The effects of olfactory and somatosensory desensitization on Fos-like immunoreactivity in the brains of pup-exposed postpartum rats

The parental umwelt: Effects of parenthood on sensory processing in rodents

An animal's umwelt, comprising its perception of the sensory environment, which is inherently subjective, can change across the lifespan in accordance with major life events. In mammals, the onset of motherhood, in particular, is associated with a neural and sensory plasticity that alters a mother's detection and use of sensory information such as infant-related sensory stimuli. Although the literature surrounding mammalian mothers is well established, very few studies have addressed the effects of parenthood on sensory plasticity in mammalian fathers. In this review, we summarize the major findings on the effects of parenthood on behavioural and neural responses to sensory stimuli from pups in rodent mothers, with a focus on the olfactory, auditory, and somatosensory systems, as well as multisensory integration. We also review the available literature on sensory plasticity in rodent fathers. Finally, we discuss the importance of sensory plasticity for effective parental care, hormonal modulation of plasticity, and an exploration of temporal, ecological, and life-history considerations of sensory plasticity associated with parenthood. The changes in processing and/or perception of sensory stimuli associated with the onset of parental care may have both transient and long-lasting effects on parental behaviour and cognition in both mothers and fathers; as such, several promising areas of study, such as on the molecular/genetic, neurochemical, and experiential underpinnings of parenthood-related sensory plasticity, as well as determinants of interspecific variation, remain potential avenues for further exploration.

Neurobiology of Maternal Behavior in Nonhuman Mammals: Acceptance, Recognition, Motivation, and Rejection

Among the different species of mammals, the expression of maternal behavior varies considerably, although the end points of nurturance and protection are the same. Females may display passive or active responses of acceptance, recognition, rejection/fear, or motivation to care for the offspring. Each type of response may indicate different levels of neural activation. Different natural stimuli can trigger the expression of maternal and paternal behavior in both pregnant or virgin females and males, such as hormone priming during pregnancy, vagino-cervical stimulation during parturition, mating, exposure to pups, previous experience, or environmental enrichment. Herein, we discuss how the olfactory pathways and the interconnections of the medial preoptic area (mPOA) with structures such as nucleus accumbens, ventral tegmental area, amygdala, and bed nucleus of stria terminalis mediate maternal behavior. We also discuss how the triggering stimuli activate oxytocin, vasopressin, dopamine, galanin, and opioids in neurocircuitries that mediate acceptance, recognition, maternal motivation, and rejection/fear.

A Scientometric Approach to Review the Role of the Medial Preoptic Area (MPOA) in Parental Behavior

Research investigating the neural substrates underpinning parental behaviour has recently gained momentum. Particularly, the hypothalamic medial preoptic area (MPOA) has been identified as a crucial region for parenting. The current study conducted a scientometric analysis of publications from 1 January 1972 to 19 January 2021 using CiteSpace software to determine trends in the scientific literature exploring the relationship between MPOA and parental behaviour. In total, 677 scientific papers were analysed, producing a network of 1509 nodes and 5498 links. Four major clusters were identified: “C-Fos Expression”, “Lactating Rat”, “Medial Preoptic Area Interaction” and “Parental Behavior”. Their content suggests an initial trend in which the properties of the MPOA in response to parental behavior were studied, followed by a growing attention towards the presence of a brain network, including the reward circuits, regulating such behavior. Furthermore, while attention was initially directed uniquely to maternal behavior, it has recently been extended to the understanding of paternal behaviors as well. Finally, although the majority of the studies were conducted on rodents, recent publications broaden the implications of previous documents to human parental behavior, giving insight into the mechanisms underlying postpartum depression. Potential directions in future works were also discussed.

Raising overlapping litters: Differential activation of rat maternal neural circuitry after interacting with newborn or juvenile pups

The maternal behaviour of a rat dynamically changes during the postpartum period, adjusting to the characteristics and physiological needs of the pups. This adaptation has been attributed to functional modifications in the maternal circuitry. Maternal behaviour can also flexibly adapt according to different litter compositions. Thus, mothers with two overlapping litters can concurrently take care of neonate and juvenile pups, mostly directing their attention to the newborns. We hypothesised that the maternal circuitry of these mothers would show a differential activation pattern after interacting with pups depending on the developmental stage of their offspring. Thus, we evaluated the activation of several areas of the maternal circuitry in mothers of overlapping litters, using c-Fos immunoreactivity as a marker of neuronal activation, after interacting with newborns or juveniles. The results showed that mothers with overlapping litters display different behavioural responses towards their newborn and their juvenile pups. Interestingly, these behavioural displays co-occurred with specific patterns of activation of the maternal neural circuitry. Thus, a similar expression of c-Fos was observed in some key brain areas of mothers that interacted with newborns or juveniles, such as the medial preoptic area and the nucleus accumbens, whereas a differential activation was quantified in the ventral region of the bed nucleus of the stria terminalis, the infralimbic and prelimbic subregions of the medial prefrontal cortex and the basolateral and medial nuclei of the amygdala. We posit that the specific profile of activation of the neural circuitry controlling maternal behaviour in mothers with overlapping litters enables dams to respond adequately to the newborn and the juvenile pups.

Maternal care activates the ventral tegmental area but not dopaminergic cells in the rat

The ventral tegmental area (VTA), together with the preoptic area, is part of a neural circuit necessary for the expression of maternal behaviour (MB); destruction of either area disrupts MB in postpartum rats. Central to the proposal of VTA activation are dopaminergic cells, for which the cell bodies lie in the VTA and project to forebrain structures. This mesolimbic system is a motivational circuit involved in rewarding behaviours such as sex and MB. Despite their recognised importance, surprisingly, unlike the preoptic area, there are no anatomical descriptions of the pattern of VTA activation or of the dopaminergic cell activation, specifically in relation to MB in the rat. In the present study, we explore the possible activation (as indicated by Fos protein via immunohistochemistry) of the anterior and medial portions of the VTA and in the dopaminergic cells in these regions, as well as in the medial preoptic area, in lactating rats, at postpartum day 7 (after a 12-hour mother/pups separation), and in dioestrous females. After 12 hours, mothers were perfused at that moment or after a 90 minutes of interaction, or not, with their pups. We found a strong significant Fos induction in both the preoptic area and in the anterior portion of VTA in dams that interacted with their pups. The number of dopaminergic cells that coexpressed Fos did not differ across groups. Additionally, we determined Fos and GABA colocalisation in the anterior part of the VTA and found dense GABAergic processes, possibly varicosities, in the area of increased Fos expression. The results of the present study support a proposed GABAergic pathway from medial preoptic area to VTA cells, critical for the expression of MB. Future experiments are warranted to explore the neurochemical identity of the Fos and no-Fos expressing cells that are recipients of GABAergic processes in the VTA, aiming to better understand the neural circuitry of the VTA in relation to MB.

Thalamic integration of social stimuli regulating parental behavior and the oxytocin system

Critically important components of the maternal neural circuit in the preoptic area robustly activated by suckling were recently identified. In turn, suckling also contributes to hormonal adaptations to motherhood, which includes oxytocin release and consequent milk ejection. Other reproductive or social stimuli can also trigger the release of oxytocin centrally, influencing parental or social behaviors. However, the neuronal pathways that transfer suckling and other somatosensory stimuli to the preoptic area and oxytocin neurons have been poorly characterized. Recently, a relay center of suckling was determined and characterized in the posterior intralaminar complex of the thalamus (PIL). Its neurons containing tuberoinfundibular peptide 39 project to both the preoptic area and oxytocin neurons in the hypothalamus. The present review argues that the PIL is a major relay nucleus conveying somatosensory information supporting maternal behavior and oxytocin release in mothers, and may be involved more generally in social cue evoked oxytocin release, too.

The birth of new neurons in the maternal brain: Hormonal regulation and functional implications

The maternal brain is remarkably plastic and exhibits multifaceted neural modifications. Neurogenesis has emerged as one of the mechanisms by which the maternal brain exhibits plasticity. This review highlights what is currently known about peripartum-associated changes in adult neurogenesis and the underlying hormonal mechanisms. We also consider the functional consequences of neurogenesis in the peripartum brain and extent to which this process may play a role in maternal care, cognitive function and postpartum mood. Finally, while most work investigating the effects of parenting on adult neurogenesis has focused on mothers, a few studies have examined fathers and these results are also discussed.

Maternally responsive neurons in the bed nucleus of the stria terminalis and medial preoptic area: Putative circuits for regulating anxiety and reward

Postpartum neuropsychiatric disorders are a major source of morbidity and mortality and affect at least 10% of childbearing women. Affective dysregulation within this context has been identified in association with changes in reproductive steroids. Steroids promote maternal actions and modulate affect, but can also destabilize mood in some but not all women. Potential brain regions that mediate these effects include the medial preoptic area (mPOA) and ventral bed nucleus of the stria terminalis (vBNST). Herein, we review the regulation of neural activity in the mPOA/vBNST by environmental and hormonal concomitants in puerperal females. Such activity may influence maternal anxiety and motivation and have significant implications for postpartum affective disorders. Future directions for research are also explored, including physiological circuit-level approaches to gain insight into the functional connectivity of hormone-responsive maternal circuits that modulate affect.

Preoptic inputs and mechanisms that regulate maternal responsiveness

The preoptic area is a well-established centre for the control of maternal behaviour. An intact medial preoptic area (mPOA) is required for maternal responsiveness because lesion of the area abolishes maternal behaviours. Although hormonal changes in the peripartum period contribute to the initiation of maternal responsiveness, inputs from pups are required for its maintenance. Neurones are activated in different parts of the mPOA in response to pup exposure. In the present review, we summarise the potential inputs to the mPOA of rodent dams from the litter that can activate mPOA neurones. The roles of potential indirect effects through increased prolactin levels, as well as neuronal inputs to the preoptic area, are described. Recent results on the pathway mediating the effects of suckling to the mPOA suggest that neurones containing the neuropeptide tuberoinfundibular peptide of 39 residues in the posterior thalamus are candidates for conveying the suckling information to the mPOA. Although the molecular mechanism through which these inputs alter mPOA neurones to support the maintenance of maternal responding is not yet known, altered gene expression is a likely candidate. Here, we summarise gene expression changes in the mPOA that have been linked to maternal behaviour and explore the idea that chromatin remodelling during mother-infant interactions mediates the long-term alterations in gene expression that sustain maternal responding.

Effectiveness of topical anesthetics on reducing tactile sensitivity in the paws of newborn rats

The aim of this study was to evaluate the effectiveness of three local, topical anesthetics on touch response thresholds of the paws of 1-day-old rats. Touch response thresholds were measured using Semmes Weinstein monofilaments after treatment of the paws with EMLA (2.5% lidocaine and 2.5% prilocaine), alcaine (.5% proparacaine), triocaine (20% benzocaine, 6% lidocaine, and 4% tetracaine), or petroleum jelly (treatment control). Touch thresholds significantly increased after treatment with EMLA 18% of the time, and there was no evidence of a systemic effect. Touch thresholds were not significantly altered after treatment with alcaine, triocaine, or petroleum jelly. Therefore, EMLA appears to be a slightly effective topical anesthetic for reducing tactile sensitivity in newborn rats.

Naturally occurring variation in vasopressin immunoreactivity is associated with maternal behavior in female Peromyscus mice

In many mammals, species-appropriate social behavior is necessary for an individual's ability to survive and reproduce. In the present study, we examined whether arginine-vasopressin (AVP) pathways that have been associated with social behavior differed between two closely related species of Peromyscus mice with different patterns of maternal behavior. We also tested whether individual levels of AVP-immunoreactive staining (AVP-ir) were associated with individual levels of maternal behavior as measured using a composite score consisting of huddling, nursing, grooming and time spent inside the nest (HNGI score). In addition, we examined whether these associations between vasopressin and behavior differed between species. Females from the highly biparental species, California mice, displayed higher AVP-ir in the bed nucleus of the stria terminalis (BNST), which corresponded with a higher level of nest building and a higher HNGI score than was found in the less parental white-footed mice. The HNGI score was positively associated with AVP-ir in the medial amygdala in female California mice but not white-footed mice. Finally, we examined whether AVP-ir in these pathways varied based on the species-specific rearing environments by reciprocally cross-fostering California mice and white-footed mice. In contrast to previous research with male California mice, cross-fostering itself had no effect on maternal behavior or any consistent effect on AVP-ir staining in brain areas such as the BNST and associated brain areas. This suggests that there is little plasticity in maternal behavior and that the underlying AVP system in females does not respond to the postnatal environment provided by the parents. The positive associations between maternal behavior and AVP-ir indicate that AVP may regulate maternal behavior despite the lack of plasticity in AVP and maternal behavior.

Prolactin, neurogenesis, and maternal behaviors

Elevated prolactin during pregnancy increases neurogenesis in the subventricular zone of the lateral ventricle (SVZ) of the maternal brain. Evidence from our laboratory has shown that low prolactin in early pregnancy, and the consequent suppression of neurogenesis in the SVZ in the adult brain, is associated with increased postpartum anxiety and markedly impaired maternal behavior. Daughters of low prolactin mothers also display increased anxiety and a significant delay in the onset of puberty, which is associated with epigenetic changes in neuronal development (see Fig. 1). This suggests that, in rodents, low prolactin in early pregnancy exerts long-term effects that influence maternal mood postpartum, and offspring development. This mini-review aims to summarize the evidence showing that the prolactin-induced increase in SVZ neurogenesis during pregnancy underlies normal postpartum maternal interactions with pups.

A bold view of the lactating brain: functional magnetic resonance imaging studies of suckling in awake dams

Functional magnetic resonance imaging (fMRI) has been used to investigate the responsiveness of the maternal rat brain to pup-suckling under various experimental paradigms. Our research employing the lactating rat model has explored the cortical sensory processing of pup stimuli and the effect of suckling on the brain's reward system. Suckling was observed to increase blood-oxygen-level-dependent (BOLD) signal intensity in the midbrain, striatum and prefrontal cortex, which are areas that receive prominent dopaminergic inputs. The BOLD activation of the reward system occurs in parallel with the activation of extensive cortical sensory areas. The observed regions include the olfactory cortex, auditory cortex and gustatory cortex, and could correspond to cortical representations of pup odours, vocalisations and taste that are active during lactation. Activation patterns within reward regions are consistent with past research on maternal motivation and we explore the possibility that exposure to drugs of abuse might be disruptive of maternal neural responses to pups, particularly in the prefrontal cortex. Our ongoing fMRI studies support and extend past research on the maternal rat brain and its functional neurocircuitry.

Technical and conceptual considerations for performing and interpreting functional MRI studies in awake rats

Functional neuroimaging studies in rodents have the potential to provide insight into neurodevelopmental and psychiatric conditions. The strength of the technique lies in its non-invasive nature that can permit longitudinal functional studies in the same animal over its adult life. The relatively good spatial and temporal resolution and the ever-growing database on the biological and biophysical basis of the blood oxygen level dependent (BOLD) signal make it a unique technique in preclinical neuroscience research. Our laboratory has used imaging to investigate brain activation in awake rats following cocaine administration and during the presentation of lactation-associated sensory stimuli. Factors that deserve attention when planning functional magnetic resonance imaging studies in rats include technical issues, animal physiology and interpretability of the resulting data. The present review discusses the pros and cons of animal imaging with a particular focus on the technical aspects of studies with awake rats. Overall, the benefits of the technique outweigh its limitations and the rapidly evolving methods will open the way for more laboratories to employ the technique in neuroscience research.

Prolactin-induced mitogenesis in the subventricular zone of the maternal brain during early pregnancy is essential for normal postpartum behavioral responses in the mother

High prolactin during pregnancy, which is essential for normal postpartum maternal behavior, increases neurogenesis in the subventricular zone of the lateral ventricle (SVZ) of the maternal brain. Because SVZ mitogenesis generates new olfactory neurons and may contribute to perception of novel odorants, we hypothesized that the prolactin-induced increase in SVZ mitogenesis during pregnancy might be important for normal maternal interactions with pups. To investigate this hypothesis, prolactin secretion was suppressed for 3 d early in pregnancy in mice, using a carefully timed dose of bromocriptine. The bromocriptine-induced reduction in prolactin prevented the normal increase in generation of neural progenitors in the SVZ of the maternal brain. Another group of bromocriptine-treated animals were allowed to continue their pregnancy until term, and then maternal behaviors were evaluated postpartum. Low prolactin during early pregnancy, and the consequent suppression of mitogenesis in the SVZ of the maternal brain, was subsequently followed by increased postpartum anxiety and markedly impaired maternal behavior. In another group of pregnant females, injections of the mitotic inhibitor methylazoxymethanol to specifically suppress neurogenesis in the mother during early pregnancy without affecting prolactin secretion also caused postpartum anxiety and impaired maternal behavior. These data demonstrate that prolactin-induced increase in generation of neural progenitors in the SVZ of the maternal brain during early pregnancy is required for normal expression of postpartum maternal behaviors.

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

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

Nursing stimulation is more than tactile sensation: It is a multisensory experience

Novel sensory experiences, particularly those associated with epochal developmental events like nursing alter cortical representation, affecting memory, perception and behavior. Functional MRI was used here to test whether the sensoricortical map of the ventrum is modified during lactation. Three stimuli were used to drive cortical activation in primiparous rats: natural, artificial suckling stimulation and general mechanical rubbing of the skin of the ventrum. These stimuli significantly activated the somatosensory cortex of dams. Of the three stimuli, artificial and pup suckling robustly activated much of the cerebrum, most notably the visual, auditory and olfactory cortices. Surprisingly, activation occurred even in the absence of pups, with artificial suckling. This finding suggests that incoming information from a single modality was sufficient to drive activity of others. Enhanced sensitivity across the cortical mantle during nursing may help the dam to perceive, process, and remember stimuli critical to the care and protection of her young.

Arginine vasopressin V1a receptor antagonist impairs maternal memory in rats

Primiparous female rats rapidly respond to foster pups following an extended separation from pups after an initial maternal experience. This consolidation of maternal behavior has been referred to as maternal memory. The neurochemical regulation of maternal memory is not clearly understood. One neuropeptide that may mediate maternal memory is arginine vasopressin (AVP), a neuropeptide which is modulated around the time of parturition and has an established role in learning and memory processes. Thus, the present studies examine the possible involvement of AVP in the establishment of maternal memory in female rats. Pregnant rats were implanted with chronic cannulae connected to subcutaneous osmotic minipumps filled with a V1a receptor antagonist [d(CH2)5Tyr(Me)AVP, 0.1-12.5 ng/h] or saline vehicle which were chronically infused either into the lateral ventricles or bilaterally into the medial amygdala beginning on day 18 of gestation. Both the osmotic pumps and the newborn pups were removed 24 h following parturition. The effects of the V1a antagonist treatments on social recognition and maternal behavior were measured following parturition and maternal memory was assessed following a ten day separation from pups. Whereas none of the AVP treatments affected the initial establishment of maternal behavior postpartum, maternal memory was impaired in rats infused into the amygdala with the AVP antagonist (1.25 and 12.5 ng/h). Social recognition was not impaired by intracerebroventricular infusion of either the 0.1 or 1.0 ng/h dose of the V1a antagonist. The present results suggest a role for medial amygdaloid V1a receptors in the establishment of maternal memory.

Functional internal complexity of amygdala: focus on gene activity mapping after behavioral training and drugs of abuse

The amygdala is a heterogeneous brain structure implicated in processing of emotions and storing the emotional aspects of memories. Gene activity markers such as c-Fos have been shown to reflect both neuronal activation and neuronal plasticity. Herein, we analyze the expression patterns of gene activity markers in the amygdala in response to either behavioral training or treatment with drugs of abuse and then we confront the results with data on other approaches to internal complexity of the amygdala. c-Fos has been the most often studied in the amygdala, showing specific expression patterns in response to various treatments, most probably reflecting functional specializations among amygdala subdivisions. In the basolateral amygdala, c-Fos expression appears to be consistent with the proposed role of this nucleus in a plasticity of the current stimulus-value associations. Within the medial part of the central amygdala, c-Fos correlates with acquisition of alimentary/gustatory behaviors. On the other hand, in the lateral subdivision of the central amygdala, c-Fos expression relates to attention and vigilance. In the medial amygdala, c-Fos appears to be evoked by emotional novelty of the experimental situation. The data on the other major subdivisions of the amygdala are scarce. In conclusion, the studies on the gene activity markers, confronted with other approaches involving neuroanatomy, physiology, and the lesion method, have revealed novel aspects of the amygdala, especially pointing to functional heterogeneity of this brain region that does not fit very well into contemporarily active debate on serial versus parallel information processing within the amygdala.

Effect of opioid antagonist naloxone on maternal motivation in albino rats

We studied the effect of nonselective antagonist of opioid receptor naloxone on the behavior of albino female rats on days 4-6 after delivery. Intraperitoneal injection of naloxone (5 mg/kg) significantly stimulated maternal reactions (increased the number of approaches to pups, decreased the latency of their transfer into new location). Intranasal naloxone (1 mg/kg) produced similar changes. Naloxone in intraperitoneal dose of 1 mg/kg and intranasal dose of 0.2 mg/kg virtually did not modify maternal behavior.

Electrical activity of prefrontal cortex and ventral tegmental area during rat maternal behavior

Maternal behavior is a motivated behavior that includes pup-directed sequential motor acts. The dopaminergic (DAergic) brain systems have been proposed to play an important role in voluntary maternal acts, however, not much is known about the way these systems function during the performance of this behavior. The electroencephalogram (EEG) is a sensitive tool that allows determination of the simultaneous functioning of different structures in relation to specific cognitive processes or motor acts. The present study recorded the function of the two structures that constitute the mesoprefrontal DAergic system, ventral tegmental area (VTA) and prefrontal cortex (PFC) by EEG during the performance of various maternal behaviors. Bilateral EEG from the VTA and medial PFC (mPFC) was simultaneously recorded during typical maternal acts and was compared to that recorded during non-maternal behaviors in freely moving female rats. Three different frequency bands (6-7, 8-11, and 12-21 Hz) were obtained from principal component analysis applied to the EEG for both structures. In the left and right mPFC and VTA, absolute power (AP) of the 8-11 Hz band showed a significant increase during pup retrieval compared to the EEG during walking. In the left and right mPFC and VTA, AP of the three bands showed a significant increase during pup licking with respect to forepaw licking. No differences in the EEG were found during inactive nursing behaviors compared to the awake quiet condition. The mPFC and VTA presented characteristic EEG patterns during active maternal behaviors but not during inactive maternal behaviors. This provides electrical evidence of the involvement of these structures in the performance of maternal behavior.

Reproductive experience and activation of maternal memory

The maternal and neurobiological responses of biological mothers and pup-induced maternal virgin rats were compared 55 and 80 days after an initial 2-day maternal experience. When tested for home cage responsiveness after prolonged isolation from young, the biological, primiparous rats displayed shorter maternal latencies. Primiparous females tested in the presence of pups on the elevated plus-maze displayed increased exploration of the open arms and increased c-Fos expression in the cortical nucleus of the amygdala. Pup exposure and parity also enhanced activation of the nucleus accumbens shell and medial nucleus of the amygdala, respectively. Therefore, although both nulliparous and primiparous rats retain a maternal memory for a prolonged time, the memory and neurochemical response appear stronger in primiparous mothers.

Social recognition memory requires two stages of protein synthesis in mice

Olfactory recognition memory was tested in adult male mice using a social discrimination task. The testing was conducted to begin to characterize the role of protein synthesis and the specific brain regions associated with activity in this task. Long-term olfactory recognition memory was blocked when the protein synthesis inhibitor anisomycin was injected 20 min before, immediately after, or 6 h after sampling. No effect was observed when anisomycin was administered 3 h or 18 h after sampling. Immunohistochemical analysis of Fos expression revealed that sampling-like exposure to a juvenile increased the activity of a subset of cells in the accessory olfactory bulb and the brain areas that are associated with it. Additionally, increased Fos expression was measured in the main olfactory bulb and the piriform cortex, whereas no signs of activation were seen in the cortical nucleus of the amygdala, all components of the main olfactory system. No increases in Fos immunoreactivity were observed after 4 h. Our data suggest that long-lasting olfactory recognition memory requires two stages of protein synthesis. The first stage takes place within 1-2 h and the second stage between 6-7 h after sampling. The first but not the second stage is paralleled by an increase in the number of Fos-immunoreactive cells in brain areas associated with both the main and accessory olfactory systems. It therefore appears that the role of the second stage of protein synthesis in recognition memory depends on the integrity of the first stage of protein synthesis.

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.

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.

Mapping the Neural Substrates Involved in Maternal Responsiveness and Lamb Olfactory Memory in Parturient Ewes Using Fos Imaging

In sheep, recognition of the familiar lamb by the mother depends on the learning of its olfactory signature after parturition. The authors quantified Fos changes in order to identify brain regions activated during lamb odor memory formation. Brain activation was compared with those measured in anosmic ewes displaying maternal behavior but not individual lamb recognition. In intact ewes, parturition induced significant increase in Fos expression in olfactory cortical regions and in cortical amygdala, whereas in anosmic mothers, Fos expression was very low. In contrast, no difference was observed between intact and anosmic ewes in hypothalamic areas and medial amygdala, suggesting a differentiation between the neural network controlling maternal responsiveness and that involved in olfactory lamb memory.

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.

Mothering begets mothering: the transmission of behavior and its neurobiology across generations

Early experiences exert their effects on adult parental behavior in part by altering the development of neurobiological mechanisms that initiate or support the initiation and sustenance of adult parental behavior. The effects of parental behavior on sensory, perceptual and emotional mechanisms in offspring constitute an experientially based mechanism by which neurobiological factors regulating behavior can be transferred from generation to generation somewhat independently of genetic endowment.

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

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

Evidence that the medial amygdala projects to the anterior/ventromedial hypothalamic nuclei to inhibit maternal behavior in rats

The maternal behaviors shown by a rat that has given birth are not shown by a virgin female rat when she is first presented with young. This absence of maternal behavior in virgins has been attributed to the activity of a neural circuit that inhibits maternal behavior in nulliparae. The medial amygdala and regions of the medial hypothalamus such as the anterior and ventromedial hypothalamic nuclei have previously been shown to inhibit maternal behavior, in that lesions to these regions promote maternal responding. Furthermore, we have recently shown that these and other regions, such as the principal bed nucleus of the stria terminalis, the ventral lateral septum, and the dorsal premammillary nucleus, show higher pup-induced Fos-immunoreactivity in non-maternal rats exposed to pups than during the performance of maternal behavior, indicating that they too could be involved in preventing maternal responsiveness. The current study tested whether the medial amygdala projects to the anterior/ventromedial hypothalamic nuclei in a neural circuit that inhibits maternal behavior, as well as to see what other brain regions could participate in this circuit. Bilateral excitotoxic lesions of the medial amygdala, or of the anterior/ventromedial hypothalamic nuclei, promoted maternal behavior. Unilateral medial amygdala lesions caused a reduction of pup-induced Fos-immunoreactivity in the anterior/ventromedial hypothalamic nuclei in non-maternal rats ipsilateral to the lesion, as well as in the principal bed nucleus of the stria terminalis, ventral lateral septum, and dorsal premammillary nucleus. Finally, unilateral medial amygdala lesions paired with contralateral anterior/ventromedial hypothalamic nuclei lesions promoted maternal behavior, although ipsilateral lesion placements were also effective.Together, these results indicate that the medial amygdala projects to the anterior/ventromedial hypothalamic nuclei in a neural circuit that inhibits maternal behavior, and that the principal bed nucleus of the stria terminalis, ventral lateral septum, and dorsal premammillary nucleus could also be involved in this circuit.

Patterns of Fos expression in the amygdala and ventral perirhinal cortex induced by training in an olfactory fear conditioning paradigm

The activation of amygdaloid nuclei, the ventral perirhinal cortex (vPRh), and several other brain areas in the rat during the acquisition and expression of olfactory fear conditioning was assessed through Fos immunocytochemistry in 3 separate experiments. The results of Experiment 1 suggest that olfactory and somatosensory inputs may functionally converge in the anterior region ot the medial nucleus (aMe). The results of Experiment 2 indicate that the aMe exhibited significantly greater Fos-like immunoreactivity (FLI) in subjects acquiring conditioned stimulus-unconditioned stimulus associations than in those presented with the same olfactory and somatosensory stimuli in a manner that precluded acquisition. The results of Experiment 3 indicate that the vPRh appeared to exhibit learning-related increases in FLI during the expression of previously acquired associations. Collectively, these data suggest that the aMe and vPRh may be critically involved in different aspects of olfactory fear conditioning.

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.

Neural mediation of nursing and related maternal behaviors

Nursing is the behavioral concomitant of lactation and the most generalizable maternal behavior across mammals. In lactating rats nursing often occurs in the kyphotic (upright crouched) posture; like the neuroendocrine determinants of milk synthesis and release, kyphosis requires suckling by the young. The dam's active pronurturant behaviors, such as retrieval and licking of pups, requires perioral somatosensory stimulation, which is often a precursor of kyphosis as well, and is inhibited by suckling. The sequential nature of maternal behaviors and the dissociations in their somatosensory regulation are critical to understanding their neural mediation, as exemplified by our recent work in lactating rats. We found that the caudal lateral and ventrolateral midbrain periaqueductal gray (cPAGl,vl) is a sensorimotor integration site for the kyphotic nursing posture. Destruction of the cPAGl,vl, or increased activity of the inhibitory neurotransmitter GABA within it, severely reduced kyphosis, increased nursing in more atypical postures, and had little or no effect on pronurturance. Various forebrain sites are known to mediate retrieval and licking of pups. Inhibition of dopaminergic activity in the nucleus accumbens of dams via microinfusions of a mixed D1/D2 dopamine receptor antagonist, cis-flupenthixol (FLU), dose-dependently reduced these active behaviors, while increasing nursing duration. Retrieval was inhibited, however, only by infusions of FLU that included the nucleus accumbens shell, which is reciprocally connected with other sites implicated in retrieval of pups. Thus, maternal behavior is not a unitary process but rather a complex category consisting of sequential behavioral components that have their own sensory and neural determinants.

Maternally separated rats show deficits in maternal care in adulthood

Although there is considerable research on the phenomenology, neuroendocrinology, neuroanatomy, and sensory control of maternal behavior, little is known about the influences of early postnatal and postweaning experiences on the development of maternal behavior. The purpose of this study was to assess how early life separation from the mother rat affects development of the offspring's juvenile and adult maternal behavior. From postnatal Days 1 to 17, 3 female rats within each litter were separated (SEP) from the mother and the rest of the litter for 5 hr daily while 3 of their sisters were not maternally separated (NSEP). On postnatal Day 21, all subjects were weaned and randomly assigned to one of three juvenile conditions. One female from both SEP and NSEP groups was either isolated (I), given a social conspecific (S), or given 1- to 4-day-old pups (P) for 5 consecutive days. Maternal behavior of SEP and NSEP animals was assessed and recorded on each of the 5 days. Once all animals reached adulthood, they were mated, gave birth, and were assessed for their maternal behavior. We found that the effects of maternal separation on juvenile maternal-like behaviors were minimal. On the other hand, maternal separation reduced adult maternal licking and crouching over pups. In addition, there was a significant interaction between postnatal and juvenile experience on maternal crouching in maternal animals. These results are discussed in terms of the variety of possible behavioral, endocrine, and neurochemical mechanisms that mediate the effects of early life experiences on adult maternal behavior.

Decreases in calmodulin binding proteins and calmodulin dependent protein phosphorylation in the medial preoptic area at the onset of maternal behavior in the rat

The onset of maternal behavior is characterized by the action of certain hormones, neuropeptides and neurotransmitters and a concomitant increase in the expression of c-Fos in the medial preoptic area (MPOA) but the signaling events that lie between have not been characterized. Because several of these hormones, neuropeptides and neurotransmitters function by activating Ca(2+)/calmodulin (CaM) mediated signaling pathways, many of which can lead to c-Fos expression, the goal of the current work was to identify calmodulin binding proteins (CaMBPs) or specific CaM-dependent phosphoproteins that might be involved. Probing of SDS-PAGE gels of extracts from the hippocampus, parietal cortex, basolateral amygdala and MPOA with recombinant (35)S-VU1-calmodulin (CaM) revealed 30 Ca(2+)-dependent and 4-6 Ca(2+)-independent CaMBPs. Statistically significant maternal behavior-related decreases in four Ca(2+)-dependent CaMBPs ( approximately 31 kDa, 50% decrease; approximately 33 kDa, 32%; approximately 50 kDa, 35%; approximately 60 kDa, 33%) were observed specifically in the MPOA. Numerous proteins were phosphorylated in a Ca(2+) CaM-dependent manner with two (MWs approximately 61 Da, approximately 58 kDa) showing a lack of phosphophorylation only in the MPOA. The selective decrease in CaMBPs coupled with the absence of CaM-dependent phosphoproteins implies that changes in Ca(2+)/CaM-mediated signaling may mediate some of the MPOA-specific processes during the onset of maternal behavior in the rat.

Loss of calcineurin from the medial preoptic area of primiparous rats

Western blot analyses reveal that calcineurin A (CNA), which is present in the hippocampus, basolateral amygdala, parietal cortex, and MPOA of virgin males and females, is undetectable only in the MPOA of primiparous females regardless of whether they had postpartum pup contact or not. In contrast, CNB was expressed at unchanging levels in the PC and MPOA. Similarly, G(alphao) and PKA(RI) were expressed at high levels in all of the brain regions of virgin males, virgin females, and primiparous females, supporting the concept that this loss of CNA is a specific event. Understanding how and why the expression of CNA, the sole neuronal Ca2+/CaM-dependent protein phosphatase, is down-regulated specifically in the MPOA of primiparous females may yield some insight into the signal transduction events that mediate the onset of mammalian maternal behavior.

Maternal behaviour in lactating rats stimulates c-fos in glutamate decarboxylase-synthesizing neurons of the medial preoptic area, ventral bed nucleus of the stria terminalis, and ventrocaudal periaqueductal gray

Increased activity of the immediate-early gene c-fos can be observed in many areas of the lactating rat brain after dams physically interact with pups and display maternal behaviour. These sites include the medial preoptic area, ventral bed nucleus of the stria terminalis, and the ventrolateral caudal periaqueductal gray, each of which is critical for the normal performance of particular maternal behaviours. The phenotype of cells in these areas that show increased c-fos activity after maternal behaviour, however, is unknown. Via double-label immunocytochemistry, we determined if the population of cells in these sites that express c-fos after maternal behaviour in lactating rats overlaps with the population that expresses the 67,000 mol. wt isoform of glutamate decarboxlyase, the synthesizing enzyme for the inhibitory neurotransmitter GABA. Lactating rats were separated from pups beginning on day 5 postpartum, and 48h later half were allowed to interact with a litter of pups for 60min whereas the other half were not. Dams re-exposed to pups were highly maternal, retrieving and licking them as well as displaying prolonged nursing behaviour that included milk letdown. Both groups of dams had a similar number of 67,000 mol. wt glutamate decarboxylase-immunoreactive cells in each site, although the number of 67,000 mol. wt glutamate decarboxylase-immunoreactive cells per microscopic field was significantly greater in the caudal ventrolateral periaqueductal gray than in the ventral bed nucleus of the stria terminalis, which in turn was greater than the medial preoptic area. In pup-stimulated dams, two to fourfold more Fos-immunoreactive cells were found in these three sites compared with non-stimulated controls. Labeling for Fos immunoreactivity and 67,000 mol. wt glutamate decarboxylase immunoreactivity was heterogeneous within each site. In the medial preoptic area, more Fos-immunoreactive and 67,000 mol. wt glutamate decarboxylase-immunoreactive cells (either single or dual-labeled) were found dorsally than ventrally. In the ventral bed nucleus of the stria terminalis, more Fos-immunoreactive and 67,000 mol. wt glutamate decarboxylase-immunoreactive cells were found medially than laterally. Within the caudal ventrolateral periaqueductal gray, 67,000 mol. wt glutamate decarboxylase-immunoreactive labeling was greatest ventromedially, while high numbers of Fos-immunoreactive nuclei were found both ventromedially and ventrolaterally. In pup-stimulated dams, more than half (53% in the medial preoptic area, 59% in the ventral bed nucleus of the stria terminalis, and 61% in the caudal ventrolateral periaqueductal gray) of the total population of Fos-immunoreactive cells also expressed 67,000 mol. wt glutamate decarboxylase. These results suggest that many of the neurons in these sites that show elevated c-fos activity after maternal behaviour are either local inhibitory interneurons or provide inhibitory input to other neural sites. These inhibitory mechanisms may be critical for the display of postpartum nurturance, possibly facilitating maternal behaviour by removing tonic inhibition on sites necessary for maternal responding or by restricting activity in neural sites that inhibit it.

Intergenerational effects of complete maternal deprivation and replacement stimulation on maternal behavior and emotionality in female rats

The present study investigated the effects of early rearing experiences on the development of maternal behavior in Sprague-Dawley female rats. Pups from individual litters were assigned to four different groups on Day 3 of life. From days 4 to 20 of life, these were reared artificially, without mother and receiving minimal "licking-like" tactile stimulation (AR-MIN), or maximal stimulation (AR-MAX) or were reared with their mothers (MR-CONTROL and MR-SHAM). At 70-100 days all AR and MR animals were mated and then observed with their own offspring, culled to eight pups. After maternal testing open-field tests were conducted. The female offspring in these litters (all raised by their MR and AR mothers) were reared to adulthood and then observed interacting with their offspring. Results show that in adulthood AR mothers engaged in significantly fewer pup-retrievals and less pup-licking (genital and body), and crouching, but significantly more non-maternal tail-chasing, digging, and hanging/climbing. As well, they were more active in the open field. Comparisons between the two AR groups and the MR groups, showed that most of the differences were between the AR-MIN and MR groups, with the AR-MAX animals showing levels of behavior between the two, and differing from neither. Analyses of covariance indicated that early experience and adult emotional behavior both influence adult maternal behavior, but their effects are independent of one another. A cross-generational effect of artificial rearing was also found. Daughters of AR and MR mothers that were observed after the birth of their own litters in adulthood showed a pattern of behavior that mimicked the pattern shown by their mothers. These results are discussed in terms of the variety of possible behavioral, endocrine, and neurochemical mechanisms that mediate the effects of early experiences on adult maternal behavior.

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

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

The temporal course of expression of c-Fos and Fos B within the medial preoptic area and other brain regions of postpartum female rats during prolonged mother--young interactions

Maternal behavior is associated with an increase in the expression of c-Fos and Fos B within neurons of the medial preoptic area (MPOA) and ventral bed nucleus of the stria terminalis (vBST). Whether this increase wanes as the duration of mother-young interaction increases is unknown. By varying the length of mother-young interactions in postpartum rats, the authors found that within the MPOA/vBST, the levels of both c-Fos and Fos B, once elevated, remained significantly above control levels through 47 hr of pup exposure. The persistence of c-Fos and Fos B within the MPOA/vBST of females that remained with pups was almost unique in that only one other neural area, the anterior magnocellular part of the paraventricular hypothalamic nucleus, showed such a response. Because MPOA/vBST neurons are essential for maternal behavior, the results suggest that c-Fos and Fos B expression within these regions may be necessary to maintain their normal functional activity.

Combined c-fos and 14C-2-deoxyglucose method to differentiate site-specific excitation from disinhibition: analysis of maternal behavior in the rat

On the basis of evidence that 14C-2-deoxyglucose (2-DG) autoradiography indicates activity at axonal terminals, whereas c-fos immunocytochemistry indicates activity of neuronal cell bodies, we combined these techniques in adjacent histological brain sections to assess excitatory and disinhibitory synaptic relations in selected sites in female rats in which maternal behavior was elicited by natural parturition, sensitization (7- to 10-day cohabitation with foster pups), or hysterectomy. All individuals in these three groups expressed maternal behavior immediately before 2-DG injection. Controls were non-maternal virgins. Parturient and Hysterectomized groups: elevation (compared with controls) in both 2-DG and c-fos activity in medial preoptic area (MPOA) indicated an increase in its input and output activity, i.e., an excitatory interaction; the MPOA was previously shown to be critical for maternal behavior. Sensitized group: a decrease in 2-DG activity of vomeronasal nuclei (bed nucleus of the accessory olfactory tract, BAOT, and medial amygdala, ME, replicating our previous study) and an elevation in c-fos activity, jointly indicate disinhibition of these nuclei, that were previously shown to modulate pup-chemostimulation-induced sensitization. All other sites showed evidence of excitatory input-output relationships (i.e., joint increase in both 2-DG and c-fos activity), e.g., bed nucleus of the stria terminalis (BNST), lateral habenula (LHAB), central gray (CG), thalamus (THAL), septum (SEPT), and ventral tegmental area (VTA). The present study demonstrates the feasibility of measuring 2-DG and c-fos activity jointly in adjacent sections of the same brain, thereby providing evidence to distinguish between localized excitation and disinhibition.