Maternal Contact Research Articles

Behavioral and neural correlates of postnatal olfactory conditioning: I. Effect of respiration on conditioned neural responses

Following olfactory classical conditioning, infant rats exhibit a preference for the conditioned odor and exhibit enhanced uptake of focal 14C 2-deoxyglucose (2-DG) within the olfactory bulb. The present experiments assessed the role of respiration on the expression of the enhanced 2-DG uptake response. Pups were conditioned from postnatal day (PN) 1–18 with an olfactory stimulus paired with a reinforcing tactile stimulus which mimics maternal contact (Odor-Stroke). Control pups received odor only or tactile stimulation only. On PN 19, pups received 1 of 3 tests: 1) a two-odor choice test, 2) an odor/2-DG test with normal respiration allowed, or 3) an odor/2-DG test with respiration experimentally controlled. The results indicated that: 1) Odor-Stroke pups learned the conditioned odor preference, 2) Odor-Stroke, normally respiring pups exhibited enhanced olfactory bulb 2-DG uptake when compared to control pups No difference in respiration rate was detected between groups in normally respiring pups. 3) Odor-Stroke pups whose breathing was experimentally controlled exhibited enhanced olfactory bulb 2-DG uptake when compared to control pups with an identical number of respirations. Together, these results demonstrate that modified respiration during testing is not required for the expression of a modified olfactory bulb response to learned attractive odors. Therefore, the data suggest that the olfactory system itself is modified by early learning.

Changes in Family Function and Relationships in Children Who Respond to Methylphenidate

Effects of methylphenidate on family function and relationships were assessed in boys 6 to 10 years of age presenting with overactivity and/or defiance. Functioning and relationships improved among the families of the 18 children whose behavior improved significantly, but not among families of the 17 nonresponders. Among responders, there was increased maternal warmth, decreased maternal criticism, greater frequency of maternal contact, and fewer negative encounters with siblings. No significant changes occurred in the frequency of paternal contact, efficiency of parental coping, or interparental consistency. Families of children who respond to methylphenidate are likely to be more amenable to other types of intervention than before treatment.

The Social Ecology and Early Parenting of Caucasian Adolescent Mothers

Social characteristics, maternal behaviors, and the home environments of Caucasian adolescent and nonadolescent mothers were investigated in a sample of 50 primiparous low- and middle-class women and their 4-month-old infants. The mothers were interviewed about their child-care network and about stressful life events that may have occurred since the infant's birth. The HOME inventory was completed and videotapes of 2 hours of home observations were coded to assess maternal proximity, verbalizations, activity, and physical contact with the infant. Interview data indicated that adolescent mothers relied more frequently on other teenagers and other network members for help in child care than nonadolescent mothers. In addition, they also received more frequent support from their mothers and less frequent help from their partner's and partner's mother and siblings than nonadolescent mothers. During the home visit, they were less verbal with their infants and scored significantly lower on the Responsiveness and Maternal Involvement subscales as well as on the total HOME inventory; these results were replicated on subgroups matched for socioeconomic status, emphasizing the unique social context and parenting practices of teenage mothers.

Young children as a probable source of maternal and congenital cytomegalovirus infection.

To identify possible sources of cytomegalovirus infection in pregnant women, we studied seven families with a recent case of congenital or maternal cytomegalovirus infection and a history of maternal contact with a young child shedding the virus. We used restriction-endonuclease techniques to compare the DNA of viral isolates collected from family members. Five families contained an infant who had congenital or perinatal infection, a mother who had had evidence of primary infection during her most recent pregnancy, and a child less than three years of age who was excreting cytomegalovirus. All five of the young children attended day-care centers at least part-time. In each of these five families, strains from family members were identical, and it is most likely that the toddler-aged child was the source of the virus for both the mother and the fetus or infant. In two other families, acquisition of cytomegalovirus by children in a day-care center was followed by seroconversion in the mother along with excretion of a strain of the virus identical to that in her child, as demonstrated by restriction-endonuclease analysis. Five of the seven fathers were tested for antibody to cytomegalovirus; four were seronegative, ruling them out as a source of infection in the mothers. These results not only strengthen evidence for the transmission of cytomegalovirus from child to mother but also indicate that infections acquired by a mother from a child can be transmitted to her fetus.

Maternal contact inhibits pituitary-adrenal stress responses in preweanling rats.

Three experiments examined psychological factors which inhibit pituitary-adrenal activity in 12-, 16-, and 20-day-old rats. Infant rats were placed in heated novel test arenas for 30 min--a treatment which increases corticosterone secretion--and were presented with different appetitive stimuli in order to determine whether these stimuli inhibit this increased hormone secretion. The first experiment was a factorial combination of two conditions: suckling an anesthetized dam and milk ingestion through an intraoral cannula. At all ages, suckling inhibited corticosterone secretion but milk ingestion did not, nor was there an interaction of these factors. In the second experiment, the importance of suckling was assessed by allowing pups' contact with an anesthetized dam either with or without the opportunity to suckle. At all ages, contact with suckling and contact alone were equally effective in inhibiting corticosterone secretion. The third experiment asked whether contact with a lactating female is necessary for pituitary-adrenal inhibition or whether more distal cues associated with lactation are sufficient. Pups were tested under one of four treatments formed by a 2(Lactating vs. Virgin Female) X 2(Contact vs. No Contact) factorial design. At all ages inhibition of corticosterone secretion occurred only in animals which were allowed contact with an anesthetized female. Lactating and virgin females were equally effective for the 12- and 16-day-old pups, but contact with a virgin female was less effective for the 20-day-old pups. These findings indicate that neuroendocrine mechanisms subserving inhibition of the pituitary-adrenal system exist during the preweanling period in the rat, and suggest the possibility of maternal regulation of this physiological system during development.

Effects of feeding and light cycles on activity rhythms of maternally isolated rat pups

Motor activity of infant rat pups was measured continuously between days 3 and 18 of postnatal age. Mother-reared rats on a 12:12 LD cycle exhibited significant rhythmic activity in the circadian range as early as day 5 of postnatal age. Some of the pups reared in isolation from maternal and sibling contact and kept on 12:12 LD cycles, feeding cycles, or combinations of feeding, temperature, and LD cycles also showed rhythmic activity but it was less persistent and of a lower amplitude than the rhythms of the mother-reared group. In the isolated rat pups nocturnal partitioning of activity was strengthened in the presence of both a light-dark cycle and a feeding cycle but only when the feeding resembled more natural nursing rhythms. In animals kept on constant light and a feeding cycle, activity occurred slightly more often during the 12-hr interval of decreased food intake. The addition of a temperature cycle—cooler nocturnal temperature—decreased the proportions of nocturnal motor activity. These results indicate that feeding and light-dark cycles may contribute to the synchronization of activity rhythms during the early postnatal period.

Offspring of women with nonorganic psychosis: mother-infant interaction at three-and-a-half and six months of age.

Mother-infant interaction during feeding and in an unstructured play situation was studied in the home at 3.5 and 6 months of age in index mother-infant pairs in which the mother had a history of nonorganic psychosis (n = 48 and 52 at 3.5 and 6 months, respectively) and in demographically similar control pairs (n = 80 and 79). Interaction was significantly more negative in index than control cases at both ages, index cases showing decreased maternal and infant social contact and reduced maternal sensitivity to the infant's needs. Schizophrenic and Cycloid groups evidenced more negative interaction characteristics than did their matched controls, while the Affective group was not generally more negative than its controls.

Analysis of appetitive motivation in preweanling rats: Application of bromocryptine mesylate

Two experiments investigated discrimination learning with preweanling rats (Rattus norvegicus) following different experimental deprivation treatments. In Experiment 1, 10- to 11-day-old Sprague-Dawley rats were deprived for 24 h of either nutrients and maternal contact through placement in an incubator or only nutrients by placement in the nest of a bromocryptine mesylate-treated dam. Bromocryptine mesylate inhibits prolactin release and thereby prevents lactation with only minimal effect on maternal behaviors. After the deprivation period, pups were trained to perform a spatial discrimination for milk infusion into the oral cavity or for the opportunity to suckle the dry nipples of an anesthetized dam. The results revealed, irrespective of deprivation treatment, that pups failed to acquire a simple T-maze spatial discrimination for milk reward although they rapidly learned to approach and locate an anesthetized dam to suckle. Experiment 2 followed up with a different procedure. Results indicated that during bouts of suckling rat pups preferred an active, lactating dam letting down milk to an identical dam not letting down milk due to her pretreatment with bromocryptine mesylate. These results illustrate a constraint on learning which affects immature rats. The capability to learn on appetitively motivated spatial discrimination appears intricately tied to the context in which training occurs. Results are discussed according to how the organism's expectancy can mediate performance.

Thermal control of maternal contact bouts: The interbout interval

Cooling mother rats by means of sodium salicylate injections did not curtail the intervals between maternal contact bouts. To the contrary, the interbout intervals were prolonged, suggesting that the relief from hyperthermia is a necessary but not a sufficient condition for the reinitiation of pup contact by mother rats. The ability of sodium salicylate to suppress maternal temperature suggests that pyrogenic and lactational increases in temperature may have some common feature.

Effects of restricted maternal contact in neonatal rats on sexual behaviour in the adult.

Rats, deprived of maternal contact and nutrition every alternate day starting on day 5 of life, attained a body weight at 45 days of age which was 50% of that of rats which had free access to maternal contact and nutrition. After 55 days of unrestricted food availability the body weight of the neonatally deprived rats was approximately 15% lower than that of the controls. Malnourished female rats showed normal behavioural oestrous cycles and became pregnant and lactated normally as young adults. After ovariectomy they showed higher lordosis quotients in response to treatment with oestradiol benzoate and progesterone than controls but lost less body weight in response to treatment with oestradiol-filled constant-release implants. Malnourished male rats ejaculated less frequently than controls in tests with sexually receptive female rats but this difference disappeared with repeated testing. The malnourished males showed longer ejaculation latencies and had somewhat higher serum concentrations of LH than controls after castration and treatment with testosterone-filled constant-release implants which reduced serum androgen concentrations to about 30% of the intact level. The results show that rats are capable of sustaining a rather severe neonatal nutritional deprivation without losing the capacity for essentially normal mating behaviour in adulthood.

Effects of pup sucking behaviour on inhibition of sexual behaviour and ovulatory secretion of LH in lactating rats.

The time-interval between parturition and the display of sexual receptivity varied between 13.5 +/- 0.7 and 35.9 +/- 2.5 days in rats with litters of between 1 and 24 pups. Body weight gain decreased and the avidity of pup sucking behaviour, measured by the latency before the pups, placed on the ventrum of an anaesthetized mother, attached to a nipple of the mother, increased as litter size increased. Litter-shifting procedures, which introduced asynchrony between the lactational age of the mother and the age of the pups, produced deficiencies in sucking behaviour and did not prolong the time-interval between parturition and the display of sexual receptivity by the mother. By keeping the lactational age of the mother in synchrony with the age of the pups and depriving the pups of maternal contact and nutrition every alternate day, the time-interval between parturition and the display of sexual receptivity by the mother was prolonged by 17 days, the avidity of pup sucking behaviour markedly enhanced and the body weight gain of the pups retarded in comparison with mothers and pups continuously living together. The results show that the display of the first postlactational behavioural oestrus and surge of pituitary LH secretion can be greatly delayed by an increase in the avidity of pup sucking behaviour.

Effects of maternal isolation on the development of activity rhythms in infant rats

Motor activity of infant rats was measured continuously from day 3 to day 18 of post-natal age. Mother reared pups maintained on a 12 hour light/12 hour dark cycle (MRLD) show a clear predominance of nocturnal activity on day 31 post conception (post-natal day 9 or 10), 4 days before eye opening. Nocturnal partitioning increases progressively to the time of weaning. Rats reared artificially and in isolation from maternal and sibling contact but in the same light/dark regimen (ARLD) fail to develop clear nocturnal partitioning of motor activity.

Neonatal responsiveness as a function of maternal contact and obstetrical drugs.

This work was designed to study changes in neonatal behavior during the first two days of life. Infants in Part I were from middle-class backgrounds. Half of these infants had unrestricted maternal contact during the first two days of life, the other half had contact with their mothers only at feeding time. Infants in Part II were from low socio-economic backgrounds. They were cared for entirely by the nursery staff during the first two days of life, so that differences in maternal style did not affect their behavior. Half of these babies were born to mothers who received 50 mg meperidine during labor, half to mothers who received no meperidine. This work provided evidence for the sensitivity of the neonate during the first two days of life. Both those infants who received unrestricted maternal contact and those whose mothers had received no obstetrical drugs exhibited more behavioral change than those who received low maternal contact or whose mothers had received meperidine during labor. High maternal contact and absence of obstetrical drugs also resulted in increased sensitivity to some environmental stimuli.

Diurnal cycle of mother-young contact in Norway rats

Mother rats maintained on a LD 12:12 photoperiod (lights on 0800 hrs) had longer contact bouts with their offspring during the day than during the night and maternal brain temperature peaked during the night. When the daily temperature cycle was suppressed by removal of adrenal and ovarian hormones, the daily maternal contact cycle was also suppressed. These data are consistent with a thermal model for the limitation of mother-young contact bout duration.

MATERNAL BEHAVIOR DURING INTERACTION WITH PREMATURE INFANTS

A trend from infant oriented to non-infant oriented maternal behaviors has been described during the breast feeding (bf) of term infants over the first month of life. The present study describes maternal contact behavior in 10 mother-premature infant (m BW 1078gm) pairs during early bf and play interaction. Play sessions were begun when each infant was medically stable and continued weekly until discharge (with 1 follow-up visit). Bf was begun at a mean of 1300gm (mean age = 33 days) and observed weekly to discharge. 11 separate maternal behaviors were scored by a time sampling technique from 10 min videotape recordings of the sessions. Preliminary results (from 6 dyads) suggest (1) the total number of maternal behaviors during play and bf remain constant over time for each mother; but (2) the types of maternal behavior changes, shifting from infant oriented to non-infant oriented. For example, in examinations of play interactions at three points in time (1st play, last-in-hospital, follow-up), the percentage of time spent in en-face holding decreases over time (Friedman (2 df) = 6.58; p<.05), while maternal looking away behaviors increase (Fr (2) = 6.33; p<.05). Four in-hospital breastfeeding sessions were also compared: over time, maternal looking away behaviors increase (Fr (3) = 12.20; p<.01). Results indicate that the developmental sequence of interaction between premature infants and mothers is similar to that which occurs with term baby-mother dyads.

Nonnutritive, thermotactile induction of filial huddling in rat pups.

Norway rat pups, 15 days of age and older, huddle preferentially with members of their own species. This normal filial response can be reassigned, however, by altering the olfactory characteristics of the mother. The present series of experiments was designed to isolate those aspects of maternal stimulation that establish the filial huddling preferences of rat pups. Results of two-choice huddling tests indicated that daily, 4-hr exposures to a perfumed foster dam induced filial preferences for odors associated with maternal care. Similar effects were also achieved with equal amounts of "mere exposure" (familiarization) to odors. Different kinds of odor-experience pairings were evaluated with a within-subject regime of alternating, daily exposures. It was found that preferences induced by maternal contact are stronger than those resulting from familiarization. We rejected the hypothesis that the nursing relationship is a necessary or contributory factor in the establishment of the rat's filial attraction; preferences for odors associated with a nonlactating foster mother were as strong as those derived from maternal contact that included nutritive nursing. Contact interactions with an inanimate, warm, scented tube induced preferences as strong as those induced by maternal care. It was concluded that thermotactile stimulation during mother-young interactions induces olfactory preferences in the weanling rat.

Changes in appetitive behavior in weanling-age rats: transitions from suckling to feeding behavior.

To help identify determinants of rat appetitive behavior during the weanling period, rat pups 17-32 days of age were studied in a Y-maze. One arm of the maze provided pups with the opportunity to suckle a lactating or nonlactating anesthetized female. The other arm always contained a familiar food, either liquid diet or ground laboratory chow. In some experiments the dam was separated from the food compartment by a thin gauze screen. In other tests maternal contact could be maintained in the feeding goal but suckling in that compartment was prevented by nipple involution. Age was the major determinant of choice, with more older animals choosing the food arm. Availability of maternal contact in the feeding compartment increased the percentage of rats that chose to feed by about 20% at all ages studied. Food quality, but not quantity, affected choice at each age, as did lactational status. Prior food, water, and maternal deprivation (2 or 24 hr) did not affect choice behavior at any age but did influence behavior in the goal box. These findings are discussed within the context of the changing demands faced by the rats during the weaning period.

Determinants of mother-young contact in Norway rats

Rat dams choose to care for their pups in a relatively warm area, apparently because they have an elevated thermal set point for the regulation of their body temperature. Since the duration of their contact bouts with their pups is limited by an acute hyperthermia that they experience while on the pups, their choice limits the time that they can spend with their pups. When dams could choose the temperature at which they cared for their young they spent only about half the time in contact with their offspring as did dams caring for their pups at the ambient temperature of the laboratory. We conclude that rat dams do not attempt to maximize the duration of their contact bouts with their offspring. Dams also do not attempt to minimize the amount of time that they spend away from their offspring. The duration of the intervals between contact bouts was influenced by the ability of the dams to dissipiate the heat gained during the contact bout with the pups. Again, dams did not seek out a cool area in which to spend their interbout intervals, preferring to remain in relatively warm areas. Their thermal preference facilitated the retention of their body heat and prolongation of the interbout intervals. Dams may return to the nest periodically for brief bouts during which the state of the pups is monitored. Pups were found to play both passive and active roles in modulating the overall pattern of maternal contact, for dams maintained contact with pups if the pups were cool, but failure to attach to the nipples soon after contact was established frequently led to rapid bout termination, particularly with warm pups. Contact is maintained if the pups are cool or if they attach to the nipples. Finally, it was found that pups could actively curtail interbout intervals by emitting ultrasonic vocalizations.

Determinants of suckling versus drinking in weanling albino rats: influence of hydrational state and maternal contact.

Preferences of weanling albino rats (15, 20, and 25 days of age) for nonnutritive suckling or drinking were determined using a Y-maze. Age, hydrational state, and the opportunity to contact the mother all influenced choice behavior. When tested in a maze that allowed continuous maternal contact in the "drinking-goal box," dehydrated rats chose to drink, while nondehydrated rats chose to suckle. Testing dehydrated rats in a maze that precluded maternal contact in the "drinking-goal box" eliminated drinking preference at all ages. These observations identify maternal presence as an important condition for the expression of drinking behavior during the weaning period and confirm our previous demonstration of dehydration's inhibition of suckling behavior.

Is Imprinting an Appropriate Model for Human Infant Attachment?

We generalized the results of animal imprinting studies to see if they predict the development of attachment in 28 polymatrically-reared, Kenyan Gusii infants, whose ages were 6 to 30 months. The hypotheses tested were: (1) there is a sensitive phase for attachment; (2) there is an association between age of infant attachment and developmental level, as well as between age of attachment and caregiving history. Our results provide evidence against a sensitive phase for attachment: infants throughout the age range of the sample showed shifts in attachments, and no particular epoch in the infant's caregiving history was found to be most important in predicting their first attachment figure. There was an association between age of attachment, and both developmental level, and caregiving history. Early attached infants had higher scores on the Bayley Mental Development Index and less maternal body contact than their age matched peers. We may conclude, therefore, that, so far as is at present known, the way in which attachment behavior develops in the human infant and becomes focused on a discriminated figure is sufficiently like the way in which it develops in other mammals, and in birds, for it to be included, legitimately, under the heading of imprinting so long as that term is used in its current generic sense. (Bowlby 1969: 223.)