Dissimilar interaction between dopaminergic and cholinergic systems in the initiation of emission of 50-kHz and 22-kHz vocalizations

Emotional vocalizations alter behaviors and neurochemical release into the amygdala

The basolateral amygdala (BLA), a brain center of emotional expression, contributes to acoustic communication by first interpreting the meaning of social sounds in the context of the listener's internal state, then organizing the appropriate behavioral responses. We propose that modulatory neurochemicals such as acetylcholine (ACh) and dopamine (DA) provide internal-state signals to the BLA while an animal listens to social vocalizations. We tested this in a vocal playback experiment utilizing highly affective vocal sequences associated with either mating or restraint, then sampled and analyzed fluids within the BLA for a broad range of neurochemicals and observed behavioral responses of adult male and female mice. In male mice, playback of restraint vocalizations increased ACh release and usually decreased DA release, while playback of mating sequences evoked the opposite neurochemical release patterns. In non-estrus female mice, patterns of ACh and DA release with mating playback were similar to males. Estrus females, however, showed increased ACh, associated with vigilance, as well as increased DA, associated with reward-seeking. Experimental groups that showed increased ACh release also showed the largest increases in an aversive behavior. These neurochemical release patterns and several behavioral responses depended on a single prior experience with the mating and restraint behaviors. Our results support a model in which ACh and DA provide contextual information to sound analyzing BLA neurons that modulate their output to downstream brain regions controlling behavioral responses to social vocalizations.

Lateral septum as a possible regulatory center of maternal behaviors

The lateral septum (LS) is involved in controlling anxiety, aggression, feeding, and other motivated behaviors. Lesion studies have also implicated the LS in various forms of caring behaviors. Recently, novel experimental tools have provided a more detailed insight into the function of the LS, including the specific role of distinct cell types and their neuronal connections in behavioral regulations, in which the LS participates. This article discusses the regulation of different types of maternal behavioral alterations using the distributions of established maternal hormones such as prolactin, estrogens, and the neuropeptide oxytocin. It also considers the distribution of neurons activated in mothers in response to pups and other maternal activities, as well as gene expressional alterations in the maternal LS. Finally, this paper proposes further research directions to keep up with the rapidly developing knowledge on maternal behavioral control in other maternal brain regions.

Intracellular recordings reveal integrative function of the basolateral amygdala in acoustic communication

The amygdala, a brain center of emotional expression, contributes to appropriate behavior responses during acoustic communication. In support of that role, the basolateral amygdala (BLA) analyzes the meaning of vocalizations through the integration of multiple acoustic inputs with information from other senses and an animal's internal state. The mechanisms underlying this integration are poorly understood. This study focuses on the integration of vocalization-related inputs to the BLA from auditory centers during this processing. We used intracellular recordings of BLA neurons in unanesthetized big brown bats that rely heavily on a complex vocal repertoire during social interactions. Postsynaptic and spiking responses of BLA neurons were recorded to three vocal sequences that are closely related to distinct behaviors (appeasement, low-level aggression, and high-level aggression) and have different emotional valence. Our novel findings are that most BLA neurons showed postsynaptic responses to one or more vocalizations (31 of 46) but that many fewer neurons showed spiking responses (8 of 46). The spiking responses were more selective than postsynaptic potential (PSP) responses. Furthermore, vocal stimuli associated with either positive or negative valence were similarly effective in eliciting excitatory postsynaptic potentials (EPSPs), inhibitory postsynaptic potentials (IPSPs), and spiking responses. This indicates that BLA neurons process both positive- and negative-valence vocal stimuli. The greater selectivity of spiking responses than PSP responses suggests an integrative role for processing within the BLA to enhance response specificity in acoustic communication.NEW & NOTEWORTHY The amygdala plays an important role in social communication by sound, but little is known about how it integrates diverse auditory inputs to form selective responses to social vocalizations. We show that BLA neurons receive inputs that are responsive to both negative- and positive-affect vocalizations but their spiking outputs are fewer and highly selective for vocalization type. Our work demonstrates that BLA neurons perform an integrative function in shaping appropriate behavioral responses to social vocalizations.

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.

Water Drinking Behavior Associated with Aversive Arousal in Rats: An Integrative Approach

Cholinergic muscarinic stimulation of vast areas of the limbic brain induced a well-documented polydipsia in laboratory rats. This excessive water-drinking behavior has not received any convincing biological and physiological interpretation for the last 50 years. This review offers such an interpretation and suggests that cholinergically induced drinking response, mostly by carbachol, is associated with activation of the ascending mesolimbic cholinergic system that serves for initiation of emotional aversive arousal of the organism. The ascending cholinergic system originates from the laterodorsal tegmental nucleus, has a diffuse nature, and affects numerous subcortical limbic structures. It is proposed that the carbachol-induced drinking response is related to the state of anxiety and does not serve the regulation of thirst. Instead, the response is anxiety-induced polydipsia that might occur as a soothing procedure that decreases the aversiveness of the negative emotional state induced by carbachol. It is concluded that carbachol-induced water-drinking behavior is a rewarding process that contributes to alleviating the feeling of anxiety by bringing some relief from the cholinergically induced aversive state, and it is a homologue to anxiety-driven polydipsia in humans.

Increased self-triggered vocalizations in an epidermal growth factor-induced rat model for schizophrenia

Rats elicit two types of ultrasonic vocalizations (USVs), positive (30–80 kHz; high pitch) and negative (10–30 kHz; low pitch) voices. As patients with schizophrenia often exhibit soliloquy-like symptoms, we explored whether an animal model for schizophrenia is similarly characterized by such self-triggered vocalizations. We prepared the animal model by administering an inflammatory cytokine, epidermal growth factor (EGF), to rat neonates, which later develop behavioral and electroencephalographic deficits relevant to schizophrenia. EGF model rats and controls at young (8–10 weeks old) and mature (12–14 weeks old) adult stages were subjected to acclimation, female pairing, and vocalization sessions. In acclimation sessions, low pitch USVs at the mature adult stage were more frequent in EGF model rats than in controls. In the vocalization session, the occurrences of low pitch self-triggered USVs were higher in EGF model rats in both age groups, although this group difference was eliminated by their risperidone treatment. Unlike conventional negative USVs of rats, however, the present low pitch self-triggered USVs had short durations of 10–30 ms. These results suggest the potential that self-triggered vocalization might serve as a translatable pathological trait of schizophrenia to animal models.

Muscarinic regulation of self-grooming behavior and ultrasonic vocalizations in the context of open-field habituation in rats

Laboratory rats repeatedly exposed to an open field (OF) apparatus display increasingly high levels of grooming -especially that characterized by long and complex sequences- which has been taken as an additional index of novelty habituation. We hypothesized that disrupting such a learning process by administering an amnesic drug as the antimuscarinic scopolamine (SCP) could delay the appearance of more complex grooming subtypes. Thus, rats were pretreated either with SCP (15 mg/kg or 30 mg/kg) or vehicle (VEH) upon four one-day apart OF (OF1-4). On a fifth assessment, all rats received VEH to analyze the likely carry-over effect of SCP. Finally, we measured 50-kHz and 22-kHz ultrasonic vocalizations (USVs) as reliable markers of positive and negative emotionality, respectively. We found that SCP increased locomotion during OF1 and reduced rearing on OF1-OF4, causing no disruption in habituation over tests. SCP prevented the increase of total grooming time by inhibiting complex grooming subtypes and promoting short cephalic sequences. Despite the SCP-induced alterations on grooming agreed with our hypotheses, those changes may have resulted from a motor impairment that could have also affected rearing behavior. Additionally, SCP suppressed 50-kHz USVs while marginally increased 22-kHz calls. Once SCP was withdrawn, rearing, grooming, and some 50-kHz USVs subtypes returned to VEH levels, suggesting that novelty habituation occurred despite the SCP administration. Altogether, that mixed profile of SCP-induced behavioral changes may derive from the complex interplay between the contrasting action of SCP on different brain regions and the doses here used.

Individual Differences in Conditioned Fear and Extinction in Female Rats

The inability to extinguish a traumatic memory is a key aspect of post-traumatic stress disorder (PTSD). While PTSD affects 10–20% of individuals who experience a trauma, women are particularly susceptible to developing the disorder. Despite this notable female vulnerability, few studies have investigated this particular resistance to fear extinction observed in females. Similar to humans, rodent models of Pavlovian fear learning and extinction show a wide range of individual differences in fear learning and extinction, although female rodents are considerably understudied. Therefore, the present study examined individual differences in fear responses, including freezing behavior and ultrasonic vocalizations (USVs), of female Long–Evans rats during acquisition of fear conditioning and cued fear extinction. Similar to prior studies in males, female rats displayed individual variation in freezing during cued fear extinction and were divided into extinction competent (EC) and extinction resistant (ER) phenotypes. Differences in freezing between ER and EC females were accompanied by shifts in rearing during extinction, but no darting was seen in any trial. Freezing behavior during fear learning did not differ between the EC and ER females. Vocalizations emitted in the 22 and 50 kHz ranges during fear learning and extinction were also examined. Unlike vocalizations seen in previous studies in males, very few 22 kHz distress vocalizations were emitted by female rats during fear acquisition and extinction, with no difference between ER and EC groups. Interestingly, all female rats produced significant levels of 50 kHz USVs, and EC females emitted significantly more 50 kHz USVs than ER rats. This difference in 50 kHz USVs was most apparent during initial exposure to the testing environment. These results suggest that like males, female rodents show individual differences in both freezing and USVs during fear extinction, although females appear to vocalize more in the 50 kHz range, especially during initial periods of exposure to the testing environment, and emit very few of the 22 kHz distress calls that are typically observed in males during fear learning or extinction paradigms. Overall, these findings show that female rodents display fear behavior repertoires divergent from males.

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.

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.

Choline supplementation prevents the effects of bilirubin on cerebellar-mediated behavior in choline-restricted Gunn rat pups

BACKGROUND

Bilirubin is produced by the breakdown of hemoglobin and is normally catabolized and excreted. Neurotoxic accumulation of serum bilirubin often occurs in premature infants. The homozygous Gunn rat lacks uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), the enzyme needed to biotransform bilirubin. This rodent model of hyperbilirubinemia emulates many aspects of bilirubin toxicity observed in the human infant. We demonstrate that choline supplementation in early postnatal development is neuroprotective in the choline-restricted Gunn rat, when hyperbilirubinemia is induced on postnatal day 5.

METHODS

We first compared behaviors and cerebellar weight of pups born to dams consuming regular rat chow to those of dams consuming choline-restricted diets. Second, we measured behaviors and cerebellar weights of pups born to choline-restricted dams, reared on a choline-restricted diet, supplemented with or without choline, and treated with or without sulfadimethoxine (SDMX).

RESULTS

A choline-restricted diet did not change the behavioral outcomes, but cerebellar weight was reduced in the choline-restricted group regardless of genotype or SDMX administration. SDMX induced behavioral deficits in jj pups, and choline supplementation improved most behavioral effects and cerebellar weight in SDMX-treated jj rats.

CONCLUSIONS

These results suggest that choline may be used as a safe and effective neuroprotective intervention against hyperbilirubinemia in the choline-deficient premature infant.

IMPACT

This article investigates the effect of neonatal jaundice/bilirubin neurotoxicity on cerebellar-mediated behaviors. This article explores the potential use of choline as an intervention capable of ameliorating the effect of bilirubin on the choline-restricted developing brain. This article opens the door for future studies on the action of choline in the presence of hyperbilirubinemia, especially in preterm neonates.

Molecular characterization of frog vocal neurons using constellation pharmacology

Identification and characterization of neuronal cell classes in motor circuits are essential for understanding the neural basis of behavior. It is a challenging task, especially in a non-genetic-model organism, to identify cell-specific expression of functional macromolecules. Here, we performed constellation pharmacology, calcium imaging of dissociated neurons to pharmacologically identify functional receptors expressed by vocal neurons in adult male and female African clawed frogs, Xenopus laevis. Previously we identified a population of vocal neurons called fast trill neurons (FTNs) in the amphibian parabrachial nucleus (PB) that express N-methyl-d-aspartate (NMDA) receptors and GABA and/or glycine receptors. Using constellation pharmacology, we identified four cell classes of putative fast trill neurons (pFTNs, responsive to both NMDA and GABA/glycine applications). We discovered that some pFTNs responded to the application of substance P (SP), acetylcholine (ACh), or both. Electrophysiological recordings obtained from FTNs using an ex vivo preparation verified that SP and/or ACh depolarize FTNs. Bilateral injection of ACh, SP, or their antagonists into PBs showed that ACh receptors are not sufficient but necessary for vocal production, and SP receptors play a role in shaping the morphology of vocalizations. Additionally, we discovered that the PB of adult female X. laevis also contains all the subclasses of neurons at a similar frequency as in males, despite their sexually distinct vocalizations. These results reveal novel neuromodulators that regulate X. laevis vocal production and demonstrate the power of constellation pharmacology in identifying the neuronal subtypes marked by functional expression of cell-specific receptors in non-genetic-model organisms.NEW & NOTEWORTHY Molecular profiles of neurons are critical for understanding the neuronal functions, but their identification is challenging especially in non-genetic-model organisms. Here, we characterized the functional expression of membrane macromolecules in vocal neurons of African clawed frogs, Xenopus laevis, using a technique called constellation pharmacology. We discovered that receptors for acetylcholine and/or substance P are expressed by some classes of vocal neurons, and their activation plays a role in the production of normal vocalizations.