22 kHz and 55 kHz ultrasonic vocalizations differentially influence neural and behavioral outcomes: Implications for modeling anxiety via auditory stimuli in the rat

An adverse rearing environment alters maternal responsiveness to infant ultrasonic vocalizations

Rodent pups use a variety of ultrasonic vocalizations (USVs) to facilitate maternal care. Importantly, infant USV repertoires are dependent on both the age and early life experiences of the pups. We have shown that an adverse rearing environment modeled with the maternal separation (MS) paradigm alters caregiving behavior but little is known about how pup USVs differentially elicit maternal attention. In the present study, maternal approach towards a vocalizing pup over a non-vocalizing pup was tested in a Y-maze apparatus at two developmental time points over the course of MS. At postnatal day (P)10, MS dams engaged in longer interaction times with vocalizing pups compared to non-vocalizing pup, and this effect was strongest in male pups. As expected at P20, dams did not show a preference for either the vocalizing or non-vocalizing pups regardless of rearing environment; however, MS dams spent a greater amount of time in the center of the apparatus as compared to control dams, which can be interpreted as a measure of uncertainty or indecision. These effects of MS on dam USV sensitivity are important considering the sex specific effects of MS exposure across all developmental stages. Our novel findings support the hypothesis that sex-specific pup-dam interactions may drive later life outcomes following adversity.

Effects of early life adversity and adolescent basolateral amygdala activity on corticolimbic connectivity and anxiety behaviors

Early postnatal development of corticolimbic circuitry is shaped by the environment and is vulnerable to early life challenges. Prior work has shown that early life adversity (ELA) leads to hyperinnervation of glutamatergic basolateral amygdala (BLA) projections to the prefrontal cortex (PFC) in adolescence. While hyperinnervation is associated with later-life anxiety behaviors, the physiological changes underpinning corticolimbic and behavioral impacts of ELA are not understood. We tested whether postsynaptic BLA-driven PFC activity is enhanced in ELA-exposed animals, using the maternal separation (MS) model of ELA. PFC local-field potential following BLA stimulation was facilitated in MS-exposed adolescents. Since ELA increases activity of the early-developing BLA, while the PFC exhibits protracted development, we further examined impacts of glutamatergic BLA activity during early adolescence on later-life PFC innervation and heightened anxiety. In early adolescence, MS-exposed animals exhibited decreased anxiety-like behavior, and acute adolescent BLA inhibition induced behaviors that resembled those of MS animals. To examine long-lasting impacts of adolescent BLA activity on innervation, BLA-originating axonal boutons in the PFC were quantified in late adolescence after early adolescent BLA inhibition. We further tested whether late adolescent BLA-PFC changes were associated with anxious reactivity expressed as heightened acoustic startle responses. MS rearing increased BLA-PFC innervation and threat reactivity in late adolescence, however early adolescent BLA inhibition was insufficient to prevent MS effects, suggesting that earlier BLA activity or post-synaptic receptor rearrangement in the PFC drives altered innervation. Taken together, these findings highlight both pre- and postsynaptic changes in the adolescent BLA-PFC circuit following ELA.

Playback of rat 22-kHz ultrasonic vocalizations as a translational assay of negative affective states: An analysis of evoked behavior and brain activity

The subjective nature of human emotions makes them uniquely challenging to investigate in preclinical models. While behavioral assays in rodents aim to evaluate affect (i.e., anxiety, hypervigilance), they often lack ethological validity. Playback of negatively valenced 22-kHz ultrasonic vocalizations (USVs) in rats shows promise as a translational tool to investigate affective processing. Much like how human facial expressions can communicate internal states, rats emit 22-kHz USVs that similarly convey negative affective states to conspecifics indicating possible threat. 22-kHz USV playback elicits avoidance and hypervigilant behaviors, and recruit brain regions comparable to those seen in human brains evoked by viewing fearful faces. Indeed, 22-kHz playback alters neural activity in brain regions associated with negative valence systems (i.e., amygdala, bed nucleus of the stria terminalis, periaqueductal gray) alongside increases in behaviors typically associated with anxiety. Here, we present evidence from the literature that supports leveraging 22-kHz USV playback in rat preclinical models to obtain clinically relevant and translational findings to identify the neural underpinnings of affective processing and neuropathological dysfunction.

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.

The bed nucleus of the stria terminalis in threat detection: task choice and rodent experience

Behavioural reactivity to potential threat is used to experimentally refine models of anxiety symptoms in rodents. We present a short review of the literature tying the most commonly used tasks to model anxiety symptoms to functional recruitment of bed nucleus of the stria terminalis circuits (BNST). Using a review of studies that investigated the role of the BNST in anxiety-like behaviour in rodents, we flag the certain challenges for the field. These stem from inconsistent methods of reporting the neuroanatomical BNST subregions and the interpretations of specific behaviour across a wide variety of tasks as 'anxiety-like'. Finally, to assist in interpretation of the findings, we discuss the potential interactions between typically used 'anxiety' tasks of innate behaviour that are potentially modulated by the social and individual experience of the animal.

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Age- and sex-specific effects of maternal separation on the acoustic startle reflex in rats: early baseline enhancement in females and blunted response to ambiguous threat

Early life adversity (ELA) increases the incidence of later-life anxiety disorders. Dysregulated threat processing, including responsivity to ambiguous threats, is an indicator of anxiety disorders and can be influenced by childhood experiences. The acoustic startle response is a defensive reflex displayed by mammals when exposed to sudden intense stimuli reflecting individual variations in vigilance. These measures can be altered by previous experience and experimental modifications, including the introduction of unconditioned aversive stimuli. Rats emit ultrasonic vocalizations (USVs) in the 22 KHz range in negative contexts. As such, 22 KHz USVs are an ethologically relevant social cue of environmental threat shown to induce anxiety-like behavior in recipient rats. Because the timing of symptom manifestation after early life adversity can differ between sexes, the current study sought to identify the age- and sex-specific effects of daily maternal separation (MS) on responsivity to ambiguous threat in rats. In Experiment 1, rat pups underwent MS or control rearing from postnatal day (P) 2–20, then underwent behavioral testing beginning on P24, 34, or 54 to determine whether MS modified the baseline startle response or the modulation of startle by 22 KHz USVs. In Experiment 2, rats were tested in a light-enhanced startle paradigm at P54 after MS or control rearing to determine whether MS influenced light-enhanced startle. Results show an enhancement of the baseline startle magnitude by MS in females at P34. At P54, MS reduced the modulation of the startle response by 22 KHz USVs and prevented light-enhanced startle, indicating an MS-induced deficit in defensive responsivity when exposed to potential threat.

High-frequency ultrasound exposure improves depressive-like behavior in an olfactory bulbectomized rat model of depression

OBJECTIVES

According to previous studies, ultrasound exposure appears to be a noninvasive method for modulating brain activity related to cognition and consciousness; however, its effects on emotional states remain unclear. Therefore, an animal model is required in which the effects and effect mechanisms of ultrasound exposure can be investigated. Thus, we used olfactory bulbectomized rats as an animal model of depression and investigated their emotional state following ultrasound exposure.

METHODS

In male Wistar/ST olfactory bulbectomized rats, hyperemotionality was evaluated according to hyperemotionality scoring and the scores before and after 24-h ultrasound exposure were compared. Elevated plus maze (EPM) tests were also conducted after 24-h ultrasound exposure, and blood samples were collected in which plasma corticosterone concentrations were measured.

RESULTS

Following exposure to high-frequency (~50 kHz) ultrasound vocalizations (USVs) associated with the pleasant emotions of rats, the hyperemotionality scores of olfactory bulbectomized rats were significantly reduced. Additionally, the latency of the first entry into the open arm of the EPM was significantly decreased in USV-exposed olfactory bulbectomized rats, as were their plasma corticosterone levels. Furthermore, artificial ultrasound (50 kHz) at a similar frequency to that of USV also significantly decreased the hyperemotionality score of olfactory bulbectomized rats.

CONCLUSIONS

Ultrasound exposure improved depressive-like behavior in olfactory bulbectomized rats and reduced their plasma corticosterone levels. Thus, we recommend the use of olfactory bulbectomized rats as an animal model for investigating the effects and effect mechanisms of ultrasound exposure.

Stressed rats fail to exhibit avoidance reactions to innately aversive social calls

Disruptions in amygdalar function, a brain area involved in encoding emotionally salient information, has been implicated in stress-related affective disorders. Earlier animal studies on the behavioral consequences of stress-induced abnormalities in the amygdala focused on learned behaviors using fear conditioning paradigms. If and how stress affects unconditioned, innate fear responses to ethologically natural aversive stimuli remains unexplored. Hence, we subjected rats to aversive ultrasonic vocalization calls emitted on one end of a linear track. Unstressed control rats exhibited a robust avoidance response by spending more time away from the source of the playback calls. Unexpectedly, prior exposure to chronic immobilization stress prevented this avoidance reaction, rather than enhancing it. Further, this stress-induced impairment extended to other innately aversive stimuli, such as white noise and electric shock in an inhibitory avoidance task. However, conditioned fear responses were enhanced by the same stress. Inactivation of the basolateral amygdala (BLA) in control rats prevented this avoidance reaction evoked by the playback. Consistent with this, analysis of the immediate early gene cFos revealed higher activity in the BLA of control, but not stressed rats, after exposure to the playback. Further, in vivo recordings in freely behaving control rats exposed to playback showed enhanced theta activity in the BLA, which also was absent in stressed rats. These findings offer a new framework for studying stress-induced alterations in amygdala-dependent maladaptive responses to more naturally threatening and emotionally relevant social stimuli. The divergent impact of stress on defensive responses--impaired avoidance responses together with increased conditioned fear--also has important implications for models of learned helplessness and depression.

Chronic mild stress paradigm as a rat model of depression: facts, artifacts, and future perspectives

RATIONALE

The chronic mild stress (CMS) paradigm was first described almost 40 years ago and has become a widely used model in the search for antidepressant drugs for major depression disorder (MDD). It has resulted in the publication of almost 1700 studies in rats alone. Under the original CMS procedure, the expression of an anhedonic response, a key symptom of depression, was seen as an essential feature of both the model and a depressive state. The prolonged exposure of rodents to unpredictable/uncontrollable mild stressors leads to a reduction in the intake of palatable liquids, behavioral despair, locomotor inhibition, anxiety-like changes, and vegetative (somatic) abnormalities. Many of the CMS studies do not report these patterns of behaviors, and they often fail to include consistent molecular, neuroanatomical, and physiological phenotypes of CMS-exposed animals.

OBJECTIVES

To critically review the CMS studies in rats so that conceptual and methodological flaws can be avoided in future studies.

RESULTS

Analysis of the literature supports the validity of the CMS model and its impact on the field. However, further improvements could be achieved by (i) the stratification of animals into 'resilient' and 'susceptible' cohorts within the CMS animals, (ii) the use of more refined protocols in the sucrose test to mitigate physiological and physical artifacts, and (iii) the systematic evaluation of the non-specific effects of CMS and implementation of appropriate adjustments within the behavioral tests.

CONCLUSIONS

We propose methodological revisions and the use of more advanced behavioral tests to refine the rat CMS paradigm, which offers a valuable tool for developing new antidepressant medications.

Evidence for a vocal signature in the rat and its reinforcing effects: a key role for the subthalamic nucleus

Although rodents have a well-structured vocal form of communication, like humans and non-human primates, there is, to date, no evidence for a vocal signature in the well-known 50- and 22-kHz ultrasonic vocalizations (USVs) emitted by rats. Here, we show that rats can recognize the identity of the USV emitter since they choose to preferentially self-administer playback of 50-kHz USVs emitted by a stranger rat over those of their cagemate. In a second experiment, we show that only stranger, but not familiar, 50-kHz USVs reduce cocaine self-administration. Finally, to study the neurobiological substrate of these processes, we have shown that subthalamic nucleus (STN)-lesioned rats did not lever press much for any USV playback, whatever their emotional valence, nor did they seem able to differentiate familiar from stranger peer. Advocating for the existence of a vocal signature in rats, these results highlight the importance of ultrasonic communication in the socio-affective influence of behaviour, such as the influence of proximal social factors on drug consumption and confirm the role of the STN on this influence.

Evidence for a vocal signature in the rat and its reinforcing effects: a key role for the subthalamic nucleus

Although rodents have a well-structured vocal form of communication, like humans and non-human primates, there is, to date, no evidence for a vocal signature in the well-known 50- and 22-kHz ultrasonic vocalizations (USVs) emitted by rats. Here, we show that rats can recognize the identity of the USV emitter since they choose to preferentially self-administer playback of 50-kHz USVs emitted by a stranger rat over those of their cagemate. In a second experiment, we show that only stranger, but not familiar, 50-kHz USVs reduce cocaine self-administration. Finally, to study the neurobiological substrate of these processes, we have shown that subthalamic nucleus (STN)-lesioned rats did not lever press much for any USV playback, whatever their emotional valence, nor did they seem able to differentiate familiar from stranger peer. Advocating for the existence of a vocal signature in rats, these results highlight the importance of ultrasonic communication in the socio-affective influence of behaviour, such as the influence of proximal social factors on drug consumption and confirm the role of the STN on this influence.

Behavior and Fos activation reveal that male and female rats differentially assess affective valence during CTA learning and expression

Females are more affected by psychiatric illnesses including eating disorders, depression, and post-traumatic stress disorder than males. However, the neural mechanisms mediating these sex differences are poorly understood. Animal models can be useful in exploring such neural mechanisms. Conditioned taste aversion (CTA) is a behavioral task that assesses how animals process the competition between associated reinforcing and aversive stimuli in subsequent task performance, a process critical to healthy behavior in many domains. The purpose of the present study was to identify sex differences in this behavior and associated neural responses. We hypothesized that females would value the rewarding stimulus (Boost®) relative to the aversive stimulus (LiCl) more than males in performing CTA. We evaluated behavior (Boost® intake, LiCl-induced behaviors, ultrasonic vocalizations (USVs), CTA performance) and Fos activation in relevant brain regions after the acute stimuli [acute Boost® (AB), acute LiCl (AL)] and the context-only task control (COT), Boost® only task (BOT) and Boost®-LiCl task (BLT). Acutely, females drank more Boost® than males but showed similar aversive behaviors after LiCl. Females and males performed CTA similarly. Both sexes produced 55 kHz USVs anticipating BOT and inhibited these calls in the BLT. However, more females emitted both 22 kHz and 55 kHz USVs in the BLT than males: the latter correlated with less CTA. Estrous cycle stage also influenced 55 kHz USVs. Fos responses were similar in males and females after AB or AL. Females engaged the gustatory cortex and ventral tegmental area (VTA) more than males during the BOT and males engaged the amygdala more than females in both the BOT and BLT. Network analysis of correlated Fos responses across brain regions identified two unique networks characterizing the BOT and BLT, in both of which the VTA played a central role. In situ hybridization with RNAscope identified a population of D1-receptor expressing cells in the CeA that responded to Boost® and D2 receptor-expressing cells that responded to LiCl. The present study suggests that males and females differentially process the affective valence of a stimulus to produce the same goal-directed behavior.

Increased Vocalization of Rats in Response to Ultrasonic Playback as a Sign of Hypervigilance Following Fear Conditioning

We investigated the effects of prior stress on rats' responses to 50-kHz (appetitive) and 22-kHz (aversive) ultrasonic playback. Rats were treated with 0, 1, 6 or 10 shocks (1 s, 1.0 mA each) and were exposed to playbacks the following day. Previous findings were confirmed: (i) rats moved faster during 50-kHz playback and slowed down after 22-kHz playback; (ii) they all approached the speaker, which was more pronounced during and following 50-kHz playback than 22-kHz playback; (iii) 50-kHz playback caused heart rate (HR) increase; 22-kHz playback caused HR decrease; (iv) the rats vocalized more often during and following 50-kHz playback than 22-kHz playback. The previous shock affected the rats such that singly-shocked rats showed lower HR throughout the experiment and a smaller HR response to 50-kHz playback compared to controls and other shocked groups. Interestingly, all pre-shocked rats showed higher locomotor activity during 50-kHz playback and a more significant decrease in activity following 22-kHz playback; they vocalized more often, their ultrasonic vocalizations (USV) were longer and at a higher frequency than those of the control animals. These last two observations could point to hypervigilance, a symptom of post-traumatic stress disorder (PTSD) in human patients. Increased vocalization may be a valuable measure of hypervigilance used for PTSD modeling.

Biological Functions of Rat Ultrasonic Vocalizations, Arousal Mechanisms, and Call Initiation

This review summarizes all reported and suspected functions of ultrasonic vocalizations in infant and adult rats. The review leads to the conclusion that all types of ultrasonic vocalizations subserving all functions are vocal expressions of emotional arousal initiated by the activity of the reticular core of the brainstem. The emotional arousal is dichotomic in nature and is initiated by two opposite-in-function ascending reticular systems that are separate from the cognitive reticular activating system. The mesolimbic cholinergic system initiates the aversive state of anxiety with concomitant emission of 22 kHz calls, while the mesolimbic dopaminergic system initiates the appetitive state of hedonia with concomitant emission of 50 kHz vocalizations. These two mutually exclusive arousal systems prepare the animal for two different behavioral outcomes. The transition from broadband infant isolation calls to the well-structured adult types of vocalizations is explained, and the social importance of adult rat vocal communication is emphasized. The association of 22 kHz and 50 kHz vocalizations with aversive and appetitive states, respectively, was utilized in numerous quantitatively measured preclinical models of physiological, psychological, neurological, neuropsychiatric, and neurodevelopmental investigations. The present review should help in understanding and the interpretation of these models in biomedical research.

The effect of playback of 22-kHz and 50-kHz ultrasonic vocalizations on rat behaviors assessed with a modified open-field test

Juvenile and adult rats emit two affectively different types of ultrasonic vocalizations (USVs), namely aversive 22-kHz and appetitive 50-kHz USVs. Aversive 22-kHz USVs are considered to be alarm calls that communicate negative affective states to conspecific receivers. Although the alarming effects of playback of 22-kHz USVs were reported recently, behavioral data showing those effects are still not abundant. Appetitive 50-kHz USVs are considered to communicate positive affective states to conspecific receivers, to pace and coordinate social behavior. In line with this, playback of 50-kHz USVs has been found to initiate behavioral activation and induce approach behavior in receiver rats. However, most of these playback studies have used male 50-kHz USVs; thus, it seems to remain unclear whether female 50-kHz USVs exert a similar social attractant effect on male rats. To investigate these issues, we performed modified open-field tests, during which USVs were continuously presented for 15 min to male receivers. In these tests, if negative affective changes are evoked in subject rats, the time spent in the open arena decreases, while the time spent on defensive behaviors increases. In contrast, when positive affective changes are evoked, the opposite phenomenon is observed. Playback of male aversive 22-kHz USVs induced anxiety-related defensive responses in receivers. However, playback of female appetitive frequency-modulated (FM) 50-kHz USVs increased opposite, appetitive pattern of exploratory behavior with increased exploration. The results indicate that playback of male aversive 22-kHz and female appetitive 50-kHz USVs might induce behavioral responses probably associated with negative and positive affective states in male rats, respectively, suggesting the validity of rat USVs as an animal model of vocal communication of emotion.

Linking Social Cognition to Learning and Memory

Many mammals have evolved to be social creatures. In humans, the ability to learn from others' experiences is essential to survival; and from an early age, individuals are surrounded by a social environment that helps them develop a variety of skills, such as walking, talking, and avoiding danger. Similarly, in rodents, behaviors, such as food preference, exploration of novel contexts, and social approach, can be learned through social interaction. Social encounters facilitate new learning and help modify preexisting memories throughout the lifespan of an organism. Moreover, social encounters can help buffer stress or the effects of negative memories, as well as extinguish maladaptive behaviors. Given the importance of such interactions, there has been increasing work studying social learning and applying its concepts in a wide range of fields, including psychotherapy and medical sociology. The process of social learning, including its neural and behavioral mechanisms, has also been a rapidly growing field of interest in neuroscience. However, the term "social learning" has been loosely applied to a variety of psychological phenomena, often without clear definition or delineations. Therefore, this review gives a definition for specific aspects of social learning, provides an overview of previous work at the circuit, systems, and behavioral levels, and finally, introduces new findings on the social modulation of learning. We contextualize such social processes in the brain both through the role of the hippocampus and its capacity to process "social engrams" as well as through the brainwide realization of social experiences. With the integration of new technologies, such as optogenetics, chemogenetics, and calcium imaging, manipulating social engrams will likely offer a novel therapeutic target to enhance the positive buffering effects of social experiences or to inhibit fear-inducing social stimuli in models of anxiety and post-traumatic stress disorder.

Playback of Alarm and Appetitive Calls Differentially Impacts Vocal, Heart-Rate, and Motor Response in Rats

Our rudimentary knowledge about rat intraspecific vocal system of information exchange is limited by experimental models of communication. Rats emit 50-kHz ultrasonic vocalizations in appetitive states and 22-kHz ones in aversive states. Both affective states influence heart rate. We propose a behavioral model employing exposure to pre-recorded playbacks in home-cage-like conditions. Fifty-kHz playbacks elicited the most vocalizations (>60 calls per minute, mostly of 50-kHz type), increased heart rate, and locomotor activity. In contrast, 22-kHz playback led to abrupt decrease in heart rate and locomotor activity. Observed effects were more pronounced in singly housed rats compared with the paired housed group; they were stronger when evoked by natural playback than by corresponding artificial tones. Finally, we also observed correlations between the number of vocalizations, heart rate levels, and locomotor activity. The correlations were especially strong in response to 50-kHz playback.

Suppression of ovarian hormones in adolescent rats has no effect on anxiety-like behaviour or c-fos activation in the amygdala

In humans, sex differences in mood disorders emerge during adolescence, with prevalence rates being consistently higher in females than males. It has been hypothesised that exposure to endogenous ovarian hormones during adolescence enhances the susceptibility of females to mood disorders from this stage of life onwards. However, experimental evidence in favour of this hypothesis is lacking. In the present study, we examined the long-term effects of suppressing adolescent gonadal hormone levels in a group of female Lister-hooded rats via administration of a gonadotrophin-releasing hormone antagonist (Antide; administered on postnatal day [PND] 28 and 42) compared to control females and males (n = 14 per group). We predicted that, in adulthood, Antide-treated female rats would exhibit more male-like behaviour than control females in novel environments (elevated-plus maze, open field and light-dark box), in response to novel objects and novel social partners, and in an acoustic startle task. Progesterone and luteinising hormone assays (which were conducted on blood samples collected on PND 55/56 and 69/70) confirmed that the hypothalamic-pituitary-gonadal axis was temporarily suppressed by Antide treatment. In addition, Antide-treated females were found to exhibit a modest pubertal delay, as measured by vaginal opening, which was comparable in length to the pubertal delay that has been induced by adolescent exposure to alcohol or stress in previous studies of female rats. However, Antide-treated females did not substantially differ from control females on any of the behavioural tests, despite the evidence for predicted sex differences in some measures. Following the acoustic startle response task, all subjects were culled and perfused, and c-Fos staining was conducted in the medial and basolateral amygdala, with the results showing no significant differences in cell counts between the groups. These findings suggest that ovarian hormone exposure during adolescence does not have long-term effects on anxiety-related responses in female rats.

Chemogenetic manipulation of the bed nucleus of the stria terminalis counteracts social behavioral deficits induced by early life stress in C57BL/6J mice

Trauma during critical periods of development can induce long-lasting adverse effects. To study neural aberrations resulting from early life stress (ELS), many studies utilize rodent maternal separation, whereby pups are intermittently deprived of maternal care necessary for proper development. This can produce adulthood behavioral deficits related to anxiety, reward, and social behavior. The bed nucleus of the stria terminalis (BNST) encodes aspects of anxiety-like and social behaviors, and also undergoes developmental maturation during the early postnatal period, rendering it vulnerable to effects of ELS. Mice underwent maternal separation (separation 4 hr/day during postnatal day (PD)2-5 and 8 hr/day on PD6-16) with early weaning on PD17, which induced behavioral deficits in adulthood performance on two-part social interaction task designed to test social motivation (choice between a same-sex novel conspecific or an empty cup) and social novelty preference (choice between the original-novel conspecific vs. a new-novel conspecific). We used chemogenetics to non-selectively silence or activate neurons in the BNST to examine its role in social motivation and social novelty preference, in mice with or without the history of ELS. Manipulation of BNST produced differing social behavior effects in non-stressed versus ELS mice; social motivation was decreased in non-stressed mice following BNST activation, but unchanged following BNST silencing, while ELS mice showed no change in social behavior after BNST activation, but exhibited enhancement of social motivation-for which they were deficient prior-following BNST silencing. Findings emphasize the BNST as a potential therapeutic target for social anxiety disorders instigated by childhood trauma.

Sex-dependent effects of Cacna1c haploinsufficiency on behavioral inhibition evoked by conspecific alarm signals in rats

Deficits in processing social signals leads to reduced social functioning and is typically associated with neuropsychiatric disorders, including autism spectrum disorder, schizophrenia, and major depressive disorder. The cross-disorder risk gene CACNA1C is implicated in the etiology of all of these disorders and single-nucleotide polymorphisms within CACNA1C are ranked among the best replicated and most robust genetic findings from genome-wide association studies in psychiatry. Rats are highly social, live in large social groups, and communicate through ultrasonic vocalizations (USV), with low-frequency 22-kHz USV emitted in dangerous and often life-threating situations, such as predator exposure, serving an alarming function. In the present study, we applied an alarm 22-kHz USV playback paradigm to investigate the role of Cacna1c in socio-affective information processing in rats. Specifically, we assessed behavioral inhibition evoked by 22-kHz USV in constitutive heterozygous Cacna1c^+/- females and males, as compared to wildtype Cacna1c^+/+ littermate controls. To probe specificity, two sets of alarm 22-kHz USV were presented, i.e. 22-kHz USV elicited by predator urine exposure and 22-kHz USV emitted during a retention test on learned fear, together with acoustic control stimuli. Our results show that behavioral inhibition evoked by playback of alarm 22-kHz USV is robust and occurs in response to both sets, yet is modulated by Cacna1c in a sex-dependent manner. In male but not female rats, Cacna1c haploinsufficiency led to less pronounced and less specific behavioral inhibition, supporting the idea that Cacna1c haploinsufficiency results in a lower motivation and/or diminished capability to display appropriate responses to important socio-affective communication signals.

The Comparison of a New Ultrasound-Induced Depression Model to the Chronic Mild Stress Paradigm

Willner’s “chronic mild stress” (CMS) model is a globally recognized and most commonly used depression model. A depression model induced by ultrasonic exposure of variable frequencies has been created in our laboratory. This article compares two models of the depressive-like state according to three validity criteria. Face validity has been demonstrated in sucrose preference test, Porsolt test, social interest, open field and the Morris water maze. Rats after ultrasound impact have more pronounced anhedonia and social isolation. The construct validity has been proven due to increased levels of corticosterone, epinephrine and norepinephrine and reduced levels of dopamine and some of its metabolites in rat plasma after ultrasound exposure. Predictive validity has been described previously, where the therapeutic effects of various classes of antidepressants have been shown. Our study has demonstrated that the ultrasound-induced depression model is suitable, such as the generally accepted CMS protocol, and meets all required validity criteria. The model presented in this article might help to study pathogenetic mechanisms of depressive disorders, as well as to test promising methods of depression treatment.