The long lasting effects of electrical simulation of the medial preoptic area and medial amygdala on maternal behavior in female rats

Psychological and neurobiological mechanisms underlying the decline of maternal behavior

The maternal behavior decline is important for the normal development of the young and the wellbeing of the mother. This paper reviews limited research on the factors and mechanisms involved in the rat maternal behavior decline and proposes a multi-level model. Framed in the parent-offspring conflict theory (an ultimate cause) and the approach-withdrawal model (a proximate cause), the maternal behavior decline is viewed as an active and effortful process, reflecting the dynamic interplay between the mother and her offspring. It is instigated by the waning of maternal motivation, coupled with the increased maternal aversion by the mother in responding to the changing sensory and motoric patterns of pup stimuli. In the decline phase, the neural circuit that mediates the inhibitory ("withdrawal") responses starts to increase activity and gain control of behavioral outputs, while the excitatory ("approach") maternal neural circuit is being inhibited or reorganized. Various hormones and certain monoamines may play a critical role in tipping the balance between the excitatory and inhibitory neural circuits to synchronize the mother-infant interaction.

The parental brain and behavior: A target for endocrine disruption

During pregnancy, the sequential release of progesterone, 17β-estradiol, prolactin, oxytocin and placental lactogens reorganize the female brain. Brain structures such as the medial preoptic area, the bed nucleus of the stria terminalis and the motivation network including the ventral tegmental area and the nucleus accumbens are reorganized by this specific hormonal schedule such that the future mother will be ready to provide appropriate care for her offspring right at parturition. Any disruption to this hormone pattern, notably by exposures to endocrine disrupting chemicals (EDC), is therefore likely to affect the maternal brain and result in maladaptive maternal behavior. Development effects of EDCs have been the focus of intense study, but relatively little is known about how the maternal brain and behavior are affected by EDCs. We encourage further research to better understand how the physiological hormone sequence prepares the mother's brain and how EDC exposure could disturb this reorganization.

Role of oxytocin in the medial preoptic area (MPOA) in the modulation of paternal behavior in mandarin voles

Parental care plays an important role in individual survival and development in mammals. Many studies have focused on the mechanisms underlying maternal behavior. However, the underlying neural mechanisms of paternal behavior are less understood. Using monogamous mandarin voles (Microtus mandarinus), the present study found that fathers initiated more paternal behavior and the virgin male showed more infanticide. Moreover fathers had shorter latency to approach a pup at the postnatal day (PND) 10 than PND1, PND20 than nonfathers. Fathers had a shorter latency to take care of unfamiliar pups than nonfathers. They had higher levels of paternal behavior at PND 10 than PND1 and PND20 toward the mandarin vole pups. Fathers had a significantly higher serum concentration of oxytocin (OT) than virgin males. Both RT-PCR and Western blot results indicated that the levels of the oxytocin receptor (OTR) in the medial preoptic area (MPOA) of fathers were significantly higher than in virgin males, but the levels of vasopressin 1a receptor (V1AR) mRNA and protein expression in the MPOA did not show significant differences. Microinjection of an oxytocin receptor antagonist into the MPOA significantly reduced the total duration of paternal behavior and increased the latency to approach the pup and initiate paternal behavior. Our results indicated that OT plays a key role in the modulation of paternal behavior via the MPOA.

Plasticity of paternity: Effects of fatherhood on synaptic, intrinsic and morphological characteristics of neurons in the medial preoptic area of male California mice

Parental care by fathers enhances offspring survival and development in numerous species. In the biparental California mouse, Peromyscus californicus, behavioral plasticity is seen during the transition into fatherhood: adult virgin males often exhibit aggressive or indifferent responses to pups, whereas fathers engage in extensive paternal care. In this species and other biparental mammals, the onset of paternal behavior is associated with increased neural responsiveness to pups in specific brain regions, including the medial preoptic area of the hypothalamus (MPOA), a region strongly implicated in both maternal and paternal behavior. To assess possible changes in neural circuit properties underlying this increased excitability, we evaluated synaptic, intrinsic, and morphological properties of MPOA neurons in adult male California mice that were either virgins or first-time fathers. We used standard whole-cell recordings in a novel in vitro slice preparation. Excitatory and inhibitory post-synaptic currents from MPOA neurons were recorded in response to local electrical stimulation, and input/output curves were constructed for each. Responses to trains of stimuli were also examined. We quantified intrinsic excitability by measuring voltage changes in response to square-pulse injections of both depolarizing and hyperpolarizing current. Biocytin was injected into neurons during recording, and their morphology was analyzed. Most parameters did not differ significantly between virgins and fathers. However, we document a decrease in synaptic inhibition in fathers. These findings suggest that the onset of paternal behavior in California mouse fathers may be associated with limited electrophysiological plasticity within the MPOA.

Insulin-like growth factor I and its binding protein-3 are regulators of lactation and maternal responsiveness

Adaptation to motherhood includes maternal behaviour and lactation during the postpartum period. The major organizing centres of maternal behaviour and lactation are located in the hypothalamic medial preoptic area (MPOA) and the arcuate nucleus, respectively. Insulin-like growth factor I (IGF-I) is an effector of the growth hormone axis; however, its function in the brain is largely unexplored. We identified increased maternal IGF binding protein-3 (IGFBP-3) expression in preoptic rat microarray data and confirmed it by RT-PCR. In situ hybridization histochemistry showed markedly elevated IGFBP-3 expression in the MPOA and the arcuate nucleus in rat dams. Prolonged intracerebroventricular injection of IGF-I or antagonism of brain IGFBP-3 with an inhibitor (NBI-31772) using osmotic minipumps increased pup retrieval time, suggesting reduced maternal motivation. Suckling-induced prolactin release and pup weight gain were also suppressed by IGF-I, suggesting reduced lactation. In addition, IGF-I-induced tyrosine hydroxylase expression and its specific phosphorylation in tuberoinfundibular dopaminergic neurons suppress prolactin secretion. Thus, IGF-I may inhibit both behavioural and lactational alterations in mothers. Neurons in the MPOA and arcuate nuclei express IGFBP-3 during the postpartum period to neutralize IGF-I effects. IGFBP-3 can prevent the blockade of maternal behaviour and lactation exerted by IGF-I, suggesting a novel modulatory mechanism underlying the behavioural and hormonal effects during central maternal adaptations.

Pup exposure facilitates retrieving behavior via the oxytocin neural system in female mice

Parental behavior in mammals is innate, but it is also facilitated by social experience, specifically social interactions between the parent and infant. Social interactions with infants also induce the alloparental behavior of virgin animals. Oxytocin (OT) plays an important role in mediating alloparental behavior. Although parental behavior is modulated by the medial preoptic area (MPOA) and adjacent regions, it is unclear how OT acts in these regions as a control mechanism of alloparental behavior promoted by adult-pup interaction. The aim of this study was to investigate the role of OT for facilitating effects of adult-pup interactions on alloparental behavior via neural activity of preoptic area (POA), including MPOA and adjacent area. For this purpose, we conducted behavioral tests and examined the neural activity of the OT system in POA. Virgin female mice that were repeatedly exposed to pups showed shorter retrieving latencies and higher number of c-Fos expressing neurons in POA, particular in lateral preoptic area (LPO) compared to control animals that were exposed to pups only one time. In addition, repeated pup exposure increased the proportion of OT neurons and OTR neurons expressing c-Fos in POA. The concentration of OT also significantly increased in the POA. Finally, infusion of an OT antagonist into the POA area blocked the facilitating effects of repeated pup exposure on retrieving behavior. These results demonstrated that the facilitating effects of repeated pup exposure on alloparental behavior occurred via an organizational role of the OT system.

Current Models and Future Directions for Understanding the Neural Circuitries of Maternal Behaviors in Rodents

Maternal behaviors in rodents include a number of subcomponents, such as nursing, nest building, licking and grooming of pups, pup retrieval, and maternal aggression. Because each behavior involves a unique motor pattern, a unique ensemble neural circuitry must underlie each behavior. To what extent there is overlap in terms of brain regions and specific neurons for each circuit is being actively investigated. This review will first examine overlapping and separate components of pup retrieval and maternal aggression circuitries while examining a central role for medial preoptic area (MPA) in both behaviors. With an emphasis on experimental approaches, the review will then highlight recent findings and propose future directions for understanding maternal behavior regulation. Finally, examples for why studying the neural basis of maternal behaviors can bring insights to other areas of neuroscience, such as feeding, addiction, and anxiety and aggression regulation will be provided.

The maternal brain and its plasticity in humans

This article is part of a Special Issue "Parental Care". Early mother-infant relationships play important roles in infants' optimal development. New mothers undergo neurobiological changes that support developing mother-infant relationships regardless of great individual differences in those relationships. In this article, we review the neural plasticity in human mothers' brains based on functional magnetic resonance imaging (fMRI) studies. First, we review the neural circuits that are involved in establishing and maintaining mother-infant relationships. Second, we discuss early postpartum factors (e.g., birth and feeding methods, hormones, and parental sensitivity) that are associated with individual differences in maternal brain neuroplasticity. Third, we discuss abnormal changes in the maternal brain related to psychopathology (i.e., postpartum depression, posttraumatic stress disorder, substance abuse) and potential brain remodeling associated with interventions. Last, we highlight potentially important future research directions to better understand normative changes in the maternal brain and risks for abnormal changes that may disrupt early mother-infant relationships.

Neuroanatomical and neurochemical basis of parenting: Dynamic coordination of motivational, affective and cognitive processes

This article is part of a Special Issue "Parental Care". Becoming a parent is arguably the most profound transforming experience in life. It is also inherently very emotionally and physically demanding, such that the reciprocal interaction with the young changes the brain and behavior of the parents. In this review, we examine the neurobiological mechanisms of parenting primarily discussing recent research findings in rodents and primates, especially humans. We argue that it is essential to consider parenting within a conceptual framework that recognizes the dynamics of the reciprocal mother-young relationship, including both the complexity and neuroplasticity of its underlying mechanisms. Converging research suggests that the concerted activity of a distributed network of subcortical and cortical brain structures regulates different key aspects of parenting, including the sensory analysis of infant stimuli as well as motivational, affective and cognitive processes. The interplay among these processes depends on the action of various neurotransmitters and hormones that modulate the timely and coordinated execution of caregiving responses of the maternal circuitry exquisitely attuned to the young's affect, needs and developmental stage. We conclude with a summary and a set of questions that may guide future research.

Neuroplasticity in the maternal hippocampus: Relation to cognition and effects of repeated stress

This article is part of a Special Issue "Parental Care". It is becoming clear that the female brain has an inherent plasticity that is expressed during reproduction. The changes that occur benefit the offspring, which in turn secures the survival of the mother's genetic legacy. Thus, the onset of maternal motivation involves basic mechanisms from genetic expression profiles, to hormone release, to hormone-neuron interactions, all of which fundamentally change the neural architecture - and for a period of time that extends, interestingly, beyond the reproductive life of the female. Although multiple brain areas involved in maternal responses are discussed, this review focuses primarily on plasticity in the maternal hippocampus during pregnancy, the postpartum period and well into aging as it pertains to changes in cognition. In addition, the effects of prolonged and repeated stress on these dynamic responses are considered. The maternal brain is a marvel of directed change, extending into behaviors both obvious (infant-directed) and less obvious (predation, cognition). In sum, the far-reaching effects of reproduction on the female nervous system provide an opportunity to investigate neuroplasticity and behavioral flexibility in a natural mammalian model.

Common and divergent psychobiological mechanisms underlying maternal behaviors in non-human and human mammals

Maternal interactions with young occupy most of the reproductive period for female mammals and are absolutely essential for offspring survival and development. The hormonal, sensory, reward-related, emotional, cognitive and neurobiological regulators of maternal caregiving behaviors have been well studied in numerous subprimate mammalian species, and some of the importance of this body of work is thought to be its relevance for understanding similar controls in humans. We here review many of the important biopsychological influences on maternal behaviors in the two best studied non-human animals, laboratory rats and sheep, and directly examine how the conceptual framework established by some of the major discoveries in these animal "models" do or do not hold for our understanding of human mothering. We also explore some of the limits for extrapolating from non-human animals to humans. We conclude that there are many similarities between non-human and human mothers in the biological and psychological factors influencing their early maternal behavior and that many of the differences are due to species-characteristic features related to the role of hormones, the relative importance of each sensory system, flexibility in what behaviors are exhibited, the presence or absence of language, and the complexity of cortical function influencing caregiving behaviors.

Chemical olfactory signals and parenthood in mammals

This article is part of a Special Issue "Chemosignals and Reproduction". In mammalian species, odor cues emitted by the newborn are essential to establish maternal behavior at parturition and coordinate early mother-infant interactions. Offspring odors become potent attractive stimuli at parturition promoting the contact with the young to ensure that normal maternal care develops. In some species odors provide a basis for individual recognition of the offspring and highly specialized neural mechanisms for learning the infant signals have evolved. Both the main and the accessory olfactory systems are involved in the onset of maternal care, but only the former contributes to individual odor discrimination of the young. Electrophysiological and neurochemical changes occur in the main olfactory bulb leading to a coding of the olfactory signature of the familiar young. Olfactory neurogenesis could also contribute to motherhood and associated learning. Parturition and interactions with the young influence neurogenesis and some evidence indicates a functional link between olfactory neurogenesis and maternal behavior. Although a simple compound has been found which regulates anogenital licking in the rat, studies identifying the chemical nature of these odors are lacking. Neonatal body odors seem to be particularly salient to human mothers who are able to identify their infant's odors. Recent studies have revealed some neural processing of these cues confirming the importance of mother-young chemical communication in our own species.

Afferent projections to the different medial amygdala subdivisions: a retrograde tracing study in the mouse

The medial amygdaloid nucleus (Me) is a key node in the socio-sexual brain, composed of anterior (MeA), posteroventral (MePV) and posterodorsal (MePD) subdivisions. These subdivisions have been suggested to play a different role in reproductive and defensive behaviours. In the present work we analyse the afferents of the three Me subdivisions using restricted injections of fluorogold in female outbred CD1 mice. The results reveal that the MeA, MePV and MePD share a common pattern of afferents, with some differences in the density of retrograde labelling in several nuclei. Common afferents to Me subdivisions include: the accessory olfactory bulbs, piriform cortex and endopiriform nucleus, chemosensory amygdala (receiving direct inputs from the olfactory bulbs), posterior part of the medial bed nucleus of the stria terminalis (BSTM), CA1 in the ventral hippocampus and posterior intralaminar thalamus. Minor projections originate from the basolateral amygdala and amygdalo-hippocampal area, septum, ventral striatum, several allocortical and periallocortical areas, claustrum, several hypothalamic structures, raphe and parabrachial complex. MeA and MePV share minor inputs from the frontal cortex (medial orbital, prelimbic, infralimbic and dorsal peduncular cortices), but differ in the lack of main olfactory projections to the MePV. By contrast, the MePD receives preferential projections from the rostral accessory olfactory bulb, the posteromedial BSTM and the ventral premammillary nucleus. In summary, the common pattern of afferents to the Me subdivisions and their interconnections suggest that they play cooperative instead of differential roles in the various behaviours (e.g., sociosexual, defensive) in which the Me has been shown to be involved.

Storing maternal memories: hypothesizing an interaction of experience and estrogen on sensory cortical plasticity to learn infant cues

Much of the literature on maternal behavior has focused on the role of infant experience and hormones in a canonical subcortical circuit for maternal motivation and maternal memory. Although early studies demonstrated that the cerebral cortex also plays a significant role in maternal behaviors, little has been done to explore what that role may be. Recent work though has provided evidence that the cortex, particularly sensory cortices, contains correlates of sensory memories of infant cues, consistent with classical studies of experience-dependent sensory cortical plasticity in non-maternal paradigms. By reviewing the literature from both the maternal behavior and sensory cortical plasticity fields, focusing on the auditory modality, we hypothesize that maternal hormones (predominantly estrogen) may act to prime auditory cortical neurons for a longer-lasting neural trace of infant vocal cues, thereby facilitating recognition and discrimination. This couldthen more efficiently activate the subcortical circuit to elicit and sustain maternal behavior.

Melanocortin-4 receptor in the medial amygdala regulates emotional stress-induced anxiety-like behaviour, anorexia and corticosterone secretion

The central melanocortin system has been implicated in emotional stress-induced anxiety, anorexia and activation of the hypothalamo-pituitary-adrenal (HPA) axis. However, the underlying neural substrates have not been identified. The medial amygdala (MeA) is highly sensitive to emotional stress and expresses high levels of the melanocortin-4 receptor (MC4R). This study investigated the effects of activation and blockade of MC4R in the MeA on anxiety-like behaviour, food intake and corticosterone secretion. We demonstrate that MC4R-expressing neurons in the MeA were activated by acute restraint stress, as indicated by induction of c-fos mRNA expression. Infusion of a selective MC4R agonist into the MeA elicited anxiogenic-like effects in the elevated plus-maze test and decreased food intake. In contrast, local MeA infusion of SHU 9119, a MC4R antagonist, blocked restraint stress-induced anxiogenic and anorectic effects. Moreover, plasma corticosterone levels were increased by intra-MeA infusion of the MC4R agonist under non-stressed conditions and restraint stress-induced elevation of plasma corticosterone levels was attenuated by pretreatment with SHU 9119 in the MeA. Thus, stimulating MC4R in the MeA induces stress-like anxiogenic and anorectic effects as well as activation of the HPA axis, whereas antagonizing MC4R in this region blocks such effects induced by restraint stress. Together, our results implicate MC4R signalling in the MeA in behavioural and endocrine responses to stress.

Neuromolecular basis of parental behavior in laboratory mice and rats: with special emphasis on technical issues of using mouse genetics

To support the well-being of the parent-infant relationship, the neuromolecular mechanisms of parental behaviors should be clarified. From neuroanatomical analyses in laboratory rats, the medial preoptic area (MPOA) has been shown to be of critical importance in parental retrieving behavior. More recently, various gene-targeted mouse strains have been found to be defective in different aspects of parental behaviors, contributing to the identification of molecules and signaling pathways required for the behavior. Therefore, the neuromolecular basis of "mother love" is now a fully approachable research field in modern molecular neuroscience. In this review, we will provide a summary of the required brain areas and gene for parental behavior in laboratory mice (Mus musculus) and rats (Rattus norvegicus). Basic protocols and technical considerations on studying the mechanism of parental behavior using genetically-engineered mouse strains will also be presented.

The medial preoptic area is necessary for motivated choice of pup- over cocaine-associated environments by early postpartum rats

Converging evidence suggests that the motivation to seek cocaine during the postpartum period is significantly impacted by the competing incentives of offspring, a stimulus unique to this life stage. In the present study, the functional role of the medial preoptic area (mPOA), a critical site involved in maternal responsiveness, on processing incentive value of pup-associated cues and influencing response allocation for pup- over cocaine-associated environments was investigated using a concurrent pup/cocaine choice conditioned place preference (CPP) paradigm. Early postpartum females with bilateral guide cannulae aimed into the mPOA or into anatomical control sites were conditioned, from postpartum days (PPD) 4 to 7, to associate different uniquely featured environments with pups or cocaine. CPP was tested on PPD8 following intra-mPOA infusions of either 2% bupivacaine or saline vehicle. In two additional experiments, the effects of intra-mPOA infusions of bupivacaine on expression of conditioned responding induced by environments associated with either pups or cocaine were examined separately. Transient inactivation of the mPOA selectively blocked the conditioned preferences for pup-associated environments, significantly contrasting the robust pup-CPP found in non-surgical and intra-mPOA vehicle-treated females. In contrast, mPOA inactivation failed to alter cocaine-CPP in postpartum females. When given a choice between environments associated with pups or cocaine, transient functional inactivation of the mPOA altered choice behavior, biasing the preference of females toward cocaine-associated environments, such that almost all preferred cocaine- and none the pup-associated option. The anatomical specificity was revealed when inactivation of adjacent regions to the mPOA did not affect CPP responses for pups. The findings support a critical role for the mPOA in mediating pup-seeking behavior, and further suggest that the competing properties of pups over alternative incentives, including drugs of abuse, rely on mPOA integrity to provide relevant pup-related information to the circuitry underlying the choice behavior between pups and alternative stimuli.

The role of the estrogen receptor alpha in the medial amygdala and ventromedial nucleus of the hypothalamus in social recognition, anxiety and aggression

Social recognition manifests itself in decreased investigation of a previously encountered individual. Estrogen receptor alpha (ERalpha) knock out mice show deficient social recognition and anxiety. These data show that the ERalpha is involved in these effects, but they do not say anything about the brain sites important for these effects. In this study, an shRNA encoded within an AAV viral vector directed against the ERalpha receptor gene (or containing luciferase control), was injected bilaterally into the posterodorsal amygdala (MePDA) or the ventromedial nucleus of the hypothalamus (VMN) of female rats. An 81% reduction of ERalpha expression in the MePDA eliminated social recognition. Moreover, this diminution of ERalpha in the MePDA reduced anxiety in the light/dark choice test. In contrast, social recognition was unaffected after ERalpha knockdown in the VMN while aggressiveness against the juvenile was enhanced. In conclusion, social recognition and anxiety in female rats are modulated by the ERalpha in the amygdala. Moreover, aggression against juveniles but not against adults could, at least partly, depend on the ERalpha in the VMN.

Dopaminergic projections to the medial preoptic area of postpartum rats

Dopamine receptor activity in the rodent medial preoptic area (mPOA) is crucial for the display of maternal behaviors, as well as numerous other physiological and behavioral functions. However, the origin of dopaminergic input to the mPOA has not been identified through neuroanatomical tracing. To accomplish this, the retrograde tracer Fluorogold was iontophoretically applied to the mPOA of postpartum laboratory rats, and dual-label immunocytochemistry for Fluorogold and tyrosine hydroxylase later performed to identify dopaminergic cells of the forebrain and midbrain projecting to the mPOA. Results indicate that the number of dopaminergic cells projecting to the mPOA is moderate ( approximately 90 cells to one hemisphere), and that these cells have an unexpectedly wide distribution. Even so, more than half of the dual-labeled cells were found in either what has been considered extensions of the A10 dopamine group (particularly the ventrocaudal posterior hypothalamus and adjacent medial supramammillary nucleus), or in the A10 group of the ventral tegmental area. The rostral hypothalamus and surrounding region also contained numerous dual-labeled cells, with the greatest number found within the mPOA itself (including in the anteroventral preoptic area and preoptic periventricular nucleus). Notably, dual-labeled cells were rare in the zona incerta (A13), a site previously suggested to provide dopaminergic input to the mPOA. This study is the first to use anatomical tracing to detail the dopaminergic projections to the mPOA in the laboratory rat, and indicates that much of this projection originates more caudally than previously suggested.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

ERK-FosB signaling in dorsal MPOA neurons plays a major role in the initiation of parental behavior in mice

During mouse parental behavior, neurons in the dorsal medial preoptic area (MPOAd) are activated and express transcription factors such as c-Fos and FosB. FosB-knockout mice are reported to be defective in parental care. To clarify molecular signaling responsible for parental behavior, we investigated gene expression profiles in the MPOAd of parental versus nonparental mice. We identified upregulation of NGFI-B, SPRY1, and Rad in parental mice, together with c-Fos and FosB. A common inducer of these genes, the extracellular signal regulated kinase (ERK) was phosphorylated in MPOAd neurons upon pup exposure. Pharmacological blockade of ERK phosphorylation inhibited the FosB upregulation in MPOAd, and the initiation of pup retrieving in virgin female mice, but did not affect the established parenting in parous females. Furthermore, induction of SPRY1 and Rad was impaired in MPOAd of nonparental FosB-knockout mice. These results suggest the pivotal role of ERK-FosB signaling in the initiation of parental care.

Arousal regulation, emotional flexibility, medial amygdala function, and the impact of early experience: comments on the paper of Lewis et al

The balance between optimal levels of emotional arousal and cognitive performance reflects the integration of several dopaminergically and adrenergically regulated neural systems. The amygdalar system is a key region for gating stimulation to cortical regions and the medial amygdala appears to play an especially key role in mediating the fear response. More generally, these arousal regulatory neural systems are key to frustration or stress impact prefrontal cortical function. Further, the threshold for when the level of stress is overwhelming and hence impairs cognitive function reflects minimally genetic and experiential influence. An important interface between Drs. Lewis and Davis's work is how early experience, especially through early parenting, may set the threshold of responsiveness for these arousal regulatory neural systems.

Kindling increases aversion to saccharin in taste aversion learning

Kindling is a model in which an initially subconvulsive electrical stimulation of certain brain areas eventually develops a generalized seizure that produces behavioral and long term neuronal changes. In the present study we evaluated if kindling can modify conditioning taste aversion (CTA). In this paradigm animals acquire aversion to saccharin when it is presented as the conditioned stimulus (CS) followed by an injection of lithium chloride (LiCl) that induces a gastric irritation as the unconditioned stimulus (US). Male Wistar rats were implanted with bipolar electrodes aimed at the right amygdala (AMG) or at the right insular cortex (IC). The animals were stimulated daily until they reached stages 2-4 (intermediate) or until kindling was fully established (three consecutive stage 5 seizures). At least two weeks after kindling stimulation had ceased the animals were deprived of water for 24 h and given 10-min drinking sessions twice a day for 4 days. On day 5 (morning session) tap water was replaced by saccharin solution (0.1%), 20 min later the animals were injected with LiCl (7.5 ml/kg i.p., 0.2 M) to induce gastric malaise or taste aversion. After three more days of baseline consumption, water was substituted by a fresh 0.1% saccharin solution to test the aversion. AMG-kindling delayed the extinction of CTA. Animals with kindling in the IC had a higher retention than the sham kindling group; that is, they drank significantly less saccharin solution than the other groups. The results of the present experiment show that local modification of brain function induced by kindling stimulation can prolong the aversive effects of CTA.

Juvenile rats show reduced c-fos activity in neural sites associated with aversion to pups and inhibition of maternal behavior

Juvenile rats (18-23 days old) interact avidly with pups as novel stimuli and show maternal behavior after only 1-3 days of pup exposure; adults initially avoid pups and require 3-9 days of pup exposure. Upon exposure to pups as novel stimuli, adults had more c-Fos-immunoreactive neurons in the hypothalamus and amygdala--regions associated with aversion to pups--than adults exposed to familiar pup stimuli (maternal) or not exposed to pups (p < .05). In juvenile rats exposed to pups as novel stimuli, only the medial amygdala had a small significant increase of c-Fos neurons. In juveniles, this blunted engagement of c-Fos neurons may reflect the diminished activation of inhibitory neurons, facilitating the interaction of juveniles with pups as novel stimuli and onset of maternal behavior.

The vertebrate social behavior network: evolutionary themes and variations

Based on a wide variety of data, it is now clear that birds and teleost (bony) fish possess a core "social behavior network" within the basal forebrain and midbrain that is homologous to the social behavior network of mammals. The nodes of this network are reciprocally connected, contain receptors for sex steroid hormones, and are involved in multiple forms of social behavior. Other hodological features and neuropeptide distributions are likewise very similar across taxa. This evolutionary conservation represents a boon for experiments on phenotypic behavioral variation, as the extraordinary social diversity of teleost fish and songbirds can now be used to generate broadly relevant insights into issues of brain function that are not particularly tractable in other vertebrate groups. Two such lines of research are presented here, each of which addresses functional variation within the network as it relates to divergent patterns of social behavior. In the first set of experiments, we have used a sexually polymorphic fish to demonstrate that natural selection can operate independently on hypothalamic neuroendocrine functions that are relevant for (1) gonadal regulation and (2) sex-typical behavioral modulation. In the second set of experiments, we have exploited the diversity of avian social organizations and ecologies to isolate species-typical group size as a quasi-independent variable. These experiments have shown that specific areas and peptidergic components of the social behavior network possess functional properties that evolve in parallel with divergence and convergence in sociality.

Mapping of brain networks involved in consolidation of lamb recognition memory

In sheep, ewes at parturition are responsive to any newborn lamb, but within less than 1 h, mothers learn to recognize the odor of their lamb and restrict maternal care to their own offspring (maternal selectivity). In a first experiment, we investigated the long-term retention of maternal selectivity after various mother-young contact and separation durations. After 4 h of contact, 36 h of separation leads to a total loss of selectivity. Increasing contact duration to 7 days prior to this separation maintains selectivity. These data suggest that lamb memory after going through an initial labile state after parturition, is consolidated over time into a more stable long-term memory. Fos immunohistochemistry reveals that reintroduction of the lamb after 4 h of mother-young contact and 3 h of separation activates different maternal brain regions than reintroduction of the lamb after 7 days of mother-young contact and 3 h of separation. While the piriform cortex shows an enhanced activation at both times, a selective enhancement of activation is observed in the frontal medial and orbitofrontal cortices only after 7 days of mother-young contact. These data suggest that as consolidation occurs, the neurobiological networks sustaining lamb memory involve different structures.

Influence of sex, estrous cycle and motherhood on dendritic spine density in the rat medial amygdala revealed by the Golgi method

The medial nucleus of the amygdala (MeA), a sexually dimorphic area, contains estrogen and androgen receptors and has an integrative role in behavioral, vegetative and endocrine activities of rats. The density of dendritic spines along the first 40 microm of dendritic length was studied in neurons from the anterodorsal (MeAD), posterodorsal (MePD) and posteroventral (MePV) aspects of the MeA in males, in virgin females during the four phases of the estrous cycle and in multiparous females in diestrus. The single-section Golgi method was employed (N=48 observations per experimental group). In the three MeA subnuclei males showed more dendritic spines than virgin females (P<0.001), with the only exception being the MePD data of females in diestrus (P>0.05). In virgin females, whereas more dendritic spines were found in diestrus, a decline in these values was found during the proestrus, estrus and metaestrus in the MePD and MePV (P<0.05) but not in the MeAD (P>0.05). Compared with virgin females in diestrus, postpartum rats showed more spines in the MeAD (P<0.001) and fewer in the MePD (P<0.001) but no difference was found in the MePV (P>0.05). These data suggest that there are subregion-specific differences in the density of dendritic spines within the MeA and that they appear to be affected by sex, cyclic fluctuations in the levels of ovarian steroids and following pregnancy in rats. These findings may add to the understanding of the MeA neuronal plastic changes that affect the ongoing processing of sensory information and the organization of the neuroendocrine and behavioral basis of reproduction.

Olfactory regulation of maternal behavior in mammals

In mammals, olfactory cues are extensively used in many aspects of maternal care to ensure the coordination of mother-infant interactions and consequently the normal development of the offspring. Outside the period of parturition and lactation, when the young are not a behavioral priority, olfactory cues play an inhibitory role on maternal responsiveness since in most mammalian species studied so far, nonpregnant females find the odor of young aversive. On the contrary at the time of parturition, a shift in the hedonic value of infantile odors occurs so that the young now become a very potent stimulus and this sensorial processing constitutes an important part of the maternal motivational system. Moreover, infants' odors provide a basis for individual recognition by their mothers and some species (ungulates) have developed highly specialized mechanisms for processing of the infant signals. Perception of the smell of the young also regulates various aspects of maternal behavior. Dodecyl propionate, a compound released by of pup's preputial glands, has been shown to influence anogenital licking behavior, a fundamental pattern of maternal behavior in rodents. While there is no functional specificity of either the main or the accessory olfactory systems in the development of maternal behavior amongst species, it appears that only the main olfactory system is implicated when individual odor discrimination of the young is required. Neural structures, such as the main olfactory bulb, undergo profound changes when exposed to offspring odors at parturition. These changes in synaptic circuitry contribute both to maternal responsiveness to these odors, to their memorization, and to effects of long-term maternal experience.

Substance P in the medial amygdala: emotional stress-sensitive release and modulation of anxiety-related behavior in rats

Increasing evidence implicates the substance P (SP)/neurokinin-1 receptor system in anxiety and depression. However, it is not known whether emotional stimulation alters endogenous extracellular SP levels in brain areas important for processing of anxiety and mood, a prerequisite for a contribution of this neuropeptide system in modulating these behaviors. Therefore, we examined in rats whether the release of SP is sensitive to emotional stressors in distinct subregions of the amygdala, a key area in processing of emotions. By using in vivo micropush-pull superfusion and microdialysis techniques, we found a pronounced and long-lasting increase (150%) in SP release in the medial nucleus of the amygdala (MeA), but not in the central nucleus of the amygdala, in response to immobilization stress. SP release in the MeA was transiently enhanced (40%) in response to elevated platform exposure, which is regarded as a mild emotional stressor. Immobilization enhanced the anxiety-related behavior evaluated in the subsequently performed elevated plus-maze test. Bilateral microinjections of the neurokinin-1 receptor antagonist [2-cyclopropoxy-5-(5-(trifluoromethyl)tetrazol-1-yl)benzyl]-(2-phenylpiperidin-3-yl)amine into the MeA blocked the stress-induced anxiogenic-like effect, supporting a functional significance of enhanced SP release. In unstressed rats, the neurokinin-1 receptor antagonist displayed no significant anxiolytic effect but reversed the anxiogenic effect of SP microinjected into the MeA. Our findings identify the MeA as a critical brain area for the involvement of SP transmission in anxiety responses and as a putative site of action for the recently discovered therapeutic effects of SP antagonists in the treatment of stress-related disorders.

Long-term effects of prenatal morphine exposure on maternal behaviors differ from the effects of direct chronic morphine treatment

Previous studies have demonstrated that chronic morphine treatment of pregnant rats alters maternal behavior. Other studies have shown long-term effects of prenatal exposure to morphine, including changes in reproductive behavior in adult females. The present study investigated the effects of prenatal morphine exposure on a variety of maternal behaviors such as nursing, maternal activities, nonmaternal activities, and pup retrieval. Prenatal morphine exposure increased active and decreased passive nursing. There were no differences in maternal activities such as presence in the nest, contact with pups, grooming of pups, and/or manipulation of nest shavings. In the retrieval test, prenatally morphine-exposed mothers were faster in carrying the first pup, retrieving the first pup back to the nest, and returning all pups to the nest than prenatally saline-exposed mothers. Maternal and nonmaternal activities also were affected by the light: dark cycle. All saline- and morphine-exposed mothers nursed more, were more often in the nest, and more often in contact with greater than half of their litter during the light than the dark sessions. On the other hand, nonmaternal activities increased during the dark sessions: Mothers cared for themselves (groomed, ate) more and displayed more rearing and sniffing. Mothers spent more time resting with their eyes closed during the light sessions regardless of prenatal drug exposure. The present study demonstrated that the effect of morphine on maternal behavior is different in adult exposed and prenatally exposed mothers. While direct morphine treatment impaired maternal behaviors, prenatal morphine exposure has the opposite effect.

Medial preoptic area/anterior hypothalamus and sexual motivation

The medial preoptic area/anterior hypothalamus (MPOA/AH) is a brain site derived from proliferative zones from the diencephalon and telencephalon. It is probably this characteristic that makes this brain region participate in different physiological and behavioral functions. The present review addresses the role of the MPOA/AH in the control of male sexual behavior. It is clear that the MPOA/AH is a crucial site in the control of sexual behavior in males of all species studied to date. But although many different publications have followed the contribution of Heimer and Larsson there is no agreement as to what is specifically the role of the MPOA/AH in sexual behavior. At least three hypotheses have been presented. The first one suggests that this brain region is involved in the consummatory aspects (execution) of sexual behavior. The second indicates that the MPOA/AH is involved in the appetitive components (motivation) of masculine sexual behavior. The third hypothesis considers that MPOA/AH neurons are involved in the regulation of consummatory and appetitive aspects of sexual behavior. From the literature reviewed, it will become evident that the evidence supporting a role of the MPOA/AH in the execution of sexual behavior is based on a number of limited studies not easy to interpret. On the other hand, several lines of evidence using a variety of methodologies support the notion that the MPOA/AH is involved in the motivational aspects of male sexual behavior.

Facilitation of male-like coital behavior in female rats by kindling

Kindling is a model of epilepsy and brain plasticity. When applied to the medial preoptic area (MPOA) of non-copulating male rats kindling induces masculine sexual behavior. In order to test if kindling could facilitate male-like coital behavior in female rats, sexually naive females were ovariectomized and kindled in the amygdala (AMG) or the MPOA until an intermediate stage (between 1 and 3, MPOA1-3) or until stage 5 (MPOA5 group). Once kindling was established, females were treated with 2.5 mg/Kg of testosterone propionate (TP) for 15 days. Male-like coital behavior was evaluated on days 5, 10 and 15 of treatment. Subjects were then injected with a TP dose of 5 mg/kg for 15 days and tested in the same way as with the lower dose. The number of mounts was significantly increased and the mount latency was significantly reduced in the MPOA1-3 group when tested 5 days after treatment with the low dose of TP. The same facilitation was observed in MPOA1-3 and MPOA5 groups on day 10 of treatment with the low dose of TP. When the animals were under the high dose of TP treatment, the number of intromissions was increased in all experimental groups (including the AMG kindled group) in comparison to sham animals. In a second experiment we evaluated if the facilitation of male-like coital behavior induced by kindling was produced by a modification of the response of the vomeronasal system to sexually relevant cues. Ovariectomized females were stimulated until they reached kindling stage 2, then they were treated with 2.5 mg/kg of TP for 5 days. After animals were exposed for 90 min to clean sawdust or sawdust soiled by estrous females they were perfused. Fos was detected by immunocytochemistry along the vomeronasal pathway. No differences were found in Fos responses between sham and MPOA kindled females. The facilitation of masculine sexual behavior observed in AMG kindled females may be a consequence of the propagation of the AD to other brain regions involved in the expression of masculine sexual behavior. We propose that masculine sexual behavior is facilitated in MPOA kindled female rats by local neural changes produced by this kind of stimulation without modifying the response of the vomeronasal system to sexually relevant cues.

Permanent changes in sexual behavior induced by medial preoptic area kindling-like stimulation

Kindling is a model of neuronal plasticity in which repeated electrical stimulation of certain brain areas leads to the progressive development of motor seizures. We have previously shown that medial preoptic area (MPOA) kindling induces sexual behavior in non-copulating male rats. In the present experiment, we found that previously non-copulating male rats display sexual behavior even 8 months after kindling stimulation had ceased. In addition, elicitation of an afterdischarge (AD) or stimulation until an intermediate stage was sufficient to induce sexual behavior in previously non-copulating male rats. These results suggest that kindling like stimulation, without seizure development, can induce permanent behavioral changes.

Artificial rearing causes changes in maternal behavior and c-fos expression in juvenile female rats

This study investigated the effects of early-rearing experiences on responsiveness to pups and on the pattern of c-fos activation in the brain of juvenile female rats. From Days 4 to 20, littermate females were reared with their mothers (MR) or artificially (AR). AR rats received minimal licking-like tactile stimulation (AR-min) or maximal stimulation (AR-max). On Day 20, rats were exposed to pups for 4 or 8 days, exposed to a playmate for 4 or 8 days, or left in isolation for 4 or 8 days. Compared with MR rats, pup-exposed AR rats engaged in less pup licking, and all AR rats showed significant reductions in c-fos immunoreactivity in the medial preoptic area and the parietal and piriform cortices. The AR-min group showed the greatest difference in Fos-lir compared with the MR groups. Possible mechanisms that mediate the effects of rearing on the development of neural circuits underlying maternal behavior are discussed.

Emotional behaviour as the result of stochastic interactions. A process crucial for cognition

This paper is aimed at exhibiting two striking features of the usual approach of emotional expression in science and philosophy, suggesting a different perspective. One is the generally shared belief that emotions are a state of utter disarray, which hampers objective knowledge; the other is the search for causal explanation, along a wide range of categorized approaches (psychology, neurosciences, developmental biology) each proposing its own theoretical framework. In both cases the result is to play down emotional expression. Alternatively, we propose to view emotions as something crucial in the choice of our conceptual tools, ideas and involvements, in the genesis of which various explanations interact in a complex stochastic way. Rather than being a harmful disruption of the mind calling for identification of a definite causality, emotional behaviour appears as a necessary process in cognition, which is irreducible to a unique origin.

Brain preparations for maternity--adaptive changes in behavioral and neuroendocrine systems during pregnancy and lactation. An overview

Pregnancy, parturition and lactation comprise a continuum of adaptive changes necessary for the development and maintenance of the offspring. The endocrine changes that are driven by the conceptus and are essential for the maintenance of pregnancy and are involved in the preparations for motherhood are outlined. These changes include large increases in the secretion of sex steroid hormones, and the secretion of peptide hormones that are unique to pregnancy. The ability of these pregnancy hormones to alter several aspects of brain function in pregnancy is considered, and the adaptive importance of some of these changes is discussed, for example in metabolic and body fluid adjustments, and the induction of maternal behavior. The importance of sex steroids in determining the timing of the various adaptive changes in preparing for parturition and maternal behavior is emphasized, and the concept that the actions of prolactin and oxytocin, quintessential mammalian motherhood neuropeptides, can serve to coordinate a spectrum of adaptive changes is discussed. The part played by oxytocin neurons and their regulatory mechanisms is reviewed to illustrate how neural systems involved in maternity are prepared in pregnancy via changes in phenotype, synaptic organization and in the relative importance of their different inputs, to function optimally when needed. For oxytocin neurons secreting from the posterior pituitary, important in parturition and essential in lactation, these changes include mechanisms to restrain their premature activation, and adaptations to support synchronized burst firing for pulsatile oxytocin secretion in response to stimulation via afferents from the birth canal, olfactory system or suckled nipples. Within the brain, expression of oxytocin receptors permits centrally released oxytocin to facilitate the expression of maternal behavior. Changes in other neuroendocrine systems are similarly extensive, leading to lactation, suppression of ovulation, reduced stress responses and increased appetite; these changes in lactation are driven by the suckling stimulus. The possible link between these adaptations and changes in cognition and mood in pregnancy and post partum are considered, as well as the dysfunctions that lead to common problems of depression and puerperal psychoses.

Distribution of gonadal steroid receptor-containing neurons in the preoptic-periaqueductal gray-brainstem pathway: a potential circuit for the initiation of male sexual behavior

The present study used anterograde and retrograde tract tracing techniques to examine the organization of the medial preoptic-periaqueductal gray-nucleus paragigantocellularis pathway in the male rat. The location of neurons containing estrogen (alpha subtype; ER alpha) and androgen receptors (AR) were also examined. We report here that injection of the anterograde tracer biotinylated dextran amine (BDA) into the medial preoptic (MPO) produced dense labeling within the periaqueductal gray (PAG); anterogradely labeled fibers terminated in close juxtaposition to neurons retrogradely labeled from the nucleus paragigantocellularis (nPGi). Dual immunostaining for Fluoro-Gold (FG) and ER alpha or FG and AR showed that over one-third of MPO efferents to the PAG contain receptors for either estrogen or androgen. In addition, approximately 50% of PAG neurons retrogradely labeled from the nPGi were immunoreactive for either ER alpha or AR. These results are the first to establish an MPO-->PAG-->nPGi circuit and further indicate that gonadal steroids can influence neuronal synaptic activity within these sites. We reported previously that nPGi reticulospinal neurons terminate preferentially within the motoneuronal pools of the lumbosacral spinal cord that innervate the pelvic viscera. Together, we propose that the MPO-->PAG-->nPGi circuit forms the final common pathway whereby MPO neural output results in the initiation and maintenance of male copulatory reflexes.

Repeated morphine administration during pregnancy attenuates maternal behavior

The present study tested the hypothesis that repeated administration of morphine on days 11-18 of pregnancy alters maternal behavior. Saline- and morphine-treated mothers were observed with their pups in two experiments. Rats were always tested twice a day during the light and dark phases of the reverse light/dark cycle. In Experiment 1, 12 types of activities and three types of nursing positions of mothers were recorded ten times during each 50-minute session for the 23-day lactation period. A decrease in nursing and active maternal behavior, and an increase in self-care, rearing and sniffing was found in morphine-treated mothers. Additionally, both saline- and morphine-treated mothers exhibited significantly more maternal behavior during the light, and non-maternal activities during the dark sessions of each day. Moreover, both saline- and morphine-treated mothers displayed significantly less maternal behavior and more non-maternal activities as postpartum time progressed. In Experiment 2, a different group of mothers was tested for pup retrieval from postnatal days 1 through 12. Morphine-treated mothers were slower than saline-treated mothers in retrieving all pups into the nest. However, there were no differences in latency to carry the first pup and return him/her to the nest. No unusual maternal behaviors were observed during the retrieval tests. Thus, the present study suggests that morphine administration during the second half of pregnancy attenuates some components of maternal behavior and increases non-maternal activities of mothers.