Isolation-induced ultrasonic vocalizations in pups: A comparison between Long-Evans, Sprague-Dawley, and Wistar rats

Altered socio-affective communication and amygdala development in mice with protocadherin10-deficient interneurons

Autism spectrum disorder (ASD) is a group of neurodevelopmental conditions associated with deficits in social interaction and communication, together with repetitive behaviours. The cell adhesion molecule protocadherin10 (PCDH10) is linked to ASD in humans. Pcdh10 is expressed in the nervous system during embryonic and early postnatal development and is important for neural circuit formation. In mice, strong expression of Pcdh10 in the ganglionic eminences and in the basolateral complex (BLC) of the amygdala was observed at mid and late embryonic stages, respectively. Both inhibitory and excitatory neurons expressed Pcdh10 in the BLC at perinatal stages and vocalization-related genes were enriched in Pcdh10-expressing neurons in adult mice. An epitope-tagged Pcdh10-HAV5 mouse line revealed endogenous interactions of PCDH10 with synaptic proteins in the young postnatal telencephalon. Nuanced socio-affective communication changes in call emission rates, acoustic features and call subtype clustering were primarily observed in heterozygous pups of a conditional knockout (cKO) with selective deletion of Pcdh10 in Gsh2-lineage interneurons. These changes were less prominent in heterozygous ubiquitous Pcdh10 KO pups, suggesting that altered anxiety levels associated with Gsh2-lineage interneuron functioning might drive the behavioural effects. Together, loss of Pcdh10 specifically in interneurons contributes to behavioural alterations in socio-affective communication with relevance to ASD.

Mammalian NREM and REM sleep: Why, when and how

This report proposes that fish use the spinal-rhombencephalic regions of their brain to support their activities while awake. Instead, the brainstem-diencephalic regions support the wakefulness in amphibians and reptiles. Lastly, mammals developed the telencephalic cortex to attain the highest degree of wakefulness, the cortical wakefulness. However, a paralyzed form of spinal-rhombencephalic wakefulness remains in mammals in the form of REMS, whose phasic signs are highly efficient in promoting maternal care to mammalian litter. Therefore, the phasic REMS is highly adaptive. However, their importance is low for singletons, in which it is a neutral trait, devoid of adaptive value for adults, and is mal-adaptive for marine mammals. Therefore, they lost it. The spinal-rhombencephalic and cortical wakeful states disregard the homeostasis: animals only attend their most immediate needs: foraging defense and reproduction. However, these activities generate allostatic loads that must be recovered during NREMS, that is a paralyzed form of the amphibian-reptilian subcortical wakefulness. Regarding the regulation of tonic REMS, it depends on a hypothalamic switch. Instead, the phasic REMS depends on an independent proportional pontine control.

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.

Impacts of a perinatal exposure to manganese coupled with maternal stress in rats: Tests of untrained behaviors

Manganese (Mn), an element that naturally occurs in the environment, has been shown to produce neurotoxic effects on the developing young when levels exceed physiological requirements. To evaluate the effects of this chemical in combination with non-chemical factors pregnant Long-Evans rats were treated with 0, 2, or 4 mg/mL Mn in their drinking water from gestational day (GD) 7 to postnatal day (PND) 22. Half of the dams received a variable stress protocol from GD13 to PND9, that included restraint, small cage with reduced bedding, exposure to predator odor, intermittent intervals of white noise, lights on for 24 h, intermittent intervals of lights on during dark cycle and cages with grid floors and reduced bedding. One male and one female offspring from each litter were tested to assess untrained behavior. Ultrasonic vocalizations (USV) were recorded from PND13 pups while they were isolated from the litter. Locomotor activity (MA) was measured in figure-eight mazes at PND 17, 29, and 79 (different set of rats at each time point). Social approach (SA) was tested at PND48. Acoustic startle response (ASR) and pre-pulse inhibition (PPI) were measured starting at PND58. At PND53 a sweetness preference for a chocolate flavored milk solution was assessed. There were sex related differences on several parameters for the USVs. There was also a Mn by stress by sex interaction with the females from the 4 mg/mL stressed dams having more frequency modulated (FM) call elements than the 4 mg/mL non-stressed group. There was an effect of Mn on motor activity but only at PND29 with the 2 mg/mL group having higher counts than the 0 mg/mL group. The social approach test showed sex differences for both the habituation and test phase. There was an effect of Mn, with the 4 mg/mL males having a greater preference for the stimulus rat than did the 0 mg/mL males. There was also a stress by sex interaction. The ASR and PPI had only a sex effect. Thus, with only the FM call elements having a Mn by stress effect, and the PND29 MA and SA preference index having a Mn effect but at different doses requires further investigation.

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.

Effects of prenatal exposure to valproic acid or poly(I:C) on ultrasonic vocalizations in rat pups: The role of social cues

Sociocommunicative deficits commonly observed in autism spectrum disorder (ASD) can be experimentally modeled using rodents' ultrasonic vocalizations (USVs). For example, USVs emitted by pups, separated from their mothers and nest, serve as a useful tool to identify autistic-like behaviors during the early period of development. Being sensitive to social context, these neonatal calls may help to reveal reduced social attachment or abnormal processing of social information. The aim of the present study was to characterize quantitative and structural changes in USVs emitted during isolation by male and female rat pups prenatally exposed to either valproic acid (VPA) or poly(I:C). To determine whether those pups differed from controls in sensitivity to social stimuli, isolation-induced USVs were recorded under two bedding conditions, i.e., novel bedding and soiled bedding from their home cages. Our results demonstrated early communication deficits in both models of autism. We reported a reduced number of USVs emitted by both VPA- and poly(I:C)-exposed males and females. Moreover, compared to the controls, VPA (but not poly(I:C)) pups emitted shorter calls with a higher peak frequency. While VPA offspring demonstrated fewer USVs on the "safe" bedding imbued with maternal/nest odors, this calming effect was not observed in poly(I:C) males, suggesting a more specific deficit in social communication. The present results demonstrate that qualitative along with quantitative analyses of neonatal vocalizations are a useful tool for assessing early sociocommunicative deficits in ASD models. Notably, more specific changes in USV emission may be detected when introducing social context.

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.

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.