Rats bred for high versus low anxiety responses neonatally demonstrate increases in lordosis, pacing behavior, and midbrain 3 alpha, 5 alpha-THP levels as adults.

Duration and intensity of lordosis is mediated by actions of the progesterone (P) metabolite, 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-THP) at GABA-sub(A) receptors in the midbrain ventral tegmental area. Because rats selectively bred for infantile vocalizations may differ in endogenous 3 alpha,5 alpha-THP secretion, their sexual behavior, midbrain, and plasma 3 alpha,5 alpha-THP levels as adult rats in behavioral estrus was examined. Rats bred for high rates of infantile vocalizations had shorter latencies and intervals between intromissions and ejaculation, higher lordosis quotients and ratings, more pacing of their sexual contacts, and had higher P and 3 alpha,5 alpha-THP levels in plasma and midbrain than did rats bred for low rats of infantile vocalizations. Thus, levels of 3 alpha,5 alpha-THP in the midbrain are associated with differences in sexual behavior of these rats.

Maternal interactions prior to separation potentiate isolation-induced calling in rat pups.

The vocal response rates of 12-13-day-old infant rats to isolation in a bare test box are markedly increased by brief (1-min) periods of contact with an anesthetized dam prior to isolation, without affecting other isolation-induced behaviors. No such potentiation followed brief contact with littermates, novel test conditions, or experimenter handling. Brief contact with the dam was equally effective in the test chamber or home cage and was not further enhanced by repeated contact-separation sequences. Passive contact became ineffective when prolonged to 30 min, and potentiation could not be restored by providing the additional reinforcing events of continuous suckling, periodic oxytocin-induced milk letdown, or bouts of simulated maternal licking. However, when pups engaged in active interaction with an awake dam, potentiation was significantly enhanced following 1-, 10-, and 30-min periods. A working hypothesis is outlined for the adaptive role of potentiation in the development of the rat pup.

Behavioral mechanisms for active maternal potentiation of isolation calling in rat pups.

The ultrasonic vocalization (USV) response of the isolated infant rat is a promising model for studying the neurobiology of an early anxiety state, and potentiation of the USV response after brief maternal encounters is a newly discovered behavioral regulator of this state. Using experimental variations in the contexts and patterns of maternal behavior during pup encounters and manual simulations of maternal behavior, we have identified several specific mother-pup interactions that cause potentiation. When one of these, pup carrying, was manually simulated, potentiation followed only if a characteristic postural transport response had been fully expressed by the pup. These behavioral mechanisms and other data suggest hypotheses for the development and adaptive role of maternal potentiation.

Determinants of maternal child-rearing attitudes.

This study investigated the correlates of negative attitudes toward child-rearing among low-income urban black and Hispanic mothers. Using a randomized block procedure, 144 adolescents and 139 adults giving birth to healthy infants at a large metropolitan hospital were recruited. All consenting women were interviewed in the hospital within 2 days after delivery, using standardized measures of child-rearing attitudes, self-esteem, depressive symptoms, social support, and cognitive ability. Hierarchical multiple regression analyses showed that depressive symptoms, cognitive ability, and two demographic characteristics (maternal age and spoken language) accounted for 42.4% of the variance in negative childrearing attitudes during the postpartum period. The contributions of social support and self-esteem were no longer significant when the effects of the other psychosocial factors were taken into consideration simultaneously. The utility of early assessment of maternal attitudes as a marker for maternal risk status is addressed. The adaptive function of maternal attitudes and the implications for child-rearing practices are discussed in relation to the process of acculturation.

Elevated plus-maze behavior in adult offspring of selectively bred rats.

Animals sampled from the third generation (S3) of selective breeding of N:NIH strain rats based on ultrasonic vocalization (USV) rates in infancy (High, Low, and Random lines) were tested as adults on the elevated plus maze, a well-validated test of anxiety. Results showed that the Low line spent a greater percent of time in the open arms of the maze than High and Random (control) line animals, and a lower percent of time exploring from a relatively more protected position. There were no significant sex differences. The present study represents a probe into the processes at work during the early stages of selection for infant USV, and suggests that an adult measure of anxiety may be affected by selection for this infantile behavior.

Behavioral responses of juvenile rats (Rattus norvegicus) to neonates after infusion of maternal blood plasma.

Individual 18- or 30-day-old male and female Wistar rats (juveniles) were continuously exposed to 3-8-day-old pups for 5 days (sensitization) after intravenous (iv) infusion of maternal blood plasma (PL group) or 5% dextrose and water (IC group) through chronically implanted cannulas and were compared with nonhandled littermate controls (NHC group). The results showed complex interactions with sex and age of the animals tested, depending upon which maternal behaviors were examined. First, plasma from parturient females selectively increased retrieving behavior in 30-day-olds, and it was more powerful in females than in males. Second, on the first day, prior to sensitization, both PL and IC 30-day-olds showed higher frequencies of retrieving, crouching, anogenital licking, and contact than did nonhandled juveniles. Third, 30-day-olds that received maternal blood plasma continued to retrieve pups, with a latency peak for retrieving occurring at 72 hours, suggesting a long-term effect of plasma not seen in control animals. Fourth, 18-day-old subjects did not generally show effects of any of our manipulations, but they did show more nest building and contact behaviors than did 30-day-old subjects. Last, we found that the iv cannulation and infusion procedures led to a persistent dissociation of retrieving behavior from play in older animals and an integration of retrieving with crouching and licking regardless of whether maternal plasma or control infusion was administered. Retrieving behavior was associated with play behaviors (charge and pounce) in younger juveniles and in older, nonhandled control animals irrespective of treatment. For these animals, no integration of retrieving occurred with other maternal behaviors.

Hypothermic vocalizations of rat pups (Rattus norvegicus) elicit and direct maternal search behavior.

Emissions of ultrasonic vocalizations (USVs) by rat pups (Rattus norvegicus) during hypothermia have consequences for recovery and warming. We investigated the effects on dam behavior of USVs emitted by 3- to 11-day-old pups during hypothermia at rectal temperatures between 18 and 22 degrees C. Rat dams were tested in a Y maze with the home cage as a start box. Dams were given, in one condition, a choice between a hypothermic pup emitting USVs or a hypothermic, silent (anesthetized) pup and, in the other, a choice between 2 hypothermic, silent pups. Although differing in some acoustic properties from normal isolation calls, USVs emitted by hypothermic pups both elicited maternal search behavior and acted as directional cues for dams, in comparisons with control dams exposed only to silent pups. Thus USVs of pups recovering from extreme hypothermia have communicative as well as physiological significance.

Effects of biparental rearing on ultrasonic vocalization (USV) responses of rat pups (Rattus norvegicus).

This study investigated the influence of social rearing on ultrasonic vocalization (USV) responses of 11- to 12-day-old rat (Rattus norvegicus) pups in isolation to the presence or removal of an anesthetized adult. Pups were reared with the dam or dam plus a virgin female (aunt), their biological sire, or a castrated male. All pups reduced rates of USV in contact with anesthetized adults. Pups' USV rates after the adult's removal depended on their rearing experience. After removal of the dam, pups increased USV rates over baseline (potentiation). Pups reared with aunts potentiated USV after contact with adult females but suppressed USV after contact with males. Pups reared with sires potentiated USV after contact with sires or strange males. Pups reared with castrated males did not suppress USV after contact with castrates but did after contact with unfamiliar intact males. Thus, pups' differential USV responses to contact with passive adults in isolation can be acquired during prior rearing experience.

Reduction of rat pup ultrasonic vocalizations by the neuroactive steroid allopregnanolone.

Several of the recently characterized neuroactive steroids have been proposed to have anxiolytic effects in behavioral models when subjects were tested as adults. In this experiment, the effects on infant subjects were examined using the isolation distress model of anxiety. The production of ultrasonic vocalizations in week-old rat pups after maternal separation was assessed after ICV injections of vehicle or allopregnanolone (1.25-5 micrograms), or sham injections. Subjects were also observed for activity and behavioral responses and tested on three measures of sedation. Allopregnanolone caused a dose-dependent decrease in ultrasonic vocalizations, with increasing motor incoordination, ataxia, and turning at the higher doses. Sex differences were not observed for any measure. These results suggest the GABAA receptor binding site for neuroactive steroids is behaviorally active in neonates as well as in adults, and that the anxiolytic effects of the neuroactive steroids at this site may be dissociable from their sedative effects at low doses.

Development of ultrasonic vocalization responses in genetically heterogeneous National Institute of Health (N:NIH) rats. II. Associations among variables and behaviors.

In this study, the first three generations of laboratory-reared, 10-day-old pups of the N:NIH strain were examined for ultrasonic vocalizations (USV) rates in response to 2 min of isolation. The purpose of the study was to determine baseline USV rates in these progenitor (PR1, PR2, PR3) generations prior to selective breeding for high and low rates of USV. In addition, this study aimed to detect sources of variation in USV between and within generations and sexes, and factors associated with USV during isolation across the generations. Data were collected from 532 10 day-old pups in 81 litters. Evaluation by principal component analyses revealed four factors corresponding roughly to constructs indicative of: thermoregulation; maturity and exploratory behavior; distress/anxiety, in which USV consistently appeared; and activity. Different component structures for each sex suggested that USV may represent different dimensions of anxiety for component structures for each sex suggested that USV may represent different dimensions of anxiety for the sexes, with some degree of overlap. Nonetheless, all variables measured during isolation testing accounted for only a small portion of the variance in individual pup USV (less than 9%) at 10 days of age, when the effects of intercorrelations among all variables were taken into account. This suggests that variables currently measured do not represent a comprehensive model for the control of USV.

Development of maternal behaviors in prepubertal rats at three ages: age-characteristic patterns of responses.

Individual 18-, 24-, or 30-day-old male and female Wistar prepubertal rats (juveniles) were continuously exposed to 3-8-day old pups in order to determine developmental differences in the expression of maternal and other behaviors during the process of sensitization. The results that emerged from this study are as follows: Maternal behaviors are neither consistent nor integrated in their expression prepubertally; exposure to pups facilitates the emergence of some maternal behaviors in juveniles more easily than others, e.g., retrieving and anogenital licking more than ventral crouching or nestbuilding; there are age-related differences in the expression of different maternal behaviors, e.g., 24-day-olds retrieve more than at other ages; in our strain, few, if any, gender differences are apparent in the expression of maternal behaviors prepubertally; juvenile play behaviors (charge, pounce) are related to retrieving behavior in the context of exposure to pups. Overall, the results suggest that maternal behaviors are distinct developmentally and probably involve different mechanisms in prepubertal animals.

Potentiation of isolation-induced vocalization by brief exposure of rat pups to maternal cues.

Since their discovery in 1956, the highest rates of ultrasonic vocalization (USV) have been recorded from infant rats when first isolated in an unfamiliar place. We now report that peak USV rates can be doubled by allowing test pups a brief initial period of contact with their anesthetized dam (1-10 min) in the test chamber before isolating the pup by her removal. Potentiation of the isolation response was specific to the dam, for it failed to occur following initial contact with a group of 4 warm, anesthetized littermates. Control experiments showed that potentiation could not be attributed to thermal contrast, experimenter handling, general behavioral activation, novelty of maternal cues, or nursing deprivation. Furthermore, it did not occur when pups were taken for isolation testing directly from prolonged contact with their anesthetized dam in the home cage. Potentiation may be understood in terms of the communicative role of the pups' call and/or prior learning contingencies within the mother-infant interaction.

Early experience and maternal behavior in rats.

This study examined the effects of early experience (early weaning with group housing in sibling groups (EG), or early weaning plus social isolation (EI) from 14 to 24 days of age) on maternal, play, and social behaviors expressed during 5 days of sensitization at 24 days, and then later at 100 days of age. Our results showed that maternal behaviors at 24 days could be altered by these early experiences. At 24 days of age fewer EI animals retrieved compared with normally weaned controls (NW), but more showed play behavior in the presence of pups. EG animals showed intermediate levels of retrieving relative to NW controls, and no concomitant changes in play behaviors. When retested as adults, females in all groups showed similar levels of all maternal behaviors. But EI adults of both sexes showed persistent intrusion of play behaviors, and higher levels of rearing and undirected activity in the presence of neonates. Factor analyses revealed that previously sensitized adult males showed patterns of organization of maternal behaviors that resembled adult females rather than those shown by control males reared without sensitization experience. Previously sensitized females also showed a retention of the play behavior patterns characteristic of juveniles, not present in females without sensitization experience. These results show that social experience during the weaning period can affect the development of maternal and play behavior elicited by neonates during the juvenile period that persist into adulthood, and the juvenile sensitization experience exerts longterm effects on adult patterns of maternal behavior in both sexes.

Selective breeding for infant vocal response: a role for postnatal maternal effects?

N:NIH rats were selectively bred on the basis of high or low rates of ultrasonic vocalization (USV) response to isolation at 10 days of age (Brunelli et al., 1997: Dev Psychobiol 31:255-265). To examine the possibility of postnatal maternal effects in the generational transmission of divergent traits, pups were cross-fostered shortly after birth between dams of the two lines (Low- and High-USV). Controls were fostered to dams of the same line (in-fostered). Additional (population) control data were obtained from the entire 13th generation of the selectively bred lines. USV rates of cross-fostered pups in each line were not significantly different from rates of in-fostered pups of the same line. High USV line pups cross-fostered to Low USV line dams weighed significantly less than in-fostered pups, on the day of testing. The results provide no evidence for a postnatal maternal contribution to the USV phenotype. Prenatal and/or perinatal maternal effects have not been ruled out.

Ultrasonic vocalization responses of rat pups to acute separation and contact comfort do not depend on maternal thermal cues.

In order to assess the importance of maternal thermal cues in controlling the acute USV responses of rat pups to contact with her body (the contact comfort response) and to separation from her, we drastically altered maternal temperature by inducing severe hypothermia so that maternal rectal and flank temperatures averaged more than 20 degrees C below normal and 10 degrees C below ambient levels during testing. Isolated 12- to 13-day-old pups showed reductions in USV when these cold dams were presented and brisk USV accelerations when the cold dams were removed from the test chamber. These responses closely resembled those of other pups tested with warm (36 degrees C) anesthetized dams. No significant differences were found in pups' USV contact comfort responses to cold and warm dams. For acute separation, prior maternal thermal properties and other factors were found to modulate the relative intensity of the marked USV increase elicited by this event.

The effects of 24-hr maternal separation and of litter-size reduction on the isolation-distress response of 12-day-old rat pups.

We asked whether the mother-infant interaction acted over time to regulate the ultrasonic vocalization (USV) and activity responses of 12-day-old rat pups to isolation in a novel test area. In a series of four experiments, we found that 24 hr of maternal deprivation did not alter USV isolation responses, but that reduction of litter size to 4 pups from 8 markedly attenuated the USV response and increased weight gain, without effects on activity level. Ambient temperatures during 24-hr maternal separation were varied from 23 degrees to 35 degrees C without effect on subsequent USV responses, but activity levels were markedly reduced in pups separated at the low heat level. Possible mechanisms for maternal regulation of USV responses involving nutrient effects, altered processing of thermal stimuli, and the inhibition of thermogenesis by nutrient deprivation are discussed.

Developmental effects of selective breeding for an infantile trait: the rat pup ultrasonic isolation call.

This article describes how continued selection for divergent levels of the 10-day-old infant rat's ultrasonic vocal (USV) response to isolation affects the time course of development of that and other possible co-selected traits from 3 to 21 days postnatally. Since selective breeding for an infantile trait has not been reported before, we collected from colleagues a number of predicted outcomes that reflect the wide range of current opinion on the relationship between microevolutionary and developmental processes. After 15 generations of selective breeding, we found widely divergent USV responses between 10-day-old High USV line (300 USV/2 min) and low USV line (15 USV/2 min) pups. The developmental trajectory of USV responses at 3 and 7 days of age also was markedly altered in both these lines in comparison to the randomly bred controls, but was much less affected in 14-, 18-, or 21-day-old pups, contrary to all predictions. The development of other behavioral responses to isolation generally remained unaffected by the continued selection as did physical traits, measures of temperature regulation and classic developmental milestones. Only two traits showed evidence of co-selection: High line pups showed more urination/defecation in response to isolation from 10 days on, and more rapid ear canal opening at 10 days. These and other findings are presented and discussed in relation to the developmental and evolutionary concepts on which the different predictions were based.

Development of ultrasonic vocalization responses in genetically heterogeneous National Institute of Health (N:NIH) rats. I. Influence of age, testing experience, and associated factors.

The N:NIH strain of rats was developed by the National Institutes of Health to provide a maximally heterogeneous population as a base for selective breeding (Hansen & Spuhler, 1984). Using the N:NIH strain, this laboratory will selectively breed adult animals that exhibited extremes of high or low ultrasonic vocalization (USV) rates as infants. Because nothing was known about USV in N:NIH rats, we characterized the development of isolation-induced USV in the first generation of this strain born in our laboratory. In a longitudinal/cross-sectional study of pups tested at 3, 10, 15, and 18 days postnatally, N:NIH pups emitted their highest rates of USV at 3-4 days postnatally and calling remained high for 10 days before declining. USV rates were found to be a relatively environmentally stable behavioral trait in that repeated testing did not significantly affect the calling rates of either individuals or litters, and only at 3 days postnatal age did naturally occurring ambient temperature variations (6 degrees C range) significantly affect USV responses. Individual differences in USV responses emerged by 10 days of age that were not simply correlations of body weight or rectal temperature, and pups at that age showed isolation calling rates that were highly predictive of their response levels 5 days later.

Five generations of selective breeding for ultrasonic vocalization (USV) responses in N:NIH strain rats.

This article reports on early results from an ongoing selective breeding study in which rats were selected for different rates of ultrasonic vocalization (USV) in response to isolation. Using the N:NIH strain, all litters were screened at 10 (+/- 1) days of age in a 2-min isolation test, and those males and females with the highest (or lowest) rates in each litter were selected for later breeding with like breeders from unrelated litters. A Random line (unselected control) was also bred. In the first selected generation (S1), the Low line diverged from Random line controls, and has maintained significantly lower rates over all generations since. In the S3 generation, the High line diverged significantly from Random line controls, and has shown significantly higher USV rates in each succeeding generation. No line differences were found in other behaviors measured in isolation. Data from a small sample of S5 pups tested at postnatal Days 3, 10, 14, and 18 days showed that individual pups' rates of USV from Day 10 predicted those at Day 14, consistent with findings from an unselected generation. Ambient temperature, modulated by body weight, controlled USV at Day 3, whereas at Days 10 and 14 line accounted for most of the variance in USV. This is the first instance of laboratory selection occurring on the basis of an infantile trait.

The ontogeny of maternal potentiation of the infant rats' isolation call.

Previous studies have shown that preweanling rat pups double or triple their rates of ultrasonic vocalization (USV) when isolated immediately after brief periods of maternal interaction (potentiation). We studied the ontogenetic pattern of USV and other behavioral responses of pups to 3-min periods of isolation in a novel test chamber, from 5 to 25 days postnatal age, before, during, and after 1 min or 5 min of interaction with an anesthetized or an active dam. USV potentiation did not develop until 7-9 days postnatal, a week after the initial isolation and maternal contact quieting responses were well established. Potentiation reached a peak at 13 days, and then declined until all USV responses ceased after 21 days. Other behavioral responses to isolation were not enhanced by maternal interaction at any age. The distinct ontogenetic pattern of this unusual response to maternal separation has implications for understanding its mode of development and possible adaptive value.