Suppression of ovarian activity during the breeding season in suckling Japanese monkey (Macaca fuscata)

Kisspeptin and lactational anestrus: Current understanding and future prospects

Lactational anestrus, characterized by the suppression of pulsatile gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release, would be a strategic adaptation to ensure survival by avoiding pregnancy during lactation in mammals. In the present article, we first provide a current understanding of the central regulation of reproduction in mammals, i.e., a fundamental role of arcuate kisspeptin neurons in mammalian reproduction by driving GnRH/LH pulses. Second, we discuss the central mechanism inhibiting arcuate Kiss1 (encoding kisspeptin) expression and GnRH/LH pulses during lactation with a focus on suckling stimulus, negative energy balance due to milk production, and the role of circulating estrogen in rats. We also discuss upper regulators that control arcuate kisspeptin neurons in rats during the early and late lactation periods based on the findings obtained by a lactating rat model. Finally, we discuss potential reproductive technology for the improvement of reproductive performance in milking cows.

Reproductive seasonality in primates: patterns, concepts and unsolved questions

Primates, like other mammals, exhibit an annual reproductive pattern that ranges from strictly seasonal breeding to giving birth in all months of the year, but factors mediating this variation are not fully understood. We applied both a categorical description and quantitative measures of the birth peak breadth based on daily observations in zoos to characterise reproductive seasonality in 141 primate species with an average of 941 birth events per species. Absolute day length at the beginning of the mating season in seasonally reproducing species was not correlated between populations from natural habitats and zoos. The mid-point of latitudinal range was a major factor associated with reproductive seasonality, indicating a correlation with photoperiod. Gestation length, annual mean temperature, natural diet and Malagasy origin were other important factors associated with reproductive seasonality. Birth seasons were shorter with increasing latitude of geographical origin, corresponding to the decreasing length of the favourable season. Species with longer gestation periods were less seasonal than species with shorter ones, possibly because shorter gestation periods more easily facilitate the synchronisation of reproductive activity with annual cycles. Habitat conditions with higher mean annual temperature were also linked to less-seasonal reproduction, independently of the latitude effect. Species with a high percentage of leaves in their natural diet were generally non-seasonal, potentially because the availability of mature leaves is comparatively independent of seasons. Malagasy primates were more seasonal in their births than species from other regions. This might be due to the low resting metabolism of Malagasy primates, the comparatively high degree of temporal predictability of Malagasy ecosystems, or historical constraints peculiar to Malagasy primates. Latitudinal range showed a weaker but also significant association with reproductive seasonality. Amongst species with seasonal reproduction in their natural habitats, smaller primate species were more likely than larger species to shift to non-seasonal breeding in captivity. The percentage of species that changed their breeding pattern in zoos was higher in primates (30%) than in previous studies on Carnivora and Ruminantia (13 and 10%, respectively), reflecting a higher concentration of primate species in the tropics. When comparing only species that showed seasonal reproduction in natural habitats at absolute latitudes ≤11.75°, primates did not differ significantly from these two other taxa in the proportion of species that changed to a less-seasonal pattern in zoos. However, in this latitude range, natural populations of primates and Carnivora had a significantly higher proportion of seasonally reproducing species than Ruminantia, suggesting that in spite of their generally more flexible diets, both primates and Carnivora are more exposed to resource fluctuation than ruminants.

Associations between Parity, Hair Hormone Profiles during Pregnancy and Lactation, and Infant Development in Rhesus Monkeys (Macaca mulatta)

Studies examining hormones throughout pregnancy and lactation in women have been limited to single, or a few repeated, short-term measures of endocrine activity. Furthermore, potential differences in chronic hormonal changes across pregnancy/lactation between first-time and experienced mothers are not well understood, especially as they relate to infant development. Hormone concentrations in hair provide long-term assessments of hormone production, and studying these measures in non-human primates allows for repeated sampling under controlled conditions that are difficult to achieve in humans. We studied hormonal profiles in the hair of 26 female rhesus monkeys (Macaca mulatta, n=12 primiparous), to determine the influences of parity on chronic levels of cortisol (hair cortisol concentration, HCC) and progesterone (hair progesterone concentration, HPC) during early- to mid-pregnancy (PREG1), in late pregnancy/early lactation (PREG2/LACT1), and in peak lactation (LACT2). We also assessed infants' neurobehavioral development across the first month of life. After controlling for age and stage of pregnancy at the first hair sampling period, we found that HCCs overall peaked in PREG2/LACT1 (p=0.02), but only in primiparous monkeys (p<0.001). HPCs declined across pregnancy and lactation for all monkeys (p<0.01), and primiparous monkeys had higher HPCs overall than multiparous monkeys (p=0.02). Infants of primiparous mothers had lower sensorimotor reflex scores (p=0.02) and tended to be more irritable (p=0.05) and less consolable (p=0.08) in the first month of life. Moreover, across all subjects, HCCs in PREG2/LACT1 were positively correlated with irritability (r(s)=0.43, p=0.03) and negatively correlated with sensorimotor scores (r(s)=-0.41, p=0.04). Together, the present results indicate that primiparity influences both chronic maternal hormonal profiles and infant development. These effects may, in part, reflect differential reproductive and maternal effort in mothers with varied caretaking experience. In addition, infant exposure to relatively higher levels of maternal cortisol during the late fetal and early postnatal periods is predictive of poorer developmental outcomes.

Non-lactating versus lactating females: a comparison of sex steroids, sexual coloration, and sexual behavior in Japanese macaques

Female Japanese macaques are seasonal breeders distinguished by their red-colored hindquarters, face, and nipple skin areas. Intensity of coloration seems to be associated with sexual attractiveness, behavior, and fluctuating sex steroids. Our aim was to investigate whether the color intensity of these regions differed between lactating (LA) and non-lactating (NLA) females during sexually inactive (SI) and active (SA) phases. Coloration scores of 19 adult females were classified using color tables. Estrogen and progesterone metabolites were determined in fecal samples. Weekly comparison between both groups revealed significantly increased coloration of the hindquarters area from week 13 (SI) until the end of the observation period, and for the nipple skin throughout the SI and SA periods. Face coloration differed marginally. Hormonally, NLA females showed significantly increased excretion rates of sex steroids at the end of the SI phase and throughout the whole SA period. Logistic regression analyses between elevated fecal steroids and nipple coloration disclosed a significant relationship for NLA females during the SI period. This connection persisted and included hindquarter coloration during the SA period. NLA females showed increased intromission with ejaculation, but no difference was found for intromission without ejaculation. In conclusion, results demonstrate increased endocrine excretion rates for NLA females during the whole observation period, paralleled by an enhanced, fertility-signaling sexual attractiveness.

Physiological role of metastin/kisspeptin in regulating gonadotropin-releasing hormone (GnRH) secretion in female rats

Various studies have attempted to unravel the physiological role of metastin/kisspeptin in the control of gonadotropin-releasing hormone (GnRH) release. A number of evidences suggested that the population of metastin/kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) is involved in generating a GnRH surge to induce ovulation in rodents, and thus the target of estrogen positive feedback. Females have an obvious metastin/kisspeptin neuronal population in the AVPV, but males have only a few cell bodies in the nucleus, suggesting that the absence of the surge-generating mechanism or positive feedback action in males is due to the limited AVPV metastin/kisspeptin neuronal population. On the other hand, the arcuate nucleus (ARC) metastin/kisspeptin neuronal population is considered to be involved in the regulation of tonic GnRH release. The ARC metastin/kisspeptin neurons show no sex difference in their expression, which is suppressed by gonadal steroids in both sexes. Thus, the ARC population of metastin/kisspeptin neurons is a target of estrogen negative feedback action on tonic GnRH release. The lactating rat model provided further evidence indicating that ARC metastin/kisspeptin neurons are involved in GnRH pulse generation, because pulsatile release of luteinizing hormone (LH) is profoundly suppressed by suckling stimulus and the LH pulse suppression is well associated with the suppression of ARC metastin/kisspeptin and KiSS-1 gene expression in lactating rats.

Hematology of a natural population of toque macaques (Macaca sinica) at polonnaruwa, Sri Lanka

Hematological studies were conducted in three wild groups of toque macaques (Macaca sinica) inhabiting the Polonnaruwa Sanctuary in northeastern Sri Lanka. The macaques were temporarily trapped and anesthetized, and femoral blood was drawn from 35 males and 37 females (age range: 0.33-24.5 yr). Statistically significant (P<0.05) differences were observed by sex for total plasma proteins (PP), and by age for red blood cell (RBC) counts, hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular Hb (MCH), mean corpuscular Hb concentration (MCHC), PP, erythrocyte sedimentation rate (ESR), differential and absolute neutrophil counts, differential lymphocyte counts, and absolute eosinophil counts. In general, the results were similar to those reported for other species of colony-bred and free-ranging macaques. However, there also were differences. First, in contrast to earlier studies of nonhuman primates, we examined the hematology of infants. Compared to other age classes, infants (<1 yr old) had lower RBC, Hb, MCHC, and ESR values, and a higher MCV. These findings were similar to those obtained in human infants. Second, we observed variations in hematology among social groups in relation to their ecology. Two groups (IH3 and M3) had ready access to water throughout the dry season (the period of sampling), whereas the third group (J) did not. The Hb, RBC, and PP values obtained in groups IH3 and M3 were similar to those reported in other macaque species. However, these parameters in group J were significantly (P<0.01) higher, which suggests that this group (representing about 26% of the sample) had been dehydrated during the dry season. Finally, two indices indicative of injury and infection--the ESR and leukocyte counts--were higher in the wild toque macaques than has been reported for other species of macaques held in captivity, and about 15% of the toque macaques sampled had extreme outlier values for these parameters; however, none were visibly ill or died. These results suggest that wild toque macaques are subject to a wide array of physical and biological insults that are unique to natural populations.

Non-metabolic and metabolic factors causing lactational anestrus: rat models uncovering the neuroendocrine mechanism underlying the suckling-induced changes in the mother

Follicular development and ovulation are strongly inhibited during lactation. Administration of a high dose of estrogen induces luteinizing hormone (LH) surges in ovariectomized lactating rats, suggesting that brain mechanisms regulating cyclic LH release remain intact in lactating mothers. On the other hand, tonic LH release is profoundly suppressed in lactating rats. This suggests that lactational anestrus is mainly due to suppression of the mechanism regulating pulsatile gonadotropin-releasing hormone secretion in the hypothalamus, which is responsible for follicular development and steroid production. Both metabolic and non-metabolic factors are involved in suppressing pulsatile LH secretion throughout lactation in rats. During the first half of lactation, pulsatile LH secretion is strongly suppressed, even if milk production is attenuated by pharmacological blockade of prolactin secretion in ovariectomized lactating rats. Pulsatile LH release quickly recovers by removing pups or blocking neuronal input by hypothalamic deafferentation during the period. These data suggest that the suckling stimulus itself is responsible for suppression of LH release during the first half of lactation. During the second half of lactation, negative energy balance, which is caused by the milk production, appears to play a dominant role in suppressing LH secretion. Blockade of milk production by inhibiting prolactin release causes a gradual increase in LH release even if the vigorous suckling stimulus by foster pups remains. In conclusion, the suckling stimulus itself predominantly suppresses LH pulses during the first half of lactation and metabolic factors take over the role of the suckling stimulus during the second half of lactation.

Aetiological approach of female reproductive physiology in lactational amenorrhoea

There is a wide range of duration of post-partum amenorrhoea and resumption of ovulation between individuals, within an individual or between populations. Several extraneous variables, such as parity, mother's age, sex of the breast-fed baby, socioeconomic status and cultural level of the family, can be controlled; then the remaining variables will probably explain a part of the total variability in post-partum amenorrhoea duration but say nothing about the physiological process. In attempting to question physiological aspects of the return of fertility several observational studies have tended to favour one of the different factors which are supposed to play a major role in the regulation and have compared different levels of it, such as body composition of the mother (Frisch & McArthur, 1974), breast-feeding pattern (Jones, 1989) or the life style of the women. Life style can be related to women's physical activity in normal life (Ellison, 1991), the difference between urban and rural life (Carael, 1981) or the environment (Laurenson et al., 1985). Prolactin as a possible mediator of the central regulation has been carefully considered (Lunn, Austin & Whitehead, 1984; Howie et al., 1982). These studies were mainly observational rather than experimental, supplementing mothers during the lactating period or during the pregnancy. If this information is added to what is known of other animal species (Loudon, 1987) or animal experimentation (Plant et al., 1989; Williams et al., 1990a; Williams et al., 1990b), the combination of several of the main factors believed to have a major role in the human species can be clarified and the aetiology of the resumption of fertility in nursing women investigated.