Influence of acute caffeine on 50-kHz ultrasonic vocalizations in male adult rats and relevance to caffeine-mediated psychopharmacological effects

RNA m6A methyltransferase activator affects anxiety-related behaviours, monoamines and striatal gene expression in the rat

Modification of mRNA by methylation is involved in post-transcriptional regulation of gene expression by affecting the splicing, transport, stability and translation of mRNA. Methylation of adenosine at N6 (m6A) is one of the most common and important cellular modification occurring in the mRNA of eukaryotes. Evidence that m6A mRNA methylation is involved in regulation of stress response and that its dysregulation may contribute to the pathogenesis of neuropsychiatric disorders is accumulating. We have examined the acute and subchronic (up to 18 days once per day intraperitoneally) effect of the first METTL3/METTL14 activator compound CHMA1004 (methyl-piperazine-2-carboxylate) at two doses (1 and 5 mg/kg) in male and female rats. CHMA1004 had a locomotor activating and anxiolytic-like profile in open field and elevated zero-maze tests. In female rats sucrose consumption and swimming in Porsolt's test were increased. Nevertheless, CHMA1004 did not exhibit strong psychostimulant-like properties: CHMA1004 had no effect on 50-kHz ultrasonic vocalizations except that it reduced the baseline difference between male and female animals, and acute drug treatment had no effect on extracellular dopamine levels in striatum. Subchronic CHMA1004 altered ex vivo catecholamine levels in several brain regions. RNA sequencing of female rat striata after subchronic CHMA1004 treatment revealed changes in the expression of a number of genes linked to dopamine neuron viability, neurodegeneration, depression, anxiety and stress response. Conclusively, the first-in-class METTL3/METTL14 activator compound CHMA1004 increased locomotor activity and elicited anxiolytic-like effects after systemic administration, demonstrating that pharmacological activation of RNA m6A methylation has potential for neuropsychiatric drug development.

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.

Positive maternal affect during mother-litter interaction is reduced in new mother rats exhibiting a depression-like phenotype

The experience of positive affect during new motherhood is considered essential for a healthy mother-infant relationship, with life-long consequences for both mother and child. Affective availability and contingent responsiveness are often compromised in mothers experiencing postpartum depression, yet how maternal affect impacts parenting is not fully understood. In this study, we used the Wistar-Kyoto (WKY) rat model of depression and ultrasonic vocalizations to examine the relationship between maternal affect and parenting. We examined the affective and behavioral response of WKY and control new mother rats during social interactions with their offspring. Our results show that WKY mothers displayed altered USV signaling accompanying substantial disturbances in their maternal caregiving. In addition, WKY mothers failed to adjust vocal frequency in coordination with offspring proximity and interaction compared to control mothers. A follow up experiment demonstrated that the administration of the adenosine A2A receptor antagonist MSX-3 ameliorated both maternal behavioral deficits and low positive affect in WKY mothers. Together, our results highlight the importance of maternal positive affect in the dyad relationship and suggest a role for the striatopallidal pathway in the affective processing of parenting.

Transgenerational Effects of Prenatal Endocrine Disruption on Reproductive and Sociosexual Behaviors in Sprague Dawley Male and Female Rats

Endocrine-disrupting chemicals (EDCs) lead to endocrine and neurobehavioral changes, particularly due to developmental exposures during gestation and early life. Moreover, intergenerational and transgenerational phenotypic changes may be induced by germline exposure (F2) and epigenetic germline transmission (F3) generation, respectively. Here, we assessed reproductive and sociosexual behavioral outcomes of prenatal Aroclor 1221 (A1221), a lightly chlorinated mix of PCBs known to have weakly estrogenic mechanisms of action; estradiol benzoate (EB), a positive control; or vehicle (3% DMSO in sesame oil) in F1-, F2-, and F3-generation male and female rats. Treatment with EDCs was given on embryonic day (E) 16 and 18, and F1 offspring monitored for development and adult behavior. F2 offspring were generated by breeding with untreated rats, phenotyping of F2s was performed in adulthood, and the F3 generation were similarly produced and phenotyped. Although no effects of treatment were found on F1 or F3 development and physiology, in the F2 generation, body weight in males and uterine weight in females were increased by A1221. Mating behavior results in F1 and F2 generations showed that F1 A1221 females had a longer latency to lordosis. In males, the F2 generation showed decreased mount frequency in the EB group. In the F3 generation, numbers of ultrasonic vocalizations were decreased by EB in males, and by EB and A1221 when the sexes were combined. Finally, partner preference tests in the F3 generation revealed that naïve females preferred F3-EB over untreated males, and that naïve males preferred untreated over F3-EB or F3-A1221 males. As a whole, these results show that each generation has a unique, sex-specific behavioral phenotype due to direct or ancestral EDC exposure.

Acoustilytix™: A Web-Based Automated Ultrasonic Vocalization Scoring Platform

Ultrasonic vocalizations (USVs) are known to reflect emotional processing, brain neurochemistry, and brain function. Collecting and processing USV data is manual, time-intensive, and costly, creating a significant bottleneck by limiting researchers’ ability to employ fully effective and nuanced experimental designs and serving as a barrier to entry for other researchers. In this report, we provide a snapshot of the current development and testing of Acoustilytix™, a web-based automated USV scoring tool. Acoustilytix implements machine learning methodology in the USV detection and classification process and is recording-environment-agnostic. We summarize the user features identified as desirable by USV researchers and how these were implemented. These include the ability to easily upload USV files, output a list of detected USVs with associated parameters in csv format, and the ability to manually verify or modify an automatically detected call. With no user intervention or tuning, Acoustilytix achieves 93% sensitivity (a measure of how accurately Acoustilytix detects true calls) and 73% precision (a measure of how accurately Acoustilytix avoids false positives) in call detection across four unique recording environments and was superior to the popular DeepSqueak algorithm (sensitivity = 88%; precision = 41%). Future work will include integration and implementation of machine-learning-based call type classification prediction that will recommend a call type to the user for each detected call. Call classification accuracy is currently in the 71–79% accuracy range, which will continue to improve as more USV files are scored by expert scorers, providing more training data for the classification model. We also describe a recently developed feature of Acoustilytix that offers a fast and effective way to train hand-scorers using automated learning principles without the need for an expert hand-scorer to be present and is built upon a foundation of learning science. The key is that trainees are given practice classifying hundreds of calls with immediate corrective feedback based on an expert’s USV classification. We showed that this approach is highly effective with inter-rater reliability (i.e., kappa statistics) between trainees and the expert ranging from 0.30–0.75 (average = 0.55) after only 1000–2000 calls of training. We conclude with a brief discussion of future improvements to the Acoustilytix platform.

Influence of dopamine transmission in the medial prefrontal cortex and dorsal striatum on the emission of 50-kHz ultrasonic vocalizations in rats treated with amphetamine: Effects on drug-stimulated and conditioned calls

Rat ultrasonic vocalizations (USVs) of 50 kHz are increasingly being evaluated as a behavioral marker of the affective properties of drugs. Studies in amphetamine-treated rats have shown that activation of dopamine transmission in the nucleus accumbens (NAc) initiates the emission of 50-kHz USVs, but little is known on how dopamine transmission in other brain regions modulates the effects of drugs on calling behavior. To clarify this issue, we evaluated 50-kHz USV emissions in rats subjected to dopaminergic denervation of either the medial prefrontal cortex (mPFC) or the dorsal striatum (DS) and treated with amphetamine. Rats received amphetamine (1 mg/kg, i.p. × 5) on alternate days in a test cage; 7 days later, they were re-exposed to the test cage, to measure calling behavior that may reflect drug conditioning, and then challenged with amphetamine (1 mg/kg, i.p.). The numbers of total and categorized 50-kHz USVs emitted were evaluated, along with immunofluorescence for Zif-268 in the NAc. Dopamine-denervated and sham-operated rats displayed comparable patterns of calling behavior during amphetamine treatment and after amphetamine challenge. Conversely, rats that were dopamine-denervated in the mPFC, but not DS, emitted low numbers of 50-kHz USVs on test cage re-exposure. Finally, dopamine-denervated rats displayed a less marked increase in Zif-268-positive neurons in the NAc shell after amphetamine challenge, compared with sham-operated rats. These results may be relevant to identify the neuronal circuits that modulate 50-kHz USV emissions in rats treated with amphetamine, as well as the interplay between calling behavior and affective properties of drugs.

Alterations of acoustic features of 50 kHz vocalizations by nicotine and phencyclidine in rats

Ultrasonic vocalizations are widely used to examine affective states in rats, yet relatively few studies explore the acoustic features of vocalizations, especially in relation to drug exposure, and no studies have explored alterations in acoustic features over time. The goal of this study was to examine nicotine- and phencyclidine-induced alterations of bandwidth, duration, and frequency of 50 kHz vocalizations. The minimum and maximum frequency, bandwidth, and duration of calls were examined after 7 days of daily subcutaneous administration of phencyclidine (2.0 mg/kg) and nicotine (0.2 and 0.4 mg/kg) in male Sprague-Dawley rats. Bandwidth was significantly decreased in rats treated with both nicotine (0.2 and 0.4 mg/kg) and phencyclidine. Maximum frequency was lowest on the first day of exposure compared with all other days and was not altered by drug exposure. Call duration was not affected by time or drug exposure. These findings suggest the importance of studying alterations in acoustic features in time, especially those induced by drug exposure.

Rodent ultrasonic vocalizations as biomarkers of future alcohol use: A predictive analytic approach

Excessive alcohol consumption has a vast, negative impact on society. Rodent models have been successful in furthering our understanding of the biological underpinnings that drive alcohol consumption. Rodents emit ultrasonic vocalizations (USVs) that are each composed of several acoustic characteristics (e.g., frequency, duration, bandwidth, power). USVs reflect neurotransmitter activity in the ascending limb of the mesolimbic dopaminergic and cholinergic neurotransmitter systems and serve as noninvasive, real-time biomarkers of dopaminergic and cholinergic neurotransmission in the limbic system. In the present study, we recorded spontaneously emitted USVs from alcohol-naïve Long-Evans (LE) rats and then measured their alcohol intake. We compared the USV acoustic characteristics and alcohol consumption data from these LE rats with previously published data from selectively bred high-alcohol (P and HAD-1) and low-alcohol (NP and LAD-1) drinking lines from studies with the same experimental method. Predictive analytic techniques were applied simultaneously to this combined data set and revealed that (a) USVs emitted by alcohol-naïve rats accurately discriminated among high-alcohol consuming, LE, and low-alcohol consuming rat lines, and (b) future alcohol consumption in these same rat lines was reliably predicted from the USV data collected in an alcohol-naïve state. To our knowledge, this is the first study to show that alcohol consumption is predicted directly from USV profiles of alcohol-naïve rats. Because USV acoustic characteristics are sensitive to underlying neural activity, these findings suggest that baseline differences in mesolimbic cholinergic and dopaminergic tone could determine the propensity for future alcohol consumption in rodents.

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'.

Effects of anxiogenic drugs on the emission of 22- and 50-kHz ultrasonic vocalizations in adult rats

RATIONALE

Adult rat 22-kHz vocalizations are often associated with alarm or distress, whereas a subset of 50-kHz calls is preferentially emitted in response to amphetamine and other rewarding stimuli. Whether any 50-kHz calls reflect anxiety is unknown.

OBJECTIVE

To determine the effects of anxiogenic drugs on 50-kHz call rate and call subtype profile, in comparison with D-amphetamine.

METHODS

Adult male rats received systemic amphetamine (1 mg/kg) three times several days before testing. Ultrasonic vocalizations were then recorded after acute intraperitoneal injection of amphetamine or one of five anxiogenic drugs: yohimbine (2.5 mg/kg), N-methyl-β-carboline-3-carboxamide (FG 7142, 5 mg/kg), pentylenetetrazol (PTZ, 20 mg/kg), m-chlorophenylpiperazine (mCPP, 1 mg/kg), caffeine (25 mg/kg), or vehicle.

RESULTS

The duration of immobility was increased by FG 7142, PTZ, and mCPP; this measure was unchanged by yohimbine and reduced by the locomotor stimulant drugs amphetamine and caffeine. Conversely, the 50-kHz call rate was reduced by FG 7142, PTZ and mCPP, and increased by caffeine and amphetamine. Overall, the most common 50-kHz call subtypes were flat, trill, step-up, and complex. Consistent with previous reports, amphetamine increased the relative prevalence of trill calls while reducing the relative prevalence of flat calls. Yohimbine and caffeine reduced flat call prevalence, whereas mCPP reduced trill call prevalence. No other shifts in the call profile were observed, and no anxiogenic drug induced 22-kHz calls.

CONCLUSION

Anxiogenic drugs, as a class, did not uniformly alter the 50-kHz call rate or subtype profile. Amphetamine-induced effects on 50-kHz call rate and profile do not reflect anxiety.

Diazepam blocks 50 kHz ultrasonic vocalizations and stereotypies but not the increase in locomotor activity induced in rats by amphetamine

RATIONALE

We have recently shown that the benzodiazepine diazepam inhibits dopamine release in the NAc and blocks the increased release of dopamine induced by DL-amphetamine. Rewarding stimuli and many drugs of abuse can induce dopamine release in the nucleus accumbens as well as 50-kHz ultrasonic vocalizations (USVs) in rats.

OBJECTIVES

In the present study, we tested the hypothesis that diazepam can also block the increase in locomotor activity and USVs elicited by amphetamine.

METHODS

Fifty-kilohertz USVs, stereotypy, and locomotor behavior were scored in adult male Wistar rats treated with i.p. injections of saline, 3 mg/kg DL-amphetamine, 2 mg/kg diazepam, 0.2 mg/kg haloperidol, or a combination of these drugs.

RESULTS

In agreement with previous studies, amphetamine caused significant increases in the number of USV calls, stereotypies, and locomotor activity. The D2 dopamine receptor antagonist haloperidol blocked the effects of amphetamine on USVs, stereotypy, and locomotor activity. Diazepam blocked the effect of amphetamine on USV and stereotypy, but not on horizontal locomotion.

CONCLUSIONS

These results suggest that diazepam blocks the rewarding effect of amphetamine. This finding is promising for basic research regarding treatments of substance use disorders and evaluation of the impact of benzodiazepines on motivation.

Rat 50-kHz ultrasonic vocalizations as a tool in studying neurochemical mechanisms that regulate positive emotional states

BACKGROUND

Adolescent and adult rats emit 50-kHz ultrasonic vocalizations (USVs) to communicate the appetitive arousal and the presence of positive emotional states to conspecifics.

NEW METHOD

Based on its communicative function, emission of 50-kHz USVs is increasingly being evaluated in preclinical studies of affective behavior, motivation and social behavior.

RESULTS

Emission of 50-kHz USVs is initiated by the activation of dopamine receptors in the shell subregion of the nucleus accumbens. However, several lines of evidence show that non-dopaminergic receptors may influence the numbers of 50-kHz USVs that are emitted, as well as the acoustic parameters of calls.

COMPARISON WITH EXISTING METHODS

Emission of 50-kHz USVs is a non-invasive method that may be used to study reward and motivation without the need for extensive training and complex animal manipulations. Moreover, emission of 50-kHz USVs can be used alone or combined with other well-standardized behavioral paradigms (e.g., conditioned place preference, self-administration).

CONCLUSIONS

This review summarizes the current evidence concerning molecular mechanisms that regulate the emission of 50-kHz USVs. Moreover, the review discusses the usefulness of 50-kHz USVs as an experimental tool to investigate how different neurotransmitter systems regulate the manifestations of positive emotional states, and also use of this tool in preclinical modeling of psychiatric diseases.

Emission of categorized 50-kHz ultrasonic vocalizations in rats repeatedly treated with amphetamine or apomorphine: Possible relevance to drug-induced modifications in the emotional state

The emission of 50-kHz ultrasonic vocalizations (USVs) is increasingly emerging as a potential behavioral marker of the subjective effects that psychoactive drugs elicit in rats. However, multiple categories of 50-kHz USVs have been identified, which are thought to possess different behavioral significance. Besides, limited information is available on how psychoactive drugs affect the emission of categorized 50-kHz USVs. To further elucidate this issue, we evaluated the numbers of multiple categories of 50-kHz USVs emitted by rats repeatedly treated with amphetamine (1 or 2 mg/kg, i.p.) or apomorphine (2 or 4 mg/kg, i.p.), two drugs that elicit similar and dissimilar subjective effects. Amphetamine- and apomorphine-treated rats emitted patterns of categorized 50-kHz USVs that varied according to the drug administered, drug dose, and number of drug administrations. Nevertheless, the numbers of several categories of 50-kHz USVs were positively correlated with the number of total calls emitted (i.e., the sum of categorized 50-kHz USVs). Moreover, a marked interindividual variability in the emission of categorized 50-kHz USVs was observed. Taken together, the present results may be relevant to further elucidating the interplay between calling of the 50-kHz USVs group and psychopharmacological profile of drugs.

Modulation of Rat 50-kHz Ultrasonic Vocalizations by Glucocorticoid Signaling: Possible Relevance to Reward and Motivation

BACKGROUND

Rats emit 50-kHz ultrasonic vocalizations (USVs) to communicate positive emotional states, and these USVs are increasingly being investigated in preclinical studies on reward and motivation. Although it is the activation of dopamine receptors that initiates the emission of 50-kHz USVs, non-dopaminergic mechanisms may modulate calling in the 50 kHz frequency band. To further elucidate these mechanisms, the present study investigated whether the pharmacological manipulation of glucocorticoid signaling influenced calling.

METHODS

Rats were administered corticosterone (1-5 mg/kg, s.c.), the glucocorticoid receptor antagonist mifepristone (40 or 100 mg/kg, s.c.), or the corticosterone synthesis inhibitor metyrapone (50 or 100 mg/kg, i.p.). The effects of these drugs on calling initiation and on calling recorded during nonaggressive social contacts or after the administration of amphetamine (0.25 or 1 mg/kg, i.p.) were then evaluated.

RESULTS

Corticosterone failed to initiate the emission of 50-kHz USVs and did not influence pro-social and amphetamine-stimulated calling. Similarly, mifepristone and metyrapone did not initiate calling. However, metyrapone suppressed pro-social calling and calling stimulated by a moderate dose (1 mg/kg, i.p.) of amphetamine. Conversely, mifepristone attenuated calling stimulated by a low (0.25 mg/kg, i.p.), but not moderate (1 mg/kg, i.p.), dose of amphetamine and had no influence on pro-social calling.

CONCLUSIONS

The present results demonstrate that glucocorticoid signaling modulates calling in the 50 kHz frequency band only in certain conditions and suggest that mechanisms different from the inhibition of corticosterone synthesis may participate in the suppression of calling by metyrapone.

The amphetamine-associated context exerts a stronger motivational effect in low-anxiety rats than in high-anxiety rats

This study used the conditioned place preference test to explore the effects of subchronic amphetamine administration on drug-associated cues in rats with different emotional reactivity. We also examined the changes in markers of dopaminergic activity in brain regions in response to the amphetamine-paired context, after a withdrawal period preceded by subchronic amphetamine treatment. We used low-anxiety (LR) and high-anxiety (HR) rats, which are known to exhibit distinct levels of susceptibility to amphetamine. Compared to HR rats, LR rats spent significantly more time in the amphetamine-paired compartment after the withdrawal period preceded by subchronic amphetamine treatment. Compared to HR control rats, LR control rats showed higher expression of the D1 receptor in the nucleus accumbens core (NAC core) and basolateral amygdala and higher expression of the D2 receptor in the NAC core. After the amphetamine treatment and withdrawal period, the LR rats showed higher D1 receptor expression in the NAC core, an increased level of homovanilic acid (HVA) in the prefrontal cortex, the NAC and the central amygdala than HR rats, as well as lower D2 receptor expression in the NAC core and the amygdala than LR control rats. These results indicate that the differences in the activity of the dopaminergic mesolimbic system in the HR and LR rats are maintained and even enhanced after a multi-day break in the use of the drug, indicating the occurrence of sensitisation. These findings show that the innate reactivity of the limbic dopaminergic innervations, dependent on the level of emotional reactivity, may significantly and chronically modify the development and maintenance of sensitisation to amphetamine.

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

Communication is the act of information transfer between sender and receiver. In rats, vocal communication can be studied through ultrasonic vocalizations (USV). 50-kHz USV occur in appetitive situations, most notably juvenile play, likely expressing the sender׳s positive affective state. Such appetitive 50-kHz USV serve important pro-social communicative functions and elicit social exploratory and approach behavior in the receiver. Emission of 50-kHz USV can be induced pharmacologically by the administration of psychostimulant drugs, such as amphetamine. However, it is unknown whether amphetamine affects the pro-social communicative function of 50-kHz USV in the receiver. We therefore assessed dose-response effects of amphetamine (0.0mg/kg, 0.5mg/kg, 1.0mg/kg, 2.5mg/kg, 5.0mg/kg) on pro-social ultrasonic communication on both, sender and receiver, in juvenile rats. We found an inverted U-shaped effect of amphetamine on 50-kHz USV emission, with 50-kHz USV levels being strongly enhanced by moderate doses, yet less prominent effects were seen following the highest dose. Likewise, amphetamine exerted inverted U-shaped effects on social exploratory and approach behavior induced by playback of appetitive 50-kHz USV. Social approach was enhanced by moderate amphetamine doses, but completely abolished following the highest dose. Amphetamine further dose-dependently promoted the emission of 50-kHz USV following playback of appetitive 50-kHz USV, indicating more vigorous attempts to establish social proximity. Our results support an important role of dopamine in closing a perception-and-action-loop through linking mechanisms relevant for detection and production of social vocalizations. Moreover, our approach possibly provides a new means to study mania-like aberrant social interaction and communication in animal models for bipolar disorder.

Environmental and Pharmacological Modulation of Amphetamine- Induced 50-kHz Ultrasonic Vocalizations in Rats

Rats emit high-frequency 50-kHz ultrasonic vocalizations (USV) in appetitive situations like social interactions. Drugs of abuse are probably the most potent non-social elicitors of 50-kHz USV, possibly reflecting their euphorigenic properties. Psychostimulants induce the strongest elevation in 50-kHz USV emission, particularly amphetamine (AMPH), either when applied systemically or locally into the nucleus accumbens (Nacc). Emission of AMPH-induced 50-kHz USV depends on test context, such as the presence of conspecifics, and can be manipulated pharmacologically by targeting major neurotransmitter systems, including dopamine (DA), noradrenaline (NA), and serotonin (5-HT), but also protein kinase C (PKC) signaling. Several D₁ and D₂ receptor antagonists, as well as typical and atypical antipsychotics block the AMPH-induced elevation in 50-kHz USV. Inhibiting D₁ and D₂ receptors in the Nacc abolishes AMPH-induced 50-kHz USV, indicating a key role for this brain area. NA neurotransmission also regulates AMPH-induced 50-kHz USV emission given that α₁ receptor antagonists and α₂ receptor agonists exert attenuating effects. Supporting the involvement of the 5-HT system, AMPH-induced 50-kHz USV are attenuated by 5-HT_2C receptor activation, whereas 5-HT_2C receptor antagonism leads to the opposite effect. Finally, treatment with lithium, tamoxifen, and myricitrin was all found to result in a complete abolishment of the AMPH-induced increase in 50-kHz USV, suggesting the involvement of PKC signaling. Neurotransmitter systems involved in AMPH-induced 50-kHz USV emission only partially overlap with other AMPH-induced behaviors like hyperlocomotion. The validity of AMPH-induced 50-kHz USV as a preclinical model for neuropsychiatric disorders is discussed, particularly with relevance to altered drive and mood seen in bipolar disorder.

Ultrasonic Vocalizations as a Measure of Affect in Preclinical Models of Drug Abuse: A Review of Current Findings

The present review describes ways in which ultrasonic vocalizations (USVs) have been used in studies of substance abuse. Accordingly, studies are reviewed which demonstrate roles for affective processing in response to the presentation of drug-related cues, experimenter- and self-administered drug, drug withdrawal, and during tests of relapse/reinstatement. The review focuses on data collected from studies using cocaine and amphetamine, where a large body of evidence has been collected. Data suggest that USVs capture animals’ initial positive reactions to psychostimulant administration and are capable of identifying individual differences in affective responding. Moreover, USVs have been used to demonstrate that positive affect becomes sensitized to psychostimulants over acute exposure before eventually exhibiting signs of tolerance. In the drug-dependent animal, a mixture of USVs suggesting positive and negative affect is observed, illustrating mixed responses to psychostimulants. This mixture is predominantly characterized by an initial bout of positive affect followed by an opponent negative emotional state, mirroring affective responses observed in human addicts. During drug withdrawal, USVs demonstrate the presence of negative affective withdrawal symptoms. Finally, it has been shown that drug-paired cues produce a learned, positive anticipatory response during training, and that presentation of drug-paired cues following abstinence produces both positive affect and reinstatement behavior. Thus, USVs are a useful tool for obtaining an objective measurement of affective states in animal models of substance abuse and can increase the information extracted from drug administration studies. USVs enable detection of subtle differences in a behavioral response that might otherwise be missed using traditional measures.

Ultrasonic vocalization in murine experimental stroke: A mechanistic model of aphasia

PURPOSE

Approximately one-fourth of stroke survivors are aphasic. Speech therapy is the main treatment approach but leaves most patients with chronic disability. Attempts to improve this situation are hampered by a lack of mechanistic understanding of the disability and treatments, reflecting the neglect of this impairment modality in pre-clinical research. Accordingly, we devised a novel murine model of speech-related impairment after stroke to investigate the role of language- and plasticity-associated molecules. Rodents communicate socially with ultrasonic vocalizations (USVs), conveying semantic and semiotic information with complex frequency modulated "songs" and alarm calls.

METHODS

Transient focal cerebral ischemia was induced in male C57BL6 mice via either 30 or 45 minutes of reversible right MCAO using the intraluminal filament technique. Nine days post-operatively brains are stained with TTC and analyzed for infarct volume. For behavioral measures health scores are taken (days 1-4), cylinder tests and USV recordings performed at days 3 and 7 post operatively. Real time PCR was performed at 24 and 48 hour and 7 day time points to quantify mRNA expression of communication-related genes (Foxp2, Foxp1, Srpx2, Cntnap2 and Gapdh). Immunohistochemistry was performed to localize FOXP2 protein.

RESULTS

After middle cerebral artery occlusion of either 30 or 45 minutes duration, mice demonstrate profoundly impaired socially evoked USVs. In addition, there is suppression of the language-associated transcription factor, Forkhead box protein 2 (Foxp2), and its downstream binding partner, contactin-associated protein 2 (Cntnap2).

CONCLUSION

These findings set a foundation for further studies of mechanisms and novel treatment strategies for post-stroke vocalization impairments.

Novelty response and 50 kHz ultrasonic vocalizations: Differential prediction of locomotor and affective response to amphetamine in Sprague-Dawley rats

RATIONALE

Novelty and sensation seeking (NSS) predisposes humans and rats to experiment with psychostimulants. In animal models, different tests of NSS predict different phases of drug dependence. Ultrasonic vocalizations (USVs) are evoked by psychomotor stimulants and measure the affective/motivation response to stimuli, yet the role NSS has on USVs in response to amphetamine is not determined.

OBJECTIVES

The aim of the present study was to determine if individual differences in NSS and USVs can predict locomotor and USV response to amphetamine (0.0, 0.3, and 1.0 mg/kg) after acute and chronic exposure.

METHODS

Thirty male rats were tested for their response to novelty (IEN), choice to engage in novelty (NPP), and heterospecific play (H-USV). Rats were administered non-contingent amphetamine or saline for seven exposures, and USVs and locomotor activity were measured. After a 14-day rest, rats were administered a challenge dose of amphetamine.

RESULTS

Regression analyses indicated that amphetamine dose-dependently increased locomotor activity and the NPP test negatively predicted treatment-induced locomotor activity. The H-USV test predicted treatment-induced frequency-modulated (FM) USVs, but the strength of prediction depended on IEN response.

CONCLUSIONS

Results provide evidence that locomotor activity and FM USVs induced by amphetamine represent different behavioral responses. The prediction of amphetamine-induced FM USVs by the H-USV screen was changed by the novelty response, indicating that the affective value of amphetamine-measured by FM USVs-depends on novelty response. This provides evidence that higher novelty responders may develop a tolerance faster and may escalate intake faster.

Activation of adenosine A₂A receptors suppresses the emission of pro-social and drug-stimulated 50-kHz ultrasonic vocalizations in rats: possible relevance to reward and motivation

RATIONALE

Rats emit 50-kHz ultrasonic vocalizations (USVs) in response to pleasurable stimuli, and these USVs are considered a tool for investigating reward and motivation.

OBJECTIVES

This study aimed to clarify how activity of adenosine A2A receptors, which modulate reward and motivation, influences 50-kHz USV emission in rats.

METHODS

Rats received one of the following treatments in a test cage: (1) acute administration of the A2A receptor agonist CGS 21680 (0.05-0.2 mg/kg, i.p.) during social interactions; (2) long-term amphetamine (1 or 2 mg/kg, i.p.) or morphine (7.5 mg/kg, s.c.) administration on alternate days, alone or with CGS 21680, followed after 7 days of discontinuation by test cage re-exposure, to assess drug-conditioning effects, and thereafter drug challenge; (3) acute administration of the D1/D2 receptor agonist apomorphine (4 mg/kg, i.p.), alone or with CGS 21680; and (4) long-term administration of the non-selective A1/A2A receptor antagonist caffeine (15 mg/kg, i.p.), on alternate days. USVs and locomotor activity were evaluated throughout the treatments.

RESULTS

CGS 21680 attenuated 50-kHz USV emission stimulated by social interactions, amphetamine, apomorphine, and morphine, and rats administered CGS 21680 with amphetamine or morphine emitted fewer conditioned 50-kHz USVs upon test cage re-exposure, compared with rats administered amphetamine or morphine alone. Moreover, CGS 21680 administration prevented long-term changes in locomotor activity in amphetamine- and morphine-treated rats. Finally, caffeine had no effect on 50-kHz USVs.

CONCLUSIONS

These results indicate that activation of A2A receptors attenuates 50-kHz USV emission in rats and further elucidate how these receptors modulate the motivational properties of natural and pharmacological stimuli.

The dopamine D₃-preferring D₂/D₃ dopamine receptor partial agonist, cariprazine, reverses behavioural changes in a rat neurodevelopmental model for schizophrenia

Current antipsychotic medication is largely ineffective against the negative and cognitive symptoms of schizophrenia. One promising therapeutic development is to design new molecules that balance actions on dopamine D2 and D3 receptors to maximise benefits and limit adverse effects. This study used two rodent paradigms to investigate the action of the dopamine D3-preferring D3/D2 receptor partial agonist cariprazine. In adult male rats, cariprazine (0.03-0.3 mg/kg i.p.), and the atypical antipsychotic aripiprazole (1-3 mg/kg i.p.) caused dose-dependent reversal of a delay-induced impairment in novel object recognition (NOR). Treating neonatal rat pups with phencyclidine (PCP) and subsequent social isolation produced a syndrome of behavioural alterations in adulthood including hyperactivity in a novel arena, deficits in NOR and fear motivated learning and memory, and a reduction and change in pattern of social interaction accompanied by increased ultrasonic vocalisations (USVs). Acute administration of cariprazine (0.1 and 0.3 mg/kg) and aripiprazole (3 mg/kg) to resultant adult rats reduced neonatal PCP-social isolation induced locomotor hyperactivity and reversed NOR deficits. Cariprazine (0.3 mg/kg) caused a limited reversal of the social interaction deficit but neither drug affected the change in USVs or the deficit in fear motivated learning and memory. Results suggest that in the behavioural tests investigated cariprazine is at least as effective as aripiprazole and in some paradigms it showed additional beneficial features further supporting the advantage of combined dopamine D3/D2 receptor targeting. These findings support recent clinical studies demonstrating the efficacy of cariprazine in treatment of negative symptoms and functional impairment in schizophrenia patients.

Involvement of Glutamate NMDA Receptors in the Acute, Long-Term, and Conditioned Effects of Amphetamine on Rat 50 kHz Ultrasonic Vocalizations

BACKGROUND

Rats emit 50 kHz ultrasonic vocalizations (USVs) in response to either natural or pharmacological pleasurable stimuli, and these USVs have emerged as a new behavioral measure for investigating the motivational properties of drugs. Earlier studies have indicated that activation of the dopaminergic system is critically involved in 50 kHz USV emissions. However, evidence also exists that non-dopaminergic neurotransmitters participate in this behavioral response.

METHODS

To ascertain whether glutamate transmission plays a role in 50 kHz USV emissions stimulated by amphetamine, rats received five amphetamine (1-2mg/kg, i.p.) administrations on alternate days in a test cage, either alone or combined with the glutamate N-methyl-D-aspartate receptor antagonist MK-801 (0.1-0.5mg/kg, i.p.). Seven days after treatment discontinuation, rats were re-exposed to the test cage to assess drug conditioning, and afterwards received a drug challenge. USVs and locomotor activity were evaluated, along with immunofluorescence for Zif-268 in various brain regions and spontaneous alternation in a Y maze.

RESULTS

Amphetamine-treated rats displayed higher 50 kHz USV emissions and locomotor activity than vehicle-treated rats, and emitted conditioned vocalizations on test cage re-exposure. Rats co-administered amphetamine and MK-801 displayed lower and dose-dependent 50 kHz USV emissions, but not lower locomotor activity, during repeated treatment and challenge, and scarce conditioned vocalization compared with amphetamine-treated rats. These effects were associated with lower levels of Zif-268 after amphetamine challenge and spontaneous alternation deficits.

CONCLUSIONS

These results indicate that glutamate transmission participates in the acute, long-term, and conditioned effects of amphetamine on 50 kHz USVs, possibly by influencing amphetamine-induced long-term neuronal changes and/or amphetamine-associated memories.

Critical involvement of 5-HT2C receptor function in amphetamine-induced 50-kHz ultrasonic vocalizations in rats

RATIONALE

Rats emit various distinct types of ultrasonic vocalizations (USV), with high-frequency 50-kHz USV typically occurring in appetitive situations being elicited by administering drugs of abuse, most notably amphetamine (AMPH), possibly reflecting drug wanting/craving and/or liking.

OBJECTIVES

Because 50-kHz USV emission is, at least in part, dopamine (DA) dependent and 5-HT2C agonists inhibit DA neurotransmission, we hypothesized that AMPH-induced 50-kHz USV can be attenuated by pretreatment with a 5-HT2C agonist.

METHODS

In experiments I and II, a dose-response curve for AMPH-induced 50-kHz USV was established, and the partial dependency of AMPH-induced 50-kHz USV on DA neurotransmission was validated by pretreatment with the D2-antagonist eticlopride. In experiment III, rats were pretreated with the 5-HT2C agonist CP 809,101 (0.0, 0.3, 1.0, 3.0, and 10 mg/kg), while in experiment IV, CP 809,101 (3.0 mg/kg), the 5-HT2C antagonist SB 242084 (1.0 mg/kg), or the combination of the two, was applied before AMPH administration (2.0 mg/kg). Finally, in experiment V, rats were treated with SB 242084 (0.0, 0.1, 0.3, and 1.0 mg/kg) only, i.e., in absence of AMPH.

RESULTS

The 5-HT2C agonist CP 809,101 dose-dependently blocked AMPH-induced 50-kHz USV, most notably trills, a call subtype that is considered to exclusively reflect a positive affective state, while the 5-HT2C antagonist SB 242084 induced opposite effects. Moreover, SB 242084 induced 50-kHz USV by its own.

CONCLUSIONS

5-HT2C receptors are critically involved in AMPH-induced 50-kHz USV, with 5-HT2C antagonism resulting in a stimulant-like effect. Attenuation of drug wanting/craving and/or liking by coadministration of a 5-HT2C agonist could be a translational pharmacodynamic biomarker.

Repeated amphetamine administration and long-term effects on 50-kHz ultrasonic vocalizations: possible relevance to the motivational and dopamine-stimulating properties of the drug

Ultrasonic vocalizations (USVs) of 50kHz are thought to indicate positive affective states in rats, and are increasingly being used to investigate the motivational properties of drugs of abuse. However, previous studies have observed that only dopaminergic psychostimulants of abuse, but not other addictive drugs, stimulate 50-kHz USVs immediately after their administration. This would suggest that 50-kHz USVs induced by addictive dopaminergic psychostimulants might reflect rewarding dopaminergic effect, rather than motivational effect. To elucidate this issue, our study compared the effects of the psychostimulant of abuse amphetamine and the dopamine receptor agonist apomorphine on 50-kHz USVs. Rats that received five drug administrations on alternate days in a novel test-cage were first re-exposed to the test-cage 7 days after treatment discontinuation to assess drug-conditioning, and then received a drug challenge. USVs were recorded throughout the experiments together with locomotor activity. To further clarify how amphetamine and apomorphine influenced 50-kHz USVs, rats were subdivided into "low" and "high" vocalizers, and time-dependence of drug effects was assessed. Amphetamine and apomorphine stimulated both 50-kHz USVs and locomotor activity, though they elicited dissimilar changes in these behaviors, depending on drug dose, rats׳ individual predisposition to vocalize, and time. Moreover, only amphetamine-treated rats displayed both sensitized 50-kHz USVs emission and conditioned vocalizations on test-cage re-exposure. These results indicate that the effects of amphetamine on 50-kHz USVs are not mimicked by a dopaminergic agonist with a low abuse potential, and may further support the usefulness of 50-kHz USVs in the study of the motivational properties of psychoactive drugs.

Rat Ultrasonic Vocalizations and Behavioral Neuropharmacology: From the Screening of Drugs to the Study of Disease

Several lines of evidence indicate that rats emit ultrasonic vocalizations (USVs) in response to a wide range of stimuli that are capable of producing either euphoric (positive) or dysphoric (negative) emotional states. On these bases, recordings of USVs are extensively used in preclinical studies of affect, motivation, and social behavior. Rat USVs are sensitive to the effects of certain classes of psychoactive drugs, suggesting that emission of rat USVs can have relevance not only to neurobiology, but also to neuropharmacology and psychopharmacology. This review summarizes three types of rat USVs, namely 40-kHz USVs emitted by pups, 22-kHz USVs and 50-kHz USVs emitted by young and adult animals, and relevance of these vocalizations to neuropharmacological studies. Attention will be focused on the issues of how rat USVs can be used to evaluate the pharmacological properties of different classes of drugs, and how rat USVs can be combined with other behavioral models used in neuropharmacology. The strengths and limitations of experimental paradigms based on the evaluation of rat USVs will also be discussed.

Rat ultrasonic vocalizations demonstrate that the motivation to contextually reinstate cocaine-seeking behavior does not necessarily involve a hedonic response

Human self-reports often indicate that changes in mood are a major contributor to drug relapse. Still, arguments have been made that instances of drug-seeking following abstinence in animal models (i.e. relapse/reinstatement) may be outside of hedonic control. Therefore, the present study utilized ultrasonic vocalizations in the rat in order to evaluate affect during cocaine self-administration and contextual reinstatement of cocaine-seeking in a pre-clinical model of drug relapse (abstinence-reinstatement model). Results show that while subjects effectively reinstated drug-seeking (lever pressing) following 30 days of abstinence, and spontaneously recovered/reinstated drug-seeking following 60 days of abstinence, ultrasonic vocalizations did not increase over baseline levels during either reinstatement session. These results are consistent with previous results from our laboratory and current theories of addiction suggesting that cues that are weakly associated with drug consumption can motivate drug-seeking behavior that is outside of hedonic processing.

Novel humanized recombinant T cell receptor ligands protect the female brain after experimental stroke

Transmigration of peripheral leukocytes to the brain is a major contributor to cerebral ischemic cell death mechanisms. Humanized partial major histocompatibility complex class II constructs (pMHC), covalently linked to myelin peptides, are effective for treating experimental stroke in males, but new evidence suggests that some inflammatory cell death mechanisms after brain injury are sex-specific. We here demonstrate that treatment with pMHC constructs also improves outcomes in female mice with middle cerebral artery occlusion (MCAO). HLA-DR2 transgenic female mice with MCAO were treated with RTL1000 (HLA-DR2 moiety linked to human MOG-35-55 peptide), HLA-DRa1-MOG-35-55, or vehicle (VEH) at 3, 24, 48, and 72 h after reperfusion and were recovered for 96 h or 2 weeks post-injury for measurement of histology (TTC staining) or behavioral testing. RTL1000- and DRa1-MOG-treated mice had profoundly reduced infarct volumes as compared to the VEH group, although higher doses of DRa1-MOG were needed for females vs. males evaluated previously. RTL1000-treated females also exhibited strongly improved functional recovery in a standard cylinder test. In novel studies of post-ischemic ultrasonic vocalization (USV), as measured by animal calls to their cage mates, we modeled in mice the post-stroke speech deficits common in human stroke survivors. The number of calls was reduced in injured animals relative to pre-MCAO baseline regardless of RTL1000 treatment status. However, call duration was significantly improved by RTL1000 treatment, suggesting benefit to the animal’s recovery of vocalization capability. We conclude that both the parent RTL1000 molecule and the novel non-polymorphic DRα1-MOG-35-55 construct were highly effective immunotherapies for treatment of transient cerebral ischemia in females.

Ultrasonic vocalizations: evidence for an affective opponent process during cocaine self-administration

RATIONALE

Preclinical models of cocaine addiction in the rodent have shown that cocaine induces both positive and negative affective states. These observations have led to the notion that the initial positive/euphoric state induced by cocaine administration may be followed by an opposing, negative process. In the rodent, one method for inferring positive and negative affective states involves measuring their ultrasonic vocalizations (USVs). Previous USV recordings from our laboratory suggested that the transition between positive and negative affect might involve decaying or sub-satiety levels of self-administered cocaine.

OBJECTIVES

In order to explicitly test the role of cocaine levels on these affective states, the present study examined USVs when calculated body levels of cocaine were clamped (i.e., held at a constant level via experimenter-controlled infusions) at, below, or above subjects' self-determined drug satiety thresholds.

RESULTS

USVs indicated that (1) positive affect was predominantly observed during the drug loading period, but declined quickly to near zero during maintenance and exhibited little relation to calculated drug level, and (2) in contrast, negative affect was observed at sub-satiety cocaine levels, but was relatively absent when body levels of cocaine were clamped at or above subjects' satiety thresholds.

CONCLUSIONS

The results reinforce the opponent-process hypothesis of addiction and suggest that an understanding of the mechanisms underlying negative affect might serve to inform behavioral and pharmacological therapies.

Direct and long-lasting effects elicited by repeated drug administration on 50-kHz ultrasonic vocalizations are regulated differently: implications for the study of the affective properties of drugs of abuse

Several studies suggest that 50-kHz ultrasonic vocalizations (USVs) may indicate a positive affective state in rats, and these vocalizations are increasingly being used to investigate the properties of psychoactive drugs. Previous studies, however, have focused on dopaminergic psychostimulants and morphine, whereas little is known about how other drugs modulate 50-kHz USVs. To further elucidate the neuropharmacology of 50-kHz USVs, the present study characterized the direct and long-lasting effects of different drugs of abuse, by measuring the number of 50-kHz USVs and their 'trill' subtype emitted by adult male rats. Rats received repeated administrations of amphetamine (2 mg/kg, i.p.), 3,4-methylenedioxymethamphetamine (MDMA, 7.5 mg/kg, i.p.), morphine (7.5 mg/kg, s.c.), or nicotine (0.4 mg/kg, s.c.), on either consecutive or alternate days (five administrations in total) in a novel environment. Seven days later, rats were re-exposed to the drug-paired environment, subjected to USVs recording, and then challenged with the same drug. Finally, 7 d after the challenge, rats were repeatedly exposed to the drug-paired environment and vocalizations were measured. Amphetamine was the only drug to stimulate 50-kHz USVs and 'trill' subtype emission during administration and challenge. Conversely, all rats emitted 50-kHz USVs when re-exposed to the test cage, and this effect was most marked in morphine-treated rats, and less evident in nicotine-treated rats. This study demonstrates that the direct and long-lasting effects of drugs on 50-kHz USVs are regulated differently, providing a better understanding of the usefulness of these vocalizations in the study of psychoactive drugs.

Individual differences in the conditioned and unconditioned rat 50-kHz ultrasonic vocalizations elicited by repeated amphetamine exposure

RATIONALE

Adult rats often produce 50-kHz ultrasonic vocalizations (USVs), particularly the frequency-modulated varieties, in appetitive situations. These calls are thought by some to reflect positive affective states and the reinforcing value of drugs such as amphetamine and cocaine.

OBJECTIVE

The objective of this study was to determine whether the number of unconditioned 50-kHz USVs elicited by amphetamine predicts the development and/or magnitude of drug-conditioned motivation.

METHODS

In three experiments, we recorded USVs before and after injections of 1 mg/kg amphetamine (i.v. or i.p.) administered once per session. Rats were categorized as "high callers" or "low callers" according to individual differences in the number of 50-kHz USVs elicited by their first amphetamine injection. We examined the conditioned appetitive behavior and conditioned place preference (CPP) that emerged in high and low callers after repeated pairings of amphetamine with specific contexts. We also examined whether amphetamine-induced calling was affected by treatment within an unfamiliar (test chamber) versus familiar (home cage) context.

RESULTS

Within an unfamiliar environment, the high callers consistently produced more amphetamine-induced 50-kHz USVs than the low callers. Compared to the low callers, high callers showed significantly greater amphetamine CPP as well as enhanced conditioned 50-kHz USVs and locomotor activity during anticipation of amphetamine. Individual differences were stable when amphetamine was administered in test chambers, but when it was administered in home cages, low callers showed an increase in 50-kHz calling that matched the high callers.

CONCLUSIONS

These findings suggest that individual differences in drug-induced USVs can reveal environment-sensitive traits involved in drug-related appetitive motivation.

The role of dopaminergic transmission through D1-like and D2-like receptors in amphetamine-induced rat ultrasonic vocalizations

RATIONALE

Systemic amphetamine (AMPH) administration increases the rate of 50-kHz ultrasonic vocalizations (USVs) in adult rats and preferentially enhances the 'trill' subtype; these effects of AMPH critically depend on noradrenergic transmission, but the possible contributions of dopamine are unclear.

OBJECTIVE

To assess the role of dopamine in 50-kHz USVs emitted drug-free and following systemic AMPH administration.

METHODS

Adult male Long-Evans rats pre-selected for high AMPH-induced calling rates were tested with AMPH (1 mg/kg, intraperitoneal (IP)) and saline following pretreatment with the following dopamine receptor antagonists: SCH 23390 (0.005-0.02 mg/kg, subcutaneous (SC)), SCH 39166 (0.03-0.3 mg/kg, SC), haloperidol (0.1, 0.2 mg/kg, IP), sulpiride (20-80 mg/kg, SC), raclopride (0.1-0.5 mg/kg, SC), clozapine (4 mg/kg, SC), risperidone (0.5 mg/kg, SC), and pimozide (1 mg/kg, IP). The dopamine and noradrenaline reuptake inhibitors (GBR 12909 and nisoxetine, respectively) were also tested, alone and in combination.

RESULTS

SCH 23390, SCH 39166, haloperidol, and raclopride dose-dependently inhibited vocalizations under AMPH and suppressed the proportion of trill calls. Sulpiride, however, had no discernable effect on call rate or profile, even at a high dose that reduced locomotor activity. Single doses of clozapine, risperidone, and pimozide all markedly decreased calling under saline and AMPH. Finally, GBR 12909 and nisoxetine failed to promote 50-kHz USVs detectably or alter the subtype profile, when tested alone or in combination.

CONCLUSIONS

The rate of 50-kHz USVs and the call subtype profile following systemic AMPH administration depends on dopaminergic neurotransmission through D1-like and D2-like receptors. However, inhibiting dopamine and/or noradrenaline reuptake appears insufficient to induce calling.

Failure of rewarding and locomotor stimulant doses of morphine to promote adult rat 50-kHz ultrasonic vocalizations

RATIONALE

Frequency-modulated 50-kHz ultrasonic vocalizations (USVs) are emitted by adult rats in response to psychostimulants and non-pharmacological appetitive stimuli and thus have been proposed to model positive affect.

OBJECTIVE

The main aim was to determine whether rewarding doses of morphine increase 50-kHz call rate or alter the relative prevalence of the trill call subtype.

METHODS

In experiment 1, USVs were recorded from adult male Long-Evans rats after subchronic morphine (1 mg/kg subcutaneous (SC)) administration, acute challenge with morphine (1 and 3 mg/kg SC) or amphetamine (1 mg/kg IP, positive control), and in conjunction with locomotor activity tests with morphine (1 and 3 mg/kg SC). In experiments 2 and 3, the USV altering, rewarding, and locomotor effects of morphine were examined using a conditioned place preference (CPP) procedure.

RESULTS

In experiment 1, morphine (1 mg/kg) initially suppressed calling; rats became tolerant to this effect with repeated exposure. Tested subsequently in singly- and pair-tested rats, morphine markedly decreased USVs but significantly increased locomotor activity. In experiments 2 and 3, morphine produced a significant CPP without increasing either unconditioned or conditioned USV emission. Morphine did not detectably alter the relative prevalence of 50-kHz call subtypes.

CONCLUSIONS

Although 50-kHz calls, and the trill call subtype in particular, have been proposed as an animal model of positive mood, not all euphoriant drugs acutely increase the rate of 50-kHz calling or consistently promote trill calls.

A rodent "self-report" measure of methamphetamine craving? Rat ultrasonic vocalizations during methamphetamine self-administration, extinction, and reinstatement

Rats emit ultrasonic vocalizations (USVs) in a variety of contexts, and it is increasingly clear that USVs reflect more complex information than mere positive and negative affect states. We sought to examine USVs in a common model of addiction and relapse, the self-administration/reinstatement paradigm, in order to gain insight into subjective states experienced by rats during various types of methamphetamine seeking. We measured three subtypes of "50kHz" USVs [flats, trills, and non-trill frequency modulated (FM) USVs], as well as long and short duration "22kHz" USVs, during self-administration and extinction training, and during reinstatement elicited by cues, a methamphetamine prime, cues+prime, or the pharmacological stressor yohimbine. During self-administration and extinction, rats emitted many flats and FMs, (and short duration "22kHz" USVs on day 1 of self-administration), but few trills. In contrast, methamphetamine priming injections potently enhanced FMs and trills, and trill production was correlated with the degree of methamphetamine+cue-elicited reinstatement. Cues alone yielded increases only in flat USVs during reinstatement, though a subset of rats displaying strong cue-induced reinstatement also emitted long duration, aversion-related "22kHz" USVs. Although yohimbine administration caused reinstatement, it did not induce "22kHz" USVs in methamphetamine-experienced or methamphetamine-naïve rats (unlike footshock stress, which did induce long duration "22kHz" USVs). These findings demonstrate heterogeneity of rat USVs emitted during different types of methamphetamine seeking, and highlight their potential usefulness for gaining insight into the subjective states of rats in rodent models of drug addiction and relapse.

The missing variable: ultrasonic vocalizations reveal hidden sensitization and tolerance-like effects during long-term cocaine administration

RATIONALE

Subtypes of 50-kHz ultrasonic vocalizations (USVs) in rats are thought to reflect positive affect and occur with cocaine or amphetamine delivery. In contexts predicting forthcoming cocaine, pre-drug anticipatory USVs are initially minimal during daily sessions but gradually escalate over several weeks, presumably as the animal learns to expect and look forward to impending drug access. To gain more insight into motivational aspects of cocaine intake in animal models of drug dependence studies, it is important to compare experience-dependent changes in lever response rate, USVs, and locomotion during cocaine conditioning and extinction trials.

OBJECTIVE

To address whether cocaine-induced increases in lever responding and locomotor activity correspond with USV production. The study also determined whether short-term cocaine and context deprivation effects could be detected during conditioning or extinction.

METHODS

Rats underwent 20 days of 60-min sessions of self- or yoked administration of cocaine (0.75 mg/kg/infusion, i.v.), followed by 19 days of extinction training (8 weeks total, weekends off).

RESULTS

Lever responding for cocaine and cocaine-induced locomotor activity increased across conditioning sessions. In contrast, the number of frequency modulated 50-kHz USVs evoked in response to cocaine infusion decreased with cocaine experience, suggesting perhaps tolerance to the rewarding properties of the drug. In addition, USVs but not lever pressing or locomotion are affected after brief periods of drug and/or drug context abstinence.

CONCLUSIONS

Except for initial drug exposure, increased cocaine seeking during cocaine delivery could reflect either enhanced drug motivation or the development of drug tolerance, but not enhanced positive affect.

α- and β-Adrenergic receptors differentially modulate the emission of spontaneous and amphetamine-induced 50-kHz ultrasonic vocalizations in adult rats

Amphetamine (AMPH) increases adult rat 50-kHz ultrasonic vocalizations, preferentially promoting frequency-modulated (FM) calls that have been proposed to reflect positive affect. The main objective of this study was to investigate a possible noradrenergic contribution to AMPH-induced calling. Adult male Long-Evans rats were tested with AMPH (1 mg/kg intraperitoneal) or saline combined with various systemic pretreatments: clonidine (α2 adrenergic agonist), prazosin (α1 antagonist), atipamezole (α2 antagonist), propranolol, betaxolol, and/or ICI 118,551 (β1/β2, β1, and β2 antagonists, respectively), nadolol (β1/β2 antagonist, peripheral only), or NAD-299 (5HT(1A) antagonist). In addition, effects of cirazoline (α1 adrenergic agonist) and cocaine (0.25-1.5 mg/kg intravenous) were studied alone. AMPH-induced calling was suppressed by low-dose clonidine and prazosin. Cirazoline and atipamezole did not significantly affect calling rate. Propranolol, without affecting the call rate, dose dependently promoted 'flat' calls under AMPH while suppressing 'trills,' thus reversing the effects of AMPH on the 'call subtype profile.' This effect of propranolol seemed to be mediated by simultaneous inhibition of CNS β1 and β2 rather than by 5HT(1A) receptors. Finally, cocaine elicited fewer calls than did AMPH, but produced the same shift in the call subtype profile. Taken together, these results reveal differential drug effects on flat vs trill vs other FM 50-kHz calls. These findings highlight the value of detailed call subtype analyses, and show that 50-kHz calls are associated with adrenergic α1- and β-receptor mechanisms. These preclinical findings suggest that noradrenergic contributions to psychostimulant subjective effects may warrant further investigation.

Repeated intravenous cocaine experience: development and escalation of pre-drug anticipatory 50-kHz ultrasonic vocalizations in rats

Ultrasonic vocalization (USV) in the 50-kHz range occurs in rats immediately upon first-time exposure to cocaine or amphetamine, and rapidly increases with repetitive drug exposure at the same dose. This sensitized positive-affect response to these drugs of abuse is persistent in that the peak level of USVs again appears when the drug is reintroduced after several weeks of drug discontinuation. The present study explored whether with enough experience USVs might be elicited, and gradually escalate, in anticipation of impending drug delivery. Rats were trained to self-administer (SA) cocaine intravenously by lever pressing 5 days per week for 4 weeks. Yoked rats received experimenter-delivered cocaine matching that of SA rats. USVs and locomotor activity were recorded during each 10-min period prior to 60-min drug access sessions. Extinction trials in which drug access was denied were then carried out over an additional 4-week period. After about a week of cocaine experience, both the SA and yoked groups began to progressively increase USVs when placed in an environment that predicted forthcoming drug exposure. Extinction of anticipatory calls and locomotion occurred over days after drug access ended. USVs may be a useful model for specifically investigating the neural basis of drug anticipation and aid in developing and assessing new addiction treatment strategies for reducing craving and relapse.