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

Crocin (bioactive compound of Crocus sativus L.) potently restores REM sleep deprivation-induced manic- and obsessive-compulsive-like behaviors in female rats

Rapid-eye movement (REM) sleep deprivation (SD) can induce manic-like behaviors including hyperlocomotion. On the other hand, crocin (one of the main compounds of Crocus sativus L. or Saffron) may be beneficial in the improvement of mental and cognitive dysfunctions. Also, crocin can restore the deleterious effects of SD on mental and cognitive processes. In this study, we investigated the effect of REM SD on female rats' behaviors including depression- and anxiety-like behaviors, locomotion, pain perception, and obsessive-compulsive-like behavior, and also, the potential effect of crocin on REM SD effects. We used female rats because evidence on the role of REM SD in modulating psychological and behavioral functions of female (but not male) rats is limited. REM SD was induced for 14 days (6h/day), and crocin (25, 50, and 75 mg/kg) was injected intraperitoneally. Open field test, forced swim test, hot plate test, and marble burying test were used to assess rats' behaviors. The results showed REM SD-induced manic-like behavior (hyperlocomotion). Also, REM SD rats showed decreased anxiety- and depression-like behavior, pain subthreshold (the duration it takes for the rat to feel pain), and showed obsessive compulsive-like behavior. However, crocin at all doses partially or fully reversed REM SD-induced behavioral changes. In conclusion, our results suggested the possible comorbidity of OCD and REM SD-induced manic-like behavior in female rats or the potential role of REM SD in the etiology of OCD, although more studies are needed. In contrast, crocin can be a possible therapeutic choice for decreasing manic-like behaviors.

Too little or too much: nonlinear relationship between sleep duration and daily affective well-being in depressed adults

BACKGROUND

In addition to having higher negative affect and lower positive affect overall, depressed individuals exhibit heightened affective reactivity to external stimuli than non-depressed individuals. Sleep may contribute to day-to-day fluctuations in depressed individuals, given that sleep disturbance is a common symptom of depression. Yet, little is known about changes in daily affect as a function of nightly sleep duration in depressed adults and non-depressed adults. The current study examined whether and how naturally-occurring sleep duration is associated with negative and positive affect, and how these associations differ between depressed vs. non-depressed adults.

METHODS

Data were drawn from the second wave of the National Study of Daily Experiences (NSDE), a daily diary project of the Midlife in the United States (MIDUS) study. The sample of 2,012 adults (Mage=56.5; 57% female; 84% white) completed eight-day diary interviews via telephone on their daily experiences including nightly sleep duration and negative and positive affect. They also completed assessments of the Composite International Diagnostic Interview-Short form, and depressed status was determined based on DSM-III. Multilevel regression models with linear, quadratic, and cubic terms of sleep duration examined the nonlinear relationship between nightly sleep duration and daily affect. Interaction terms with depression status were added to examine differences between depressed and non-depressed adults.

RESULTS

Depressed adults exhibited significant and greater fluctuations in daily affect as a function of nightly sleep duration than non-depressed adults. Specifically, the degree of decrease in positive affect and increase in negative affect was greater when depressed adults slept 2 or more hours less or longer than their usual sleep hours. Non-depressed adults exhibited relatively stable daily affect regardless of their nightly sleep hours.

CONCLUSIONS

Sleep duration is nonlinearly associated with affect in daily lives of depressed adults, highlighting that both having too little sleep and excessive sleep are associated with adverse daily affective well-being. Implementing sleep interventions to promote an appropriate sleep duration may help improve daily affect among depressed adults.

Divergent Acute and Enduring Changes in 50-kHz Ultrasonic Vocalizations in Rats Repeatedly Treated With Amphetamine and Dopaminergic Antagonists: New Insights on the Role of Dopamine in Calling Behavior

BACKGROUND

Rats emit 50-kHz ultrasonic vocalizations (USVs) in response to nonpharmacological and pharmacological stimuli, with addictive psychostimulants being the most effective drugs that elicit calling behavior in rats. Earlier investigations found that dopamine D1-like and D2-like receptors modulate the emission of 50-kHz USVs stimulated in rats by the acute administration of addictive psychostimulants. Conversely, information is lacking on how dopamine D1-like and D2-like receptors modulate calling behavior in rats that are repeatedly treated with addictive psychostimulants.

METHODS

We evaluated the emission of 50-kHz USVs in rats repeatedly treated (×5 on alternate days) with amphetamine (1 mg/kg, i.p.) either alone or together with (1) SCH 23390 (0.1-1 mg/kg, s.c.), a dopamine D1 receptor antagonist; (2) raclopride (0.3-1 mg/kg, s.c.), a selective dopamine D2 receptor antagonist; or (3) a combination of SCH 23390 and raclopride (0.1 + 0.3 mg/kg, s.c.). Calling behavior of rats was recorded following pharmacological treatment, as well as in response to the presentation of amphetamine-paired cues and to amphetamine challenge (both performed 7 days after treatment discontinuation).

RESULTS

Amphetamine-treated rats displayed a sensitized 50-kHz USV emission during repeated treatment, as well as marked calling behavior in response to amphetamine-paired cues and to amphetamine challenge. Antagonism of D1 or D2 receptors either significantly suppressed or attenuated the emission of 50-kHz USVs in amphetamine-treated rats, with a maximal effect after synergistic antagonism of both receptors.

CONCLUSIONS

These results shed further light on how dopamine transmission modulates the emission of 50-kHz USVs in rats treated with psychoactive drugs.

Joyful by nature: approaches to investigate the evolution and function of joy in non-human animals

The nature and evolution of positive emotion is a major question remaining unanswered in science and philosophy. The study of feelings and emotions in humans and animals is dominated by discussion of affective states that have negative valence. Given the clinical and social significance of negative affect, such as depression, it is unsurprising that these emotions have received more attention from scientists. Compared to negative emotions, such as fear that leads to fleeing or avoidance, positive emotions are less likely to result in specific, identifiable, behaviours being expressed by an animal. This makes it particularly challenging to quantify and study positive affect. However, bursts of intense positive emotion (joy) are more likely to be accompanied by externally visible markers, like vocalisations or movement patterns, which make it more amenable to scientific study and more resilient to concerns about anthropomorphism. We define joy as intense, brief, and event-driven (i.e. a response to something), which permits investigation into how animals react to a variety of situations that would provoke joy in humans. This means that behavioural correlates of joy are measurable, either through newly discovered 'laughter' vocalisations, increases in play behaviour, or reactions to cognitive bias tests that can be used across species. There are a range of potential situations that cause joy in humans that have not been studied in other animals, such as whether animals feel joy on sunny days, when they accomplish a difficult feat, or when they are reunited with a familiar companion after a prolonged absence. Observations of species-specific calls and play behaviour can be combined with biometric markers and reactions to ambiguous stimuli in order to enable comparisons of affect between phylogenetically distant taxonomic groups. Identifying positive affect is also important for animal welfare because knowledge of positive emotional states would allow us to monitor animal well-being better. Additionally, measuring if phylogenetically and ecologically distant animals play more, laugh more, or act more optimistically after certain kinds of experiences will also provide insight into the mechanisms underlying the evolution of joy and other positive emotions, and potentially even into the evolution of consciousness.

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.

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.

Sounding the Alarm: Sex Differences in Rat Ultrasonic Vocalizations during Pavlovian Fear Conditioning and Extinction

Pavlovian fear conditioning is a prevalent tool in the study of aversive learning, which is a key component of stress-related psychiatric disorders. Adult rats can exhibit various threat-related behaviors, including freezing, motor responses, and ultrasonic vocalizations (USVs). While these responses can all signal aversion, we know little about how they relate to one another. Here we characterize USVs emitted by male and female rats during cued fear acquisition and extinction, and assess the relationship between different threat-related behaviors. We found that males consistently emitted >22 kHz calls (referred to here as "alarm calls") than females, and that alarm call frequency in males, but not females, related to the intensity of the shock stimulus. Interestingly, 25% of males and 45% of females did not emit any alarm calls at all. Males that did make alarm calls had significantly higher levels of freezing than males who did not, while no differences in freezing were observed between female Alarm callers and Non-alarm callers. Alarm call emission was also affected by the predictability of the shock; when unpaired from a tone cue, both males and females started emitting alarm calls significantly later. During extinction learning and retrieval sessions, males were again more likely than females to emit alarm calls, which followed an extinction-like reduction in frequency. Collectively these data suggest sex dependence in how behavioral readouts relate to innate and conditioned threat responses. Importantly, we suggest that the same behaviors can signal sex-dependent features of aversion.

Trigeminal neuropathic pain causes changes in affective processing of pain in rats

Trigeminal neuropathic pain has been modeled in rodents through the constriction of the infraorbital nerve (CCI-ION). Sensory alterations, including spontaneous pain, and thermal and mechanical hyperalgesia are well characterized, but there is a notable lack of evidence about the affective pain component in this model. Evaluation of the emotional component of pain in rats has been proposed as a way to optimize potential translational value of non-clinical studies. In rats, 22 and 50 kHz ultrasonic vocalizations (USVs) are considered well-established measures of negative and positive emotional states, respectively. Thus, this study tested the hypothesis that trigeminal neuropathic pain would result, in addition to the sensory alterations, in a decrease of 50 kHz USV, which may be related to altered function of brain areas involved in emotional pain processing. CCI-ION surgery was performed on 60-day-old male Wistar rats. 15 days after surgery, von Frey filaments were applied to detect mechanical hyperalgesia, and USV was recorded. At the same timepoint, systemic treatment with d,l-amphetamine (1 mg/kg) allowed investigation of the involvement of the dopaminergic system in USV emission. Finally, brain tissue was collected to assess the change in tyrosine hydroxylase (TH) expression in the nucleus accumbens (NAc) and c-Fos expression in brain areas involved in emotional pain processing, including the prefrontal cortex (PFC), amygdala, and NAc. The results showed that CCI-ION rats presented mechanical hyperalgesia and a significant reduction of environmental-induced 50 kHz USV. Amphetamine caused a marked increase in 50 kHz USV emission in CCI-ION rats. In addition, TH expression was lower in constricted animals and c-Fos analysis revealed an increase in neuronal activation. Taken together, these data indicate that CCI-ION causes a reduction in the emission of environmental-induced appetitive calls concomitantly with facial mechanical hyperalgesia and that both changes may be related to a reduction in the mesolimbic dopaminergic activity.

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

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

Different Anesthetic Drugs Mediate Changes in Neuroplasticity During Cognitive Impairment in Sleep-Deprived Rats via Different Factors

Background

Perioperative neuro-cognitive disorders (PND) are preoperative and postoperative complications of multiple nervous systems, typically manifested as decreased memory and learning ability after surgery. It was used to replace the original definition of postoperative cognitive dysfunctions (POCD) from 2018. Our previous studies have shown that sevoflurane inhalation can lead to cognitive dysfunction in Sprague-Dawley rats, but the specific mechanism is still unclear.

Material/Methods

Thirty-six male Sprague-Dawley rats were randomly divided into 6 groups (n=6): the SD group was given 24-h acute sleep deprivation; Sevoflurane was inhaled for 2 h in the Sevo group. Two mL propofol was injected into the tail vein of rats in the Prop group. The rats in the SD+Sevo group and SD+Prop group were deprived of sleep before intervention in the same way as before.

Results

We noted significant behavioral changes in rats treated with SIK3 inhibitors or tau phosphorylation agonists before propofol injection or sevoflurane inhalation, with associated protein levels and dendritic spine density documented. Sevoflurane anesthesia-induced cognitive impairment following acute sleep deprivation was more pronounced than sleep deprivation-induced cognitive impairment alone and resulted in increased brain SIK3 levels, increased phosphorylation of total tau and tau, and decreased acetylation modifications. After using propofol, the cognitive function returned to baseline levels with a series of reversals of cognitive dysfunction.

Conclusions

These results suggest that sevoflurane inhalation via the SIK3 pathway aggravates cognitive impairment after acute sleep deprivation and that propofol anesthesia reverses the effects of sleep deprivation by affecting modifications of tau protein.

Anticipatory 50-kHz Precontact Ultrasonic Vocalizations and Sexual Motivation: Characteristic Pattern of Ultrasound Subtypes in an Individual Analyzed Profile

We verified the hypothesis of the existence of forms of individual-specific differences in the emission of anticipatory precontact vocalization (PVs) indicating individualization related to sexual experience and motivation in male rats. Long-Evans males were individually placed in a chamber and 50-kHz ultrasounds were recorded during 5-min periods. In experiment 1, PVs were recorded before the introduction of a female in four consecutive sessions during the acquisition of sexual experience. In experiment 2, PVs were analyzed in three groups of sexually experienced males: with the highest, moderate, and the lowest sexual motivation based on previous copulatory activity. In both experiments, the total number of ultrasounds, as well as 14 different specific subtypes, was measured. The ultrasound profiles for each male were created by analyzing the proportions of specific dominant subtypes of so-called 50-kHz calls. We decided that the dominant ultrasounds were those that represented more than 10% of the total recorded signals in a particular session. The number of PVs was positively correlated with the acquisition of sexual experience and previous copulatory efficiency (measured as the number of sessions with ejaculation). Furthermore, PVs showed domination of the frequency modulated signals (complex and composite) as well as flat and short with upward ramp ultrasounds with some individual differences, regardless of the level of sexual motivation. The results show a characteristic pattern of PVs and confirm the hypothesis that the number of PVs is a parameter reflecting the level of sexual motivation.

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.

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.

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.

The chronotherapeutic treatment of bipolar disorders: A systematic review and practice recommendations from the ISBD task force on chronotherapy and chronobiology

AIMS

To systematically review the literature on the efficacy and tolerability of the major chronotherapeutic treatments of bipolar disorders (BD)-bright light therapy (LT), dark therapy (DT), treatments utilizing sleep deprivation (SD), melatonergic agonists (MA), interpersonal social rhythm therapy (IPSRT), and cognitive behavioral therapy adapted for BD (CBTI-BP)-and propose treatment recommendations based on a synthesis of the evidence.

METHODS

PRISMA-based systematic review of the literature.

RESULTS

The acute antidepressant (AD) efficacy of LT was supported by several open-label studies, three randomized controlled trials (RCTs), and one pseudorandomized controlled trial. SD showed rapid, acute AD response rates of 43.9%, 59.3%, and 59.4% in eight case series, 11 uncontrolled, studies, and one RCT, respectively. Adjunctive DT obtained significant, rapid anti-manic results in one RCT and one controlled study. The seven studies on MA yielded very limited data on acute antidepressant activity, conflicting evidence of both antimanic and maintenance efficacy, and support from two case series of improved sleep in both acute and euthymic states. IPSRT monotherapy for bipolar II depression had acute response rates of 41%, 67%, and 67.4% in two open studies and one RCT, respectively; as adjunctive therapy for bipolar depression in one RCT, and efficacy in reducing relapse in two RCTs. Among euthymic BD subjects with insomnia, a single RCT found CBTI-BP effective in delaying manic relapse and improving sleep. Chronotherapies were generally safe and well-tolerated.

CONCLUSIONS

The outcome literature on the adjunctive use of chronotherapeutic treatments for BP is variable, with evidence bases that differ in size, study quality, level of evidence, and non-standardized treatment protocols. Evidence-informed practice recommendations are offered.

Characterization of rat ultrasonic vocalization in the orofacial formalin test: Influence of the social context

Rats emit ultrasonic vocalizations (USVs) about 22 kHz and 50 kHz sound frequency to communicate the presence of negative or positive emotional states, respectively. The calling behavior may be influenced by several factors, including environmental factors. Likewise, pain behavior can be modulated according to the social context, and also can be transferred to conspecifics through direct observation and/or social interaction. Herein we investigated if acute pain induction was related to changes in emission of aversive and appetitive calls and how different social contexts affected the nociceptive behavior and USVs. Our results demonstrated that orofacial formalin injection in rats induced aversive calls in addition to the nociceptive behavior, and both are reduced by systemic treatment with morphine (2.5 mg/kg). Exposure of formalin-injected rats to cagemates had no effect on the nociceptive behavior or calls emitted by the demonstrator, but the observer showed emotional contagion of pain. In contrast, exposure of formalin-injected rats to non-cagemates decreased the nociceptive behavior of the demonstrator, without affecting the calls emission. The emotional contagion was not detected in non-cagemates or in cagemates separated by a visual barrier. In conclusion, we suggest that familiarity and the visual contact contributes to emotional contagion of pain. USV analysis may represent an additional measure in the evaluation of the emotional aspect of orofacial pain, and for the study of pain modulation.

Using anticipatory and drug-evoked appetitive ultrasonic vocalization for monitoring the rewarding effect of amphetamine in a rat model of drug self-administration

Measuring ultrasonic vocalizations (USVs) allows studying psychoactive drug use-related affective states in laboratory rats and may help understand changes underlying the progress of addictions. We aimed at finding an effective scheme for amphetamine self-administration training in rats, identifying factors affecting their anticipatory and drug-evoked, frequency-modulated 50-kHz USV responses, and verifying whether the rewarding action of amphetamine promotes current drug intake during the training. Therefore, we monitored amphetamine intake and anticipatory and drug-evoked USVs in two rat cohorts trained using two different training schemes. Then we retrospectively divided these cohorts into low-amphetamine and high-amphetamine intake subsets and analyzed their frequency-modulated 50-kHz USV responses accordingly. Anticipatory (i.e., drug-context-related) USVs as well as USVs induced by self-administration training-related non-pharmacological manipulations (tested in an additional rat group) showed surprisingly high call rates but faded spontaneously relatively quickly. Only the scheme employing short cycles of training sessions (two instead of six) and intermittent instead of continuous intra-session drug availability yielded long-lasting escalation of amphetamine intake in a sizable subset. This subset showed high initial amphetamine-evoked USV call rate, which suggests that a strong rewarding action of the drug early in the SA training favors intake escalation. A major decrease in the drug-evoked USVs during advanced training indicated the emergence of tolerance to the rewarding action in these rats, a phenomenon that is characteristic of addiction. Frequency-modulated 50-kHz rat USVs are a good index of the rewarding action of amphetamine at the absence of USVs induced by drug context and other training-related factors.

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'.