Stimulus control of maternal responsiveness to Norway rat ( Rattus norvegicus) pup ultrasonic vocalizations.

Mother rats (Rattus norvegicus; 6 to 8 days postpartum) approach and maintain proximal orientation to a pup that is emitting ultrasonic vocalizations (USVs) far more than do virgin females (W. J. Farrell & J. R. Alberts, 2002). We used a playback regimen to examine the roles of acoustic and nonacoustic cues in regulating maternal proximal orientation toward vocalizing pups. When presented with recorded USVs, mothers of 6- to 8-day-old pups and nulliparous virgin females exhibited equivalent levels of proximal orientation toward the playback speaker. Mothers did show enhanced proximal orientation toward recorded USVs, however, if a silent pup was positioned below the speaker. Pup odors appear to be crucial for the maternal response to vocalizing pups, as peripherally induced anosmia attenuated maternal proximal orientation toward a vocalizing pup. Furthermore, spatial contiguity between olfactory and auditory stimuli was required for a maximal maternal response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maternal responsiveness to infant Norway rat ( Rattus norvegicus) ultrasonic vocalizations during the maternal behavior cycle and after steroid and experiential induction regimens.

When removed from the nest and placed in a cool environment, Norway rat (Rattus norvegicus) pups emit ultrasonic vocalizations that can elicit maternal search behavior. The authors examined the behavior of pregnant dams, mothers, and virgin females during exposure to a pup that was either warm and silent or cool and vocalizing. Results indicate potentiated maternal reactions to a vocalizing pup: Mothers approached and maintained proximal orientation to a vocalizing pup far more than did virgin females. Elevated levels of proximal orientation appeared within hours of birth, increased during the 1st week postpartum, and declined by the time of weaning. Estrogen plus progesterone administration facilitated virgin females' proximal orientation toward vocalizing pups, whereas prolonged exposure to pups in the absence of hormones was without effect, suggesting that the ontogeny of the maternal response is regulated, at least in part, by maternal hormones. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasonic vocalization, laryngeal braking, and thermogenesis in rat pups: A reappraisal.

Tested the hypothesis that the respiratory events underlying rat pup ultrasonic vocalization (USV) facilitate brown adipose tissue (BAT) thermogenesis, as proposed by M. S. Blumberg and J. R. Alberts (1990). Laryngeal denervation of tracheostomy were used to reduce or eliminate laryngeal braking and prevent USV in 9- to 10-day-old pups during recovery from deep hypothermia and during cooling induced by isolation for 1 hr at room temperature. Both forms of devocalization slowed rewarming of hypothermic pups, but neither had any effects on cooling rate or BAT thermogenesis in normothermic pups that were allowed to cool from 35°C to 29°C. Physiological effects of laryngeal braking on thermogenesis appear to be limited to conditions, such as severe hypothermia, in which ventilatory and oxygen transport functions are compromised. Results have implications for understanding the regulation and evolution of USV. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mother-Infant Interactions in Rats Lacking CCKA Receptors.

Mediation of mother-infant interactions by the brain-gut peptide cholecystokinin (CCK) was examined by observing behavior of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which lack functional CCKA receptors because of a genetic abnormality. OLETF (n = 10) and control (Long-Evans Tokushima Otsuka [LETO] n = 10) dams interacted with 1 pup of each line on Postpartum Days 6-9. OLETF pups received more body and anogenital licking and emitted substantially more ultrasonic vocalizations than LETO pups. OLETF dams carried pups less frequently and showed a nursing position more frequently than LETO dams. No significant Pup X Dam Line interactions or line differences in dams' activity were detected. The results provide convergent validity to previous pharmacological studies implicating CCK mediation of both infant and maternal behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separable Brainstem and Forebrain Contributions to Ultrasonic Vocalizations in Infant Rats.

Competing views persist concerning the functional significance of ultrasonic vocalizations (USVs) emitted by infant rats. One perspective holds that USVs result from an emotional state of fear and anxiety, the adult expression of which depends in part on forebrain mechanisms. Here the authors examine whether pups lacking forebrain input are capable of emitting USVs. Aspirations of neocortex and hippocampus or precollicular decerebrations were performed on 8-day-old rats. After the rats recovered, USV responses were recorded for 10 min at room temperature (Phase 1) followed by enhanced cooling for 20 min (Phase 2). Experimental pups emitted significantly fewer USVs than shams during Phase 1 but vocalized at similar rates during Phase 2. Thus, in infants, brainstem neural circuitry is sufficient to support emission of USVs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preputial glands of infant rats (Rattus norvegicus) provide chemosignals for maternal discrimination of sex.

In 4 experiments, dams were presented with simultaneous choice tests of pup odors, and their investigatory sniffing was measured. Dams did not show differential sniffing of male and female bladder urine or urine voided by pups with preputial glands removed (PPX). They preferred urine voided by intact male pups to that voided by intact females, and they preferred urine voided by intact pups to that of PPX pups within each sex. Finally, they preferred water homogenates of preputial glands removed from male pups to those of female pups. It is concluded that the neonatal preputial gland is a source of chemosignals that are attractive to dams and that are used by dams to identify sex of pup. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in urinary odors produced by young laboratory rats (Rattus norvegicus).

Examined the responses of 75 primiparous Long-Evans rat dams and 20 nonmaternal Long-Evans females to male and female pup urine in 3 experiments. Investigatory sniffing of male and female pup urine deposits by maternal Ss was compared in a series of simultaneous choice tests given at 3-day intervals between Day 2 and Day 17 postpartum. Male urine was consistently preferred. Introduction of male but not female pup urine to the nest was found to significantly elevate maternal licking of anogenital regions of pups. Thus, urine from pups of various ages contains sex-identifying odors that differentially elicit spontaneous maternal interest. The odor of male urine may provide a sufficient stimulus to account for the greater anogenital licking that males of this species normally receive. Nonmaternal, naive, adult Ss behaved like maternal Ss, preferring male urine in the choice test, which indicates that the maternal condition of a dam is not necessary either for the olfactory discrimination or for the male odor preference. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Activation of Fos-like immunoreactivity in the medial preoptic area and limbic structures of maternal and social interactions in rats.

Examined the number of cells showing Fos-like immunoreactivity (Fos-lir) in the brains of hormonally primed parturient rat dams immediately following their 1st behavioral interactions with pups. Groups were exposed to newborn pups (pup), adult conspecifics (social), or a new food (food), or they were left alone in cages (control/isolate) for a 1-hr period. Rats were then killed, and their brains were prepared for immunohistochemical detection of Fos-lir. Rats in the pup group had higher numbers of cells showing Fos-lir within the medial preoptic area (MPOA) nuclei than did the social, control/isolate, and, marginally, food groups and higher levels of Fos-lir in a number of amygdaloid nuclei (medial and cortical) and in cingulate and somatosensory cortices than did control/isolate or food groups. Fos-lir in amygdala did not differ between pup and social groups. There were also group differences in Fos-labeling in the olfactory bulbs, with the pup group showing the highest densities. These results show elevated expression of Fos-lir in brain structures that were activated during the expression of maternal behavior, including the olfactory structures, amygdala, and MPOA. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of two positive reinforcing stimuli: Pups and cocaine throughout the postpartum period.

This set of experiments investigated the appetitive or motivational processes underlying the performance of maternal behavior. The place preference paradigm was adapted to simultaneously investigate the reinforcing properties of cocaine and pups for maternal, lactating dams. These modifications allowed the authors to assess which stimulus, either a 10 mg/kg sc injection of cocaine or 3 pups, had the strongest reinforcing value. At Postpartum Days 10 and 16, the dams preferred the cocaine cue-associated chamber, whereas the dams tested at Postpartum Day 8 preferred the pup cue-associated chamber. Overall, the data revealed an interaction between the postpartum period at testing and the exhibited preference for cocaine or pups. Further testing will investigate the neural circuitry underlying the appetitive processes of each stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Normal maternal behavior, but increased pup mortality, in conditional oxytocin receptor knockout females.

Oxytocin (Oxt) and the Oxt receptor (Oxtr) are implicated in the onset of maternal behavior in a variety of species. Recently, we developed two Oxtr knockout lines: a total body knockout (Oxtr–/–) and a conditional Oxtr knockout (OxtrFB/FB) in which the Oxtr is lacking only in regions of the forebrain, allowing knockout females to potentially nurse and care for their biological offspring. In the current study, we assessed maternal behavior of postpartum OxtrFB/FB females toward their own pups and maternal behavior of virgin Oxtr–/– females toward foster pups and compared knockouts of both lines to wildtype (Oxtr+/+) littermates. We found that both Oxtr–/– and OxtrFB/FB females appear to have largely normal maternal behaviors. However, with first litters, approximately 40% of the OxtrFB/FB knockout dams experienced high pup mortality, compared to fewer than 10% of the Oxtr+/+ dams. We then went on to test whether or not this phenotype occurred in subsequent litters or when the dams were exposed to an environmental disturbance. We found that regardless of the degree of external disturbance, OxtrFB/FB females lost more pups on their first and second litters compared to wildtype females. Possible reasons for higher pup mortality in OxtrFB/FB females are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hormonal responses of male gerbils to stimuli from their mate and pups

Following copulation and cohabitation with a pregnant female, male gerbils show high levels of parental behavior toward their pups. The initiation of male parental behavior may be the result of neuroendocrine changes induced by cohabiting with the pregnant female or by pup stimuli. Experiment 1 examines the changes in androgen and prolactin levels in male gerbils cohabiting with females over the reproductive cycle. Gerbils were mated and blood samples taken from males for hormone analysis 1, 10, and 20 days after pairing and 3, 10, and 20 days after pups were born. A group of unmated male gerbils served as controls. Plasma prolactin levels of males were elevated throughout the female's pregnancy and lactation periods, but were only statistically significantly higher than those of unmated males 20 days after pups were born. Androgen levels rose during pregnancy and dropped significantly after the birth of the pups. These hormonal changes are similar to those found in males of monogamous birds and differ from those found in males of polygynous rodents such as the rat. Experiment 2 examined the hormonal responses of male and female gerbils to pup replacement after 4 hr of parent-pup separation. Female gerbils showed a significant elevation of prolactin levels 1 hr after pup replacement, but males did not. Males with pups returned showed no difference in androgen levels from males who did not have pups returned. Thus, male gerbils show neuroendocrine changes following long-term cohabitation with their mate and pups, but do not show acute hormone responses to pup removal and replacement. These results indicate that parental males have neuroendocrine changes associated with parental behavior and these differ from the neuroendocrine changes underlying female parental behavior.     

Prenatal cocaine but not prenatal malnutrition affects foster mother-pup interactions in rats

The separate and combined effects of prenatal cocaine exposure and malnutrition on mother-pup interactions in rats were assessed daily from postnatal day 2 to day 21. Sprague-Dawley dams were fed a diet of low protein content (6% casein), an isocaloric diet of adequate protein content (25% casein, control), or a laboratory chow diet prior to mating and throughout pregnancy. Within each diet group, rats received either cocaine injections (30 mg/kg IP two times per week prior to mating and then 30 mg/kg SC daily from days 3 to 18 of pregnancy) or saline injections. Litters were fostered on the day of birth to control mothers (i.e., nondrug-exposed dams fed the control or chow diet). Foster mothers fed the 25% casein diet showed increased contact with cocaine-exposed pups compared with nondrug-exposed pups in the second postnatal week but lower levels as the pups approached weaning. Passive nursing was increased in dams caring for prenatally malnourished, cocaine-exposed pups compared with those caring for similar pups with no drug exposure. Chow-fed mothers did not differ in their behavior towards pups with or without prenatal cocaine treatment. Prenatal cocaine and malnutrition independently compromised birth weight and various reflexive milestones but the attainment of physical milestones was affected only by prenatal cocaine. There were no additive effects of the two prenatal insults on any measure of mother-pup interaction or pup development.     

Lactational exposure and neonatal kinetics of methylmercury and inorganic mercury in mice

The concentration of mercury in milk and the distribution pattern in the sucking pup was followed over time after administration of a single iv injection of 0.5 mg/kg body wt of 203Hg-labeled methylmercuric chloride or mercuric chloride to lactating mice on Day 10 of lactation. Mercury concentrations in milk of the dams and in whole body, blood, plasma, GI-tract, liver, kidneys, and brain of the offspring were followed up to 11 days after dosing (until lactational Day 21). Following the inorganic mercury dose to the dams, most of the mercury in milk was delivered to the pups during the first 24 h, but the maximum mercury concentration in plasma and tissues of pups was not reached until 7 days after dosing, indicating a prolonged absorption of inorganic mercury in the sucking pup. Pups of dams given methylmercury were exposed to a much lower and constant mercury concentration in milk. The estimated accumulated mercury dose via milk per pup of dams given methylmercury was less than half of that estimated after the inorganic mercury dose. When the accumulated dose via milk from methylmercury-exposed dams was compared to the amount of mercury in pup's carcass (whole body minus GI-tract including content), it was revealed that almost all mercury delivered via milk was absorbed, and that the suckling pups had a very low elimination of mercury until lactational Day 17. Lactational exposure following a maternal methylmercury or inorganic mercury dose resulted in almost similar mercury concentrations in liver, kidneys, and plasma of the suckling, but higher concentrations in brain (as most 14 times) and also twice as high mercury body burden in the methylmercury group. Thus, differences in kinetics indicate that lactational exposure of methylmercury is a greater hazard for the breast-fed infant than inorganic mercury.     

Perioral somatosensory determinants of nursing behavior in Norway rats (Rattus norvegicus).

Prior to assuming the upright crouching posture over their pups during nursing bouts, lactating rats typically engage in several oral behaviors, including nuzzling, licking and rearranging pups. By acutely depriving dams of various aspects of perioral stimulation from pups (with anesthesia of the mystacial pads or of the tongue, with mouth suturing, or with muzzling), we found the following: (1) distal stimulation from pups maintains proximity-seeking behavior, but is insufficient to stimulate nursing behavior. (2) Lack of tongue feedback decreases pup licking and hastens the onset of crouching. (3) Snout, but not tongue, contact with pups is required for hovering over them. (4) The position of the dam while hovering over her litter enables the pups to gain access to her ventrum, thereby provoking her upright, crouching posture. (5) Older pups are capable of bypassing dam's perioral attentions and stimulating crouching directly by burrowing under the dam's ventrum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pup and object carrying by maternally and nonmaternally behaving female albino rats (Rattus norvegicus).

Pups and toys (rubber dropper-bulbs) were presented to 48 nulliparous and 10 lactating female albino Sprague-Dawley rats either together (choice test) or in separate tests. Regardless of their reproductive state, Ss fell into 3 categories according to their behavior: (a) Postpartum Ss as well as virgins that behaved maternally picked up pups much faster than toys, carried more pups than toys, gathered young into the nest, but scattered toys outside the nest site. (b) Virgins that carried young spontaneously but did not show any other elements of maternal behavior picked up pups and toys after equal latencies, carried pups and toys in equal numbers, and scattered both the pups and the toys about the floor of the cage. (c) Virgins that ignored pups did not carry young, but they did show high levels of toy carrying and dispersed the toys about the cage. It is proposed that the term retrieving should be limited, by its definition, to those cases in which the objects are carried to a specific location. Thus, pup retrieval was seen exclusively in Ss that showed maternal behavior (i.e., crouching, pup licking), because only these Ss carried pups consistently to the nest. On the other hand, pup carrying shown by nonmaternally behaving Ss and toy carrying shown by all Ss are both cases of scattered, nondirected object carrying, rather than retrieving. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physiological and behavioral consequences in rats of water recycling during lactation.

Reports that radioactive water injected into 10-day-old Sprague-Dawley rats could be recovered the following day from their mothers' blood. This transfer of water was nearly eliminated by ligating the injected pups' urethras, a result indicating that mother rats consume their offspring's urine. Preventing urine consumption by ligating urethras of all pups in a litter doubled the plasma volume deficit in dams produced by 24 hrs of water deprivation alone and led to increased isotonic saline but not water intake following water deprivation. Dams' daily water intake increased after they were deprived of pup urine, and their pup-licking behavior increased following water deprivation. Findings from 3 experiments indicate that urine consumption by mother rats has both physiological and behavioral consequences and suggest that pup licking is, in part, an ingestive behavior. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Litter gender composition affects maternal behavior of the primiparous mouse dam (Mus musculus).

Thirty-nine litters of the outbred Swiss CD-1 mouse strain were reduced at birth to 6 pups, according to three conditions MM (all males), MF (3 males and 3 females), or FF (all females). The maternal behavior of their respective dams (frequency and duration of nursing, licking, nestbuilding, and other activities such as eating, drinking, sniffing, grooming, and undirected locomotor activity) were scored during a single 10-min session on Days 2, 3, 5, 7, 10, 14, and 18. Dams rearing MM litters showed higher scores of maternal care on Days 2 and 18 in the case of nursing, on Days 2, 7, and 10 in the case of nest-building, and on Day 18 in the case of licking. These results confirm previous rat data, which indicated that male and female pups are exposed early in infancy to a different pattern of maternal behavior. Concomitant measurements of pup development (body-weight gain and achievement of a number of physiological and neurobehavioral landmarks) indicated that these effects of litter gender composition are not mediated by gross changes in the maturational trends of the pups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intravenous gestational cocaine in rats: effects on offspring development and weanling behavior

Pregnant rats were injected with cocaine (CN; 6 mg/kg) or an equal volume of saline (SAL), via the tail vein, on gestation days 8-20. A third group was untreated (UT). Maternal weight gain was not affected by dam treatment despite slight differences in food intake. Litter characteristics (e.g., litter size, pup weight) did not differ among groups. Indices of fetal mortality were not affected by the treatments. Developmental tests, initiated on postnatal day (PND) 2, indicated slight delays in the negative geotaxic response and eye opening in cocaine-exposed pups. Open-field and tail-flick tests were performed on PND 21. Pups were acutely injected with cocaine (10 mg/kg, IP), saline, or received no treatment before placement in a novel open field; morphine (1.5 mg/kg, SC) or saline was injected prior to the tail flick test. Pups from CN dams exhibited a significant decrease in spontaneous exploratory behavior compared to both controls, and a time-dependent increase in rearing compared to pups from UT dams. The acute cocaine injection prior to placement in the open field did not alter locomotion or rearing among dam treatment groups. However, the acute cocaine injection did increase stereotypy ratings for female pups from CN dams compared to similarly treated males, and females from SAL and UT dams. No differences were observed among groups in the tail-flick test. These data suggest that the IV route of administration provides a viable method of cocaine delivery in pregnant rats, and provides further evidence of the developmental and behavioral teratogenicity of prenatal cocaine exposure.     

Juvenile Rats Show Reduced c-fos Activity in Neural Sites Associated With Aversion to Pups and Inhibition of Maternal Behavior.

Juvenile rats (18-23 days old) interact avidly with pups as novel stimuli and show maternal behavior after only 1-3 days of pup exposure; adults initially avoid pups and require 3-9 days of pup exposure. Upon exposure to pups as novel stimuli, adults had more c-Fos-immunoreactive neurons in the hypothalamus and amygdala--regions associated with aversion to pups--than adults exposed to familiar pup stimuli (maternal) or not exposed to pups (p     

Selective retrieving by maternal and nonmaternal female rats.

Conducted an investigation to learn whether nonpregnant female rats made maternal by exposure to pups would act more like nonmaternal females than lactating mothers. Ss were 32 nulliparous females of the Charles River CD strain and an additional number of females that provided pups for inducing maternal behavior in virgins and in testing all Ss in pup vs toy tests. The behavior toward a pup and a toy was studied in 1 group of nonmaternal virgins, 2 groups of maternal virgins, and 1 group of lactating mothers, during 7 daily 5-min tests. Measures of the frequency and duration of retrieving-related behavior and analysis of behavioral sequences in relation to the pup or toy showed that pup-induced maternal virgins more closely resemble the lactating mothers than nonmaternal virgins. (PsycINFO Database Record (c) 2010 APA, all rights reserved)