Edinger-Westphal peptidergic neurons enable maternal preparatory nesting

The neurobiology of parenting and infant-evoked aggression

Parenting behavior comprises a variety of adult-infant and adult-adult interactions across multiple timescales. The state transition from nonparent to parent requires an extensive reorganization of individual priorities and physiology and is facilitated by combinatorial hormone action on specific cell types that are integrated throughout interconnected and brainwide neuronal circuits. In this review, we take a comprehensive approach to integrate historical and current literature on each of these topics across multiple species, with a focus on rodents. New and emerging molecular, circuit-based, and computational technologies have recently been used to address outstanding gaps in our current framework of knowledge on infant-directed behavior. This work is raising fundamental questions about the interplay between instinctive and learned components of parenting and the mutual regulation of affiliative versus agonistic infant-directed behaviors in health and disease. Whenever possible, we point to how these technologies have helped gain novel insights and opened new avenues of research into the neurobiology of parenting. We hope this review will serve as an introduction for those new to the field, a comprehensive resource for those already studying parenting, and a guidepost for designing future studies.

Virtual reality-empowered deep-learning analysis of brain cells

Automated detection of specific cells in three-dimensional datasets such as whole-brain light-sheet image stacks is challenging. Here, we present DELiVR, a virtual reality-trained deep-learning pipeline for detecting c-Fos+ cells as markers for neuronal activity in cleared mouse brains. Virtual reality annotation substantially accelerated training data generation, enabling DELiVR to outperform state-of-the-art cell-segmenting approaches. Our pipeline is available in a user-friendly Docker container that runs with a standalone Fiji plugin. DELiVR features a comprehensive toolkit for data visualization and can be customized to other cell types of interest, as we did here for microglia somata, using Fiji for dataset-specific training. We applied DELiVR to investigate cancer-related brain activity, unveiling an activation pattern that distinguishes weight-stable cancer from cancers associated with weight loss. Overall, DELiVR is a robust deep-learning tool that does not require advanced coding skills to analyze whole-brain imaging data in health and disease.

Activation of lateral preoptic neurons is associated with nest-building in male mice

Nest-building behavior is a widely observed innate behavior. A nest provides animals with a secure environment for parenting, sleep, feeding, reproduction, and temperature maintenance. Since animal infants spend their time in a nest, nest-building behavior has been generally studied as parental behaviors, and the medial preoptic area (MPOA) neurons are known to be involved in parental nest-building. However, nest-building of singly housed male mice has been less examined. Here we show that male mice spent longer time in nest-building at the early to middle dark phase and at the end of the dark phase. These two periods are followed by sleep-rich periods. When a nest was removed and fresh nest material was introduced, both male and female mice built nests at Zeitgeber time (ZT) 6, but not at ZT12. Using Fos-immunostaining combined with double in situ hybridization of Vgat and Vglut2, we found that Vgat- and Vglut2-positive cells of the lateral preoptic area (LPOA) were the only hypothalamic neuron population that exhibited a greater number of activated cells in response to fresh nest material at ZT6, compared to being naturally awake at ZT12. Fos-positive LPOA neurons were negative for estrogen receptor 1 (Esr1). Both Vgat-positive and Vglut2-positive neurons in both the LPOA and MPOA were activated at pup retrieval by male mice. Our findings suggest the possibility that GABAergic and glutamatergic neurons in the LPOA are associated with nest-building behavior in male mice.

Benchtop mesoSPIM: a next-generation open-source light-sheet microscope for cleared samples

In 2015, we launched the mesoSPIM initiative, an open-source project for making light-sheet microscopy of large cleared tissues more accessible. Meanwhile, the demand for imaging larger samples at higher speed and resolution has increased, requiring major improvements in the capabilities of such microscopes. Here, we introduce the next-generation mesoSPIM ("Benchtop") with a significantly increased field of view, improved resolution, higher throughput, more affordable cost, and simpler assembly compared to the original version. We develop an optical method for testing detection objectives that enables us to select objectives optimal for light-sheet imaging with large-sensor cameras. The improved mesoSPIM achieves high spatial resolution (1.5 µm laterally, 3.3 µm axially) across the entire field of view, magnification up to 20×, and supports sample sizes ranging from sub-mm up to several centimeters while being compatible with multiple clearing techniques. The microscope serves a broad range of applications in neuroscience, developmental biology, pathology, and even physics.

The Benchtop mesoSPIM: a next-generation open-source light-sheet microscope for large cleared samples

In 2015, we launched the mesoSPIM initiative (www.mesospim.org), an open-source project for making light-sheet microscopy of large cleared tissues more accessible. Meanwhile, the demand for imaging larger samples at higher speed and resolution has increased, requiring major improvements in the capabilities of light-sheet microscopy. Here, we introduce the next-generation mesoSPIM ("Benchtop") with significantly increased field of view, improved resolution, higher throughput, more affordable cost and simpler assembly compared to the original version. We developed a new method for testing objectives, enabling us to select detection objectives optimal for light-sheet imaging with large-sensor sCMOS cameras. The new mesoSPIM achieves high spatial resolution (1.5 μm laterally, 3.3 μm axially) across the entire field of view, a magnification up to 20x, and supports sample sizes ranging from sub-mm up to several centimetres, while being compatible with multiple clearing techniques. The new microscope serves a broad range of applications in neuroscience, developmental biology, and even physics.

The neuropeptidergic connectome of C. elegans

Efforts are ongoing to map synaptic wiring diagrams, or connectomes, to understand the neural basis of brain function. However, chemical synapses represent only one type of functionally important neuronal connection; in particular, extrasynaptic, "wireless" signaling by neuropeptides is widespread and plays essential roles in all nervous systems. By integrating single-cell anatomical and gene-expression datasets with biochemical analysis of receptor-ligand interactions, we have generated a draft connectome of neuropeptide signaling in the C. elegans nervous system. This network is characterized by high connection density, extended signaling cascades, autocrine foci, and a decentralized topology, with a large, highly interconnected core containing three constituent communities sharing similar patterns of input connectivity. Intriguingly, several key network hubs are little-studied neurons that appear specialized for peptidergic neuromodulation. We anticipate that the C. elegans neuropeptidergic connectome will serve as a prototype to understand how networks of neuromodulatory signaling are organized.

Imprinted genes and the manipulation of parenting in mammals

Genomic imprinting refers to the parent-of-origin expression of genes, which originates from epigenetic events in the mammalian germ line. The evolution of imprinting may reflect a conflict over resource allocation early in life, with silencing of paternal genes in offspring soliciting increased maternal provision and silencing of maternal genes limiting demands on the mother. Parental caregiving has been identified as an area of potential conflict, with several imprinted genes serendipitously found to directly influence the quality of maternal care. Recent systems biology approaches, based on single-cell RNA sequencing data, support a more deliberate relationship, which is reinforced by the finding that imprinted genes expressed in the offspring influence the quality of maternal caregiving. These bidirectional, reiterative relationships between parents and their offspring are critical both for short-term survival and for lifelong wellbeing, with clear implications for human health.

Hormone-mediated neural remodeling orchestrates parenting onset during pregnancy

During pregnancy, physiological adaptations prepare the female body for the challenges of motherhood. Becoming a parent also requires behavioral adaptations. Such adaptations can occur as early as during pregnancy, but how pregnancy hormones remodel parenting circuits to instruct preparatory behavioral changes remains unknown. We found that action of estradiol and progesterone on galanin (Gal)-expressing neurons in the mouse medial preoptic area (MPOA) is critical for pregnancy-induced parental behavior. Whereas estradiol silences MPOAGal neurons and paradoxically increases their excitability, progesterone permanently rewires this circuit node by promoting dendritic spine formation and recruitment of excitatory synaptic inputs. This MPOAGal-specific neural remodeling sparsens population activity in vivo and results in persistently stronger, more selective responses to pup stimuli. Pregnancy hormones thus remodel parenting circuits in anticipation of future behavioral need.

Genotypic sex shapes maternal care in the African pygmy mouse, Mus minutoides

Sexually dimorphic behaviours, such as parental care, have long been thought to be mainly driven by gonadal hormones. In the past two decades, a few studies have challenged this view, highlighting the direct influence of the sex chromosome complement (XX versus XY or ZZ versus ZW). The African pygmy mouse, Mus minutoides, is a wild mouse species with naturally occurring XY sex reversal induced by a third, feminizing X* chromosome, leading to three female genotypes: XX, XX* and X*Y. Here, we show that sex reversal in X*Y females shapes a divergent maternal care strategy (maternal aggression, pup retrieval and nesting behaviours) from both XX and XX* females. Although neuroanatomical investigations were inconclusive, we show that the dopaminergic system in the anteroventral periventricular nucleus of the hypothalamus is worth investigating further as it may support differences in pup retrieval behaviour between females. Combining behaviours and neurobiology in a rodent subject to natural selection, we evaluate potential candidates for the neural basis of maternal behaviours and strengthen the underestimated role of the sex chromosomes in shaping sex differences in brain and behaviours. All things considered, we further highlight the emergence of a third sexual phenotype, challenging the binary view of phenotypic sexes.

Peptidergic and functional delineation of the Edinger-Westphal nucleus

Many neuronal populations that release fast-acting excitatory and inhibitory neurotransmitters in the brain also contain slower-acting neuropeptides. These facultative peptidergic cell types are common, but it remains uncertain whether neurons that solely release peptides exist. Our fluorescence in situ hybridization, genetically targeted electron microscopy, and electrophysiological characterization suggest that most neurons of the non-cholinergic, centrally projecting Edinger-Westphal nucleus in mice are obligately peptidergic. We further show, using anterograde projection mapping, monosynaptic retrograde tracing, angled-tip fiber photometry, and chemogenetic modulation and genetically targeted ablation in conjunction with canonical assays for anxiety, that this peptidergic population activates in response to loss of motor control and promotes anxiety responses. Together, these findings elucidate an integrative, ethologically relevant role for the Edinger-Westphal nucleus and functionally align the nucleus with the periaqueductal gray, where it resides. This work advances our understanding of peptidergic modulation of anxiety and provides a framework for future investigations of peptidergic systems.

A Sleep-Specific Midbrain Target for Sevoflurane Anesthesia

Sevoflurane has been the most widely used inhaled anesthetics with a favorable recovery profile; however, the precise mechanisms underlying its anesthetic action are still not completely understood. Here the authors show that sevoflurane activates a cluster of urocortin 1 (UCN1+ )/cocaine- and amphetamine-regulated transcript (CART+ ) neurons in the midbrain involved in its anesthesia. Furthermore, growth hormone secretagogue receptor (GHSR) is highly enriched in sevoflurane-activated UCN1+ /CART+ cells and is necessary for sleep induction. Blockade of GHSR abolishes the excitatory effect of sevoflurane on UCN1+ /CART+ neurons and attenuates its anesthetic effect. Collectively, their data suggest that anesthetic action of sevoflurane necessitates the GHSR activation in midbrain UCN1+ /CART+ neurons, which provides a novel target including the nucleus and receptor in the field of anesthesia.

Angular head velocity cells within brainstem nuclei projecting to the head direction circuit

An animal's perceived sense of orientation depends upon the head direction (HD) system found in several limbic structures and depends upon an intact peripheral vestibular labyrinth. However, how the vestibular system influences the generation, maintenance, and updating of the HD signal remains poorly understood. Anatomical and lesion studies point towards three key brainstem nuclei as being potential critical components in generating the HD signal: nucleus prepositus hypoglossi (NPH), supragenual nucleus (SGN), and dorsal paragigantocellularis reticular nuclei (PGRNd). Collectively, these nuclei are situated between the vestibular nuclei and the dorsal tegmental and lateral mammillary nuclei, which are thought to serve as the origin of the HD signal. To test this hypothesis, extracellular recordings were made in these areas while rats either freely foraged in a cylindrical environment or were restrained and rotated passively. During foraging, a large subset of cells in all three nuclei exhibited activity that correlated with changes in the rat's angular head velocity (AHV). Two fundamental types of AHV cells were observed: 1) symmetrical AHV cells increased or decreased their neural firing with increases in AHV regardless of the direction of rotation; 2) asymmetrical AHV cells responded differentially to clockwise (CW) and counter-clockwise (CCW) head rotations. When rats were passively rotated, some AHV cells remained sensitive to AHV whereas others had attenuated firing. In addition, a large number of AHV cells were modulated by linear head velocity. These results indicate the types of information conveyed in the ascending vestibular pathways that are responsible for generating the HD signal.

Significance Statement

Extracellular recording of brainstem nuclei (nucleus prepositus hypoglossi, supragenual nucleus, and dorsal paragigantocellularis reticular nucleus) that project to the head direction circuit identified different types of angular head velocity (AHV) cells while rats freely foraged in a cylindrical environment. The firing of many cells was also modulated by linear velocity. When rats were restrained and passively rotated some cells remained sensitive to AHV, whereas others had attenuated firing. These brainstem nuclei provide critical information about the rotational movement of the rat's head in the azimuthal plane.

Influence of grazing on the activity pattern and temporal niche of two dominant rodent species in Alxa desert

Grazing by large herbivores can potentially affect interspecific interactions between small herbivores by reducing the ecological fitness of animals. Desert rodents are important components in desert ecosystems and indicators of environmental change. Grazing reduces food resources, but rodents can decrease interspecific niche overlap by adaptive behavior. However, the key factors driving rodent behavioral activities and coexistence in the Alxa desert remains unstudied. We monitored population density and behavioral activities of Midday gerbil (Meriones meridianus) and northern three-toed jerboa (Dipus sagitta) in a grazing exclusion experiment in Alxa desert, Inner Mongolia, China, in 2017. We assessed the relationship between environmental factors (such as plant height, density, coverage, rainfall and temperature) and the behavioral activities of two coexisting rodent species. The results showed that: (1) In summer, grazing significantly reduced the activity time of gerbil and jerboa compared to that in grazing exclusion areas (gerbil: F = 5.98, p < 0.05, η2 = 0.22; jerboa: F = 8.57, p < 0.01, η2 = 0.28). Grazing reduced the temporal niche overlap with an obvious shifting of activity peaks between two species. (2) Grazing exclusion enhanced the temporal niche overlap between the two rodent species due to greater food availability which relieved inter-specific competition in each season. (3) Grazing strengthened the sensitivity of rodents to environmental changes in all seasons. These results indicated that grazing affected competition between the rodent species by altering vegetation conditions, which in turn affected the temporal niche and activity patterns of rodents.

Transient receptor potential ankyrin 1 ion channel expressed by the Edinger-Westphal nucleus contributes to stress adaptation in murine model of posttraumatic stress disorder

The centrally projecting Edinger-Westphal nucleus (EWcp) is involved in stress adaptation. Transient receptor potential ankyrin 1 (TRPA1) mRNA was previously shown to be expressed abundantly in mouse and human EWcp urocortin 1 (UCN1) positive neurons and reacted to chronic stress. Since UCN1 neurons are deeply implicated in stress-related disorders, we hypothesized that TRPA1/UCN1 neurons are also affected in posttraumatic stress disorder (PTSD). We examined male Trpa1 wild type (WT) and gene-deficient (KO) mice in the single prolonged stress (SPS) model of PTSD. Two weeks later the behavioral changes were monitored by forced swim test (FST) and restraint. The Trpa1 and Ucn1 mRNA expression and the UCN1 peptide content were assessed by RNAscope in situ hybridization technique combined with immunofluorescence labeling in the EWcp. SPS-induced immobility was lower in Trpa1 KO compared to WT animals, both in the FST and restraint, corresponding to diminished depression-like behavior. The copy number of Trpa1 mRNA decreased significantly in EWcp of WT animals in response to SPS. Higher basal Ucn1 mRNA expression was observed in the EWcp of KO animals, that was not affected by SPS exposure. EWcp neurons of WT animals responded to SPS with substantially increased amount of UCN1 peptide content compared to control animals, whereas such changes were not observable in KO mice. The decreased Trpa1 mRNA expression in the SPS model of PTSD associated with increased neuronal UCN1 peptide content suggests that this cation channel might be involved in the regulation of stress adaptation and may contribute to the pathomechanism of PTSD.

Enhanced pup retrieval behaviour in a mouse model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy to affect women of reproductive-age world-wide. Hyperandrogenism is both a hallmark feature of PCOS, and is hypothesised to be an underlying mechanism driving the development of the condition in utero. With circulating hormones known to profoundly influence maternal responses in females, we aimed to determine whether maternal behaviour is altered in a well-described prenatally androgenised (PNA) mouse model of PCOS. Mouse dams were administered with dihydrotestosterone or vehicle on days 16, 17 and 18 of pregnancy. Maternal responses were assessed in both the dihydrotestosterone-injected dams following parturition and in their adult female PNA offspring. Exposure of dams to excess androgens during late pregnancy had no detrimental effects on pregnancy outcomes, including gestation length, pup survival and gestational weight gain, or on subsequent maternal behaviour following parturition. By contrast, PNA virgin females, modelling PCOS, exhibited enhanced maternal behaviour when tested in an anxiogenic novel cage environment, with females rapidly retrieving pups and nesting with them. In comparison, most control virgin females failed to complete this retrieval task in the anxiogenic environment. Assessment of progesterone receptor and oestrogen receptor α immunoreactivity in the brains of virgin PNA and control females revealed increased numbers of oestrogen receptor α positive cells in the brains of PNA females in regions well known to be important for maternal behaviour. This suggests that increased oestrogenic signalling in the neural circuit that underlies maternal behaviour may be a possible mechanism by which maternal behaviour is enhanced in PNA female mice.

Single Nuclei Analyses Reveal Transcriptional Profiles and Marker Genes for Diverse Supraspinal Populations

The mammalian brain contains numerous neurons distributed across forebrain, midbrain, and hindbrain that project axons to the lower spinal cord and work in concert to control movement and achieve homeostasis. Extensive work has mapped the anatomic location of supraspinal cell types and continues to establish specific physiological functions. The patterns of gene expression that typify and distinguish these disparate populations, however, are mostly unknown. Here, using adult mice of mixed sex, we combined retrograde labeling of supraspinal cell nuclei with fluorescence-activated nuclei sorting and single-nuclei RNA sequencing analyses to transcriptionally profile neurons that project axons from the brain to lumbar spinal cord. We identified 14 transcriptionally distinct cell types and used a combination of established and newly identified marker genes to assign an anatomic location to each. To validate the putative marker genes, we visualized selected transcripts and confirmed selective expression within lumbar-projecting neurons in discrete supraspinal regions. Finally, we illustrate the potential utility of these data by examining the expression of transcription factors that distinguish different supraspinal cell types and by surveying the expression of receptors for growth and guidance cues that may be present in the spinal cord. Collectively, these data establish transcriptional differences between anatomically defined supraspinal populations, identify a new set of marker genes of use in future experiments, and provide insight into potential differences in cellular and physiological activity across the supraspinal connectome.SIGNIFICANCE STATEMENT The brain communicates with the body through a wide variety of neuronal populations with distinct functions and differential sensitivity to damage and disease. We have used single-nuclei RNA sequencing technology to distinguish patterns of gene expression within a diverse set of neurons that project axons from the mouse brain to the lumbar spinal cord. The results reveal transcriptional differences between populations previously defined on the basis of anatomy, provide new marker genes to facilitate rapid identification of cell type in future work, and suggest distinct responsiveness of different supraspinal populations to external growth and guidance cues.

Neural and behavioral plasticity across the female reproductive cycle

Sex is fundamental for the evolution and survival of most species. However, sex can also pose danger, because it increases the risk of predation and disease transmission, among others. Thus, in many species, cyclic fluctuations in the concentration of sex hormones coordinate sexual receptivity and attractiveness with female reproductive capacity, promoting copulation when fertilization is possible and preventing it otherwise. In recent decades, numerous studies have reported a wide variety of sex hormone-dependent plastic rearrangements across the entire brain, including areas relevant for female sexual behavior. By contrast, how sex hormone-induced plasticity alters the computations performed by such circuits, such that collectively they produce the appropriate periodic switches in female behavior, is mostly unknown. In this review, we highlight the myriad sex hormone-induced neuronal changes known so far, the full repertoire of behavioral changes across the reproductive cycle, and the few examples where the relationship between sex hormone-dependent plasticity, neural activity, and behavior has been established. We also discuss current challenges to causally link the actions of sex hormones to the modification of specific cellular pathways and behavior, focusing on rodents as a model system while drawing a comparison between rodents and humans wherever possible.

Neural circuit mechanisms of the cholecystokinin (CCK) neuropeptide system in addiction

Given historical focus on the roles for cholecystokinin (CCK) as a peripheral hormone controlling gastrointestinal processes and a brainstem peptide regulating food intake, the study of CCK as a limbic neuromodulator coordinating reward-seeking and emotional behavior remains underappreciated. Furthermore, localization of CCK to specialized interneurons throughout the hippocampus and cortex relegated CCK to being examined primarily as a static cell type marker rather than a dynamic functional neuromodulator. Yet, over three decades of literature have been generated by efforts to delineate the central mechanisms of addiction-related behaviors mediated by the CCK system across the striatum, amygdala, hypothalamus, and midbrain. Here, we cover fundamental findings that implicate CCK neuron activity and CCK receptor signaling in modulating drug intake and drug-seeking (focusing on psychostimulants, opioids, and alcohol). In doing so, we highlight the few studies that indicate sex differences in CCK expression and corresponding drug effects, emphasizing the importance of examining hormonal influences and sex as a biological variable in translating basic science discoveries to effective treatments for substance use disorders in human patients. Finally, we point toward understudied subcortical sources of endogenous CCK and describe how continued neurotechnology advancements can be leveraged to modernize understanding of the neural circuit mechanisms underlying CCK release and signaling in addiction-relevant behaviors.

Oxytocin Receptors in the Mouse Centrally-projecting Edinger-Westphal Nucleus and their Potential Functional Significance for Thermoregulation

The centrally-projecting Edinger-Westphal nucleus (EWcp) has been shown to contribute to regulation of multiple functions, including responses to stress and fear, attention, food consumption, addiction, body temperature and maternal behaviors. However, receptors involved in regulation of these behaviors through EWcp remain poorly characterized. On the other hand, the oxytocin peptide (OXT) is also known to regulate a substantial number of physiological responses and behaviors. Here we show that mRNA encoding OXT receptors (Oxtr) is expressed in EWcp of male and female C57BL/6J mice. These receptors are present on urocortin 1 (Ucn) mRNA-containing neurons and, to a lesser extent, on neurons in EWcp expressing the vesicular glutamate transporter 2 (Vglut2) mRNA of EWcp. Using RNAscope in situ hybridization, we show that neurons containing Ucn and Vglut2 mRNAs are two intermingled, but independent subpopulations in EWcp and characterize their relationship with other populations of neurons in the vicinity of this nucleus. Using immunohistochemistry, we show that intraperitoneal (IP) administration of OXT can induce FOS in Oxtr-containing neurons, suggesting that these receptors on EWcp neurons are functional. A follow up study showed that injection of OXT (2.3 or 7.7 mg/kg, IP) is accompanied by a decrease in body temperature. Since EWcp is known to be involved in regulation of body temperature, we hypothesize that OXT's effects on body temperature could be mediated through the EWcp. The contribution of OXTR in EWcp to regulation of various functions of EWcp and OXT needs to be deciphered.

Preparatory neurons for building a nest

Mothers build nests in anticipation of the delivery of their offspring. How the brain coordinates this behavior is unknown. Topilko et al. (2022) demonstrate that nest building in pregnant females relies on the activity of peptidergic neurons in the Edinger-Westphal nucleus.