A novel reticular node in the brainstem synchronizes neonatal mouse crying with breathing

Afferent and Efferent Connections of the Postinspiratory Complex (PiCo) Revealed by AAV and Monosynaptic Rabies Viral Tracing

The control of the respiratory rhythm and airway motor activity is essential for life. Accumulating evidence indicates that the postinspiratory complex (PiCo) is crucial for generating behaviors that occur during the postinspiratory phase, including expiratory laryngeal activity and swallowing. Located in the ventromedial medulla, PiCo is defined by neurons co-expressing two neurotransmitter markers (ChAT and Vglut2/Slc17a6). Here, we mapped the input-output connections of these neurons using viral tracers and intersectional viral-genetic tools. PiCo neurons were specifically targeted by focal injection of a doubly conditional Cre- and FlpO-dependent AAV8 viral marker (AAV8-Con/Fon-TVA-mCherry) into the left PiCo of adult ChatCre/wt: Vglut2FlpO/wt mice, for anterograde axonal tracing. These experiments revealed projections to various brain regions, including the Cu, nucleus of the solitary tract (NTS), Amb, X, XII, Sp5, RMg, intermediate reticular nucleus (IRt), lateral reticular nucleus (LRt), pre-Bötzinger complex (preBötC), contralateral PiCo, laterodorsal tegmental nucleus (LDTg), pedunculopontine tegmental nucleus (PPTg), periaqueductal gray matter (PAG), Kölliker-Fuse (KF), PB, and external cortex of the inferior colliculus (ECIC). A rabies virus (RV) retrograde transsynaptic approach was taken with EnvA-pseudotyped G-deleted (RV-SAD-G-GFP) to similarly target PiCo neurons in ChatCre/wt: Vglut2FlpO/wt mice, following prior injections of helper AAVs (a mixture of AAV-Ef1a-Con/Fon oG and viral vector AAV8-Con/Fon-TVA-mCherry). This combined approach revealed prominent synaptic inputs to PiCo neurons from NTS, IRt, and A1/C1. Although PiCo neurons project axons to the contralateral PiCo area, this approach did not detect direct contralateral connections. We suggest that PiCo serves as a critical integration site, projecting and receiving neuronal connections implicated in breathing, arousal, swallowing, and autonomic regulation.

The ultrasonic vocalization (USV) syllable profile during neonatal opioid withdrawal and a kappa opioid receptor component to increased USV emissions in female mice

RATIONALE

Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.

OBJECTIVES

We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.

METHODS

We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.

RESULTS

On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.

CONCLUSIONS

We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity.

The ultrasonic vocalization (USV) syllable profile during neonatal opioid withdrawal and a kappa opioid receptor component to increased USV emissions in female mice

Rationale

Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.

Objectives

We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.

Methods

We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.

Results

On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.

Conclusions

We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity.

The breath shape controls intonation of mouse vocalizations

Intonation in speech is the control of vocal pitch to layer expressive meaning to communication, like increasing pitch to indicate a question. Also, stereotyped patterns of pitch are used to create distinct sounds with different denotations, like in tonal languages and, perhaps, the 10 sounds in the murine lexicon. A basic tone is created by exhalation through a constricted laryngeal voice box, and it is thought that more complex utterances are produced solely by dynamic changes in laryngeal tension. But perhaps, the shifting pitch also results from altering the swiftness of exhalation. Consistent with the latter model, we describe that intonation in most vocalization types follows deviations in exhalation that appear to be generated by the re-activation of the cardinal breathing muscle for inspiration. We also show that the brainstem vocalization central pattern generator, the iRO, can create this breath pattern. Consequently, ectopic activation of the iRO not only induces phonation, but also the pitch patterns that compose most of the vocalizations in the murine lexicon. These results reveal a novel brainstem mechanism for intonation.

Neuropeptide Modulation Enables Biphasic Internetwork Coordination via a Dual-Network Neuron

Linked rhythmic behaviors, such as respiration/locomotion or swallowing/chewing, often require coordination for proper function. Despite its prevalence, the cellular mechanisms controlling coordination of the underlying neural networks remain undetermined in most systems. We use the stomatogastric nervous system of the crab Cancer borealis to investigate mechanisms of internetwork coordination, due to its small, well-characterized feeding-related networks (gastric mill [chewing, ∼0.1 Hz]; pyloric [filtering food, ∼1 Hz]). Here, we investigate coordination between these networks during the Gly1-SIFamide neuropeptide modulatory state. Gly1-SIFamide activates a unique triphasic gastric mill rhythm in which the typically pyloric-only LPG neuron generates dual pyloric-plus gastric mill-timed oscillations. Additionally, the pyloric rhythm exhibits shorter cycles during gastric mill rhythm-timed LPG bursts, and longer cycles during IC, or IC plus LG gastric mill neuron bursts. Photoinactivation revealed that LPG is necessary to shorten pyloric cycle period, likely through its rectified electrical coupling to pyloric pacemaker neurons. Hyperpolarizing current injections demonstrated that although LG bursting enables IC bursts, only gastric mill rhythm bursts in IC are necessary to prolong the pyloric cycle period. Surprisingly, LPG photoinactivation also eliminated prolonged pyloric cycles, without changing IC firing frequency or gastric mill burst duration, suggesting that pyloric cycles are prolonged via IC synaptic inhibition of LPG, which indirectly slows the pyloric pacemakers via electrical coupling. Thus, the same dual-network neuron directly conveys excitation from its endogenous bursting and indirectly funnels synaptic inhibition to enable one network to alternately decrease and increase the cycle period of a related network.

The breath shape controls intonation of mouse vocalizations

Intonation in speech is the control of vocal pitch to layer expressive meaning to communication, like increasing pitch to indicate a question. Also, stereotyped patterns of pitch are used to create distinct sounds with different denotations, like in tonal languages and, perhaps, the ten sounds in the murine lexicon. A basic tone is created by exhalation through a constricted laryngeal voice box, and it is thought that more complex utterances are produced solely by dynamic changes in laryngeal tension. But perhaps, the shifting pitch also results from altering the swiftness of exhalation. Consistent with the latter model, we describe that intonation in most vocalization types follows deviations in exhalation that appear to be generated by the re-activation of the cardinal breathing muscle for inspiration. We also show that the brainstem vocalization central pattern generator, the iRO, can create this breath pattern. Consequently, ectopic activation of the iRO not only induces phonation, but also the pitch patterns that compose most of the vocalizations in the murine lexicon. These results reveal a novel brainstem mechanism for intonation.

Brainstem control of vocalization and its coordination with respiration

Phonation critically depends on precise controls of laryngeal muscles in coordination with ongoing respiration. However, the neural mechanisms governing these processes remain unclear. We identified excitatory vocalization-specific laryngeal premotor neurons located in the retroambiguus nucleus (RAmVOC) in adult mice as being both necessary and sufficient for driving vocal cord closure and eliciting mouse ultrasonic vocalizations (USVs). The duration of RAmVOC activation can determine the lengths of both USV syllables and concurrent expiration periods, with the impact of RAmVOC activation depending on respiration phases. RAmVOC neurons receive inhibition from the preBötzinger complex, and inspiration needs override RAmVOC-mediated vocal cord closure. Ablating inhibitory synapses in RAmVOC neurons compromised this inspiration gating of laryngeal adduction, resulting in discoordination of vocalization with respiration. Our study reveals the circuits for vocal production and vocal-respiratory coordination.

Evolution of air-borne vocalization: Insights from neural studies in the archeobatrachian species Bombina orientalis

Vocalization of tetrapods evolved as an air-driven mechanism. Thus, it is conceivable that the underlaying neural network might have evolved from more ancient respiratory circuits and be made up of homologous components that generate breathing rhythms across vertebrates. In this context, the extant species of stem anurans provide an opportunity to analyze the connection of the neural circuits of lung ventilation and vocalization. Here, we analyzed the fictive lung ventilation and vocalization behavior of isolated brains of the Chinese fire-bellied toad Bombina orientalis during their mating season by nerve root recordings. We discovered significant differences in durations of activation of male brains after stimulation of the statoacoustic nerve or vocalization-relevant forebrain structures in comparison to female brains. The increased durations of motor nerve activities in male brains can be interpreted as fictive calling, as male's advertisement calls in vivo had the same general pattern compared to lung ventilation, but longer duration periods. Female brains react to the corresponding stimulations with the same shorter activity pattern that occurred spontaneously in both female and male brains and thus can be interpreted as fictive lung ventilations. These results support the hypothesis that vocal circuits evolved from ancient respiration networks in the anuran caudal hindbrain. Moreover, we could show that the terrestrial stem archeobatrachian Bombina spec. is an appropriate model to study the function and evolution of the shared network of lung ventilation and vocal generation.

Latent neural population dynamics underlying breathing, opioid-induced respiratory depression and gasping

Breathing is vital and must be concurrently robust and flexible. This rhythmic behavior is generated and maintained within a rostrocaudally aligned set of medullary nuclei called the ventral respiratory column (VRC). The rhythmic properties of individual VRC nuclei are well known, yet technical challenges have limited the interrogation of the entire VRC population simultaneously. Here we characterize over 15,000 medullary units using high-density electrophysiology, opto-tagging and histological reconstruction. Population dynamics analysis reveals consistent rotational trajectories through a low-dimensional neural manifold. These rotations are robust and maintained even during opioid-induced respiratory depression. During severe hypoxia-induced gasping, the low-dimensional dynamics of the VRC reconfigure from rotational to all-or-none, ballistic efforts. Thus, latent dynamics provide a unifying lens onto the activities of large, heterogeneous populations of neurons involved in the simple, yet vital, behavior of breathing, and well describe how these populations respond to a variety of perturbations.

A brainstem circuit for phonation and volume control in mice

Mammalian vocalizations are critical for communication and are produced through the process of phonation, in which expiratory muscles force air through the tensed vocal folds of the larynx, which vibrate to produce sound. Despite the importance of phonation, the motor circuits in the brain that control it remain poorly understood. In this study, we identified a subpopulation of ~160 neuropeptide precursor Nts (neurotensin)-expressing neurons in the mouse brainstem nucleus retroambiguus (RAm) that are robustly activated during both neonatal isolation cries and adult social vocalizations. The activity of these neurons is necessary and sufficient for vocalization and bidirectionally controls sound volume. RAm Nts neurons project to all brainstem and spinal cord motor centers involved in phonation and activate laryngeal and expiratory muscles essential for phonation and volume control. Thus, RAm Nts neurons form the core of a brain circuit for making sound and controlling its volume, which are two foundations of vocal communication.

Temporal dynamics of isolation calls emitted by pups in environmental and genetic mouse models of autism spectrum disorder

Introduction

Environmental and genetic factors contribute to the increased risk for neurodevelopmental disorders, including deficits in the development of social communication. In the mouse, ultrasonic vocalizations emitted by the pup stimulate maternal retrieval and potentiate maternal care. Therefore, isolation induced ultrasonic vocalization emitted by pups provides a means to evaluate deficits in communication during early development, before other ways of communication are apparent. Previous studies in our labs showed that gestational exposure to the pesticide chlorpyrifos (CPF) and the Methylenetetrahydrofolate (Mthfr)-knock-out mice are associated with impaired social preference, restricted or repetitive behavior and altered spectral properties of pups' ultrasonic vocalization. In this study, we explore the temporal dynamics of pups' vocalization in these Autism spectrum disorder (ASD) models.

Methods

We utilized the maternal potentiation protocol and analyzed the time course of pup vocalizations following isolation from the nest. Two models of ASD were studied: gestational exposure to the pesticide CPF and the Mthfr-knock-out mice.

Results

Vocalization emitted by pups of both ASD models were dynamically modified in quantity and spectral structure within each session and between the two isolation sessions. The first isolation session was characterized by a buildup of call quantity and significant effects of USV spectral structure variables, and the second isolation session was characterized by enhanced calls and vocalization time, but minute effect on USV properties. Moreover, in both models we described an increased usage of harmonic calls with time during the isolation sessions.

Discussion

Communication between two or more individuals requires an interplay between the two sides and depends on the response and the time since the stimulus. As such, the presence of dynamic changes in vocalization structure in the control pups, and the alteration observed in the pups of the ASD models, suggest impaired regulation of vocalization associated with the environmental and genetic factors. Last, we propose that temporal dynamics of ultrasonic vocalization communication should be considered in future analysis in rodent models of ASD to maximize the sensitivity of the study of vocalizations.

Brainstem premotor mechanisms underlying vocal production and vocal-respiratory coordination

Speech generation critically depends on precise controls of laryngeal muscles and coordination with ongoing respiratory activity. However, the neural mechanisms governing these processes remain unknown. Here, we mapped laryngeal premotor circuitry in adult mice and viral-genetically identified excitatory vocal premotor neurons located in the retroambiguus nucleus (RAm VOC ) as both necessary and sufficient for driving vocal-cord closure and eliciting mouse ultrasonic vocalizations (USVs). The duration of RAm VOC activation determines the lengths of USV syllables and post-inspiration phases. RAm VOC -neurons receive inhibitory inputs from the preBötzinger complex, and inspiration needs can override RAm VOC -mediated vocal-cord closure. Ablating inhibitory synapses in RAm VOC -neurons compromised this inspiration gating of laryngeal adduction, resulting in de-coupling of vocalization and respiration. Our study revealed the hitherto unknown circuits for vocal pattern generation and vocal-respiratory coupling.

One-Sentence Summary

Identification of RAm VOC neurons as the critical node for vocal pattern generation and vocal-respiratory coupling.

Role of NaV1.6-mediated persistent sodium current and bursting-pacemaker properties in breathing rhythm generation

Inspiration is the inexorable active phase of breathing. The brainstem pre-Bötzinger complex (preBötC) gives rise to inspiratory neural rhythm, but its underlying cellular and ionic bases remain unclear. The long-standing "pacemaker hypothesis" posits that the persistent Na+ current (INaP) that gives rise to bursting-pacemaker properties in preBötC interneurons is essential for rhythmogenesis. We tested the pacemaker hypothesis by conditionally knocking out and knocking down the Scn8a (Nav1.6 [voltage-gated sodium channel 1.6]) gene in core rhythmogenic preBötC neurons. Deleting Scn8a substantially decreases the INaP and abolishes bursting-pacemaker activity, which slows inspiratory rhythm in vitro and negatively impacts the postnatal development of ventilation. Diminishing Scn8a via genetic interference has no impact on breathing in adult mice. We argue that the Scn8a-mediated INaP is not obligatory but that it influences the development and rhythmic function of the preBötC. The ubiquity of the INaP in respiratory brainstem interneurons could underlie breathing-related behaviors such as neonatal phonation or rhythmogenesis in different physiological conditions.

Group I metabotropic glutamate receptor-triggered temporally patterned action potential-dependent spontaneous synaptic transmission in mouse MNTB neurons

Rhythmic action potentials (AP) are generated via intrinsic ionic mechanisms in pacemaking neurons, producing synaptic responses of regular inter-event intervals (IEIs) in their targets. In auditory processing, evoked temporally patterned activities are induced when neural responses timely lock to a certain phase of the sound stimuli. Spontaneous spike activity, however, is a stochastic process, rendering the prediction of the exact timing of the next event completely based on probability. Furthermore, neuromodulation mediated by metabotropic glutamate receptors (mGluRs) is not commonly associated with patterned neural activities. Here, we report an intriguing phenomenon. In a subpopulation of medial nucleus of the trapezoid body (MNTB) neurons recorded under whole-cell voltage-clamp mode in acute mouse brain slices, temporally patterned AP-dependent glycinergic sIPSCs and glutamatergic sEPSCs were elicited by activation of group I mGluRs with 3,5-DHPG (200 µM). Auto-correlation analyses revealed rhythmogenesis in these synaptic responses. Knockout of mGluR5 largely eliminated the effects of 3,5-DHPG. Cell-attached recordings showed temporally patterned spikes evoked by 3,5-DHPG in potential presynaptic VNTB cells for synaptic inhibition onto MNTB. The amplitudes of sEPSCs enhanced by 3,5-DHPG were larger than quantal size but smaller than spike-driven calyceal inputs, suggesting that non-calyceal inputs to MNTB might be responsible for the temporally patterned sEPSCs. Finally, immunocytochemical studies identified expression and localization of mGluR5 and mGluR1 in the VNTB-MNTB inhibitory pathway. Our results imply a potential central mechanism underlying the generation of patterned spontaneous spike activity in the brainstem sound localization circuit.

Role of the postinspiratory complex in regulating swallow-breathing coordination and other laryngeal behaviors

Breathing needs to be tightly coordinated with upper airway behaviors, such as swallowing. Discoordination leads to aspiration pneumonia, the leading cause of death in neurodegenerative disease. Here, we study the role of the postinspiratory complex (PiCo) in coordinating breathing and swallowing. Using optogenetic approaches in freely breathing anesthetized ChATcre:Ai32, Vglut2cre:Ai32 and intersectional recombination of ChATcre:Vglut2FlpO:ChR2 mice reveals PiCo mediates airway protective behaviors. Activation of PiCo during inspiration or the beginning of postinspiration triggers swallow behavior in an all-or-nothing manner, while there is a higher probability for stimulating only laryngeal activation when activated further into expiration. Laryngeal activation is dependent on stimulation duration. Sufficient bilateral PiCo activation is necessary for preserving the physiological swallow motor sequence since activation of only a few PiCo neurons or unilateral activation leads to blurred upper airway behavioral responses. We believe PiCo acts as an interface between the swallow pattern generator and the preBötzinger complex to coordinate swallow and breathing. Investigating PiCo's role in swallow and laryngeal coordination will aid in understanding discoordination with breathing in neurological diseases.

Whole-brain mapping of neuronal activity evoked by maternal separation in neonatal mice: An association with ultrasound vocalization

Neonatal mice emit ultrasonic vocalizations (USVs) when separated from their mothers. Since the USVs attract their mothers' attention and trigger maternal retrieval, they are considered to serve as social signals for communication. We have modeled paternal aging effects on the vocal communication of offspring in mice. However, little is known about the neural basis underlying neonatal USV production. To identify responsible brain regions driving the vocal behavior, we comprehensively mapped the neuronal activity associated with USV production in the entire brain of mice at postnatal day 6 (P6). Using an expression of immediate-early gene c-Fos as a neuronal activity marker, correlations between the numbers of USVs and c-Fos positive neurons were analyzed. We identified 23 candidate brain regions associated with USV production in the mice at P6. Our study would be a first step toward comprehensively understanding the neuronal mechanisms that regulate and develop vocal behaviors in neonatal mice.

Transformation of Our Understanding of Breathing Control by Molecular Tools

The rhythmicity of breath is vital for normal physiology. Even so, breathing is enriched with multifunctionality. External signals constantly change breathing, stopping it when under water or deepening it during exertion. Internal cues utilize breath to express emotions such as sighs of frustration and yawns of boredom. Breathing harmonizes with other actions that use our mouth and throat, including speech, chewing, and swallowing. In addition, our perception of breathing intensity can dictate how we feel, such as during the slow breathing of calming meditation and anxiety-inducing hyperventilation. Heartbeat originates from a peripheral pacemaker in the heart, but the automation of breathing arises from neural clusters within the brainstem, enabling interaction with other brain areas and thus multifunctionality. Here, we document how the recent transformation of cellular and molecular tools has contributed to our appreciation of the diversity of neuronal types in the breathing control circuit and how they confer the multifunctionality of breathing.

Gasotransmitter modulation of hypoglossal motoneuron activity

Obstructive sleep apnea (OSA) is characterized by sporadic collapse of the upper airway leading to periodic disruptions in breathing. Upper airway patency is governed by genioglossal nerve activity that originates from the hypoglossal motor nucleus. Mice with targeted deletion of the gene Hmox2, encoding the carbon monoxide (CO) producing enzyme, heme oxygenase-2 (HO-2), exhibit OSA, yet the contribution of central HO-2 dysregulation to the phenomenon is unknown. Using the rhythmic brainstem slice preparation that contains the preBötzinger complex (preBötC) and the hypoglossal nucleus, we tested the hypothesis that central HO-2 dysregulation weakens hypoglossal motoneuron output. Disrupting HO-2 activity increased the occurrence of subnetwork activity from the preBötC, which was associated with an increased irregularity of rhythmogenesis. These phenomena were also associated with the intermittent inability of the preBötC rhythm to drive output from the hypoglossal nucleus (i.e. transmission failures), and a reduction in the input-output relationship between the preBötC and the motor nucleus. HO-2 dysregulation reduced excitatory synaptic currents and intrinsic excitability in inspiratory hypoglossal neurons. Inhibiting activity of the CO-regulated H2S producing enzyme, cystathionine-γ-lyase (CSE), reduced transmission failures in HO-2 null brainstem slices, which also normalized excitatory synaptic currents and intrinsic excitability of hypoglossal motoneurons. These findings demonstrate a hitherto uncharacterized modulation of hypoglossal activity through mutual interaction of HO-2/CO and CSE/H2S, and support the potential importance of centrally derived gasotransmitter activity in regulating upper airway control.

Rates of ultrasonic vocalizations are more strongly related than acoustic features to non-vocal behaviors in mouse pups

Mouse pups produce. ultrasonic vocalizations (USVs) in response to isolation from the nest (i.e., isolation USVs). Rates and acoustic features of isolation USVs change dramatically over the first two weeks of life, and there is also substantial variability in the rates and acoustic features of isolation USVs at a given postnatal age. The factors that contribute to within age variability in isolation USVs remain largely unknown. Here, we explore the extent to which non-vocal behaviors of mouse pups relate to the within age variability in rates and acoustic features of their USVs. We recorded non-vocal behaviors of isolated C57BL/6J mouse pups at four postnatal ages (postnatal days 5, 10, 15, and 20), measured rates of isolation USV production, and applied a combination of pre-defined acoustic feature measurements and an unsupervised machine learning-based vocal analysis method to examine USV acoustic features. When we considered different categories of non-vocal behavior, our analyses revealed that mice in all postnatal age groups produce higher rates of isolation USVs during active non-vocal behaviors than when lying still. Moreover, rates of isolation USVs are correlated with the intensity (i.e., magnitude) of non-vocal body and limb movements within a given trial. In contrast, USVs produced during different categories of non-vocal behaviors and during different intensities of non-vocal movement do not differ substantially in their acoustic features. Our findings suggest that levels of behavioral arousal contribute to within age variability in rates, but not acoustic features, of mouse isolation USVs.

Effect of pharmacological inhibition of the pontine respiratory group on swallowing interneurons in the dorsal medulla oblongata

OBJECTIVES

To examine the role of neurons of the pontine respiratory group (PRG) overlapping with the Kölliker-Fuse nucleus in the regulation of swallowing, we compared the activity of swallowing motor activities and interneuron discharge in the dorsal swallowing group in the medulla before and after pharmacological inhibition of the PRG.

METHODS

In 23 in situ perfused brainstem preparation of rats, we recorded the activities of the vagus (VNA), hypoglossal (HNA), and phrenic nerves (PNA), and swallowing interneurons of the dorsal medulla during fictive swallowing elicited by electrical stimulation of the superior laryngeal nerve or oral water injection. Subsequently, respiratory- and swallow-related motor activities and single unit cell discharge were assessed before and after local microinjection of the GABA-receptor agonist muscimol into the area of PRG ipsilateral to the recording sites of swallowing interneurons.

RESULTS

After muscimol injection, the amplitude and duration of swallow-related VNA bursts decreased to 71.3 ± 2.84 and 68.1 ± 2.76 % during electrically induced swallowing and VNA interburst intervals during repetitive swallowing decreased. Similar effects were observed for swallowing-related HNA. The swallowing motor activity was similarly qualitatively altered during physiologically induced swallowing. All 23 neurons were changed in either discharge duration or frequency after PRG inhibition, however, the general discharge patterns in relation to the motor output remained unchanged.

CONCLUSION

Descending synaptic inputs from PRG provide control of the primary laryngeal sensory gate and synaptic activity of the PRG partially determine medullary cell and cranial motor nerve activities that govern the pharyngeal stage of swallowing.

Convergent and divergent neural circuit architectures that support acoustic communication

Vocal communication is used across extant vertebrates, is evolutionarily ancient, and been maintained, in many lineages. Here I review the neural circuit architectures that support intraspecific acoustic signaling in representative anuran, mammalian and avian species as well as two invertebrates, fruit flies and Hawaiian crickets. I focus on hindbrain motor control motifs and their ties to respiratory circuits, expression of receptors for gonadal steroids in motor, sensory, and limbic neurons as well as divergent modalities that evoke vocal responses. Hindbrain and limbic participants in acoustic communication are highly conserved, while forebrain participants have diverged between anurans and mammals, as well as songbirds and rodents. I discuss the roles of natural and sexual selection in driving speciation, as well as exaptation of circuit elements with ancestral roles in respiration, for producing sounds and driving rhythmic vocal features. Recent technical advances in whole brain fMRI across species will enable real time imaging of acoustic signaling partners, tying auditory perception to vocal production.

Large-Scale Mapping of Vocalization-Related Activity in the Functionally Diverse Nuclei in Rat Posterior Brainstem

The identity and location of vocalization pattern generating (VPG) circuits in mammals is debated. Based on physiological experiments, investigators suggested anterior brainstem circuits in the reticular formation, and anatomic evidence suggested the nucleus retroambiguus (NRA) in the posterior brainstem, or combinations of these sites as the putative mammalian VPG. Additionally, vocalization loudness is a critical factor in acoustic communication. However, many of the underlying neuronal mechanisms are still unknown. Here, we evoked calls by stimulation of the periaqueductal gray in anesthetized male rats, performed a large-scale mapping of vocalization-related activity using the activity marker c-fos, and high-density recordings of brainstem circuits using Neuropixels probes. Both c-fos expression and recording of vocalization-related activity point to a participation of the NRA in vocalization. More important, among our recorded structures, we found that the NRA is the only brainstem area showing a strong correlation between unit activity and call intensity. In addition, we observed functionally diverse patterns of vocalization-related activity in a set of regions around NRA. Dorsal to NRA, we observed activity specific to the beginning and end of vocalizations in the posterior level of the medullary reticular nucleus, dorsal part, whereas medial and lateral to the NRA, we observed activity related to call initiation. No clear vocalization-related activity was observed at anterior brainstem sites. Our findings suggest a set of functionally heterogeneous regions around the NRA contribute to vocal pattern generation in rats.SIGNIFICANCE STATEMENT Vocalization patterns are shaped in the mammalian brainstem, but the identity and location of the circuits involved is debated. Additionally, the neuronal mechanisms of vocal intensity control are still unknown. This study consisted of a large-scale mapping of brainstem vocalization circuits based on the activity marker c-fos and high-density recordings with Neuropixels probes. The results confirm the role of nucleus retroambiguus in call production and point to a key role of neurons in this nucleus in loudness control. Dorsal to the nucleus retroambiguus and in the posterior medulla, the authors identify neurons with activity specific to the beginning and end of vocalizations. The results point to specific neural dials for various aspects of rat vocalization control in the posterior brainstem.

Multiple intrinsic membrane properties are modulated in a switch from single- to dual-network activity

Neural network flexibility includes changes in neuronal participation between networks, such as the switching of neurons between single- and dual-network activity. We previously identified a neuron that is recruited to burst in time with an additional network via modulation of its intrinsic membrane properties, instead of being recruited synaptically into the second network. However, the modulated intrinsic properties were not determined. Here, we use small networks in the Jonah crab (Cancer borealis) stomatogastric nervous system (STNS) to examine modulation of intrinsic properties underlying neuropeptide (Gly1-SIFamide)-elicited neuronal switching. The lateral posterior gastric neuron (LPG) switches from exclusive participation in the fast pyloric (∼1 Hz) network, due to electrical coupling, to dual-network activity that includes periodic escapes from the fast rhythm via intrinsically generated oscillations at the slower gastric mill network frequency (∼0.1 Hz). We isolated LPG from both networks by pharmacology and hyperpolarizing current injection. Gly1-SIFamide increased LPG intrinsic excitability and rebound from inhibition and decreased spike frequency adaptation, which can all contribute to intrinsic bursting. Using ion substitution and channel blockers, we found that a hyperpolarization-activated current, a persistent sodium current, and calcium or calcium-related current(s) appear to be primary contributors to Gly1-SIFamide-elicited LPG intrinsic bursting. However, this intrinsic bursting was more sensitive to blocking currents when LPG received rhythmic electrical coupling input from the fast network than in the isolated condition. Overall, a switch from single- to dual-network activity can involve modulation of multiple intrinsic properties, while synaptic input from a second network can shape the contributions of these properties.NEW & NOTEWORTHY Neuropeptide-elicited intrinsic bursting was recently determined to switch a neuron from single- to dual-network participation. Here we identified multiple intrinsic properties modulated in the dual-network state and candidate ion channels underlying the intrinsic bursting. Bursting at the second network frequency was more sensitive to blocking currents in the dual-network state than when neurons were synaptically isolated from their home network. Thus, synaptic input can shape the contributions of modulated intrinsic properties underlying dual-network activity.

Breathing Rhythm and Pattern and Their Influence on Emotion

Breathing is a vital rhythmic motor behavior with a surprisingly broad influence on the brain and body. The apparent simplicity of breathing belies a complex neural control system, the breathing central pattern generator (bCPG), that exhibits diverse operational modes to regulate gas exchange and coordinate breathing with an array of behaviors. In this review, we focus on selected advances in our understanding of the bCPG. At the core of the bCPG is the preBötzinger complex (preBötC), which drives inspiratory rhythm via an unexpectedly sophisticated emergent mechanism. Synchronization dynamics underlying preBötC rhythmogenesis imbue the system with robustness and lability. These dynamics are modulated by inputs from throughout the brain and generate rhythmic, patterned activity that is widely distributed. The connectivity and an emerging literature support a link between breathing, emotion, and cognition that is becoming experimentally tractable. These advances bring great potential for elucidating function and dysfunction in breathing and other mammalian neural circuits.