Ultrasound-induced Parental Behaviour in House Mice is Controlled by Female Sex Hormones and Parental Experience

Tactile Mechanisms and Afferents Underlying the Rat Pup Transport Response

Juvenile rodents and other altricial mammals react with calming, immobility and folding up of feet to parental pickup, a set of behaviors referred to as transport response. Here we investigate sensory mechanisms underlying the rat transport response. Grasping rat pups in anterior neck positions evokes strong immobility and folding up of feet, whereas more posterior grasping positions have lesser effects on immobility and foot position. Transport responses are enhanced by slow (1Hz) and even more so by fast (4Hz) gentle shaking and translation of the pup, features consistent with parental transport. In response to lateral grasping, the forepaw below the grasping position points downwards and the forepaw lateral to the grasping position points upwards and medially. Such forepaw adjustments put the pup's center of gravity below the grasping point, optimizing pup transportability along with folding up of feet and tail lifting. Tactile stimuli on the back, belly, tail, whisker, dorsal forepaws and dorsal hind-paws do not significantly affect the behaviour of anterior-neck-held pups. Instead, ground contact or paw stimulation consistent with ground contact disrupts transport responses. We identify afferents mediating the transport response by examining membrane labelling with FM1-43 following anterior neck grasping. We observe a dense innervation of the anterior neck skin region (~30 terminals/ mm2). We also observed an age-related decrease of cytochrome oxidase reactivity in the rat somatosensory cortical neck representation, a possible correlate to the developmental decrease in the pup transport response. We conclude anterior neck grasping and loss of ground contact trigger calming and postural adjustments for parental transport in rat pups, responses putatively driven from the densely innervated anterior neck skin.

Neural responses to pup calls and pup odors in California mouse fathers and virgin males

The onset of mammalian maternal care is associated with plasticity in neural processing of infant-related sensory stimuli; however, little is known about sensory plasticity associated with fatherhood. We quantified behavioral and neural responses of virgin males and new fathers to olfactory and auditory stimuli from young, unfamiliar pups in the biparental California mouse (Peromyscus californicus). Each male was exposed for 10minutes to one of four combinations of a chemosensory stimulus (pup-scented or unscented cotton [control]) and an auditory stimulus (pup vocalizations or white noise [control]). Behavior did not differ between fathers and virgins during exposure to sensory stimuli or during the following hour; however, males in both groups were more active both during and after exposure to pup-related stimuli compared to control stimuli. Fathers had lower expression of Fos in the main olfactory bulbs (MOB) but higher expression in the medial preoptic area (MPOA) and bed nucleus of the stria terminalis medial division, ventral part (STMV) compared to virgins. Lastly, males had higher Fos expression in MPOA when exposed to pup odor compared to control stimuli, and when exposed to pup odor and pup calls compared to pup calls only or control stimuli. These findings suggest that the onset of fatherhood alters activity of MOB, MPOA and STMV and that pup odors and vocalizations have additive or synergistic effects on males' behavior and MPOA activation.

Activation of the medial preoptic area (MPOA) ameliorates loss of maternal behavior in a Shank2 mouse model for autism

Impairments in social relationships and awareness are features observed in autism spectrum disorders (ASDs). However, the underlying mechanisms remain poorly understood. Shank2 is a high‐confidence ASD candidate gene and localizes primarily to postsynaptic densities (PSDs) of excitatory synapses in the central nervous system (CNS). We show here that loss of Shank2 in mice leads to a lack of social attachment and bonding behavior towards pubs independent of hormonal, cognitive, or sensitive deficits. Shank2^−/− mice display functional changes in nuclei of the social attachment circuit that were most prominent in the medial preoptic area (MPOA) of the hypothalamus. Selective enhancement of MPOA activity by DREADD technology re‐established social bonding behavior in Shank2^−/− mice, providing evidence that the identified circuit might be crucial for explaining how social deficits in ASD can arise.

Neural Regulation of Paternal Behavior in Mammals: Sensory, Neuroendocrine, and Experiential Influences on the Paternal Brain

Across the animal kingdom, parents in many species devote extraordinary effort toward caring for offspring, often risking their lives and exhausting limited resources. Understanding how the brain orchestrates parental care, biasing effort over the many competing demands, is an important topic in social neuroscience. In mammals, maternal care is necessary for offspring survival and is largely mediated by changes in hormones and neuropeptides that fluctuate massively during pregnancy, parturition, and lactation (e.g., progesterone, estradiol, oxytocin, and prolactin). In the relatively small number of mammalian species in which parental care by fathers enhances offspring survival and development, males also undergo endocrine changes concurrent with birth of their offspring, but on a smaller scale than females. Thus, fathers additionally rely on sensory signals from their mates, environment, and/or offspring to orchestrate paternal behavior. Males can engage in a variety of infant-directed behaviors that range from infanticide to avoidance to care; in many species, males can display all three behaviors in their lifetime. The neural plasticity that underlies such stark changes in behavior is not well understood. In this chapter we summarize current data on the neural circuitry that has been proposed to underlie paternal care in mammals, as well as sensory, neuroendocrine, and experiential influences on paternal behavior and on the underlying circuitry. We highlight some of the gaps in our current knowledge of this system and propose future directions that will enable the development of a more comprehensive understanding of the proximate control of parenting by fathers.

Effects of repeated pup exposure on behavioral, neural, and adrenocortical responses to pups in male California mice (Peromyscus californicus)

In biparental mammals, the factors facilitating the onset of male parental behavior are not well understood. While hormonal changes in fathers may play a role, prior experience with pups has also been implicated. We evaluated effects of prior exposure to pups on paternal responsiveness in the biparental California mouse (Peromyscus californicus). We analyzed behavioral, neural, and corticosterone responses to pups in adult virgin males that were interacting with a pup for the first time, adult virgin males that had been exposed to pups 3 times for 20min each in the previous week, and new fathers. Control groups of virgins were similarly tested with a novel object (marble). Previous exposure to pups decreased virgins' latency to approach pups and initiate paternal care, and increased time spent in paternal care. Responses to pups did not differ between virgins with repeated exposure to pups and new fathers. In contrast, repeated exposure to a marble had no effects. Neither basal corticosterone levels nor corticosterone levels following acute pup or marble exposure differed among groups. Finally, Fos expression in the medial preoptic area, ventral and dorsal bed nucleus of the stria terminalis was higher following exposure to a pup than to a marble. Fos expression was not, however, affected by previous exposure to these stimuli. These results suggest that previous experience with pups can facilitate the onset of parental behavior in male California mice, similar to findings in female rodents, and that this effect is not associated with a general reduction in neophobia.

Knowledge About Sounds-Context-Specific Meaning Differently Activates Cortical Hemispheres, Auditory Cortical Fields, and Layers in House Mice

Activation of the auditory cortex (AC) by a given sound pattern is plastic, depending, in largely unknown ways, on the physiological state and the behavioral context of the receiving animal and on the receiver's experience with the sounds. Such plasticity can be inferred when house mouse mothers respond maternally to pup ultrasounds right after parturition and naïve females have to learn to respond. Here we use c-FOS immunocytochemistry to quantify highly activated neurons in the AC fields and layers of seven groups of mothers and naïve females who have different knowledge about and are differently motivated to respond to acoustic models of pup ultrasounds of different behavioral significance. Profiles of FOS-positive cells in the AC primary fields (AI, AAF), the ultrasonic field (UF), the secondary field (AII), and the dorsoposterior field (DP) suggest that activation reflects in AI, AAF, and UF the integration of sound properties with animal state-dependent factors, in the higher-order field AII the news value of a given sound in the behavioral context, and in the higher-order field DP the level of maternal motivation and, by left-hemisphere activation advantage, the recognition of the meaning of sounds in the given context. Anesthesia reduced activation in all fields, especially in cortical layers 2/3. Thus, plasticity in the AC is field-specific preparing different output of AC fields in the process of perception, recognition and responding to communication sounds. Further, the activation profiles of the auditory cortical fields suggest the differentiation between brains hormonally primed to know (mothers) and brains which acquired knowledge via implicit learning (naïve females). In this way, auditory cortical activation discriminates between instinctive (mothers) and learned (naïve females) cognition.

Adult plasticity in the subcortical auditory pathway of the maternal mouse

Subcortical auditory nuclei were traditionally viewed as non-plastic in adulthood so that acoustic information could be stably conveyed to higher auditory areas. Studies in a variety of species, including humans, now suggest that prolonged acoustic training can drive long-lasting brainstem plasticity. The neurobiological mechanisms for such changes are not well understood in natural behavioral contexts due to a relative dearth of in vivo animal models in which to study this. Here, we demonstrate in a mouse model that a natural life experience with increased demands on the auditory system - motherhood - is associated with improved temporal processing in the subcortical auditory pathway. We measured the auditory brainstem response to test whether mothers and pup-naïve virgin mice differed in temporal responses to both broadband and tone stimuli, including ultrasonic frequencies found in mouse pup vocalizations. Mothers had shorter latencies for early ABR peaks, indicating plasticity in the auditory nerve and the cochlear nucleus. Shorter interpeak latency between waves IV and V also suggest plasticity in the inferior colliculus. Hormone manipulations revealed that these cannot be explained solely by estrogen levels experienced during pregnancy and parturition in mothers. In contrast, we found that pup-care experience, independent of pregnancy and parturition, contributes to shortening auditory brainstem response latencies. These results suggest that acoustic experience in the maternal context imparts plasticity on early auditory processing that lasts beyond pup weaning. In addition to establishing an animal model for exploring adult auditory brainstem plasticity in a neuroethological context, our results have broader implications for models of perceptual, behavioral and neural changes that arise during maternity, where subcortical sensorineural plasticity has not previously been considered.

Estrogenic modulation of auditory processing: a vertebrate comparison

Sex-steroid hormones are well-known regulators of vocal motor behavior in several organisms. A large body of evidence now indicates that these same hormones modulate processing at multiple levels of the ascending auditory pathway. The goal of this review is to provide a comparative analysis of the role of estrogens in vertebrate auditory function. Four major conclusions can be drawn from the literature: First, estrogens may influence the development of the mammalian auditory system. Second, estrogenic signaling protects the mammalian auditory system from noise- and age-related damage. Third, estrogens optimize auditory processing during periods of reproductive readiness in multiple vertebrate lineages. Finally, brain-derived estrogens can act locally to enhance auditory response properties in at least one avian species. This comparative examination may lead to a better appreciation of the role of estrogens in the processing of natural vocalizations and mayprovide useful insights toward alleviating auditory dysfunctions emanating from hormonal imbalances.

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.

A role for maternal physiological state in preserving auditory cortical plasticity for salient infant calls

A growing interest in sensory system plasticity in the natural context of motherhood has created the need to investigate how intrinsic physiological state (e.g., hormonal, motivational, etc.) interacts with sensory experience to drive adaptive cortical plasticity for behaviorally relevant stimuli. Using a maternal mouse model of auditory cortical inhibitory plasticity for ultrasonic pup calls, we examined the role of pup care versus maternal physiological state in the long-term retention of this plasticity. Very recent experience caring for pups by Early Cocarers, which are virgins, produced stronger call-evoked lateral-band inhibition in auditory cortex. However, this plasticity was absent when measured post-weaning in Cocarers, even though it was present at the same time point in Mothers, whose pup experience occurred under a maternal physiological state. A two-alternative choice phonotaxis task revealed that the same animal groups (Early Cocarers and Mothers) demonstrating stronger lateral-band inhibition also preferred pup calls over a neutral sound, a correlation consistent with the hypothesis that this inhibitory mechanism may play a mnemonic role and is engaged to process sounds that are particularly salient. Our electrophysiological data hint at a possible mechanism through which the maternal physiological state may act to preserve the cortical plasticity: selectively suppressing detrimental spontaneous activity in neurons that are responsive to calls, an effect observed only in Mothers. Taken together, the maternal physiological state during the care of pups may help maintain the memory trace of behaviorally salient infant cues within core auditory cortex, potentially ensuring a more rapid induction of future maternal behavior.

Limbic brain activation for maternal acoustic perception and responding is different in mothers and virgin female mice

Mothers are primed to become maternal through hormonal changes during pregnancy and delivery of young, virgin females need experience with young for performing maternally. The activation of brain areas controlling maternal behavior can be studied by stimulus-induced expression of the immediate-early gene Fos and immunocytochemical labeling of the FOS protein in activated cells. With this technique we identified areas of the mouse limbic system stimulated by acoustically adequate or inadequate models of pup ultrasounds that, if perceived as adequate, direct the search for lost pups (phonotaxis). Behavioral observations and neural activation data suggest that adequate (50 kHz long tones) and inadequate ultrasound models (50 kHz short or 20 kHz long tones) are differently processed in limbic areas of mothers and virgin females with 1 or 5 days of pup-caring experience depending on the news value and the recognition of the stimuli: High numbers of FOS-positive cells in the medial preoptic area, lateral septum, and bed nucleus of the stria terminalis (mothers and virgins) relate to the salience (news value) of the perceived sounds; contextual stress may be reflected by high activation in parts of the amygdala and the ventromedial hypothalamus (virgins); high activation in the piriform cortex suggests associative learning of adequate sounds and in the entorhinal cortex remembering associations of adequate sounds with pups (virgins). Thus brain areas were differently activated in animals with maternal emotions, however different responses to pup cues depending on how they got primed to behave maternally and on how they evaluated the stimulation context.

Oestrogen-independent, experience-induced maternal behaviour in female mice

Nulliparous female mice that have not experienced mating, pregnancy or parturition show near immediate spontaneous maternal behaviour when presented with foster pups. The fact that virgin mice display spontaneous maternal behaviour indicates that the hormonal events of pregnancy and parturition are not necessary to produce a rapid onset of maternal behaviour in mice. However, it is not known how similar maternal behaviour is between virgin and lactating mice. In the present study, we show that naturally postpartum females are faster to retrieve pups and spend more time crouching over pups than spontaneously maternal virgin females, and that these differences diminish with increased maternal experience. Moreover, 4 days of experience with pups induced pup retrieval on a novel T-maze. Furthermore, the effects of experience on subsequent maternal responsiveness are not dependent on gonadal hormones because ovariectomised females with 4 days of pup experience show pup retrieval on a novel T-maze similar to that of postpartum mice. Four days of maternal experience also induced T-maze pup retrieval in ovariectomised aromatase knockout female mice that was not significantly different from the maternal responsiveness of ovariectomised wild-type littermates. These data suggest that maternal experience can induce maternal behaviour in females that have never been exposed to oestradiol at any time in development or adulthood. Finally, ovariectomised pup-experienced females continue to retrieve pups on a novel T-maze 1 month after the initial experience, suggesting that, even in the absence of oestradiol, maternal experience produces long-lasting modifications in maternal responsiveness.

Dissecting natural sensory plasticity: hormones and experience in a maternal context

There is a growing consensus that the auditory system is dynamic in its representation of behaviorally relevant sounds. The auditory cortex in particular seems to be an important locus for plasticity that may reflect the memory of such sounds, or functionally improve their processing. The mechanisms that underlie these changes may be either intrinsic because they depend on the receiver's physiological state, or extrinsic because they arise from the context in which behavioral relevance is gained. Research in a mouse model of acoustic communication between offspring and adult females offers the opportunity to explore both of these contributions to auditory cortical plasticity in a natural context. Recent works have found that after the vocalizations of infant mice become behaviorally relevant to mothers, auditory cortical activity is significantly changed in a way that may improve their processing. Here we consider the hypothesis that maternal hormones (intrinsic factor) and sensory experience (extrinsic factor) contribute together to drive these changes, focusing specifically on the evidence that well-known experience-dependent mechanisms of cortical plasticity can be modulated by hormones.

Ultrasonic vocalizations in rat and mouse pups

The ultrasonic vocalization (USV), or isolation calling response, of infant rats and mice has been studied as a measure of the intensity of an aversive affective state and as an early communicative behavior between pup and mother. The four protocols described in this unit are for the basic isolation testing procedure, and for elicitation of the contact quieting response to littermates and/or dam, the potentiation of isolation calling response by a prior brief maternal interaction and the predator-induced suppression of USV by the scent of an unfamiliar male. These procedures for the elicitation of USV, and for its regulation by different kinds of social interaction, provides the basis for experimental research on the early development of emotion and communication in an animal model system.

FMRI activations of amygdala, cingulate cortex, and auditory cortex by infant laughing and crying

One of the functions of emotional vocalizations is the regulation of social relationships like those between adults and children. Listening to infant vocalizations is known to engage amygdala as well as anterior and posterior cingulate cortices. But, the functional relationships between these structures still need further clarification. Here, nonparental women and men listened to laughing and crying of preverbal infants and to vocalization-derived control stimuli, while performing a pure tone detection task during low-noise functional magnetic resonance imaging. Infant vocalizations elicited stronger activation in amygdala and anterior cingulate cortex (ACC) of women, whereas the alienated control stimuli elicited stronger activation in men. Independent of listeners' gender, auditory cortex (AC) and posterior cingulate cortex (PCC) were more strongly activated by the control stimuli than by infant laughing or crying. The gender-dependent correlates of neural activity in amygdala and ACC may reflect neural predispositions in women for responses to preverbal infant vocalizations, whereas the gender-independent similarity of activation patterns in PCC and AC may reflect more sensory-based and cognitive levels of neural processing. In comparison to our previous work on adult laughing and crying, the infant vocalizations elicited manifold higher amygdala activation.

Improved cortical entrainment to infant communication calls in mothers compared with virgin mice

There is a growing interest in the use of mice as a model system for species-specific communication. In particular, ultrasonic calls emitted by mouse pups communicate distress, and elicit a search and retrieval response from mothers. Behaviorally, mothers prefer and recognize these calls in two-alternative choice tests, in contrast to pup-naïve females that do not have experience with pups. Here, we explored whether one particular acoustic feature that defines these calls-- the repetition rate of calls within a bout-- is represented differently in the auditory cortex of these two animal groups. Multiunit recordings in anesthetized CBA/CaJ mice revealed that: (i) neural entrainment to repeated stimuli extended up to the natural pup call repetition rate (5 Hz) in mothers; but (ii) neurons in naïve females followed repeated stimuli well only at slower repetition rates; and (iii) entrained responses to repeated pup calls were less sensitive to natural pup call variability in mothers than in pup-naïve females. In the broader context, our data suggest that auditory cortical responses to communication sounds are plastic, and that communicative significance is correlated with an improved cortical representation.

A review of the methods of studies on infant ultrasound production and maternal retrieval in small rodents

Ultrasonic vocalizations or calls produced by young rodents have been associated with aspects of maternal behavior, in particular retrieving. We reviewed the methods of study used by investigators on each topic, focusing on intrinsic or subject variables and extrinsic or experimental variables. Intrinsic variables included the species studied, genotypes employed, number and sex composition of the litters, and the ages of mothers and pups. Extrinsic variables for studies on ultrasonic calling included: eliciting stimuli, test surroundings, and the length of observation. Extrinsic variables in studies of maternal retrieval included the testing procedure and the length of observation. The methods used in studies within each topic vary greatly. In an effort to facilitate progress in the areas, especially with respect to isolating individual genes with a contribution to ultrasonic call production or studying the effects of pharmaceutical agents on either behavior, we propose some standardization of nomenclature and/or procedure in four areas: (1) the stimuli or situations used to elicit ultrasonic calls, (2) the length of observation in ultrasonic call studies, (3) the number of pups per litter and the sex composition of litters in both ultrasonic call and maternal retrieval studies and finally, (4) the apparatus or testing situation used in studies of pup retrieval.

Infant Rodent Ultrasounds ? A Gate to the Understanding of Sound Communication

Components of the communication system between infant and adult rodents based on ultrasonic vocalizations (USVs) of infants are analyzed. USVs are most often emitted from a pup lost outside the nest in response to changes of: (i) body temperature, (ii) contact with adults/littermates, (iii) handling, and (iv) smell. These changes modulate the state of arousal and the emotional/motivational states and, as a result, USVs are produced. Acoustic properties of USVs seem to reflect the degrees of changes in arousal and emotion/motivation. Adult rodents are aroused by perceiving the USVs, locate the sender and show a phonotaxic approach to the sender. Acoustic properties of USVs in the frequency and time domains are described based on which adult rodents discriminate the USVs from other ultrasounds and take the USVs or adequate models of them as preferred goals of their phonotaxic approach. The preferred approach to adequate USVs is modulated by emotions/motivations, the sex of the receiver, hormonal states, experience with pups and neurotransmitter systems of the brain. The phonotaxis can be understood as the appetitive component of a pup-caring instinct. The consummatory act of the instinct is the retrieval of the lost pup. This retrieval is independent of USV presence, but it closes the communication loop activated by the emission of USVs. Communication with USVs can be used as a tool to investigate genetic and brain mechanisms of behavioral control.

Multiple regulators of ultrasonic vocalization in the infant rat

This paper reviews our growing understanding of the external environmental and the internal neuroregulatory mechanisms for the infant rat's vocal response to abrupt isolation from nest, littermates and mother. Interactions of the rat pup with specific components of its animate and inanimate environment have been identified and found to exert a tonic regulatory action on the neural systems mediating ultrasonic vocalization (USV). In isolation, withdrawal of these regulators produces an acute outburst of calling. Changes in rate of ultrasonic calling in response to administration of receptor agonist and antagonist agents generally correspond to the effects of those agents on measures of anxiety in adult animals and in human clinical populations, suggesting a conservation of neural substrates for anxiety in evolution and in development. The inhibition of isolation calling in response to predator cues and its potentiation by brief exposure to maternal cues, represent novel forms of regulation with implications for neuroendocrine development and for the neurobiology of early cognitive-emotional processes.

Estrogen-receptor occurrence in the female mouse brain: effects of maternal experience, ovariectomy, estrogen and anosmia

Maternal behavior (ultrasound-induced pup-searching and retrieving) was studied in eight groups of female house mice with various hormonal backgrounds, experience with pups and function of the olfactory system. In their brains, estrogen receptor immunoreactive (ER-IR) cells were localized and quantified. All animals of all groups had ER-IR cells in a 'reliable subset' of brain areas, the medial preoptic area (MPOA) and ventromedial (VMH) and arcuate nucleus (ARH) of the hypothalamus. In another subset of brain areas, the anterior hypothalamic area (AHA) and cortical (CA) and medial (MA) amygdaloid nucleus, ER-IR cells can be expected in at least some animals of all experimental groups ('expected subset'). In a variable subset of additional brain areas (bed nucleus of the stria terminalis, BNST; suprachiasmatic nucleus, SC; lateral septal nuclei, LS; paraventricular nucleus of the hypothalamus, PVH; entorhinal and piriform cortex, ENT, PIR; subiculum, SUB; hippocampus, HPC; periventricular gray of the midbrain, PVG), ER-IR cells occurred only in some animals of some groups. Numbers of ER-IR cells in a given brain area, volumes occupied by these cells, and cell densities varied considerably among the groups. A covariation of cell counts and volumes was significant for most brain areas indicating that increases of numbers of ER-IR cells relate mainly to volume increases within a given brain area. Experience with pups correlated with an increase of ER presence in the AHA, VMH, ENT, PIR, SUB, HPC and PVG, however, only in the presence of estrogen. Estrogen and pup-experience together led to an increased ER presence in mainly the VMH, ENT and PIR, however, only in females with intact olfaction. Full maternal behavior (retrieving, ultrasound recognition) occurred after the high pregnancy- or experience-induced ER content was reduced to lower levels. The ER occurrence in lactating and experienced virgin females differed, however, in the AHA, BNST, SC, PVH, ENT, PIR, SUB, HPC and PVG showing that the maintenance of maternal behavior can run under different profiles of ER content in the brain. Ovariectomy and/or prolonged high blood-estrogen levels correlated significantly with decreased levels of ER-IR cells in most brain areas which could not be increased by pup-experience.

Parental behavior in the mouse: effects of lesions in the entorhinal/piriform cortex

The effects of bilateral radiofrequency lesions in the region of the entorhinal and piriform cortex (ENT/PIR cortex) on pup-retrieving and ultrasound-elicited pup-searching behavior were investigated in ovariectomized estrogen-treated female mice, which were sensitized to pups by co-caring for a litter for 5 days together with the mother (FoEBex), as well as in primiparous lactating females (Flact). A further group of FoEBex were rendered anosmic by an intranasal treatment with zinc sulfate-solution before the sensitization period and tests for parental motivation. Both pup-retrieving and pup-searching behavior were disturbed to the same extent by ENT/PIR lesions and ZnSO4-induced anosmia in FoEBex. In Flact, however, pup-retrieving was not affected by the lesion, while ultrasound-recognition leading to pup-searching was disrupted. The present data suggest sensitization to pups as a case of olfactory learning and thus, the effects of the ENT/PIR lesions are regarded as anterograde olfactory amnesia. From the present data and results reported in the literature, it is suggested to differentiate between the neural substrates processing stimuli relevant for the appetitive component (pup-searching) of parental behavior (among others, the region of the entorhinal and piriform cortex), and the mechanisms regulating the consummatory component (pup-retrieving).

Estradiol and parental experience, but not prolactin are necessary for ultrasound recognition and pup-retrieving in the mouse

The effects of estradiol, prolactin and experience with pups on pup-retrieving and on the recognition of ultrasonic distress calls of the young by adult ovariectomized female mice were studied. Treatment with estradiol benzoate or experience with pups (for 5 days) induced pup-retrieving in 40% and 60% of the animals, respectively, as compared to 0% in inexperienced ovariectomized females. However, if pup-experience was achieved in the presence of estradiol, retrieving was shown by 90.5% of the animals. In addition, in this case models of the ultrasonic distress calls of the pups were significantly preferred ("recognized") in a discrimination task by the females. These females also showed a sharp increase in serum prolactin concentrations. Depleting prolactin from the blood by cysteamine, however, neither reduced the retrieving score nor disturbed ultrasound recognition. Thus prolactin is dispensable for maintaining maternal pup-retrieving and ultrasound recognition. The process of achieving pup-experience is enhanced by the presence of estradiol. Possible actions of estradiol in the brain are discussed.