Effects of amphetamine on pro-social ultrasonic communication in juvenile rats: Implications for mania models

Emotional contagion in rodents: A comprehensive exploration of mechanisms and multimodal perspectives

Emotional contagion, a fundamental aspect of empathy, is an automatic and unconscious process in which individuals mimic and synchronize with the emotions of others. Extensively studied in rodents, this phenomenon is mediated through a range of sensory pathways, each contributing distinct insights. The olfactory pathway, marked by two types of pheromones modulated by oxytocin, plays a crucial role in transmitting emotional states. The auditory pathway, involving both squeaks and specific ultrasonic vocalizations, correlates with various emotional states and is essential for expression and communication in rodents. The visual pathway, though less relied upon, encompasses observational motions and facial expressions. The tactile pathway, a more recent focus, underscores the significance of physical interactions such as allogrooming and socio-affective touch in modulating emotional states. This comprehensive review not only highlights plausible neural mechanisms but also poses key questions for future research. It underscores the complexity of multimodal integration in emotional contagion, offering valuable insights for human psychology, neuroscience, animal welfare, and the burgeoning field of animal-human-AI interactions, thereby contributing to the development of a more empathetic intelligent future.

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.

Rodent models for mood disorders - understanding molecular changes by investigating social behavior

Mood disorders, including depressive and bipolar disorders, are the group of psychiatric disorders with the highest prevalence and disease burden. However, their pathophysiology remains poorly understood. Animal models are an extremely useful tool for the investigation of molecular mechanisms underlying these disorders. For psychiatric symptom assessment in animals, a meaningful behavioral phenotype is needed. Social behaviors constitute naturally occurring complex behaviors in rodents and can therefore serve as such a phenotype, contributing to insights into disorder related molecular changes. In this narrative review, we give a fundamental overview of social behaviors in laboratory rodents, as well as their underlying neuronal mechanisms and their assessment. Relevant behavioral and molecular changes in models for mood disorders are presented and an outlook on promising future directions is given.

Contingent Social Interaction Does Not Prevent Habituation towards Playback of Pro-Social 50-kHz Calls: Behavioral Responses and Brain Activation Patterns

Rats, which are highly social animals, are known to communicate using ultrasonic vocalizations (USV) in different frequency ranges. Calls around 50 kHz are related to positive affective states and promote social interactions. Our previous work has shown that the playback of natural 50-kHz USV leads to a strong social approach response toward the sound source, which is related to activation in the nucleus accumbens. In male Wistar rats, the behavioral response habituates, that is, becomes weaker or is even absent, when such playback is repeated several days later, an outcome found to be memory-dependent. Here, we asked whether such habituation is due to the lack of a contingent social consequence after playback in the initial test and whether activation of the nucleus accumbens, as measured by c-fos immunohistochemistry, can still be observed in a retest. To this end, groups of young male Wistar rats underwent an initial 50-kHz USV playback test, immediately after which they were either (1) kept temporarily alone, (2) exposed to a same-sex juvenile, or (3) to their own housing group. One week later, they underwent a retest with playback; this time not followed by social consequences but by brain removal for c-fos immunohistochemistry. Consistent with previous reports, behavioral changes evoked by the initial exposure to 50-kHz USV playback included a strong approach response. In the retest, no such response was found, irrespective of whether rats had experienced a contingent social consequence after the initial test or not. At the neural level, no substantial c-fos activation was found in the nucleus accumbens, but unexpected strong activation was detected in the anterior cingulate cortex, with some of it in GABAergic cells. The c-fos patterns did not differ between groups but cell numbers were individually correlated with behavior, i.e., rats that still approached in response to playback in the retest showed more activation. Together, these data do not provide substantial evidence that the lack of a contingent social consequence after 50-kHz USV playback accounts for approach habituation in the retest. Additionally, there is apparently no substantial activation of the nucleus accumbens in the retest, whereas the exploratory findings in the anterior cingulate cortex indicate that this brain area might be involved when individual rats still approach 50-kHz USV playback.

Different oxytocin and corticotropin-releasing hormone system changes in bipolar disorder and major depressive disorder patients

Background

Oxytocin (OXT) and corticotropin-releasing hormone (CRH) are both produced in hypothalamic paraventricular nucleus (PVN). Central CRH may cause depression-like symptoms, while peripheral higher OXT plasma levels were proposed to be a trait marker for bipolar disorder (BD). We aimed to investigate differential OXT and CRH expression in the PVN and their receptors in prefrontal cortex of major depressive disorder (MDD) and BD patients. In addition, we investigated mood-related changes by stimulating PVN-OXT in mice.

Methods

Quantitative immunocytochemistry and in situ hybridization were performed in the PVN for OXT and CRH on 6 BD and 6 BD-controls, 9 MDD and 9 MDD-controls. mRNA expressions of their receptors (OXTR, CRHR1 and CRHR2) were determined in anterior cingulate cortex and dorsolateral prefrontal cortex (DLPFC) of 30 BD and 34 BD-controls, and 24 MDD and 12 MDD-controls. PVN of 41 OXT-cre mice was short- or long-term activated by chemogenetics, and mood-related behavior was compared with 26 controls.

Findings

Significantly increased OXT-immunoreactivity (ir), OXT-mRNA in PVN and increased OXTR-mRNA in DLPFC, together with increased ratios of OXT-ir/CRH-ir and OXTR-mRNA/CRHR-mRNA were observed in BD, at least in male BD patients, but not in MDD patients. PVN-OXT stimulation induced depression-like behaviors in male mice, and mixed depression/mania-like behaviors in female mice in a time-dependent way.

Interpretation

Increased PVN-OXT and DLPFC-OXTR expression are characteristic for BD, at least for male BD patients. Stimulation of PVN-OXT neurons induced mood changes in mice, in a pattern different from BD.

Funding

10.13039/501100001809National Natural Science Foundation of China (81971268, 82101592).

Appetitive 50 kHz calls in a pavlovian conditioned approach task in Cacna1c haploinsufficient rats

We have previously shown that rats emit high-frequency 50 kHz ultrasonic vocalizations (USV) during sign- and goal-tracking in a common Pavlovian conditioned approach task. Such 50 kHz calls are probably related to positive affect and are associated with meso-limbic dopamine function. In humans, the CACNA1C gene, encoding for the α_1C subunit of the L-type voltage-gated calcium channel Ca_V1.2, is implicated in several mental disorders, including mood disorders associated with altered dopamine signaling. In the present study, we investigated sign- and goal-tracking behavior and the emission of 50 kHz USV in Cacna1c haploinsufficent rats in a task where food pellet delivery is signaled by an appearance of an otherwise inoperable lever. Over the course of this Pavlovian training, these rats not only increased their approach to the reward site, but also their rates of pressing the inoperable lever. During subsequent extinction tests, where reward delivery was omitted, extinction patterns differed between reward site (i.e. magazine entries) and lever, since magazine entries quickly declined whereas behavior towards the lever transiently increased. Based on established criteria to define sign- or goal-tracking individuals, no CACNA1C rat met a sign-tracking criterion, since around 42% of rats tested where goal-trackers and the other 58% fell into an intermediate range. Regarding USV, we found that the CACNA1C rats emitted 50 kHz calls with a clear subject-dependent pattern; also, most of them were of a flat subtype and occurred mainly during initial habituation phases without cues or rewards. Compared, to previously published wildtype controls, Cacna1c haploinsufficent rats displayed reduced numbers of appetitive 50 kHz calls. Moreover, similar to wildtype littermate controls, 50 kHz call emission in Cacna1c haploinsufficent rats was intra-individually stable over training days and was negatively associated with goal-tracking. Together, these findings provide evidence in support of 50 kHz calls as trait marker. The finding that Cacna1c haploinsufficent rats show reductions of 50 kHz calls accompanied with more goal-tracking, is consistent with the assumption of altered dopamine signaling in these rats, a finding which supports their applicability in models of mental disorders.

The Effects of Drugs on Behavior Maintained by Social Contact: Role of Monoamines in Social Reinforcement

Drug use is highly concordant among members of adolescent and young adult peer groups. One potential explanation for this observation is that drugs may increase the reinforcing effects of social contact, leading to greater motivation to establish and maintain contact with other members of the peer group. Several classes of drugs, particularly drugs that increase synaptic dopamine, increase the reinforcing effects of contextual stimuli, but the extent to which these drugs enhance the reinforcing effects of social contact is not known. The purpose of this study was to determine the extent to which drugs that increase synaptic dopamine, norepinephrine, and serotonin enhance the positive reinforcing effects of social contact. To this end, male and female Long-Evans rats were pretreated with acute doses of the selective dopamine reuptake inhibitor, WIN-35,428, the selective norepinephrine reuptake inhibitor, atomoxetine, the selective serotonin reuptake inhibitor, fluoxetine, the non-selective monoamine reuptake inhibitor, cocaine, and the non-selective monoamine releasers d-amphetamine and (±)-MDMA. Ten minutes later, the positive reinforcing effects of 30-s access to a same-sex social partner was examined on a progressive ratio schedule of reinforcement. To determine whether the reinforcement-altering effects of these drugs were specific to the social stimulus, the reinforcing effects of a non-social stimulus (30-s access to an athletic sock of similar size and coloring as another rat) was determined in control subjects. WIN-35,428, d-amphetamine, and cocaine, but not atomoxetine, fluoxetine, or MDMA, dose-dependently increased breakpoints maintained by a social partner under conditions in which responding maintained by a non-social stimulus was not affected. These data indicate that increases in extracellular dopamine, but not extracellular norepinephrine or serotonin, increases the positive reinforcing effects of social contact in both male and female rats. These data also provide support for the hypothesis that some drugs with high abuse liability increase the motivation to establish and maintain contact with social peers.

Response Calls Evoked by Playback of Natural 50-kHz Ultrasonic Vocalizations in Rats

Rats are highly social animals known to communicate with ultrasonic vocalizations (USV) of different frequencies. Calls around 50 kHz are thought to represent a positive affective state, whereas calls around 22 kHz are believed to serve as alarm or distress calls. During playback of natural 50-kHz USV, rats show a reliable and strong social approach response toward the sound source. While this response has been studied in great detail in numerous publications, little is known about the emission of USV in response to natural 50-kHz USV playback. To close this gap, we capitalized on three data sets previously obtained and analyzed USV evoked by natural 50-kHz USV playback in male juvenile rats. We compared different rat stocks, namely Wistar (WI) and Sprague-Dawley (SD) and investigated the pharmacological treatment with the dopaminergic D2 receptor antagonist haloperidol. These response calls were found to vary broadly inter-individually in numbers, mean peak frequencies, durations and frequency modulations. Despite the large variability, the results showed no major differences between experimental conditions regarding call likelihood or call parameters, representing a robust phenomenon. However, most response calls had clearly lower frequencies and were longer than typical 50-kHz calls, i.e., around 30 kHz and lasting generally around 0.3 s. These calls resemble aversive 22-kHz USV of adult rats but were of higher frequencies and shorter durations. Moreover, blockade of dopamine D2 receptors did not substantially affect the emission of response calls suggesting that they are not dependent on the D2 receptor function. Taken together, this study provides a detailed analysis of response calls toward playback of 50-kHz USV in juvenile WI and SD rats. This includes calls representing 50-kHz USV, but mostly calls with lower frequencies that are not clearly categorizable within the so far known two main groups of USV in adult rats. We discuss the possible functions of these response calls addressing their communicative functions like contact or appeasing calls, and whether they may reflect a state of frustration. In future studies, response calls might also serve as a new read-out in rat models for neuropsychiatric disorders, where acoustic communication is impaired, such as autism spectrum disorder.

Nucleus Accumbens Chemogenetic Inhibition Suppresses Amphetamine-Induced Ultrasonic Vocalizations in Male and Female Rats

Adult rats emit ultrasonic vocalizations (USVs) related to their affective states, potentially providing information about their subjective experiences during behavioral neuroscience experiments. If so, USVs might provide an important link between invasive animal preclinical studies and human studies in which subjective states can be readily queried. Here, we induced USVs in male and female Long Evans rats using acute amphetamine (2 mg/kg), and asked how reversibly inhibiting nucleus accumbens neurons using designer receptors exclusively activated by designer drugs (DREADDs) impacts USV production. We analyzed USV characteristics using "Deepsqueak" software, and manually categorized detected calls into four previously defined subtypes. We found that systemic administration of the DREADD agonist clozapine-n-oxide, relative to vehicle in the same rats, suppressed the number of frequency-modulated and trill-containing USVs without impacting high frequency, unmodulated (flat) USVs, nor the small number of low-frequency USVs observed. Using chemogenetics, these results thus confirm that nucleus accumbens neurons are essential for production of amphetamine-induced frequency-modulated USVs. They also support the premise of further investigating the characteristics and subcategories of these calls as a window into the subjective effects of neural manipulations, with potential future clinical applications.

Diazepam attenuates the effects of cocaine on locomotion, 50-kHz ultrasonic vocalizations and phasic dopamine in the nucleus accumbens of rats

BACKGROUND AND PURPOSE

Currently, there is no effective drug to treat cocaine-use disorder, which affects millions of people worldwide. Benzodiazepines are potential therapeutic candidates, as microdialysis and voltammetry studies have shown that they can decrease dopamine concentrations in the nucleus accumbens of rodents and block the increase in dopamine levels and appetitive 50-kHz ultrasonic vocalizations (USVs) induced by amphetamine in rats.

EXPERIMENTAL APPROACH

Here, we tested whether administration of 2.5-mg·kg^-1 diazepam (i.p.) in adult male rats could block the effects of 20-mg·kg^-1 cocaine (i.p.) on electrically evoked phasic dopamine signals in the nucleus accumbens measured by fast-scan cyclic voltammetry, as well as 50-kHz USV and locomotor activity.

KEY RESULTS

Cocaine injection increased evoked dopamine signals up to threefold within 5 min, and the increase was significantly higher than baseline for at least 75 min. The injection of diazepam, 5 min after cocaine, attenuated the cocaine effect by nearly 50%, and this attenuation was maintained for at least 40 min. Behaviourally, cocaine increased the number of appetitive 50-kHz calls by about 12-fold. Diazepam significantly blocked this effect for the entire duration of the session. Also, cocaine-treated rats were more active than controls and diazepam significantly attenuated cocaine-induced locomotion, by up to 50%.

CONCLUSION AND IMPLICATIONS

These results suggest that the neurochemical and psychostimulant effects of cocaine can be mitigated by diazepam.

Andrographolide blocks 50-kHz ultrasonic vocalizations, hyperlocomotion and oxidative stress in an animal model of mania

In rats, lisdexamfetamine (LDX) induces manic-like behaviors such as hyperlocomotion and increases in appetitive 50-kHz ultrasonic vocalizations (USV), which are prevented by antimanic drugs, such as lithium. Inhibition of glycogen synthase kinase 3 beta (GSK3β) and antioxidant activity have been associated with antimanic effects. Thus, the aim of the present study was to evaluate the possible antimanic-like effects of andrographolide (ANDRO), a GSK3β inhibitor, on LDX-induced hyperlocomotion and 50-kHz USV increases. In addition, the effect of ANDRO was studied on LDX-induced oxidative stress. Lithium was used as positive control. Adult Wistar rats were treated with vehicle, lithium (100 mg/kg i.p., daily) or ANDRO (2 mg/kg i.p., 3 times a week) for 21 days. On the test day, either 10 mg/kg LDX or saline was administered i.p. and USV and locomotor activity were recorded. LDX administration increased the number of 50-kHz calls, as well as locomotor activity. Repeated treatment with lithium or ANDRO prevented these effects of LDX on 50-kHz USV and locomotor activity. LDX increased lipid peroxidation (LPO) levels in rat striatum and both lithium and ANDRO prevented this effect. LPO levels in rat striatum were positively correlated with increases in 50-kHz USV emission as well as hyperlocomotion. In conclusion, the present results indicate that ANDRO has antimanic-like effects, which may be mediated by its antioxidant properties.

Increased emissions of 50-kHz ultrasonic vocalizations in hemiparkinsonian rats repeatedly treated with dopaminomimetic drugs: A potential preclinical model for studying the affective properties of dopamine replacement therapy in Parkinson's disease

Dopamine replacement therapy used in Parkinson's disease (PD) may induce alterations in the emotional state that can underlie the manifestation of iatrogenic psychiatric-like disturbances. The preclinical investigation of these disturbances is limited, also because few reliable paradigms are available to study the affective properties of dopaminomimetic drugs in parkinsonian animals. To provide a relevant experimental tool in this respect, we evaluated whether dopaminomimetic drugs modified the emission of 50-kHz ultrasonic vocalizations (USVs), a behavioral marker of positive affect, in rats bearing a unilateral lesion with 6-hydroxydopamine in the medial forebrain bundle. Apomorphine (2 or 4 mg/kg, i.p.), L-3,4-dihydroxyphenilalanine (L-DOPA, 6 or 12 mg/kg, i.p.), or pramipexole (2 or 4 mg/kg, i.p.) were administered in a test cage (× 5 administrations) on alternate days. Seven days after treatment discontinuation, rats were re-exposed to the test cage to measure conditioned calling behavior and thereafter received a drug challenge. Hemiparkinsonian rats treated with either apomorphine or L-DOPA, but not pramipexole, markedly vocalized during repeated treatment and after challenge, and showed conditioned calling behavior. Moreover, apomorphine, L-DOPA and pramipexole elicited different patterns of 50-kHz USV emissions and rotational behavior, indicating that calling behavior in hemiparkinsonian rats treated with dopaminomimetic drugs is not a byproduct of motor activation. Taken together, these results suggest that measuring 50-kHz USV emissions may be a relevant experimental tool for studying how dopaminomimetic drugs modify the affective state in parkinsonian rats, with possible implications for the preclinical investigation of iatrogenic psychiatric-like disturbances in PD.

Social Behavior and Ultrasonic Vocalizations in a Genetic Rat Model Haploinsufficient for the Cross-Disorder Risk Gene Cacna1c

The top-ranked cross-disorder risk gene CACNA1C is strongly associated with multiple neuropsychiatric dysfunctions. In a recent series of studies, we applied a genomically informed approach and contributed extensively to the behavioral characterization of a genetic rat model haploinsufficient for the cross-disorder risk gene Cacna1c. Because deficits in processing social signals are associated with reduced social functioning as commonly seen in neuropsychiatric disorders, we focused on socio-affective communication through 22-kHz and 50-kHz ultrasonic vocalizations (USV). Specifically, we applied a reciprocal approach for studying socio-affective communication in sender and receiver by including rough-and-tumble play and playback of 22-kHz and 50-kHz USV. Here, we review the findings obtained in this recent series of studies and link them to the key features of 50-kHz USV emission during rough-and-tumble play and social approach behavior evoked by playback of 22-kHz and 50-kHz USV. We conclude that Cacna1c haploinsufficiency in rats leads to robust deficits in socio-affective communication through 22-kHz and 50-kHz USV and associated alterations in social behavior, such as rough-and-tumble play behavior.

Limited generalizability, pharmacological modulation, and state-dependency of habituation towards pro-social 50-kHz calls in rats

Communication constitutes a fundamental component of mammalian social behavior. Rats are highly social animals and emit 50-kHz ultrasonic vocalizations (USV), which function as social contact calls. Playback of 50-kHz USV leads to strong and immediate social approach responses in receiver rats, but this response is weak or even absent during repeated 50-kHz USV playback. Given the important role of 50-kHz USV in initiating social contact and coordinating social interactions, the occurrence of habituation is highly unexpected. It is not clear why a social signal characterized by significant incentive salience loses its power to change the behavior of the receiver so rapidly. Here, we show that the habituation phenomenon displayed by rats in response to repeated playback of 50-kHz USV (1) is characterized by limited generalizability because it is present in Wistar but not Sprague-Dawley rats, (2) can be overcome by amphetamine treatment, and (3) depends on the subject’s internal state.

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Rats display social approach in response to playback of pro-social 50-kHz calls

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Repeated playback leads to habituation with limited generalizability

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Habituation can be overcome by amphetamine treatment

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Habituation depends on the subject’s internal state

Measuring mania-like elevated mood through amphetamine-induced 50-kHz ultrasonic vocalizations in rats

Rats emit 50-kHz ultrasonic vocalizations (USV) in appetitive situations, reflecting a positive affective state. Particularly high rates of 50-kHz USV are elicited by the psychostimulant d-amphetamine. Exaggerated 50-kHz USV emission evoked by d-amphetamine is modulated by dopamine, noradrenaline and 5-hydroxytyrptamine receptor ligands and inhibited by the mood stabilizer lithium, the gold standard anti-manic drug for treating bipolar disorder. This indicates that exaggerated 50-kHz USV emission can serve as a reliable and valid measure for assessing mania-like elevated mood in rats with sufficient translational power for gaining a better understanding of relevant pathophysiological mechanisms and the identification of new therapeutic targets. The improved capacity to study the effects of anti-manic pharmacological interventions on a broader range of behaviours by including exaggerated 50-kHz USV emission as preclinical outcome measure complementary to locomotor hyperactivity will refine rodent models for mania.

Lack of drug- and cue-stimulated emissions of ultrasonic vocalizations in C57BL/6J mice repeatedly treated with amphetamine

The emission of ultrasonic vocalizations (USVs) is thought to communicate the behavioral and emotional states elicited in rodents by social and non-social stimuli. On this basis, studies of psychopharmacology in rats are increasingly utilizing USVs as a behavioral marker to evaluate the effects of drugs on the emotional state. Conversely, very limited information is available as to whether psychoactive drugs influence USV emissions in mice. To provide new insights in this respect, we evaluated the emission of USVs in C57BL/6J mice subjected to repeated treatment with the dopaminergic psychostimulant of abuse amphetamine. Mice were first allowed to perform social contacts in dyads, and 2 days later they received amphetamine (1-4 mg/kg, i.p.) in a test cage (× 5 administrations) on alternate days. Seven days after treatment discontinuation, mice were re-exposed to the test cage to evaluate whether the presentation of drug-paired environmental cues elicited calling behavior, and thereafter received an amphetamine challenge. An additional group of animals received the dopamine receptor agonist apomorphine (1-4 mg/kg, i.p.), to further clarify the role of dopamine transmission in calling behavior of mice. C57BL/6J mice emitted USVs during social contacts, but did not significantly vocalize after amphetamine administration, in response to amphetamine-paired environmental cues, and after apomorphine administration. These results indicate that C57BL/6J mice may respond differently to social and pharmacological stimuli in terms of USV emissions, and may lay the foundation for future studies aimed at clarifying whether USVs may be a useful behavioral marker in studies of psychopharmacology in mice.

Ultrasonic vocalizations and individual differences in rats performing a Pavlovian conditioned approach task

Rats emit distinct types of ultrasonic vocalizations (USV), including high-frequency 50-kHz USV, which occur in appetitive situations. Such 50-kHz USV are thought to reflect positive affective states, for example in case of reward anticipation, and are linked to dopamine signaling. The present study was conducted to investigate whether rats emit 50-kHz USV during a Pavlovian conditioned approach task and whether trait-like differences in 50-kHz USV emission are associated with sign- versus goal-tracking. We hypothesize that individuals engaging more with a cue predicting a food reward will also elicit more 50-kHz USV. In order to test this, we investigated 34 female rats and gauged USV while they underwent a Pavlovian conditioned approach training and extinction paradigm. For one, we found a high subject-dependent variability in the emission of 50-kHz calls. These were not largely affected by state differences, since these 50-kHz USV were observed throughout the task. During task progress and in most subjects, there was a rather complete shift toward goal-tracking, but subjects engaging more with the cue predicting a reward also emitted higher numbers of appetitive 50-kHz calls. This supports the hypothesis that sign-tracking is positively associated with the emission of 50-kHz USV. The high subject-dependent variability in the emission of 50-kHz calls warrants special attention in future appetitive studies.

Effects of nicotine, nornicotine and cotinine, alone or in combination, on locomotor activity and ultrasonic vocalization emission in adult rats

RATIONALE

The behavioral effects of the nicotine metabolites nornicotine and cotinine have not been investigated extensively.

OBJECTIVES

To evaluate the effects of nicotine, cotinine, and nornicotine, given alone or in combination, on locomotor activity and emission of ultrasonic vocalizations in male adult rats.

METHODS

Rats were first given home cage nicotine injections to make them tolerant to the drug's locomotor depressant effects. On subsequent days, locomotor activity (LMA) and ultrasonic vocalizations were recorded in an open field, for 60 min after challenge injection, using repeated measures designs. In single-drug experiments, subjects were tested with nicotine 0.05-0.4 mg/kg, cotinine 0.03-3 mg/kg, or nornicotine 0.1-10 mg/kg. In drug-combination experiments, saline or nicotine 0.2 mg/kg challenge was preceded by cotinine (0, 0.3, 3 mg/kg) or nornicotine (0, 0.1, 0.3, 1, 3 mg/kg) injection.

RESULTS

High doses of nornicotine increased LMA and blunted the locomotor stimulant effect of nicotine. Less consistently, nicotine and high doses of nornicotine decreased the 50-kHz call rate, with no clear evidence of a nornicotine × nicotine interaction. Cotinine, given alone or before nicotine injection, altered neither LMA nor the call rate. No drug altered the relative prevalence of flat vs. trill 50-kHz call subtypes, except that the highest dose of nornicotine promoted flat calls over trills. No drug evoked 22-kHz calls.

CONCLUSION

Nornicotine can exert an acute anti-nicotine effect in vivo, as previously reported in vitro. The finding that nicotine did not detectably alter the 50-kHz call profile appears consistent with this drug's mild subjective effects in human subjects.

Playback of 50-kHz ultrasonic vocalizations overcomes psychomotor deficits induced by sub-chronic haloperidol treatment in rats

RATIONALE

In rodents, acute haloperidol treatment induces psychomotor impairments known as catalepsy, which models akinesia in humans and is characterized as an animal model of acute Parkinsonism, whereas sub-chronic haloperidol reduces exploratory behavior, which resembles bradykinesia. Haloperidol-induced catalepsy in rats can be ameliorated by playback of 50-kHz ultrasonic vocalizations (USV), an emotionally and motivationally relevant appetitive auditory stimulus, representing an animal model of paradoxical kinesia. In a condition like PD where patients suffer from chronic motor impairments, it is paramount to assess the long-term symptom relief in an animal model of Parkinsonism.

OBJECTIVES

We investigated whether 50-kHz USV playback ameliorates psychomotor deficits induced by haloperidol in a sub-chronic dosing regimen.

METHODS

In phase 1, distance traveled and number of rearing behavior were assessed in an activity chamber in order to investigate whether sub-chronic haloperidol treatment induced psychomotor impairments. In phase 2, we investigated whether 50-kHz USV playback could overcome these impairments by assessing exploratory behaviors and approach behavior towards the sound source in the 50-kHz USV radial maze playback paradigm.

RESULTS

Sub-chronic haloperidol treatment led to psychomotor deficits since the distance traveled and number of rearing behavior were reduced as compared to saline control group or baseline. These psychomotor impairments were ameliorated during playback of 50-kHz USV, with haloperidol treated rats showing a clear social approach behavior towards the sound source exclusively during playback.

CONCLUSIONS

This study provides evidence that 50-kHz USV playback induces paradoxical kinesia in rats exhibiting motor deficits after sub-chronic haloperidol, as we previously showed after acute haloperidol treatment.

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.

Neurobiology of the major psychoses: a translational perspective on brain structure and function-the FOR2107 consortium

Genetic (G) and environmental (E) factors are involved in the etiology and course of the major psychoses (MP), i.e. major depressive disorder (MDD), bipolar disorder (BD), schizoaffective disorder (SZA) and schizophrenia (SZ). The neurobiological correlates by which these predispositions exert their influence on brain structure, function and course of illness are poorly understood. In the FOR2107 consortium, animal models and humans are investigated. A human cohort of MP patients, healthy subjects at genetic and/or environmental risk, and control subjects (N = 2500) has been established. Participants are followed up after 2 years and twice underwent extensive deep phenotyping (MR imaging, clinical course, neuropsychology, personality, risk/protective factors, biomaterials: blood, stool, urine, hair, saliva). Methods for data reduction, quality assurance for longitudinal MRI data, and (deep) machine learning techniques are employed. In the parallelised animal cluster, genetic risk was introduced by a rodent model (Cacna1c deficiency) and its interactions with environmental risk and protective factors are studied. The animals are deeply phenotyped regarding cognition, emotion, and social function, paralleling the variables assessed in humans. A set of innovative experimental projects connect and integrate data from the human and animal parts, investigating the role of microRNA, neuroplasticity, immune signatures, (epi-)genetics and gene expression. Biomaterial from humans and animals are analyzed in parallel. The FOR2107 consortium will delineate pathophysiological entities with common neurobiological underpinnings ("biotypes") and pave the way for an etiologic understanding of the MP, potentially leading to their prevention, the prediction of individual disease courses, and novel therapies in the future.

Mania-like elevated mood in rats: Enhanced 50-kHz ultrasonic vocalizations after sleep deprivation

Mania is characterized by elevated drive and mood but animal models of mania have often neglected elevated mood. Ultrasonic vocalizations (USV) of 50-kHz emitted by rats are thought to index the subject's positive affective state. Fifty-kHz USV emission is increased by amphetamine, an effect blocked by lithium administration. Sleep deprivation (SD) is an environmental model of mania and the present study evaluated SD effects on behavioral activity and USV emission, together with the impact of lithium treatment. Adult rats were submitted to 24h or 72h SD, and locomotor activity and USV emission were assessed. To test their sensitivity to a standard antimanic drug, these behavioral parameters were also evaluated after acute administration of lithium carbonate (25, 50 or 100 mg/kg, i.p.). Striatal monoamine content was measured post-mortem. SD (24h and 72h) led to increased locomotor activity, rearing behavior and 50-kHz USV emission, together with a change in the call profile characterized by an increase in the percentage of frequency-modulated 50-kHz USV, which may indicate the mania-like consequences of SD. Importantly, all SD effects were reverted by lithium administration. SD also led to a decrease in dopamine content in the ventral striatum, while increasing dopamine turnover. In conclusion, SD increased 50-kHz USV emission, an effect prevented by acute lithium administration. This suggests 50-kHz USV as a new marker for mania-like elevated mood, which shows construct validity (associated with increased dopaminergic tone), face validity (reflecting increased positive affect) and predictive validity (high sensitivity to lithium treatment).

Immunity and ultrasonic vocalization in rodents

Ultrasonic vocalizations (USVs) serve important communicative functions in rodents. Different types of USVs can be triggered in the sender, for example, by maternal separation, social interactions, or exposure to predators, and they evoke affiliative or alarming behaviors in recipients. This review focusses on studies evaluating possible links between immunity and USVs. Most studies have been performed in a murine model of maternal immune activation and subsequent evaluation of effects in the offspring. This model has received large attention in recent years because it mimics behavioral abnormalities observed in certain human neuropsychiatric disorders, including autism spectrum disorder. Although there is still some controversy, the results indicate that stimulation of the immune system of mice and rats during pregnancy affects ultrasonic calling in pups. Few studies are available on immunization during adulthood and USVs. In most cases, immune stimulation led to disease, complicating conclusions about a possible direct link between vocalization and immunity. Although much work is still needed, this is certainly a rather new and promising aspect of interactions between the immune system and behavior.

Cacna1c haploinsufficiency leads to pro-social 50-kHz ultrasonic communication deficits in rats

The cross-disorder risk gene CACNA1C is strongly implicated in multiple neuropsychiatric disorders, including autism spectrum disorder (ASD), bipolar disorder (BPD) and schizophrenia (SCZ), with deficits in social functioning being common for all major neuropsychiatric disorders. In the present study, we explored the role of Cacna1c in regulating disorder-relevant behavioral phenotypes, focusing on socio-affective communication after weaning during the critical developmental period of adolescence in rats. To this aim, we used a newly developed genetic Cacna1c rat model and applied a truly reciprocal approach for studying communication through ultrasonic vocalizations, including both sender and receiver. Our results show that a deletion of Cacna1c leads to deficits in social behavior and pro-social 50-kHz ultrasonic communication in rats. Reduced levels of 50-kHz ultrasonic vocalizations emitted during rough-and-tumble play may suggest that Cacna1c haploinsufficient rats derive less reward from playful social interactions. Besides the emission of fewer 50-kHz ultrasonic vocalizations in the sender, Cacna1c deletion reduced social approach behavior elicited by playback of 50-kHz ultrasonic vocalizations. This indicates that Cacna1c haploinsufficiency has detrimental effects on 50-kHz ultrasonic communication in both sender and receiver. Together, these data suggest that Cacna1c plays a prominent role in regulating socio-affective communication in rats with relevance for ASD, BPD and SCZ.

This article has an associated First Person interview with the first author of the paper.

Summary: The present study suggests that Cacna1c plays a prominent role in regulating socio-affective communication in rats with relevance for neuropsychiatric disorders.

Paradoxical kinesia induced by appetitive 50-kHz ultrasonic vocalizations in rats depends on glutamatergic mechanisms in the inferior colliculus

Paradoxical kinesia is a sudden transient ability of akinetic patients to perform motor tasks they are otherwise unable to perform. This phenomenon is known to depend on the patient's emotional state and external stimuli. Paradoxical kinesia can be induced by appetitive 50-kHz ultrasonic vocalizations (USV) in rats displaying catalepsy following systemic haloperidol. We investigated the role of the inferior colliculus (IC) in paradoxical kinesia induced by 50-kHz USV, since the IC modulates haloperidol-induced catalepsy. We focused on glutamatergic and GABAergic neurotransmission, with male rats receiving intracollicular NMDA or the GABA receptor agonist diazepam 10 min before systemic haloperidol. Catalepsy time was assessed by means of the bar test, during which rats were exposed to playback of 50-kHz USV, white noise, and background noise. Our results show that playback of 50-kHz USV induced paradoxical kinesia by reducing haloperidol-induced catalepsy in rats which had received saline intracollicular microinjection. This paradoxical kinesia effect of 50-kHz USV playback on haloperidol-induced catalepsy was prevented by intracollicular NMDA administration. Although intracollicular diazepam microinjection potentiated haloperidol-induced catalepsy, it did not affect the response to 50-kHz USV playback. Together, NMDA receptor agonist suppressed the effectiveness of 50-kHz USV playback, whereas diazepam did not. These findings suggest that the IC is a key structure involved in paradoxical kinesia, with relevant processes being glutamatergic rather than GABAergic. Our approach thus appears useful for uncovering neural mechanisms of paradoxical kinesia and it might help identifying novel therapeutic targets for Parkinson's disease.

Developmental social communication deficits in the Shank3 rat model of phelan-mcdermid syndrome and autism spectrum disorder

Mutations in the SHANK3 gene have been discovered in autism spectrum disorder (ASD), and the intellectual disability, Phelan-McDermid Syndrome. This study leveraged a new rat model of Shank3 deficiency to assess complex behavioral phenomena, unique to rats, which display a richer social behavior repertoire than mice. Uniquely detectable emissions of ultrasonic vocalizations (USV) in rats serve as situation-dependent affective signals and accomplish important communicative functions. We report, for the first time, a call and response acoustic playback assay of bidirectional social communication in juvenile Shank3 rats. Interestingly, we found that Shank3-deficient null males did not demonstrate the enhanced social approach behavior typically exhibited following playback of pro-social USV. Concomitantly, we discovered that emission of USV in response to playback was not genotype-dependent and emitted response calls were divergent in meaning. This is the first report of these socially relevant responses using a genetic model of ASD. A comprehensive and empirical analysis of vigorous play during juvenile reciprocal social interactions further revealed fewer bouts and reduced durations of time spent playing by multiple key parameters, including reduced anogenital sniffing and allogrooming. We further discovered that male null Shank3-deficient pups emitted fewer isolation-induced USV than Shank3 wildtype controls. Postnatal whole brain anatomical phenotyping was applied to visualize anatomical substrates that underlie developmental phenotypes. The data presented here lend support for the important role of Shank3 in social communication, the core symptom domain of ASD. By increasing the number of in vivo functional outcome measures, we improved the likelihood for identifying and moving forward with medical interventions. Autism Res 2018, 11: 587-601. © 2018 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Clinically relevant outcomes are required to demonstrate the utility of therapeutics. We introduce findings in a rat model, and assess the impact of mutations in Shank3, an autism risk gene. We found that males with deficient expression of Shank3 did not demonstrate typical responses in a bi-directional social communication test and that social interaction was lower on key parameters. Outcome measures reported herein extend earlier results in mice and capture responses to acoustic calls, which is analogous to measuring receptive and expressive communication.

Cognitive Phenotypes for Biomarker Identification in Mental Illness: Forward and Reverse Translation

Psychiatric illness has been acknowledged for as long as people were able to describe behavioral abnormalities in the general population. In modern times, these descriptions have been codified and continuously updated into manuals by which clinicians can diagnose patients. None of these diagnostic manuals have attempted to tie abnormalities to neural dysfunction however, nor do they necessitate the quantification of cognitive function despite common knowledge of its ties to functional outcome. In fact, in recent years the National Institute of Mental Health released a novel transdiagnostic classification, the Research Domain Criteria (RDoC), which utilizes quantifiable behavioral abnormalities linked to neurophysiological processes. This reclassification highlights the utility of RDoC constructs as potential cognitive biomarkers of disease state. In addition, with RDoC and cognitive biomarkers, the onus of researchers utilizing animal models no longer necessitates the recreation of an entire disease state, but distinct processes. Here, we describe the utilization of constructs from the RDoC initiative to forward animal research on these cognitive and behavioral processes, agnostic of disease. By linking neural processes to these constructs, identifying putative abnormalities in diseased patients, more targeted therapeutics can be developed.

Mapping trait-like socio-affective phenotypes in rats through 50-kHz ultrasonic vocalizations

RATIONALE

Fifty-kilohertz ultrasonic vocalizations (USV) in rats are believed to express inter-individual differences in trait-like positive affective phenotypes. Emission of 50-kHz USV can be induced by amphetamine (AMPH) to model mania-like positive affect, raising the possibility that predispositions for high 50-kHz USV production confer susceptibility to mania-like states. Such 50-kHz USV presumably express the sender's motivation for social contact and elicit social approach behavior in receivers.

OBJECTIVES

We recently showed that AMPH-induced 50-kHz USV are paralleled by mania-like patterns of enhanced social approach behavior towards playback of 50-kHz USV. Here, we assessed whether these AMPH effects are dependent on trait-like inter-individual differences in 50-kHz USV production.

METHODS

To this aim, we subdivided juvenile rats into those emitting low (LC) and high (HC) rates of baseline 50-kHz USV and compared them across four AMPH dosage conditions: 0.0, 0.5, 1.0, and 2.5 mg/kg.

RESULTS

HC rats were considerably more susceptible to AMPH in inducing 50-kHz USV than LC rats, consistently across all examined doses. They further appeared to attribute more incentive salience to signals of rewarding social contact, as evidenced by enhanced social approach behavior towards 50-kHz USV playback, a response pattern also seen in LC rats after receiving AMPH treatment. HC but not LC rats emitted aversive 22-kHz USV following 50-kHz USV playback, indicating increased proneness to experience negative affective states if no actual social consequence followed the incentive signal.

CONCLUSION

Inter-individual differences in 50-kHz USV map onto a unique trait-like socio-affective phenotype associated with enhanced emotional reactivity towards social and non-social reward, possibly conferring risk to mania-like states.

Mapping trait-like socio-affective phenotypes in rats through 50-kHz ultrasonic vocalizations

RATIONALE

Fifty-kilohertz ultrasonic vocalizations (USV) in rats are believed to express inter-individual differences in trait-like positive affective phenotypes. Emission of 50-kHz USV can be induced by amphetamine (AMPH) to model mania-like positive affect, raising the possibility that predispositions for high 50-kHz USV production confer susceptibility to mania-like states. Such 50-kHz USV presumably express the sender's motivation for social contact and elicit social approach behavior in receivers.

OBJECTIVES

We recently showed that AMPH-induced 50-kHz USV are paralleled by mania-like patterns of enhanced social approach behavior towards playback of 50-kHz USV. Here, we assessed whether these AMPH effects are dependent on trait-like inter-individual differences in 50-kHz USV production.

METHODS

To this aim, we subdivided juvenile rats into those emitting low (LC) and high (HC) rates of baseline 50-kHz USV and compared them across four AMPH dosage conditions: 0.0, 0.5, 1.0, and 2.5 mg/kg.

RESULTS

HC rats were considerably more susceptible to AMPH in inducing 50-kHz USV than LC rats, consistently across all examined doses. They further appeared to attribute more incentive salience to signals of rewarding social contact, as evidenced by enhanced social approach behavior towards 50-kHz USV playback, a response pattern also seen in LC rats after receiving AMPH treatment. HC but not LC rats emitted aversive 22-kHz USV following 50-kHz USV playback, indicating increased proneness to experience negative affective states if no actual social consequence followed the incentive signal.

CONCLUSION

Inter-individual differences in 50-kHz USV map onto a unique trait-like socio-affective phenotype associated with enhanced emotional reactivity towards social and non-social reward, possibly conferring risk to mania-like states.