Lever pressing for pups: Evidence for hormonal influence upon maternal behavior of mice

Five experiments were performed to determine the extent to which hormones influence maternal behavior of the female mouse. The number of pup-reinforced lever presses served as the measure of maternal behavior. In Experiment 1 it was found that postpartum mice performed significantly more pup-reinforced lever presses than intact or ovariectomized virgins. The second experiment showed that the augmentation of responding was unique to the postpartum period since responding was not facilitated during the last three days of pregnancy. Experiment 3 established that the postpartum augmentation of responding was mediated by the termination of pregnancy and not by parturition per se. It also was observed that the earlier during gestation pregnancy was terminated the greater the decline in response rate. Experiment 4 proved that ovarian secretions play a critical role in the pregnancy-terminated facilitation of pup-reinforced lever pressing. The final experiment demonstrated that the termination-of-pregnancy effect on responding in all likelihood is mediated by the synergistic actions of estrogen stimulation and progesterone withdrawal. The results show that the maternal behavior of the mouse, like that of the rat, is responsive to hormonal stimulation.     

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.     

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.     

Effects of early life social stress on endocrinology,maternal behavior,and lactation in rats

Exposure to early life stress is a predictor of mental health disorders, and two common forms of early life stress are social conflict and impaired maternal care, which are predominant features of postpartum mood disorders. Exposure of lactating female rats to a novel male intruder involves robust social conflict and induces deficits in maternal care towards the F1 offspring. This exposure is an early life social stressor for female F1 pups that induces inefficient lactation associated with central changes in oxytocin (OXT), prolactin (PRL), and arginine vasopressin (AVP) gene expression in adult F1 females.     

Taurine depletion of lactating rats: Effects on developing pups

Taurine is in high concentration in the milk of most mammals. Intraperitoneal injection of [35S]taurine into lactating rats leads to the appearance of label in the milk, and the dpm/ml milk are significantly decreased by treatment with guanidinoethyl sulfonate (GES), an analog of taurine. Pups nursed by GES-treated mothers have retinal taurine levels about 45% lower than controls during the period from birth to 17 days old suggesting a dependence of retinal taurine on dietary intake during the neonatal period. These deficits in taurine may be associated with visual dysfunction as seen in adult rats depleted of retinal taurine.     

Influence of the estrous cycle on the behavior of rats in the elevated T-maze

The elevated T-maze is an animal anxiety model which can discriminate between anxiety-like and fear-like behaviors. The estrous cycle is an important variable of the response in animal anxiety tests and is known to affect other models. The aim of the present study was to investigate the influence of the estrous cycle on behavior displayed in the elevated T-maze test. Seventeen male and 60 female rats were submitted to one session in this test, with the females being screened for the estrous cycle and divided into groups according to the various phases. The elevated T-maze had three arms of equal dimensions ( 50 cm x 10 cm), one enclosed by 40-cm high walls and perpendicular to the others, the apparatus being elevated 50 cm above the floor. Each rat was placed in the end of the enclosed arm and the latency for it to leave this arm was recorded. These measurements were repeated three times separated by 30-s intervals (passive avoidance). After trial 3, each rat was placed at the distal end of the right open arm and the latency to exit this arm was recorded. Whenever latencies were greater than 300 s the trial was finished. The results demonstrated females in diestrus exhibited anxiety-like behaviors while females in metaestrus behaved in a similar way as the males. There were no differences between groups in fear-like behaviors. The results also indicate the elevated T-maze to be a sensitive test to measure anxiety.     

Experiential and hormonal correlates of maternal behavior in teen and adult mothers

This study explores the role of cortisol and early life experiences in the regulation of maternal behavior and mood in teen and adult mothers. Primiparous mothers (n=119) (teen mothers < 19 years, n=42), young mothers (19-25 years, n= 4), and mature mothers, (>25 years, n=43) were assessed for their maternal behavior, mood, and hormonal profile at approximately 6 weeks postpartum. Outcome measures were analyzed as a function of age and early life experience. Results showed an interaction between age and type of maternal behavior, where teen mothers engaged in more instrumental (e.g. changing diapers, adjusting clothes) less affectionate (e.g., stroking, kissing, patting) behavior, and mature mothers engaged in more affectionate and less instrumental behavior. When groups were reassessed based on early life experience (consistency of care during the first 12 years of life: consistent care; having at least one consistent caregiver, inconsistent care; having multiple and changing caregivers), an interaction was also found between consistency of care and type of behavior shown, where mothers who received inconsistent care engaged in more instrumental and less affectionate behavior. Compared to mature mothers, teen mothers who were breast feeding also had higher salivary cortisol levels, and high cortisol in teen mothers related to decreased fatigue and increased energy. These results suggest that early life experiences are linked to mothering behavior and are consistent with the emerging human and animal literature on intergenerational effects of mothering style.     

Effects of hypoxic preconditioning on memory evaluated using the T-maze behavior test

Perioperative brain ischemia and stroke are leading causes of morbidity and mortality. Brief hypoxic preconditioning is known to have protective effects against hypoxic-ischemic insult in the brain. Current studies on the neuroprotective effects of ischemic preconditioning are based on histologic findings and biomarker changes. However, studies regarding effects on memory are rare. To precondition zebrafish to hypoxia, they were exposed to a dissolved oxygen (DO) concentration of 1.0?±?0.5?mg/L in water for 30?s. The hypoxic zebrafish were then exposed to 1.0?±?0.5?mg/L DO until the third stage of hypoxia, for 10 min?±?30?s. Zebrafish were assessed for memory retention after the hypoxic event. Learning and memory were tested using the T-maze, which evaluates memory based on whether or not zebrafish moves to the correct target compartment. In the hypoxic preconditioning group, infarct size was reduced compared with the hypoxic-only treated zebrafish group; memory was maintained to a degree similar to that in the hypoxia-untreated group. The hypoxic-only group showed significant memory impairments. In this study, we used a hypoxic zebrafish model and assessed the effects of ischemic preconditioning not only on histological damages but also on brain function, especially memory. This study demonstrated that a brief hypoxic event has protective effects in hypoxic brain damage and helped maintain memory in zebrafish. In addition, our findings suggest that the zebrafish model is useful in rapidly assessing the effects of ischemic preconditioning on memory.     

Postpartum copulatory and maternal behaviour in Norway rats under seminatural conditions

Virgin female rats were mated at a freely cycling oestrus, and then again with the same males at the subsequent postpartum oestrus. Copulatory behaviour at each mating was compared and the temporal patterning of the female's mating and maternal behaviour was analysed. Postpartum females were found to conserve the number of ejaculatory series received, yet the series were shorter, resulting in a shorter time being occupied, by this mating. During mating, females spent little time with their litters, and then mainly in the post-ejaculatory intervals. Ejaculatory series were rarely disrupted by nesting. The postpartum female rat seems to engage in behavioural time-sharing.     

Effects of prenatal maternal stress on the pituitary adrenocortical reactivity in guinea-pig pups

Seven days before term, pregnant guinea-pigs were subjected to a psychosomatic stress. Adrenocorticotrophin (ACTH), cortisol and aldosterone concentrations increased in maternal and fetal plasma immediately after stress. In the offspring born from prenatally-stressed mothers that were resubjected to stress, the increases in plasma ACTH and cortisol level were lower than in the control offspring. Plasma aldosterone levels increased after stress in 12 days-old pups but did not change neither in 50 days-old animals nor in 12 days-old guinea-pigs born of prenatally stressed mothers. Thus prenatal stress of mother resulted in lowered response of pituitary-adrenocortical axis of offspring subjected to stress.     

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)     

Effects of maternal separation, early handling, and standard facility rearing on orienting and impulsive behavior of adolescent rats

Effects of maternal separation in rats have been extensively investigated, but no studies have examined its effects in rat adolescence. We examined the effects of neonatal infant-mother separation (MS) for 6h/day and early handling (EH) for 10 days during the first 2 weeks of life by comparing MS and EH groups to standard facility reared (SFR) controls. At adolescence, the animals were evaluated in a novel and familiar open-field, the light-dark box, and the sucrose consumption test. Behavioral indices included orienting behavior (rearing frequency and duration), impulsive behavior (movement velocity and risk taking by entering the center of the open field or the light compartment of the light-dark box), hyperactivity (ambulatory distance and stereotypic movement), and reward-seeking behavior (sucrose drinking time). The prolonged MS during the first 2 weeks of life resulted in decreased orienting behavior and increased impulsive behavior in adolescence. Measures of ambulatory and stereotypic movements showed that MS rats were hyperactive in the novel environment whereas EH rats were less active overall. The impulsive/hyperactive phenotype produced by this MS protocol may provide a useful animal model to investigate the neurological basis for the similar behavioral phenotype found in attention deficit/hyperactivity disorder.     

Antagonism of V1b receptors promotes maternal motivation to retrieve pups in the MPOA and impairs pup-directed behavior during maternal defense in the mpBNST of lactating rats

Recent studies using V1b receptor (V1bR) knockout mice or central pharmacological manipulations in lactating rats highlighted the influence of this receptor for maternal behavior. However, its role in specific brain sites known to be important for maternal behavior has not been investigated to date. In the present study, we reveal that V1bR mRNA (qPCR) and protein levels (Western blot) within either the medial preoptic area (MPOA) or the medial-posterior part of the bed nucleus of the stria terminalis (mpBNST) did not differ between virgin and lactating rats. Furthermore, we characterized the effects of V1bR blockade via bilateral injections of the receptor subtype-specific antagonist SSR149415 within the MPOA or the mpBNST on maternal behavior (maternal care under non-stress and stress conditions, maternal motivation to retrieve pups in a novel environment, maternal aggression) and anxiety-related behavior in lactating rats. Blocking V1bR within the MPOA increased pup retrieval, whereas within the mpBNST it decreased pup-directed behavior, specifically licking/grooming the pups, during the maternal defense test. In addition, immediately after termination of the maternal defense test, V1bR antagonism in both brain regions reduced nursing, particularly arched back nursing. Anxiety-related behavior was not affected by V1bR antagonism in either brain region. In conclusion our data indicate that V1bR antagonism significantly modulates different aspects of maternal behavior in a brain region-dependent manner.     

Lordotic behavior in male rats: genetic and hormonal regulation of sexual differentiation

The male offspring of Long-Evans rats treated with the aromatization inhibitor ATD (1,4,6-androstatriene-3,17-dione) during pregnancy show high levels of lordotic behavior when treated with estrogen and progesterone in adulthood. The male offspring of Sprague-Dawley dams treated in the same way show only a slight facilitation of lordotic potential. These strain differences could reflect strain differences in gestation length and therefore differences in the timing of the sensitive period of sexual differentiation; they could reflect differences in the sensitivity to the defeminizing actions of gonadal hormones; or they could reflect differences in the sensitivity to ATD treatment. We therefore directly compared the effects of prenatal and early postnatal treatment with ATD on the potential of male Long-Evans and Sprague-Dawley rats to show lordosis when given estrogen and progesterone in adulthood. In both strains ATD treatment facilitated adult lordotic behavior. Treatment appeared to have a greater effect in the Long-Evans strain. However, control Long-Evans males were substantially more responsive to hormone treatment in adulthood than were Sprague-Dawley males. In the Long-Evans strain short-term ATD treatment (Days 20-23 of pregnancy) was as effective as long-term treatment (Days 10-23). In the Sprague-Dawley strain, ATD treatment was most effective when given prenatally and postnatally. Strain differences in hormonal sensitivity best account for the present findings.     

Induction of maternal behavior and some hormonal and physiological correlates in the domestic hen

The manifestation of maternal behavior and the variations of plasmatic levels of gonadic hormones (testosterone, delta 4-androstenedione, and 17 beta-estradiol) have been studied in two groups of domestic hens (layers and nonlayers) during a forced adoption experiment. Maternal behavior appears later in actively laying hens than in nonlayers. The former hens show a higher level of androgens (T and delta 4). The appearance of typical maternal behavior coincides with a pause in laying and a decrease in all the plasmatic steroid levels measured.     

Postpartum depression: Etiology,treatment and consequences for maternal care

This article is part of a Special Issue “Parental Care”. Pregnancy and postpartum are associated with dramatic alterations in steroid and peptide hormones which alter the mothers' hypothalamic pituitary adrenal (HPA) and hypothalamic pituitary gonadal (HPG) axes. Dysregulations in these endocrine axes are related to mood disorders and as such it should not come as a major surprise that pregnancy and the postpartum period can have profound effects on maternal mood. Indeed, pregnancy and postpartum are associated with an increased risk for developing depressive symptoms in women. Postpartum depression affects approximately 10–15% of women and impairs mother–infant interactions that in turn are important for child development. Maternal attachment, sensitivity and parenting style are essential for a healthy maturation of an infant's social, cognitive and behavioral skills and depressed mothers often display less attachment, sensitivity and more harsh or disrupted parenting behaviors, which may contribute to reports of adverse child outcomes in children of depressed mothers. Here we review, in honor of the “father of motherhood”, Jay Rosenblatt, the literature on postnatal depression in the mother and its effect on mother–infant interactions. We will cover clinical and pre-clinical findings highlighting putative neurobiological mechanisms underlying postpartum depression and how they relate to maternal behaviors and infant outcome. We also review animal models that investigate the neurobiology of maternal mood and disrupted maternal care. In particular, we discuss the implications of endogenous and exogenous manipulations of glucocorticoids on maternal care and mood. Lastly we discuss interventions during gestation and postpartum that may improve maternal symptoms and behavior and thus may alter developmental outcome of the offspring.