Opposite effects of short- and long-duration isolation on ultrasonic vocalization, startle and prepulse inhibition in rats

Altered vocal communication in adult vasopressin-deficient Brattleboro rats

The neuropeptide, arginine vasopressin (AVP), has been implicated in social communication across a diverse array of species. Many rodents communicate basic behavioral states with negative versus positive valence through high-pitched vocalizations above the human hearing range (ultrasonic vocalizations; USVs). Previous studies have found that Brattleboro (Bratt) rats, which have a mutation in the Avp gene, exhibit deficits in their USVs from the early postnatal period through adolescence, but the magnitude of this effect appears to decrease from the juvenile to adolescent phase. The present study tested whether Bratt rats continue to exhibit USV deficits in adulthood. USVs of adult male and female Bratt and wild type (WT) rats were recorded in two contexts: a novel environment (empty arena) and a social context (arena filled with bedding soiled by same-sex conspecifics). The number, frequency, and duration of 50 kHz USVs were quantified by DeepSqueak after validation with manual scoring. Twenty-two kHz measures were quantified by manual scoring because DeepSqueak failed to accurately detect USVs in this frequency range. Adult Bratt rats did not exhibit deficits in the number of 50 kHz USVs: male Bratt rats emitted similar 50 kHz USVs as male WT rats, whereas female Bratt rats emitted more USVs than female WT rats. USV frequency and duration were altered in adult Bratt rats, but in a context-dependent manner. Twenty-two kHz USVs were less affected by the Bratt mutation. The present study demonstrates how chronic AVP deficiency impacts social communication across the lifespan. The present findings reveal a complex role for AVP in vocal communication, whereby disruption to the Avp gene leads to sex-, context-, and developmental phase-specific effects on the quantity and spectrotemporal characteristics of rat USVs.

Stress-Induced Ultrasonic Vocalization in Laboratory Rats and Mice: A Scoping Review

Introduction: Ultrasonic vocalization (USV) can indicate affective states-including psychosocial stress-in mice and rats. However, stress-induced USV changes could be confounded by laboratory experimental variables such as the type of behavioral stress paradigm, the elicitation method, rodent strain, etc. We sought to provide a review of the current literature to delineate how psychosocial stress-altered rodent USVs may be affected by factors of age, sex, strain, species, elicitation paradigm, and stressor. Methods: We used PubMed, Scopus (Elsevier), PsycINFO (EBSCO), and the following Web of Science (Clarivate) databases: Biological Abstracts, CAB Abstracts, Science Citation Index-Expanded, and Emerging Sources Citation Index. The studies identified by our search strategy were independently screened by two authors with the following inclusion criteria: peer-reviewed, in English, reported original data, and described USV in response to stress in rats or mice. The data extracted included USV acoustic parameters (mean peak frequency and mean amplitude (loudness)), details of the stress and USV elicitation paradigms, rodent species, age, and sex variables. Results: The following screening of 5309 titles/abstracts and 687 full-text articles revealed 148 articles. Footshock (20%), cold exposure (14%), and maternal separation (23.5%) were the most commonly used stress paradigms (duration and type of stressor varied across studies), with the total number of USV calls being the most commonly reported acoustic outcome. In rats, 121 articles described stress-altered USVs, while 25 studies reported the same in mice, and two reported multiple rodent species (rats and mice, alongside other rodent species such as gerbils). With respect to stress-altered USV changes with age, mice and rats increase USV rates after birth, with a peak around 6 to 10 days, and decrease USVs until weanling age. Of the five studies that reported sex-related differences in stress-induced USVs, females had an increased number of calls and lower average peak frequency in response to stress when compared to males. Only two to four studies reported strain-related differences in stress-induced vocalizations in rats and mice, respectively. Conclusions: The data from this review lay the groundwork for better understanding rodent USVs in response to psychosocial stress with effects of elicitation paradigm, stressor, age, and sex.

Solitude and serotonin: juvenile isolation alters the covariation between social behavior and cFos expression by serotonergic neurons

Variation in the mutual responsiveness of social partners to each other can be reflected in behavioral suites that covary with neural activity in ways that track the salience or valence of interactions. Juvenile social isolation alters social behavior and neural activity during social interaction, but whether and how it alters the covariation between behavior and neural activity has not been as well explored. To address this issue, four classes of experimental subjects: isolated males, socially housed males, isolated females, and socially housed females, were paired with an opposite-sex social partner that had been socially housed. Social behaviors and c-Fos expression in the serotonergic dorsal raphe nucleus (DRN) were then measured in subjects following the social interactions. Relative to social housing, postweaning isolation led to a decrease in the density of neurons double-labeled for tryptophan hydroxylase and c-Fos in the dorsomedial subdivision of the DRN, regardless of sex. Vocal and non-vocal behaviors were also affected by isolation. In interactions with isolated males, both ultrasonic vocalization (USVs) and broadband vocalizations (squeaks) increased in conjunction with greater male investigation of females. Neural and behavioral measures also correlated with each other. In the isolated male group, the density of double-labeled neurons in the dorsomedial DRN was negatively correlated with USV production and positively correlated with a principal component of non-vocal behavior corresponding to greater defensive kicking by females and less investigation and mounting behavior. This correlation was reversed in direction for socially housed males, and for isolated males versus isolated females. These findings confirm that the dynamics of social interactions are reflected in c-Fos activation in the dorsomedial DRN, and suggest an altered responsiveness of serotonergic neurons to social interaction following social isolation in males, in parallel with an altered male response to female cues.

Intracerebral injection of R-(-)-Apomorphine into the nucleus accumbens decreased carbachol-induced 22-kHz ultrasonic vocalizations in rats

Rats can produce ultrasonic vocalizations (USVs) in a variety of different contexts that signal their emotional state to conspecifics. Under distress, rats can emit 22-kHz USVs, while during positive pro-social interactions rats can emit frequency-modulated (FM) 50-kHz USVs. It has been previously reported that rats with increasing emission of FM 50-kHz USVs in anticipation of rewarding electrical stimulation or positive pro-social interaction decrease the number of emitted 22-kHz USVs. The purpose of the present investigation was to determine, in a pharmacological-behavioural experiment, if the positive emotional arousal of the rat indexed by the number of emitted FM 50-kHz USVs can decrease the magnitude of a subsequent negative emotional state indexed by the emission of 22-kHz USVs. To induce a positive emotional state, an intracerebral injection of a known D₁/D₂ agonist R-(-)-apomorphine (3.0 μg/0.3 μl) into the medial nucleus accumbens shell was used, while a negative emotional state was induced by intracerebral injection of carbachol (1.0 μg/0.3 μl), a known broad-spectrum muscarinic agonist, into the anterior hypothalamic-medial preoptic area. Our results demonstrated that initiation of a positive emotional state was able to significantly decrease the magnitude of subsequently expressed negative emotional state measured by the number of emitted 22-kHz USVs. The results suggest the neurobiological substrates that initiate positive emotional state indirectly antagonize the brain regions that initiate negative emotional states.

Ultrasonic vocalizations as a tool in studying emotional states in rodent models of social behavior and brain disease

Rodents emit ultrasonic vocalizations (USVs) to communicate the presence of positive or negative emotional states and to coordinate social interactions. On this basis, USVs are increasingly being used as a behavioral readout in rodent studies of affect, motivation and social behavior. Notably, several investigations have demonstrated that rodents emit USVs when tested in experimental paradigms that are used in preclinical studies of psychiatric and neurological diseases. Moreover, it has been shown that calling behavior may be influenced by genetic and/or environmental factors (i.e., stress), early rearing conditions that have been implicated in brain disease, as well as psychoactive drugs. Hence, measuring USV emissions has emerged as a useful tool in studying the mechanisms that underlie the emotional disturbances featuring certain brain diseases, as well as in the development of suited pharmacological therapies. This review provides an overview of the behavioral significance of USV emissions and describes the contexts that promote calling behavior in rats and mice. Moreover, the review summarizes the current evidence concerning the use of USVs as a marker of affect in rat and mouse models of sociability, psychiatric diseases and neurological diseases, and discusses the strengths and current limitations of using USVs as a behavioral readout in rodent studies of emotional behavior. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

Intranasal administration of dopamine attenuates unconditioned fear in that it reduces restraint-induced ultrasound vocalizations and escape from bright light

BACKGROUND

Although substantial evidence suggests that dopamine (DA) enhances conditioned fear responses, few studies have examined the role of DA in unconditioned fear states. Whereas DA does not cross the blood-brain barrier, intranasally-applied dopamine reaches the brain directly via the nose-brain pathways in rodents, providing an alternative means of targeting DA receptors. Intranasal dopamine (IN-DA) has been demonstrated to bind to DA transporters and to increase extracellular DA in the striatum as well as having memory-promoting effects in rats. The purpose of this study was to examine the influence of IN-DA in three tests of fear/anxiety.

METHODS

The three doses of DA hydrochloride (0.03, 0.3, or 1 mg/kg) were applied in a viscous castor oil gel in a volume of 5 µl to each of both nostrils of adult Wistar rats prior to testing of (a) escape from a bright light, using a two-chamber procedure, (b) restraint-induced 22 kHz ultrasound vocalizations (USVs), and (c) exploratory behavior in the elevated plus-maze (EPM).

RESULTS

IN-DA dose-dependently reduced escape from bright light and the number of USV responses to restraint. It had no influence on the exploratory behavior in the EPM.

CONCLUSIONS

IN-DA application reduced escape behavior in two tests of unconditioned fear (escape from bright light and USV response to immobilization). These findings may be interpreted in light of the known antidepressant action of IN-DA and DA reuptake blockers. The results also confirm the promise of the nasal route as an alternative means for targeting the brain's dopaminergic receptors with DA.

Acoustic Communication in Rats: Effects of Social Experiences on Ultrasonic Vocalizations as Socio-affective Signals

Ultrasonic vocalizations (USV) serve important communicative functions as socio-affective signals in rats. In aversive situations, such as inter-male aggression and predator exposure, 22-kHz USV are emitted. They likely function as appeasement signals during fighting and/or as alarm calls to warn conspecifics. In appetitive situations, 50-kHz USV are uttered, most notably during social interactions, such as rough-and-tumble play and mating. It is believed that they fulfill an affiliative function as social contact calls. Social experiences or their lack, such as social isolation, can have profound impact on the emission of 22- and 50-kHz USV by the sender in later life, albeit direction and strength of observed effects vary, with time point of occurrence and duration being critical determinants. Little, however, is known about how social experiences affect the behavioral responses evoked by 22- and 50-kHz USV in the recipient. By means of our 50-kHz USV radial maze playback paradigm, we recently showed that the behavioral response elicited in the recipient is affected by post-weaning social isolation. Rats exposed to four weeks of isolation during the rough-and-tumble play period did not display social approach behavior toward 50-kHz USV but some signs of social avoidance. We further found that physical environmental enrichment providing minimal opportunities for social interactions has similar detrimental effects. Together, this indicates that social experiences can affect socio-affective communication in rodents, both at the level of sender and recipient. Deficits seen following post-weaning social isolation or physical environmental enrichment might be useful to model aspects of neurodevelopmental disorders characterized by social and communication deficits, such as autism and schizophrenia.

Ameliorative effects of brief daily periods of social interaction on isolation-induced behavioral and hormonal alterations

The present study investigated the effects of brief daily periods of social interaction on social-isolation-induced behavioral and hormonal alterations and deficits. Adult male Wistar rats were allocated to one of three housing conditions: 1) social housing (two per cage); 2) social isolation (one per cage); or partial social isolation (one per cage with access to another male rat for 60 min/day). After 14 days in these different housing conditions, the animals were subjected to various behavioral tests, including sucrose preference test, acoustic startle response, two-way active shuttle avoidance, pre-pulse inhibition, open field, cooperation learning task, and levels of corticosterone. Results revealed that social isolation had a substantial impact on rats' performance on most behavioral tests as well as on their corticosterone levels. Importantly, however, the results clearly demonstrate that allowing otherwise isolated animals to have a brief (60 min) daily social contact with another rat to a great extent abolishes or ameliorates most of the isolation-induced behavioral and hormonal alterations. Hence, providing isolated animals with brief daily periods of social contact may be used as a "preventive treatment" in order to protect them from the deleterious effects of isolation.

Risk assessment behaviors associated with corticosterone trigger the defense reaction to social isolation in rats: role of the anterior cingulate cortex

The extent to which the hypothalamic-pituitary-adrenal axis is activated by short-term and long-term consequences of stress is still open to investigation. This study aimed to determine (i) the correlation between plasma corticosterone and exploratory behavior exhibited by rats subjected to the elevated plus maze (EPM) following different periods of social isolation, (ii) the effects of the corticosterone synthesis blocker, metyrapone, on the behavioral consequences of isolation, and (iii) whether corticosterone produces its effects through an action on the anterior cingulate cortex, area 1 (Cg1). Rats were subjected to 30-min, 2-h, 24-h, or 7-day isolation periods before EPM exposure and plasma corticosterone assessments. Isolation for longer periods of time produced greater anxiogenic-like effects on the EPM. However, stretched attend posture (SAP) and plasma corticosterone concentrations were increased significantly after 30 min of isolation. Among all of the behavioral categories measured in the EPM, only SAP positively correlated with plasma corticosterone. Metyrapone injected prior to the 24 h isolation period reversed the anxiogenic effects of isolation. Moreover, corticosterone injected into the Cg1 produced a selective increase in SAP. These findings indicate that risk assessment behavior induced by the action of corticosterone on Cg1 neurons initiates a cascade of defensive responses during exposure to stressors.

On the relationships between ultrasonic calling and anxiety-related behavior in rats

In the present review, the phenomenon of ultrasonic vocalization in rats will be outlined, including the three classes of vocalizations, namely 40-kHz calls of pups, and 22- and 50-kHz calls of juvenile and adult rats, their general relevance to behavioral neuroscience, and their special relevance to research on anxiety, fear, and defense mechanisms. Here, the emphasis will be placed on 40- and 22-kHz calls, since they are typical for various situations with aversive properties. Among other topics, we will discuss whether such behavioral signals can index a certain affective state, and how these signals can be used in social neuroscience, especially with respect to communication. Furthermore, we will address the phenomenon of inter-individual variability in ultrasonic calling and what we currently know about the mechanisms, which may determine such variability. Finally, we will address the current knowledge on the neural and pharmacological mechanisms underlying 22-kHz ultrasonic vocalization, which show a substantial overlap with mechanisms known from other research on fear and anxiety, such as those involving the periaqueductal gray or the amygdala.

Involvement of midbrain tectum neurokinin-mediated mechanisms in fear and anxiety

Electrical stimulation of midbrain tectum structures, particularly the dorsal periaqueductal gray (dPAG) and inferior colliculus (IC), produces defensive responses, such as freezing and escape behavior. Freezing also ensues after termination of dPAG stimulation (post-stimulation freezing). These defensive reaction responses are critically mediated by _Y-aminobutyric acid and 5-hydroxytryptamine mechanisms in the midbrain tectum. Neurokinins (NKs) also play a role in the mediation of dPAG stimulation-evoked fear, but how NK receptors are involved in the global processing and expression of fear at the level of the midbrain tectum is yet unclear. The present study investigated the role of NK-1 receptors in unconditioned defensive behavior induced by electrical stimulation of the dPAG and IC of male Wistar rats. Spantide (100 pmol/0.2 µL), a selective NK-1 antagonist, injected into these midbrain structures had anti-aversive effects on defensive responses and distress ultrasonic vocalizations induced by stimulation of the dPAG but not of the IC. Moreover, intra-dPAG injections of spantide did not influence post-stimulation freezing or alter exploratory behavior in rats subjected to the elevated plus maze. These results suggest that NK-1 receptors are mainly involved in the mediation of defensive behavior organized in the dPAG. Dorsal periaqueductal gray-evoked post-stimulation freezing was not affected by intra-dPAG injections of spantide, suggesting that NK-1-mediated mechanisms are only involved in the output mechanisms of defensive behavior and not involved in the processing of ascending aversive information from the dPAG.

Lipopolysaccharide-induced sickness behaviour evaluated in different models of anxiety and innate fear in rats

The fact that there is a complex and bidirectional communication between the immune and nervous systems has been well demonstrated. Lipopolysaccharide (LPS), a component of gram-negative bacteria, is widely used to systematically stimulate the immune system and generate profound physiological and behavioural changes, also known as 'sickness behaviour' (e.g. anhedonia, lethargy, loss of appetite, anxiety, sleepiness). Different ethological tools have been used to analyse the behavioural modifications induced by LPS; however, many researchers analysed only individual tests, a single LPS dose or a unique ethological parameter, thus leading to disagreements regarding the data. In the present study, we investigated the effects of different doses of LPS (10, 50, 200 and 500 μg/kg, i.p.) in young male Wistar rats (weighing 180-200 g; 8-9 weeks old) on the ethological and spatiotemporal parameters of the elevated plus maze, light-dark box, elevated T maze, open-field tests and emission of ultrasound vocalizations. There was a dose-dependent increase in anxiety-like behaviours caused by LPS, forming an inverted U curve peaked at LPS 200 μg/kg dose. However, these anxiety-like behaviours were detected only by complementary ethological analysis (stretching, grooming, immobility responses and alarm calls), and these reactions seem to be a very sensitive tool in assessing the first signs of sickness behaviour. In summary, the present work clearly showed that there are resting and alertness reactions induced by opposite neuroimmune mechanisms (neuroimmune bias) that could lead to anxiety behaviours, suggesting that misunderstanding data could occur when only few ethological variables or single doses of LPS are analysed. Finally, it is hypothesized that this bias is an evolutionary tool that increases animals' security while the body recovers from a systemic infection.

Neurobiology of aversive states

Hoebel and colleagues are often known as students of reward and how it is coded in the CNS. This article, however, attempts to focus on the significant advances by Hoebel and others in dissecting out behavioral components of distinct aversive states and in understanding the neurobiology of aversion and the link between aversive states and addictive behaviors. Reward and aversion are not necessarily dichotomous and may reflect an affective continuum contingent upon environmental conditions. Descriptive and mechanistic studies pioneered by Bart Hoebel have demonstrated that the shift in the reward-aversion spectrum may be, in part, a result of changes in central dopamine/acetylcholine ratio, particularly in the nucleus accumbens. The path to aversion appears to include a specific neurochemical signature: reduced dopamine release and increased acetylcholine release in "reward centers" of the brain. Opioid receptors may have a neuromodulatory role on both of these neurotransmitters.

Evidence for mediation of nociception by injection of the NK-3 receptor agonist, senktide, into the dorsal periaqueductal gray of rats

RATIONALE

Ultrasound vocalizations (USVs) at approximately 22 kHz are usual components of the defensive response of rats. However, depending on the neural substrate that is activated, such as the dorsal periaqueductal gray (dPAG), USV emissions may be reduced. Activation of neurokinin-1 (NK-1)-mediated mechanisms of the dPAG causes analgesia, reduced 22 kHz USVs, and anxiogenic-like effects in rats exposed to the elevated plus maze (EPM). Involvement of other types of neurokinin receptors in this activation has not yet been evaluated.

OBJECTIVES

The present study examined whether local injections of the selective NK-3 agonist senktide (1-100 pmol/0.2 microL) into the dPAG can (1) cause anxiogenic effects in the EPM, (2) influence novelty-induced 22 kHz USVs, or (3) change nociceptive reactivity in the tail-flick test.

RESULTS

Senktide elicited a significant increase in exploratory behavior, an effect accompanied by hyperalgesia and an increase in the number of 22 kHz USVs. The nociceptive effects, increased locomotor activity, and USV emissions elicited by local injections of senktide (50 pmol/0.2 microL) were reduced by prior injections of the selective NK-3 receptor antagonist SB222200 (50 pmol/0.2 microL) into the dPAG.

CONCLUSIONS

These findings show that NK-3 receptors in the dPAG mediate nociceptive responses in this area, contrasting with the known fear-related processes mediated by NK-1 receptors in the dPAG. Both hyperalgesia and fear-related processes are accompanied by emissions of 22 kHz USVs.

Ultrasonic vocalisations explain unexpected effects on pre-pulse inhibition responses in rats chronically pre-treated with phencyclidine

Deficits in pre-pulse inhibition (PPI-indicative of psychosis in humans) can be replicated in rats using the NMDA receptor antagonist phencyclidine (PCP). Ultrasonic vocalisations (USVs) produced by rats in response to acoustic startle are indicative of heightened anxiety; here we tested the predictive validity of USVs as an indicator of PPI. Male juvenile Sprague-Dawley rats (n=10) were treated for 14 days with either PCP (5mg/kg i.p.) or saline controls (1 ml/kg i.p.). PPI responses and USVs were recorded on days 16 and 19. PCP-treated rats showed decreased PPI performance on day 16 compared to controls; an observation that was unexpectedly reversed on day 19. Call parameters indicated that both treatment groups experienced similar levels of anxiety in response to the PPI paradigm on day 16. On day 19, the controls showed increased call duration and latency to onset (LtO) of calling, but decreased in the total number of calls produced compared to day 16. The calling period was significantly reduced compared to PCP-treated animals on say 19, whilst the LtO and duration were significantly increased. These changes were considered indicative of heightened levels of anxiety, most likely due to inadvertent fear conditioning (supported by reduced PPI performance) acquired during PPI testing. In contrast, the stability of USV characteristics emitted by PCP treated animals likely signified the detrimental effects of chronic PCP treatment on working memory. These results suggest that USVs are a valuable additional measure during PPI testing, helping to explain the unexpected results from our control group.

Anxiogenic effects of activation of NK-1 receptors of the dorsal periaqueductal gray as assessed by the elevated plus-maze, ultrasound vocalizations and tail-flick tests

Ultrasound vocalizations (USVs) known as 22kHz are usual components of the defensive responses of rats exposed to threatening conditions. The amount of emission of 22kHz USVs depends on the intensity of the aversive stimuli. While moderate fear causes an anxiolytic-sensitive enhancement of the defensive responses, high fear tended to reduce the defensive performance of the animals to aversive stimuli. The dorsal periaqueductal gray (dPAG) is an important vocal center and a crucial structure for the expression of defensive responses. Substance P (SP) is involved in the modulation of the defensive response at this midbrain level, but the type of neurokinin receptors involved in this action is not completely understood. In this study we examined whether local injections of the selective NK-1 agonist SAR-MET-SP (10-100 pmol/0.2microL) into the dPAG (i) cause anxiogenic effects in the elevated plus-maze (EPM) (Exp. I), (ii) influence the novelty-induced 22kHz USVs recorded within the frequency range of 20-26kHz (Exp. II) and (iii) change the nociceptive reactivity to heat applied to the rat's tail (Exp III). The data obtained showed that SAR-MET-SP elicited significant "anxiety-like" behaviors, as revealed by the decrease in the number of entries into and time spent onto the open arms of the EPM. These anxiogenic effects were accompanied with antinociception and disruption of the novelty-induced increase in the number and duration of 22kHz USVs. These findings are in agreement with the notion that NK-1 receptors of the dPAG may be an important neurochemical target for new selective drugs aimed at the control of pathological anxiety states.

Substance P injected into the dorsal periaqueductal gray causes anxiogenic effects similar to the long-term isolation as assessed by ultrasound vocalizations measurements

Housing conditions change the emotional state of the animals. Ultrasound vocalizations (USVs) termed as 22 kHz are the usual components of the defensive responses of rats exposed to threatening conditions such as isolation. The amount of emission of 22 kHz USVs depends on the intensity of the aversive stimuli. While short periods of isolation caused an anxiolytic-sensitive enhancement of the defensive responses, long-term isolation tended to reduce the defensive performance of the animals to aversive stimuli. The dorsal periaqueductal gray (dPAG) is an important vocal center and a crucial structure for the expression of defensive response. While it has been shown that Substance P (SP) at this midbrain level is involved in the modulation of the defensive response, its role in the emission of ultrasound vocalizations has not been evaluated. In this study we examined whether the resocialization and local injections of SP into the dPAG have an influence on the isolation-induced 22 kHz USVs recorded within the frequency range of 18-26 kHz. Rats isolated for 1 day showed a significant increase in the number and duration of USVs, which were reversed by resocialization. On the other hand, 2-week isolation reduced the number and duration of 22 kHz USVs, which could not be reversed by resocialization. SP injections into the dPAG (35 pmol/0.2 microL) caused a reduction in the 22 kHz USVs. Pretreatment with the NK-1 receptor antagonist spantide (100 pmol/0.2 microL) blocked these effects but exhibited no effect when given alone. These findings suggest that 1-day and 2-week isolation recruit distinct brain defensive systems. Also, in agreement with the notion that intense fear is associated with the neural substrates of fear of the dPAG, activation of NK-1 receptors of this midbrain structure reduces the 22 kHz USVs.