Stress-induced vocalisation in adult animals. A valid model of anxiety?

Anxiolytic-like effects of YL-IPA08, a potent ligand for the translocator protein (18 kDa) via regulating the synaptic plasticity in hippocampus

TSPO, translocator protein (18 kDa) ligands have demonstrated consistent antidepression and anxiolytic effects in several preclinical studies. This study aimed to examine whether YL-IPA08[N-ethyl-N-(2-pyridinylmethyl)-2-(3,4-ichlorophenyl) -7-methylimidazo [1,2-a] pyridine-3-acetamide hydrochloride], a potent and selective TSPO ligand synthesized by our institute, could alleviate anxiety-related behaviors induced by electric shock (ES) and investigate its underlying mechanism. As expected, we showed that chronic treatment with YL-IPA08 significantly reversed anxiety-related behaviors induced by electrical stimulation (0.5 mA, 12 times, duration 1s, interval 10s) exposure. Using the analysis of RNA-sequencing (RNA-seq) technology, it was found that the differential genes associated with the anxiolytic effect of YL-IPA08 were mainly related to synaptic plasticity. Furthermore, YL-IPA08 restored the decreased levels of brain-derived neurotrophic factor (BDNF), synapse-related protein (e.g. synapsin-1 and post-synaptic density95, PSD95), and the number of doublecortin (DCX) + neurons in the hippocampus of post-ES mice. In addition, YL-IPA08 also enhanced the dendritic complexity and dendritic spine density of hippocampal dentate gyrus (DG) granule neurons. Meanwhile, the induction of long-term potentiation (LTP) was significantly enhanced by YL-IPA08. In summary, the findings from the current study showed that YL-IPA08 exerted a clear anxiolytic effect, which might be partially mediated by promoting hippocampal neuroplasticity.

Acute anxiogenic effects of escitalopram are associated with mild alterations in D-amphetamine-induced behavior and social approach evoked by playback of 50-kHz ultrasonic vocalizations in rats

Rats communicate through auditory signals in the ultrasonic range, so-called ultrasonic vocalizations (USV). Short, high-frequency 50-kHz USV are associated with positive affective states and are emitted in appetitive situations, often rewarding social interactions, such as rough-and-tumble play and mating. Exaggerated levels of 50-kHz USV emission can be observed in response to psychostimulants, most notably d-amphetamine (AMPH). There is robust evidence suggesting that 50-kHz USV serve as affiliative signals and help to maintain or re-establish social proximity. A key neurotransmitter involved in behavioral regulation is serotonin (5-hydroxytryptamine, 5-HT). This includes both, the regulation of anxiety-related behavior and ultrasonic communication. Here, we show that acute treatment with the selective 5-HT reuptake inhibitor (SSRI) escitalopram (ESC) leads to increased anxiety-related behavior in the elevated plus maze and tested whether such acute anxiogenic effects of ESC result in alterations in ultrasonic communication in sender and/or receiver. To this aim, we conducted a dose-response study in male rats and assessed AMPH-induced hyperactivity and 50-kHz ultrasonic calling in the sender and social approach behavior evoked by playback of pro-social 50-kHz USV in the receiver. Acute ESC treatment affected both, sender and receiver. This was reflected in a lack of AMPH-induced changes in acoustic features of 50-kHz USV and absence of social exploratory behavior evoked by 50-kHz USV playback, respectively. Albeit the SSRI effects were relatively mild, this supports the notion that the 5-HT system is involved in the regulation of a key aspect of the social behavior repertoire of rodents, namely socio-affective communication through 50-kHz USV.

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

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

Association between Novel Object Recognition/Spontaneous Alternation Behavior and Emission of Ultrasonic Vocalizations in Rats: Possible Relevance to the Study of Memory

Rats emit ultrasonic vocalizations (USVs) in situations with emotional valence, and USVs have also been proposed as a marker for memories conditioned to those situations. This study investigated whether USV emissions can predict and/or be associated with the behavior of rats in tests that evaluate unconditioned memory. To this end, rats were subjected to “tickling”, a procedure of heterospecific play that has emotional valence and elicits the emission of USVs, and afterwards evaluated in the novel object recognition test (NOR) and in the single trial continuous spontaneous alternation behavior (SAB) test in a Y maze. The number of 22-kHz USVs (aversive) and 50-kHz USVs (appetitive) emitted in response to tickling and during NOR and SAB tests were scored, and the correlations among them and with rats’ behavior evaluated. Rats emitted 50-kHz USVs, but not 22-kHz USVs, during the NOR and SAB tests, and such calling behavior was not linked with the behavioral readouts indicative of memory function in either test. However, rats that prevalently emitted 22-kHz USVs in response to tickling displayed an impaired NOR performance. These findings suggest that measuring the emission of USVs could be of interest in studies of unconditioned memory, at least with regard to 22-kHz USVs.

Neurotoxic Effects of Neonicotinoids on Mammals: What Is There beyond the Activation of Nicotinic Acetylcholine Receptors?-A Systematic Review

Neonicotinoids are a class of insecticides that exert their effect through a specific action on neuronal nicotinic acetylcholine receptors (nAChRs). The success of these insecticides is due to this mechanism of action, since they act as potent agonists of insect nAChRs, presenting low affinity for vertebrate nAChRs, which reduces potential toxic risk and increases safety for non-target species. However, although neonicotinoids are considered safe, their presence in the environment could increase the risk of exposure and toxicity. On the other hand, although neonicotinoids have low affinity for mammalian nAChRs, the large quantity, variety, and ubiquity of these receptors, combined with its diversity of functions, raises the question of what effects these insecticides can produce in non-target species. In the present systematic review, we investigate the available evidence on the biochemical and behavioral effects of neonicotinoids on the mammalian nervous system. In general, exposure to neonicotinoids at an early age alters the correct neuronal development, with decreases in neurogenesis and alterations in migration, and induces neuroinflammation. In adulthood, neonicotinoids induce neurobehavioral toxicity, these effects being associated with their modulating action on nAChRs, with consequent neurochemical alterations. These alterations include decreased expression of nAChRs, modifications in acetylcholinesterase activity, and significant changes in the function of the nigrostriatal dopaminergic system. All these effects can lead to the activation of a series of intracellular signaling pathways that generate oxidative stress, neuroinflammation and, finally, neuronal death. Neonicotinoid-induced changes in nAChR function could be responsible for most of the effects observed in the different studies.

Animal models of fibromyalgia: What is the best choice?

Fibromyalgia (FM) is a complex syndrome, with an indefinite aetiology and intricate pathophysiology that affects 2 - 3% of the world population. From the beginning of the 2000s, experimental animal models have been developed to mimic clinical FM and help obtain a better understanding of the relevant neurobiology. These animal models have enabled a broad study of FM symptoms and mechanisms, as well as new treatment strategies. Current experimental FM models include the reserpine-induced systemic depletion of biogenic amines, muscle application of acid saline, and stress-based (cold, sound, or swim) approaches, among other emerging models. FM models should: (i) mimic the cardinal symptoms and complaints reported by FM patients (e.g., spontaneous nociception, muscle pain, hypersensitivity); (ii) mimic primary comorbidities that can aggravate quality of life and lead to worse outcomes (e.g., fatigue, sleep disturbance, depression, anxiety); (iii) mimic the prevalent pathological mechanisms (e.g., peripheral and central sensitization, inflammation/neuroinflammation, change in the levels of the excitatory and inhibitory neurotransmitters); and (iv) demonstrate a pharmacological profile similar to the clinical treatment of FM. However, it is difficult for any one of these models to include the entire spectrum of clinical FM features once even FM patients are highly heterogeneous. In the past six years (2015 - 2020), a wide range of experimental FM studies has amounted to the literature reinforcing the need for an updated review. Here we have described, in detail, several approaches used to experimentally study FM, with a focus on recent studies in the field and in previously less discussed mechanisms. We highlight each model's challenges, limitations, and future directions, intending to help preclinical researchers establish the correct experimental FM model to use depending on their goals.

Reduced emission of alarm 22-kHz ultrasonic vocalizations during fear conditioning in rats lacking the serotonin transporter

Rats display a rich social behavioral repertoire. An important component of this repertoire is the emission of whistle-like calls in the ultrasonic range, so-called ultrasonic vocalizations (USV). Long low-frequency 22-kHz USV occur in aversive situations, including aggressive interactions, predator exposure, and electric shocks during fear conditioning. They are believed to reflect a negative affective state akin to anxiety and fear. A prominent theory suggests that 22-kHz USV function as alarm calls to warn conspecifics. Serotonin (5-hydroxytryptamine, 5-HT) is strongly implicated in the regulation of affective states, particularly anxiety and fear. A key component of the system is the 5-HT transporter (5-HTT, also known as SERT), regulating 5-HT availability in the synaptic cleft. In the present experiment, we studied the effects of SERT deficiency on overt fear-related behavior and alarm 22-kHz USV during fear conditioning in male and female rats. While overt fear-related behavior was not affected by SERT deficiency and sex, the emission of alarm 22-kHz USV was clearly reduced in homozygous SERT^-/- but not heterozygous SERT^+/- mutants, as compared to their wildtype SERT^+/+ littermate controls. Genotype effects were particularly prominent in females. Females in general emitted fewer alarm 22-kHz USV than males. This supports the view that 22-kHz USV are, at least partly, independently regulated from anxiety or fear and as socially mediated alarm calls do not simply express a negative affective state. Reduced 22-kHz USV emission in rats lacking SERT might be due to social deficits in the use of 22-kHz USV as a socio-affective signal to warn conspecifics about threats.

Effect of Neuropeptide S Administration on Ultrasonic Vocalizations and Behaviour in Rats with Low vs. High Exploratory Activity

Neuropeptide S (NPS) is a peptide neurotransmitter that in animal studies promotes wakefulness and arousal with simultaneous anxiety reduction, in some inconsistency with results in humans. We examined the effect of NPS on rat ultrasonic vocalizations (USV) as an index of affective state and on behaviour in novel environments in rats with persistent inter-individual differences in exploratory activity. Adult male Wistar rats were categorised as of high (HE) or low (LE) exploratory activity and NPS was administered intracerebroventricularly (i.c.v.) at a dose of 1.0 nmol/5 µL, after which USVs were recorded in the home-cage and a novel standard housing cage, and behaviour evaluated in exploration/anxiety tests. NPS induced a massive production of long and short 22 kHz USVs in the home cage that continued later in the novel environment; no effect on 50 kHz USVs were found. In LE-rats, the long 22 kHz calls were emitted at lower frequencies and were louder. The effects of NPS on behaviour appeared novelty- and test-dependent. NPS had an anxiolytic-like effect in LE-rats only in the elevated zero-maze, whereas in HE-rats, locomotor activity in the zero-maze and in a novel standard cage was increased. Thus NPS appears as a psychostimulant peptide but with a complex effect on dimensions of affect.

CRF-5-HT interactions in the dorsal raphe nucleus and motivation for stress-induced opioid reinstatement

RATIONALE

The serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Our previous data show that stressors can inhibit 5-HT neuronal activity and release by stimulating the release of the stress neurohormone corticotropin-releasing factor (CRF) within the serotonergic dorsal raphe nucleus (DRN). The inhibitory effects of CRF on 5-HT DRN neurons are indirect, mediated by CRF-R1 receptors located on GABAergic afferents.

OBJECTIVES

We tested the hypothesis that DRN CRF-R1 receptors contribute to stress-induced reinstatement of morphine-conditioned place preference (CPP). We also examined the role of this circuitry in stress-induced negative affective state with 22-kHz distress ultrasonic vocalizations (USVs), which are naturally emitted by rats in response to environmental challenges such as pain, stress, and drug withdrawal.

METHODS

First, we tested if activation of CRF-R1 receptors in the DRN with the CRF-R1-preferring agonist ovine CRF (oCRF) would reinstate morphine CPP and then if blockade of CRF-R1 receptors in the DRN with the CRF-R1 antagonist NBI 35965 would attenuate swim stress-induced reinstatement of morphine CPP. Second, we tested if intra-DRN pretreatment with NBI 35965 would attenuate foot shock stress-induced 22-kHz USVs.

RESULTS

Intra-DRN injection of oCRF reinstated morphine CPP, while intra-DRN injection of NBI 35965 attenuated swim stress-induced reinstatement. Moreover, intra-DRN pretreatment with NBI 35965 significantly reduced 22-kHz distress calls induced by foot shock.

CONCLUSIONS

These data provide evidence that stress-induced negative affective state is mediated by DRN CRF-R1 receptors and may contribute to reinstatement of morphine CPP.

Are There Multiple Motivators for Helping Behavior in Rats?

Empathy is the ability to (a) be affected by and share the emotional state of another; (b) assess the reasons for the other’s state; and (c) identify with the other, adopting their perspective. This phenomenon has been shown to exist in several species and is proposed as a motivator for prosocial behavior. The experimental study of this feature in laboratory rodents is a more viable alternative in comparison to wild animals. A recent report showed that rats opened a door to free their cage mate from a restraint box. Although this behavior has been suggested to be motivated by empathy, this fact has been questioned by several studies that proposed other motivators for the releasing behavior. In the present study, we use an adaptation of the protocol of releasing behavior to investigate aspects of empathy and pro-sociality such as familiarity and reciprocity. In addition, we addressed some potential motivational factors that could influence this behavior. The main results showed that (1) rats opened the restraint box to free conspecifics most of the time; (2) direct reciprocity or past restriction experience did not improve releasing performance, probably due to a ceiling effect; (3) after a series of trials in the presence of a restricted conspecific, the free rat continues to open the restraint box even if it is empty; (4) in general, the opening performance improves across trials and phases, resembling learning curves; (5) if the first series of trials occurs with the empty box, the opening behavior does not occur and is modest in subsequent trials with a trapped animal; (6) the exploratory drive toward the restraint box and desire for social contact do not seem to function as key motivators for releasing behavior. In conclusion, our findings do not support that the opening behavior is exclusively related to empathic motivation. While multiple factors might be involved, our study suggests that task learning triggered (and possibly reinforced) by the presence of the restricted rat can function as a motivator. Further investigations are required to fully understand the mechanisms and motivation factors guiding the releasing behavior.

Personality driven alcohol and drug abuse: New mechanisms revealed

While the majority of the regular consumers of alcohol controls their consumption well over life span and even takes instrumentalization benefits from it, a minority, but yet high total number of users develops an alcohol addiction. It has long been known that particular personality types are more addiction prone than others. Here we review recent progress in the understanding of neurobiological pathways that determine personality and facilitate drug abuse. Novel approaches to characterize personality traits leading to addiction proneness in social settings in mice are discussed. A common genetic and neurobiological base for the behavioural traits of sensation seeking or a depressed phenotype and escalating alcohol consumption are reviewed. Furthermore, recent progress on how social and cognitive factors, including impulsivity and decision making, act at brain level to make an individual more vulnerable to alcohol abuse, are discussed. Altogether, this review provides an update on brain mechanisms underlying a broad spectrum of personality traits that make an individual more prone to alcohol and drug abuse and addiction.

Social context increases ultrasonic vocalizations during restraint in adult mice

Adult mice emit many ultrasonic vocalizations (USVs) during social interaction tasks, but only a few studies have yet reported USVs in stressed adult mice. Our aim was to study which experimental conditions favor USV emission during behaviors associated with different emotional states. As USVs likely mediate social communication, we hypothesized that temporary social isolation followed by exposure to a novel social congener would promote USV emission. USVs were recorded in three different behavioral paradigms: restraint, free moving in a new environment, and during a social interaction task. We compared USV emission, with or without the presence of a social congener, in animals socially isolated during different periods (0, 6 or 21 days). Social isolation decreased the number of USVs during free moving, whereas it increased during restraint. During the social interaction task, animals produced high-frequency USVs (median: 72.6 kHz, 25-75% range: 67.6-78.2 kHz), especially when the social partner was active and social motivation was high. During restraint, presence of a social congener increased the call rate of low-frequency USVs (median: 52.4 kHz, 25-75% range: 44.8-56.5 kHz). USV frequency followed two unimodal distributions that distinguished low-frequency USVs (≤ 60 kHz) mainly emitted during free-moving (90.9% of total USVs) and restraint (93.1%) conditions, from high-frequency USVs (> 60 kHz) mainly emitted during the social interaction task (85.1% of total USVs). The present study confirms that USV call rate and frequency depend on behavioral states, and provides evidence that the presence of a congener promotes ultrasonic vocalizations in restrained adult mice.

Potential Impact of Construction Noise on Selected Zoo Animals

In anticipation of a major construction project in an urban New Zealand zoo, a study was initiated to assess the response to construction noise of selected animal species (elephant, giraffe, emu and alligator) previously observed to be sensitive to this kind of noise. The overall aim was to detect any signs of aversive responses to this noise to enable keepers to recognize these and take any necessary mitigating actions during the construction period. The experimental approach involved the creation of acoustic maps of each focal animal enclosure, a series of 90-min video recordings of the animals' behavior in response to ambient noise (control) and amplified broadcast of pre-recorded continuous and intermittent construction noise. Concentration of fecal corticosterone metabolites was also measured for the emus. Key findings were that giraffes, elephants and emus appeared to show an increase in behaviors that could indicate stress or agitation including vigilance and locomotion and may prefer quieter regions of their enclosure during sound exposure. Giraffes also increased close contact with conspecifics when exposed to construction noise. While alligators did not show clear evidence of noise-related stress, our findings indicated that all focal species showed some behavioral responses to recorded construction noise.

Short-term, low-dose fluoxetine prevents oestrous cycle-linked increase in anxiety-like behaviour in female rats

BACKGROUND AND AIMS

We sought a robust behavioural test that evoked increased anxiety-like behaviour during the late dioestrus phase of the oestrous cycle (similar to the premenstrual period in women) and tested whether this could be prevented by acute low-dose fluoxetine (FLX).

METHODS

Female Wistar rats in different stages of their cycle were exposed to four different tests of anxiety-like behaviour.

RESULTS

No oestrous cycle differences were detected in fear potentiated startle or conditioned freezing to an aversive context. In a light switch-off test where rats move from one compartment of a shuttle-box to the other to turn off an aversive light, females displayed enhanced responding in late dioestrus. During isolation restraint stress females in late dioestrus emitted three times more 22 kHz ultrasound vocalisations (USV) than at other cycle stages. Using the USV test, short-term administration of low-dose FLX (1.75 mg kg^-1, i.p.) designed to blunt the sharp fall in brain allopregnanolone concentration during late dioestrus but without affecting 5-HT systems, prevented the increase in isolation stress-evoked USVs.

CONCLUSIONS

The light switch-off and isolation restraint-induced USV tests evoke unconditioned adverse emotional responses that are ethologically relevant and sensitive to oestrous cycle stage. The USV test fulfils many criteria required of a model for premenstrual syndrome in women. Using the USV test, short-term administration of FLX to increase brain allopregnanolone concentration without affecting 5-HT systems prevented the increased USV responding in late dioestrus. Short-term low-dose FLX treatment may have potential to alleviate development of adverse premenstrual symptoms in women.

Emission of 22 kHz vocalizations in rats as an evolutionary equivalent of human crying: Relationship to depression

There is no clear relationship between crying and depression based on human neuropsychiatric observations. This situation originates from lack of suitable animal models of human crying. In the present article, an attempt will be made to answer the question whether emission of rat aversive vocalizations (22 kHz calls) may be regarded as an evolutionary equivalent of adult human crying. Using this comparison, the symptom of crying in depressed human patients will be reanalyzed. Numerous features and characteristics of rat 22 kHz aversive vocalizations and human crying vocalizations are equivalent. Comparing evolutionary, biological, physiological, neurophysiological, social, pharmacological, and pathological aspects have shown vast majority of common features. It is concluded that emission of rat 22 kHz vocalizations may be treated as an evolutionary vocal homolog of human crying, although emission of 22 kHz calls is not exactly the same phenomenon because of significant differences in cognitive processes between these species. It is further concluded that rat 22 kHz vocalizations and human crying vocalizations are both expressing anxiety and not depression. Analysis of the relationship between anxiety and depression reported in clinical studies supports this conclusion regardless of the nature and extent of comorbidity between these pathological states.

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

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

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.

NOAEL-dose of a neonicotinoid pesticide, clothianidin, acutely induce anxiety-related behavior with human-audible vocalizations in male mice in a novel environment

Neonicotinoids are novel systemic pesticides acting as agonists on the nicotinic acetylcholine receptors (nAChRs) of insects. Experimental studies have revealed that neonicotinoids pose potential risks for the nervous systems of non-target species, but the brain regions responsible for their behavioral effects remain incompletely understood. This study aimed to assess the neurobehavioral effects of clothianidin (CTD), a later neonicotinoid developed in 2001 and widely used worldwide, and to explore the target regions of neonicotinoids in the mammalian brain. A single-administration of 5 or 50mg/kg CTD to male C57BL/6N mice at or below the no-observed-adverse-effect level (NOAEL) induced an acute increase in anxiety during the elevated plus-maze test. In addition, mice in the CTD-administered group spontaneously emitted human-audible vocalizations (4-16kHz), which are behavioral signs of aversive emotions, and showed increased numbers of c-fos immunoreactive cells in the paraventricular thalamic nucleus and dentate gyrus of the hippocampus. In conclusion, mice exposed to NOAEL-dose CTD would be rendered vulnerable to a novel environment via the activation of thalamic and hippocampal regions related to stress responses. These findings should provide critical insight into the neurobehavioral effects of neonicotinoids on mammals.

Neurotensin NTS1 and NTS2 receptor agonists produce anxiolytic-like effects in the 22-kHz ultrasonic vocalization model in rats

Neurotensin is a neuropeptide neurotransmitter that interacts with multiple neurotransmitter systems, including those regulating amygdalar function, via NTS₁ and NTS₂ receptors. Both receptors are expressed in the amygdala and agonists for NTS₁ or NTS₂ receptors have exhibited anxiolytic effects in animal models. Systemic adminstration of NTS₁ receptor agonist PD149163 was recently shown to reduce footshock conditioned 22-kHz ultrasonic vocalizations in rats, suggesting that PD149163 produced an anxiolytic effect. The effects that neurotensin may have or a selective NTS₂ receptor agonist may have on 22-kHz vocalizations has yet to be examined. The current study evaluated the effects of intracerebroventricularly administered neurotensin (0.1-10.0μg), PD149163 (0.1-10.0ng), or the NTS₂ receptor agonist JMV-431 (0.1-1.0μg) on footshock conditioned 22-kHz vocalizations in male Wistar rats. Neurotensin, PD149163, and JMV-431 all significantly reduced the number 22-kHz calls. No changes in call duration were found, suggesting that non-specific drug effects do not account for the reductions in 22-kHz calls. These data support anxiolytic effects produced by activation of NTS₁ or NTS₂ receptors, and suggest that neurotensin plays a natural role in the expression of conditioned USVs. These data suggest that both receptor subtypes are putative pharmacologic targets.

Severity assessment and scoring for neurosurgical models in rodents

The most important acute neurological diseases seen at neurosurgery departments are traumatic brain injuries (TBI) and subarachnoid hemorrhages (SAH). In both diseases the pathophysiological sequela are complex and have not been fully understood up to now, and rodent models using rats and mice are most suitable for the investigation of the pathophysiological details. In both models, surgery is performed under anesthesia, followed by assessment of their functional outcome and behavioral testing before brain tissue analysis after euthanasia. Postoperative analgesia is mandatory, and supplementary care is highly recommended for refinement purposes. Pain and stress assessment is mainly based on clinical and behavioral signs, and further research is needed to improve the evaluation of severity in these models.

Social defeat protocol and relevant biomarkers, implications for stress response physiology, drug abuse, mood disorders and individual stress vulnerability: a systematic review of the last decade

INTRODUCTION

Social defeat (SD) in rats, which results from male intraspecific confrontations, is ethologically relevant and useful to understand stress effects on physiology and behavior.

METHODS

A systematic review of studies about biomarkers induced by the SD protocol and published from 2002 to 2013 was carried out in the electronic databases PubMed, Web of Knowledge and ScienceDirect. The search terms were: social defeat, rat, neurotrophins, neuroinflammatory markers, and transcriptional factors.

RESULTS

Classical and recently discovered biomarkers were found to be relevant in stress-induced states. Findings were summarized in accordance to the length of exposure to stress: single, repeated, intermittent and continuous SD. This review found that the brain-derived neurotrophic factor (BDNF) is a distinct marker of stress adaptation. Along with glucocorticoids and catecholamines, BDNF seems to be important in understanding stress physiology.

CONCLUSION

The SD model provides a relevant tool to study stress response features, development of addictive behaviors, clinic depression and anxiety, as well as individual differences in vulnerability and resilience to stress.

Behavioral and pharmacological validation of an integrated fear-potentiated startle and prepulse inhibition paradigm

Fear-potentiated startle (FPS) and prepulse inhibition (PPI) of acoustic startle are two widely used paradigms specifically designed to capture the impact of negative emotion (e.g. fear) and preattentive function on startle response. Currently, there is no single paradigm that incorporates both FPS and PPI, making it impossible to examine the potential interactions between fear and attention in the regulation of startle response. In this study, we developed an integrated FPS and PPI test protocol and validated it with psychoactive drugs. In Experiment 1, male Sprague-Dawley rats were randomly assigned to one of five groups, receiving either Light -Shock conditioning trials, non-overlapping Lights and Shocks, Light alone, Shock alone, or no Light and Shock. They were then tested for startle response and PPI concurrently, under the Light or No Light. FPS was observed only in rats subjected to fear conditioning, whereas all rats showed PPI and startle habituation. Experiment 2 used this paradigm and demonstrated a dissociative effect between diazepam (an anxiolytic drug) and phencyclidine (a nonselective NMDA receptor antagonist) on FPS and PPI. Diazepam suppressed both FPS and PPI, while PCP selectively disrupted PPI but not FPS. The diazepam's anxiolytic effect on FPS was further confirmed in the elevated plus maze test. Together, our findings indicate that our paradigm combines FPS and PPI into a single paradigm, and that is useful to examine potential interactions between multiple psychological processes, to identify the common neural substrates and to screen new drugs with multiple psychoactive effects.

Air puff-induced 22-kHz calls in F344 rats

Air puff-induced ultrasonic vocalizations in adult rats, termed "22-kHz calls," have been applied as a useful animal model to develop psychoneurological and psychopharmacological studies focusing on human aversive affective disorders. To date, all previous studies on air puff-induced 22-kHz calls have used outbred rats. Furthermore, newly developed gene targeting technologies, which are essential for further advancement of biomedical experiments using air puff-induced 22-kHz calls, have enabled the production of genetically modified rats using inbred rat strains. Therefore, we considered it necessary to assess air puff-induced 22-kHz calls in inbred rats. In this study, we assessed differences in air puff-induced 22-kHz calls between inbred F344 rats and outbred Wistar rats. Male F344 rats displayed similar total (summed) duration of air puff-induced 22 kHz vocalizations to that of male Wistar rats, however, Wistar rats emitted fewer calls of longer duration, while F344 rats emitted higher number of vocalizations of shorter duration. Additionally, female F344 rats emitted fewer air puff-induced 22-kHz calls than did males, thus confirming the existence of a sex difference that was previously reported for outbred Wistar rats. The results of this study could confirm the reliability of air puff stimulus for induction of a similar amount of emissions of 22-kHz calls in different rat strains, enabling the use of air puff-induced 22-kHz calls in inbred F344 rats and derived genetically modified animals in future studies concerning human aversive affective disorders.

Resolving the neural circuits of anxiety

Although anxiety disorders represent a major societal problem demanding new therapeutic targets, these efforts have languished in the absence of a mechanistic understanding of this subjective emotional state. While it is impossible to know with certainty the subjective experience of a rodent, rodent models hold promise in dissecting well-conserved limbic circuits. The application of modern approaches in neuroscience has already begun to unmask the neural circuit intricacies underlying anxiety by allowing direct examination of hypotheses drawn from existing psychological concepts. This information points toward an updated conceptual model for what neural circuit perturbations could give rise to pathological anxiety and thereby provides a roadmap for future therapeutic development.

Attenuation of social interaction-associated ultrasonic vocalizations and spatial working memory performance in rats exposed to chronic unpredictable stress

Exposure to unpredictable chronic mild stress (CUS) is a commonly used protocol in rats that is reported to evoke antidepressant-reversible behaviors such as loss of preference for a sweetened water solution which is taken as an analog of the anhedonia seen in major depression. However, the induction of anhedonic-like behavior by chronic mild stress, gauged by an animal's preference for sucrose solution, is not fully reproducible and consistent across laboratories. In this study, we compared a widely used behavioral marker of anhedonia - the sucrose preference test, with another phenotypic marker of emotional valence, social interaction-associated ultrasonic vocalizations as well as a marker of an anxiety-like phenotype, novelty-suppressed feeding, and cognitive performance in the eight arm radial maze task in adult male Sprague-Dawley rats. Chronic four-week exposure to unpredictable mild stressors resulted in 1) attenuation of social interaction-associated ultrasonic vocalizations 2) attenuation of spatial memory performance on the radial arm maze 3) attenuation of body weight gain and 4) increased latency to feed in a novelty-suppressed feeding task. However, chronic exposure to CUS did not result in any significant change in sucrose preference at one-week and three-week intervals. Our results argue for the utility of ultrasonic vocalizations in a social interaction context as a comparable alternative or adjunct to the sucrose preference test in determining the efficacy of CUS to generate an anhedonic-like phenotypic state.

The long-lasting antidepressant effects of rapastinel (GLYX-13) are associated with a metaplasticity process in the medial prefrontal cortex and hippocampus

Rapastinel (GLYX-13) is an N-methyl-d-aspartate receptor (NMDAR) modulator that has characteristics of a glycine site partial agonist. Rapastinel is a robust cognitive enhancer and facilitates hippocampal long-term potentiation (LTP) of synaptic transmission in slices. In human clinical trials, rapastinel has been shown to produce marked antidepressant properties that last for at least one week following a single dose. The long-lasting antidepressant effect of a single dose of rapastinel (3mg/kg IV) was assessed in rats using the Porsolt, open field and ultrasonic vocalization assays. Cognitive enhancement was examined using the Morris water maze, positive emotional learning, and contextual fear extinction tests. LTP was assessed in hippocampal slices. Dendritic spine morphology was measured in the dentate gyrus and the medial prefrontal cortex. Significant antidepressant-like or cognitive enhancing effects were observed that lasted for at least one week in each model. Rapastinel facilitated LTP 1day-2weeks but not 4weeks post-dosing. Biweekly dosing with rapastinel sustained this effect for at least 8weeks. A single dose of rapastinel increased the proportion of whole-cell NMDAR current contributed by NR2B-containing NMDARs in the hippocampus 1week post-dosing, that returned to baseline by 4weeks post-dosing. The NMDAR antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) blocked the antidepressant-like effect of rapastinel 1week post dosing. A single injection of rapastinel also increased mature spine density in both brain regions 24h post-dosing. These data demonstrate that rapastinel produces its long-lasting antidepressant effects via triggering NMDAR-dependent processes that lead to increased sensitivity to LTP that persist for up to two weeks. These data also suggest that these processes led to the alterations in dendritic spine morphologies associated with the maintenance of long-term changes in synaptic plasticity associated with learning and memory.

Ultrasonic vocalizations during intermittent swim stress forecasts resilience in a subsequent juvenile social exploration test of anxiety

Current behavioral paradigms of stress resilience traditionally employ forms of prior manipulation or subsequent testing. Recent work has reported adult rat ultrasonic vocalizations (USVs) emitted during intermittent swim stress (ISS) may serve as a predictor of resilience. ISS-induced USVs predicted resilience on several endpoints of behavioral depression and may be considered a forecast of innate resilience. However, a potential problem for these previous findings is the lack of generalizability to other contexts, because both the stress induction and post-stress testing occur in water. The current study tests the generalizability of USVs as a predictor of stress resilience in a non-water-based post-test, the juvenile social exploration test of anxiety. The results provide further support that USVs emitted during ISS predict resilience to depression- and anxiety-like behaviors. Extensions of this work to examine the neurobiology of innate resilience associated with ISS-induced USVs are discussed with comparisons to extant models of learned resilience.

The emission of stress-induced 22-kHz calls in female rats is independent of testosterone levels

Although emission of ultrasonic calls in rats induced by stress, referred to as "22-kHz calls," is dependent on circulating testosterone levels in males, it is still unknown whether the same testosterone-based regulation is applicable to female rats. In this study, we investigated the sex difference in the emission of air-puff-induced 22-kHz calls in rats on the basis of the hypothesis that female rats would emit fewer 22-kHz calls, and assessed whether male-like circulating testosterone levels can also influence the emission of 22-kHz calls in females. The experimental results showed that female rats emit significantly fewer 22-kHz calls than male rats. However, male-like circulating testosterone levels have little effect on the emission of 22-kHz calls in females. Hence, it is suggested that there is a sex difference in stress-induced 22-kHz calls in rats and, in contrast to male rats, the emission of 22-kHz calls in female rats may be independent of circulating testosterone levels, as tested in response to air-puff stimulation.

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.

Pharmacological and methodological aspects of the separation-induced vocalization test in guinea pig pups; a systematic review and meta-analysis

The separation-induced vocalization test in guinea pig pups is one of many that has been used to screen for anxiolytic-like properties of drugs. The test is based on the cross-species phenomenon that infants emit distress calls when placed in social isolation. Here we report a systematic review and meta-analysis of pharmacological intervention in the separation-induced vocalization test in guinea pig pups. Electronic databases were searched for original research articles, yielding 32 studies that met inclusion criteria. We extracted data on pharmacological intervention, animal and methodological characteristics, and study quality indicators. Meta-analysis showed that the different drug classes in clinical use for the treatment of anxiety disorders, have comparable effects on vocalization behaviour, irrespective of their mechanism of action. Of the experimental drugs, nociception (NOP) receptor agonists proved very effective in this test. Analysis further indicated that the commonly used read-outs total number and total duration of vocalizations are equally valid. With regard to methodological characteristics, repeated testing of pups as well as selecting pups with moderate or high levels of vocalization were associated with larger treatment effects. Finally, reporting of study methodology, randomization and blinding was poor and Egger's test for small study effects showed that publication bias likely occurred. This review illustrates the value of systematic reviews and meta-analyses in improving translational value and methodological aspects of animal models. It further shows the urgent need to implement existing publication guidelines to maximize the output and impact of experimental animal studies.

Relationship between 22-kHz calls and testosterone in male rats

Ultrasonic calls in rats induced by the presence of a predator, referred to as "22-kHz calls," are mainly emitted by socially dominant male rats. Testosterone levels are closely related to social dominance in male rats. In the present study, we investigated the relationship between the emission of stress-induced 22-kHz calls and circulating testosterone levels in male rats, using a combination of surgery (castration or sham operation) and chronic steroid administration (testosterone or cholesterol) to modify circulating testosterone levels. We also assessed the effects of androgen and/or estrogen receptor antagonists on the emission of 22-kHz calls in male rats. An air puff stimulus, known to reliably induce 22-kHz calls in rats, was used as a stressor. Castrated rats with cholesterol implants exhibited significantly fewer 22-kHz calls than rats that had received a sham operation and cholesterol implants, and there was no significant difference between castrated rats with testosterone implants and rats that had received a sham operation and cholesterol implants. Only male rats pretreated with a binary mixture of androgen and estrogen antagonists exhibited significantly fewer 22-kHz calls than controls. These results show that testosterone in male rats has a positive effect on the emission of stress-induced 22-kHz calls, and the calls may be regulated by the activation of both androgen and estrogen receptors.

Effect of prenatal cocaine on early postnatal thermoregulation and ultrasonic vocalization production

Prenatal cocaine exposure can alter the postnatal care received by rat pups. Such effects could be caused in part by alterations in pup-produced stimuli that elicit early postnatal maternal care. Pup ultrasonic vocalizations are thought to be a particularly salient stimulus, and when paired with other cues, may elicit maternal attention. Cocaine is known to acutely alter thermoregulatory and cardiac function, thus prenatal cocaine may affect vocalizations through altering these functions. The data presented here determine the impact of full term prenatal cocaine exposure, saline exposure, or no exposure on thermogenic capacity, cardiac function, and the resulting ultrasonic vocalizations across the early postnatal period (days 1–5). Results indicated that while sharing many similar characteristics with saline-exposed and untreated animals, prenatal cocaine exposure was associated with specific alterations in vocalization characteristics on postnatal day 1 (PND 1), including call amplitude. Furthermore, numerous spectral parameters of their vocalizations were found altered on PND 3, including rate, call duration, and frequency, while no alterations were found on PND 5. Additionally, cocaine-exposed pups also showed a reduced thermoregulatory capacity compared to saline animals and reduced cardiac mass compared to untreated animals on PND 5. Together, these findings indicate that prenatal cocaine may be altering the elicitation of maternal care through its impact on vocalizations and thermoregulation, and suggests a potential mechanism for these effects through cocaine's impact on developing stress systems.

The role of the serotonergic and GABA system in translational approaches in drug discovery for anxiety disorders

There is ample evidence that genetic factors play an important role in anxiety disorders. In support, human genome-wide association studies have implicated several novel candidate genes. However, illumination of such genetic factors involved in anxiety disorders has not resulted in novel drugs over the past decades. A complicating factor is the heterogeneous classification of anxiety disorders in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and diverging operationalization of anxiety used in preclinical and clinical studies. Currently, there is an increasing focus on the gene × environment (G × E) interaction in anxiety as genes do not operate in isolation and environmental factors have been found to significantly contribute to the development of anxiety disorders in at-risk individuals. Nevertheless, extensive research on G × E mechanisms in anxiety has not resulted in major breakthroughs in drug discovery. Modification of individual genes in rodent models has enabled the specific study of anxiety in preclinical studies. In this context, two extensively studied neurotransmitters involved in anxiety are the gamma-aminobutyric acid (GABA) and 5-HT (5-hydroxytryptamine) system. In this review, we illustrate the complex interplay between genes and environment in anxiety processes by reviewing preclinical and clinical studies on the serotonin transporter (5-HTT), 5-HT1A receptor, 5-HT2 receptor, and GABAA receptor. Even though targets from the serotonin and GABA system have yielded drugs with known anxiolytic efficacy, the relation between the genetic background of these targets and anxiety symptoms and development of anxiety disorders is largely unknown. The aim of this review is to show the vast complexity of genetic and environmental factors in anxiety disorders. In light of the difficulty with which common genetic variants are identified in anxiety disorders, animal models with translational validity may aid in elucidating the neurobiological background of these genes and their possible role in anxiety. We argue that, in addition to human genetic studies, translational models are essential to map anxiety-related genes and to enhance our understanding of anxiety disorders in order to develop potentially novel treatment strategies.

Ultrasonic vocalization of rats in various motivational and emotional states

We studied the specific features of ultrasonic vocalization of Wistar rats in various motivational and emotional states. No significant changes were found in ultrasonic vocalization of rats during experimental food motivation and after the satisfaction of food requirements. The state of thirst and satisfaction of water requirements in animals were associated with an increase in the mean frequency of ultrasound and dominance of ultrasonic waves of a higher frequency. The formation of a negative emotional state in rats after immobilization with simultaneous electrocutaneous stimulation was accompanied by a decrease in the total duration of ultrasonic vocalization and shift in the power spectrum of ultrasound towards the dominant frequencies of 20-30, 40-50, and 80-90 kHz. During the post-stress period, the maximum power of ultrasonic waves approached the baseline (30-40 kHz). Our results indicate that the formation of various motivational and emotional states in rats is characterized by specific patterns of ultrasonic vocalization. Therefore, the parameters of ultrasonic vocalization can serve as an objective criteria for the subjective state of a living organism.

Levomilnacipran (F2695), a norepinephrine-preferring SNRI: profile in vitro and in models of depression and anxiety

Levomilnacipran (LVM; F2695) is the more active enantiomer of the serotonin/norepinephrine (5-HT/NE) reuptake inhibitor (SNRI) milnacipran and is currently under development for the treatment of major depressive disorder. LVM was benchmarked against two other SNRIs, duloxetine and venlafaxine, in biochemical, neurochemical and pharmacological assays. LVM exhibited high affinity for human NE (Ki = 92.2 nM) and 5-HT (11.2 nM) transporters, and potently inhibited NE (IC50 = 10.5 nM) and 5-HT (19.0 nM) reuptake (human transporter) in vitro. LVM had 2-fold greater potency for norepinephrine relative to serotonin reuptake inhibition (i.e. NE/5-HT potency ratio: 0.6) and 17 and 27 times higher selectivity for NE reuptake inhibition compared with venlafaxine and duloxetine, respectively. LVM did not exhibit affinity for 23 off-target receptors. LVM (i.p.) increased cortical extracellular levels of 5-HT, and NE (minimal effective doses: MEDs = 20 and 10 mg/kg, respectively). In anti-depressive/anti-stress models, i.p. LVM diminished immobility time in the mouse forced swim (MED = 20 mg/kg) and tail suspension (MED = 2.5 mg/kg) tests, and reduced shock-induced ultrasonic vocalizations in rats (MED = 5 mg/kg). Duloxetine and venlafaxine were less potent (MEDs ≥ 10 mg/kg). At doses active in these three therapeutically-relevant models, LVM (i.p.) did not significantly affect spontaneous locomotor activity. In summary, LVM is a potent, selective inhibitor of NE and 5-HT transporters with preferential activity at the former. It is efficacious in models of anti-depressive/anti-stress activity, with minimal potential for locomotor side effects.

Patterns of phosphorylated tyrosine hydroxylase vary with song production in female starlings

Vocal signal production in male songbirds is well studied, but the neural correlates of female song production are poorly understood. In European starlings, females sing to defend nesting resources, and song can be considered agonistically motivated. Across vertebrates catecholamines strongly influence motivated, agonistic social behaviors. The present study was designed to provide insight into a possible role for catecholamine activity in territorial song in female starlings. We presented females that were defending nest-cavities with an unfamiliar female and assessed song production. We then measured immunolabeling for phosphorylated tyrosine hydroxylase (pTH-ir), the rate-limiting enzyme for catecholamine synthesis, in brain regions in which catecholamines stimulate agonistic behavior. Females that sang had higher pTH-ir in the caudomedial ventral tegmental area and the lateral septum than females that did not sing. Furthermore, the number of songs produced correlated positively with pTH-ir in the medial preoptic nucleus. Phosphorylation of TH is thought to occur after catecholamine release, so these results link increased catecholamine activity in several brain regions governing agonistic behavior to territorial song production in females.

The critical point at which post-weaning individual housing conditions affect the emission of 22-kHz calls in male rats

It is known that long-term post-weaning individual housing significantly reduces emissions of 22-kHz calls in male rats. In this study, we assessed post-weaning successive changes in 22-kHz calls emitted by male rats under two different types of post-weaning housing conditions (individually and socially). In addition, we evaluated the critical point at which a significant reduction in 22-kHz calls could be observed in male rats housed individually after weaning. Significantly fewer 22-kHz calls were emitted by individually housed rats compared to socially housed rats at 16 weeks of age, indicating that 13 weeks after weaning may be a critical point for the reduction of 22-kHz calls caused by post-weaning individual housing.

Interactions of CB1 and mGlu5 receptor antagonists in food intake, anxiety and memory models in rats

CB(1) receptor antagonists proved to be effective anti-obesity drugs, however, their depressive and anxiogenic effects became also evident. Finding solution to overcome these psychiatric side effects is still in focus of research. Based on the available clinical and preclinical results we hypothesized that the combination of CB(1) and mGlu(5) receptor antagonisms may result in a pharmacological intervention, where the anxiolytic mGlu(5) receptor inhibition may counteract the anxiogenic psychiatric side effects of CB(1) antagonism, while CB(1) antagonism may ameliorate the memory impairing effect of mGlu(5) receptor antagonism. Further, the two components will synergistically interact in blocking food-intake and reducing obesity. For testing the interaction of mGlu(5) and CB(1) receptor antagonism MTEP [3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pridine; SIB-1757, 6-methyl-2-(phenylazo)-3-pyridinol)] (mGlu(5) antagonist) and rimonabant [(5-(4-Chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-N-(piperidin-1-yl)-1H-pyrazole-3-carboxamide)hydrochloride] (CB(1) antagonist) were used. All experiments were carried out in rats. Effects of the compounds on anxiety were tested in two foot shock induced ultrasonic vocalization paradigms, appetite suppression was assessed in the food intake test, while memory effects were tested in a context conditioned ultrasonic vocalization setup. MTEP abolished the anxiogenic effect of rimonabant, while there was an additive cooperation in suppressing appetite. However, rimonabant did not ameliorate the memory impairing effect of MTEP. By combination of CB(1) and mGluR5 antagonism, anxiety related side effects might be attenuated, appetite suppression maintained, nevertheless, the possible emergence of unwanted memory impairments can overshadow its therapeutic success.

Juvenile stress potentiates aversive 22-kHz ultrasonic vocalizations and freezing during auditory fear conditioning in adult male rats

Traumatic experiences that occur during adolescence can render individuals vulnerable to mood and anxiety disorders. A model in juvenile rats (age: 27-29 days) was developed previously to study the long-term effects of adolescent stress exposure on behaviour and physiology. This paradigm, termed juvenile stress, involves subjecting juvenile rats to different stressors on consecutive days over a 3-day period. Here, we investigated the effects of the juvenile stress paradigm on freezing behaviour and aversive 22-kHz ultrasonic vocalizations (USVs) during auditory fear conditioning in adult male rats (age: 68-90 days). We found that rats previously subjected to juvenile stress increased aversive 22-kHz USVs (total calls and time spent calling) compared with controls during fear-conditioning training. The acoustic USV parameters between control and juvenile stress rats were largely equivalent, including duration, peak frequency and amplitude. While rats did not differ in freezing behaviour during fear conditioning, juvenile stress rats exhibited greater cue-conditioned freezing upon testing 24 h later. Our results show that juvenile stress elicited different long-term changes in freezing and aversive USVs during fear conditioning. Furthermore, they highlight the importance of assessing USVs to detect experience-dependent differences between control and stress-exposed animals which are not detectable by measuring visible behaviour.

Reciprocal cooperation between unrelated rats depends on cost to donor and benefit to recipient

BACKGROUND

Although evolutionary models of cooperation build on the intuition that costs of the donor and benefits to the receiver are the most general fundamental parameters, it is largely unknown how they affect the decision of animals to cooperate with an unrelated social partner. Here we test experimentally whether costs to the donor and need of the receiver decide about the amount of help provided by unrelated rats in an iterated prisoner's dilemma game.

RESULTS

Fourteen unrelated Norway rats were alternately presented to a cooperative or defective partner for whom they could provide food via a mechanical apparatus. Direct costs for this task and the need of the receiver were manipulated in two separate experiments. Rats provided more food to cooperative partners than to defectors (direct reciprocity). The propensity to discriminate between helpful and non-helpful social partners was contingent on costs: An experimentally increased resistance in one Newton steps to pull food for the social partner reduced the help provided to defectors more strongly than the help returned to cooperators. Furthermore, test rats provided more help to hungry receivers that were light or in poor condition, which might suggest empathy, whereas this relationship was inverse when experimental partners were satiated.

CONCLUSIONS

In a prisoner's dilemma situation rats seem to take effect of own costs and potential benefits to a receiver when deciding about helping a social partner, which confirms the predictions of reciprocal cooperation. Thus, factors that had been believed to be largely confined to human social behaviour apparently influence the behaviour of other social animals as well, despite widespread scepticism. Therefore our results shed new light on the biological basis of reciprocity.