Abstracts for symposia presentations and other talks

Abstracts for symposia presentations and other talks are listed chronologically according to their scheduled times during the meeting.

All talks—unless otherwise noted—will be in Alumni Hall in the Indiana Memorial Union.

Thursday, June 20, 2019

SYMPOSIUM 1: Neural circuits for socially motivated behaviors

S1.1 A hypothalamic to PAG circuit controls aggressive motivation and action
Annegret Falkner, Princeton University USA

[abstract not available]

S1.2 Oxytocin in the bed nucleus of the stria terminalis induces social anxiety
Brian Trainor, University of California, Davis USA

Oxytocin is a well-known modulator of social behaviors, and has been put forth as a possible therapeutic for social anxiety disorder. However, studies in humans have found that oxytocin can either increase or decrease social anxiety. How can the same neuropeptide exert such different effects on behavior? In a series of studies using the California mouse model of social defeat, we demonstrate that oxytocin produced and acting within the bed nucleus of the stria terminalis promotes social avoidance and vigilance. Our results suggest that sex differences in how social stressors affect the activity of oxytocin producing neurons are a major contributing factor in determining sex differences in how stress affects social behavior. Consistent with work in other species, we also show oxytocin acting in the nucleus accumbens promotes social approach. Together, these results suggest that oxytocin works in complementary neural circuits to produce divergent effects on social behaviors.

S1.3 Understanding the neural basis of social attachment
Devanand Manoli, University of California, San Francisco USA

[abstract not available]

S1.4 Socially-transmitted motivation for maternal behavior
Ioana Carcea, Rutgers University USA

Maternal care is profoundly important for mammalian survival, and maternal behaviors can also be expressed by non-biological parents after experience with infants. One critical molecular signal for maternal behavior is oxytocin, released by hypothalamic paraventricular nucleus (PVN) and enabling plasticity within auditory cortex for recognizing infant vocalizations. To determine how these changes occur during natural experience, we continuously monitored homecage behavior of female virgin mice co-housed for days with an experienced mother and litter, synchronized with in vivo recordings from virgin PVN/oxytocin neurons. Mothers engaged virgins in maternal care by ensuring that virgins were in the nest, and demonstrated maternal behavior by self-generating pup retrieval episodes. These social interactions activated virgin PVN and gated behaviorally-relevant cortical plasticity for pup distress calls. Thus rodent maternal behavior can be learned by social transmission, and our results describe a mechanism for adapting the brains of new parents to infant needs via endogenous oxytocin.


Pleiotropic effects of testosterone on a sexually selected trait: birdsong
Gregory F. Ball, University of Maryland USA

Male birdsong functions as a courtship or territorial signal often in a reproductive context. Testosterone (T) increases during the reproductive phase of the annual cycle and can enhance song production. T can exert its effects in the brain on song and other reproductive behaviors via its estrogenic and androgenic metabolites. The neural control of birdsong is highly modular, with distinct regions and circuits regulating different aspects of song learning and production. The widespread distribution of nuclear androgen receptors in the song system as well as the occurrence of estrogen receptors in one key forebrain nucleus and the presence of both receptor types in the diencephalon and the midbrain raises questions as to where and how T is exerting its myriad effects on song. By selectively implanting T or androgen antagonists into specific brain regions or in the periphery of castrated male canaries, we have identified a modular organization of the androgenic activation of birdsong. T acting in the preoptic area (POM) induces singing at high rates, but song quality is impaired. Placing T in the song nucleus HVC and the POM rescues some of these effects. Blocking T action selectively in forebrain song nuclei can modulate independently effects on acoustic stereotypy of individual syllables and trills as opposed to effects on syllable-type usage or syllable-type sequence variability. Measures of song performance preferred by females can be modulated by selectively blocking T action in the syrinx. Thus, song behaviors are regulated by androgens acting at multiple levels in a non-redundant fashion

SYMPOSIUM 2: Recent updates on sex differences in epigenetic modifications on the neuroendocrine control of behavior

S2.1 Neuroepigenetic mechanisms of behavioural adaptation in the zebra finch
David Clayton, Queen Mary University of London UK

Behavioural adaptation is key to an organism’s success, on both proximal and evolutionary timescales. We are working on several models of behavioural adaptation in songbirds, testing the hypothesis that stable adaptations involve neuroepigenetic mechanisms – in particular changes in DNA methylation. In one model, we find that the experience of being placed alone overnight in a sound isolation chamber triggers changes in DNA methylation in the auditory forebrain of adult zebra finches. These genes including BDNF (a neurotrophic factor) and FKBP5 (a co-chaperone of the glucocorticoid receptor). We hypothesise that such changes support a broad re-tuning of the nervous system related to the shift in social context. In another model, we find that habituation of responses to song playbacks is correlated with other changes in DNA methylation, possibly related to formation of new song associations. Most recently we have begun studying developmental reprogramming of zebra finch embryos following parental “incubation calls” (Mariette & Buchanan, Science, 2016), testing the hypothesis of potential epigenetic mechanisms in this phenomenon, too. These observations suggest the deep involvement of epigenetic mechanisms in diverse behavioural adaptations and on multiple timescales.

S2.2 Epigenetic potential in introduced populations
Haley Hanson, University of South Florida USA

All organisms must respond to environmental stimuli and do so through alterations of the endocrine system. Phenotypic plasticity is common and the interconnectedness of the endocrine system makes it so many modifications can impact subsequent phenotypes and potentially the fitness of that organism, especially during development and vulnerable life-history stages. Epigenetic potential, defined as the capacity for epigenetically-mediated phenotypic plasticity, may be mediating endocrine phenotypes in response to environmental effects. Thus, epigenetic potential is expected to play an important role in range expansions, and other contexts in which the environment is novel or unpredictable, especially when it occurs in regulatory elements of the endocrine system. Here, we predicted which genes in the hypothalamic-pituitary-adrenal (HPA) axis are most likely to be epigenetically-regulated, and consequently, might be most impacted by epigenetic potential. Our top predicted components were mainly receptors: (in order) corticotropin-releasing hormone receptor 2, corticotropin-releasing receptor 1, adrenocorticotropic hormone receptor, and glucocorticoid receptor. This sparked a more intensive study into how one form of epigenetic potential (i.e. the abundance and/or position of CpG sites within gene promoters) varied among introduced populations of house sparrows (Passer domesticus) by targeting candidate genes and using epi- and ddRADseq methods.

S2.3 Transcriptomics of sexual differentiation of the brain
Margaret McCarthy, University of Maryland, Baltimore USA

In mammals, a perinatal surge in androgen production by the fetal testis initiates masculinization of the developing brain. The process is complete within days of birth but the consequences must endure for weeks, months or even decades depending upon the species. Exploration of epigenetic modifiers and sex differences in the transcriptome reveal multiple region specific mechanisms and profiles. These range from steroid modulation of the activity of enzymes that methylate DNA, divergent roles for chromatin versus DNA in males and females and the potential for sex-specific transcriptional networks underlying complex social behavior. Both the advantages and challenges of transcriptomic and epigenetic approaches will be discussed.

S2.4 Epigenetic development of the juvenile social brain
Anthony Auger, University of Wisconsin USA

[abstract not available]

Friday, June 21, 2019

SYMPOSIUM 3: New Investigator Symposium

S3.1 W.C. Young Lecture: Cancer and sleep—Understanding how tumors talk to the brain
Jeremy Borniger, Stanford University USA

[abstract not available]

S3.2 Lyn Clemens Lecture: Cross-species examination of the role of estradiol in sleep and memory in females
Nicole J. Gervais, University of Toronto Canada

Ovarian hormone deprivation following natural menopause is associated with sleep disturbance, memory complaints and increased risk of mild cognitive impairment and Alzheimer’s disease (AD) later in life. This risk is exacerbated following ovarian removal prior to natural menopause. Studies in humans and animals demonstrate the protective effects of estradiol (E2) on sleep and memory formation, and while sleep is known to promote memory and brain function, limited attention has been paid to understanding the contribution of poor sleep to memory decline following menopause. Our findings demonstrate the protective effects of E2 on both sleep and memory across three species (rat, marmosets, and humans). Our human studies provide novel insight into the importance of stratifying samples based on menopause type (e.g. natural vs surgical). Our discussion focuses on memory abilities that are dependent on structures within the medial temporal lobe or the prefrontal cortex. We show that E2 improves memory function across species, and promotes synaptic density and structural integrity of structures within the medial temporal lobe. We also show that menopause is associated with worse sleep in both marmosets and humans, which is protected by E2 use. Our recent data demonstrate that poor sleep is related to reduced hippocampal volume and lower memory performance in menopausal women. These studies take an integrative and translational approach to explore the contribution of ovarian hormone deprivation to menopausal symptoms and elevated dementia risk, and identify potential early markers associated with memory decline.

S3.3 Involvement of the ventral tegmental area in socially rewarding behavior in juvenile male and female rats
Christina J. Reppucci, Michigan State University USA

The ventral tegmental area (VTA) is an essential component of the mesocorticolimbic dopamine reward system and an important node of the Social Decision-Making Network. Yet, the role of the VTA in socially rewarding behaviors, especially during early adolescence, is understudied. Here, using juvenile male and female rats, we focused on social play, a highly rewarding behavior predominately displayed by juveniles and expressed by nearly all mammals. In Experiment 1, using combined Fos and tyrosine hydroxylase (TH) immunohistochemistry we found that subjects exposed to social play had greater activation of the VTA and its dopaminergic neurons than subjects in the no play control condition. In Experiment 2, temporary inactivation of the VTA via bilateral infusion of the GABAA agonist muscimol selectively decreased the expression of social play while leaving social investigation intact. In Experiment 3, using intra-VTA in vivo microdialysis we found that social play was associated with dynamic changes in the extracellular levels of glutamate, GABA, and dopamine. In Experiment 4, subjects were exposed to social play one week after unilateral injections of the retrograde tracer CTB into the VTA, and then Fos immunohistochemistry was used to determine activation of VTA afferents. Of note, subjects in the play condition had greater activation of VTA-projecting lateral septum neurons compared to the no play control condition. Together, these experiments provide evidence that the VTA is a key node in the network underlying social play, and that activation of the VTA supports the expression of social play behavior in juvenile rats.

S3.4 Noncanonical genomic imprinting reveals novel subpopulations of monoaminergic neurons in the brain
Paul Bonthuis, University of Utah USA

In published RNAseq studies, we discovered a network of monoamine neurotransmitter genes exhibiting “noncanonical” genomic imprinting effects in the mouse brain. Canonical imprinting involves complete silencing of a gene’s maternal or paternal allele, whereas noncanonical imprinting involves a bias to express either the maternal or paternal allele at the tissue level. Leading theories claim genomic imprinting in the brain functions to impact social behavior. Neurotransmitters known to regulate social behavior, including the monoamines dopamine, serotonin, and norepinephrine, are downstream products of dopa decarboxylase (Ddc), a monoamine synthesis enzyme, which exhibits a maternal allele bias in the brain. To investigate allelic bias at the cellular level in monoaminergic neurons, CRISPR-Cas9 mediated knockin made Ddc Allele-Tag mice expressing GFP and RFP from the maternal and paternal alleles (DdcGFP/RFP), respectively. These mice, and reciprocals (DdcRFP/GFP), were used to produce a brain atlas identifying imprinted monoamine cell populations. Fourteen (out of 52) high-confidence discrete regions, mostly in dopaminergic nuclei of the hypothalamus, contained subpopulations of DDC+ cells monoallelically expressing only the maternal allele. Also, Ddc maternal bias is enhanced in the hypothalamus of lactating females, and correlates with nursing litter size. Furthermore, compound heterozygous females that inherit multiple mutant monoamine synthesis alleles from their mother, as opposed to their father, display differences in maternal behavior phenotypes. These results indicate that noncanonical imprinting at the tissue level comprises a mixture of biallelic and imprinted monoallelic subpopulations at the cellular level, imprinting effects can change in response to environmental stimuli, and monoamine imprinting impacts social behavior.

S3.5 Regulation of fluid homeostasis during mammalian hibernation: Behavioral, hormonal, and neural mechanisms
Ni Y. Feng, Yale University USA

Hibernation is a fascinating physiological phenomenon during which animals rely solely on the management of internal resources for long-term survival. Winter hibernation in rodents can last up to nine months, during which animals cycle between weeks-long torpor bouts of severe hypothermia and hypometabolism interspersed by short interbout arousals (IBA), when major physiological parameters return to normal “active” levels. We use the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) as a model to characterize how peripheral, central, and behavioral components of the fluid homeostatic pathway are tuned to enable hibernation. We show that despite not having access to external water, squirrels avoid dehydration and decrease serum concentration (osmolality) by 30 mOsmol/kg during torpor. This decrease is mainly due to changes in the internal distribution of ions, but not to increased drinking prior to hibernation or increased renal water retention via vasopressin or oxytocin production. During IBA, serum osmolality increase to active levels, but squirrels display lowered baseline drinking activity, suggesting an escape from the aversive drive of thirst during hibernation. However, acute dehydration via hypertonic saline injection is able to induce thirst in IBA animals, suggesting the underlying thirst neural circuit can be activated in hibernation. Supporting this conclusion, hypertonic saline injection elevates the expression of cFOS in the subfornical organ of both active and IBA animals. Together, our results demonstrate that during hibernation, squirrels escape dehydration by regulating the internal distribution of ions, exhibit lowered baseline thirst, but possess a functional thirst neural circuit capable of responding to signals of fluid imbalance.


The female power grid controlled by sex-dependent neurocircuits in the MBH
Holly Ingraham, University of California, San Francisco USA

We seek to discover sex-differences in the central control of female physiology across the lifespan. We found that central estrogen signaling is linked to sex-dependent anabolic bone responses in female mice. In our recently published work, a stunning increase in bone mass occurs after deleting estrogen hormone signaling in the female arcuate nucleus of the hypothalamus (ARC). In female mice, the robust increase in new bone formation stems from loss rather than gain of estrogen signaling in the ARC and is uncoupled from high circulating peripheral estradiol (E2). Four independent and intersectional models confirmed that ablating estrogen receptor alpha (ERa) signaling in ARC neurons leads to a robust increase in bone density and bone strength only in female mice. We identified ARC Kiss1 neurons in the medial basal hypothalamus (MBH) as the critical node for this powerful neuroskeletal circuit. These findings established that a sex-dependent brain-to-bone pathway normally restrains bone metabolism to divert energy resources elsewhere. When disrupted, a robust anabolic bone response is permanently triggered in young and old mutant female mice. In parallel studies we have identified a small cluster of ~100 estrogen-responsive neurons in the ventrolateral subregion of the ventromedial hypothalamus (VMHvl) that create an ancillary female-specific circuit to integrate melanocortin and estrogen signaling, promoting both activity and obsessive-like behaviors. Surprisingly, food intake was unaffected in all of our models that manipulate estrogen-signaling in the MBH. We conclude that hormone-sensitive, sex-dependent circuits in the hypothalamus are essential for coordinating energy allocation and utilization in females.

SYMPOSIUM 4: Mechanisms underlying experience-dependent neural plasticity during development and adulthood

S4.1 Brain plasticity and perineuronal nets in songbirds
Jacques Balthazart, University of Liège Belgium

The morphology of the oscine song control system can be regulated by changes in the hormonal and social environment. This plasticity includes a modulation of neurogenesis in HVC, but also changes in cell size, long distance connectivity and perineuronal nets (PNN) density. PNN are aggregations of extracellular matrix components surrounding the soma of specific neurons that limit synaptogenesis and mark the end of sensitive periods. In zebra finches, PNN expression in HVC and the nucleus robustus arcopallialis (RA) is higher in males than in females and higher in adult than in juvenile males. PNN increase in the developing zebra finch brain correlates with the timing of sensitive periods for song learning and PNN maturation is delayed in birds deprived from a tutor. Similarly, in first year male canaries, PNN density reaches its maximum in the fall in HVC and in early winter in RA when birds are crystalizing their song. PNN are also more densely expressed in the song control system of zebra finches than in European starlings and canaries, two species that exhibit open-ended learning. Although PNN density did not change across conditions representing the different seasonal stages in starlings, testosterone increases the number of PNN in castrated male and in female canaries and their density seems to vary across seasons in some of the male song control nuclei. We are currently investigating whether dissolution of PNN in HVC by application of chondroitinase sulfate affects song structure and song (re)learning in adult male canaries.

S4.2 Do perineuronal nets close the postnatal sensitive period for steroid-dependent organization of behavior?
Kalynn Schulz, University of Tennessee USA

The factors mediating a successful transition from adolescence to adulthood range from social to biological. One factor that has received increased investigation in recent years is the timing of puberty. Whether individuals undergo pubertal development early or late relative to their peers increases risk for mental illness. Scientific explanations of the relationship between pubertal timing and mental illness tend to focus on the social and emotional consequences of developing earlier or later than one’s peers. However, our work demonstrates that gonadal hormones permanently alter neural networks and behavior during adolescence. We have also shown that sensitivity to the organizing actions of steroid hormones decreases across postnatal development, with adolescence marking the end of postnatal sensitive period. However, the mechanisms governing the timing of the postnatal sensitive period for steroid-dependent organization of behavior are unknown. My laboratory is currently investigating whether adolescent increases in perineuronal nets close the sensitive period for steroid-dependent organization of reproductive behavior in mice. Perineuronal nets (PNNs) are specialized extracellular matrix structures that preferentially wrap around parvalbumin-expressing GABAergic neurons as they mature. PNN increases are associated with the closing of many other sensitive periods of development such as visual acuity, fear conditioning, and song learning in birds. We are testing whether testosterone in males, and estradiol in females, directly impacts PNN development to close the postnatal sensitive period for steroid-dependent organization of reproductive behavior in mice. The outcomes will advance our understanding of the factors mediating the timing of postnatal brain sensitivity to gonadal steroid hormones.

S4.3 Role of perineuronal nets surrounding parvalbumin+GABAergic neurons in regulating learning and execution of maternal behavior
Keerthi Krishnan, University of Tennessee USA

Cohabitation of adult nulliparous mice with pups and mother induces maternal behavior in them in a hormone-independent manner. Such non-hormonal factors are important in mediating plasticity, likely through chromatin remodeling of specific neural circuitry (Stolzenberg and Champagne, 2016,). We have previously shown that nulliparous mice deficient in Methyl CpG-binding protein 2 (MECP2), an epigenetic regulator, display inefficient pup gathering behavior (Krishnan, Lau et al, 2017). We identified a crucial mechanism involving extracellular matrix structures called perineuronal nets (PNNs) which play a major role in structural plasticity of parvalbumin+ GABAergic networks in the auditory cortex. The auditory cortex of MECP2-deficient females had increased numbers of PNNs, which when removed, improved pup gathering performance, demonstrating the crucial structural role that PNNs provide in learning and plasticity.

Many questions remain: How do the nulliparous wild types learn and perform the behavior well? What stimuli and factors are critical for priming efficient retrieval? What neural circuits are essential for processing sensory information, motor outputs and context-specific responses? We answer these questions by utilizing integrative approaches from histology/microscopy to detailed behavioral coding, in order to gain a better understanding of the mechanisms underlying adult experience-dependent plasticity. I will be presenting our recent, unpublished data on somatosensory cortex plasticity, ultrasonic vocalizations during retrieval and detailed behavioral observations.

S4.4 Dynamic regulation of sound learning in adult auditory cortex
Robert Liu, Emory University USA

The mechanisms by which we learn from and reshape our perception of the world based on experience are of long-standing interest within the neuroscience community. One continuing mystery is how we manage to incorporate newly learned stimuli into our neural networks without drastically disrupting the processing of previously learned stimuli. We have been investigating such mechanisms in the context of more ethologically motivated sensory learning paradigms – both appetitive and aversive – in mice. An emerging picture based on work in both a maternal model for sensory learning of infant sounds, and an auditory fear conditioning model, suggests that context-dependent disinhibition of auditory cortex may be essential for plasticity to learn the behavioral relevance of new sounds from experiences. But how do these changes manage to persist despite further ongoing experiences? One contributing mechanism within auditory cortex appears to be the dynamic regulation of the extracellular matrix by sound learning. Although perineuronal nets (PNNs) are generally thought to be inhibitory to neural plasticity and stable in adulthood, we discovered that after an auditory fear conditioning session, PNN components are actually dynamically upregulated about 4 hours later before returning to baseline the next day. Moreover, digesting PNNs immediately after training impairs the consolidation of auditory fear memories, as assayed in subsequent fear expression tests. These results are consistent with a working model wherein the transient increase in PNNs might place a brake on further plasticity during a window of potential interference from new experiences during memory consolidation.