Effects of estrogen, androgen, and phytoestrogen on retrieving and licking behaviors in nulliparous and male rats

In order to examine the effects of estrogen, androgen, and phytoestrogen on maternal behavior induced by exposure to fresh pups in ovariectomized nulliparous rats, 1 mg estradiol benzoate (EB), 1 mg testosterone propionate (TP), 1 mg coumestrol (CM), or oil (female control) was injected subcutaneously daily for 10 days. To elucidate the sex difference, 1 mg EB or oil (male control) was injected in orchidectomized rats by the same method as that used in nulliparous rats. Exposure to fresh pups was started 6 days after the first injection. Behavioral tests were carried out daily for 5 days from the first exposure to the last on the 10th day. In the behavioral test, the onset of retrieving and licking behaviors was recorded. In female control rats, the median onset day of retrieving behavior was day 5. Onset in the EB female group was day 1.5, which was shorter than that in the female control (P<0.05). TP female and CM female rats started to show retrieving at day 5 and day 4.5, respectively, comparable to the female controls. In males, the median day of retrieving onset in the control and EB groups was over day 5 and day 4.5, respectively. No statistical difference was seen between the female and male controls. In contrast, there was a difference between the EB-treated female and EB male groups. Licking activity was less frequent than seen in the retrieving behavior among all groups, but there was no statistical difference among the groups. These results suggest that estrogen facilitates retrieving behavior in female, but not in male rats. TP and CM have no effect on retrieving behavior in female rats.     

Sex difference and postnatal change of maternal behavioral patterns in juvenile male and female rats

Juvenile rats are known to show certain elements of maternal behavior. In this experiment, to investigate sex difference and postnatal change of retrieving and pup-cleaning (licking) behaviors in juvenile rats, these behaviors were recorded using new observation method at 20, 30 and 45 days of age in female and male Wistar rats. At 20 days of age, maternal behavior was observed in a common plastic observation cage (test A) and then test B was performed. In the test B, observation was carried out using a cage with a wooden box that was open on one side, helping the juveniles to establish a nest. As the results of day 20, most rats in all groups showed licking behavior in both the test A and B. The incidence of retrieving behavior increased from the test A to the test B with the box in both sexes, especially in males (p<0.01). The box is thought to play a facilitative role in induction of retrieving. Moreover, the incidence in males was higher than that in females in the test B (p<0.001). At 30 and 45 days of age, only a test B with box was performed. The incidences of licking and retrieving behaviors at 30 days of age were decreased significantly compared to those at 20 days of age in both sexes(p<0.001). Further decrease from 30 days to 45 days was observed. These results suggest that in juvenile rat, incidence of retrieving behavior in males is higher than that in females but there is no sex difference in incidence of licking behavior. Potency to show these behaviors decreases acutely before puberty in rats.     

The effects of adrenalectomy and corticosterone replacement on induction of maternal behavior in the virgin female rat

Maternal behavior of the sensitized virgin rat is affected by approach-avoidance systems as well as by hypothalamic-pituitary-adrenal (HPA) axis, which is also activated during stress. The present experiments investigated the effects of adrenalectomy and of varying corticosterone concentrations on the onset and expression of maternal behavior in sensitized virgin rats. In the first experiment, latency to onset of maternal behavior and time spent licking once maternal were positively related to endogenous levels of corticosterone. However, few rats showed licking. In the second experiment, virgin rats were adrenalectomized or given sham surgeries before being sensitized and being given 0, 25, 100, 300, or 500 microg/mL of corticosterone in their drinking water. In the third experiment, virgin rats were adrenalectomized or given sham surgeries and given either control or corticosterone time-release pellets after being sensitized. Maternal behavior was then tested. Adrenalectomy increased licking in the second experiment and time over pups in the third experiment. Corticosterone replacement reduced licking in the second experiment and both licking and time over pups in the third experiment. In conclusion, exogenous corticosterone had an inhibitory effect on the expression of maternal behavior in the sensitized virgin rat, unlike the facilitatory effect previously found in the postpartum rat.     

Functional Mapping of Dorsal and Median Raphe 5-Hydroxytryptamine Pathways in Forebrain of the Rat Using Microdialysis

Abstract: Recent neurochemical studies of the properties of 5-hydroxytryptamine (5-HT) pathways arising from the dorsal raphe nucleus (DRN) and median raphe nucleus (MRN) have measured extracellular 5-HT in brain regions with reported preferential DRN or MRN 5-HT inputs. Here, we have tested whether electrical stimulation of the DRN and MRN releases 5-HT in rat forebrain regions in a pattern that fits the reported distribution of DRN/MRN pathways. The effect on extracellular 5-HT of electrical stimulation (5 Hz, 300 µA, 20 min) of the DRN, and then MRN, was determined in six regions of the anaesthetised rat. Stimulation of the DRN evoked a short-lasting but clear-cut release of 5-HT (+70–100%) in regions (frontal cortex, dorsal striatum, globus pallidus, and ventral hippocampus) reported to receive a 5-HT projection from the DRN. Regions receiving an MRN innervation (dorsal hippocampus, medial septum, and ventral hippocampus) released 5-HT (+70–100%) in response to MRN stimulation. Regions reported to receive a preferential DRN innervation (frontal cortex, dorsal striatum, and globus pallidus) did not respond to MRN stimulation. Of two regions (dorsal hippocampus and medial septum) reported to receive a preferential MRN innervation, one did not respond to DRN stimulation (dorsal hippocampus) although the other (medial septum) did. In summary, electrical stimulation of the DRN and MRN released 5-HT in a regionally specific pattern. With the exception of one region (medial septum), this pattern of release bears a strong relationship to the distribution of 5-HT projections from the DRN and MRN reported by anatomical studies. The combination of raphe stimulation with microdialysis may be a useful way to study the in vivo neurochemistry of DRN/MRN 5-HT pathways.     

Mammary stimulation and maternal aggression in rodents: thelectomy fails to reduce pre- or postpartum aggression in rats

In mice, tactile stimulation of the nipples appears to be critical for the onset of postpartum maternal aggression. Surgical removal of the nipples (thelectomy) blocks aggression if performed prior to parturition. In rats, indirect evidence suggests a similar role for nipple stimulation in maternal aggression. Two experiments were undertaken to determine whether thelectomy prior to mating reduces pregnancy-induced and/or postpartum aggression in this species. In the first, thelectomized and sham-thelectomized females were subjected to home cage tests (pups, if any, present) with unfamiliar male intruders on Gestation Days 18 and 21 and Lactation Days 3 and 5. Additional groups of thelectomized females were tested one time only on either Lactation Day 5 or 12. Thelectomized and control females were equally aggressive; postpartum, nearly all females in both groups attacked. Experiment 2 used females that were hysterectomized-ovariectomized (HO) on Gestation Day 16. Such females are not aggressive prior to initiating maternal behavior, but become highly aggressive (over 80% attacking) after commencing maternal care. Females again were thelectomized or sham-thelectomized prior to mating. On Day 16 HO was performed, and 48 hr later continuous exposure to pups was begun. After the females had displayed maternal behavior for 1.5-2 days, intruder tests were conducted. All females attacked at least once, with no differences between treatment groups. Thus thelectomy does not reduce maternal aggression in the rat. This finding, however, does not preclude a role for tactile ventral stimulation in mediating maternal aggression.     

Differential Roles of Raphe Nuclei in the Regulation of Dopamine β-Hydroxylase in the Adrenal Gland of the Rat

The effect of reserpine on the activity of dopamine beta-hydroxylase (DBH) in the adrenal gland of the rat was determined following electrolytic lesion of the dorsal raphe nucleus (DRN) or medial raphe nucleus (MRN). In sham-operated rats, as well as in those with a lesion of the DRN, there was no significant modification of the action of reserpine on this enzyme. However, a lesion of MRN potentiated the inducing action of the drug. A specific role of MRN in the serotonergic regulation of adrenal DBH is suggested by this work.     

The effects of adrenalectomy and corticosterone replacement on maternal memory in postpartum rats

Hormones associated with parturition prime rats to behave maternally, although hormonal changes are not necessary for these behaviors to occur. Experience with pups after birth enhances maternal responsiveness after a period of isolation, creating a maternal memory. The purpose of this study was to determine the role of corticosterone in the formation of maternal memory. Adrenalectomy or sham surgeries were performed in late gestation with corticosterone or vehicle pellets being given to adrenalectomized rats. Pups were removed immediately following parturition, and half of the rats received 4 h of pup experience, while the other half received only brief pup experience associated with parturition. Ten days following pup experience, foster pups were given to all rats. Latency to become maternal and maternal behaviors on the first 2 days of re-exposure and the first two maternal days were recorded. Among adrenalectomized rats given corticosterone, 4-h experience with pups decreased maternal latency when compared to brief experience with pups. This maternal experience effect was not found in comparisons between adrenalectomized rats not given corticosterone. In addition, corticosterone decreased latencies regardless of pup experience. Corticosterone also increased maternal behavior upon initial exposure to foster pups. In conclusion, corticosterone enhanced maternal memory and initial maternal behavior in postpartum rats.     

孕期接触四氯联苯对大鼠母性行为的影响

为评价多氯联苯对人体发育的影响,本研究以大鼠为模型,研究多氯联苯（PCB）对母性行为的影响。将50只同期怀孕的Long-Evans大鼠随机分为5组,在怀孕第7－18天,每天给大鼠肌注四氯联苯或芝麻油。1组、2组,按每kg体重分别注射1mg、20mg2,2′,4,4′－四氯联苯（PCB47）;3组、4组,按每kg体重分别注射0.25mg、1mg3,3′,4,4′－四氯联苯（PCB77）;5组（对照组）注射芝麻油。产仔后的第0、3、6、12、15天分别观察母鼠的筑窝、舔仔、自发叼仔和诱发叼仔、蹲伏和在窝内的时间。结果表明：对照组母鼠在30min的观察中,其窝内时间与幼仔出生后天娄和负相关,而接触PCB的母鼠的窝内时间与幼仔出生天数无相关关系。接触PCB47的母鼠的筑巢、蹲伏、舔仔、自发叼仔行为在幼仔出生后的第0天和6天与对照组有显著差异,而接触PCB77的母鼠仅在第15天与对照组大鼠有区别。在诱导叼仔的实验中,接触PCB77的母鼠的叼仔时间在幼仔出生后的第12天增加。     

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.     

The effects of early rearing environment on the hormonal induction of maternal behavior in virgin rats

The present study investigated the effects of isolation rearing, through the artificial rearing paradigm (AR), on the hormonal induction of maternal behavior (MB) in female Sprague-Dawley rats. Between postnatal days (PND) 4 and 18, rat pups were raised either with their mothers (MR) or artificially, without their mothers (AR). As well, some of the AR pups were provided with additional maternal-like licking stimulation (AR-MAX) while the others were not given any additional stimulation (AR-MIN). At PND 60-100, AR (n = 28) and MR (n = 25) animals were ovariectomized (OVX). One week after the surgery, rats were either treated with a 2-week estrogen (E2) and progesterone (P) hormonal regimen or not treated with the hormone replacement. Maternal behavior testing with foster pups commenced 24 h following the removal of P treatment. Results demonstrated that MR animals showed increased pup licking and hover-crouching in comparison to AR animals and that hormonally primed groups became maternal more quickly than non-primed groups, regardless of the rearing history. There was also a significant interaction between the rearing condition (MR vs. AR) and hormonal treatment on the quality of maternal behavior exhibited. The highest level of licking and crouching was shown by the hormone-treated MR group. Mechanisms for these effects are discussed.     

The effects of early rearing environment on the hormonal induction of maternal behavior in virgin rats

The present study investigated the effects of isolation rearing, through the artificial rearing paradigm (AR), on the hormonal induction of maternal behavior (MB) in female Sprague–Dawley rats. Between postnatal days (PND) 4 and 18, rat pups were raised either with their mothers (MR) or artificially, without their mothers (AR). As well, some of the AR pups were provided with additional maternal-like licking stimulation (AR-MAX) while the others were not given any additional stimulation (AR-MIN). At PND 60–100, AR (n = 28) and MR (n = 25) animals were ovariectomized (OVX). One week after the surgery, rats were either treated with a 2-week estrogen (E2) and progesterone (P) hormonal regimen (Bridges, R.S., 1984. A quantitative analysis of the roles of dosage, sequence, and duration of estradiol and progesterone exposure in the regulation of maternal behavior in the rat. Endocrinology 114, 930–940) or not treated with the hormone replacement. Maternal behavior testing with foster pups commenced 24 h following the removal of P treatment. Results demonstrated that MR animals showed increased pup licking and hover-crouching in comparison to AR animals and that hormonally primed groups became maternal more quickly than non-primed groups, regardless of the rearing history. There was also a significant interaction between the rearing condition (MR vs. AR) and hormonal treatment on the quality of maternal behavior exhibited. The highest level of licking and crouching was shown by the hormone-treated MR group. Mechanisms for these effects are discussed.     

Individual differences in novelty-seeking and emotional reactivity correlate with variation in maternal behavior

Numerous studies have demonstrated that Sprague-Dawley rats exhibit a wide range of locomotor reactivity when placed in a novel environment. High Responder (HR) rats show exaggerated locomotor response to novelty, enhanced neuroendocrine stress reactivity, decreased anxiety-like behavior, and propensity to self-administer psychostimulants, compared to the less active Low Responder (LR) animals. Few studies have explored the early environmental factors which may underlie the HR-LR differences in emotional reactivity. Considering the enormous impact of maternal care on rodent neurodevelopment, we sought to examine maternal behavior in HR-LR dams to determine whether they exhibit differences which could contribute to their offspring's differential temperaments. Females, like males, can be classified as HR versus LR, showing marked differences in novelty-induced locomotor activity and anxiety-like behavior. HR-LR mothers behaved differently with their pups during the first two postpartum weeks. LR dams spent greater time licking and nursing their pups compared to HR dams, with the most prominent differences occurring during the second postpartum week. By contrast, when non-lactating HR-LR females were presented with orphaned pups, the pattern of maternal response was reversed. HR females were more responsive and showed greater maternal care of the novel pups compared to LR females, which were probably inhibited due to fear of the unfamiliar pups. This underscores the critical interplay between the female's emotional phenotype, her hormonal status and her familiarity with the pup as key factors in determining maternal behavior. Future work should explore neural and hormonal mechanisms which drive these HR-LR differences in maternal behavior and their impact on the development of the offspring.     

Effect of mammillary body lesions in adult rats on the survival and development of their young

The lesion of the mammillary bodies in the adult female did not alter the oestrous cycle, sexual behavior, parturition, or the number and weight of pups at birth. Neither did it alter maternal behavior (nesting behavior, cleaning of the pups, placentophagia, nursing position, retrieving, etc.). Nevertheless, more than 30% of the pups born from the mothers with total lesions of the mammillary bodies died during the first 10 days after birth. The weight of the surviving pups was greatly impaired and the pups showed severe undernourishment. The effects of the lesion of the mammillary bodies on the survival and weight of the pups were dependent on the mass of tissue destroyed in that structure.     

Associations among within-litter differences in early mothering received and later emotional behaviors,mothering, and cortical tryptophan hydroxylase-2 expression in female laboratory rats

This article is part of a Special Issue “Parental Care”. The effects of differential maternal care received on offspring phenotype in rodents has been extensively studied between litters, but the consequences of differential mothering within litters on offspring neurobehavioral development have been rarely examined. We here investigated how variability in maternal care received among female rat siblings (measured four times daily on postnatal days 4, 6, 8, and 10) relates to the siblings' later emotional and maternal behaviors. As previously reported, we found that some female pups received up to three times more maternal licking bouts compared to their sisters; this difference was positively correlated with the pups' body weights. The number of maternal licking bouts that females received was negatively correlated with their later neophobic behaviors in an open field during periadolescence, but positively correlated with their anxiety-related behavior in an elevated plus maze during adulthood. Licking received was also positively correlated with females' later likelihood to retrieve pups in a maternal sensitization paradigm. In addition, females' neophobia during adolescence and anxiety-related behavior during adulthood predicted some aspects of both postpartum and sensitized maternal responsiveness. Medial prefrontal cortex expression of tryptophan hydroxylase-2 (TPH2; enzyme necessary for serotonin synthesis) was negatively associated with early maternal licking received. Interestingly, cortical TPH2 was positively associated with the maternal responsiveness of sensitized virgins but negatively associated with it in postpartum females. These results indicate that within-litter differences in maternal care received is an often neglected, but important, contributor to individual differences in offspring socioemotional behaviors as well as to the cortical serotonin neurochemistry that may influence these behaviors.     

Lactational performance, consummatory behavior, and suppression of estrous cyclicity in rats suckling underfed pups

The role of pups' appetite in the regulation of maternal consummatory behavior (food intake of nursing mothers), lactational performance and postpartum diestrus was studied over a period of 45 days postpartum in rats chronically exposed to either underfed or normally fed pups. Experimental rats (n = 10) daily received 5 pups, 4-10-days-old, that had been deprived of food for the preceding 24 h while under the care of nonlactating foster mothers. Control rats (n = 10) received normally fed pups obtained daily from lactating foster mothers. Throughout the experimental period, the daily milk yield (estimated by litter weight gain), the intake of food and water by the mother, as well as the ratio of litter weight gain to mother's intake of food and water were all markedly higher in rats nursing underfed pups than in rats nursing normally fed pups. After a peak in lactation around Day 15 postpartum, experimental rats produced the same amount of milk during extended lactation as they did in the beginning of lactation, while control rats produced only half the amount of milk during extended lactation as they did in early lactation. Regardless of the nutritional state of the suckling pups, maternal body weight increased progressively over the first four weeks of lactation and remained unchanged during the time of extended lactation. The postpartum diestrus and the subsequent diestrous phase in the time of extended lactation were considerably longer in duration in rats that nursed underfed pups. On Day 45 of lactation, prolactin levels were higher and the adrenal glands were larger in experimental rats than in controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variation in maternal and anxiety-like behavior associated with discrete patterns of oxytocin and vasopressin 1a receptor density in the lateral septum

The relationship between anxiety and maternal behavior has been explored across species using a variety of approaches, yet there is no clear consensus on the nature or direction of this relationship. In the current study, we have assessed stable individual differences in anxiety-like behavior in a large cohort (n=57) of female F2 hybrid mice. Using open-field behavior as a continuous and categorical (high vs. low) measure we examined the relationship between the anxiety-like behavior of virgin F2 females and the subsequent maternal behavior of these females. In addition, we quantified oxytocin (OTR) and vasopressin (V1a) receptor density within the lateral septum to determine the possible correlation with anxiety-like and maternal behavior. We find that, though activity levels within the open-field do predict latency to engage in pup retrieval, anxiety-like measures on this test are otherwise not associated with subsequent maternal behavior. OTR density in the dorsal lateral septum was found to be negatively correlated with activity levels in the open-field and positively correlated with frequency of nursing behavior. V1a receptor density was significantly correlated with postpartum licking/grooming of pups. Though we do not find support for the hypothesis that individual differences in trait anxiety predict variation in maternal behavior, we do find evidence for the role of OTR and V1a receptors in predicting maternal behavior in mice and suggest possible methodological issues (such as distinguishing between trait and state anxiety) that will be a critical consideration for subsequent studies of the anxiety-maternal behavior relationship. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.     

Impaired Maternal Behavior in Usp46 Mutant Mice: A Model for Trans-Generational Transmission of Maternal Care

Usp46 mutant mice (congenic strain on a B6 genetic background; MT mice) have a low weaning rate and display poor maternal behavior compared to C57BL/6J mice (B6 mice). Based on these observations, we examined how maternal behavior is shaped by cross-fostering and in-fostering MT and B6 mice. The experiments consisted of six groups: B6 mice fostered by their biological mother (B6-CO); MT mice fostered by their biological mother (MT-CO); B6 mice fostered by a different B6 mother (B6-IF); MT mice fostered by a different MT mother (MT-IF); B6 mice fostered by an MT mother (B6-CF); and MT mice fostered by a B6 mother (MT-CF). Maternal behavior was assessed using the pup-retrieval test in adult female offspring, and four parameters, time nursing pups in the nest, time sniffing or licking pups, rearing behavior, and latency to retrieve pups, were measured. Cross-fostering significantly reduced time spent nursing and sniffing/licking pup, and increased the number of instances of rearing in the B6-CF group, and improved three parameters of maternal behaviors (nursing, rearing and latency) in the MT-CF group. These results indicate that the level of maternal care is transmitted to their pups and proper maternal behaviors can be shaped if adequate postpartum maternal care is given, even in genetically vulnerable mice. However, the offspring’s genotype may also influence the development of maternal behaviors in adulthood. Thus, MT mice may prove useful as a model for trans-generational transmission of maternal care, and these findings may provide insight into the mechanisms of maltreating behaviors in human child abuse.     

Postpartum,hormonal, and nonhormonal induction of maternal behavior in rats: Effects on T-maze retrieval of pups

It is known that the home-cage maternal behavior of rats which become maternal after daily pup exposure (sensitization) is almost indistinguishable from that of lactating mothers, but that sensitized and lactating rats can be distinguished by their pup-retrieval performance in a T-maze extension of the home cage. The present study explored this difference further. Postpartum mothers which could not suckle due to prior nipple removal (thelectomy) retrieved as well, if not better, than intact controls in the T-maze. Hormonal induction of maternal behavior (in ? 3 days) was carried out by hysterectomy-ovariectomy plus 100 μg/kg estradiol benzoate; the performance of these females was similar to that of the postpartum groups. In contrast, only a small percentage of the sensitized mothers retrieved in the T-maze, whether the latency to onset of their maternal behavior was long (4–10 days) or short (? 3 days). Thus, hormonal factors associated with pregnancy and/or parturition, but not suckling stimulation, may facilitate T-maze retrieval of pups. The possible ethological significance of the T-maze test as a measure of maternal responsiveness is discussed.     

An olfactory basis for maternal discrimination of sex of offspring in rats (rattus norvegicus)

Lactating Long-Evans rats (Rattus norvegicus) were presented with three-day-old male and female pups that were either untreated, coated with collodion in the anogenital region or on the neck, or perfumed; or with female pups odorized with either male or female pup urine. As measured by related t-tests of maternal anogenital licking, male and female pups were discriminated in the untreated condition, but not when masking stimuli were present. Female pups treated with male urine elicited more licking than female pups treated with female urine. Overall, maternal licking was decreased by olfactory masking agents and increased by pup urine. It was concluded that olfactory stimuli from pups both stimulate maternal licking and serve as a basis for discriminating male and female offspring.