Alison S. Fleming

Timidity prevents the virgin female rat from being a good mother: Emotionality differences between nulliparous and parturient females

Abstract In the first study, nulliparous and parturient female rats were tested daily for their responses to neonatal foster pups placed into the quadrant of the cage in which the adults were observed to spend most of their time on the previous day (designated the “preferred” quadrant). On the first few days of exposure to pups, nulliparous females tended to switch their preferred quadrant. This tendency to avoid pups ended before animals began to show maternal responses to pups. In contrast, parturient females did not switch the preferred quadrant and responded maternally on the first test day. To determine whether the differences in pup-avoidance shown by nulliparous and parturient females is due to emotionality differences between the two kinds of animal, in the next two studies nulliparous and parturient animals were compared in an emergence test, an open-field test and in their reactions to an unfamiliar conspecific introduced into their home cages. Nulliparous animals were found to be more fearful than parturient animals: they had longer emergence latencies, they ambulated less in the open field, they crossed proportionately fewer central, as opposed to peripheral, squares in the field, and they were more inclined to flee from the intruder. The implications of these emotionality differences for differences in maternal responsiveness between nulliparous and parturient females are discussed.

Amygdaloid inhibition of maternal behavior in the nulliparous female rat

Abstract In the first experiment, the effects of lesions of (1) the amygdala, (2) its major efferent projection system, the stria terminalis or (3) other non-limbic brain sites on the induction of maternal behavior in the nulliparous female rat were investigated. Animals sustaining lesions of either the amygdala or the stria terminalis became maternal more rapidly than did control animals. In the second study the effects of lesions to different portions of the amygdala on both maternal and fear responding were investigated. It was found that animals sustaining damage to the corticomedial amygdaloid nuclei became maternal more quickly than did animals sustaining either basolateral amygdaloid damage or no amygdaloid damage. Also in comparison to lesioned controls, animals with lesions of the amygdala showed reduced ‘fearfulness’ on a number of fear-mediated tasks. The third study attempted to interrelate fear responsiveness and maternal behavior by observing nulliparous animals with amygdaloid or stria terminalis lesions for their responses to unfamiliar foster pups placed daily into their preferred nesting quadrant. While control animals actively avoided pups placed into their nest sites (by moving their nest site to another quadrant of the cage), animals with amygdaloid lesions or lesions of the stria terminalis, did not. These results are interpreted to mean that nulliparous females generally do not respond maternally to pups because these females are, in general, more neophobic than parturient females and they tend to find pups and their novel odors, aversive. This aspect of their behavior is likely mediated by the amygdala. These data are discussed in terms of their relevance to the rapid maternal responsiveness normally shown by the female at parturition.

Mother rats bar-press for pups: effects of lesions of the mpoa and limbic sites on maternal behavior and operant responding for pup-reinforcement

This series of studies explored the operant response rates for pup-reinforcement of female Sprague Dawley rats that were either postpartum or cycling and sustained lesions of the medial preoptic area (mpoa), the lateral amygdala, the nucleus accumbens, or sham lesions. The last experiment tested the effects on operant responding of preventing direct access to pups in mpoa and sham-lesioned postpartum mothers. All animals were trained prior to mating on an FR-1 bar-press schedule to criterion (50 presses in 30 min) for a food (Froot Loops) reward in an operant chamber. At the end of pregnancy animals that were to be tested postpartum were provided in their home cages with six newborn foster pups; mother-litter interactions were observed on the last 3 days of pregnancy and throughout the postpartum period. On each of these same days after a period of separation from pups, females were tested in the operant box for delivery of rat pups. With each bar-press response, a rat pup rather than a Fruit Loop was delivered down a gentle shoot into the hopper. Non-postpartum, but maternal, multiparous animals who were showing estrous cycles were tested using the same procedures. The first and second studies showed that animals (both postpartum and as cycling multiparous animals) with mpoa lesions exhibited a significant reduction in bar-press rate for pup reinforcement in the operant box. In postpartum animals, amygdala lesions also produced a bar-press deficit, whereas nucleus accumbens lesions did not. All lesioned groups showed deficits in maternal responding in the home cage and deficits in retrieval in the operant box. These results indicate that systems associated with the mpoa mediate both the stereotypical maternal behaviors and pup-reinforcement. In contrast, the expression of home cage maternal behavior is dependent on the integrity of both the amygdala and nucleus accumbens, whereas operant responding need not be. These results indicate a dissociation of mechanisms mediating expression of the species-typical maternal behavior and pup-reinforcement.

Mothering begets mothering: The transmission of behavior and its neurobiology across generations

Early experiences exert their effects on adult parental behavior in part by altering the development of neurobiological mechanisms that initiate or support the initiation and sustenance of adult parental behavior. The effects of parental behavior on sensory, perceptual and emotional mechanisms in offspring constitute an experientially based mechanism by which neurobiological factors regulating behavior can be transferred from generation to generation somewhat independently of genetic endowment.

Changes in the marital relationship during the transition to first time motherhood: Effects of violated expectations concerning division of household labor.

This research combined cross-sectional and longitudinal analyses to evaluate the hypothesis that violated expectations with respect to sharing child care and housekeeping responsibilities contribute to womens dissatisfactions with their marital relationships after the birth of their first child. The cross-sectional sample consisted of 670 women who completed questionnaires at one of six phases in relation to birth. The longitudinal sample consisted of 48 women who filled out questionnaires late in pregnancy and at three periods postpartum. The results showed, consistent with previous findings, that women reported less positive feelings about their husbands during the postpartum period than during pregnancy, and that women reported doing much more of the housework and child care than they had expected. Moreover, regression analyses indicated, as predicted, that violated expectations concerning division of labor were related to negative feelings postpartum concerning some aspects of the marital relationship. Additional findings suggested that the negative implications of the birth of a baby for the marital relationship may not be as great as has been emphasized in previous literature, and that expectancy violations affect some parts of the relationship but not necessarily the core affective feeling.

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

The researchers examined the number of cells showing Fos-like immunoreactivity (Fos-lir) in the brains of hormonally primed parturient rat dams immediately following their first 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.

Rat pups are potent reinforcers to the maternal animal : effects of experience, parity, hormones, and dopamine function

These experiments were designed to determine whether the parity difference in robustness of a maternal experience reflects a parity difference in the reinforcing value of pups and factors affecting pup reinforcement. Postpartum and virgin animals were exposed for 15, 30, or 60 min to a novel environment (either a horizontally or vertically striped box) in the presence or absence of pups (or food stimuli) over a 2-, 4-, or 8-day period and then tested for their box preference in a two-choice conditioned place preference paradigm. Postpartum animals preferred the pup-associated box to the alternative box; nulliparous animals did not. The reverse pattern was found when food, rather than pups, was paired with the distinctive environment. However, if nulliparous animals were induced to become maternal either by induction procedures or by hormonal manipulation, they also preferred the pup-associated box. The effect was most robust when animals were stimulated to be maternal by hormones. Finally, pup reinforcement shares properties with other types of reinforcers in being dependent on the functional integrity of the dopamine system. Postpartum animals treated with cis(Z)-flupentixol, a dopamine antagonist, do not develop a conditioned place preference when pups are the reinforcing stimulus. Taken together, these experiments show that pups are potent reinforcers to the maternal animal, regardless of how animals become maternal, but that the hormones of parturition may augment these effects. They show further that pup reinforcement, like food or drug reinforcement, is dopamine dependent.

Experience with pups sustains maternal responding in postpartum rats

In these studies, we investigated the sustaining of postpartum maternal responsiveness through pup experience. In the first study, females were tested for maternal behavior at various times after pregnancy termination by Caesarean section (CS) at term. The females remained rapidly responsive to young for 7 days after pregnancy termination, but were no more responsive than virgins after 10 days. In the second study, females were allowed varying times of complete access to pups, beginning 24 hours after CS, and were tested for maternal behavior 10 days later. Females who retrieved and cared for pups for 30 minutes during exposure, remained rapidly maternal 10 days after CS; those who were allowed only 15 minutes of caring for pups did not. In the third study, females received 24 hours of exposure to distal sensory stimuli from pups, beginning 24 hours after CS. The proportion of females who became maternal within 24 hours of the beginning of maternal testing, 10 days after CS, was greater than that among females who received no exposure to pups.

Plasticity in the maternal circuit: effects of maternal experience on Fos-Lir in hypothalamic, limbic, and cortical structures in the postpartum rat.

To determine what brain sites are activated during the acquisition and retention of a maternal experience in postpartum rats, 3 studies examined the number of cells showing Fos-like immunoreactivity (Fos-lir) in brains following reexposure to pups and pup-associated cues in maternally experienced and inexperienced rats. Day 1 postpartum rats were given a 2- or 4-hr interactive experience with pups and then reexposed to pups in a perforated box, or to a neutral stimulus (perforated box only) 4 or 10 days later. At the end of the test phase, brains were prepared for immunohistochemical detection of Fos-lir. The brain sites showing the most consistent difference between experienced and inexperienced rats were the medical preoptic area, the basolateral amygdala, the parietal cortex, and the prefrontal cortex.

Transition to motherhood and the self: Measurement, stability, and change.

Different ways of conceptualizing and measuring change in attitudes during transition to motherhood are examined. A series of analyses was performed on data from a cross-sectional sample (N = 667) and a smaller longitudinal sample (n = 48) to demonstrate sound psychometric properties for 2 new scales and to show construct comparability across different phases of childbearing. For Childbearing Attitudes Questionnaire, results demonstrated equality of covariance for 16 scales and comparability of structure and meaning of 4 higher order factors--identification with motherhood, social orientation, self-confidence, and negative aspects of giving birth. For Mothering Self-Definition Questionnaire, results demonstrated equality of covariance of 5 scales and comparability of structure and meaning of a single higher order factor, interpreted as reflecting positive feelings about ones mothering characteristics. Analyses of correlations and mean differences identified areas of change and stability.