Bipolar-associated miR-499-5p controls neuroplasticity by downregulating the Cav1.2 subunit CACNB2.

Bipolar disorder (BD) is a chronic mood disorder characterized by manic and depressive episodes. Dysregulation of neuroplasticity and calcium homeostasis are frequently observed in BD patients, but the underlying molecular mechanisms are largely unknown. Here, we show that miR-499-5p regulates dendritogenesis and cognitive function by downregulating the BD risk gene CACNB2. miR-499-5p expression is increased in peripheral blood of BD patients, as well as in the hippocampus of rats which underwent juvenile social isolation. In rat hippocampal neurons, miR-499-5p impairs dendritogenesis and reduces surface expression and activity of the L-type calcium channel Cav1.2. We further identified CACNB2, which encodes a regulatory ß-subunit of Cav1.2, as a direct functional target of miR-499-5p in neurons. miR-499-5p overexpression in the hippocampus in vivo induces short-term memory impairments selectively in rats haploinsufficient for the Cav1.2 pore forming subunit Cacna1c. In humans, miR-499-5p expression is negatively associated with gray matter volumes of the left superior temporal gyrus, a region implicated in auditory and emotional processing. We propose that stress-induced miR-499-5p overexpression contributes to dendritic impairments, deregulated calcium homeostasis, and neurocognitive dysfunction in BD.

Calcium Handling Remodeling Underlies Impaired Sympathetic Stress Response in Ventricular Myocardium from Cacna1c Haploinsufficient Rats.

CACNA1C encodes the pore-forming α1C subunit of the L-type Ca2+ channel, Cav1.2. Mutations and polymorphisms of the gene are associated with neuropsychiatric and cardiac disease. Haploinsufficient Cacna1c+/- rats represent a recently developed model with a behavioral phenotype, but its cardiac phenotype is unknown. Here, we unraveled the cardiac phenotype of Cacna1c+/- rats with a main focus on cellular Ca2+ handling mechanisms. Under basal conditions, isolated ventricular Cacna1c+/- myocytes exhibited unaltered L-type Ca2+ current, Ca2+ transients (CaTs), sarcoplasmic reticulum (SR) Ca2+ load, fractional release, and sarcomere shortenings. However, immunoblotting of left ventricular (LV) tissue revealed reduced expression of Cav1.2, increased expression of SERCA2a and NCX, and augmented phosphorylation of RyR2 (at S2808) in Cacna1c+/- rats. The ß-adrenergic agonist isoprenaline increased amplitude and accelerated decay of CaTs and sarcomere shortenings in both Cacna1c+/- and WT myocytes. However, the isoprenaline effect on CaT amplitude and fractional shortening (but not CaT decay) was impaired in Cacna1c+/- myocytes exhibiting both reduced potency and efficacy. Moreover, sarcolemmal Ca2+ influx and fractional SR Ca2+ release after treatment with isoprenaline were smaller in Cacna1c+/- than in WT myocytes. In Langendorff-perfused hearts, the isoprenaline-induced increase in RyR2 phosphorylation at S2808 and S2814 was attenuated in Cacna1c+/- compared to WT hearts. Despite unaltered CaTs and sarcomere shortenings, Cacna1c+/- myocytes display remodeling of Ca2+ handling proteins under basal conditions. Mimicking sympathetic stress with isoprenaline unmasks an impaired ability to stimulate Ca2+ influx, SR Ca2+ release, and CaTs caused, in part, by reduced phosphorylation reserve of RyR2 in Cacna1c+/- cardiomyocytes.

Long-term environmental impact on object recognition, spatial memory and reversal learning capabilities in Cacna1c-haploinsufficient rats.

Genetic and environmental influences are thought to interact in their contribution to the etiology of major neuropsychiatric disorders. One of the best replicated findings obtained in genome-wide association studies are genetic variants in the CACNA1C gene. Here, we used our constitutive heterozygous Cacna1c rat model in combination with a 4-week exposure to either post-weaning social isolation, standard housing or social and physical environmental enrichment during the critical juvenile developmental period to observe their long-term interactive effects with Cacna1c haploinsufficiency. Our study provides evidence for a gene × environment interaction, i.e. an interplay between Cacna1c haploinsufficiency and environment during juvenile development, on object recognition, spatial memory and reversal learning capabilities. Social and physical enrichment had a positive influence on Cacna1c+/- rats and Cacna1c+/+ littermate controls on spatial and reversal learning, while post-weaning social isolation negatively affected novel object recognition in both genotypes. Despite intact spatial learning and re-learning abilities in all groups, slight but consistent deficits were evident in Cacna1c+/- rats previously housed under standard conditions particularly during reversal learning but not Cacna1c+/- rats previously exposed to social and physical enrichment. Together, this supports the notion that Cacna1c interacts with the environment to shape disease vulnerability and associated alterations in cognitive functioning.

Sex differences in the acoustic features of social play-induced 50-kHz ultrasonic vocalizations: A detailed spectrographic analysis in wild-type Sprague-Dawley and Cacna1c haploinsufficient rats.

Sexual dimorphisms are widespread in the animal kingdom. At the behavioral level, there is evidence for sex differences in social play behavior. In rats, males typically engage more in rough-and-tumble play than females. One prominent component of the rough-and-tumble play repertoire in rats is the emission of 50-kHz ultrasonic vocalizations (USV). Such 50-kHz USV reflect the rewarding nature of play and serve as socioaffective signals. Here, we provide evidence for sexual dimorphisms within rough-and-tumble play-induced 50-kHz USV in juvenile rats. Specifically, females displayed reduced 50-kHz USV emission during playful interactions. This reduction was associated with changes in 50-kHz USV emission rates and subtype profiles during specific rough-and-tumble components, i.e., pinning, wrestling, and chasing, as well as differences in acoustic parameters. Interestingly, sex differences were modulated by Cacna1c, a gene strongly implicated in major neuropsychiatric disorders, often characterized by prominent sex biases, most notably autism. Specifically, Cacna1c haploinsufficiency affected the emission of 50-kHz USV during rough-and-tumble play in female rats and we provide evidence supporting the notion that such effects of Cacna1c haploinsufficiency are driven by male-typical features of 50-kHz USV emission. This is in line with the hypermasculinized social play repertoire previously observed in juvenile Cacna1c haploinsufficient females.

Fear Extinction and Predictive Trait-Like Inter-Individual Differences in Rats Lacking the Serotonin Transporter.

Anxiety disorders are associated with a failure to sufficiently extinguish fear memories. The serotonergic system (5-hydroxytryptamine, 5-HT) with the 5-HT transporter (5-HTT, SERT) is strongly implicated in the regulation of anxiety and fear. In the present study, we examined the effects of SERT deficiency on fear extinction in a differential fear conditioning paradigm in male and female rats. Fear-related behavior displayed during acquisition, extinction, and recovery, was measured through quantification of immobility and alarm 22-kHz ultrasonic vocalizations (USV). Trait-like inter-individual differences in novelty-seeking, anxiety-related behavior, habituation learning, cognitive performance, and pain sensitivity were examined for their predictive value in forecasting fear extinction. Our results show that SERT deficiency strongly affected the emission of 22-kHz USV during differential fear conditioning. During acquisition, extinction, and recovery, SERT deficiency consistently led to a reduction in 22-kHz USV emission. While SERT deficiency did not affect immobility during acquisition, genotype differences started to emerge during extinction, and during recovery rats lacking SERT showed higher levels of immobility than wildtype littermate controls. Recovery was reflected in increased levels of immobility but not 22-kHz USV emission. Prominent sex differences were evident. Among several measures for trait-like inter-individual differences, anxiety-related behavior had the best predictive quality.

Sex-specific effects of Cacna1c haploinsufficiency on object recognition, spatial memory, and reversal learning capabilities in rats.

The CACNA1C gene is strongly implicated in the etiology of multiple major neuropsychiatric disorders, such as bipolar disorder, major depression, and schizophrenia, with cognitive deficits being a common feature. It is unclear, however, by which mechanisms CACNA1C variants advance the risk of developing neuropsychiatric disorders. This study set out to investigate cognitive functioning in a newly developed genetic Cacna1c rat model. Specifically, spatial and reversal learning, as well as object recognition memory were assessed in heterozygous Cacna1c+/- rats and compared to wildtype Cacna1c+/+ littermate controls in both sexes. Our results show that both Cacna1c+/+ and Cacna1c+/- animals were able to learn the rewarded arm configuration of a radial maze over the course of seven days. Both groups also showed reversal learning patterns indicative of intact abilities. In females, genotype differences were evident in the initial spatial learning phase, with Cacna1c+/- females showing hypo-activity and fewer mixed errors. In males, a difference was found during probe trials for both learning phases, with Cacna1c+/- rats displaying better distinction between previously baited and non-baited arms; and regarding cognitive flexibility in favor of the Cacna1c+/+ animals. All experimental groups proved to be sensitive to reward magnitude and fully able to distinguish between novel and familiar objects in the novel object recognition task. Taken together, these results indicate that Cacna1c haploinsufficiency has a minor, but positive impact on (spatial) memory functions in rats.

Isolation-induced ultrasonic vocalizations in pups: A comparison between Long-Evans, Sprague-Dawley, and Wistar rats.

Rat pup ultrasonic vocalizations (USV) are usually studied in outbred rats belonging to either Long-Evans, Sprague-Dawley, or Wistar stocks, but these were not compared so far. We therefore performed a stock comparison and analyzed USV of male pups (postnatal day 11) belonging to these three stocks. Pups of all three stocks showed substantial isolation-induced USV, but differed in various call features, like call numbers, peak frequency, and frequency modulation. Also, three different call types were identified by means of a quantitative approach based on peak frequency and frequency modulation, and it was found that their proportions differed between stocks. These results are discussed with respect to functional aspects of pup USV.

Aberrant cognitive phenotypes and altered hippocampal BDNF expression related to epigenetic modifications in mice lacking the post-synaptic scaffolding protein SHANK1: Implications for autism spectrum disorder.

Autism spectrum disorder (ASD) is a class of neurodevelopmental disorders characterized by persistent deficits in social communication/interaction, together with restricted/repetitive patterns of behavior. ASD is among the most heritable neuropsychiatric conditions, and while available evidence points to a complex set of genetic factors, the SHANK gene family has emerged as one of the most promising candidates. Here, we assessed ASD-related phenotypes with particular emphasis on social behavior and cognition in Shank1 mouse mutants in comparison to heterozygous and wildtype littermate controls across development in both sexes. While social approach behavior was evident in all experimental conditions and social recognition was only mildly affected by genotype, Shank1-/- null mutant mice were severely impaired in object recognition memory. This effect was particularly prominent in juveniles, not due to impairments in object discrimination, and replicated in independent mouse cohorts. At the neurobiological level, object recognition deficits were paralleled by increased brain-derived neurotrophic factor (BDNF) protein expression in the hippocampus of Shank1-/- mice; yet BDNF levels did not differ under baseline conditions. We therefore investigated changes in the epigenetic regulation of hippocampal BDNF expression and detected an enrichment of histone H3 acetylation at the Bdnf promoter1 in Shank1-/- mice, consistent with increased learning-associated BDNF. Together, our findings indicate that Shank1 deletions lead to an aberrant cognitive phenotype characterized by severe impairments in object recognition memory and increased hippocampal BDNF levels, possibly due to epigenetic modifications. This result supports the link between ASD and intellectual disability, and suggests epigenetic regulation as a potential therapeutic target.

Phasic dopamine release in the nucleus accumbens in response to pro-social 50 kHz ultrasonic vocalizations in rats.

Rats emit ultrasonic vocalizations (USVs) that are thought to serve as situation-dependent affective signals and accomplish important communicative functions. In appetitive situations, rats produce 50 kHz USVs, whereas 22 kHz USVs occur in aversive situations. Reception of 50 kHz USVs induces social approach behavior, while 22 kHz USVs lead to freezing behavior. These opposite behavioral responses are paralleled by distinct brain activation patterns, with 50 kHz USVs, but not 22 kHz USVs, activating neurons in the nucleus accumbens (NAcc). The NAcc mediates appetitive behavior and is critically modulated by dopaminergic afferents that are known to encode the value of reward. Therefore, we hypothesized that 50 kHz USVs, but not 22 kHz USVs, elicit NAcc dopamine release. While recording dopamine signaling with fast-scan cyclic voltammetry, freely moving rats were exposed to playback of four acoustic stimuli via an ultrasonic speaker in random order: (1) 50 kHz USVs, (2) 22 kHz USVs, (3) time- and amplitude-matched white noise, and (4) background noise. Only presentation of 50 kHz USVs induced phasic dopamine release and elicited approach behavior toward the speaker. Both of these effects, neurochemical and behavioral, were most pronounced during initial playback, but then declined rapidly with subsequent presentations, indicating a close temporal relationship between the two measures. Moreover, the magnitudes of these effects during initial playback were significantly correlated. Collectively, our findings show that NAcc dopamine release encodes pro-social 50 kHz USVs, but not alarming 22 kHz USVs. Thus, our results support the hypothesis that these call types are processed in distinct neuroanatomical regions and establish a functional link between pro-social communicative signals and reward-related neurotransmission.

A new dopaminergic nigro-olfactory projection.

Parkinson disease (PD) is a neurodegenerative disorder characterized by massive loss of midbrain dopaminergic neurons. Whereas onset of motor impairments reflects a rather advanced stage of the disorder, hyposmia often marks the beginning of the disease. Little is known about the role of the nigro-striatal system in olfaction under physiological conditions and the anatomical basis of hyposmia in PD. Yet, the early occurrence of olfactory dysfunction implies that pathogens such as environmental toxins could incite the disease via the olfactory system. In the present study, we demonstrate a dopaminergic innervation from neurons in the substantia nigra to the olfactory bulb by axonal tracing studies. Injection of two dopaminergic neurotoxins-1-methyl-4-phenylpyridinium and 6-hydroxydopamine-into the olfactory bulb induced a decrease in the number of dopaminergic neurons in the substantia nigra. In turn, ablation of the nigral projection led to impaired olfactory perception. Hyposmia following dopaminergic deafferentation was reversed by treatment with the D1/D2/D3 dopamine receptor agonist rotigotine. Hence, we demonstrate for the first time the existence of a direct dopaminergic projection into the olfactory bulb and identify its origin in the substantia nigra in rats. These observations may provide a neuroanatomical basis for invasion of environmental toxins into the basal ganglia and for hyposmia as frequent symptom in PD.

Affective communication in rodents: serotonin and its modulating role in ultrasonic vocalizations.

Serotonin (5-hydroxytryptamine, 5-HT) is an important modulatory neurotransmitter and functions as a key neurodevelopmental signal in the mammalian brain. 5-HT plays a prominent role in regulating various types of psychological processes and functions, including mood and emotion, particularly anxiety, but also in regulating social behavior. Consequently, the 5-HT system is implicated in various neuropsychiatric disorders, such as anxiety disorders and depression or autism spectrum disorders (ASD), with selective 5-HT reuptake inhibitors being the frontline medication. Mice and rats perceive and emit ultrasonic vocalizations (USV). It is widely believed that the various distinct USV types reflect the animal's affective state, such as anxiety or pleasure. Furthermore, they serve communicative functions, for instance, as alarm calls or social contact calls. Manipulations targeting the 5-HT system alter affective ultrasonic communication in rodents throughout life, probably because of its important role in regulating anxiety and social behavior. Ample evidence indicates the involvement of the 5-HT system in modulating isolation-induced USV in pups. Later in life, the 5-HT system plays a strong modulatory role in the emission of aversive 22-kHz USV in rats. So far, little is known about the role of 5-HT in the production of interaction-induced USV in mice and appetitive 50-kHz USV in rats, although recent findings also suggest a modulatory effect of the 5-HT system. Assessment of rodent USV is a valuable method to investigate mood and emotion, and to enhance our understanding of, and develop novel pharmacological therapies for neuropsychiatric disorders, such as anxiety disorders and depression or ASD.

Behaviorally conditioned effects of psychoactive drugs in experimental animals: What we have learned from nearly a century of research and what remains to be learned.

Continuous treatment with drugs is a crucial requirement for managing various clinical conditions, including chronic pain and neuropsychiatric disorders such as depression or schizophrenia. Associative learning processes, i.e. Pavlovian conditioning, can play an important role for the effects of drugs and could open new avenues for optimizing patient treatment. In this narrative literature review, we summarize available data in experimental animals regarding the behaviorally conditioned effects of psychostimulants such as d-amphetamine and cocaine, the dopamine receptor agonist apomorphine, the dopamine receptor antagonist haloperidol, morphine and antidepressant drugs. In each section, the drug under discussion is briefly introduced, followed by a detailed examination of conditioning features, including doses and dosing regimens, characteristics of the conditioning process such as test environments or specific conditioned stimuli, testing and conditioned response characteristics, possible extinction or reconditioning or reversal training, neural mechanisms, and finally, the potential clinical relevance of the research area related to the drug. We focus on key outcomes, delve into methodical issues, identify gaps in current knowledge, and suggest future research directions.

Biperiden reverses the increase in 50-kHz ultrasonic vocalizations but not the increase in locomotor activity induced by cocaine.

Cocaine use disorder (CUD) is a worldwide public health problem, associated with severe psychosocial and economic impacts. Currently, no FDA-approved treatment is available for CUD. However, an emerging body of evidence from clinical and preclinical studies suggests that biperiden, an M1 muscarinic receptor antagonist, presents potential therapeutic use for CUD. These studies have suggested that biperiden may reduce the reinforcing effects of cocaine. It is well established that rodents emit 50-kHz ultrasonic vocalizations (USV) in response to natural rewards and stimulant drugs, including cocaine. Nonetheless, the effects of biperiden on the cocaine-induced increase of 50-kHz USV remains unknown. Here, we hypothesized that biperiden could antagonize the acute effects of cocaine administration on rat 50-kHz USV. To test this hypothesis, adult male Wistar rats were divided into four experimental groups: saline, 5 mg/kg biperiden, 10 mg/kg cocaine, and biperiden/cocaine (5 and 10 mg/kg, i.p., respectively). USV and locomotor activity were recorded in baseline and test sessions. As expected, cocaine administration significantly increased the number of 50-kHz USV. Biperiden administration effectively antagonized the increase in 50-kHz USV induced by cocaine. Cocaine administration also increased the emission of trill and mixed 50 kHz USV subtypes and this effect was antagonized by biperiden. Additionally, we showed that biperiden did not affect the cocaine-induced increase in locomotor activity, although biperiden administration per se increased locomotor activity. In conclusion, our findings indicate that administering biperiden acutely reduces the positive affective effects of cocaine, as demonstrated by its ability to inhibit the increase in 50-kHz USV.

Affective communication in rodents: ultrasonic vocalizations as a tool for research on emotion and motivation.

Mice and rats emit and perceive calls in the ultrasonic range, i.e., above the human hearing threshold of about 20 kHz: so-called ultrasonic vocalizations (USV). Juvenile and adult rats emit 22-kHz USV in aversive situations, such as predator exposure and fighting or during drug withdrawal, whereas 50-kHz USV occur in appetitive situations, such as rough-and-tumble play and mating or in response to drugs of abuse, e.g., amphetamine. Aversive 22-kHz USV and appetitive 50-kHz USV serve distinct communicative functions. Whereas 22-kHz USV induce freezing behavior in the receiver, 50-kHz USV lead to social approach behavior. These opposite behavioral responses are paralleled by distinct patterns of brain activation. Freezing behavior in response to 22-kHz USV is paralleled by increased neuronal activity in brain areas regulating fear and anxiety, such as the amygdala and periaqueductal gray, whereas social approach behavior elicited by 50-kHz USV is accompanied by reduced activity levels in the amygdala but enhanced activity in the nucleus accumbens, a brain area implicated in reward processing. These opposing behavioral responses, together with distinct patterns of brain activation, particularly the bidirectional tonic activation or deactivation of the amygdala elicited by 22-kHz and 50-kHz USV, respectively, concur with a wealth of behavioral and neuroimaging studies in humans involving emotionally salient stimuli, such as fearful and happy facial expressions. Affective ultrasonic communication therefore offers a translational tool for studying the neurobiology underlying socio-affective communication. This is particularly relevant for rodent models of neurodevelopmental disorders characterized by social and communication deficits, such as autism and schizophrenia.

Behavioral analysis in laboratory rats: Challenges and usefulness of 50-kHz ultrasonic vocalizations.

Many rodent species emit and detect vocalizations in the ultrasonic range. Rats use three classes of ultrasonic vocalizations depending on developmental stage, experience and the behavioral situation. Calls from one class emitted by juvenile and adult rats, the so-called 50-kHz calls, are typical for appetitive and social situations. This review provides a brief historical account on the introduction of 50-kHz calls in behavioral research followed by a survey of their scientific applications focusing on the last five years, where 50-kHz publications reached a climax. Then, specific methodological challenges will be addressed, like how to measure and report 50-kHz USV, the problem of assignment of acoustic signals to a specific sender in a social situation, and individual variability in call propensity. Finally, the intricacy of interpreting 50-kHz results will be discussed focusing on the most prevalent ones, namely as communicative signals and/or readouts of the sender's emotional status.

Paradoxical kinesia may no longer be a paradox waiting for 100 years to be unraveled.

Parkinson's disease (PD) is a progressive neurodegenerative disorder mainly characterized by bradykinesia and akinesia. Interestingly, these motor disabilities can depend on the patient emotional state. Disabled PD patients remain able to produce normal motor responses in the context of urgent or externally driven situations or even when exposed to appetitive cues such as music. To describe this phenomenon Souques coined the term "paradoxical kinesia" a century ago. Since then, the mechanisms underlying paradoxical kinesia are still unknown due to a paucity of valid animal models that replicate this phenomenon. To overcome this limitation, we established two animal models of paradoxical kinesia. Using these models, we investigated the neural mechanisms of paradoxical kinesia, with the results pointing to the inferior colliculus (IC) as a key structure. Intracollicular electrical deep brain stimulation, glutamatergic and GABAergic mechanisms may be involved in the elaboration of paradoxical kinesia. Since paradoxical kinesia might work by activation of some alternative pathway bypassing basal ganglia, we suggest the IC as a candidate to be part of this pathway.

Acute anxiogenic effects of escitalopram are associated with mild alterations in D-amphetamine-induced behavior and social approach evoked by playback of 50-kHz ultrasonic vocalizations in rats.

Rats communicate through auditory signals in the ultrasonic range, so-called ultrasonic vocalizations (USV). Short, high-frequency 50-kHz USV are associated with positive affective states and are emitted in appetitive situations, often rewarding social interactions, such as rough-and-tumble play and mating. Exaggerated levels of 50-kHz USV emission can be observed in response to psychostimulants, most notably d-amphetamine (AMPH). There is robust evidence suggesting that 50-kHz USV serve as affiliative signals and help to maintain or re-establish social proximity. A key neurotransmitter involved in behavioral regulation is serotonin (5-hydroxytryptamine, 5-HT). This includes both, the regulation of anxiety-related behavior and ultrasonic communication. Here, we show that acute treatment with the selective 5-HT reuptake inhibitor (SSRI) escitalopram (ESC) leads to increased anxiety-related behavior in the elevated plus maze and tested whether such acute anxiogenic effects of ESC result in alterations in ultrasonic communication in sender and/or receiver. To this aim, we conducted a dose-response study in male rats and assessed AMPH-induced hyperactivity and 50-kHz ultrasonic calling in the sender and social approach behavior evoked by playback of pro-social 50-kHz USV in the receiver. Acute ESC treatment affected both, sender and receiver. This was reflected in a lack of AMPH-induced changes in acoustic features of 50-kHz USV and absence of social exploratory behavior evoked by 50-kHz USV playback, respectively. Albeit the SSRI effects were relatively mild, this supports the notion that the 5-HT system is involved in the regulation of a key aspect of the social behavior repertoire of rodents, namely socio-affective communication through 50-kHz USV.

Wildtype peers rescue social play and 50-kHz ultrasonic vocalization deficits in juvenile female Cacna1c heterozygous rats.

Background: Healthy brain development depends on early social practices and experiences. The risk gene CACNA1C is implicated in numerous neuropsychiatric disorders, in which key characteristics include deficits in social functioning and communication. Recently, we reported sex-dependent impairments in social behavior and ultrasonic vocalizations (USV) in juvenile heterozygous Cacna1c+/- (HET) rats. Specifically, HET females displayed increases in rough-and-tumble play that eliminated the typically observed sex difference between male and female rats. Interestingly, female wild-type Cacna1c+/+ (WT) pairs also showed a similar increase in social play when housed with HET females, suggesting their behavior may be influenced by HET cage mates. This indicates that the genetic makeup of the social environment related to Cacna1c can influence social play, yet systematic studies are lacking. Methods: In the present study, we housed juvenile females in MIXED- or SAME-genotype cages and tested them in a social play paradigm with a same- and opposite-genotype partner. Results: The results show that the early social environment and the genotype of the play partner influence social play and 50-kHz USV emission. Experience with a WT play partner appears necessary for HET females to show comparable levels of play and 50-kHz USV emission. Same-genotype HET pairs played less and emitted fewer 50-kHz USV than same-genotype WT or opposite-genotype pairs; however, we found that the decrease in social play and 50-kHz USV in HET pairs can be rescued by playing with a WT partner. The effect was particularly prominent when the first play partner was WT, as we found it increased play and 50-kHz USV emission in all subsequent interactions with ensuing partners. Conclusion: These findings suggest that the genetic makeup related to the social environment and/or social peers influences social play in Cacna1c+/- haploinsufficient rats. Specifically, our results show that WT peers can rescue behavior and communication alterations in Cacna1c female rats. Our findings have important implications because they show that the genetic makeup of the social environment can divulge phenotypic changes in genetic rat models of neuropsychiatric disorders.

Testing social acoustic memory in rats: effects of stimulus configuration and long-term memory on the induction of social approach behavior by appetitive 50-kHz ultrasonic vocalizations.

Rats emit distinct types of ultrasonic vocalizations (USVs), which serve as situation-dependent affective signals. In appetitive situations, such as rough-and-tumble-play, high-frequency 50-kHz USVs occur, whereas low-frequency 22-kHz USVs can be observed in aversive situations, such as social defeat. USVs serve distinct communicative functions and induce call-specific behavioral responses in the receiver. While aversive 22-kHz USVs serve as alarm calls and induce behavioral inhibition, appetitive 50-kHz USVs have a pro-social communicative function and elicit social approach behavior, supporting the notion that they serve as social contact calls to (re)establish or maintain contact among conspecifics. The aim of the present study was to use the rat's ability to communicate in the ultrasonic range via high-frequency 50-kHz USVs in order to develop a test for social acoustic memory in rats with relevance for human verbal memory. Verbal learning and memory is among the seven cognitive domains identified as commonly deficient in human schizophrenia patients, but particularly difficult to model. We therefore tested whether the induction of social approach behavior by playback of appetitive 50-kHz USVs is dependent on (1) acoustic stimulus configuration and (2) social long-term memory, and whether (3) social long-term memory effects can be blocked by the administration of scopolamine, a muscarinic acetylcholine antagonist producing amnesia. Results show that social approach behavior in response to playback of natural 50-kHz USVs depends on acoustic stimulus configuration and occurs only when sound energy is concentrated to a critical frequency band in the ultrasonic range. Social approach behavior was detected during the first exposure to playback of 50-kHz USVs, whereas no such response was observed during the second exposure 1week later, indicating a stable memory trace. In contrast, when memory formation was blocked by i.p. administration of scopolamine (0.5mg/kg or 1.5mg/kg) immediately after the first exposure, rats displayed social approach behavior during the second exposure as well. Induction of social approach behavior in response to repeated playback of natural 50-kHz USVs may therefore provide a new and rather unique approach for testing social acoustic memory in rats with relevance to human verbal memory.

Juvenile stress potentiates aversive 22-kHz ultrasonic vocalizations and freezing during auditory fear conditioning in adult male rats.

Traumatic experiences that occur during adolescence can render individuals vulnerable to mood and anxiety disorders. A model in juvenile rats (age: 27-29 days) was developed previously to study the long-term effects of adolescent stress exposure on behaviour and physiology. This paradigm, termed juvenile stress, involves subjecting juvenile rats to different stressors on consecutive days over a 3-day period. Here, we investigated the effects of the juvenile stress paradigm on freezing behaviour and aversive 22-kHz ultrasonic vocalizations (USVs) during auditory fear conditioning in adult male rats (age: 68-90 days). We found that rats previously subjected to juvenile stress increased aversive 22-kHz USVs (total calls and time spent calling) compared with controls during fear-conditioning training. The acoustic USV parameters between control and juvenile stress rats were largely equivalent, including duration, peak frequency and amplitude. While rats did not differ in freezing behaviour during fear conditioning, juvenile stress rats exhibited greater cue-conditioned freezing upon testing 24 h later. Our results show that juvenile stress elicited different long-term changes in freezing and aversive USVs during fear conditioning. Furthermore, they highlight the importance of assessing USVs to detect experience-dependent differences between control and stress-exposed animals which are not detectable by measuring visible behaviour.