Physiological and Behavioral Responses to Vocalization Playback in Mice

Autistic-relevant behavioral phenotypes of a mouse model of cyclin-dependent kinase-like 5 deficiency disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene and characterized by early-onset epilepsy, intellectual disability, and autistic features. To date, the etiological mechanisms underlying CDD are largely unknown and no effective therapies are available. The Cdkl5 knock-out (KO) mouse has been broadly employed in preclinical studies on CDD; Cdkl5-KO mice display neurobehavioral abnormalities recapitulating most CDD symptoms, including alterations in motor, sensory, cognitive, and social abilities. However, most available preclinical studies have been carried out on adult Cdkl5-KO mice, so little is known about the phenotypic characteristics of this model earlier during development. Furthermore, major autistic-relevant phenotypes, for example, social and communication deficits, have been poorly investigated and mostly in male mutants. Here, we assessed the autistic-relevant behavioral phenotypes of Cdkl5-KO mice during the first three post-natal weeks and in adulthood. Males and females were tested, the latter including both heterozygous and homozygous mutants. Cdkl5 mutant pups showed qualitative and quantitative alterations in ultrasonic communication, detected first at 2 weeks of age and confirmed later in adulthood. Increased levels of anxiety-like behaviors were observed in mutants at 3 weeks and in adulthood, when stereotypies, reduced social interaction and memory deficits were also observed. These behavioral effects of the mutation were evident in both sexes, being more marked and varied in homozygous than heterozygous females. These findings provide novel evidence for the autistic-relevant behavioral profile of the Cdkl5 mouse model, thus supporting its use in future preclinical studies investigating CDD pathology and autism spectrum disorders.

Emotional vocalizations alter behaviors and neurochemical release into the amygdala

The basolateral amygdala (BLA), a brain center of emotional expression, contributes to acoustic communication by first interpreting the meaning of social sounds in the context of the listener's internal state, then organizing the appropriate behavioral responses. We propose that modulatory neurochemicals such as acetylcholine (ACh) and dopamine (DA) provide internal-state signals to the BLA while an animal listens to social vocalizations. We tested this in a vocal playback experiment utilizing highly affective vocal sequences associated with either mating or restraint, then sampled and analyzed fluids within the BLA for a broad range of neurochemicals and observed behavioral responses of adult male and female mice. In male mice, playback of restraint vocalizations increased ACh release and usually decreased DA release, while playback of mating sequences evoked the opposite neurochemical release patterns. In non-estrus female mice, patterns of ACh and DA release with mating playback were similar to males. Estrus females, however, showed increased ACh, associated with vigilance, as well as increased DA, associated with reward-seeking. Experimental groups that showed increased ACh release also showed the largest increases in an aversive behavior. These neurochemical release patterns and several behavioral responses depended on a single prior experience with the mating and restraint behaviors. Our results support a model in which ACh and DA provide contextual information to sound analyzing BLA neurons that modulate their output to downstream brain regions controlling behavioral responses to social vocalizations.

Variation in responses to conspecific and heterospecific advertisement vocalizations in sympatric grasshopper mice (Onychomys)

Advertisement vocalizations that function in mate acquisition and resource defense within species may also mediate behavioral interactions among species. While olfactory signals play an important role in mate choice and territoriality in rodents, less is known about the function of acoustic signals in influencing interspecific interactions. In this study, we used playback experiments in the laboratory to assess the function of long-distance vocalizations within and among three sympatric species of grasshopper mice. We found that, within each species, individuals of both sexes varied widely in spontaneous vocal behavior and response to playback. The largest species (Onychomys leucogaster) was most responsive to conspecifics, but smaller O. arenicola and O. torridus exhibited no clear pattern in their vocal behavior and were even responsive to the white noise controls. Our results indicate that grasshopper mice are broadly responsive to a range of sounds that resemble calls and that long-distance vocalizations function primarily as signals that facilitate localization for subsequent close-distance assessment by both sexes in various social contexts. Variation in vocal responses among species may depend on competitive dominance, degree of interaction, acoustic similarity, or behavioral changes resulting from captivity. Replicating playback experiments in the field will help validate whether the observed variation in the laboratory reflects ecologically relevant patterns in nature.

Rodent tests of depression and anxiety: Construct validity and translational relevance

Behavioral testing constitutes the primary method to measure the emotional states of nonhuman animals in preclinical research. Emerging as the characteristic tool of the behaviorist school of psychology, behavioral testing of animals, particularly rodents, is employed to understand the complex cognitive and affective symptoms of neuropsychiatric disorders. Following the symptom-based diagnosis model of the DSM, rodent models and tests of depression and anxiety focus on behavioral patterns that resemble the superficial symptoms of these disorders. While these practices provided researchers with a platform to screen novel antidepressant and anxiolytic drug candidates, their construct validity-involving relevant underlying mechanisms-has been questioned. In this review, we present the laboratory procedures used to assess depressive- and anxiety-like behaviors in rats and mice. These include constructs that rely on stress-triggered responses, such as behavioral despair, and those that emerge with nonaversive training, such as cognitive bias. We describe the specific behavioral tests that are used to assess these constructs and discuss the criticisms on their theoretical background. We review specific concerns about the construct validity and translational relevance of individual behavioral tests, outline the limitations of the traditional, symptom-based interpretation, and introduce novel, ethologically relevant frameworks that emphasize simple behavioral patterns. Finally, we explore behavioral monitoring and morphological analysis methods that can be integrated into behavioral testing and discuss how they can enhance the construct validity of these tests.

The Mouse Inferior Colliculus Responds Preferentially to Non-Ultrasonic Vocalizations

The inferior colliculus (IC), the midbrain auditory integration center, analyzes information about social vocalizations and provides substrates for higher level processing of vocal signals. We used multichannel recordings to characterize and localize responses to social vocalizations and synthetic stimuli within the IC of female and male mice, both urethane anesthetized and unanesthetized. We compared responses to ultrasonic vocalizations (USVs) with other vocalizations in the mouse repertoire and related vocal responses to frequency tuning, IC subdivisions, and sex. Responses to lower frequency, broadband social vocalizations were widespread in IC, well represented throughout the tonotopic axis, across subdivisions, and in both sexes. Responses to USVs were much more limited. Although we observed some differences in tonal and vocal responses by sex and subdivision, representations of vocal responses by sex and subdivision were largely the same. For most units, responses to vocal signals occurred only when frequency response areas overlapped with spectra of the vocal signals. Since tuning to frequencies contained within the highest frequency USVs is limited (<15% of IC units), responses to these vocalizations are correspondingly limited (<5% of sound-responsive units). These results highlight a paradox of USV processing in some rodents: although USVs are the most abundant social vocalization, their representation and the representation of corresponding frequencies are less than lower frequency social vocalizations. We interpret this paradox in light of observations suggesting that USVs with lower frequency elements (<50 kHz) are associated with increased emotional intensity and engage a larger population of neurons in the mouse auditory system.

The Mouse Inferior Colliculus Responds Preferentially to Non-Ultrasonic Vocalizations

The inferior colliculus (IC), the midbrain auditory integration center, analyzes information about social vocalizations and provides substrates for higher level processing of vocal signals. We used multi-channel recordings to characterize and localize responses to social vocalizations and synthetic stimuli within the IC of female and male mice, both urethane-anesthetized and unanesthetized. We compared responses to ultrasonic vocalizations (USVs) with other vocalizations in the mouse repertoire and related vocal responses to frequency tuning, IC subdivisions, and sex. Responses to lower frequency, broadband social vocalizations were widespread in IC, well represented throughout the tonotopic axis, across subdivisions, and in both sexes. Responses to USVs were much more limited. Although we observed some differences in tonal and vocal responses by sex and subdivision, representations of vocal responses by sex and subdivision were largely the same. For most units, responses to vocal signals occurred only when frequency response areas overlapped with spectra of the vocal signals. Since tuning to frequencies contained within the highest frequency USVs is limited (< 15% of IC units), responses to these vocalizations are correspondingly limited (< 5% of sound-responsive units). These results highlight a paradox of USV processing in some rodents: although USVs are the most abundant social vocalization, their representation and the representation of corresponding frequencies is less than lower frequency social vocalizations. We interpret this paradox in light of observations suggesting that USVs with lower frequency elements (<50 kHz) are associated with increased emotional intensity and engage a larger population of neurons in the mouse auditory system.

SIGNIFICANCE STATEMENT

The inferior colliculus (IC) integrates multiple inputs to analyze information about social vocalizations. In mice, we show that the most common type of social vocalization, the ultrasonic vocalization or USV, was poorly represented in IC compared to lower frequency vocalizations. For most neurons, responses to vocal signals occurred only when frequency response areas overlapped with vocalization spectra. These results highlight a paradox of USV processing in some rodent auditory systems: although USVs are the most abundant social vocalization, their representation and representation of corresponding frequencies is less than lower frequency social vocalizations. These results suggest that USVs with lower frequency elements (<50 kHz)-associated with increased emotional intensity-will engage a larger population of neurons in the mouse auditory system.

Listening to your partner: serotonin increases male responsiveness to female vocal signals in mice

The context surrounding vocal communication can have a strong influence on how vocal signals are perceived. The serotonergic system is well-positioned for modulating the perception of communication signals according to context, because serotonergic neurons are responsive to social context, influence social behavior, and innervate auditory regions. Animals like lab mice can be excellent models for exploring how serotonin affects the primary neural systems involved in vocal perception, including within central auditory regions like the inferior colliculus (IC). Within the IC, serotonergic activity reflects not only the presence of a conspecific, but also the valence of a given social interaction. To assess whether serotonin can influence the perception of vocal signals in male mice, we manipulated serotonin systemically with an injection of its precursor 5-HTP, and locally in the IC with an infusion of fenfluramine, a serotonin reuptake blocker. Mice then participated in a behavioral assay in which males suppress their ultrasonic vocalizations (USVs) in response to the playback of female broadband vocalizations (BBVs), used in defensive aggression by females when interacting with males. Both 5-HTP and fenfluramine increased the suppression of USVs during BBV playback relative to controls. 5-HTP additionally decreased the baseline production of a specific type of USV and male investigation, but neither drug treatment strongly affected male digging or grooming. These findings show that serotonin modifies behavioral responses to vocal signals in mice, in part by acting in auditory brain regions, and suggest that mouse vocal behavior can serve as a useful model for exploring the mechanisms of context in human communication.

Predictive Mouse Ultrasonic Vocalization Sequences: Uncovering Behavioral Significance, Auditory Cortex Neuronal Preferences, and Social-Experience-Driven Plasticity

Mouse ultrasonic vocalizations (USVs) contain predictable sequential structures like bird songs and speech. Neural representation of USVs in the mouse primary auditory cortex (Au1) and its plasticity with experience has been largely studied with single-syllables or dyads, without using the predictability in USV sequences. Studies using playback of USV sequences have used randomly selected sequences from numerous possibilities. The current study uses mutual information to obtain context-specific natural sequences (NSeqs) of USV syllables capturing the observed predictability in male USVs in different contexts of social interaction with females. Behavioral and physiological significance of NSeqs over random sequences (RSeqs) lacking predictability were examined. Female mice, never having the social experience of being exposed to males, showed higher selectivity for NSeqs behaviorally and at cellular levels probed by expression of immediate early gene c-fos in Au1. The Au1 supragranular single units also showed higher selectivity to NSeqs over RSeqs. Social-experience-driven plasticity in encoding NSeqs and RSeqs in adult females was probed by examining neural selectivities to the same sequences before and after the above social experience. Single units showed enhanced selectivity for NSeqs over RSeqs after the social experience. Further, using two-photon Ca2+ imaging, we observed social experience-dependent changes in the selectivity of sequences of excitatory and somatostatin-positive inhibitory neurons but not parvalbumin-positive inhibitory neurons of Au1. Using optogenetics, somatostatin-positive neurons were identified as a possible mediator of the observed social-experience-driven plasticity. Our study uncovers the importance of predictive sequences and introduces mouse USVs as a promising model to study context-dependent speech like communications.SIGNIFICANCE STATEMENT Humans need to detect patterns in the sensory world. For instance, speech is meaningful sequences of acoustic tokens easily differentiated from random ordered tokens. The structure derives from the predictability of the tokens. Similarly, mouse vocalization sequences have predictability and undergo context-dependent modulation. Our work investigated whether mice differentiate such informative predictable sequences (NSeqs) of communicative significance from RSeqs at the behavioral, molecular, and neuronal levels. Following a social experience in which NSeqs occur as a crucial component, mouse auditory cortical neurons become more sensitive to differences between NSeqs and RSeqs, although preference for individual tokens is unchanged. Thus, speech-like communication and its dysfunction may be studied in circuit, cellular, and molecular levels in mice.

Early-life stress affects Mongolian gerbil interactions with conspecific vocalizations in a sex-specific manner

During development, early-life stress (ELS) impairs cognition, learning, and emotional regulation, in part by disrupting neural circuitry in regions underlying these higher-order functions. In addition, our recent work indicates that ELS also alters simple sensory perception: ELS impaired auditory perception and neural encoding of short gaps in sounds, which are essential for vocal communication. The combination of higher-order and basic sensory disruption suggests that ELS is likely to affect both the perception and interpretation of communication signals. We tested this hypothesis by measuring behavioral responses to conspecific vocalizations (those emitted by other gerbils) in ELS and untreated Mongolian gerbils. Because stress effects often differ by sex, we separately examined females and males. To induce ELS, pups were intermittently maternally separated and restrained from post-natal days (P) 9-24, a time window when the auditory cortex is most sensitive to external disruption. We measured the approach responses of juvenile (P31-32) gerbils to two types of conspecific vocalizations: an alarm call, which is emitted to alert other gerbils of a potential threat, and the prosocial contact call, which is emitted near familiar gerbils, especially after separation. Control males, Control females, and ELS females approached a speaker emitting pre-recorded alarm calls, while ELS males avoided this source, suggesting that ELS affects the response to alarm calls in male gerbils. During playback of the pre-recorded contact call, Control females and ELS males avoided the sound source, while Control males neither approached nor avoided, and ELS females approached the sound. These differences cannot be accounted for by changes in locomotion or baseline arousal. However, ELS gerbils slept more during playback, suggesting that ELS may reduce arousal during vocalization playback. Further, male gerbils made more errors than females on a measure of working memory, but the sex difference of cognition in this context may stem from novelty aversion rather than impaired memory. These data indicate that ELS influences behavioral responses to ethologically relevant communication sounds in a sex-specific manner, and are among the first to demonstrate an altered response to auditory stimuli following ELS. Such changes may arise from differences in auditory perception, cognition, or a combination of factors, and suggest that ELS may affect auditory communication in human adolescents.

Playback of broadband vocalizations of female mice suppresses male ultrasonic calls

Although male vocalizations during opposite- sex interaction have been heavily studied as sexually selected signals, the understanding of the roles of female vocal signals produced in this context is more limited. During intersexual interactions between mice, males produce a majority of ultrasonic vocalizations (USVs), while females produce a majority of human-audible squeaks, also called broadband vocalizations (BBVs). BBVs may be produced in conjunction with defensive aggression, making it difficult to assess whether males respond to BBVs themselves. To assess the direct effect of BBVs on male behavior, we used a split-cage paradigm in which high rates of male USVs were elicited by female presence on the other side of a barrier, but which precluded extensive male-female contact and the spontaneous production of BBVs. In this paradigm, playback of female BBVs decreased USV production, which recovered after the playback period. Trials in which female vocalizations were prevented by the use of female bedding alone or of anesthetized females as stimuli also showed a decrease in response to BBV playback. No non-vocal behaviors declined during playback, although digging behavior increased. Similar to BBVs, WNs also robustly suppressed USV production, albeit to a significantly larger extent. USVs suppression had two distinct temporal components. When grouped in 5-second bins, USVs interleaved with bursts of stimulus BBVs. USV suppression also adapted to BBV playback on the order of minutes. Adaptation occurred more rapidly in males that were housed individually as opposed to socially for a week prior to testing, suggesting that the adaptation trajectory is sensitive to social experience. These findings suggest the possibility that vocal interaction between male and female mice, with males suppressing USVs in response to BBVs, may influence the dynamics of communicative behavior.

Beyond the three-chamber test: toward a multimodal and objective assessment of social behavior in rodents

MAIN: In recent years, substantial advances in social neuroscience have been realized, including the generation of numerous rodent models of autism spectrum disorder. Still, it can be argued that those methods currently being used to analyze animal social behavior create a bottleneck that significantly slows down progress in this field. Indeed, the bulk of research still relies on a small number of simple behavioral paradigms, the results of which are assessed without considering behavioral dynamics. Moreover, only few variables are examined in each paradigm, thus overlooking a significant portion of the complexity that characterizes social interaction between two conspecifics, subsequently hindering our understanding of the neural mechanisms governing different aspects of social behavior. We further demonstrate these constraints by discussing the most commonly used paradigm for assessing rodent social behavior, the three-chamber test. We also point to the fact that although emotions greatly influence human social behavior, we lack reliable means for assessing the emotional state of animals during social tasks. As such, we also discuss current evidence supporting the existence of pro-social emotions and emotional cognition in animal models. We further suggest that adequate social behavior analysis requires a novel multimodal approach that employs automated and simultaneous measurements of multiple behavioral and physiological variables at high temporal resolution in socially interacting animals. We accordingly describe several computerized systems and computational tools for acquiring and analyzing such measurements. Finally, we address several behavioral and physiological variables that can be used to assess socio-emotional states in animal models and thus elucidate intricacies of social behavior so as to attain deeper insight into the brain mechanisms that mediate such behaviors. CONCLUSIONS: In summary, we suggest that combining automated multimodal measurements with machine-learning algorithms will help define socio-emotional states and determine their dynamics during various types of social tasks, thus enabling a more thorough understanding of the complexity of social behavior.

Hearing, touching, and multisensory integration during mate choice

Mate choice is a potent generator of diversity and a fundamental pillar for sexual selection and evolution. Mate choice is a multistage affair, where complex sensory information and elaborate actions are used to identify, scrutinize, and evaluate potential mating partners. While widely accepted that communication during mate assessment relies on multimodal cues, most studies investigating the mechanisms controlling this fundamental behavior have restricted their focus to the dominant sensory modality used by the species under examination, such as vision in humans and smell in rodents. However, despite their undeniable importance for the initial recognition, attraction, and approach towards a potential mate, other modalities gain relevance as the interaction progresses, amongst which are touch and audition. In this review, we will: (1) focus on recent findings of how touch and audition can contribute to the evaluation and choice of mating partners, and (2) outline our current knowledge regarding the neuronal circuits processing touch and audition (amongst others) in the context of mate choice and ask (3) how these neural circuits are connected to areas that have been studied in the light of multisensory integration.

Activation of locus coeruleus to rostromedial tegmental nucleus (RMTg) noradrenergic pathway blunts binge-like ethanol drinking and induces aversive responses in mice

There is strong evidence that ethanol entails aversive effects that can act as a deterrent to overconsumption. We have found that in doses that support the development of a conditioned taste aversion ethanol increases the activity of tyrosine hydroxylase (TH) positive neurons in the locus coeruleus (LC), a primary source of norepinephrine (NE). Using cre-inducible AAV8-ChR2 viruses in TH-ires-cre mice we found that the LC provides NE projections that innervate the rostromedial tegmental nucleus (RMTg), a brain region that has been implicated in the aversive properties of drugs. Because the neurocircuitry underlying the aversive effects of ethanol is poorly understood, we characterized the role of the LC to RMTg circuit in modulating aversive unconditioned responses and binge-like ethanol intake. Here, both male and female TH-ires-cre mice were cannulated in the RMTg and injected in the LC with rAVV viruses that encode for a Gq-expressing designer receptor exclusively activated by designer drugs (DREADDs) virus, or its control virus, to directly control the activity of NE neurons. A Latin Square paradigm was used to analyze both 20% ethanol and 3% sucrose consumption using the "drinking-in-the-dark" (DID) paradigm. Chemogenetic activation of the LC to RMTg pathway significantly blunted the binge-ethanol drinking, with no effect on the sucrose consumption, increased the emission of mid-frequency vocalizations and induced malaise-like behaviors in mice. The present findings indicate an important involvement of the LC to RMTg pathway in reducing ethanol consumption, and characterize unconditioned aversive reactions induced by activation of this noradrenergic pathway.

Inter-individual variability in habituation of anxiety-related responses within three mouse inbred strains

Inter-individual variability in behavioral and physiological response has become a well-established phenomenon in animal models of anxiety and other disorders. Such variability is even demonstrated within mouse inbred strains. A recent study showed that adaptive and non-adaptive anxiety phenotypes (measured as habituation and/or sensitization of anxiety responses) may differ within cohorts of 129 mice. This variability was expressed across both anxiety- and activity-related behavioral dimensions. These findings were based however on re-analysis of previously published data. The present study therefore aimed to empirically validate these findings in 129 mice. In addition, we assessed such inter-individuality in two other strains: BALB/c and C57BL/6. Males of three mouse inbred strains (BALB/c, C57BL/6 and 129S2) were behaviorally characterized through repeated exposure to a mild aversive stimulus (modified Hole Board, 4 consecutive trials). Behavioral observations were supplemented with assessment of circulating corticosterone levels. Clustering the individual response trajectories of behavioral and endocrine responses yielded two multidimensional response types of different adaptive value. Interestingly, these response types were displayed by individuals of all three strains. The response types differed significantly on anxiety and activity related behavioral dimensions but not on corticosterone concentrations. This study empirically confirms that adaptive capacities may differ within 129 cohorts. In addition, it extends this inter-individual variability in behavioral profiles to BALB/c and C57BL/6. Whether these two sub-types constitute differential anxiety phenotypes may differ per strain and requires further study.

Social Experience Interacts with Serotonin to Affect Functional Connectivity in the Social Behavior Network following Playback of Social Vocalizations in Mice

Past social experience affects the circuitry responsible for producing and interpreting current behaviors. The social behavior network (SBN) is a candidate neural ensemble to investigate the consequences of early-life social isolation. The SBN interprets and produces social behaviors, such as vocalizations, through coordinated patterns of activity (functional connectivity) between its multiple nuclei. However, the SBN is relatively unexplored with respect to murine vocal processing. The serotonergic system is sensitive to past experience and innervates many nodes of the SBN; therefore, we tested whether serotonin signaling interacts with social experience to affect patterns of immediate early gene (IEG; cFos) induction in the male SBN following playback of social vocalizations. Male mice were separated into either social housing of three mice per cage or into isolated housing at 18-24 d postnatal. After 28-30 d in housing treatment, mice were parsed into one of three drug treatment groups: control, fenfluramine (FEN; increases available serotonin), or pCPA (depletes available serotonin) and exposed to a 60-min playback of female broadband vocalizations (BBVs). FEN generally increased the number of cFos-immunoreactive (-ir) neurons within the SBN, but effects were more pronounced in socially isolated mice. Despite a generalized increase in cFos immunoreactivity, isolated mice had reduced functional connectivity, clustering, and modularity compared with socially reared mice. These results are analogous to observations of functional dysconnectivity in persons with psychopathologies and suggests that early-life social isolation modulates serotonergic regulation of social networks.