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 < .05). In juvenile rats exposed to pups as novel stimuli, only the medial amygdala had a small significant increase of c-Fos neurons. In juveniles, this blunted engagement of c-Fos neurons may reflect the diminished activation of inhibitory neurons, facilitating the interaction of juveniles with pups as novel stimuli and onset of maternal behavior.     

Perinatal high-fat diet impairs pup retrieval and induces sex-specific changes in ultrasonic vocalization characteristics of rat pups

Rodent pups emit ultrasonic vocalizations (USVs) to solicit maternal behavior, promoting their survival. Conversely, maternal behaviors affect the expression of pup USVs. We previously demonstrated that a maternal diet high in saturated fat (HFD) alters maternal behavior and is associated with early maturation of pups and their stress physiology. Here, we assessed the developmental profiles of pup USVs using quantitative and qualitative measures on postnatal days (PND)7 and 13. Quantitative measures included call counts, duration, and frequency, while qualitative measures examined calls' sonographic structures. HFD offspring lacked the typical decrease in USV numbers with age observed among control offspring. They also had shorter calls at PND7 compared to control and HFD offspring at PND13. HFD female offspring showed a greater number of one-frequency-sweep calls, while male pups showed a greater number of two-frequency-sweep calls compared to control offspring. Concomitantly, HFD dams showed impaired pup retrieval on PND7. The data suggest that fewer USVs of shorter duration in HFD offspring may alter dam solicitation and thus impair maternal pup retrieval. This study highlights the impacts of perinatal HFD exposure on the dyadic reciprocal interaction between dam and pups, which may set the stage for long-lasting effects on offspring physiology and behavior.     

Sensory regulation of maternal behavior in rats: Effects of pup age

Maternal behavior (retrieving, crouching, and licking) was induced in Sprague-Dawley virgin female rats by constant exposure to pups aged 1-2, 3-4, 5-6, 7-8, 9-10, 11-12, 13-14, or 15-16 days. The incidence of spontaneous components of maternal behavior, notably retrieving, was geater towards pups 1-8 days of age than towards older pups, whereas the occurrence of cannibalism did not differ as a function of pup age. With pups 1-2 through 13-14 days, the latency to onset of full maternal behavior was shortest with 1-2-day-old pups (2-day median) and longest with 13-14-day-old pups (7-day median). Females exposed to pups aged 3-4 through 11-12 days did not differ significantly in their latencies, the medians of which ranged from 4.0 to 5.5 days. Only 1 female out of 8 exposed to pups aged 15-16 days became fully maternal, but 5 more displayed components of maternal responsiveness. The optimal nature of neonates and the general attractiveness of a wider range of pup ages as stimuli for the elicitation of maternal behavior in rats, as well as comparisons to mice and hamsters, were discussed.     

Methamphetamine administration during gestation impairs maternal behavior

Previous studies demonstrated that repeated drug exposure, such as opiates or cocaine, during the gestation period attenuates maternal behavior of rats; however, it is not known whether methamphetamine (MA), a drug whose usage has increased recently, negatively affects maternal behavior as well. Therefore, the present study tested the hypothesis that repeated subcutaneous administration of MA (5 mg/kg daily) throughout the entire gestation period alters maternal behavior. Dams (control, saline-, and MA-treated) were observed with their pups in two types of tests. In the observation test, 11 types of activities and three types of nursing positions of mothers were recorded 10 times during each 50-min session for the 22-day lactation period. A decrease in nursing and active maternal behavior was found in MA-treated mothers relative to control rats. In addition, stereotypic behavior such as rearing and sniffing was increased in MA- as well as in saline-treated mothers relative to controls. All mothers, regardless of the treatment, displayed significantly less maternal behavior and more nonmaternal activities as postpartum time progressed. In the retrieval test, mothers also were tested for pup retrieval from postpartum Days 1 through 12. MA-treated mothers were slower in retrieving the first pup, returning the first pup into the nest, and returning all pups into the nest relative to controls or saline-treated mothers. Interestingly, the latency to return all pups to the nest was longer in saline-treated mothers relative to controls. In conclusion, the present study demonstrates a novel finding that MA administered during the gestation period has a negative effect on maternal behavior.     

Long-term effects of prenatal morphine exposure on maternal behaviors differ from the effects of direct chronic morphine treatment

Previous studies have demonstrated that chronic morphine treatment of pregnant rats alters maternal behavior. Other studies have shown long-term effects of prenatal exposure to morphine, including changes in reproductive behavior in adult females. The present study investigated the effects of prenatal morphine exposure on a variety of maternal behaviors such as nursing, maternal activities, nonmaternal activities, and pup retrieval. Prenatal morphine exposure increased active and decreased passive nursing. There were no differences in maternal activities such as presence in the nest, contact with pups, grooming of pups, and/or manipulation of nest shavings. In the retrieval test, prenatally morphine-exposed mothers were faster in carrying the first pup, retrieving the first pup back to the nest, and returning all pups to the nest than prenatally saline-exposed mothers. Maternal and nonmaternal activities also were affected by the light: dark cycle. All saline- and morphine-exposed mothers nursed more, were more often in the nest, and more often in contact with greater than half of their litter during the light than the dark sessions. On the other hand, nonmaternal activities increased during the dark sessions: Mothers cared for themselves (groomed, ate) more and displayed more rearing and sniffing. Mothers spent more time resting with their eyes closed during the light sessions regardless of prenatal drug exposure. The present study demonstrated that the effect of morphine on maternal behavior is different in adult exposed and prenatally exposed mothers. While direct morphine treatment impaired maternal behaviors, prenatal morphine exposure has the opposite effect.     

Effects of stress during pregnancy on maternal behavior in mice

The effects of stress experienced during pregnancy and raising stressed offspring on maternal behavior were investigated in Swiss-Webster mice. Dams were either stressed or not stressed during pregnancy, and raised either prenatally stressed or nonstressed cross-fostered pups. Maternal behaviors such as grooming, nursing, pup retrieval and maternal aggression were assessed during the first 4 days after birth. Nonstressed dams raising stressed pups and stressed dams raising nonstressed pups groomed and nursed their pups significantly less than did control dams (stressed dams raising stressed pups and nonstressed dams raising nonstressed pups). Nonstressed dams raising stressed pups were also the slowest to retrieve both the first and last pup in retrieval tests. Nonstressed dams raising nonstressed pups were significantly less aggressive than other dams. In contrast, stressed dams raising stressed pups exhibited high levels of nursing and grooming, retrieved their pups rapidly and were very aggressive towards an intruder. These results indicate that raising stressed pups, or experiencing stress during a pregnancy can have significant effects on maternal behaviors. Stressed dams raising stressed pups exhibit maternal care comparable to that of nonstressed dams raising nonstressed pups at least for nesting/nurturing behaviors, and show increased levels of aggression and pup retrieval.     

Effects of prenatal alcohol exposure on rat pups' ability to elicit retrieval behavior from dams

Research on fetal alcohol syndrome (FAS) has historically held that postnatal deficits result directly from prenatal alcohol exposure. Such exposure may alter infant behavior, and this in turn may affect maternal responsiveness and consequently increase the infant's risk for postnatal deficits. This study examined the effect of prenatal alcohol exposure on postnatal blood ethanol concentrations, pup development, and the ability of pups to elicit retrieval behaviors from the dam. Dams given access to a 15% ethanol solution throughout gestation and lactation showed blood ethanol concentrations of 0.1%, whereas their pups had concentrations below the sensitivity of the test. Prenatal alcohol exposure was shown to have pharmacological effects on the pup's righting reflex and nutritional effects on its rate of weight gain. Control pups were better able to elicit retrieval behavior from control and alcoholic dams than were fetally alcoholic pups. These results indicate that the condition of the pup can influence maternal responsiveness which, in turn, can influence pup development.     

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. © 1997 John Wiley & Sons, Inc. Dev Psychobiol 30: 115–126, 1997     

Cyclic AMP response element-binding protein is required for normal maternal nurturing behavior

Analysis of mice with targeted disruptions of fosB or the gene encoding dopamine beta-hydroxylase suggests that FosB and adrenergic signaling play critical roles in maternal nurturing behavior. The majority of neonates born to null females from either mutation fail to thrive, and virgin mutant females of both lines exhibit impaired pup retrieval. Considering whether FosB and adrenergic signaling might share a signaling pathway important for maternal behavior, we examined the role of a potential intermediary, cyclic AMP response element-binding protein (CREB). Here we report that approximately 40% of neonates (all heterozygous) born to mice lacking the major isoforms of CREB (Creb-alphaDelta-/-) died within several days of birth. In contrast, heterozygotes born to Creb-alphaDelta+/- females thrived. Cross-fostering demonstrated that neonates born to Creb-alphaDelta(-/dagger/-) females thrived when reared by wild-type females, and that Creb-alphaDelta-/- females were capable of rearing neonates whose maternal care was initiated by wild-type females. Further, virgin Creb-alphaDelta-/- females were deficient in pup retrieval despite exhibiting normal investigation of pups and of novel objects. No maternal behavior phenotype was present in mice with a null mutation of the cyclic AMP response element modulator (Crem) gene. Interestingly, the number of cells immunostaining for phospho-CREB (on Ser(133)) in the medial preoptic area of the hypothalamus, a key region for the expression of maternal behavior, increased nearly three-fold in wild-type mice following exposure to pups but not to novel objects. On the other hand, basal expression and induction of FosB in response to pup exposure appeared to be independent of CREB because levels were equivalent between wild-type and Creb-alphaDelta-/- females. These results implicate CREB in maternal nurturing behavior and suggest that CREB is not critical for expression or induction of FosB in adult virgin female mice.     

Effects of mother-litter separation on later maternal responsiveness in the hamster

Primiparous hamsters were permitted either 1,24, or 48 hr of contact with their own litters beginning at parturition followed by varying periods of separation from pups. A different subgroup in each of these 3 conditions was tested for maternal behavior each day starting 24 hr after litter removal. Testing for the display of retrieving and the adoption of the nursing posture using 1–2 day old foster pups continued for each condition until 2 subgroups failed to behave maternally on 2 consecutive days. Nulliparous females were similarly exposed to foster pups and tested at selected intervals; regardless of initial exposure, only 4 of 24 nulliparous animals ultimately displayed maternal behavior. Different primiparous subgroups given 1 hr of exposure were maternal on Days 2–4 postpartum but not on Days 5 or 6 while females in the 24 hr group were maternal on Days 3–5 but not on Days 7 or 8. Groups permitted 48 hr of litter stimulation were maternal through Day 15 postpartum demonstrating that the initial 24–48 hr of pup contact is essential for the development of a long-term mother-young bond.     

A Review of the Methods of Studies on Infant Ultrasound Production and Maternal Retrieval in Small Rodents

Ultrasonic vocalizations or calls produced by young rodents have been associated with aspects of maternal behavior, in particular retrieving. We reviewed the methods of study used by investigators on each topic, focusing on intrinsic or subject variables and extrinsic or experimental variables. Intrinsic variables included the species studied, genotypes employed, number and sex composition of the litters, and the ages of mothers and pups. Extrinsic variables for studies on ultrasonic calling included: eliciting stimuli, test surroundings, and the length of observation. Extrinsic variables in studies of maternal retrieval included the testing procedure and the length of observation. The methods used in studies within each topic vary greatly. In an effort to facilitate progress in the areas, especially with respect to isolating individual genes with a contribution to ultrasonic call production or studying the effects of pharmaceutical agents on either behavior, we propose some standardization of nomenclature and/or procedure in four areas: (1) the stimuli or situations used to elicit ultrasonic calls, (2) the length of observation in ultrasonic call studies, (3) the number of pups per litter and the sex composition of litters in both ultrasonic call and maternal retrieval studies and finally, (4) the apparatus or testing situation used in studies of pup retrieval.     

Neonatal Ethanol Exposure but not Neonatal Cocaine Selectively Reduces Specific Isolation-Induced Vocalization Waveforms in Rats

This study was designed to examine the interaction of neonatal ethanol and cocaine exposure on isolation induced ultrasonic vocalizations using an oral gavage method of drug administration. There were 5 neonatal treatment groups including 3.0 g/kg ethanol, 20 mg/kg cocaine, both 3.0 g/kg ethanol and 20 mg/kg cocaine, an intubated control and a nonintubated control. Drug was administered twice daily from postnatal days (PND) 4 – 10. On PND 14, subjects were tested for a 6 min test to assess the rate and type of ultrasonic vocalizations displayed. As previously reported using an intragastric artificial rearing administration procedure, pups exposed to ethanol displayed reductions in the number of ultrasonic vocalizations across the test session. Pups exposed to both drugs showed similar deficits to those pups receiving ethanol alone. In contrast, cocaine had no effect on this outcome measure. Sonographic analysis of the vocalizations revealed that ethanols effects appeared to be selective to certain waveforms rather than a general reduction across all wave types and again, cocaine had no impact on the proportion of the various wave types. These findings provide further support that neonatal ethanol exposure can have significant effects on maternal/infant communication and may play a role in many of the long-term effects associated with ethanol exposure during development.     

Maternal behavior,pup vocalizations,and pup temperature changes following handling in mice of 2 inbred strains

A cross-fostering design was used to examine maternal behavior, pup vocalizations, and pup temperature changes following an infantile handling procedure in C57BL/6J (C) and A/J (A) mice. In Experiment I, maternal behavior of C and A mothers after infantile handling differed in a number of ways irrespective of the strain of the foster pups. In addition, A pups were retrieved faster but licked less than were C pups by mothers of both strains. Handling appeared to increase the probability that strain differences would occur in that no differences between the lines, in either the behavior of the mothers or the capacity of the pups to elicit maternal behavior, were found during observations made just prior to daily handling. These observations also revealed that mothers of both strains treated same-strain foster pups differently than they treated foster pups of another strain. In Experiment II, A pups were found to emit more ultrasound following handling than were C pups, suggesting that retrieval but not pup-licking was stimulated by ultrasonic signals. Measurement of pup temperature during and following the handling procedure showed that (1) strain differences in ultrasonic signaling were not related to strain differences in the degree of hypothermia experienced by the pups; (2) recovery of body temperature following handling was slow for pups of both strains, and depended to some degree on the strain of the pup's foster mother; and (3) development of thermoregulation occurred more rapidly in C than A pups.     

Attenuation of maternal behavior in virgin CD-1 mice by methylphenidate hydrochloride

The administration of methylphenidate hydrochloride (MPH) to girls and women has increased in the last decade and the potential for mothers to receive this medication has also increased. Because substances that alter the dopaminergic systems can also disrupt maternal behavior, and MPH acts on dopaminergic neurons, we evaluated the influence of MPH on maternal behavior. The maternal induction paradigm allowed us to assess changes in spontaneous maternal behavior as a result of repeated exposure to MPH without exposing pups to the drug. Virgin female CD-1 mice received MPH (5 mg/kg) or saline daily, starting 3 days before pup exposure, and for the duration of the 10-day test period. Naïve groups of three pups were placed with the female each day and maternal behavior was assessed during 10-minute observation periods 1 h post-injection. MPH-treated females showed significantly less maternal behavior, including reduced pup licking and crouching over pups, compared to saline treated females. MPH-treated females also exhibited higher activity levels than saline treated females. Given the disruption in spontaneous maternal behavior of MPH-treated mice, further research examining the relationship between maternal behavior and MPH exposure is warranted.     

Selective retrieval of jimpy mutant pups over normal male littermates by lactating female B6CBACa-A w-J /A-Ta jp mice

The jimpy sex-linked mutation results in dysmyelination throughout the CNS although myelination in the peripheral nervous system is unaffected. Jimpy pups (jp/Y) weigh less, produce fewer ultrasonic vocalizations, and spend less time engaged in coordinated activity than their normal littermates and rarely live past 30 days of age. Both jp/Y and normal male pups occur within the same litter, making it possible to examine maternal responsiveness to the two types of pups. Using maternal retrieval as a measure of maternal responsiveness, we predicted, in agreement with parental investment theory, that mothers would retrieve normal littermates in preference to mutant pups. When tested for pup retrieval preferences in a T-maze at 2-day intervals from day 3 to day 15 postpartum, mothers retrieved the mutant mouse first on 78 to 100% of the trials and carried him back to the stem section of the T-maze before returning for the normal littermate. We are thus left with the paradox that the mother appears to prefer the mutant pup to the normal littermate, despite its smaller size, reduced ultrasonic vocalization rate, and compromised fitness.     

Changes in responsiveness to newborn pups in pregnant,nulliparous golden hamsters

Virgin female hamsters were mated and tested once daily for maternal retrieving behavior beginning on days 0, 5, 9, 13, 15, of the 16 day gestation period to determine if responsiveness toward newborn pups changes as pregnancy proceeds. Upon initial exposure to 3 newborn pups, only a small percentage of early-to-mid-pregnant females exhibited maternal retrieving behavior spontaneously. In contrast, over half of the 15 day pregnant females displayed retrieving during the first test. Despite the high frequency of initial pup-directed aggression and cannibalism, maternal retrieval was induced in the majority of the females in all groups by repeated daily exposure to 3 newborn pups. However, no significant differences were observed in the number of pup exposure periods required to induce maternal retrieving in 0, 5, and 9 day pregnant females. It is concluded that the high level of maternal responsiveness observed in the parturient hamster develops somewhat abruptly during late pregnancy. In this respect, the pattern observed in the hamster differs from the more gradual increase in maternal responsiveness reported in mid-to-late-pregnant mice and rats.     

Pup exposure differentially enhances foraging ability in primiparous and nulliparous rats

The role of maternal experience (i.e., pregnancy and pup exposure) on rats' performance in a foraging task was assessed. Primiparous (P) and nulliparous (N) animals were either exposed to pups for 21 days (+) or received no pup exposure (-). Following habituation trials, all animals were tested in spatial and cued versions of the dry land maze (DLM) for three days (three trials per day). In the spatial DLM, the presence of pups decreased latencies in both N and P groups in Trial 5 and P+ rats exhibited shorter latencies to baited food wells than P- animals on Trial 6. In the subsequent probe trial, P+ animals spent significantly more time in proximity to the previously baited well than P- rats. Pups enhanced performance of both P+ and N+ groups in trial 6 of the cued test. Thus, in the spatial task, the individual components of the maternal experience (e.g., pregnancy, parturition, lactation, and pup exposure) converge to produce behavioral modifications in the DLM spatial and probe tasks that enable the female to care for her offspring, in this case, by enhancing foraging behavior. Further, in one trial of each version of the task, pup exposure enhanced performance in N animals suggesting that, in isolation, pup exposure may be a more important influence on ancillary maternal behavior than the pregnancy itself.     

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.     

Effects of Genetic Background,Gender, and Early Environmental Factors on Isolation-Induced Ultrasonic Calling in Mouse Pups: An Embryo-Transfer Study

Infant rodents emit ultrasonic vocalizations when isolated from dam and littermates. Due to the context of their occurrence and the well described bidirectional modulation by substances known for their capability to influence emotionality, it was postulated that such calls reflect a negative affective state akin anxiety. Comparative studies observed pronounced differences in calling behavior between strains, which were paralleled by differences in maternal care. Therefore, it was recently hypothesized that early environmental factors may have strong impact on call production. Here, the relative contributions of genetic background, gender, and early environmental factors on calling behavior in C57BL/6JOlaHsd and C57BL/6NCrl were studied by using an embryo-transfer procedure. The results show that these sub-strains differ in the amount of calling and specific call features, like call frequency and amplitude. The embryo-transfer procedure indicated that the observed differences in the amount of ultrasonic calling are dependent on the dyadic interaction between mother and pup. Conversely, call features were primarily dependent on the genotype of the pup. Thus, call frequency and frequency modulation were solely dependent on the pup, i.e. its genotype and gender. However, there was one exception, namely call amplitude, which was solely dependent on the genotype of the mother, i.e. on early environmental factors. Furthermore, it was shown that particularly changes in call amplitude might be of high functional relevance, since a sub-strain dependent preference towards pups emitting calls with high amplitudes was observed. In total, it can be concluded that both genomic and nongenomic factors can tune calling behavior in mouse pups.     

Variability in "spontaneous" maternal behavior is associated with anxiety-like behavior and affiliation in naïve juvenile and adult female prairie voles (Microtus ochrogaster)

Juvenile female prairie voles (Microtus ochrogaster) are spontaneously maternal, while virgin adult females show significant variability in their response to first pup exposure, ranging from infanticidal to full maternal behavior. In the present study, we investigated whether differences in anxiety-like behavior and affiliation are associated with juvenile-adult and adult individual differences in the response to pups. Forty juvenile (19-20 days) and 42 adult (60-90 days) female prairie voles were exposed to pups for the first time and tested for maternal behavior, anxiety-like behavior (elevated plus maze, open field), and affiliation toward age-matched, same sex conspecifics. Juveniles displayed less anxiety-like behavior, were more affiliative to unfamiliar conspecifics, and interacted with pups more positively than adults. Adults that displayed maternal behavior spent less time immobile, made more crosses through the center of the open field arena, and were more affiliative than adults that attacked the pups. This suggests that lower locomotion or exploration in a novel environment and poor affiliative behavior are negatively associated with maternal responsiveness in female prairie voles.