Modulation of 22-khz postejaculatory vocalizations by conditioning to new place: Evidence for expression of a positive emotional state

Ultrasonic vocalisation rate tracks the diurnal pattern of activity in winter phenotype Djungarian hamsters (Phodopus sungorus)

Vocalisations are increasingly being recognised as an important aspect of normal rodent behaviour yet little is known of how they interact with other spontaneous behaviours such as sleep and torpor, particularly in a social setting. We obtained chronic recordings of the vocal behaviour of adult male and female Djungarian hamsters (Phodopus sungorus) housed under short photoperiod (8 h light, 16 h dark, square wave transitions), in different social contexts. The animals were kept in isolation or in same-sex sibling pairs, separated by a grid which allowed non-physical social interaction. On approximately 20% of days hamsters spontaneously entered torpor, a state of metabolic depression that coincides with the rest phase of many small mammal species in response to actual or predicted energy shortages. Animals produced ultrasonic vocalisations (USVs) with a peak frequency of 57 kHz in both social and asocial conditions and there was a high degree of variability in vocalisation rate between subjects. Vocalisation rate was correlated with locomotor activity across the 24-h light cycle, occurring more frequently during the dark period when the hamsters were more active and peaking around light transitions. Solitary-housed animals did not vocalise whilst torpid and animals remained in torpor despite overlapping with vocalisations in social-housing. Besides a minor decrease in peak USV frequency when isolated hamsters were re-paired with their siblings, changing social contexts did not influence vocalisation behaviour or structure. In rare instances, temporally overlapping USVs occurred when animals were socially-housed and were grouped in such a way that could indicate coordination. We did not observe broadband calls (BBCs) contemporaneous with USVs in this paradigm, corroborating their correlation with physical aggression which was absent from our experiment. Overall, we find little evidence to suggest a direct social function of hamster USVs. We conclude that understanding the effects of vocalisations on spontaneous behaviours, such as sleep and torpor, will inform experimental design of future studies, especially where the role of social interactions is investigated.

Neuronal, affective, and sensory correlates of targeted helping behavior in male and female Sprague Dawley rats

Introduction

Empathic behaviors are driven by the ability to understand the emotional states of others along with the motivation to improve it. Evidence points towards forms of empathy, like targeted helping, in many species including rats. There are several variables that may modulate targeted helping, including sex, sensory modalities, and activity of multiple neural substrates.

Methods

Using a model of social contact-independent targeted helping, we first tested whether sex differences exist in helping behavior. Next, we explored sex differences in sensory and affective signaling, including direct visualization and an analysis of ultrasonic vocalizations made between animal pairs. Finally, we examined the neural activity in males and females of multiple regions of interest across time. Here, we aim to examine any behavioral differences in our lab's social contact independent targeted helping task between males and females.

Results and Discussion

These findings are the first to intimate that, like other prosocial behaviors, males and females may exhibit similar social-independent targeted helping behavior, but the underlying sensory communication in males and females may differ. In addition, this is the first set of experiments that explore the neural correlates of social-independent targeted helping in both males and females. These results lay the groundwork for future studies to explore the similarities and differences that drive targeted helping in both sexes.

Neurophysiology of male sexual arousal-Behavioral perspective

In the presented review, we analyzed the physiology of male sexual arousal and its relation to the motivational aspects of this behavior. We highlighted the distinction between these processes based on observable physiological and behavioral parameters. Thus, we proposed the experimentally applicable differentiation between sexual arousal (SA) and sexual motivation (SM). We propose to define sexual arousal as an overall autonomic nervous system response leading to penile erection, triggered selectively by specific sexual cues. These autonomic processes include both spinal and supraspinal neuronal networks, activated by sensory pathways including information from sexual partner and sexual context, as well as external and internal genital organs. To avoid misinterpretation of experimental data, we also propose to precise the term "sexual motivation" as all actions performed by the individual that increase the probability of sexual interactions or increase the probability of exposition to sexual context cues. Neuronal structures such as the amygdala, bed nucleus of stria terminalis, hypothalamus, nucleus raphe, periaqueductal gray, and nucleus paragigantocellularis play crucial roles in controlling the level of arousal and regulating peripheral responses via specific autonomic effectors. On the highest level of CNS, the activity of cortical structures involved in the regulation of the autonomic nervous system, such as the insula and anterior cingulate cortex, can visualize an elevated level of SA in both animal and human brains. From a preclinical perspective, we underlie the usefulness of the non-contact erection test (NCE) procedure in understanding factors influencing sexual arousal, including studies of sexual preference in animal models. Taken together results obtained by different methods, we wanted to focus attention on neurophysiological aspects that are distinctly related to sexual arousal and can be used as an objective parameter, leading to higher translational transparency between basic, preclinical, and clinical studies.

Hippocampus Modulates Vocalizations Responses at Early Auditory Centers

Despite its prominence in learning and memory, hippocampal influence in early auditory processing centers remains unknown. Here, we examined how hippocampal activity modulates sound-evoked responses in the auditory midbrain and thalamus using optogenetics and functional MRI (fMRI) in rodents. Ventral hippocampus (vHP) excitatory neuron stimulation at 5 Hz evoked robust hippocampal activity that propagates to the primary auditory cortex. We then tested 5 Hz vHP stimulation paired with either natural vocalizations or artificial/noise acoustic stimuli. vHP stimulation enhanced auditory responses to vocalizations (with a negative or positive valence) in the inferior colliculus, medial geniculate body, and auditory cortex, but not to their temporally reversed counterparts (artificial sounds) or broadband noise. Meanwhile, pharmacological vHP inactivation diminished response selectivity to vocalizations. These results directly reveal the large-scale hippocampal participation in natural sound processing at early centers of the ascending auditory pathway. They expand our present understanding of hippocampus in global auditory networks.

A Protocol for the Non-invasive Method of Ultrasound Separation During the Sociosexual Vocal-Non-contact Model in Rats

Ultrasonic vocalization (USV) is one of the measurable behavioral parameters of sociosexual interactions in rats. To precisely and accurately describe the neurobehavioral properties of USV and the potentially related specific emotional responsiveness of animals, we need to know which animals vocalize and what is their exact behavioral and physiological response. To this end, we modified the non-contact cage [non-contact erection model (NCE)] by adding a modification [vocalization-non-contact erection (VOC-NCE)] that makes it possible to assign emitted ultrasonic signals to a particular animal. Typically, the NCE cage consists of two compartments separated by perforated baffles. A male is placed in one section, and a receptive female is placed in the other section. This makes possible the accurate description of sexual parameters related to the cues controlled by the experimenter. In VOC-NCE, we completely separated the male USV from the female USV by three appropriately perforated baffles and located microphones combined with ultrasonic screening. We recorded emission in both typical bands, the so-called 22- and 50-kHz bands, with various subtypes, thus highlighting the utility of our protocol to investigate the sexual dimorphism of vocalization. Similar to the anticipatory model, we showed that emission can occur without acoustic feedback from concomitants during the VOC-NCE test. Therefore, we propose a relatively simple method for assigning individual vocalization. We discuss its usefulness and limitations in assessing vocal differentiation related to sexual parameters, adaptive changes during conditioning procedures, and further applications.

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

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

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

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

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

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

Early Life Maternal Separation and Maternal Behaviour Modulate Acoustic Characteristics of Rat Pup Ultrasonic Vocalizations

Early separation of preterm infants from their mothers has adverse, long-term neurodevelopmental consequences. We investigated the effects of daily maternal separation (MS) of rat pups from postnatal days 2-10 (PND2-10) on neurobehavioural responses to brief isolation at PND12 compared with pups receiving controlled handling without MS. Ultrasonic vocalizations (USV) were measured at PND12 during two, 3-minute isolations occurring immediately before and after a 3-minute maternal reunion. There were no significant differences in acoustic characteristics between MS and control animals in the first isolation. However, in the second isolation, MS pups produced a greater proportion of high (~60 kHz) vs low (~40 kHz) frequency calls. During this isolation, control pups made longer and louder low frequency calls compared to the first isolation, whereas MS pups did the opposite. Maternal behaviour of control and MS mothers modulated pup acoustic characteristics in opposite directions; higher maternal care was associated with more low frequency calls in control pups but more high frequency calls in MS pups. We hypothesize that MS results in USV emission patterns reflective of a greater stress response to isolation. This translational model can be used to identify mechanisms and interventions that may be exploited to overcome the negative, long-term effects of MS.

The Sexual Motivation of Male Rats as a Tool in Animal Models of Human Health Disorders

Normal or dysfunctional sexual behavior seems to be an important indicator of health or disease. Many health disorders in male patients affect sexual activity by directly causing erectile dysfunction, affecting sexual motivation, or both. Clinical evidence indicates that many diseases strongly disrupt sexual motivation and sexual performance in patients with depression, addiction, diabetes mellitus and other metabolic disturbances with obesity and diet-related factors, kidney and liver failure, circadian rhythm disorders, sleep disturbances including obstructive sleep apnea syndrome, developmental and hormonal disorders, brain damages, cardiovascular diseases, and peripheral neuropathies. Preclinical studies of these conditions often require appropriate experimental paradigms, including animal models. Male sexual behavior and motivation have been intensively investigated over the last 80 years in animal rat model. Sexual motivation can be examined using such parameters as: anticipatory behavior and 50-kHz ultrasonic vocalizations reflecting the emotional state of rats, initiation of copulation, efficiency of copulation, or techniques of classical (pavlovian) and instrumental conditioning. In this review article, we analyze the behavioral parameters that describe the sexual motivation and sexual performance of male rats in the context of animal experimental models of human health disorders. Based on analysis of the parameters describing the heterogeneous and complex structure of sexual behavior in laboratory rodents, we propose an approach that is useful for delineating distinct mechanisms affecting sexual motivation and sexual performance in selected disease states and the efficacy of therapy in preclinical investigations.

Development of ultrasonic calls in rat pups follows similar patterns regardless of isolation distress

Ultrasonic vocalizations (USVs) emitted by rat pups have been extensively studied in the context of isolation from their mother and littermates. The heightened call rate of isolation-induced USVs indicates increased anxiety, whereas other acoustic parameters, such as frequency and call duration, are thought to be useful in reflecting developmental changes, which by weaning have developed into their adult form. However, it is possible that stress can affect the quality as well as the quantity of calls, and that as the pups become more mobile, the effects of the stress may change. Therefore, in the present study rats were tested in a test arena either in isolation or with littermates, so as to assess the effects of isolation stress on the developmental changes reported in the literature. Rat pups of both sexes were tested on multiple days from postnatal day (PND) 7 to weaning. Overall, the main changes in the frequency, duration, and types of calls were accounted for by age. The effects of isolation were minor, as were sex differences. This study indicates that the development of USVs in infant rats is a robust process and seemingly resistant to the effects of isolation-induced stress.

Effects of ovarian hormones on the emission of 50-kHz ultrasonic vocalizations during distributed clitoral stimulation in the rat

Fifty-kHz ultrasonic vocalizations (USVs) are emitted by adult rats during appetitive phases of behavior in response to stimuli thought to be associated with a positive affective state. In particular, 50-kHz USVs with rapid frequency oscillations, known as trills and flat-trills, in which these oscillations are flanked by a monotonic portion, are together positively correlated with appetitive behaviors such as rough and tumble play, drug and natural reward, and mating. Female rats produce 50-kHz USVs during a variety of sexual contexts, yet data are still vague as female sexual behavior is seldom studied on its own. Distributed clitoral stimulation (CLS) offers a unique approach to investigating female 50-kHz USVs as it mimics stimulation received during mating. Although CLS induces a sexual reward state, it is unknown whether CLS elicits trills and flat-trills. We addressed this question using eight ovariectomized rats, we investigated whether ovarian hormones augmented these call subtypes in response to CLS. The combined and separate effects of estradiol benzoate (EB) and progesterone (P), and oil vehicle were assessed through comparison of these call subtypes between CLS and inter-CLS interval. We found that CLS with EB + P significantly increased call duration and rate, lowered peak frequency, and widened the bandwidth of trills. Flat-trills showed a similar pattern except for call duration. Call distribution during the CLS and inter-CLS interval suggest that trill and flat-trills may be indicative of both anticipatory and sexual reward.

Avoiding escalation from play to aggression in adult male rats: The role of ultrasonic calls

Play fighting is most commonly associated with juvenile animals, but in some species, including rats, it can continue into adulthood. Post-pubertal engagement in play fighting is often rougher and has an increased chance of escalation to aggression, making the use of play signals to regulate the encounter more critical. During play, both juvenile and adult rats emit many 50-kHz calls and some of these may function as play facilitating signals. In the present study, unfamiliar adult male rats were introduced in a neutral enclosure and their social interactions were recorded. While all pairs escalated their playful encounters to become rougher, only the pairs in which one member was devocalized escalated to serious biting. A Monte Carlo shuffling technique was used for the analysis of the correlations between the overt playful and aggressive actions performed and the types and frequencies of various 50-kHz calls that were emitted. The analysis revealed that lower frequency (20-30kHz) calls with a flat component maybe particularly critical for de-escalating encounters and so allowing play to continue. Moreover, coordinating calls reciprocally, with either the same call mimicked in close, temporal association or with complementary calls emitted by participants as they engage in complementary actions (e.g., attacking the nape, being attacked on the nape), appeared to be ways with which calls could be potentially used to avoid escalation to aggression and so sustain playful interactions.