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Genital stimulation facilitates maternal behavior in estrous ewes.

Only a small proportion of ewes at estrus have been found to respond maternally to newborn lambs, and this low maternal responsiveness may be partially attributable to the absence of the genital stimulation which occurs at parturition. Therefore, the effect of artificial genital stimulation on maternal behavior of estrous ewes was investigated. Estrus was synchronized in 33 ewes by placement and withdrawal of progestin-saturated vaginal sponges. Estrous ewes were divided into two groups, a control group and a group receiving 5 min of artificial genital stimulation, and observed following presentation of newborn lambs. Significantly more stimulated ewes licked the lamb and emitted low-pitched bleats in a 30-min test. When genital stimulation was subsequently administered to control ewes, more of them also became maternal so that the two groups were no longer significantly different. These results indicate that absence of genital stimulation is one of the factors contributing to the low maternal responsiveness of estrous ewes. They also demonstrate for the first time that artificial genital stimulation is effective in eliciting maternal behavior in nonpregnant ewes even at physiological concentrations of estradiol.

Animals↗

Maternal behavior of SHR rats and its relationship to offspring blood pressures.

In Part I of this study maternal behavior of 15 spontaneously hypertensive (SHR) and 11 Wistar-Kyoto (WKY) rat mothers was recorded throughout the preweaning period. SHR mothers were observed: 1) in arched-and blanket-nursing postures more often, and in passive-nursing posture less often, 2) licking their pups more often, and 3) resting less often. Further, SHR mothers retrieved their pups more quickly than did WKY. In the second part of this study we found that a composite maternal behavior score, derived from summing occurrences of mother/pup contact, arched-nursing, and pup-licking, was positively correlated with the offspring blood pressures. This relationship, which accounted for 43.5% of the variance in adult blood pressure, suggests that certain types of interactions between mothers and their pups may contribute to individual differences in cardiovascular system development.

Animals↗

Ingestion of amniotic fluid by postpartum rats enhances morphine antinociception without liability to maternal behavior.

Ingestion of amniotic fluid or placenta by rats has been shown to enhance opioid-mediated analgesia induced by morphine injection, foot shock, vaginal/cervical stimulation, or late pregnancy. The present study was designed to determine whether this mechanism might be a means of providing greater analgesia during the periparturitional period without contributing to the disruption of maternal behavior (measured primarily as retrieval) that can result from excessive opioid levels. Postpartum primiparous rats, injected with either 2 or 3 mg/kg morphine sulfate or vehicle and given orogastric infusions of either amniotic fluid or saline, were tested for maternal behavior. Pain threshold (determined by tail-flick latency test) in rats injected with 2 mg/kg morphine and infused with amniotic fluid was elevated to a level that did not differ significantly from that of a separate group of rats injected with 3 mg/kg morphine and infused with saline. This enhanced analgesia was not, however, accompanied by the significant disruption of maternal behavior found among the rats receiving the higher morphine dose.

Amniotic Fluid↗

Maternal behavior of dams treated with ACTH during pregnancy.

Experimental female rats were injected with ACTH during the last third of their pregnancy. This treatment resulted in prolongation of gestation and in abnormal development of the young. The number of resorptions, stillbirths, and congenitally malformed pups was increased and those that appeared normal had lower body weights. The experimental treatment also severely affected the ability of the dams to exhibit normal maternal behavior. Significant individual differences were noted in the sensitivity of the dams to the experimental treatment. Cross-fostering experiments revealed that experimental dams exhibited normal maternal behavior towards control foster pups, after an initial delay of 24 h. When experimental pups, born after a prolonged gestation, or delivered by caesarian section after the normal duration of gestation, were given to control mothers, normal maternal behavior was observed, but the survival rate of the young was not increased.

Abnormalities, Drug-Induced↗

Affect and nurturance: mechanisms mediating maternal behavior in two female mammals.

This review will discuss hormonal and psychological factors involved in the initiation and maintenance of maternal behavior during the postpartum period in rat and human mothers. Research on primiparous rats suggests that among the ways hormones act to promote maternal responsiveness are by increasing the mother's attraction to odors of young pups, decreasing her natural neophobia and fearfulness, and increasing the ease with which experiences obtained during initial mother-young contacts are retained. Long-term maintenance of elevated maternal responsiveness in the rat is not directly under hormonal control but instead depends on a minimal period of direct interaction with young during the early postpartum. In human first-time mothers, the onset of maternal responsiveness is also directly affected by their mood state as well as their attraction to infants; these factors are, in turn, influenced by the amount of prior experience women have had caring for young. While the role of hormones in mediating maternal behavior in women is still unclear, initial results indicate they may facilitate responsiveness during the puerperium.

Affect↗

Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement.

This series of studies explored the operant response rates for pup-reinforcement of female Sprague Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygdala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mating on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy animals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on the last 3 days of pregnancy and throughout the postpartum period. On each of these same days after a period of separation from pups, females were tested in the operant box for delivery of rat pups. With each bar-press response, a rat pup rather than a Fruit Loop was delivered down a gentle shoot into the hopper. Non-postpartum, but maternal, multiparous animals who were showing estrous cycles were tested using the same procedures. The first and second studies showed that animals (both postpartum and as cycling multiparous animals) with mpoa lesions exhibited a significant reduction in bar-press rate for pup reinforcement in the operant box. In postpartum animals, amygdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These results indicate that systems associated with the mpoa mediate both the stereotypical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the amygdala and nucleus accumbens, whereas operant responding need not be. These results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement.

Amygdala↗

Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement.

This series of studies explored the operant response rates for pup-reinforcement of female Sprague Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygdala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mating on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy animals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on the last 3 days of pregnancy and throughout the postpartum period. On each of these same days after a period of separation from pups, females were tested in the operant box for delivery of rat pups. With each bar-press response, a rat pup rather than a Fruit Loop was delivered down a gentle shoot into the hopper. Non-postpartum, but maternal, multiparous animals who were showing estrous cycles were tested using the same procedures. The first and second studies showed that animals (both postpartum and as cycling multiparous animals) with mpoa lesions exhibited a significant reduction in bar-press rate for pup reinforcement in the operant box. In postpartum animals, amygdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These results indicate that systems associated with the mpoa mediate both the stereotypical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the amygdala and nucleus accumbens, whereas operant responding need not be. These results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement.

Amygdala↗

Trigeminal lesions and maternal behavior in Norway rats: III. Experience with pups facilitates recovery.

In lactating rats, upper snout desensitization by trigeminal denervation severely impairs maternal behavior, with substantial recovery 12-24 hr later. The potential effects of interaction with pups on this recovery was investigated. Dams were subjected to bilateral infraorbital denervation or sham surgery on Day 5 postpartum and observed for 30 min with 6 foster pups 24 hr later, after separation from pups for 4 or 24 hr. Long separation reduced likelihood of retrieval and nursing behavior, infraorbital denervation reduced duration of pup licking, and these deprivations combined greatly increased latencies of pup sniffing and durations of facial self-grooming. Both conditions, and especially their combination, prolonged retrieval duration, the retrieval sequence being interrupted by other pup contact, such as licking. Thus, interaction with pups and adequate trigeminal stimulation maintain normal maternal behavior. These findings are possibly relevant to the normal decline of maternal responsiveness during late lactation and to other lesion-induced deficits.

Analysis of Variance↗

A neuroanatomical correlate of paternal and maternal behavior in the biparental California mouse (Peromyscus californicus).

The medial preoptic area (MPOA) is important in the control of maternal behavior in rodents, and it is sexually dimorphic. This study demonstrates that the MPOA of nonparental virgin male Peromyscus californicus (n = 10) is larger than that of virgin females (n = 9) because of a significantly greater number of neurons in the MPOA of virgin males. However, this sex difference in MPOA volume disappeared when males and females became parents. Soma size increased significantly when females became mothers. These data suggest that maternal behavior may require a structural change in the MPOA, whereas paternal responsivity, which is normally inhibited in virgin males, may require a change in neuronal activity. Furthermore, these results underscore the importance of reproductive status in examination of sexually dimorphic nuclear structures.

Animals↗

The impact of maternal behavior on children's pain experiences: an experimental analysis.

OBJECTIVE: To provide an experimental investigation of the impact of maternal behavior on children's pain experiences. METHOD: Participants were 120 healthy children (60 boys, 60 girls) between the ages of 8 and 12 years and their mothers. Mothers were randomly assigned and trained to interact with their children in one of three ways while the children were exposed to lab-induced cold pressor pain: (1) a pain-promoting interaction, (2) a pain-reducing interaction, and (3) a no training control group. Training was based on behaviors presumed to have the expected impact, as based on correlational studies reported in the literature. Children's pain experiences during the cold pressor were assessed using self-reports of intensity and affect, coding of facial activity, tolerance, and heart rate responsiveness. RESULTS: Girls whose mothers interacted with them in the pain-promoting manner reported more pain than daughters of mothers in the control group, who in turn reported more pain than girls whose mothers interacted with them in the pain-reducing manner. This effect was not significant for boys. Maternal interaction type had no effect on children's pain affect, facial activity, tolerance, or heart rate. CONCLUSIONS: Results indicate that maternal behavior can have a direct impact on their daughters' subjective reports of pain. These data support the importance of social learning factors in influencing children's pain experiences.

Adaptation, Psychological↗

Corticotropin-releasing hormone inhibits maternal behavior and induces pup-killing.

Behavioral responses to stressors and the effects of stressors on maternal behavior change with mothering experience. Corticotropin-releasing hormone (CRH) is released by stressors and produces stress-like behavioral effects. We tested the effects of ICV infusion of ovine CRH (0.5-4 ug) on pup-directed behaviors in ovariectomized, ovarian steroid-treated virgin rats that were either naive to pups or that had three days of mothering experience. CRH inhibited maternal behavior in naive and experienced rats in a dose-related manner. The magnitude and duration of inhibition, especially at the 1 ug dose, were less in rats with mothering experience. Higher doses of CRH (1 - 4 ug) significantly increased pup-killing in rats that were naive to pups. In contrast, CRH produced no pup-killing in rats with mothering experience.

Animals↗

Ovarian hormone-induced short-latency maternal behavior in ovariectomized virgin Long-Evans rats.

Two ovarian hormone regimens reported to induce rapid-onset maternal behavior (MB) in maternally naive virgin, ovariectomized Sprague-Dawley (SD) albino rats (R. S. Bridges, 1984, Endocrinology 114, 930-940; A. L. Giordano, 1987, Doctoral Dissertation, Rutgers University, Newark, NJ) were assessed in Long-Evans (LE) hooded rats, a strain which tends to be less maternally responsive in various situations dissociated from parturition. The combination of sufficiently high and long-lasting treatments with estradiol (E, 10-mm Silastic capsule, sc, on Day 1) and progesterone (P, 3 x 30-mm Silastic capsules, Days 3-13) resulted in a mean MB onset latency (after pup presentation on Day 14) of 1.8 days. In contrast, no-hormone or P-only controls had latencies of about 5.5 days. However, the E + P combination was completely ineffective if the E capsule was withdrawn along with the P capsules, unlike the case for SD rats. Also in contrast to the albinos, E alone was ineffective, while E treatment following P withdrawal was only partially effective. The most efficacious regimen, which included a P treatment (injections of 4 mg/day, Days 3-12 or 3-15) known to maintain pregnancy in ovariectomized rats, resulted in mean latencies of less than or equal to 1 day; 39% overall displayed MB rapidly, i.e., retrieval within 15 min of exposure to pups and crouching by 3 hr, and 89% became maternal by the next day. With this regimen, neither duration of 4 mg/day P treatment (10 or 13 days) nor hysterectomy 2 days before testing affected MB latencies. Thus, the essential features of the previously reported ovarian hormone regimens for induction of short-latency MB are efficacious in LE rats, but the hormonal requirements in this strain seem to be more precise. Factors which might contribute to an even higher percentage maternal on the first day of pup exposure are considered.

Animals↗

Maternal behavior: activation of the central oxytocin receptor system in parturient rats?

Parturition plays a critical role in the full expression of maternal behavior in postpartum females, yet the precise mechanism remains unclear. Here we examined the role of parturition in the activation of Fos and FosB in the central oxytocin receptor (OTR) system in rats. Although expression of FosB, not Fos, was seen in the piriform cortex (Pir) and caudate putamen of virgin and pregnant females, activation of Fos and FosB with extensive co-localization was found in the medial preoptic area, the bed nucleus of the stria terminalis and Pir of parturient brain. This parturition induced activation of Fos and FosB was identified in the central OTR-expressing cells as well as in oxytocinergic neurons. Our data provide direct evidence, for the first time, that parturition activates Fos and FosB in the central OTR system. We propose that Fos and FosB may have comparable functions on initiating maternal behavior at parturition.

Animals↗

The effects of early rearing environments on maternal behavior in adult female rats.

The purpose of this study was to determine the effect of presence of siblings and exposure to colony cues during early life on the onset of maternal behavior at 20 and 75 days of life, and on subsequent emotional behavior in juvenile and adult female rats. Different groups of animals were reared either with a large number or a small number of siblings (sibling factor), or in the colony room or in a room apart from other mothers with pups (colony factor). Animals were tested for latency (in days) to show maternal behavior at either 20 or 75 days of age, and for emotional behavior (using the open field apparatus) at either 20-40 or 80-100 days of age. Exposure to colony sensory cues significantly reduced latencies for pup retrieval and nest-building in adults, but not in juveniles. Exposure to a large number of siblings reduced the latencies, in both adults and juveniles, to nest build; in juveniles, to lie over 75% of the litter; and in adults, to adopt a nursing posture. Consistent with prior research, juveniles had longer latencies than adults for a number of pup-directed behaviors including: latency to become maternal, latency to retrieve pups, latency to adopt a lactating posture, latency to lick/genital lick, and latency to nest-build. In the emotionality tests, the young animals scored as less emotional than the adults, an effect which was further exaggerated by early colony exposure. Overall results indicated that manipulation of early rearing environments does have a significant positive effect on later responses to young pups by both juvenile and adult female rats.

Age Factors↗

Experience-hormone interactions and maternal behavior in rats.

Three studies were conducted to determine the effects of reproductive condition and hormonal background on the acquisition and retention of a prior maternal experience. In the first study five experience conditions were compared. All animals gave birth and received either no postpartum contact with pups or 1/2 hr, 1 hr, 2 hr or 24 hr of pup contact and were tested for maternal behavior 10 days later. Animals receiving pregnancy and parturitional experience, but minimal social experience with young, exhibited significantly longer maternal onset latencies than did groups receiving 2 or 24 hr of prior experience; also, comparisons of 10- and 30-day retention intervals indicated that animals tested 10 days after a 24-hr experience exhibited shorter latencies than those tested 30 days later. Thus, the duration of the postpartum experience and the interval since prior experience both affect the level of maternal responsiveness shown. In the second study six groups of females were tested. Four groups were permitted one day of interaction with pups either after parturition (primiparous animals) or following pup induction procedures (nulliparous animals) and were tested for their maternal responsiveness to foster pups 25-35 days later, either on day 19 of a subsequent pregnancy or following resumption of estrous cycling. For most measures of maternal behavior there were significant main experience and test effects; experienced and pregnant animals exhibited shorter latencies to retrieve, lick and crouch over pups than did inexperienced and cycling animals, respectively. Significant interactions were also found for genital licking latency as well as for retrieval and crouch frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Exposure to hexanal odor influences maternal behavior and induces neonatal death in Fyn tyrosine kinase-deficient mice.

Fyn-deficient pups born of Fyn-deficient parents die because they fail to suckle within 1-2 days after birth. Here we demonstrate that the neonatal death phenotype was influenced by the genetic background and an environmental odor. The odor of hexanal (C6-aldehyde) partially impaired mouse maternal behavior and induced the neonatal death of Fyn-deficient pups born of Fyn-deficient parents. This death phenotype was first observed in the breeding environment using autoclaved chips of Douglas fir. An analysis of the volatile chemicals in the autoclaved chips revealed an approximately 10-fold greater amount of hexanal than in non-autoclaved chips. Hexanal influenced the length of time virgin female mice engage in the maternal crouching behavior. In addition, Fyn-deficient females exhibited defects in the maternal behavior of nest building and pup retrieval, regardless of exposure to hexanal. These observations provide new insights into the regulation of maternal behavior by environmental and genetic factors.

Aldehydes↗

The effect of maternal depressive symptomatology on maternal behaviors associated with child health.

National prevalence rates for depression among women are twofold compared with those of men, with women of childbearing age at greatest risk. Maternal depression not only negatively affects the health of the mother but may also influence the health and development of her offspring. This study examined the relationship between maternal depression and its influence on certain maternal behaviors associated with child health. A nationally representative, longitudinal data set with information on demographic, behavioral, and health care variables obtained from women in 1988 and 1991 was used. The results from logistic regression modeling indicate that maternal depression is associated with maternal behaviors (i.e., an increased likelihood of engagement in smoking, in not administering vitamins to a child, and not restraining children in appropriate car seats). Moreover, race differentials were found among these relationships. The implications of these results suggest the need to screen for depression among mothers of young children.

Adolescent↗

Effects of repeated cross-fosterings on preweaning behavior and growth performance of piglets and on maternal behavior of sows.

Extensive cross-fostering is widely used in early-weaning units in order to standardize and improve body weight at weaning. However, young suckling piglets develop teat fidelity and repeated cross-fosterings could go against this behavior. This experiment was therefore conducted to compare the behavior and growth of 13 control and 14 fostered litters. Once every 3 d (from d 1 to 16 of lactation), all piglets were weighed and three piglets were switched between two fostered litters. Their unfostered littermates were called residents. Behavior was recorded for 2 h after weighing and(or) adoption and during one nursing period 24 h later. Fights were more frequent (P < 0.05) in treated than in control litters during and between nursings at all ages of adoption except d 1. Most fights occurred between resident and fostered piglets (P < 0.001), except at d 1. Fights during nursing were still more frequent in treated than in control litters 24 h after adoption (P < 0.02), except at d 1 and 16. More piglets had skin lacerations in treated than in control litters except at d 1 (P < 0.05), and scratches were more frequent in fostered than in resident piglets at d 1 (P = 0.07), 7, 13, and 16 (P < 0.01). At all ages except d 1, failed nursings and snaps at piglets were more frequent in fostered than in control litters (P < 0.05), most snaps being directed at adopted piglets (P < 0.001). In fostered litters, sows spent 15 to 30% less time lying on their sides at d 4, 7, 13, and 16 (P < 0.05). Finally, adopted piglets were 13% lighter than controls at weaning (P < 0.001), whereas residents were heavier than adopted piglets (P < 0.05) but lighter than controls (P = 0.1). These data demonstrate that cross-fostering done repeatedly during lactation is stressful for piglets and sows and does not improve body weight at weaning.

Adaptation, Physiological↗