Aging leads to sex-dependent effects on pair bonding and increased number of oxytocin-producing neurons in monogamous prairie voles.

Pair bonds powerfully modulate health, which becomes particularly important when facing the detrimental effects of aging. To examine the impact of aging on relationship formation and response to loss, we examined behavior in naive 6-, 12-, and 18-month male and female prairie voles, a monogamous species that forms mating-based pair bonds. We found that older males (18-months) bonded quicker than younger voles, while similarly aged female voles increased partner directed affiliative behaviors. Supporting sex differences in bonding behaviors, we found that males were more likely to sample both partner and stranger voles while females were more likely to display partner preference during the initial 20 min of the test. We also found that male voles of all ages show enduring bonding behavior despite four weeks of partner separation while females show an overall decrease in partner-directed affiliation, including an erosion of partner preference in 12-month females. Finally, we found that the number of oxytocin, but not vasopressin, cells in the paraventricular hypothalamus increased at 18 months of age. These results establish prairie voles as a novel model to study the effects of normal and abnormal aging on pair bonding.

A neuronal signature for monogamous reunion.

Pair-bond formation depends vitally on neuromodulatory signaling within the nucleus accumbens, but the neuronal dynamics underlying this behavior remain unclear. Using 1-photon in vivo Ca2+ imaging in monogamous prairie voles, we found that pair bonding does not elicit differences in overall nucleus accumbens Ca2+ activity. Instead, we identified distinct ensembles of neurons in this region that are recruited during approach to either a partner or a novel vole. The partner-approach neuronal ensemble increased in size following bond formation, and differences in the size of approach ensembles for partner and novel voles predict bond strength. In contrast, neurons comprising departure ensembles do not change over time and are not correlated with bond strength, indicating that ensemble plasticity is specific to partner approach. Furthermore, the neurons comprising partner and novel-approach ensembles are nonoverlapping while departure ensembles are more overlapping than chance, which may reflect another key feature of approach ensembles. We posit that the features of the partner-approach ensemble and its expansion upon bond formation potentially make it a key neuronal substrate associated with bond formation and maturation.

Integrative genomic analysis reveals cancer-associated mutations at diagnosis of CML in patients with high-risk disease.

Genomic events associated with poor outcome in chronic myeloid leukemia (CML) are poorly understood. We performed whole-exome sequencing, copy-number variation, and/or RNA sequencing for 65 patients to discover mutations at diagnosis and blast crisis (BC). Forty-six patients with chronic-phase disease with the extremes of outcome were studied at diagnosis. Cancer gene variants were detected in 15 (56%) of 27 patients with subsequent BC or poor outcome and in 3 (16%) of 19 optimal responders (P = .007). Frequently mutated genes at diagnosis were ASXL1, IKZF1, and RUNX1 The methyltransferase SETD1B was a novel recurrently mutated gene. A novel class of variant associated with the Philadelphia (Ph) translocation was detected at diagnosis in 11 (24%) of 46 patients comprising fusions and/or rearrangement of genes on the translocated chromosomes, with evidence of fragmentation, inversion, and imperfect sequence reassembly. These were more frequent at diagnosis in patients with poor outcome: 9 (33%) of 27 vs 2 (11%) of 19 optimal responders (P = .07). Thirty-nine patients were tested at BC, and all had cancer gene variants, including ABL1 kinase domain mutations in 58%. However, ABL1 mutations cooccurred with other mutated cancer genes in 89% of cases, and these predated ABL1 mutations in 62% of evaluable patients. Gene fusions not associated with the Ph translocation occurred in 42% of patients at BC and commonly involved fusion partners that were known cancer genes (78%). Genomic analysis revealed numerous relevant variants at diagnosis in patients with poor outcome and all patients at BC. Future refined biomarker testing of specific variants will likely provide prognostic information to facilitate a risk-adapted therapeutic approach.

How prior pair-bonding experience affects future bonding behavior in monogamous prairie voles.

Monogamous prairie voles (Microtus ochrogaster) form mating-based pair bonds. Although wild prairie voles rarely re-pair following loss of a partner, laboratory studies have shown that previous pairing and mating does not negate the ability to form a new partner preference. However, little is known about how prior bond experience may alter the trajectory and display of a new pair bond. In the present study, we disrupted an initial pair bond by separating partners and then varied the amount of time before a new partner was introduced. We assessed how separation time affected the stability of partner preference over time and influenced decision-making in male voles performing a head-to-head partner preference test in which they chose between the first and second partner. We found that the ability to consistently display a preference for the second partner, supplanting the initial pair bond, depended on how long the test animal was separated from their first partner. Prior bonding experience also shaped the subsequent effects of mating on partner preference. Partner preference strength was sensitive to latency to mate with the second partner but not the first partner, irrespective of separation time. These results suggest that the ability to form a consistent, strong preference for a new partner after an initial pair bond depends upon the amount of time that has passed since separation from the first partner. These results provide valuable insight into how social bonds are dynamically shaped by prior social experience and identify variables that contribute to recovery from partner loss and the ability to form a new pair bond. They also delineate a behavioral trajectory essential for future work examining the hormonal and genetic changes that enable recovery from partner loss.

Optogenetic stimulation of dentate gyrus engrams restores memory in Alzheimer's disease mice.

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by amyloid-beta (Aß) plaques and tau neurofibrillary tangles. APPswe/PS1dE9 (APP/PS1) mice have been developed as an AD model and are characterized by plaque formation at 4-6 months of age. Here, we sought to better understand AD-related cognitive decline by characterizing various types of memory. In order to better understand how memory declines with AD, APP/PS1 mice were bred with ArcCreERT2 mice. In this line, neural ensembles activated during memory encoding can be indelibly tagged and directly compared with neural ensembles activated during memory retrieval (i.e., memory traces/engrams). We first administered a battery of tests examining depressive- and anxiety-like behaviors, as well as spatial, social, and cognitive memory to APP/PS1 × ArcCreERT2 × channelrhodopsin (ChR2)-enhanced yellow fluorescent protein (EYFP) mice. Dentate gyrus (DG) neural ensembles were then optogenetically stimulated in these mice to improve memory impairment. AD mice had the most extensive differences in fear memory, as assessed by contextual fear conditioning (CFC), which was accompanied by impaired DG memory traces. Optogenetic stimulation of DG neural ensembles representing a CFC memory increased memory retrieval in the appropriate context in AD mice when compared with control (Ctrl) mice. Moreover, optogenetic stimulation facilitated reactivation of the neural ensembles that were previously activated during memory encoding. These data suggest that activating previously learned DG memory traces can rescue cognitive impairments and point to DG manipulation as a potential target to treat memory loss commonly seen in AD.

Prognosis for patients with CML and >10% BCR-ABL1 after 3 months of imatinib depends on the rate of BCR-ABL1 decline.

In chronic myeloid leukemia (CML) patients, a breakpoint cluster region-Abelson (BCR-ABL1) value >10% at 3 months of therapy is statistically associated with poorer outcome, yet many of these patients still achieve satisfactory outcomes. We investigated 528 first-line imatinib-treated patients to determine whether patients with the poorest outcome can be better discriminated at 3 months. All outcomes were significantly superior for the 410 patients with BCR-ABL1 ≤10% at 3 months (P < .001). However, the poorest outcomes among the 95 evaluable patients with BCR-ABL1 >10% at 3 months were identified by the rate of BCR-ABL1 decline from baseline, assessed by estimating the number of days over which BCR-ABL1 halved. Patients with BCR-ABL1 halving time <76 days (n = 74) had significantly superior outcomes compared with patients whose BCR-ABL1 values did not halve by 76 days (n = 21; 4-year overall survival, 95% vs 58%, P = .0002; progression-free survival, 92% vs 63%, P = .008; failure-free survival, 59% vs 6%, P < .0001; and major molecular response, 54% vs 5%, P = .008). By multivariate analysis, the halving time was an independent predictor of outcome in this poor risk group. Our study highlighted that the rate of BCR-ABL1 decline may be a critical prognostic discriminator of the patients with very poor outcome among those >10% at 3 months. The International Randomized IFN vs STI571 (IRIS) trial was registered at http://www.clinicaltrials.gov as #NCT00006343. The Tyrosine Kinase Inhibitor Optimization and Selectivity (TOPS) trial was registered at http://www.clinicaltrials.gov as #NCT00124748. The Therapeutic Intensification in DE-novo Leukaemia (TIDEL) I trial was registered at http://www.ANZCTR.org.au as #ACTRN12607000614493. The TIDEL II trial was registered at http://www.ANZCTR.org.au as #ACTRN12607000325404.

The relative contribution of proximal 5' flanking sequence and microsatellite variation on brain vasopressin 1a receptor (Avpr1a) gene expression and behavior.

Certain genes exhibit notable diversity in their expression patterns both within and between species. One such gene is the vasopressin receptor 1a gene (Avpr1a), which exhibits striking differences in neural expression patterns that are responsible for mediating differences in vasopressin-mediated social behaviors. The genomic mechanisms that contribute to these remarkable differences in expression are not well understood. Previous work has suggested that both the proximal 5' flanking region and a polymorphic microsatellite element within that region of the vole Avpr1a gene are associated with variation in V1a receptor (V1aR) distribution and behavior, but neither has been causally linked. Using homologous recombination in mice, we reveal the modest contribution of proximal 5' flanking sequences to species differences in V1aR distribution, and confirm that variation in V1aR distribution impacts stress-coping in the forced swim test. We also demonstrate that the vole Avpr1a microsatellite structure contributes to Avpr1a expression in the amygdala, thalamus, and hippocampus, mirroring a subset of the inter- and intra-species differences observed in central V1aR patterns in voles. This is the first direct evidence that polymorphic microsatellite elements near behaviorally relevant genes can contribute to diversity in brain gene expression profiles, providing a mechanism for generating behavioral diversity both at the individual and species level. However, our results suggest that many features of species-specific expression patterns are mediated by elements outside of the immediate 5' flanking region of the gene.

Prairie voles as a model for adaptive reward remodeling following loss of a bonded partner.

Loss of a loved one is a painful event that substantially elevates the risk for physical and mental illness and impaired daily function. Socially monogamous prairie voles are laboratory-amenable rodents that form life-long pair bonds and exhibit distress upon partner separation, mirroring phenotypes seen in humans. These attributes make voles an excellent model for studying the biology of loss. In this review, we highlight parallels between humans and prairie voles, focusing on reward system engagement during pair bonding and loss. As yearning is a unique feature that differentiates loss from other negative mental states, we posit a model in which the homeostatic reward mechanisms that help to maintain bonds are disrupted upon loss, resulting in yearning and other negative impacts. Finally, we synthesize studies in humans and voles that delineate the remodeling of reward systems during loss adaptation. The stalling of these processes likely contributes to prolonged grief disorder, a diagnosis recently added to the Diagnostic and Statistical Manual for Psychiatry.

Social neuroscience: When more is merrier.

Spiny mice are gregarious animals that prefer to socialize with large groups. A new pioneering study reveals an underlying neural circuit governing this social preference.

Aging leads to sex-dependent effects on pair bonding and increased number of oxytocin-producing neurons in monogamous prairie voles.

Pair bonds powerfully modulate health, which becomes particularly important when facing the detrimental effects of aging. To examine the impact of aging on relationship formation and response to loss, we examined behavior in 6-, 12-, and 18-month male and female prairie voles, a monogamous species that forms mating-based pair bonds. We found that older males (18-months) bonded quicker than younger voles, while similarly aged female voles increased partner directed affiliative behaviors. Supporting sex differences in bonding behaviors, we found that males were more likely to sample both partner and novel voles while females were more likely to display partner preference during the initial 20 minutes of the test. Using partner separation to study loss, we observed an erosion of partner preference only in 12-month females, but an overall decrease in partner-directed affiliation in females across all groups, but not in males. Finally, we found that the number of oxytocin, but not vasopressin, cells in the paraventricular hypothalamus increased during aging. These results establish prairie voles as a novel model to study the effects of normal and abnormal aging on pair bonding. Highlights: 18-month male voles demonstrate accelerated bond formation18-month female voles increase partner-directed huddling after 2 wksBonds erode faster in 12-month female voles after partner separationFemale behavior from partner preference tests is reflected in free interactionThe number of paraventricular hypothalamus oxytocin cells increase during aging.

Nucleus accumbens dopamine release reflects the selective nature of pair bonds.

In monogamous species, prosocial behaviors directed toward partners are dramatically different from those directed toward unknown individuals and potential threats. Dopamine release in the nucleus accumbens has a well-established role in social reward and motivation, but how this mechanism may be engaged to drive the highly divergent social behaviors directed at a partner or unfamiliar conspecific remains unknown. Using monogamous prairie voles, we first employed receptor pharmacology in partner preference and social operant tasks to show that dopamine is critical for the appetitive drive for social interaction but not for low-effort, unconditioned consummatory behaviors. We then leveraged the subsecond temporal resolution of the fluorescent biosensor, GRABDA, to ask whether differential dopamine release might distinguish between partner and novel social access and interaction. We found that partner seeking, anticipation, and interaction resulted in more accumbal dopamine release than the same events directed toward a novel vole. Further, partner-associated dopamine release decreased after prolonged partner separation. Our results are consistent with a model in which dopamine signaling plays a prominent role in the appetitive aspects of social interactions. Within this framework, differences in partner- and novel-associated dopamine release reflect the selective nature of pair bonds and may drive the partner- and novel-directed social behaviors that reinforce and cement bonds over time. This provides a potential mechanism by which highly conserved reward systems can enable selective, species-appropriate social behaviors.

Prairie vole pair bonding and plasticity of the social brain.

In monogamous species, pair bonding leads to striking changes in social behavior and neural circuitry. We outline the cognitive building blocks of monogamous pair bonding in prairie voles (Microtus ochrogaster), as well as opportunities afforded by the species to investigate diverse mechanisms underlying social experience-dependent plasticity and gain insights into the neurobiology of complex social behavior more generally.

PhAT: A flexible open-source GUI-driven toolkit for photometry analysis.

Photometry approaches detect sensor-mediated changes in fluorescence as a proxy for rapid molecular changes within the brain. As a flexible technique with a relatively low cost to implement, photometry is rapidly being incorporated into neuroscience laboratories. While multiple data acquisition systems for photometry now exist, robust analytical pipelines for the resulting data remain limited. Here we present the Ph otometry A nalysis T oolkit (PhAT) - a free open source analysis pipeline that provides options for signal normalization, incorporation of multiple data streams to align photometry data with behavior and other events, calculation of event-related changes in fluorescence, and comparison of similarity across fluorescent traces. A graphical user interface (GUI) enables use of this software without prior coding knowledge. In addition to providing foundational analytical tools, PhAT is designed to readily incorporate community-driven development of new modules for more bespoke analyses, and data can be easily exported to enable subsequent statistical testing and/or code-based analyses. In addition, we provide recommendations regarding technical aspects of photometry experiments including sensor selection and validation, reference signal considerations, and best practices for experimental design and data collection. We hope that the distribution of this software and protocol will lower the barrier to entry for new photometry users and improve the quality of collected data, increasing transparency and reproducibility in photometry analyses. Basic Protocol 1: Software Environment InstallationBasic Protocol 2: GUI-driven Fiber Photometry AnalysisBasic Protocol 3: Adding Modules.

PhAT: A Flexible Open-Source GUI-Driven Toolkit for Photometry Analysis.

Photometry approaches detect sensor-mediated changes in fluorescence as a proxy for rapid molecular changes within the brain. As a flexible technique with a relatively low cost to implement, photometry is rapidly being incorporated into neuroscience laboratories. Yet, although multiple data acquisition systems for photometry now exist, robust analytical pipelines for the resulting data remain limited. Here we present the Photometry Analysis Toolkit (PhAT)-a free open-source analysis pipeline that provides options for signal normalization, incorporation of multiple data streams to align photometry data with behavior and other events, calculation of event-related changes in fluorescence, and comparison of similarity across fluorescent traces. A graphical user interface (GUI) enables use of this software without prior coding knowledge. In addition to providing foundational analytical tools, PhAT is designed to readily incorporate community-driven development of new modules for more bespoke analyses, and enables data to be easily exported to enable subsequent statistical testing and/or code-based analyses. In addition, we provide recommendations regarding technical aspects of photometry experiments, including sensor selection and validation, reference signal considerations, and best practices for experimental design and data collection. We hope that the distribution of this software and protocols will lower the barrier to entry for new photometry users and improve the quality of collected data, increasing transparency and reproducibility in photometry analyses. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Software and environment installation Alternate Protocol 1: Software and environment update Basic Protocol 2: GUI-driven fiber photometry analysis Support Protocol 1: Examining signal quality Support Protocol 2: Interacting with graphs Basic Protocol 3: Adding modules to PhAT Alternate Protocol 2: Creating functions for use in Jupyter Notebook.

Prolonged partner separation erodes nucleus accumbens transcriptional signatures of pair bonding in male prairie voles.

The loss of a spouse is often cited as the most traumatic event in a person's life. However, for most people, the severity of grief and its maladaptive effects subside over time via an understudied adaptive process. Like humans, socially monogamous prairie voles (Microtus ochrogaster) form opposite-sex pair bonds, and upon partner separation, show stress phenotypes that diminish over time. We test the hypothesis that extended partner separation diminishes pair bond-associated behaviors and causes pair bond transcriptional signatures to erode. Opposite-sex or same-sex paired males were cohoused for 2 weeks and then either remained paired or were separated for 48 hours or 4 weeks before collecting fresh nucleus accumbens tissue for RNAseq. In a separate cohort, we assessed partner-directed affiliation at these time points. We found that these behaviors persist despite prolonged separation in both same-sex and opposite-sex paired voles. Opposite-sex pair bonding led to changes in accumbal transcription that were stably maintained while animals remained paired but eroded following prolonged partner separation. Eroded genes are associated with gliogenesis and myelination, suggesting a previously undescribed role for glia in pair bonding and loss. Further, we pioneered neuron-specific translating ribosomal affinity purification in voles. Neuronally enriched transcriptional changes revealed dopaminergic-, mitochondrial-, and steroid hormone signaling-associated gene clusters sensitive to acute pair bond disruption and loss adaptation. Our results suggest that partner separation erodes transcriptomic signatures of pair bonding despite core behavioral features of the bond remaining intact, revealing potential molecular processes priming a vole to be able to form a new bond.

Losing a spouse or life partner is a deeply traumatic event that can have long-term repercussions. Given enough time, however, most surviving partners are able to process their grief. The neural processes that enable people to adapt to their loss remain unknown. To explore this question, scientists often turn to animals that form long-term mating based pair bonds and can be raised in the laboratory. Monogamous prairie voles enter lifelong partnerships where the two individuals live together, prefer to cuddle with each other, and take care of their pups as a team. After having lost their mate, they show signs of distress that eventually subside with time. Sadino et al. examined the biological impact of partner loss in these animals by focusing on the nucleus accumbens, a brain region important for social connections. This involved tracking gene expression ­ which genes were switched on and off in this area ­ as the voles established their pair bonds, and then at different time points after one of the partners had been removed. The experiments revealed that establishing a relationship leads to a stable shift in nucleus accumbens gene expression, which may help maintain bonds over time. In particular, genes related to glia (the non-neuronal cells which assist neurons in their tasks) see their expression levels increase, indicating a previously undescribed role for this cell type in regulating pair bonding. Having their partner removed led to an erosion of the gene expression pattern that had emerged during pair bonding; this may help the remaining vole adapt to its loss and go on to form a new bond. In addition, Sadino et al. explored the gene expression of only neurons in the nucleus accumbens and uncovered biological processes distinct from those that occur in glia after partner separation. Together, these results shed light on the genetic and neuronal mechanisms which underlie adaptation to loss; this knowledge could one day inform how to better support individuals during this time.

Sex differences in the reward value of familiar mates in prairie voles.

The rewarding properties of social interactions facilitate relationship formation and maintenance. Prairie voles are one of the few laboratory species that form selective relationships, manifested as "partner preferences" for familiar partners versus strangers. While both sexes exhibit strong partner preferences, this similarity in outward behavior likely results from sex-specific neurobiological mechanisms. We recently demonstrated that in operant trials, females worked hardest for access to familiar conspecifics of either sex, while males worked equally hard for access to any female, indicating a sex difference in social motivation. As tests were performed with one social target at a time, males might have experienced a ceiling effect, and familiar females might be more relatively rewarding in a choice scenario. Here we performed an operant social choice task in which voles lever-pressed to gain temporary access to either the chamber containing their mate or one containing a novel opposite-sex vole. Females worked hardest to access their mate, while males pressed at similar rates for either female. Individual male behavior was heterogeneous, congruent with multiple mating strategies in the wild. Voles exhibited preferences for favorable over unfavorable environments in a non-social operant task, indicating that lack of social preference does not reflect lack of discrimination. Natural variation in oxytocin receptor genotype at the intronic single nucleotide polymorphism NT213739 was associated with oxytocin receptor density, and predicted individual variation in stranger-directed aggressive behavior. These findings suggest that convergent preference behavior in male and female voles results from sex-divergent pathways, particularly in the realm of social motivation.

Emergent intra-pair sex differences and organized behavior in pair bonded prairie voles (Microtus ochrogaster).

In pair bonding animals, coordinated behavior between partners is required for the pair to accomplish shared goals such as raising young. Despite this, experimental designs rarely assess the behavior of both partners within a bonded pair. Thus, we lack an understanding of the interdependent behavioral dynamics between partners that likely facilitate relationship success. To identify intra-pair behavioral correlates of pair bonding, we used socially monogamous prairie voles (Microtus ochrogaster) and tested both partners using social choice and non-choice tests at short- and long-term pairing timepoints. Females developed a preference for their partner more rapidly than males, with preference driven by different behaviors in each sex. Further, as bonds matured, intra-pair behavioral sex differences and organized behavior emerged-females consistently huddled more with their partner than males did regardless of overall intra-pair affiliation levels. When animals were allowed to freely interact with a partner or a novel vole in sequential free interaction tests, pairs spent more time interacting together than either animal did with a novel vole, consistent with partner preference in the more commonly employed choice test. Total pair interaction in freely moving voles was correlated with female, but not male, behavior. Via a social operant paradigm, we found that pair-bonded females, but not males, are more motivated to access and huddle with their partner than a novel vole. Together, our data indicate that as pair bonds mature, sex differences and organized behavior emerge within pairs, and that these intra-pair behavioral changes are likely organized and driven by the female animal.

Oxytocin, Dopamine, and Opioid Interactions Underlying Pair Bonding: Highlighting a Potential Role for Microglia.

Pair bonds represent some of the strongest attachments we form as humans. These relationships positively modulate health and well-being. Conversely, the loss of a spouse is an emotionally painful event that leads to numerous deleterious physiological effects, including increased risk for cardiac dysfunction and mental illness. Much of our understanding of the neuroendocrine basis of pair bonding has come from studies of monogamous prairie voles (Microtus ochrogaster), laboratory-amenable rodents that, unlike laboratory mice and rats, form lifelong pair bonds. Specifically, research using prairie voles has delineated a role for multiple neuromodulatory and neuroendocrine systems in the formation and maintenance of pair bonds, including the oxytocinergic, dopaminergic, and opioidergic systems. However, while these studies have contributed to our understanding of selective attachment, few studies have examined how interactions among these 3 systems may be essential for expression of complex social behaviors, such as pair bonding. Therefore, in this review, we focus on how the social neuropeptide, oxytocin, interacts with classical reward system modulators, including dopamine and endogenous opioids, during bond formation and maintenance. We argue that an understanding of these interactions has important clinical implications and is required to understand the evolution and encoding of complex social behaviors more generally. Finally, we provide a brief consideration of future directions, including a discussion of the possible roles that glia, specifically microglia, may have in modulating social behavior by acting as a functional regulator of these 3 neuromodulatory systems.

Wireless multilateral devices for optogenetic studies of individual and social behaviors.

Advanced technologies for controlled delivery of light to targeted locations in biological tissues are essential to neuroscience research that applies optogenetics in animal models. Fully implantable, miniaturized devices with wireless control and power-harvesting strategies offer an appealing set of attributes in this context, particularly for studies that are incompatible with conventional fiber-optic approaches or battery-powered head stages. Limited programmable control and narrow options in illumination profiles constrain the use of existing devices. The results reported here overcome these drawbacks via two platforms, both with real-time user programmability over multiple independent light sources, in head-mounted and back-mounted designs. Engineering studies of the optoelectronic and thermal properties of these systems define their capabilities and key design considerations. Neuroscience applications demonstrate that induction of interbrain neuronal synchrony in the medial prefrontal cortex shapes social interaction within groups of mice, highlighting the power of real-time subject-specific programmability of the wireless optogenetic platforms introduced here.