Exposure to PCB 77 affects the maternal behavior of rats

Polychlorinated biphenyls are environmental contaminants known to affect neurobehavioral development in many laboratory studies using different animal models. Because of their bioaccumulation and long half-life they are a serious concern for our own species. The dioxin-like PCB congener 3,4,3',4'-tetrachlorobiphenyl (PCB 77) has estrogenic and anti-estrogenic properties, and has been shown to affect brain chemistry and behavior of developing rats when administered during gestation. Since many developmental outcomes in mammals depend upon the type of maternal care provided by the dams, we investigated the effects of two doses of PCB 77 (2 and 4 mg/kg administered during gestational days 6-18) on the maternal behavior of the treated dams. Both doses of PCB 77 reduced the amount of nursing time in which the dams displayed the high-crouch posture over postnatal days 1-6. In addition, the high dose increased the amount of maternal licking and grooming of the litters and the amount of time the dams spent on the nest. The high dose also increased pup mortality, and both doses reduced the weight gain of the litters during the first 6 days of life. These results document effects of PCB 77 on maternal behavior and serve to raise questions about the importance of maternal contributions to the developmental effects of this and similar contaminants.     

Exposure to PCB 77 affects partner preference but not sexual behavior in the female rat

In rats, exposure to the polychlorinated biphenyl congener 3, 4, 3′, 4′-tetrachlorobiphenyl (PCB 77) affects the brain and behavior of the offspring as well as the maternal behavior of the dams. In the present study, a cross-fostering design was used to examine the effects of pre- and/or postnatal exposure to PCB 77 on sexual behavior and partner preference in female rats, and to determine the role of altered maternal behavior in the mediation of these effects. Pregnant rats were treated with oil or PCB dissolved in oil (2 mg/kg b.w.) on gestation days 6-18 and then given pups that had been exposed to either the oil vehicle or PCB during gestation. As adults, the female offspring were tested for partner preference (that is, whether they preferred to spend time with a sexually receptive female or a sexually active male) and sexual behavior. None of the treatments affected female sexual behavior. However, both double exposure and postnatal exposure diminished the animals' preference for a male over a female stimulus, but partner preference was not affected by prenatal exposure alone. There were no significant correlations between the changes in partner preferences due to PCB exposure and the amount of maternal grooming and licking received by the treated litters. Thus, female partner preference is affected by early PCB exposure, and the effects depend upon whether the exposure is in utero or via lactation and may be independent of any effects of the PCB on maternal care.     

Developmental exposure to polychlorinated biphenyls affects sexual behavior of rats

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that have the potential to disrupt reproduction through a variety of different pathways. In the present study, we investigated the effects of fetal and lactational PCB exposure on reproductive behavior in male and female laboratory rats. These pregnant rats were injected daily with either 2,4,2',4'-tetrachlorobiphenyl (PCB 47) at the dosage of 1 or 20 mg/kg body weight or 3,4,3',4'-tetrachlorobiphenyl (PCB 77) at the dosage of 0.25 or 1 mg/kg body weight or sesame oil (control group) from gestational days 7 to 18. Offspring were then tested for sexual behavior as adults. Exposure to both PCB 77 and PCB 47 reduced the level of sexual receptivity in the female offspring, but had no detectable effects on the sexual behavior of the male offspring. In addition to changes in adult sexual behavior in the females, both PCBs produced a significant increase in the females' anogenital distance, suggesting a modification of androgen responsiveness in females resulting from PCB exposure during development. Similar effects were not seen with the males.     

The effects of paraventricular hypothalamic lesions on maternal behavior in rats

The present study was undertaken to determine whether the disruptive effects of knife cuts which sever the lateral connections of the medial preoptic area (MPOA) on maternal behavior are mediated by interfering with the output of the paraventricular hypothalamic nucleus (PVN). Postpartum rats received one of the following: Knife cuts severing the lateral connections of the MPOA; knife cuts severing the lateral connections of the PVN; radiofrequency lesions of the PVN; sham lesions or knife cuts. Only females that received knife cuts severing the lateral connections of the MPOA showed severe deficits in maternal behavior. These results indicate that the influence of the MPOA on maternal behavior is not mediated by the output of the PVN. Since the PVN is the major source of oxytocin input to other brain regions, these results also suggest that oxytocinergic neural pathways are not critical for postpartum maternal behavior. Another important finding was that females with MPOA knife cuts that did not retrieve their young were capable of hoarding candy, suggesting that the retrieval deficit was not the result of a general oral motor deficit.     

Repeated cross-fostering affects maternal behavior and olfactory preferences in rat pups

Disturbances in early mother–infant relationships are strongly associated with changes in the development of a number of physiological and behavioral systems in the neonate that can create a complex change in patterns of vulnerability throughout life. Institutionalized children, despite receiving adequate care, display important behavioral changes in adult life, and such changes are strongly associated with a lack of selective and consistent attachment to the maternal figure in early life. It is not yet clear how human adoption processes alter the mother–infant relationship early in life. Here, to mimic the situation of human adoption and explore the impact on the formation of attachment between the infant and a caregiver, we use a repeated cross-fostering (RCF) model in rodents in two postnatal periods, postnatal days (PND) 1 to 3 (early RCF) and 9 to 11 (late RCF). Early exposure but not late exposure to RCF reduces the pups' preference for the odor of the mother figure. Moreover, early exposure and slightly later exposure to RCF reduce maternal care and motivation in collecting the pups and bringing them to the nest. The RCF protocol creates an unstable environment for mother–pup interaction, but it seems to affect learned attachment to the mother only when it occurs during the corresponding sensitive period of development.     

Olfactory bulbectomy: influences on maternal behavior in primiparous and multiparous rats

Bilateral olfactory bulb ablation resulted in deficits in several components of maternal behavior in lactating, primiparous female rats. These females frequently cannibalized pups shortly after parturition. Furthermore, bilaterally bulbectomized, primiparous females spent less time nursing their pups and retrieved fewer pups than unilaterally bulbectomized or sham-operated females. In contrast to the situation in primiparous females, in multiparous females bilateral bulbectomy failed to influence any parameter of maternal behavior.     

Induction of maternal behavior in the virgin rat by lactating-rat brain extracts

Maternal behavior was induced in naive virgin rats by treatment with extracts of brain obtained from lactating mothers killed on day 16 of lactation. Neither blood nor kidney extracts from the same lactating rats were effective in initiating the maternal response. When the recipients were injected with extracts of brain prepared from virgin rats or from primiparous rats killed on postpartum day 1, none of the animals displayed maternal behavior during the 72 hr of trial. The results suggest the development, within the brain of the lactating mother, of a factor capable of inducing maternal behavior in a non-lactating rat. The “factor” appears to be located in the microsomal and soluble fraction of the brain homogenate.     

Disruption of maternal behavior in rats with lesions of the septal area

Rats given septal lesions prior to mating did not build nests or nurse their pups. During retrieving tests they carried pups about the cage repeatedly and dropped them in scattered locations. Virgin rats induced to be maternal by housing with foster pups showed similar, but less marked, behavioral deficits. Rats administered septal lesions after parturition became hyperresponsive, ceased all maternal behaviors, and cannibalized their pups. The results indicated that the aberrant maternal behaviors shown by rats with septal lesions did not result from alterations in hormonal status. It was concluded that the lesions disrupted the typical pattern or sequence of maternal activities and that the deficits were probably related to an enhancement of response perseveration.     

Effects of ethanol consumption on maternal behavior in the female rat

Female rats consuming 30% ethanol (v/v) for 30 days prior to and during gestation, and during the post-partum period were tested for maternal behavior with either their own pups or pups provided by normal foster mothers. When tested with their own pups, ethanol consuming females displayed significant deficits in maternal behavior. However, when a second group of ethanol consuming females were tested with normal pups, the females displayed maternal behavior comparable to that of control females. These data suggest that gestational ethanol consumption per se does not produce a deficit in the ability to display maternal behavior. Possibly, due to ethanol related changes in the pup's own characteristics, they became a less attractive stimulus in eliciting the display of maternal behaviors from their mothers.     

Neonatal bonadal hormones: effect on maternal and sexual behavior in the male rat

Neonatal exposure of rats to androgen results in alteration of adult sex behavior and gonadotropin release. Other sexually dimorphic adult behaviors have also been shown to be dependent, either in part or in full, upon exposure to androgen neonatally. The present study was conducted to determine the effect of neonatal androgens in organizing the brain of the male rat (Long-Evans strain) with regard to maternal behavior. The results indicate that males neonatally exposed to androgen exhibit poor maternal behavior as adults when compared to males castrated at birth and males receiving gonadotropin antiserum in infancy. The males castrated at birth and males receiving gonadotropin antiserum in infancy, when primed with estrogen and progesterone, showed high levels of female sexual behavior when compared to controls. In terms of male sex behavior, the control groups performed slightly better than the males castrated at birth and males receiving antisera in infancy. The results suggest that the neonatal pituitary gland has an indirect role in the process of sexual differentiation.     

Effects of adrenalectomy on maternal behavior in pregnancy-terminated rats

Latencies to the onset of maternal behavior were measured in 16 day pregnancy-terminated rats. Three conditions were tested and included hysterectomy-ovariectomy (HO) with testing beginning 24 hr after surgery and HO plus a concurrent subcutaneous injection of 5 μg/kg estradiol benzoate or hysterectomy only (H) with testing starting 48 hr post-operatively. Within each condition, one group was also adrenalectomized while another was sham-operated at the same time as HO or H. There were no differences in the distribution of latencies between the adrenalectomized and sham-operated controls in any of the conditions although a significantly greater percentage of the sham adrenalectomized H animals were maternal by Day 2 of testing. It was concluded that adrenal secretions are not essential for the onset of maternal behavior in pregnancy-terminated animals while they may add a facilitatory effect following H only.     

Tail-pinch facilitates onset of maternal behavior in rats

Previous reports indicated that non-maternal female rats display a component of maternal behavior, namely, ano-genital licking of pups during, but not after a mild tail-pinch. The present study extends these findings and demonstrates that intermittent applications of brief tail-pinches accelerate in a dose-dependent pattern, the onset of all components of pup-stimulated maternal behavior in virgins. This suggests that the behavioral effects of tail-pinch stimulation outlast the pinch period and are cumulative.     

Estrogen-induced maternal behavior in hysterectomized-overiectomized virgin rats.

A single injection of 100 μg/kg estradiol benzoate (EB) either alone or in combination with 0.5 mg progesterone resulted in a significant reduction in the latency for the onset of maternal behavior in hysterectomized-ovariectomized virgin rats as compared to the latencies of groups which either remained intact or were hysterectomized, hysterectomized-ovariectomized, hysterectomized-ovariectomized and treated with 20 μg/kg EB, or ovariectomized-sham hysterectomized and injected with 100 μg/kg EB. In contrast to recent research, there was no shortening of the maternal latencies when ovariectomy or combined hysterectomy-ovariectomy was performed 8 weeks prior to testing while the administration of EB 8 weeks postoperatively was still effective in stimulating short-latency maternal care in hysterectomized-ovariectomized females and increased the percentage of ovariectomized sham hysterectomized animals responding maternally. It was concluded that estrogen is capable of inducing, not suppressing, maternal behavior in virgin rats and that the uterus may play an important but as yet undetermined role.     

Failure of pituitary transplants to facilitate the onset of maternal behavior in ovariectomized virgin rats

Ovariectomized virgin female rats received two pituitary glands grafted under a kidney capsule in an attempt to assess the effect of chronically increased plasma levels of prolactin on the onset of maternal behavior. When exposed to fresh foster pups on 6 consecutive days, only 5 out of 12 of these females and 2 out of 12 females in an ovariectomized control group displayed maternal behavior, whereas all 4 rats in an additional control group of lactating mothers were maternal throughout these tests. Ovariectomized animals which failed to become maternal then received subcutaneous injections of either 10 μg estradiol benzoate (EB) or oil on two consecutive days, and 1 day thereafter foster pups were again presented to these females for 18 hr. Significantly more EB-treated females displayed maternal behavior, regardless of whether or not they bore pituitary grafts, suggesting that estradiol and not prolactin may be essential for the rapid onset of maternal behavior in parturient rats.     

Male copulatory behavior and female maternal behavior in neonatally bulbectomized rats

Olfactory bulbs were destroyed in six-day-old male and female rats, and anosmia was confirmed in adulthood. Bulbectomized males initiated apparently normal sexual activity at the same age as did control animals. As virgins, bulbectomized females did not injure foster young; when allowed to mate and deliver young, they displayed apparently normal maternal behavior. It was concluded that neonatal olfactory bulbectomy does not preclude the development of essentially normal copulatory behavior in the male rat and maternal behavior in the female rat.     

The effects of sensitization and social isolation on maternal behavior in the virgin rat

Thirty-three out of 67 virgin Sprague-Dawley rats spontaneously retrieved 5–10-day-old foster pups in a pretest. The 34 rats not responding immediately were randomly divided into three groups to study the effects of direct and exteroceptive exposure to young on the induction of maternal behavior. Retrieving, licking and crouching behavior appeared in a higher proportion of cage rats (n = 12) which received a fresh group of pups to live with throughout each day than in control rats (n = 10) that had only 5 min daily exposure. However basket rats (n = 12) also became maternal merely by exposure to exteroceptive stimuli from pups living in baskets fixed to the cage wall. In a second experiment, virgin rats that spontaneously retrieved pups were socially isolated for 2–4 weeks. As a result, a 50–60% decrease in the number of rats showing retrieval was found not only in an independent sample of rats (n = 20) but also in a related group (n = 13) that practiced the response in the week between a pretest and Week 2 in isolation. Therefore, the results demonstrate that exteroceptive cues from pups alone may be sufficient to induce maternal behavior in nonspontaneously retrieving virgin rats, and that isolation from pups and other social stimuli reduce retrieving behavior in initially responsive virgin rats.     

Pregnancy duration and fetal number: Effects on maternal behavior in rats

It was shown previously that in rats postpartum mothers are much more likely than pup sensitized virgin mothers to retrieve pups from a T-maze extension of their home cage. In the present experiment, the physiological basis of this difference was explored further by inducing maternal behavior (retrieving, crouching, licking) following hysterectomy-ovariectomy on Days 21, 16, and 10 of pregnancy. In general, the longer the duration of pregnancy, the shorter the latency to become maternal and the greater the propensity to retrieve pups from the T-maze. An additional group of Day 16 pregnancy terminated rats carrying six or fewer fetuses were not impaired with respect to onset of maternal behavior compared to their large-litter counterparts, but only a small percentage of these females retrieved in the T-maze. These findings suggest that both the late pregnancy estrogen surge and progesterone withdrawal after its peak and sustained secretion enhance maternal responsiveness and that T-maze pup retrieval (but not onset latency) may be additionally affected by the level of placental hormones.     

Effects of high fat,protein supplemented diets on maternal behavior in rats

Female albino rats were maintained on either chow, a 25% fat, protein supplemented diet or a 45% fat, protein supplemented diet during breeding, gestation and lactation. Materanal behavior was assessed using observational techniques. Maternal bodyweight of the females on the high fat diets was not different from females on chow. Reproductive success, as indicated by pregnancy and pup survival, was reduced in the females on the 45% fat diet. However, unlike offspring of obese dams, pup growth was enhanced in most of the offspring of the dams on the high fat, protein supplemented diets. The dams on these diets showed more postural nursing, less non-postural nursing, more pup grooming and were observed more frequently with a majority of their pups. These dietary differences in maternal behavior did not appear to be necessarily due to differences in the body weight of the pups.     

Effects of intranasal zinc sulfate on open field and maternal behavior in female rats

Nulliparous white rats were injected intranasally (IN) or intraperitoneally (IP) with zinc sulfate (Zn) or were injected IN with saline or air, and were induced to show maternal behavior through continuous pup exposure begun 24 or 48 hr after treatment. ZnIN and ZnIP groups all showed declines in locomotor activity and rearing in an open field. ZnIN females sniffed less and groomed more often and for more total time than ZnIP or AIR females, effects attributed to nasal irritation and impaired olfaction. Declines in activity did not appear due to systemic absorption of zinc sulfate. Induction of maternal behavior was facilitated by ZnIN but not by ZnIP. Modifications of IN injection procedures were felt to have reduced post-treatment debilitation caused by accidental aspiration of zinc sulfate.     

Centrally and peripherally induced anosmia: influences on maternal behavior in lactating female rats.

Bilateral removal of the olfactory bulbs was found to produce deficits in several components of the maternal behavior of lactating, primiparous female rats. More dead pups were found in the cages of bilaterally bulbectomized females shortly after parturition than in the cages of unilaterally bulbectomized, sham operated, or unoperated females. Futhermore, bilaterally bulbectomized females showed deficits in pup retrieval relative to females in the other surgical conditions, and pups reared by bilaterally bulbectomized females weighed less at weaning than pups reared by females in the other surgical conditions. In contrast to bilateral bulbecomy, zinc sulphate treatments had no influence on pup mortality at parturition. However, zinc sulphate treated females did exhibit deficits in pup retrieval relative to saline treated females.