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

Sleep- and sleep deprivation-related changes of vertex auditory evoked potentials during the estrus cycle in female rats

The estrus cycle in female rodents has been shown to affect a variety of physiological functions. However, little is known about its presumably thorough effect on auditory processing during the sleep-wake cycle and sleep deprivation. Vertex auditory evoked potentials (vAEPs) were evoked by single click tone stimulation and recorded during different stages of the estrus cycle and sleep deprivation performed in metestrus and proestrus in female rats. vAEPs showed a strong sleep-dependency, with the largest amplitudes present during slow wave sleep while the smallest ones during wakefulness. Higher amplitudes and longer latencies were seen in the light phase during all vigilance stages. The largest amplitudes were found during proestrus (light phase) while the shortest latencies were seen during estrus (dark phase) compared to the 2nd day diestrus baseline. High-amplitude responses without latency changes were also seen during metestrus with increased homeostatic sleep drive. More intense and faster processing of auditory information during proestrus and estrus suggesting a more effective perception of relevant environmental cues presumably in preparation for sexual receptivity. A 4-h sleep deprivation resulted in more pronounced sleep recovery in metestrus compared to proestrus without difference in delta power replacement suggesting a better tolerance of sleep deprivation in proestrus. Sleep deprivation decreased neuronal excitability and responsiveness in a similar manner both during metestrus and proestrus, suggesting that the negative consequences of sleep deprivation on auditory processing may have a limited correlation with the estrus cycle stage.

Sex-specific effects of neuromodulatory drugs on normal and stress-induced social dominance and aggression in rats

BACKGROUND

Social hierarchies are important for individual's well-being, professional and domestic growth, harmony of the society, as well as survival and morbidity. Studies have revealed sexual dimorphism in the social abilities; however, data is limited on the sex-specific effects of various drugs used to treat psychiatric disorders and social deficits.

OBJECTIVE

The present study aimed at evaluating the sex-dependent effects of Risperidone (antipsychotic that targets D2 dopaminergic, 5HT2A serotonergic, and α-adrenergic receptors), Donepezil (a reversible acetylcholinesterase inhibitor), and Paroxetine (a selective serotonin reuptake inhibitor) on social hierarchy in rats under normal and stressed states.

METHODS

8-12 weeks old male and female Wistar rats were divided into sex-wise 4-4 groups, i.e., 1. control group, 2. Risperidone treated group (3 mg/kg/day), 3. Donepezil treated group (5 mg/kg/day), and Paroxetine treated group (10 mg/kg/day). Rats were treated with these drugs in phase I for 21 days in distilled drinking water, followed by a no (drugs) treatment break of 10 days. After the break phase II started with the administration of drugs (same as in phase I) along with tilt-cage stress for 21 days. Home cage activity assessment was performed once a week during both phases (I & II), while tube dominance and resident intruder tests were performed at the end of each phase.

RESULTS

In phase I in both sexes, Risperidone treatment decreased social interaction and motor activity while Paroxetine treatment increased these in both sexes compared to their respective control groups. Social dominance and aggression were reduced after treatment with both of these drugs. In contrast, Donepezil treatment caused an increase in motor activity in females whereas reduced motor activity in males. Furthermore, Donepezil treatment caused reduction in interaction but increased social dominance and aggression were observed in both sexes. In phase II, stress led to an overall decrease in motor activity and social interaction of animals. Treatment with Risperidone, Paroxetine, and Donepezil caused a sex-specific effect on, motor activity, social interaction, and social exploration.

CONCLUSION

These results showed that Risperidone has stronger effects on male social behavior whereas Paroxetine and Donepezil differentially affect social abilities in both sexes during normal and stressed situations.

Sexually Dimorphic Effects of Neuromodulatory Drugs on Normal and Stress-Induced Social Interaction in Rats

Social behavior is a complex term which involves different interactions between various individuals of a community. It is controlled by different neurotransmitter systems in a sexually dimorphic way. Certain environmental factors, like stress, cause various neurological disorders with associated social abnormalities in a sexually dimorphic way. Multiple drugs are used in clinical settings to treat behavioral disorders. However, the sexually dimorphic effects of these drugs, particularly on social behavior, still need to be studied. The present study was designed to investigate the sex-dependent effects of Risperidone, Donepezil, and Paroxetine in 8-12 weeks old male and female rats under normal and stressed conditions. There were four male and four female groups, i.e., control group (no drug treatment), Risperidone (3 mg/kg/day) treated group, Donepezil (5 mg/kg/day) treated group, and Paroxetine (10 mg/kg/day) treated group. Each group received its respective drug during phase 1 for 21 days, followed by a 10-day break with no drug treatment. After the break, same groups received the same drugs along with tilt-cage stress for an additional 21 days during phase 2. A social preference and novelty test was performed at the end of both phases (1 and 2). During phase 1, Risperidone treatment caused impaired social behavior and reduced locomotion in the male group only, compared to its control group. Donepezil treatment caused a reduction in social interaction, while Paroxetine treatment caused increased social interaction and locomotion in a sex-dependent manner. During phase 2, social novelty was affected in both male and female stress groups. Treatment with drugs along with stress showed differential sex-dependent effects. The study showed a predominant effect of Risperidone on males while there were differential effects of Donepezil and Paroxetine on both sexes. This study has paved the way for the development of more targeted and effective neuromodulatory drugs for use against various psychiatric and social deficits.

ChAT::Cre transgenic rats show sex-dependent altered fear behaviors, ultrasonic vocalizations and cholinergic marker expression

The cholinergic system is a critical regulator of Pavlovian fear learning and extinction. As such, we have begun investigating the cholinergic system's involvement in individual differences in cued fear extinction using a transgenic ChAT::Cre rat model. The current study extends behavioral phenotyping of a transgenic ChAT::Cre rat line by examining both freezing behavior and ultrasonic vocalizations (USVs) during a Pavlovian cued fear learning and extinction paradigm. Freezing, 22 kHz USVs, and 50 kHz USVs were compared between male and female transgenic ChAT::Cre+ rats and their wildtype (Cre-) littermates during fear learning, contextual and cue-conditioned fear recall, cued fear extinction, and generalization to a novel tone. During contextual and cued fear recall ChAT::Cre+ rats froze slightly more than their Cre- littermates, and displayed significant sex differences in contextual and cue-conditioned freezing, 22 kHz USVs, and 50 kHz USVs. Females showed more freezing than males in fear recall trials, but fewer 22 kHz distress calls during fear learning and recall. Females also produced more 50 kHz USVs during exposure to the testing chambers prior to tone (or shock) presentation compared with males, but this effect was blunted in ChAT::Cre+ females. Corroborating previous studies, ChAT::Cre+ transgenic rats overexpressed vesicular acetylcholine transporter immunolabeling in basal forebrain, striatum, basolateral amygdala, and hippocampus, but had similar levels of acetylcholinesterase and numbers of ChAT+ neurons as Cre- rats. This study suggests that variance in behavior between ChAT::Cre+ and wildtype rats is sex dependent and advances theories that distinct neural circuits and processes regulate sexually divergent fear responses.

Ability to share emotions of others as a foundation of social learning

The natural habitats of most species are far from static, forcing animals to adapt to continuously changing conditions. Perhaps the most efficient strategy addressing this challenge consists of obtaining and acting upon pertinent information from others through social learning. We discuss how animals transfer information via social channels and what are the benefits of such exchanges, playing out on different levels, from theperception of socially delivered information to emotional sharing, manifesting themselves across different taxa of increasing biological complexity. We also discuss how social learning is influenced by different factors including pertinence of information for survival, the complexity of the environment, sex, genetic relatedness, and most notably, the relationship between interacting partners. The results appear to form a consistent picture once we shift our focus from emotional contagion as a prerequisite for empathy onto the role of shared emotions in providing vital information about the environment. From this point of view, we can propose approaches that are the most promising for further investigation of complex social phenomena, including learning from others.

Effect of Estrous Cycle on Behavior of Females in Rodent Tests of Anxiety

Anxiety disorders are more prevalent in women than in men. In women the menstrual cycle introduces another variable; indeed, some conditions e.g., premenstrual syndrome, are menstrual cycle specific. Animal models of fear and anxiety, which form the basis for research into drug treatments, have been developed almost exclusively, using males. There remains a paucity of work using females and the available literature presents a confusing picture. One confound is the estrous cycle in females, which some authors consider, but many do not. Importantly, there are no accepted standardized criteria for defining cycle phase, which is important given the rapidly changing hormonal profile during the 4-day cycle of rodents. Moreover, since many behavioral tests that involve a learning component or that consider extinction of a previously acquired association require several days to complete; the outcome may depend on the phase of the cycle on the days of training as well as on test days. In this article we consider responsiveness of females compared to males in a number of commonly used behavioral tests of anxiety and fear that were developed in male rodents. We conclude that females perform in a qualitatively similar manner to males in most tests although there may be sex and strain differences in sensitivity. Tests based on unconditioned threatening stimuli are significantly influenced by estrous cycle phase with animals displaying increased responsiveness in the late diestrus phase of the cycle (similar to the premenstrual phase in women). Tests that utilize conditioned fear paradigms, which involve a learning component appear to be less impacted by the estrous cycle although sex and cycle-related differences in responding can still be detected. Ethologically-relevant tests appear to have more translational value in females. However, even when sex differences in behavior are not detected, the same outward behavioral response may be mediated by different brain mechanisms. In order to progress basic research in the field of female psychiatry and psychopharmacology, there is a pressing need to validate and standardize experimental protocols for using female animal models of anxiety-related states.

Fear Extinction and Predictive Trait-Like Inter-Individual Differences in Rats Lacking the Serotonin Transporter

Anxiety disorders are associated with a failure to sufficiently extinguish fear memories. The serotonergic system (5-hydroxytryptamine, 5-HT) with the 5-HT transporter (5-HTT, SERT) is strongly implicated in the regulation of anxiety and fear. In the present study, we examined the effects of SERT deficiency on fear extinction in a differential fear conditioning paradigm in male and female rats. Fear-related behavior displayed during acquisition, extinction, and recovery, was measured through quantification of immobility and alarm 22-kHz ultrasonic vocalizations (USV). Trait-like inter-individual differences in novelty-seeking, anxiety-related behavior, habituation learning, cognitive performance, and pain sensitivity were examined for their predictive value in forecasting fear extinction. Our results show that SERT deficiency strongly affected the emission of 22-kHz USV during differential fear conditioning. During acquisition, extinction, and recovery, SERT deficiency consistently led to a reduction in 22-kHz USV emission. While SERT deficiency did not affect immobility during acquisition, genotype differences started to emerge during extinction, and during recovery rats lacking SERT showed higher levels of immobility than wildtype littermate controls. Recovery was reflected in increased levels of immobility but not 22-kHz USV emission. Prominent sex differences were evident. Among several measures for trait-like inter-individual differences, anxiety-related behavior had the best predictive quality.

Relaying Aversive Ultrasonic Alarm Calls Depends on Previous Experience. Empathy, Social Buffering, or Panic?

Ultrasonic vocalizations are among the oldest evolutionarily forms of animal communication. In order to study the communication patterns in an aversive social situation, we used a behavioral model in which one animal, the observer, is witnessing as his cagemate, the demonstrator, is experiencing a series of mild electrical foot shocks. We studied the effect of the foot shock experience on the observer and the influence of a warning sound (emitted shortly before the shock) on USV communication. These experiments revealed that such a warning seems to increase the arousal level, which differentiates the responses depending on previous experience. This can be identified by the emission of characteristic, short 22 kHz calls of a duration below 100 ms. Two rats emitted calls that overlapped in time. Analysis of these overlaps revealed that in ‘warned’ pairs with a naive observer, 22 kHz calls were mixed with 50 kHz calls. This fact, combined with a high fraction of very high-pitched 50 kHz calls (over 75 kHz), suggests the presence of the phenomenon of social buffering. Pure 22 kHz overlaps were mostly found in ‘warned’ pairs with an experienced observer, suggesting a possible fear contagion with distress sharing. The results show the importance of dividing 22 kHz calls into long and short categories.

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.

Biological and Acoustic Sex Differences in Rat Ultrasonic Vocalization

The rat model is a useful tool for understanding peripheral and central mechanisms of laryngeal biology. Rats produce ultrasonic vocalizations (USVs) that have communicative intent and are altered by experimental conditions such as social environment, stress, diet, drugs, age, and neurological diseases, validating the rat model's utility for studying communication and related deficits. Sex differences are apparent in both the rat larynx and USV acoustics and are differentially affected by experimental conditions. Therefore, the purpose of this review paper is to highlight the known sex differences in rat USV production, acoustics, and laryngeal biology detailed in the literature across the lifespan.

Post-weaning stroking stimuli induce affiliative behavior toward humans and influence brain activity in female rats

Gentle touch contributes to affiliative interactions. We investigated the effects of gentle stroking in female rats on the development of affiliative behaviors toward humans and we exploratively examined brain regions in which activity was influenced by stroking. Rats that had received stroking stimuli repeatedly after weaning emitted 50-kHz calls, an index of positive emotion, and showed affiliative behaviors toward the experimenter. Hypothalamic paraventricular oxytocin neurons were activated in the rats after stroking. The septohypothalamic nucleus (SHy) in the post-weaningly stroked rats showed decreased activity in response to stroking stimuli compared with that in the non-stroked control group. There were negative correlations of neural activity in hypothalamic regions including the SHy with the number of 50-kHz calls. These findings revealed that post-weaning stroking induces an affiliative relationship between female rats and humans, possibly via activation of oxytocin neurons and suppression of the activity of hypothalamic neurons.

Sex-dependent effects of Cacna1c haploinsufficiency on behavioral inhibition evoked by conspecific alarm signals in rats

Deficits in processing social signals leads to reduced social functioning and is typically associated with neuropsychiatric disorders, including autism spectrum disorder, schizophrenia, and major depressive disorder. The cross-disorder risk gene CACNA1C is implicated in the etiology of all of these disorders and single-nucleotide polymorphisms within CACNA1C are ranked among the best replicated and most robust genetic findings from genome-wide association studies in psychiatry. Rats are highly social, live in large social groups, and communicate through ultrasonic vocalizations (USV), with low-frequency 22-kHz USV emitted in dangerous and often life-threating situations, such as predator exposure, serving an alarming function. In the present study, we applied an alarm 22-kHz USV playback paradigm to investigate the role of Cacna1c in socio-affective information processing in rats. Specifically, we assessed behavioral inhibition evoked by 22-kHz USV in constitutive heterozygous Cacna1c^+/- females and males, as compared to wildtype Cacna1c^+/+ littermate controls. To probe specificity, two sets of alarm 22-kHz USV were presented, i.e. 22-kHz USV elicited by predator urine exposure and 22-kHz USV emitted during a retention test on learned fear, together with acoustic control stimuli. Our results show that behavioral inhibition evoked by playback of alarm 22-kHz USV is robust and occurs in response to both sets, yet is modulated by Cacna1c in a sex-dependent manner. In male but not female rats, Cacna1c haploinsufficiency led to less pronounced and less specific behavioral inhibition, supporting the idea that Cacna1c haploinsufficiency results in a lower motivation and/or diminished capability to display appropriate responses to important socio-affective communication signals.

LPS-induced sickness behavior is not affected by selenium but is switched off by psychogenic stress in rats

Sickness behavior (SB) is considered part of the adaptive behavioral and neuroimmune changes that occur in response to inflammatory processes. However, SB is a motivational state modulated by the environmental context. The objective of this study was to evaluate if selenium could ameliorate symptoms of SB and if stress would affect these responses. We induced SB in rats using lipopolysaccharide (LPS). We choose selenium based on our findings of LPS-exposure decreasing selenium levels in rats. We exposed these rats to a psychogenic stress and studied motivational modulation paradigms, such as cure of the organism, preservation of the species, and fight or flight. We studied ultrasonic vocalizations, open-field behaviors, body weight, and IL-1 beta and IFN-gamma serum levels. LPS-induced SB was evidenced by decreased motor/exploratory activity and increased proinflammatory mediators' levels. Selenium treatment did not exert beneficial effects on SB, revealing that probably the selenium deficiency was not related to SB. When analyzed with the stress paradigm, the behavior of rats was differentially affected. LPS did not affect behavior in the presence of stress. SB was abrogated during stressor events to prioritize survival behaviors, such as fight-or-flight. Contrarily, the association of LPS, selenium, and stress induced SB even during stressor events, revealing that this combination induced a cumulative toxic effect.

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.

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.