Maternal behavior,milk ejection,and plasma hormones in Hatano high- and low-avoidance rats

Hatano high- and low-avoidance (in a two-way active avoidance task) animals (HAA and LAA, respectively) were successfully selected from a Sprague-Dawley rat population. Pup growth of both strains was dependent on the maternal strain in a cross-fostering study. To determine whether there are strain-specific differences between HAA and LAA in maternal care, both strains of dams were subjected to a test battery as measured by nest building, home cage behavior, pup retrieval, and milk ejection tests. In addition, changes in plasma concentrations of lactotropic and corticotropic hormones such as prolactin, ACTH, and corticosterone were examined during lactation. The test battery indicated that the dams of both strains built good nests and spent an identical amount of time with their offspring. However, LAA dams showed a prolonged latency time for pup retrieval and often left pups outside the nest until the end of the test period. LAA dams also showed a decreased amount of milk ejection, whereas no strain differences were observed in milk ejection after oxytocin treatment. During lactation, a lesser increase in plasma concentrations of prolactin and a greater increase in ACTH were found in LAA dams. There were no differences between the two strains in plasma concentrations of corticosterone. These results clearly demonstrated decreases in maternal behavior and milk ejection in LAA as compared to HAA dams. The present results also suggest that maternal motivation and mechanisms responsible for maternal hormones related to suckling are involved in the degree of pup growth.     

Comparison of the "nursing" and other parental behaviors of nulliparous and lactating female rats

Virgin female rats display maternal behaviors after continuous exposure to pups (sensitization) that are in some respects similar to those of postpartum females. We herein provide a detailed comparison of the "nursing" and other parental behaviors of maternally sensitized virgin females and postpartum lactating dams. Ovariectomized and intact virgin females were exposed to pups until displaying maternal behavior. On the females' fourth day of maternal responsiveness, the pups were removed for 3 h and then returned, and subject-litter interactions were observed for 45 min. Behavior of maternal virgins was compared with that of lactating dams observed on day 4 postpartum interacting with either suckling pups or pups unable to suckle due to perioral anesthesia. Ovariectomy had no effect on behavior of virgins. Retrieval and licking of pups were deficient in virgins compared with lactating dams. Suckled dams showed prolonged kyphosis (upright crouched nursing), whereas nonsuckled dams displayed little kyphosis but rather were often in a hunched position over pups. Some aspects of quiescent "nursing" behaviors of virgins were surprisingly similar to those of suckled dams, including the latency to and duration of quiescence. Nonsuckling pup stimulation elicited more kyphosis in virgins than in lactating dams, which was still much less than in suckled dams. Virgins also "nursed" pups in hunched and prone postures. Differences between sensitized and postpartum females in their maternal behaviors likely reflect differences in motivation as well as sensory inputs they receive from pups. In particular, sensory regulation of "nursing" behaviors is influenced by reproductive state because nonsuckling pups elicit different postural responses in sensitized and lactating mothers.     

Parity-related differences in suckling behavior and nipple preference among free-ranging Japanese macaques

Suckling behavior of primiparae in free-ranging Japanese macaques (Macaca fuscata) was compared with that of multiparae at Jigokudani Monkey Park, the Shiga Heights, Nagano Prefecture, Japan, from April 1984 to June 1994. The estimated rates of milk secretion in a single preferred nipple among primiparae were lower than those among multiparae from birth to 5 months of age. Milk secretion capabilities of primiparous mothers, hence, appear to be inferior to those of multiparous mothers. In nutritive sucking, although Japanese macaque infants preferred one single nipple, nipple preferences in primiparae were weaker than those in multiparae. With supplementary two-nipple use during sucking, however, the infants of primiparae appear to overcome a suckling flaw of their primiparous mothers. After infants were 5 months of age and after a drop (from approximately 10% to approximately 5%) in the rates of milk secretion, however, milk secretion rates in a single preferred nipple among primiparae were similar to those in multiparae and the supplementary two-nipple use in primiparous mother-infant dyads disappeared. Am. J. Primatol. 42:331–339, 1997. © 1997 Wiley-Liss, Inc.     

Litter Size Determines Circadian Periodicity of Nursing in Rabbits

Nursing in rabbits occurs inside the nest with circadian periodicity. To determine the contribution of suckling stimulation in regulating such periodicity, we varied the size of the litters provided (1, 2, 4, or 6–8 pups). Nursing does, kept under a 14:10 (L:D) photoperiod, were continuously videotaped from parturition into lactation day 15. Although parturitions occurred throughout the day, a significant negative linear correlation (p?<?0.0001; r?=??0.68) was evident between time of delivery and time of nursing on lactation day 1, regardless of newborn number: longer intervals between these two events were seen in does delivering in the early morning than in those that gave birth late in the day. In rabbits suckling 6–8 pups, a Rayleigh analysis revealed that the population vector best describing their nursing pattern (across lactation days 1–15) had a phase angle?=?58° (corresponding to solar time 0352?h and rho?=?0.78; p?<?0.001). In contrast, the nursing pattern of does nursing litters smaller than 6 pups did not show circadian periodicity; rather, mothers showed multiple entrances into the nest box throughout the day. Cluster analysis revealed that the main equilibrium point of intervals between suckling bouts shifted from 24?h (6–8 pups) to 6?h (4 and 2 pups) and to as low as 4?h with 1 pup. In the groups nursing 2, 4, or 6–8 pups, most nursing episodes were followed by food and water intake. Those mothers also showed self-grooming of the ventrum and nipples after nursing. The incidence of these behaviors was lower in does nursing 1 pup. In conclusion, nursing in rabbits spontaneously occurs with circadian periodicity, but it is largely modulated by a threshold of suckling stimulation. (Author correspondence: gabygmm@gmail.com)     

The effect of a mixed-management system on the release of oxytocin, prolactin, and cortisol in ewes during suckling and machine milking

Milk yield and plasma oxytocin (OT), prolactin (PRL), and cortisol (CORT) during suckling and machine milking were measured in multiparous ewes subjected to a mixed management system of 3 sucklings and two daily milkings. Peak hormones were significantly increased and were similar during suckling and milking for PRL (181 vs. 163.3 ng x mL(-1)) and CORT (12.5 vs. 11.5 ng x mL(-1)). During the period of exclusive suckling, OT was always significantly released (90.3 pg x mL(-1)); however, during the period of mixed management, OT concentrations only increased during suckling compared to milking (91.7 vs. 13.1 pg x mL(-1)). The mean volume of milk obtained during suckling (632 mL) was significantly higher than during milking (255 mL). Thus, during a mixed management system, oxytocin and prolactin releases are not under similar central regulation. A mixed system, without OT release during milking, does not contribute to accelerate the conditioning of ewes for machine milking.     

(d-Met2,Pro5)Enkephalinamide causes a decrease in plasma prolactin levels of lactating rats continuously suckled and an increase in those deprived of their litter

The effect of an enkephalin analogue, (d-Met²,Pro⁵)enkephalinamide (EKNH₂) on prolactin (PRL) secretion of lactating rats continuously suckled or separated from their pups was investigated. In rats together with their pups 0.5 mg/kg EKNH₂ caused a dramatic decrease, 0.25 mg/kg a mild and short-lasting reduction in plasma PRL levels. In contrast, in lactating rats separated for 4 h from their pups 0.5 mg/kg of the drug induced a slight and 1.0 mg/kg a considerable increase in plasma PRL levels. The data indicate that in lactating rats depending on the circumstances the enkephalin analogue causes opposite effects on PRL secretion.     

Effect of prolactin and glucocorticoids on P-enolpyruvate carboxykinase activity in liver and mammary gland from diabetic and lactating rats

Summary The administration of 2 bromo--ergocryptine, to reduce serum prolactin decreased the activity of cytosolic P-enolpyruvatc carboxykinase (GTP) (EC4.1.1.32) about 50% in both liver and mammary gland of lactating animals. Adrenalectomy had similar effects to those of bromo-a-ergocryptine. In contrast, there was a 50% increase in enzyme activity in the mammary gland of diabetic, lactating rats and a 10-fold increase in liver as compared with normal rats. P-enolpyruvate carboxykinase activity in mammary gland as liver is coordinately regulated by prolactin, glucocorticoids and insulin.     

Maternal protectiveness and response to the unfamiliar in vervet monkeys

Vervet monkeys (Cercopithecus aethiops sabaeus) show individual differences in approach-avoidance behavior when faced with an unfamiliar and potentially threatening situation. Prior research from our colony demonstrated that juveniles who had experienced high levels of early maternal protectiveness were more cautious in response to novelty, compared to juveniles who had had less protective mothers. The research reported here was designed to verify this result in a paradigm that experimentally varied maternal protectiveness through the introduction of new breeding adult males. Mothers responded to the presence of new males by increased maternal protectiveness toward infants born in the year following the introductions. Individual differences in response to the unfamiliar were later evaluated by measuring the latency to approach within 1 m of novel food containers placed into the home enclosure of four naturally composed social groups. Infants approached with the same latency and in the same order as their mothers. Juveniles approached sooner than, and independent of, their mother's current behavior, but their latency to approach could be predicted by the experimentally induced variation in maternal protectiveness they had experienced as infants. Immatures who had been born in New Male years, when maternal protectiveness was high, were more cautious and had significantly longer latencies to approach the novel stimulus compared to immatures who had been born in Resident Male years. © 1993 Wiley-Liss, Inc.     

Intermittent suckling enables estrus and pregnancy during lactation in sows: effects of stage of lactation and lactation during early pregnancy

Previously we demonstrated that pre-ovulatory LH and post-ovulatory progesterone (P4) concentrations in plasma were low and embryo development was retarded when sows were induced to ovulate during lactation by submitting them to intermittent suckling (IS). The present study investigated whether this was due to: (1) stage of lactation when IS was initiated, and (2) continuation of IS post-ovulation. Multiparous Topigs40 sows were studied under three conditions: conventional weaning at Day 21 of lactation (C21; n = 30), intermittent suckling from Day 14 of lactation (IS14; n = 32), and intermittent suckling from Day 21 of lactation (IS21; n = 33). Sows were separated from piglets for 12 h daily during IS. IS sows were either weaned at ovulation or 20 d following ovulation. One-third (21/63) of the IS21 and C21 sows had already ovulated or had large pre-ovulatory follicles at Day 21 and were excluded from further study. Initiation of IS at Day 14 instead of Day 21 of lactation tended to reduce P4 at 7 d post-ovulation (P = 0.07), did not affect pregnancy rate, and tended to reduce embryo survival (P = 0.06). Continuation of IS during pregnancy resulted in lower P4 at 7 and 12 d post-ovulation, tended to reduce embryo weight and pregnancy rate (P < 0.10), whereas embryo survival was not affected. This study presents data for a population of sows in which follicle growth and ovulation are easily triggered under suckling conditions. Further, when these sows are bred during lactation, initiation of IS at 21 rather than 14 d of lactation with weaning at ovulation yields the most desirable reproductive performance.     

Maternal chitosan oligosaccharide supplementation affecting expression of circadian clock genes,and possible association with hepatic cholesterol accumulation in suckling piglets

Chitosan oligosaccharide (COS) has been shown to reduce lipid accumulation in liver in mice and rats. The purpose of this study was to investigate whether maternal COS feeding affects hepatic lipid metabolism via influencing the expression of circadian clock genes in piglets. From day (d) 85 of gestation to d 14 of lactation, sixteen pregnant sows were divided into a control group (basal diet without COS supplementation) and a COS group (30 mg COS/kg basal diet). After farrowing, one piglet per litter in each group was selected for the collection of plasma and liver samples on d 0 and d 14 of age, respectively. Interestingly and significantly, we found that maternal COS supplementation promoted plasma and hepatic cholesterol accumulation and up-regulated the mRNA level of negative-regulated element period 1 (Per1), and reduced the abundance of the positive elements, circadian locomotor output cycles kaput (CLOCK), and brain muscle Arnt-like 1 (BMAL1) in the suckling piglets on d 14. These alterations may promote the hepatic cholesterol accumulation, which, in turn, activates hepatic bile acid metabolism and attenuates the relative expression levels of lipid metabolism-associated genes in the liver. However, the expression of CLOCK and BMAL1 and the lipid profile in the plasma and liver were not affected by COS supplementation on d 0. Collectively, our results indicate that maternal supplementation with COS postpartum up-regulates cholesterol accumulation in suckling piglets at age d 14, in part, by the regulation of circadian clock genes.     

Dopaminergic mediation of Y-aminobutyric acid in the control of prolactin release: Plasma prolactin and brain tyrosine hydroxylase levels in ovariectomized conscious rats

The present experiments were carried out to further elucidate the mechanism by which dopamine mediates the actions of Y-aminobutyric acid on prolactin release from anterior pituitary following its intraventricular injection in overiectomized conscious rats, Y-Aminobutyric acid significantly suppressed the prolactin levels at 0.1 Μmol concentration while at 4 Μmol dose, the level was elevated. The activity of tyrosine hydroxylase was increased significantly in the anterior pituitary at the lower dose while the higher concentration of Y-aminobutyric acid did not bring about any change in the activity both in the hypothalamus and the anterior pituitary. The results presented suggest that intracellular dopamine in the anterior pituitary may directly inhibit prolactin release; the plasma prolactin level is elevated by Y-aminobutyric acid, by way of either inhibiting dopaminergic tone or possible stimulation of a physiological prolactin releasin g hormone.     

Effects of reduced suckling on days to estrus, conception during lactation and embryo survival in sows

Trials to investigate the effects of limited suckling on sow reproduction and piglet growth were conducted using 41 first parity and 32 second parity Yorkshire sows. Separation of sows from their litters (22 hrs/day, days 21-35 postpartum) induced estrus in 60% of primiparous and 72% of second parity sows during lactation. Compared to control group animals, primiparous sows had higher weaning weights and second parity sows higher rates of embryo survival on day 30 of gestation. Piglets subjected to suckling restriction had weights, at 2 weeks after weaning, equal to those weaned after 5 weeks of unrestricted suckling. We conclude that suckling restriction can provide the dual benefits of an extended piglet nursing period and a decreased breeding to breeding interval in sows.     

Effect of calf suckling on oxytocin,prolactin, growth hormone and milk yield in crossbred Gir x Holstein cows during milking

This study evaluated the effect of different milking managements on oxytocin, prolactin and growth hormone release in Gir x Holstein cows. Six cows were suckled by their calves, before and after milking (SM group); another six cows were submitted to exclusive milking (M group). High OT levels were observed during suckling of the SM group, however both groups had similar levels of OT during milking. The SM group presented PRL levels significantly higher than the M group, however only during suckling. For GH levels, the SM group showed higher levels than the M group, however this difference was significant only during the first suckling, cleaning of the teats and at the beginning of machine milking. Despite these results, SM cows produced more milk (milking plus suckling) than M cows, however milk obtained by milking was similar for both groups.     

Testosterone and prolactin are associated with emotional responses to infant cries in new fathers

To determine the responsiveness of new fathers and non-fathers toward infant cues, we exposed fathers and non-fathers to infant cries and to control stimuli and we measured affective, heart-rate, and endocrine responses, including salivary testosterone and cortisol and plasma prolactin concentrations prior to and after cry presentations. We found that (1) fathers hearing the cry stimuli felt more sympathetic and more alert compared to groups who did not hear the cries or to non-fathers who heard the cries; (2) fathers and non-fathers with lower testosterone levels had higher sympathy and/or need to respond to the infant cries than fathers with higher testosterone levels; (3) fathers with higher, as opposed to lower, prolactin levels were also more alert and more positive in response to the cries; (4) fathers hearing the cry stimuli showed greater percentage increase in testosterone than fathers not hearing the cry stimuli; (5) experienced fathers hearing the cries showed a greater percentage increase in prolactin levels compared to first-time fathers or to any group of fathers hearing control stimuli; finally, (6) partial correlations with parity and experience entered as a covariates indicated that both experience and testosterone contributed to the variance in fathers' affective responses to infant cries. Taken together, these results indicate that, as with a number of other biparental species, human fathers are more responsive to infant cues than are non-fathers and fathers' responses to infant cues are related to both hormones and to caregiving experience.     

Endocrine changes, with special emphasis on oestradiol-17 beta, prolactin and oxytocin, before and during labour and delivery in goats

Jugular plasma concentrations of oestradiol-17 beta, prolactin, progesterone and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM) were measured at 2-h intervals during the last 4 days of pregnancy in 6 goats. During advanced labour and delivery, samples were obtained more frequently and assayed for oxytocin. The animals were housed in a barn with continuous dim lighting. A distinct pattern of oscillation in prolactin concentrations, with peaks during the late afternoon, was apparent during the last 3 days. Geometric means of peak concentrations doubled each day and became of longer duration; night-time nadir values remained low except during the last night before parturition. A progressive increase in oestradiol-17 beta, with mean levels doubling every 36 h, was apparent during the last 3 days. There was no sharp pre-partum increase in oestradiol-17 beta. Correlated (r = 0.83) with the increase in oestradiol-17 beta was a gradual increase in PGFM and when the latter reached approximately 1000 pg/ml, the non-reversible decline in progesterone reflecting pre-partum luteolysis occurred. Subsequent changes in PGFM related closely to an approximately 20-fold increase in the ratio of oestradiol-17 beta to progesterone until maximal PGFM levels of 26.5 +/- 4.2 ng/ml were reached at delivery. Basal concentrations of oxytocin (8-15 microU/ml) were measured before the last 60 min and markedly higher, though erratic, concentrations were detected at various times before appearance of the allantochorion. Maximal oxytocin values (range 180-1570 microU/ml) occurred within minutes before or after delivery of the first fetus. The results suggest that increased pre-partum production of oestradiol-17 beta, in addition to provoking sufficient release of prostaglandins to cause luteolysis, may modulate either the sensitivity or set-points for an endogenous rhythm in prolactin secretion at the end of pregnancy. The nature of the oxytocin changes suggest that, after labour has evolved sufficiently, delivery is precipitated by an abrupt increase in oxytocin secretion.     

Infradian rhythmicity in lactogenic hormone (prolactin,growth hormone,cortisol and thyroid hormone) secretion throughout the lactation cycle in mithun cows (Bos frontalis): variation among strains

The role of lactogenic hormones (prolactin, growth hormone, cortisol and thyroid hormone) on lactation yield in Mithun cows as well as their rhythmicity throughout the lactation cycle were studied in Mizoram (n = 4) and Nagaland (n = 7) strain of mithun (Bos frontalis). Blood samples were collected from all the animals from the day of calving to the complete dry off at an interval of 15 days. All the hormones were estimated in the serum by commercially available ELISA kits. Plasma level of cortisol (μg/dl), growth hormone (GH, in ng/ml), prolactin (PRL, in μIU/ml), triiodothyronine (T₃, in nmol/μl) and thyroxin (T₄, in ng/ml) were 20.84 ± 0.29, 28.08 ± 0.56, 9.87 ± 0.20, 27.82 ± 0.56 and 51.33 ± 0.48, respectively, in mithun irrespective of strains during the lactation period. Levels of all the hormones varied significantly (p ≤ 0.01) during different days of lactation cycle but, there was no significant difference among strain. Levels of PRL, GH, cortisol and T₃ were significantly (p < 0.01) higher around calving and declined sharply. The hormones remained in almost steady state during mid-lactation and declined during late lactation. All the hormones stated above were positively correlated with lactational yield thus their role on lactogenesis and galactopoiesis was established.     

Maternal and paternal care in the rock cavy,Kerodon rupestris,a South American hystricomorph rodent

The maternal and paternal behavior of Kerodon rupestris was examined. Quantitative differences between fathers and mothers and between mothers raising young with fathers present and with fathers absent were assessed. Growth rates of young raised by paired females and by lone females were compared. The male provides direct paternal care to the young by engaging in allogrooming, sniffing, and huddling. There is no significant difference between the sexes in the amount of contact promoting behavior given to the offspring, nor are the sexes significantly different in the amount of exploratory sniffing of the offspring. When the male is absent, the female spends a greater amount of time in contact with the young. Young raised by lone females gained significantly more weight than young raised by paired females. The suggestion that indirect paternal care acts to reduce female aggression to the young and relieve the energy expenditure burden of the female is discussed. The results indicate that social experience is gained at the expense of physical nurturing when the male is present.     

Manipulation of the oxytocin system alters social behavior and attraction in pair-bonding primates, Callithrix penicillata

The establishment and maintenance of stable, long-term male-female relationships, or pair-bonds, are marked by high levels of mutual attraction, selective preference for the partner, and high rates of sociosexual behavior. Central oxytocin (OT) affects social preference and partner-directed social behavior in rodents, but the role of this neuropeptide has yet to be studied in heterosexual primate relationships. The present study evaluated whether the OT system plays a role in the dynamics of social behavior and partner preference during the first 3 weeks of cohabitation in male and female marmosets, Callithrix penicillata. OT activity was stimulated by intranasal administration of OT, and inhibited by oral administration of a non-peptide OT-receptor antagonist (L-368,899; Merck). Social behavior throughout the pairing varied as a function of OT treatment. Compared to controls, marmosets initiated huddling with their social partner more often after OT treatments but reduced proximity and huddling after OT antagonist treatments. OT antagonist treatment also eliminated food sharing between partners. During the 24-h preference test, all marmosets interacted more with an opposite-sex stranger than with the partner. By the third-week preference test, marmosets interacted with the partner and stranger equally with the exception that intranasal-OT treatments facilitated initial partner-seeking behavior over initial contact with the stranger. Our findings demonstrate that pharmacological manipulations of OT activity alter partner-directed social behavior during pair interactions, suggesting that central OT may facilitate the process of pair-bond formation and social relationships in marmoset monkeys.     

Maternal expenditure in the polygynous and monomorphic guanaco: suckling behavior, reproductive effort, yearly variation, and influence on juvenile survival

We investigated patterns of maternal expenditure and its influenceonjuvenile survival in the polygynous monomorphic guanaco (Lamaguanicoe)in southern Chile from 1990 to 1994. Birth weight and growthrate(until age 1) of males and females were similar. Suckling ratesof malesand females were not significantly different, althoughmothers of malesrejected suckling attempts more often thanmothers of females during fall andwinter. Mothers with sonsterminated suckling bouts in equal proportion as didmotherswith daughters. Our estimated level of reproductive effort forguanacosfalls within the range of species exhibiting no sex-biased maternalexpenditureon offspring. Mean yearly birth weight was negatively correlatedwithpopulation density. Mean suckling time throughout the year differedamongcohorts, as did the mean number of suckling attempts andrejected sucklingattempts per hour throughout the year. Juvenilesurvival was estimated untilage 1. Of the model with five covariatesincluding juvenile sex, birth weight,adult female aggressiontoward taggers, mean suckling time, and populationdensity,only mean suckling time and population density were significantlyrelatedto survival. The risk ratio for mean suckling time indicatesthat therisk of mortality increases as suckling time increases,whereas the risk ratiofor population density indicates thatthe risk of mortality decreases aspopulation density increases.Under some conditions increasing populationdensity may be correlatedwith lower offspring birth weight, yet enhancedjuvenile survival.This effect on survival was possibly associated with thenumberof predators on the study area from year to year.