod indoles in post-implantation mouse embryos. Gen 40: 495-502. Pharmacol 26: 1113-1118.

35 Kivela A (1991) Serum melatonin during human preg- 47 Gorman MR, Ferkin MH, Dark J (1994) Melatonin nancy. Acta Endocrinol 124: 233-237. influences sex-specific prenatal mortality in meadow voles. Biol Reprod 51: 873-878. 36 Yellon SM, Longo LD (1988) Effect of maternal pinealectomy and reverse photoperiod on the circa- 48 Diaz B, Diaz E, Colmenero Mf M, Arce A, Esquifino dian melatonin rhythm in the sheep and fetus during A, Marin B (1999) Maternal melatonin influences rates the last trimester of pregnancy. Biol Repro. 39: 1093- of somatic and reproductive organs postnatal devel- 1099. opment of male rat offspring. Neuro-Endocrinol Lett 20: 69-76. 37 Klein DC (1972) Evidence for the placental transfer of 3 H-acetyl-melatonin. Nat New Biol 237: 117-118. 49 Fernandez B, Diaz E, Colmenero MD, Diaz B (1995) Maternal pineal gland participates in prepubertal rats’ 38 Reppert SM, Chez RA, Anderson A, Klein DC (1979) ovarian oocyte development. Anat Rec 243: 461-465. Maternal-fetal transfer of melatonin in the non- human primate. Pediatr Res 13: 788-791. 50 Colmenero MD, Diaz B, Miguel JL, Gonzalez ML, Esquifino A, Marin B (1991) Melatonin administra- 39 Velazquez E, Esquifino AI, Zueco JA, Ruiz Albusac tion during pregnancy retards sexual maturation of JM, Blazquez E (1992) Evidence that the circadian female offspring in the rat. J Pineal Res 11: 23-27. variations of circulating melatonin levels in fetal and suckling rats are dependent on maternal melatonin 51 Reiter RJ (1998) Melatonin and human reproduction. transfer. Neuroendocrinology 55: 321-326. Ann Med 30: 103-108.

40 Yellon SM, Longo LD (1987) Melatonin rhythms in 52 Sandell M (1990) The evolution of seasonal delayed fetal and maternal circulation during pregnancy in implantation. Q Rev Biol 65: 23-42. sheep. Am J Physiol 252: E799-802. 53 May R, Mead RA (1986) Evidence for pineal involve- 41 Nowak R, Young IR, McMillen IC (1990) Emergence ment in timing implantation in the western spotted of the diurnal rhythm in plasma melatonin concen- skunk. J Pineal Res 3: 1-8. trations in newborn lambs delivered to intact or 54 McConnell SJ, Tyndale-Biscoe CH, Hinds LA (1986) pinealectomized ewes. J Endocrinol 125: 97-102. Change in duration of elevated concentrations of me- 12 Haldar C and Yadav R et al

latonin is the major factor in photoperiod response 63 Matsumoto T, Hess DL, Kaushal KM, Valenzuela GJ, of the tammar, Macropus eugenii. J Reprod Fertil Yellon SM, Ducsay CA (1991) Circadian myometrial 77: 623-632. and endocrine rhythms in pregnant rhesus macaque: effects of constant light and timed melatonin infu- 55 Murphy BD, DiGregorio GB, Douglas DA, Gonzalez- sion. Am J Obstet Gynecol 165:1777-1784. Reyna A (1990) Interactions between melatonin and prolactin during gestation in mink (Mustela vison). J 64 Ayar A, Kutlu S, Yilmaz B, Kelestimur H (2001) Me- Reprod Fertil 89: 423-429. latonin inhibits spontaneous and oxytocin-induced contractions of rat myometrium in vitro. 56 Renfree MB, Lincoln DW, Almeida OF, Short RV Neuroendocrinol Lett 22:199-207. (1981) Abolition of seasonal embryonic diapause in 65 Schlabritz-Loutsevitch N, Hellner N, Middendorf R, a wallaby by pineal denervation. Nature 293: 138- Müller D, Olcese J (2003) The human myometrium 139. as a target of melatonin. J Clin Endocrinol Metab 57 Sandyk R, Anastasiadis PG, Anninos PA, Tsagas N 88:908-913. (1992) The pineal gland and spontaneous abortions: implications for therapy with melatonin and magnetic 66 Zhao H, Pang SF, Poon AMS (2002) Variations of field. Int J Neurosci 62: 243-250. mt1 melatonin receptor density in the rat uterus during decidualization, the estrous cycle and in response 58 Bishnupuri KS, Haldar C (2001) Maternal transfer of to exogenous steroid treatment. J Pineal Res 33: 140- melatonin alters the growth and sexual maturation 145. of young Indian palm squirrel Funambulus pennanti. 67 Lang U, Beguin PC, Sizonenko JD (1986) Fetal and Biol Signals Recent 10:317-325. maternal melatonin concentrations at birth in humans. 59 Nakamura Y, Tamura H, Kashida S, Takayama H, J Neural Tradin Suppl 21: 479-480. Yamagata Y, Karube A, Sugino N, Kato H (2001) 68 Okatani Y, Okamoto K, Hayashi K, Wakatsuki A, Changes of serum melatonin level and its relation- Tamura S, Sagara Y (1998) Maternal-fetal transfer ship to feto-placental unit during pregnancy. J Pineal of melatonin in pregnant women near term. J Pineal Res 30: 29-33. Res 25: 129-139. 60 Haldar C, Yadav R, Alipreeta (2006) Annual repro- 69 Waldhauser F, Boepple PA, Schemper M, Mansfield ductive synchronization in ovary and pineal gland function of female short-nosed fruit bat, Cynopterus MJ, Crowley WF Jr (1991) Serum melatonin in cen- sphinx. Comp Biochem Physiol (in press). tral precocious puberty is lower than in age-matched prepubertal children. J Clin Endocrinol Metab 73: 793- 61 Krishna A, Dominic CJ (1982) Differential rates of 796. fetal growth in two successive pregnancies in the 70 Silman AJ (1991) Melatonin and the human gona- emballonurid bat, Taphozous longimanus Hardwicke. dotropin-releasing hormone pulse generator. J BiolReprod 27: 351-353. Endocrinol 128: 7-11. 62 Alipreeta (1998) Physiology of the pineal organ of short- nosed fruit bat Cynopterus sphinx. Ph.D dis- sertation, Banaras Hindu University, Varanasi, India.