Expression Of Maternal Behavior Research Articles

Specifying the Neurobiological Basis of Human Attachment: Brain, Hormones, and Behavior in Synchronous and Intrusive Mothers

The mother-infant bond provides the foundation for the infant's future mental health and adaptation and depends on the provision of species-typical maternal behaviors that are supported by neuroendocrine and motivation-affective neural systems. Animal research has demonstrated that natural variations in patterns of maternal care chart discrete profiles of maternal brain-behavior relationships that uniquely shape the infant's lifetime capacities for stress regulation and social affiliation. Such patterns of maternal care are mediated by the neuropeptide Oxytocin and by stress- and reward-related neural systems. Human studies have similarly shown that maternal synchrony--the coordination of maternal behavior with infant signals--and intrusiveness--the excessive expression of maternal behavior--describe distinct and stable maternal styles that bear long-term consequences for infant well-being. To integrate brain, hormones, and behavior in the study of maternal-infant bonding, we examined the fMRI responses of synchronous vs intrusive mothers to dynamic, ecologically valid infant videos and their correlations with plasma Oxytocin. In all, 23 mothers were videotaped at home interacting with their infants and plasma OT assayed. Sessions were micro-coded for synchrony and intrusiveness. Mothers were scanned while observing several own and standard infant-related vignettes. Synchronous mothers showed greater activations in the left nucleus accumbens (NAcc) and intrusive mothers exhibited higher activations in the right amygdala. Functional connectivity analysis revealed that among synchronous mothers, left NAcc and right amygdala were functionally correlated with emotion modulation, theory-of-mind, and empathy networks. Among intrusive mothers, left NAcc and right amygdala were functionally correlated with pro-action areas. Sorting points into neighborhood (SPIN) analysis demonstrated that in the synchronous group, left NAcc and right amygdala activations showed clearer organization across time, whereas among intrusive mothers, activations of these nuclei exhibited greater cross-time disorganization. Correlations between Oxytocin with left NAcc and right amygdala activations were found only in the synchronous group. Well-adapted parenting appears to be underlay by reward-related motivational mechanisms, temporal organization, and affiliation hormones, whereas anxious parenting is likely mediated by stress-related mechanisms and greater neural disorganization. Assessing the integration of motivation and social networks into unified neural activity that reflects variations in patterns of parental care may prove useful for the study of optimal vs high-risk parenting.

Breed differences in the expression of maternal care at parturition persist throughout the lactation period in sheep

Maternal care plays an important role in the survival of offspring in mammals. In the ewe initial maternal care is expressed by nurturing the young and formation of an exclusive olfactory bond with the lamb. After the neonatal period, maternal care is associated with co-operation with sucking interactions, maintenance of a close ewe–lamb relationship, communication with lambs, vigilance and a tendency to seek absent lambs. Two breeds of ewe, Suffolk and Scottish Blackface, have previously been shown to differ in their expression of early maternal care, and in lamb survival. It was hypothesised that these differences in the expression of maternal behaviour would persist throughout the lactation period and continue to be expressed in other aspects of maternal care. The maternal behaviour of 32 primiparous ewes (18 Suffolk, 14 Blackface) was observed from birth until weaning at 12 weeks of age. As shown previously, Blackface ewes spent more time grooming their lambs than Suffolk ewes ( P < 0.001), and were more cooperative with the early sucking behaviour of their offspring ( P < 0.01). Blackface ewes were significantly closer to their lambs from birth and throughout the lactation period ( P < 0.05). There were no significant differences between breeds in maternal vocal communication with their lambs, however, Blackface ewes were significantly more vigilant (head alert) than Suffolk ewes from week 4 of lactation onwards ( P < 0.01). The lambs of Suffolk ewes had a significantly higher frequency of sucking bouts ( P < 0.05) than lambs of Blackface ewes in the first weeks of lactation. However, Blackface ewes accepted a greater proportion of lamb sucking attempts than Suffolk ewes ( P < 0.01), and these sucking bouts were longer than with Suffolk ewes ( P < 0.05). The results therefore show that differences in the expression of maternal care seen in the initial post partum period in sheep persist throughout lactation, and would be expected to contribute to lamb survival.

Open field behavior and intra-nucleus accumbens dopamine release in vivo in virgin and lactating rats.

behavioral, endocrine, and neurochemical implications. This experience causes behavioral and neurochemical changes that involve several brain areas important for the expression of maternal behavior. The present study showed that lactating rats exhibited reduced general locomotor activity in the open field test compared with virgin animals. Our hypothesis was that nucleus accumbens dopamine, which regulates maternal behavior in lactating rats, is also involved in the low expression of maternal locomotion in the open field test observed during the early stages of lactation and reflects decreased motivation. Initially we compared open field behavior in virgin and lactating rats to confirm our previous data. Thus, the in vivo release of dopamine in the nucleus accumbens in virgin and lactating female rats was measured. Perfusate concentrations of extracellular dopamine and its metabolites showed no differences between virgin and lactating rats. Thus, the reduced general activity observed in lactating rats might not be related to intra-nucleus accumbens dopamine control. Keywords: maternal behavior, virgin rats, lactating rats, nucleus accumbens, dopamine.

Maternal behaviour and peripartum levels of oestradiol and progesterone show little difference in Merino ewes selected for calm or nervous temperament under indoor housing conditions

Temperament influences the expression of maternal behaviour in sheep under experimental field conditions. We investigated whether maternal behaviour between ewes selected for a calm or nervous temperament is independent from environmental conditions. In addition, the level of maternal behaviour expressed by mothers is correlated with the concentration of hormones during the peripartum period. Therefore, we investigated whether the selection for temperament had resulted in hormonal differences between the two lines with regard to the hormones that could be involved in the onset of maternal behaviour. Oestradiol, progesterone and cortisol concentrations from 4 days before parturition to 24 h after parturition were determined from blood samples collected from 10 calm and 12 nervous ewes. Behavioural interactions between ewe and lamb were also recorded for 2 h starting at parturition. Mothers of both temperament lines showed adequate maternal behaviour under the controlled conditions of the study. Therefore, the results of the study do not suggest that selection for a calm or nervous temperament has profoundly affected the intrinsic ability of mothers to display adequate maternal behaviour. Hormonal differences between the two temperament lines were generally small and their possible influence on the display of maternal behaviour in the two temperament lines would have to be demonstrated.

The neuroendocrinology of primate maternal behavior

In nonhuman primates and humans, similar to other mammals, hormones are not strictly necessary for the expression of maternal behavior, but nevertheless influence variation in maternal responsiveness and parental behavior both within and between individuals. A growing number of correlational and experimental studies have indicated that high circulating estrogen concentrations during pregnancy increase maternal motivation and responsiveness to infant stimuli, while effects of prepartum or postpartum estrogens and progestogens on maternal behavior are less clear. Prolactin is thought to play a role in promoting paternal and alloparental care in primates, but little is known about the relationship between this hormone and maternal behavior. High circulating cortisol levels appear to enhance arousal and responsiveness to infant stimuli in young, relatively inexperienced female primates, but interfere with the expression of maternal behavior in older and more experienced mothers. Among neuropeptides and neurotransmitters, preliminary evidence indicates that oxytocin and endogenous opioids affect maternal attachment to infants, including maintenance of contact, grooming, and responses to separation. Brain serotonin affects anxiety and impulsivity, which in turn may affect maternal behaviors such as infant retrieval or rejection of infants' attempts to make contact with the mother. Although our understanding of the neuroendocrine correlates of primate maternal behavior has grown substantially in the last two decades, very little is known about the mechanisms underlying these effects, e.g., the extent to which these mechanisms may involve changes in perception, emotion, or cognition.

Inactivation or inhibition of neuronal activity in the medial prefrontal cortex largely reduces pup retrieval and grouping in maternal rats

Previous research suggests that the maternal medial prefrontal cortex (mPFC) may play a role in maternal care and that cocaine sensitization before pregnancy can affect neuronal activity within this region. The present work was carried out to test whether the mPFC does actually play a role in the expression of maternal behaviors in the rats and to understand what specific behaviors this cortical area may modulate. In the first experiment, tetrodotoxin (TTX) was used to chemically inactivate the mPFC during tests for maternal behavior latencies. Lactating rats were tested on postpartum days 7–9. The results of this first experiment indicate that there is a large effect of TTX-induced inactivation on retrieval behavior latencies. TTX nearly abolished the expression of maternal retrieval of pups without significantly impairing locomotor activity. In the second experiment, GABA-mediated inhibition was used to test maternal behavior latencies and durations of maternal and other behaviors in postpartum dams. In agreement with experiment 1, it was observed that dams capable of retrieving are rendered incapable by inhibition in the mPFC. GABA-mediated inhibition in the mPFC largely reduced retrieval without altering other indices of maternal care and non-specific behavior such as ambulation time, self-grooming, and inactivity. Moreover, in both experiments, dams were able to establish contact with pups within seconds. The overall results indicate that the mPFC may play an active role in modulating maternal care, particularly retrieval behavior. External factors that affect the function of the frontal cortical site may result in significant impairments in maternal goal-directed behavior as reported in our earlier work.

The plasticity of human maternal brain: Longitudinal changes in brain anatomy during the early postpartum period.

Animal studies suggest that structural changes occur in the maternal brain during the early postpartum period in regions such as the hypothalamus, amygdala, parietal lobe, and prefrontal cortex and such changes are related to the expression of maternal behaviors. In an attempt to explore this in humans, we conducted a prospective longitudinal study to examine gray matter changes using voxel-based morphometry on high resolution magnetic resonance images of mothers' brains at two time points: 2-4 weeks postpartum and 3-4 months postpartum. Comparing gray matter volumes across these two time points, we found increases in gray matter volume of the prefrontal cortex, parietal lobes, and midbrain areas. Increased gray matter volume in the midbrain including the hypothalamus, substantia nigra, and amygdala was associated with maternal positive perception of her baby. These results suggest that the first months of motherhood in humans are accompanied by structural changes in brain regions implicated in maternal motivation and behaviors.

The changing role of the medial preoptic area in the regulation of maternal behavior across the postpartum period: Facilitation followed by inhibition

Maternal behavior in rats undergoes considerable plasticity in parallel to the developmental stage of the pups, resulting in distinct patterns of maternal behavior and care at different postpartum time points. The medial preoptic area (mPOA) of the hypothalamus is one critical neural substrate underlying the onset and early expression of maternal behavior in rats but little is known about its specific functional role in the evolving expression of maternal behavior across the postpartum period. The present study uses a reversible local neural inactivation method to examine the role of the mPOA in the regulation of maternal behavior throughout the postpartum period, particularly extending into the late postpartum, a little examined period. This approach avoids the compensatory plasticity in CNS that occurs after permanent lesions, and allows the repeated testing of same individuals. Early (PPD7–8) and late (PPD13–14) postpartum maternal behavior was evaluated in female rats following infusions of bupivacaine or vehicle into the mPOA or into control areas. As expected, mPOA inactivation severely but transiently disrupted early postpartum maternal behavior whereas infusion of vehicle or inactivation of adjacent control sites did not. Later in the postpartum period, however, transient mPOA inactivation facilitated the expression of maternal behaviors, highly contrasting the behavioral expression levels characteristic of late postpartum. Results strongly demonstrate that the mPOA is differentially engaged throughout postpartum in orchestrating appropriate maternal responses with the developmental stage of the pups.

P.1.03 Effects of chronic citalopram treatment on the kainic acid induced neurogenesis in adult mouse hippocampus

Brief contact with pups at parturition enables the female rat to establish and retain the full repertoire of maternal behaviors, allowing her to respond rapidly to pups in the future. To determine whether the dopamine system is involved in the retention of maternal behavior, females were continuously infused with dopamine antagonists during the periparturitional period and then allowed either a brief interaction period with pups (3 h) or no interaction with pups (pups removed as they were born). Females were exposed to either the D1-like antagonist SCH 23390 (0.1 or 1.0 mg/kg/day) or the D2-like antagonist clebopride (0.5 or 1.0 mg/kg/day). The high dose of either DA antagonist resulted in significant attenuation of maternal care immediately postpartum. When tested for the retention of maternal behavior 7 days later, however, only the females exposed to the D2 antagonist displayed a delayed response to shown full maternal behavior (FMB) towards donor pups. Thus, while both dopamine receptor subtypes appear necessary for the full and rapid expression of maternal behavior during the early postpartum period, only the D2 receptor subtype appears to be involved in the retention of this behavior.

A Twist – Snail axis critical for TrkB-induced metastasis

The expression of maternal behavior in mammals is regulated by the developmental and experiential events over a female’s lifetime. In this review the relationships between the endocrine and neural systems that play key roles in these developmental and experiential processes that affect both the establishment and maintenance of maternal care are presented. The involvement of the hormones estrogen, progesterone, and lactogens are discussed in the context of ligand, receptor, and gene activity in rodents and to a lesser extent in higher mammals. The roles of neuroendocrine factors, including oxytocin, vasopressin, classical neurotransmitters, and other neural gene products that regulate aspects of maternal care are set forth, and the interactions of hormones with central nervous system mediators of maternal behavior are discussed. The impact of prior developmental factors, including epigenetic events, and maternal experience on subsequent maternal care are assessed over the course of the female’s lifespan. It is proposed that common neuroendocrine mechanisms underlie the regulation of maternal care in mammals.

Individual Variation in the Expression of Maternal Behaviour: A Review of the Neuroendocrine Mechanisms in the Sheep

Individual variation in the expression of maternal behaviour can affect offspring development and survival. Ewes showing a poorer quality of maternal behaviour (low levels of licking and grooming, infrequent low-pitched bleating, inconsistent udder acceptance) at parturition and throughout lactation (large ewe-lamb distance, low vigilance) form a weaker bond with their lambs, and have higher lamb mortality, than ewes which show high levels of grooming and low-pitched bleating, close ewe-lamb distances and high levels of vigilance. Using two models of variation in maternal behaviour in the sheep (differences between ewes of two breeds, and differences between primiparous and multiparous ewes), the neuroendocrine mechanisms that underpin these differences are explored. In both cases, significant variation in oestrogen priming is observed, with breed differences in circulating concentrations of oestrogen in late gestation, and parity effects on receptor density but not circulating concentrations. The consequences of these differences for central oxytocin release and binding are discussed. In addition, preliminary data suggest that opioid modulation, in both breed and parity models, may also play a role in mediating individual variation in maternal behaviour in the sheep.

Genetic and physiological determinants of maternal behavior and lamb survival: Implications for low-input sheep management1,2

The relatively intensive supervision afforded many ewes at lambing time is a barrier to the development of low-input sheep management systems. However, in some flocks, reduction in this level of supervision may initially affect lamb mortality and animal welfare. In this review, possibilities for optimizing behavioral interaction between the ewe and lamb are considered, with the goal of improving lamb survival without the need for high levels of human supervision. At birth, ewes show specific behavioral patterns (e.g., licking or grooming, low-pitched bleats, udder acceptance) that facilitate the transition of the lamb from pre- to postnatal life and that accompany the formation of an exclusive olfactory memory for the lamb. The lamb also performs a specific sequence of behaviors directed toward standing, finding the udder, and sucking. The successful accomplishment of these behavior patterns is vital for the formation of a strong attachment between both partners, and for lamb survival. The expression of maternal behavior in the ewe is affected by her previous maternal experience, by nutrition in pregnancy, by breed, by temperament, and, to some extent, by the behavior of her lamb. The maternal care expressed by a ewe at parturition is indicative of her behavior throughout that lactation and in successive pregnancies, suggesting an underlying basis to maternal care intrinsic to that ewe. Studies with Scottish Blackface and Suffolk ewes show that ewes expressing high levels of maternal care have elevated plasma estradiol in late gestation compared with ewes with poorer maternal care, and that circulating estradiol concentration is correlated with maternal behaviors. Although the genetic basis of maternal behaviors has still to be fully determined, there are possibilities of improving maternal behavior by selection, and a better understanding of the neuroendocrine processes underlying individual differences in maternal behavior may help in developing selection strategies. In addition, selection on lamb behaviors, which show some genetic basis, may also be a route to improve lamb survival. Because behavior of both the ewe and lamb is affected by environmental factors, appropriate management, through pregnancy and at parturition, will enhance the expression of maternal behavior and lamb vigor, and so contribute to improving lamb survival.

Mother rabbits and their offspring: Timing is everything

Mother rabbits nurse once every 24 hr for ca. 3 min. The contribution of pup stimulation to the regulation of this process was investigated by: reducing litter size to one pup, covering all the mother's nipples, or taping the mouths of an eight-pup litter. Time inside the nest box with the young significantly increased under all these conditions. Yet, eight pups sucking on a single nipple allowed a normal time in the nest box. Bringing the litter to the mother earlier than usual promoted maternal behavior expression twice in 24 hr; the proportion of responsive females and the time at which they responded depended on the size of the litter suckled. These findings indicate that: (a) suckling determines the time inside the nest box and prevents mothers from responding to further pup stimulation for a variable time; (b) pup exposure promotes maternal behavior, even "out of phase" with circadian rhythmicity.

The effects of adrenalectomy and corticosterone replacement on induction of maternal behavior in the virgin female rat

Maternal behavior of the sensitized virgin rat is affected by approach–avoidance systems as well as by hypothalamic–pituitary–adrenal (HPA) axis, which is also activated during stress. The present experiments investigated the effects of adrenalectomy and of varying corticosterone concentrations on the onset and expression of maternal behavior in sensitized virgin rats. In the first experiment, latency to onset of maternal behavior and time spent licking once maternal were positively related to endogenous levels of corticosterone. However, few rats showed licking. In the second experiment, virgin rats were adrenalectomized or given sham surgeries before being sensitized and being given 0, 25, 100, 300, or 500 μg/mL of corticosterone in their drinking water. In the third experiment, virgin rats were adrenalectomized or given sham surgeries and given either control or corticosterone time-release pellets after being sensitized. Maternal behavior was then tested. Adrenalectomy increased licking in the second experiment and time over pups in the third experiment. Corticosterone replacement reduced licking in the second experiment and both licking and time over pups in the third experiment. In conclusion, exogenous corticosterone had an inhibitory effect on the expression of maternal behavior in the sensitized virgin rat, unlike the facilitatory effect previously found in the postpartum rat.

Steroid-induced alterations in mRNA expression of the long form of the prolactin receptor in the medial preoptic area of female rats: Effects of exposure to a pregnancy-like regimen of progesterone and estradiol

It is firmly established that the onset of maternal behavior in the female rat is stimulated by a combination of hormones that include prolactin (PRL), estradiol (E 2), and progesterone (P 4). Specifically, nulliparous rats display short latencies to respond to foster young when primed with Silastic capsules filled with P 4 and E 2 and then administered PRL centrally to the medial preoptic area (MPOA), an area integrally involved in the expression of maternal behavior in this species. PRL or P 4 treatments alone are ineffective in stimulating the expression of maternal care. Since the actions of PRL in the MPOA appear to be mediated by PRL receptors, it was of interest to determine whether and how treatment with P 4 and E 2 together or separately might alter mRNA expression of the long form of the PRL receptor (PRL-R L) in the MPOA. Using in situ hybridization histochemistry (ISHH), mRNA expression of the PRL-R L was measured in the MPOA of ovariectomized, nulliparous rats treated with various combinations of P 4 and E 2. Treatment of animals with P 4 alone for 10 days or with P 4 followed by E 2 for 1 or 4 days resulted in reductions in PRL receptor mRNA expression in the MPOA when compared with the expression in animals treated with E 2 alone or blank capsules. The actions of P 4 on mRNA expression of the PRL-R L were more pronounced in the dorsal MPOA. Circulating PRL levels collected at the time of sacrifice were elevated in all groups treated with E 2, but no association between PRL levels and receptor mRNA expression within the MPOA was evident. These findings indicate that the dorsal MPOA may be one site of progesterone's action in facilitating prolactin-mediated maternal behavior.

Cyclic AMP response element-binding protein is required for normal maternal nurturing behavior

Analysis of mice with targeted disruptions of fosB or the gene encoding dopamine β-hydroxylase suggests that FosB and adrenergic signaling play critical roles in maternal nurturing behavior. The majority of neonates born to null females from either mutation fail to thrive, and virgin mutant females of both lines exhibit impaired pup retrieval. Considering whether FosB and adrenergic signaling might share a signaling pathway important for maternal behavior, we examined the role of a potential intermediary, cyclic AMP response element-binding protein (CREB). Here we report that ∼40% of neonates (all heterozygous) born to mice lacking the major isoforms of CREB ( Creb-αΔ −/−) died within several days of birth. In contrast, heterozygotes born to Creb-αΔ +/− females thrived. Cross-fostering demonstrated that neonates born to Creb-αΔ −/†/− females thrived when reared by wild-type females, and that Creb-αΔ −/− females were capable of rearing neonates whose maternal care was initiated by wild-type females. Further, virgin Creb-αΔ −/− females were deficient in pup retrieval despite exhibiting normal investigation of pups and of novel objects. No maternal behavior phenotype was present in mice with a null mutation of the cyclic AMP response element modulator ( Crem) gene. Interestingly, the number of cells immunostaining for phospho-CREB (on Ser 133) in the medial preoptic area of the hypothalamus, a key region for the expression of maternal behavior, increased nearly three-fold in wild-type mice following exposure to pups but not to novel objects. On the other hand, basal expression and induction of FosB in response to pup exposure appeared to be independent of CREB because levels were equivalent between wild-type and Creb-αΔ −/− females. These results implicate CREB in maternal nurturing behavior and suggest that CREB is not critical for expression or induction of FosB in adult virgin female mice.

Prefrontal and tegmental electrical activity during olfactory stimulation in virgin and lactating rats

This study was designed to analyze if the electroencephalographic (EEG) activity of the medial prefrontal cortex (mPFC) and the ventral tegmental area (VTA) was modified throughout various reproductive stages of female rats exposed to pup-associated or non-associated odors. Simultaneous EEG recordings were obtained from right and left mPFC and VTA in adult female rats during the smelling of nest bedding and female bedding under three reproductive states: proestrus–estrus (P–E), diestrus (D) and lactation (L). Absolute (AP) and relative (RP) powers of three EEG band frequencies, and interhemispheric correlation ( r) of EEG activity were calculated and compared among conditions. During the awake–quiet condition, RP of the 12–21 Hz band was significantly higher in the right and left mPFC as well as in the right VTA of lactating rats as compared to P–E rats. During the smelling of nest bedding, the RP of the 8–11 Hz in the mPFC became increased while that of the 6–7 and 12–21 Hz decreased in the three reproductive stages. In the VTA, this phenomenon was mainly observed in lactating rats. Only the RP of the lower frequencies (6–7 and 8–11 Hz bands) was higher in the right mPFC and in the left and right VTA, respectively, of the lactating rats with respect to P–E rats, while that of the 12–21 Hz band was lower in lactating as compared to P–E rats. Moreover, the interprefrontal correlation of the lower-frequency bands was higher in relation to smelling of nest bedding in diestrus and lactating rats, whereas during the smelling of female bedding the correlation of the 6–7 Hz band was increased only in the diestrus rats as compared to P–E rats. These data indicate that EEG activity recording is a sensitive tool to study the functionality of the mPFC and VTA during different reproductive states and suggest the possible participation of these structures in the processing of olfactory stimuli associated to pups to modulate the motivational and performance processes, crucial for the expression of maternal behavior.

Prepartum plasma estradiol and postpartum cortisol, but not oxytocin, are associated with interindividual and breed differences in the expression of maternal behaviour in sheep

Consistent, individual differences in the expression of maternal behaviour have been described in several species including the sheep. The neuroendocrine mechanisms underlying the onset of maternal behaviour in the sheep have been described, although the relationship between hormonal events and individual differences in behaviour has yet to be determined. In this study, we examined whether the individual differences in plasma estradiol, progesterone, oxytocin and cortisol concentrations were related to observed individual and breed differences in maternal behaviours in two breeds of sheep (Scottish Blackface and Suffolk) known to differ in maternal behavioural expression. Maternal estradiol concentration increased rapidly before parturition and was higher in Blackface ewes than Suffolk ewes. Plasma progesterone declined before parturition and was higher in Suffolk than Blackface ewes. Prepartum estradiol, but not progesterone, was related to individual differences in maternal grooming of the lamb. Plasma oxytocin did not differ between breeds in late gestation. There was a tendency for oxytocin to be higher in Blackface than Suffolk ewes immediately after birth. However, there were no significant relationships between prepartum or postpartum oxytocin and any maternal behaviours. Plasma cortisol was higher in Blackface than Suffolk ewes in the last days of pregnancy but rose in both breeds over the last 24 h before parturition and did not differ at delivery. Cortisol peripartum was negatively related to individual differences in maternal affiliative behaviours. These data suggest that estradiol, and potentially cortisol, may mediate individual differences in maternal behaviour in sheep.

Removal of the accessory olfactory bulbs promotes maternal behavior in virgin rabbits

Virgin rabbits exposed to foster pups for 14 days did not show maternal responsiveness. However, surgical removal of the accessory olfactory bulbs (AOB) activated maternal responsiveness (crouching over the litter inside the nest box for about 3 min, which is the normal duration of a nursing bout) in 37% of virgin rabbits ( P<0.007). This behavior appeared abruptly and was first observed between days 3 and 13 of pup exposure. This variation in the latency to respond maternally was not related with the number of sniffings or entrances into the nest box displayed by a female on the days that preceded crouching over the litter. Maternal responsiveness was not observed in any AOB-lesioned animals that were also ovariectomized ( P<0.02 versus AOB-lesioned with ovaries). These results indicate a tonic inhibitory action of the AOB over the expression of maternal behavior in virgin rabbits and a stimulation of maternal responsiveness by ovarian hormones following AOB lesions.

Maternal behavior: activation of the central oxytocin receptor system in parturient rats?

Parturition plays a critical role in the full expression of maternal behavior in postpartum females, yet the precise mechanism remains unclear. Here we examined the role of parturition in the activation of Fos and FosB in the central oxytocin receptor (OTR) system in rats. Although expression of FosB, not Fos, was seen in the piriform cortex (Pir) and caudate putamen of virgin and pregnant females, activation of Fos and FosB with extensive co-localization was found in the medial preoptic area, the bed nucleus of the stria terminalis and Pir of parturient brain. This parturition induced activation of Fos and FosB was identified in the central OTR-expressing cells as well as in oxytocinergic neurons. Our data provide direct evidence, for the first time, that parturition activates Fos and FosB in the central OTR system. We propose that Fos and FosB may have comparable functions on initiating maternal behavior at parturition.