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PubMed2001

Neuroendocrinology of maternal behavior in the rabbit.

Rabbit maternal behavior consists of building an underground nest of straw and body hair during late pregnancy and displaying, with circadian periodicity, a single 3-min nursing bout/day across lactation. Estrogen, androgen, progesterone, and prolactin regulate specific aspects of nest-building and promote the onset of maternal responsiveness. However, the maintenance of this behavior relies on stimuli from the litter: by preventing mother/young contact at parturition or during early lactation maternal responsiveness is altered or abolished. The brain areas controlling the expression of nest-building and nursing were investigated by implanting estradiol, locating the distribution of estrogen and prolactin receptors, quantifying the expression of immediate-early genes, and lesioning structures of the olfactory system. These studies revealed that: (a) estrogen receptor-alpha, alpha, present in the preoptic region, may mediate the stimulation of nest-building by estradiol; (b) prolactin binding sites, located mainly in periventricular structures, are more abundant in late pregnancy and early lactation; (c) the number of FOS-immunoreactive neurons increases in the lateral septum, but not in the mediobasal hypothalamus, following nursing; (d) the accessory olfactory bulb tonically inhibits the expression of maternal behavior because its removal promotes maternal responsiveness in virgins, which are otherwise unresponsive to daily pup exposure. In summary, rabbits rely on the same hormonal and extrahormonal factors that stimulate maternal behavior in other mammals, yet the way in which such factors promote elaborate nest-building and the unfailing display of circadian nursing is unique to rabbits and warrants future investigation.

Animals↗
PubMed2002

A functional neuroanatomical investigation of the role of the medial preoptic area in neural circuits regulating maternal behavior.

The medial preoptic area (MPOA) is essential for normal maternal behavior in the rat. Hormone stimulation of the MPOA facilitates the behavior and lesions of the MPOA and the adjoining ventral part of the bed nucleus of the stria terminalis (vBST) disrupt the behavior. The MPOA/vBST also show increases in Fos protein expression during maternal behavior. The present study examines the larger neural circuitry within which the MPOA/vBST might operate to influence maternal behavior. Combining Fos immunocytochemistry with unilateral excitotoxic amino acid lesions or lateral knife cuts of the MPOA/vBST, we sought to identify brain regions which might be under the influence of Fos expressing neurons in the MPOA/vBST. Two brain regions, the shell of the nucleus accumbens (NAs), and the intermediate part of the lateral septum (LSi) were identified. Both the NAs and LSi exhibited elevated Fos expression during maternal behavior, while unilateral MPOA/vBST damage resulted in an ipsilateral reduction of maternal behavior-induced Fos expression in each area, suggesting that MPOA/vBST neurons modulate Fos expression and associated neural activity in both of these structures during maternal behavior. Importantly, these unilateral preoptic lesions also depressed maternal behavior-induced Fos expression in the ipsilateral MPOA and vBST. The effects of these lesions on Fos expression in the periaqueductal gray (PAG) and other brain regions are also presented.

Animals↗
PubMed1978

Sensory regulation of maternal behavior in rats: effects of pup age.

Maternal behavior (retrieving, crouching, and licking) was induced in Sprague-Dawley virgin female rats by constant exposure to pups aged 1-2, 3-4, 5-6, 7-8, 9-10, 11-12, 13-14, or 15-16 days. The incidence of spontaneous components of maternal behavior, notably retrieving, was greater towards pups 1-8 days of age than towards older pups, whereas the occurrence of cannibalism did not differ as a function of pup age. With pups 1-2 through 13-14 days, the latency to onset of full maternal behavior was shortest with 1-2-day-old pups (2-day median) and longest with 13-14-day-old pups (7-day median). Females exposed to pups aged 3-4 through 11-12 days did not differ significantly in their latencies, the medians of which ranged from 4.0 to 5.5 days. Only 1 female out of 8 exposed to pups aged 15-16 days became fully maternal, but 5 more displayed components of maternal responsiveness. The optimal nature of neonates and the general attractiveness of a wider range of pup ages as stimuli for the elicitation of maternal behavior in rats, as well as comparisons to mice and hamsters, were discussed.

Age Factors↗
PubMed2002

Role of maternal behavior on aggression, fear and anxiety.

Concomitant to the expression of maternal behavior, the lactating female develops anxiolysis in the elevated plus maze test, aggression towards intruders and reduced fear in response to a sudden auditory stimulus. This study aims to determine if these behavioral changes are associated with maternal behavior independently of the endocrine status that characterizes gestation, parturition and lactation. To assess this purpose, the behavior of lactating females was compared to that exhibited by maternal and nonmaternal ovariectomized rats untreated with steroid hormones. In contrast with lactating dams, sensitized animals (rats that displayed maternal behavior after a continuous contact with young pups) did not display reduced anxiety in the plus maze test. However, the sensitized females showed behaviors characteristic of lactating rats, such as some components of maternal aggression and reduced fear, though much less intensely than dams. These results suggest that aggression and reduced fear, but not anxiolysis, partially depend on the development of maternal behavior.

Aggression↗
PubMed1990

Prolactin (PRL) regulation of maternal behavior in rats: bromocriptine treatment delays and PRL promotes the rapid onset of behavior.

Recent findings indicate that PRL helps stimulate the onset of maternal behavior in inexperienced hypophysectomized steroid-treated female rats. In a series of five experiments we have further examined the involvement of PRL in maternal behavior using nonhypophysectomized ovariectomized rats treated concurrently (type I) or sequentially (type II) with progesterone (P) and estradiol (E2) and administered either bromocriptine (to suppress endogenous PRL secretion) or bromocriptine plus ovine PRL. In Exp 1 plasma PRL concentrations were measured in ovariectomized rats treated for 2 weeks with a combination of E2 and P Silastic implants. Type I steroid-treated (2mm E2, days 1-24; three 30 mm P, days 3-13) rats exhibited elevated plasma PRL levels throughout the sampling period compared with nonsteroid-treated controls. In contrast, PRL concentrations in type II steroid-treated (P, days 3-13; E2, days 13-24) females were low (similar to controls) from days 3-13 when the type II steroid-treated females were exposed to P only. Like type I treated rats, PRL levels in type II steroid-treated rats were elevated from day 13 onward after E2 capsule insertion. In Exp 2, treatment of both type I and type II steroid-treated rats with bromocriptine (2 mg/kg, sc) twice daily beginning on treatment day 13 suppressed basal PRL concentrations and prevented the estrogen-induced diurnal PRL surge. Whereas PRL was effectively suppressed by bromocriptine in both steroid-treated groups, the absolute levels of PRL were lower in rats treated with the type II steroid regimen. Behavioral analyses in Exp 3, 4, and 5 revealed that bromocriptine administration, while failing to interfere with the onset of maternal behavior in rats treated with the type I concurrent steroid regimen, disrupted the onset of maternal care in rats treated with the type II sequential steroid regimen. When a separate set of type II steroid-treated rats was given both bromocriptine (2 mg/kg) plus ovine PRL (0.5 mg, sc) twice daily, maternal behavior rapidly appeared. Thus, suppression of endogenous PRL secretion delays the onset of maternal behavior in nonhypophysectomized steroid-primed rats, an effect prevented by concurrent administration of ovine PRL. In addition to providing further experimental support for PRL's role in maternal behavior, the development of this endocrine regimen provides researchers with a potentially fruitful model to examine neural sites and mechanisms of PRL regulation of maternal behavior in mammals.

Animals↗
PubMed2006

Periaqueductal gray cholecystokinin infusions block morphine-induced disruption of maternal behavior.

Cholecystokinin (CCK) and opiates interaction is critical for maintaining maternal behavior during lactation. Morphine inhibits while CCK restores maternal behavior. Recently we have shown that periaqueductal gray (PAG) is a region critically involved in the opioidergic blockade of maternal behavior. A critical level of morphine-induced activation of the rostral lateral PAG is required to inhibit maternal behavior in lactating rats. Since central CCK injections reverted morphine-induced inhibition of maternal behavior, we tested whether this peptide would act similarly in the PAG. This hypothesis was confirmed in experiments showing that morphine's inhibitory effect on maternal responsiveness was blocked by 1.0 and 0.2 nmol CCK injections into the rostral PAG, but not in nearby regions of the mesencephalic reticular nucleus. To test for possible compensatory changes the CCK2 receptor due to morphine treatments the expression of CCK2 receptor mRNA was evaluated in the PAG. PAG CCK2 receptor cDNA amplification revealed no difference in morphine treated animals. These results broaden understanding of the role played by CCK in the PAG. This CCK action might not depend on changes in its receptor.

Animals↗
PubMed2001

Central infusions of the recombinant human prolactin receptor antagonist, S179D-PRL, delay the onset of maternal behavior in steroid-primed, nulliparous female rats.

The expression of maternal behavior in the newly parturient rat is under endocrine regulation. Blocking endogenous PRL secretion with bromocriptine delays the normal rapid expression of maternal care shown toward foster young in steroid-primed virgin female rats. The recent development of the PRL receptor antagonist S179D-PRL, a mutant of human PRL in which the serine residue at the 179 position is replaced with aspartate, provides a potentially useful tool to examine the role of PRL in neural processing. In the present report, three experiments were conducted that examined the effects of this PRL antagonist on the induction of maternal behavior. In each experiment, ovariectomized, nulliparous rats were treated sequentially with SILASTIC capsules implanted sc with progesterone (days 1-11) and estradiol (days 11-17), a treatment that stimulates a rapid onset of maternal behavior in virgin rats. On day 11, females were implanted with Alzet miniosmotic pumps connected to cannulae directed unilaterally at the lateral ventricle (Exp 1) or bilaterally at the medial preoptic area (MPOA; Exp 2 and 3). Pumps contained either doses of S179D-PRL (0.115 or 1.15 mg/ml; Exp 1 and 2), wild-type human PRL (1.15 mg/ml; Exp 3), or the saline vehicle (Exp 1-3). Testing for maternal behavior began on day 12, a day after pump insertion, and animals were tested daily for 6 days. Latencies to contact, retrieve, and group foster test young were recorded. Administration of both the high and low doses of S179D-PRL infused into the lateral ventricle (Exp 1) or MPOA (Exp 2) significantly delayed the onset of maternal behavior. In contrast, MPOA infusions of the control hormone, wild-type human PRL, in Exp 3 did not delay the onset of maternal behavior. These findings support the concept that the effects of S179D-PRL are caused by its actions as a PRL receptor antagonist rather than by a nonspecific effect of the protein. Overall, these results demonstrate the effectiveness of S179D-PRL acting at the level of the central nervous system (and, more specifically, within the MPOA) to regulate maternal behavior, a PRL-mediated response.

Animals↗
PubMed2006

Infant and maternal behavior moderate reactivity to novelty to predict anxious behavior at 2.5 years.

The degree to which infant regulatory behaviors, together with infant reactivity to novelty, predicted anxious behavior at 2.5 years, and the moderating effect of maternal behavior were tested. Sixty-four low-risk mothers and infants participated. Mothers rated infant negative reactivity and anxious behavior; infant and maternal behaviors were observed at 6 months postpartum. Based on results of hierarchical, multiple regressions, infant regulatory behaviors (i.e., attention control, withdrawal) moderated associations between reactivity to novelty and later anxious behavior, but predictions depended also on maternal behavior. High reactivity to novelty, in conjunction with withdrawal and with poor attention control, predicted anxious behavior only when mothers were less engaged or less sensitive, suggesting that maternal behavior alters developmental trajectories associated with infant temperament.

Adult↗
PubMed1988

Neural transection between preoptic area and septum inhibits maternal behavior in female and male rats.

Artificially-induced maternal behavior was examined in inexperienced female and male rats following neural transection between the preoptic area and the septum. Anterior roof deafferentation (ARD) of the preoptic area (POA) was performed with an L-shaped microknife. Virgin female and male rats with or without ARD were exposed to the continuous presence of normal pups to induce maternal behavior 3 weeks after surgery. ARD resulted in a significant delay of the onset of maternal behavior in females and a lack of complete development of maternal behavior in males, compared with corresponding sham-operated and intact controls. The results indicate that neural substrates dorsal to the POA play an important role in modulating the expression of maternal behavior in the rat.

Animals↗
PubMed2000

Induction of c-fos-like and fosB-like immunoreactivity reveals forebrain neuronal populations involved differentially in pup-mediated maternal behavior in juvenile and adult rats.

Juvenile rats can exhibit maternal behavior after being exposed continuously to rat pups, a process called sensitization. Maternal behavior in juveniles is robust and is similar to adult maternal behavior (Mayer and Rosenblatt [1979] Dev. Psychobiol. 12:407-424; Gray and Chesley [684] J. Comp. Psychol. 98:91-99). In this study, immunocytochemical detection of the protein products of two immediate-early genes, c-fos and fosB, was used as a tool to identify forebrain neuronal populations involved in the maternal behavior of 27-day-old juvenile rats compared with 60-day-old adults. To sensitize them, rats were exposed continuously to foster pups. Once they were maternal, they were isolated from pups overnight, reexposed to pups for 2 hours, and then killed. Nonmaternal control animals also were isolated overnight and were either reexposed to pups for 2 hours or kept isolated from pups before killing. The lateral habenula (LH) was the only area in which both maternal juveniles and maternal adults had more c-Fos-immunoreactive (-Ir) neurons compared with controls. In maternal adults, the number of neurons that expressed c-Fos and FosB immunoreactivity increased in the medial preoptic area (MPO) and the ventral bed nucleus of the stria terminalis (BSTv), whereas the dorsal bed nucleus of the stria terminalis (BSTd) and the medial and cortical nuclei of the amygdala (MEA and COA, respectively) had increases only in the number of neurons that expressed c-Fos immunoreactivity. In contrast, juveniles, whether or not they were maternal, had the same number of c-Fos-IR and FosB-Ir neurons in all these areas. The adult-like increase in the number of c-Fos-Ir neurons found in maternal juveniles suggests that the juvenile LH participates in the neural circuit that supports maternal behavior in an adult-like manner. The lack of c-fos or fosB induction in the MPO, BSTv, BSTd, COA, or MEA of maternal juveniles compared with maternal adults may reflect the immaturity of these brain regions in juvenile rats. Exactly what this immaturity consists of and when the responses of these regions become adult-like remain to be determined.

Aging↗
PubMed1997

Central lactogenic regulation of maternal behavior in rats: steroid dependence, hormone specificity, and behavioral potencies of rat prolactin and rat placental lactogen I.

Adult virgin female rats display maternal behavior when continuously exposed to foster young for 5-6 days. Central infusions of PRL or placental lactogens (PLs) together with systemic treatment of progesterone (P) and estradiol (E2) stimulate maternal behavior in 1-2 days. In the present set of studies, it was asked whether the actions of lactogenic hormones are dependent upon both E2 and P and specific to lactogenic molecules. Moreover, we wanted to know whether central infusions of rat (r) PRL and PLs were equally effective in inducing maternal behavior. In the first study, adult virgin rats were ovariectomized (ovx) and stereotaxically fitted with bilateral cannulas directed at the medial preoptic area (MPOA). Rats were then assigned to one of four groups: P plus E2, blank (B) plus E2, P plus B, and B plus B. P-filled or B capsules were implanted sc on treatment day 1 and removed on day 11, whereas E2 or B capsules were implanted on day 11. All groups were infused with rPRL (40 ng/side) five times from days 11-13 and injected with bromocriptine (CB-154) sc (days 11-17) to suppress endogenous PRL release. Behavioral testing was conducted daily from days 12-17. It was found that exposure to both P and E2 was necessary to induce a fast onset of maternal behavior in PRL-infused females; priming with P or E2 alone in PRL-treated rats failed to stimulate a fast onset of behavior relative to that in nonsteroid-treated controls. In the second experiment to determine the biochemical specificity of PRL's action, adult nulliparous rats were ovx, implanted with bilateral cannulas directed at the MPOA, treated with both P and E2, injected with CB-154, and infused centrally (five times) with 40 ng (per side) of bovine GH, ovine LH, or vehicle. Central infusions of either bovine GH or ovine LH failed to stimulate maternal behavior, suggesting that the stimulatory actions of PRL are related to its lactogenic properties. In the final study, rats were ovx, fitted with bilateral cannulas directed at the MPOA; treated with P, E2, and CB-154; and given a single set of bilateral infusions of rPL-I or rPRL (40 ng/side.infusion) on day 11, three sets of infusions of rPL-I or rPRL (days 11 and 12), or vehicle infusions. Rats given three infusions of rPL-I and rPRL responded faster than controls, although the effect was not as robust as that in animals given five infusions in the initial study. rPL-I and rPRL groups did not differ from one another. Together these studies indicate that 1) both P and E2 are required for lactogenic stimulation of maternal behavior; 2) the stimulatory actions of PRL and rPLs on maternal behavior are related to their lactogenic properties; 3) extended treatment of females with lactogenic hormones is more effective in stimulating the onset of maternal behavior; and 4) the neural potencies of rPRL and rPL-I are similar. These findings provide support for the idea that the induction of maternal behavior is stimulated by the central actions of lactogenic hormones.

Animals↗
PubMed1997

Microinjection of the tachykinin neuropeptide K into the ventromedial hypothalamus disrupts the hormonal onset of maternal behavior in female rats.

The medial amygdala exerts an inhibition of maternal behavior in virgin rats, but neither the site to which it projects to exert this effect nor the neurotransmitter used in such a pathway is known. There is also evidence that the ventromedial nucleus of the hypothalamus exerts an inhibition of maternal behavior, and the medial amygdala projects to this nucleus, suggesting that it may receive a projection from the medial amygdala which is inhibitory for maternal behavior. Tachykinin injection into the hypothalamus inhibits reproductive behavior in male rats, and there is a tachykininergic projection from the medial amygdala to the ventromedial hypothalamus. Consequently, the present study was conducted to evaluate the hypothesis that the tachykinin neuropeptide K can inhibit maternal behavior after injection into the ventromedial hypothalamus. Female rats were primed to be maternal by pregnancy termination and estrogen injection. Four doses of the peptide (279 pmol, 186 pmol, 116 pmol, and 66 pmol) were bilaterally injected into the ventromedial hypothalamus, and all were effective in delaying the onset of maternal behavior. Evidence that neuropeptide K disrupts maternal behavior in animals that have already begun to be maternal is also presented. Site specificity of neuropeptide K's effect to within the region of the ventromedial hypothalamus was supported, as injection into the mediodorsal thalamus was without effect. Some possibly relevant neuroendocrine effects are addressed, as well as the possibility that tachykinins may act within the ventromedial hypothalamus to promote virgin female rats' fear of pup odors.

Animals↗
PubMed2006

Oxytocin receptors in the nucleus accumbens facilitate "spontaneous" maternal behavior in adult female prairie voles.

Oxytocin and the nucleus accumbens have been extensively implicated in the regulation of maternal behavior, and the processing of pup-related stimuli relevant for this behavior. Oxytocin receptor density in the nucleus accumbens is highly variable in virgin female prairie voles, as is their behavioral response to pups, ranging from neglecting and infanticidal to full maternal behavior. We hypothesized that oxytocin receptor in the nucleus accumbens facilitates the expression of "spontaneous" maternal behavior in prairie voles. Forty sexually-naive adult females were exposed to pups for the first time and tested for maternal behavior. Oxytocin receptor binding in the nucleus accumbens and other brain regions was later determined using autoradiography. Females that showed maternal behavior (lick and groom the pups and hover over them for at least 30 s, n=24) had higher oxytocin receptor density in the nucleus accumbens (shell subregion) (P<0.05) than females that did not show maternal behavior or attacked the pups (n=16). No differences were found in other brain regions (medial preoptic area, septum, prelimbic cortex). In a second experiment, we tested whether infusions of the oxytocin receptor antagonist (d(CH2)5(1),Tyr(Me)2,Orn8)-AVT into the nucleus accumbens would block "spontaneous" maternal behavior. As a control region, oxytocin receptor antagonist was also infused into the caudate putamen. Ten females were infused bilaterally into the nucleus accumbens or caudate putamen with either 2 ng/0.5 microl of oxytocin receptor antagonist or CSF (vehicle). While five of 10 nucleus accumbens CSF-infused animals showed maternal behavior, none of the nucleus accumbens oxytocin receptor antagonist-infused subjects did (0/10; chi2, P<0.01). Nucleus accumbens oxytocin receptor antagonist-infused females recovered the next day and were not different from controls. Animals infused with CSF or oxytocin receptor antagonist into the caudate putamen did not differ (four/10, four/10). This is the first study to show that the nucleus accumbens is involved in the regulation of "spontaneous" maternal behavior and that oxytocin receptor in this brain region facilitates maternal responses.

Animals↗
PubMed1975

Decline of maternal behavior in the virgin and lactating rat.

Sensitized virgins and postpartum lactating mothers, both exhibiting maternal behavior, were given donor litters that increased in age by 1 day, for 28 days, starting at the onset of maternal behavior. Each day females were tested for maternal behavior with pups 4-8 days old: Maternal care (i.e., nursing/crouching, retrieving, nest building and licking) and maternal withdrawal, rejection, and prevention of nursing were recorded. After the ninth day, females were also tested with the progressively older pups from 10 to 28 days of age with which they were living. Virgins and lactating mothers showed generally similar patterns of maternal care although some differences were found, and they declined in maternal behavior toward the older pups in a similar manner. Maternal behavior did not decline in tests with younger pups. The results are interpreted as supporting the hypothesis that the decline as well as the maintenance of maternal behavior postpartum is nonhormonally mediated.

Age Factors↗
PubMed1988

Prenatal stress and maternal behavior in intact virgin rats: response latencies are decreased in males and increased in females.

The repeated findings that levels of various male-typical behaviors (e.g., copulatory behavior and intermale aggression) are reduced in prenatally stressed (P-S) males, coupled with reports of effects on female physiology and behavior, prompted us to examine the maternal behaviors of P-S animals toward young. Sprague-Dawley female rats were timed-mated (+ sperm = Day 1). From Gestation Days 15 to 22 experimental females were subjected to heat and restraint stress. Control females remained undisturbed throughout pregnancy. The offspring, as adults, were assessed for maternal behavior. P-S males exhibited a significantly shorter latency (in days) to show full maternal behavior (FMB) than Control males, median = 5.0 vs 8.0, respectively. P-S females, on the other hand, exhibited a significantly longer latency than Control females to show FMB (7.0 vs 3.0, respectively). as well as longer latencies to retrieve one, two, or three pups, to begin to crouch over pups, and to build nests in response to young. Sex differences were apparent between Control males and Control females (females were more responsive to young). In contrast, P-S males and Control females exhibited similar latencies to show components of FMB (3-5 days), as did P-S females and Control males (7-9 days). These data demonstrate, therefore, that prenatal stress eliminates the sex difference normally observed in pup-induced maternal behavior. Moreover, the data suggest that prenatal stress renders the male's responsiveness to young more "female-like," while conversely rendering the response of the female more "male-like."

Animals↗
PubMed1993

Excitotoxic amino acid injections into the medial amygdala facilitate maternal behavior in virgin female rats.

The inhibitory role of the medial amygdala (MA) in maternal behavior control was explored. Injections of N-methyl-D,L-aspartic acid (NMA), an excitotoxic amino acid, into the MA resulted in a dramatic facilitation of maternal behavior in virgin female rats when pups were presented to them 12 days following the injections. This effect was specific to MA in that NMA injections into the basolateral amygdala were ineffective. The facilitatory effect of NMA injections into MA was found to be hormone dependent in that ovariectomies abolished the effect. Subsequent experiments provided evidence that NMA injections into MA induced a pseudopregnant state lasting about 13 days, and that maternal behavior was greatly facilitated only when pups were presented to such females coincident with pseudopregnancy termination. When pups were presented 24 days following injections of NMA into MA, rather than 12 days, only a modest facilitation of maternal behavior was observed. It was concluded that NMA injections into MA influence maternal behavior in two ways: By inducing an hormonal state stimulatory for maternal behavior and by removing neural inhibition over maternal behavior.

Amygdala↗
PubMed1986

Effects of hypothalamic knife cuts and experience on maternal behavior in the rat.

Recent investigations suggest that the disruption of placentophagia, pup-directed maternal behavior, and nestbuilding seen after lesions of the medial preoptic area (MPO) or the lateral hypothalamus may be due to the interruption at different points of a single longitudinal neural system mediating these behaviors. To test this, we compared the effects of knife cuts on the lateral border of the MPO, and of the posterior medial forebrain bundle (MFB), with asymmetrical cuts combining a unilateral MPO cut with a contralateral MFB cut. We observed placentophagia, nestbuilding, and pup-directed maternal behaviors at, and after, parturition in both primiparous and biparous rats. In primiparae, MPO cuts (a) disrupted placentophagia, (b) delayed the onset of crouching and pup-licking, and (c) eliminated retrieval and nestbuilding. MFB cuts (a) disrupted placentophagia, (b) delayed the onset of maternal behavior, and (c) eliminated nestbuilding. Asymmetrical cuts (a) disrupted placentophagia, and (b) delayed the onset of maternal behavior. In biparous rats, MPO cuts eliminated nestbuilding and retrieval. MFB cuts (a) disrupted placentophagia, and (b) eliminated nestbuilding. Asymmetrical cuts (a) delayed nestbuilding. These results suggest the involvement of a longitudinal neural system in the production of immediate pup-directed maternal behavior, placentophagia, and nestbuilding in parturient primiparae, but which is not critical for the eventual display of maternal behavior and nestbuilding in maternally naive rats, nor for the immediate onset of placentophagia and maternal behavior in maternally experienced rats.

Animals↗
PubMed2000

Maternal behavior stimulates c-fos activity within estrogen receptor alpha-containing neurons in lactating rats.

Estradiol and other hormones are thought to be critical for the onset, but not maintenance, of maternal behavior in rats. Maternal behavior is instead maintained postpartum by tactile stimulation that dams receive during interactions with pups, and many neural sites implicated in the control of maternal behavior show elevated c-fos activity in response to this stimulation. Many of these sites also contain neurons that express the alpha subtype of the estrogen receptor (ERalpha). Because of possible interactions between tactile stimulation from pups, c-fos, and ERalpha in the lactating rat brain, we determined if populations of cells that show increased c-fos activity after maternal behavior in lactating rats also contain ERalpha. Dams were separated from their pups for 48 h beginning on day 5 postpartum. On day 7 postpartum, experimental dams were reunited with pups and mother-litter interactions were observed for 60 min. Control dams received no pup stimulation. Subjects were sacrificed 60 min later and brain sections were double immunolabeled for the Fos and ERalpha proteins. As expected, the number of ERalpha-immunoreactive (ERalpha-ir) neurons did not differ between the two groups in the eight areas analyzed (lateral region of the lateral septum, posterodorsal medial amygdala, dorsal and ventral medial preoptic area, dorsal and ventral bed nucleus of the stria terminalis, lateral habenula, and ventrolateral caudal periaqueductal gray). Consistent with previous reports, maternal dams had 2- to 7-fold more Fos-immunoreactive (Fos-ir) neurons in these sites compared with nonstimulated controls. Maternal dams had significantly more Fos-ir neurons that also contained ERalpha-ir in all sites, with the greatest increases in the ventral medial preoptic area, lateral habenula, and ventral bed nucleus of the stria terminalis. Between approximately 25 and 45% of the Fos-ir cells in the sites examined also expressed ERalpha. Thus, a substantial number of neurons that are genomically activated during maternal behavior contain ERalpha, raising the possibility that the postpartum display of maternal behavior can be influenced by ERalpha activity.

Animals↗