Mother rats interact differently with male amd female offspring.

60 lactating Long-Evans rats were observed to interact differently with male and female pups during the 1st 18 days postpartum. Differences were related to the gender composition of the home litter (GHL), to the sex of a single introduced pup, and to the sex of individual pups within the litter. Major differences were the greater time spent in licking the anogenital region of own male pups and the greater stimulation of anogenital licking by male foster pups, an effect that did not interact with GHL or age of pup. GHL interacted with day of testing to affect nest building and time spent near pups. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in patterns of pup care in Mus musculus: VI. Uses of segregating generations to dissociate behavioral units in retrieving.

A genetic analysis of 2 inbred strains of mice (NZB and CBA/H) and their Mendelian crosses conducted by C. Michard and P. Roubertoux (see record 1985-05922-001) demonstrated genetic correlates for 3 variables selected to measure retrieval behavior (first retrieval latency, move away without transporting pups, and nest with all pups). Because these behavioral phenotypes were intercorrelated in the 11 strains making up the population, the present study tested for correlations among their genetic correlates, that is, whether these variables were functionally dependent or were genetically correlated (pleiotropy, linkage). Findings indicate that the correlations are significant for the nonsegregating generations (parental strains NZB and CBA/H, and their F?s) and decrease significantly in at least some segregating generations (F? and backcrosses). The decrease in correlation implies that the genetic correlates of the 3 variables are different. The physiological mechanisms underlying the maintenance of pup care behavior are discussed. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses of virgin mice, and of maternal females, to normal and caesarian-section delivered pups.

Conducted 2 experiments in which Porton strain mouse pups were presented to a total of 100 male and female adult Porton mice. Significantly more mothers and virgin females retrieved pups to the nest than did virgin males. More virgin females than males licked pups, built nests, and assumed lactation posture. Differences were significant even if males that attacked pups were excluded from consideration. Latencies to 1st appearance of maternal activities were higher than reported by most other workers. Possible genetic strain differences in the response of virgin mice to pups are discussed. In Exp II pups delivered by caesarian section with placentas attached were used. More mothers than either virgin males or females cleaned and accepted pups, indicating that pup cleaning may be controlled by factors different from those influencing other maternal activities. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enclosure size and hormonal state affect timing of nest return in female meadow voles (Microtus pennsylvanicus).

We investigated 2 aspects of the hormonal regulation of maternal behavior in meadow voles (Microtus pennsylvanicus): (a) when the transition in maternal responsiveness from primarily hormonal control to regulation by pup cues occurs; and (b) the effect of housing enclosure size on maternal nest attendance in voles injected with a prolactin suppressant, cysteamine hydrochloride (150 mg/kg) on Postnatal Day 2. In Experiment 1, meadow voles required 96 hr of pup contact to finish the transition from hormonal to pup-mediated maternal behavior; a period longer than found in other rodents. In Experiment 2, females housed in larger enclosures spent less time with pups after drug injection, primarily because they increased the amount of time they stayed away from the nest each time they left. In contrast, drug-treated females in standard cages showed no change in their patterns of nest attendance, possibly due to the presence of salient cues from nearby pups. Under naturalistic conditions, a female vole’s hormonal state may regulate nest approach, and help establish the necessary alternation between leaving the nest (e.g., to forage) and attending pups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maternal behavior of mice with cingulate cortical, amygdala, or septal lesions.

Evaluated nest building, pup retrieving, and pup survival and growth in 11 primiparous female CF-1 strain mice and in 36 others with cingulate cortical, neocortical, amygdala, or septal lesions. Ss with neocortical or amygdala lesions showed little or no deficits in maternal behavior. Ss with septal lesions were severely impaired in all aspects of maternal care. These did not build nests, showed a variety of aberrant behaviors during pup retrieving, and their pups died or gained significantly less weight than those of controls. Ss with cingulate cortical lesions retrieved pups more slowly than controls, and retrieving deficits were correlated with the extent of retrograde degeneration found in the anterior thalamic nuclei. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of maternal behavior in nulliparous rats (Rattus norvegicus): Effects of sex and early maternal experience.

72 weanling female and male CD rats were exposed to either pups or pup-sized toys for 10 days beginning at 22 days of age in order to assess differences between pup-directed and toy-directed behaviors and to determine whether exposure to pups at this time increases susceptibility to maternal sensitization in adulthood. Adult sensitization involved exposing each S to pups for 10 days beginning at 78 days of age. Weanlings retrieved, licked, and lay over pups but not toys, and chewed on toys but not pups. Weanling males showed more pup retrieval than weanling females. Females and males preexposed to pups showed more retrieval and licking of pups in adulthood than those not preexposed to pups. Adult females were more fully maternal or nonmaternal than were adult males or weanlings of either sex, as indicated by their lower "partial retrieval" and "inconsistent retrieval" scores, their tendency to retrieve rapidly or not at all, and the greater correlation between their retrieval and nest construction. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial prefrontal cortex lesions in the female rat affect sexual and maternal behavior and their sequential organization.

Temporal sequences of sexual and maternal behaviors in female rats and their correlation with each other and with performance on a sensory-motor gating response inhibition task assessed by prepulse inhibition (PPI) were investigated following medial prefrontal cortex (mPFC) lesions. Following excitotoxic mPFC (n = 10) or sham (n = 9) lesions, sexual behaviors across the ovarian cycle were scored. After mating and parturition, maternal interactions were scored until pups reached postnatal Day 10. After resumption of the ovarian cycle, the female rats were tested for PPI. Compared with sham lesions, mPFC lesions impaired proceptive behaviors and some maternal behaviors (e.g., pup retrieval, pup licking) but did not affect others (e.g., nest building, pup mouthing). Lesions disrupted temporal sequences of solicitations (number of male orientations followed, within 4 s, by a level change) and pup retrievals (number of pup retrievals followed, within 5 s, by another retrieval). These sequential behavior patterns were significantly correlated with each other and with PPI. However, when PPI effects were partialled out, group differences were less strong, but persisted. This study demonstrated that mPFC manipulations affect actions rich in sequential structure in response to biologically relevant stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retention of maternal behavior in nulliparous and primiparous rats: Effects of duration of previous maternal experience.

Lactating primiparous and nonlactating pup-induced maternal nulliparous female CD rats were given 1, 4, or 9 days of maternal experience with rat pups before they were isolated from the young. 25 days later, Ss were reexposed to 3–8 day old foster pups, and latencies to show maternal behavior in the home cage and a T-maze test were scored. In the home cage, the latencies of all nulliparous groups were shorter upon reinduction. Comparisons of primiparous and nulliparous groups revealed that primiparous females (1, 4, and 9 days combined) carried a pup, crouched, retrieved, and grouped the pups and built a good nest faster than did nulliparous females (combined groups). The number of behavioral differences between specific primiparous and nulliparous groups decreased as the length of prior maternal experience increased. In the T-maze, latencies to retrieve a pup were shorter in primiparous females. Results indicate that the processes underlying establishment of the long-term retention of short-latency maternal behavior in these groups may be comparable. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermotaxis in golden hamster pups.

Notes that during the 1st 10 days of life, golden hamster pups lack physiological mechanisms for thermoregulation, and are thus ectothermic (i.e., they depend on heat from the environment). In their mother's absence, they conserve heat by burying together, thus reducing the amount of surface area exposed to the air. In the 6 experiments reported here, it is shown that the neonatal pup is extraordinarily sensitive to thermal gradients, and under conditions of heat loss pups demonstrate this sensitivity by moving rapidly away from cooler regions. Results suggest that the pup's high sensitivity is due to spatial and/or temporal integration of thermal information from all parts of its body. Such thermal responsivity would be sufficient to account for the pup's burying behavior in the nest. The thermotaxic response weakens after 8 days of age, probably as a result of decreasing thermal sensitivity and the maturation of competing responses. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Paternal behavior in the male Long-Evans rat (Rattus norvegicus).

Five studies examined the paternal behavior of monogamously housed male and female, individually housed male, and virgin male and female Long-Evans rats. Findings indicate that males cohabiting monogamously with females showed low levels of pup contact and parental behavior, and the frequency of these behaviors did not increase with experience, possibly because the lactating females kept the males away from the pups. When presented with pups in their own cage, sexually experienced and naive males did not differ in the latency or frequency of parental behavior, and both groups showed more parental behavior than monogamously housed males. Males that had formerly exhibited infanticide showed as much parental behavior as noninfanticidal males. The frequency of pup contact and parental behavior increased as the pups grew older. Although virgin males showed the same latency as virgin females to exhibit parental behaviors, females showed these behaviors more frequently than males. Results suggest that the responsiveness of noninfanticidal male rats to infants may depend on the test situation and the age of the infants. (45 ref) (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)     

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)     

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)     

Communal reproductive success in rats (Rattus norvegicus): Effects of group composition and prior social experience.

Compared the reproductive success and maternal behavior of sibling pairs of female Long-Evans rats (Rattus norvegicus) housed together from birth (familiar) to that of pairs of unrelated females housed apart during development (unfamiliar). Sires either remained in the colonies through weaning of their pups or were removed before parturition. Familiar animals reared more pups to weaning, were more likely to share in caring for pups, and were less likely to exhibit infanticide than were unfamiliar ones. The presence of males in cages with pups had no direct effect on the reproductive success of females, but female pairs housed with males spent less time than female pairs housed alone caring for pups together in a combined nest. Conflicting evidence for communal rearing in populations of wild rats may reflect differences in the genetic relatedness or early social experience of female rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of the social environment on parental behavior and pup development of meadow voles (Microtus pennsylvanicus) and prairie voles (M. Ochrogaster).

Parental behavior and pup development in meadow and prairie voles were examined. Social units were manipulated for the presence of fathers and of juveniles. Meadow vole mothers alone with pups showed less maternal care and spent more time resting than did mothers with juveniles or with fathers and juveniles. Pups reared only with mothers developed faster than did pups under other conditions. Number of animals in the social unit was negatively correlated with the rate of pup development. Meadow vole fathers and juveniles showed no parental care. In contrast, prairie vole mothers spent less time in the nest when both fathers and juveniles were present. Fathers assisted in rearing pups, and litters developed more rapidly when fathers were present. Juveniles remained in the natal nest and engaged in parentlike behavior. The findings relate to differences in the life history strategy for the 2 vole species. (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)     

Ruling out postnatal origins to attention-deficit/hyperactivity disorder (ADHD)-like behaviors in a seizure-prone rat strain.

Adult Fast (seizure-prone) and Slow (seizure-resistant) kindling rat strains exhibit divergent behaviors in paradigms relevant to attention-deficit/hyperactivity disorder (ADHD) in humans. Similar dissociations in rodent behavior have been linked to disparities in early life experience, suggesting that differential maternal care or postnatal interactions may underlie these behaviors. Consequently, the authors compared maternal behavior and preweaning pup weights in these 2 strains under control and cross-fostered conditions and examined its effects on subsequent adult offspring behavior. Ultimately, several distinct maternal behaviors were apparent between the 2 strains under control conditions, and some of those behaviors were then malleable by pup condition. Yet, in spite of the resultant complex maternal patterns across groups, all offspring showed behavioral phenotypes akin to their genetic strain. Thus, a specific postnatal environment is unlikely to underwrite ADHD-like behaviors in the seizure-prone Fast rats, which implicates a genetic or prenatal origin for the ADHD phenotype. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hormonal influences during the ontogeny of maternal behavior in female rats.

Two experiments involving a total of 223 female and 46 male CD rats examined the influence of ovarian hormones on sensitization latencies at different periods in ontogeny and on the olfactory inhibition of maternal behavior, maternal nest building, and pup retrievals from a T-maze extension of the home cage. Ss ovariectomized before puberty failed to show a decline in sensitization latencies when tested 3.5 wks postoperatively; Ss ovariectomized during and after puberty had significantly longer latencies than sham operates when tested 8 or more weeks later. Interrupting olfaction by intranasal ZnSO? reduced latencies. Ovariectomized Ss built less compact maternal nests, and fewer retrieved pups from a –T maze than did sham operates. Estradiol benzoate prior to pup exposure significantly reduced sensitization latencies of ovariectomized Ss, increased the proportion retrieving pups from the maze, and tended to increase maternal nest ratings. Findings indicate that ovarian hormones, primarily estrogen, exert a tonic facilitatory influence on maternal responsiveness, beginning at puberty. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hormonal interaction with stimulus situational factors in the initiation of maternal behavior in nonpregnant rats.

Previous hormonal studies have identified the hormonal and stimulus factors mediating the initiation of maternal behavior but have failed to reduce hormone-induced latencies of nonpregnant females to less than 1–2 days of continuous pup exposure. For the purpose of testing whether this delay is due to an olfactory-vomeronasal-mediated aversive reaction to pups like that found in untreated virgins, in 3 experiments estrogen-injected hysterectomized-ovariectomized (HO-EB) nonpregnant Charles River CD females were subjected to olfactory-vomeronasal deafferentation. Findings indicate that after HO-EB treatment, tendencies to initially avoid pup contact remain strong. Next, the hypothesis was explored that experiences during late pregnancy and/or parturition interact with hormonal priming to modify pup avoidance. Nonpregnant HO-EB females that had been exposed to pregnant-parturient females for 2 wks were tested under conditions simulating parturition. A high percentage rapidly initiated maternal behavior, but conditions during testing proved more important than prior exposure to pregnancy/parturition. Hormonally treated but not sham-treated females initiated maternal behavior most rapidly when first exposed to 1 newborn in the nest during the light phase. Prepartum caesarean-delivered females, however, responded maternally to 4 3–8 day old pups outside the nest, which indicates that additional factors operate at parturition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of lesion location within the medial preoptic-anterior hypothalamic continuum on maternal and male sexual behaviors in female rats.

Lesions of the medial preoptic-anterior hypothalamic continuum (MPOA-AH) disrupt both maternal behavior and male sexual behavior in the rat. To test the hypothesis that the 2 behaviors involve different neural systems in the MPOA-AH, small bilateral lesions were made in different anterior-posterior locations in the MPOA-AH of 41 maternal-sensitized Charles River female rats treated with testosterone propionate (.5 mg/day, sc), and the effects of these lesions on maternal and male sexual behaviors were assessed. Lesions centering in the MPOA disrupted maternal behavior (pup retrieval, nest building, and nursing), with anterior MPOA lesions being more effective (on pup retrieval and nest building) than posterior MPOA lesions. Lesions centering in the AH had little or no effect on maternal behavior. By contrast, male sexual behavior (mounting) was strongly disrupted by lesions in either the MPOA or the AH, with lesions in the rostral AH being most effective. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)