Diverse roles of pontine NPS-expressing neurons in sleep regulation.

Neuropeptide S (NPS) was postulated to be a wake-promoting neuropeptide with unknown mechanism, and a mutation in its receptor (NPSR1) causes the short sleep duration trait in humans. We investigated the role of different NPS+ nuclei in sleep/wake regulation. Loss-of-function and chemogenetic studies revealed that NPS+ neurons in the parabrachial nucleus (PB) are wake-promoting, whereas peri-locus coeruleus (peri-LC) NPS+ neurons are not important for sleep/wake modulation. Further, we found that a NPS+ nucleus in the central gray of the pons (CGPn) strongly promotes sleep. Fiber photometry recordings showed that NPS+ neurons are wake-active in the CGPn and wake/REM-sleep active in the PB and peri-LC. Blocking NPS-NPSR1 signaling or knockdown of Nps supported the function of the NPS-NPSR1 pathway in sleep/wake regulation. Together, these results reveal that NPS and NPS+ neurons play dichotomous roles in sleep/wake regulation at both the molecular and circuit levels.

Top-down control of flight by a non-canonical cortico-amygdala pathway.

Survival requires the selection of appropriate behaviour in response to threats, and dysregulated defensive reactions are associated with psychiatric illnesses such as post-traumatic stress and panic disorder1. Threat-induced behaviours, including freezing and flight, are controlled by neuronal circuits in the central amygdala (CeA)2; however, the source of neuronal excitation of the CeA that contributes to high-intensity defensive responses is unknown. Here we used a combination of neuroanatomical mapping, in vivo calcium imaging, functional manipulations and electrophysiology to characterize a previously unknown projection from the dorsal peduncular (DP) prefrontal cortex to the CeA. DP-to-CeA neurons are glutamatergic and specifically target the medial CeA, the main amygdalar output nucleus mediating conditioned responses to threat. Using a behavioural paradigm that elicits both conditioned freezing and flight, we found that CeA-projecting DP neurons are activated by high-intensity threats in a context-dependent manner. Functional manipulations revealed that the DP-to-CeA pathway is necessary and sufficient for both avoidance behaviour and flight. Furthermore, we found that DP neurons synapse onto neurons within the medial CeA that project to midbrain flight centres. These results elucidate a non-canonical top-down pathway regulating defensive responses.

Interaction between Kölliker-Fuse/A7 and the parafacial respiratory region on the control of respiratory regulation.

Respiration is regulated by various types of neurons located in the pontine-medullary regions. The Kölliker-Fuse (KF)/A7 noradrenergic neurons play a role in modulating the inspiratory cycle by influencing the respiratory output. These neurons are interconnected and may also project to brainstem and spinal cord, potentially involved in regulating the post-inspiratory phase. In the present study, we hypothesize that the parafacial (pF) neurons, in conjunction with adrenergic mechanisms originating from the KF/A7 region, may provide the neurophysiological basis for breathing modulation. We conducted experiments using urethane-anesthetized, vagotomized, and artificially ventilated male Wistar rats. Injection of L-glutamate into the KF/A7 region resulted in inhibition of inspiratory activity, and a prolonged and high-amplitude genioglossal activity (GGEMG). Blockade of the α1 adrenergic receptors (α1-AR) or the ionotropic glutamatergic receptors in the pF region decrease the activity of the GGEMG without affecting inspiratory cessation. In contrast, blockade of α2-AR in the pF region extended the duration of GG activity. Notably, the inspiratory and GGEMG activities induced by KF/A7 stimulation were completely blocked by bilateral blockade of glutamatergic receptors in the Bötzinger complex (BötC). While our study found a limited role for α1 and α2 adrenergic receptors at the pF level in modulating the breathing response to KF/A7 stimulation, it became evident that BötC neurons are responsible for the respiratory effects induced by KF/A7 stimulation.

A medullary hub for controlling REM sleep and pontine waves.

Rapid-eye-movement (REM) sleep is a distinct behavioral state associated with vivid dreaming and memory processing. Phasic bursts of electrical activity, measurable as spike-like pontine (P)-waves, are a hallmark of REM sleep implicated in memory consolidation. However, the brainstem circuits regulating P-waves, and their interactions with circuits generating REM sleep, remain largely unknown. Here, we show that an excitatory population of dorsomedial medulla (dmM) neurons expressing corticotropin-releasing-hormone (CRH) regulates both REM sleep and P-waves in mice. Calcium imaging showed that dmM CRH neurons are selectively activated during REM sleep and recruited during P-waves, and opto- and chemogenetic experiments revealed that this population promotes REM sleep. Chemogenetic manipulation also induced prolonged changes in P-wave frequency, while brief optogenetic activation reliably triggered P-waves along with transiently accelerated theta oscillations in the electroencephalogram (EEG). Together, these findings anatomically and functionally delineate a common medullary hub for the regulation of both REM sleep and P-waves.

Pontine Waves Accompanied by Short Hippocampal Sharp Wave-Ripples During Non-rapid Eye Movement Sleep.

Ponto-geniculo-occipital or pontine (P) waves have long been recognized as an electrophysiological signature of rapid eye movement (REM) sleep. However, P-waves can be observed not just during REM sleep, but also during non-REM (NREM) sleep. Recent studies have uncovered that P-waves are functionally coupled with hippocampal sharp wave ripples (SWRs) during NREM sleep. However, it remains unclear to what extent P-waves during NREM sleep share their characteristics with P-waves during REM sleep and how the functional coupling to P-waves modulates SWRs. Here, we address these issues by performing multiple types of electrophysiological recordings and fiber photometry in both sexes of mice. P-waves during NREM sleep share their waveform shapes and local neural ensemble dynamics at a short (~100 milliseconds) timescale with their REM sleep counterparts. However, the dynamics of mesopontine cholinergic neurons are distinct at a longer (~10 seconds) timescale: although P-waves are accompanied by cholinergic transients, the cholinergic tone gradually reduces before P-wave genesis during NREM sleep. While P-waves are coupled to hippocampal theta rhythms during REM sleep, P-waves during NREM sleep are accompanied by a rapid reduction in hippocampal ripple power. SWRs coupled with P-waves are short-lived and hippocampal neural firing is also reduced after P-waves. These results demonstrate that P-waves are part of coordinated sleep-related activity by functionally coupling with hippocampal ensembles in a state-dependent manner.

Upper brainstem cholinergic neurons project to ascending and descending circuits.

BACKGROUND: Based on their anatomical location, rostral projections of nuclei are classified as ascending circuits, while caudal projections are classified as descending circuits. Upper brainstem neurons participate in complex information processing and specific sub-populations preferentially project to participating ascending or descending circuits. Cholinergic neurons in the upper brainstem have extensive collateralizations in both ascending and descending circuits; however, their single-cell projection patterns remain unclear because of the lack of comprehensive characterization of individual neurons. RESULTS: By combining fluorescent micro-optical sectional tomography with sparse labeling, we acquired a high-resolution whole-brain dataset of pontine-tegmental cholinergic neurons (PTCNs) and reconstructed their detailed morphology using semi-automatic reconstruction methods. As the main source of acetylcholine in some subcortical areas, individual PTCNs had abundant axons with lengths up to 60 cm and 5000 terminals and innervated multiple brain regions from the spinal cord to the cortex in both hemispheres. Based on various collaterals in the ascending and descending circuits, individual PTCNs were grouped into four subtypes. The morphology of cholinergic neurons in the pedunculopontine nucleus was more divergent, whereas the laterodorsal tegmental nucleus neurons contained richer axonal branches and dendrites. In the ascending circuits, individual PTCNs innervated the thalamus in three different patterns and projected to the cortex via two separate pathways. Moreover, PTCNs targeting the ventral tegmental area and substantia nigra had abundant collaterals in the pontine reticular nuclei, and these two circuits contributed oppositely to locomotion. CONCLUSIONS: Our results suggest that individual PTCNs have abundant axons, and most project to various collaterals in the ascending and descending circuits simultaneously. They target regions with multiple patterns, such as the thalamus and cortex. These results provide a detailed organizational characterization of cholinergic neurons to understand the connexional logic of the upper brainstem.

Opioid suppression of an excitatory pontomedullary respiratory circuit by convergent mechanisms.

Opioids depress breathing by inhibition of interconnected respiratory nuclei in the pons and medulla. Mu opioid receptor (MOR) agonists directly hyperpolarize a population of neurons in the dorsolateral pons, particularly the Kölliker-Fuse (KF) nucleus, that are key mediators of opioid-induced respiratory depression. However, the projection target and synaptic connections of MOR-expressing KF neurons are unknown. Here, we used retrograde labeling and brain slice electrophysiology to determine that MOR-expressing KF neurons project to respiratory nuclei in the ventrolateral medulla, including the preBötzinger complex (preBötC) and rostral ventral respiratory group (rVRG). These medullary-projecting, MOR-expressing dorsolateral pontine neurons express FoxP2 and are distinct from calcitonin gene-related peptide-expressing lateral parabrachial neurons. Furthermore, dorsolateral pontine neurons release glutamate onto excitatory preBötC and rVRG neurons via monosynaptic projections, which is inhibited by presynaptic opioid receptors. Surprisingly, the majority of excitatory preBötC and rVRG neurons receiving MOR-sensitive glutamatergic synaptic input from the dorsolateral pons are themselves hyperpolarized by opioids, suggesting a selective opioid-sensitive circuit from the KF to the ventrolateral medulla. Opioids inhibit this excitatory pontomedullary respiratory circuit by three distinct mechanisms-somatodendritic MORs on dorsolateral pontine and ventrolateral medullary neurons and presynaptic MORs on dorsolateral pontine neuron terminals in the ventrolateral medulla-all of which could contribute to opioid-induced respiratory depression.

Whole brain inputs to major descending pathways of the anterior lateral motor cortex.

The anterior lateral motor cortex (ALM) is critical to subsequent correct movements and plays a vital role in predicting specific future movements. Different descending pathways of the ALM are preferentially involved in different roles in movements. However, the circuit function mechanisms of these different pathways may be concealed in the anatomy circuit. Clarifying the anatomy inputs of these pathways should provide some helpful information for elucidating these function mechanisms. Here, we used a retrograde trans-synaptic rabies virus to systematically generate, analyze, and compare whole brain maps of inputs to the thalamus (TH)-, medulla oblongata (Med)-, superior colliculus (SC)-, and pontine nucleus (Pons)-projecting ALM neurons in C57BL/6J mice. Fifty-nine separate regions from nine major brain areas projecting to the descending pathways of the ALM were identified. Brain-wide quantitative analyses revealed identical whole brain input patterns between these descending pathways. Most inputs to the pathways originated from the ipsilateral side of the brain, with most innervations provided by the cortex and TH. The contralateral side of the brain also sent sparse projections, but these were rare, emanating only from the cortex and cerebellum. Nevertheless, the inputs received by TH-, Med-, SC-, and Pons-projecting ALM neurons had different weights, potentially laying an anatomical foundation for understanding the diverse functions of well-defined descending pathways of the ALM. Our findings provide anatomical information to help elucidate the precise connections and diverse functions of the ALM.NEW & NOTEWORTHY Distinct descending pathways of anterior lateral motor cortex (ALM) share common inputs. These inputs are with varied weights. Most inputs were from the ipsilateral side of brain. Preferential inputs were provided by cortex and thalamus (TH).

Valence processing in pons.

In this issue of Neuron, Xiao et al.1 reported that inhibitory and excitatory neurons in the pontine central gray encode and transmit opposite valences of sensory stimuli through parallel circuits to a distributed brain network.

Fentanyl effects on respiratory neuron activity in the dorsolateral pons.

Opioids suppress breathing through actions in the brainstem, including respiratory-related areas of the dorsolateral pons, which contain multiple phenotypes of respiratory patterned neurons. The discharge identity of dorsolateral pontine neurons that are impacted by opioids is unknown. To address this, single neuronal units were recorded in the dorsolateral pons of arterially perfused in situ rat preparations that were perfused with an apneic concentration of the opioid agonist fentanyl, followed by the opioid antagonist naloxone (NLX). Dorsolateral pontine neurons were categorized based on respiratory-associated discharge patterns, which were differentially affected by fentanyl. Inspiratory neurons and a subset of inspiratory/expiratory phase-spanning neurons were either silenced or had reduced firing frequency during fentanyl-induced apnea, which was reversed upon administration of naloxone. In contrast, the majority of expiratory neurons continued to fire tonically during fentanyl-induced apnea, albeit with reduced firing frequency. In addition, pontine late-inspiratory and postinspiratory neuronal activity were absent from apneustic-like breaths during the transition to fentanyl-induced apnea and the naloxone-mediated transition to recovery. Thus, opioid-induced deficits in respiratory patterning may occur due to reduced activity of pontine inspiratory neurons, whereas apnea occurs with loss of all phasic pontine activity and sustained tonic expiratory neuron activity.NEW & NOTEWORTHY Opioids can suppress breathing via actions throughout the brainstem, including the dorsolateral pons. The respiratory phenotype of dorsolateral pontine neurons inhibited by opioids is unknown. Here, we describe the effect of the highly potent opioid fentanyl on the firing activity of these dorsolateral pontine neurons. Inspiratory neurons were largely silenced by fentanyl, whereas expiratory neurons were not. We provide a framework whereby this differential sensitivity to fentanyl can contribute to respiratory pattern deficits and apnea.

Chemogenetic activation of noradrenergic A5 neurons increases blood pressure and visceral sympathetic activity in adult rats.

In mammals, the pontine noradrenergic system influences nearly every aspect of central nervous system function. A subpopulation of pontine noradrenergic neurons, called A5, are thought to be important in the cardiovascular response to physical stressors, yet their function is poorly defined. We hypothesized that activation of A5 neurons drives a sympathetically mediated increase in blood pressure (BP). To test this hypothesis, we conducted a comprehensive assessment of the cardiovascular effects of chemogenetic stimulation of A5 neurons in male and female adult rats using intersectional genetic and anatomical targeting approaches. Chemogenetic stimulation of A5 neurons in freely behaving rats elevated BP by 15 mmHg and increased cardiac baroreflex sensitivity with a negligible effect on resting HR. Importantly, A5 stimulation had no detectable effect on locomotor activity, metabolic rate, or respiration. Under anesthesia, stimulation of A5 neurons produced a marked elevation in visceral sympathetic nerve activity (SNA) and no change in skeletal muscle SNA, showing that A5 neurons preferentially stimulate visceral SNA. Interestingly, projection mapping indicates that A5 neurons target sympathetic preganglionic neurons throughout the spinal cord and parasympathetic preganglionic neurons throughout in the brainstem, as well as the nucleus of the solitary tract, and ventrolateral medulla. Moreover, in situ hybridization and immunohistochemistry indicate that a subpopulation of A5 neurons coreleases glutamate and monoamines. Collectively, this study suggests A5 neurons are a central modulator of autonomic function with a potentially important role in sympathetically driven redistribution of blood flow from the visceral circulation to critical organs and skeletal muscle.

The topography of corticopontine projections is controlled by postmitotic expression of the area-mapping gene Nr2f1.

Axonal projections from layer V neurons of distinct neocortical areas are topographically organized into discrete clusters within the pontine nuclei during the establishment of voluntary movements. However, the molecular determinants controlling corticopontine connectivity are insufficiently understood. Here, we show that an intrinsic cortical genetic program driven by Nr2f1 graded expression is directly implicated in the organization of corticopontine topographic mapping. Transgenic mice lacking cortical expression of Nr2f1 and exhibiting areal organization defects were used as model systems to investigate the arrangement of corticopontine projections. By combining three-dimensional digital brain atlas tools, Cre-dependent mouse lines and axonal tracing, we show that Nr2f1 expression in postmitotic neurons spatially and temporally controls somatosensory topographic projections, whereas expression in progenitor cells influences the ratio between corticopontine and corticospinal fibres passing the pontine nuclei. We conclude that cortical gradients of area-patterning genes are directly implicated in the establishment of a topographic somatotopic mapping from the cortex onto pontine nuclei.

Molecular ontology of the parabrachial nucleus.

Diverse neurons in the parabrachial nucleus (PB) communicate with widespread brain regions. Despite evidence linking them to a variety of homeostatic functions, it remains difficult to determine which PB neurons influence which functions because their subpopulations intermingle extensively. An improved framework for identifying these intermingled subpopulations would help advance our understanding of neural circuit functions linked to this region. Here, we present the foundation of a developmental-genetic ontology that classifies PB neurons based on their intrinsic, molecular features. By combining transcription factor labeling with Cre fate-mapping, we find that the PB is a blend of two, developmentally distinct macropopulations of glutamatergic neurons. Neurons in the first macropopulation express Lmx1b (and, to a lesser extent, Lmx1a) and are mutually exclusive with those in a second macropopulation, which derive from precursors expressing Atoh1. This second, Atoh1-derived macropopulation includes many Foxp2-expressing neurons, but Foxp2 also identifies a subset of Lmx1b-expressing neurons in the Kölliker-Fuse nucleus (KF) and a population of GABAergic neurons ventrolateral to the PB ("caudal KF"). Immediately ventral to the PB, Phox2b-expressing glutamatergic neurons (some coexpressing Lmx1b) occupy the KF, supratrigeminal nucleus, and reticular formation. We show that this molecular framework organizes subsidiary patterns of adult gene expression (including Satb2, Calca, Grp, and Pdyn) and predicts output projections to the amygdala (Lmx1b), hypothalamus (Atoh1), and hindbrain (Phox2b/Lmx1b). Using this molecular ontology to organize, interpret, and communicate PB-related information could accelerate the translation of experimental findings from animal models to human patients.

The role of lumbosacral innervating noradrenergic neurons in micturition control.

A long-standing observation is that the micturition reflex receives supraspinal descending control. Although one supraspinal nucleus (Barrington's nucleus) is identified as the pontine micturition center, it remains largely unknown whether and how other supraspinal tracts are involved in micturition control. Here, we focused on the role of lumbosacral projecting neurons located in the Locus Coeruleus (LC) in modulating micturition, since previous studies indicated that the LC is involved in controlling bladder contraction. First, by performing an AAV mediated retrograde labeling using a TH-iCre mouse line, we demonstrated specific targeting of LC noradrenergic neurons innervating the lumbosacral spinal cord with high efficiency. Next, by lumbosacral injection of a retro-AAV carrying Cre-dependent human diphtheria toxin receptors (DTR), we achieved specific ablation of LC NA+ neurons with lumbosacral projections upon the administration of diphtheria toxin. Our results showed that specific ablation of theseneurons led to overflow incontinence leaks and lower void efficiency. Mechanistically, by performing the urodynamics analysis, we showed that ablation of lumbosacral innervating NAneurons resulted in detrusor-sphincter dyssynergia. Taken together, our study provided novel insights into the underlying mechanisms of supraspinal control of micturition reflex and thus shed light on developing novel treatment to improve micturition control in patients with SCI or lower urinary tract symptoms.

Social isolation uncovers a circuit underlying context-dependent territory-covering micturition.

The release of urine, or micturition, serves a fundamental physiological function and, in many species, is critical for social communication. In mice, the pattern of urine release is modulated by external and internal factors and transmitted to the spinal cord via the pontine micturition center (PMC). Here, we exploited a behavioral paradigm in which mice, depending on strain, social experience, and sensory context, either vigorously cover an arena with small urine spots or deposit urine in a few isolated large spots. We refer to these micturition modes as, respectively, high and low territory-covering micturition (TCM) and find that the presence of a urine stimulus robustly induces high TCM in socially isolated mice. Comparison of the brain networks activated by social isolation and by urine stimuli to those upstream of the PMC identified the lateral hypothalamic area as a potential modulator of micturition modes. Indeed, chemogenetic manipulations of the lateral hypothalamus can switch micturition behavior between high and low TCM, overriding the influence of social experience and sensory context. Our results suggest that both inhibitory and excitatory signals arising from a network upstream of the PMC are integrated to determine context- and social-experience-dependent micturition patterns.

Endogenous Cholinergic Signaling Modulates Sound-Evoked Responses of the Medial Nucleus of the Trapezoid Body.

The medial nucleus of trapezoid body (MNTB) is a major source of inhibition in auditory brainstem circuitry. The MNTB projects well-timed inhibitory output to principal sound-localization nuclei in the superior olive (SOC) as well as other computationally important centers. Acoustic information is conveyed to MNTB neurons through a single calyx of Held excitatory synapse arising from the cochlear nucleus. The encoding efficacy of this large synapse depends on its activity rate, which is primarily determined by sound intensity and stimulus frequency. However, MNTB activity rate is additionally influenced by inhibition and possibly neuromodulatory inputs, albeit their functional role is unclear. Happe and Morley (2004) discovered prominent expression of α7 nAChRs in rat SOC, suggesting possible engagement of ACh-mediated modulation of neural activity in the MNTB. However, the existence and nature of this putative modulation have never been physiologically demonstrated. We probed nicotinic cholinergic influences on acoustic responses of MNTB neurons from adult gerbils (Meriones unguiculatus) of either sex. We recorded tone-evoked MNTB single-neuron activity in vivo using extracellular single-unit recording. Piggyback multibarrel electrodes enabled pharmacological manipulation of nAChRs by reversibly applying antagonists to two receptor types, α7 and α4ß2. We observed that tone-evoked responses are dependent on ACh modulation by both nAChR subtypes. Spontaneous activity was not affected by antagonist application. Functionally, we demonstrate that ACh contributes to sustaining high discharge rates and enhances signal encoding efficacy. Additionally, we report anatomic evidence revealing novel cholinergic projections to MNTB arising from pontine and superior olivary nuclei.SIGNIFICANCE STATEMENT This study is the first to physiologically probe how acetylcholine, a pervasive neuromodulator in the brain, influences the encoding of acoustic information by the medial nucleus of trapezoid body, the most prominent source of inhibition in brainstem sound-localization circuitry. We demonstrate that this cholinergic input enhances neural discrimination of tones from noise stimuli, which may contribute to processing important acoustic signals, such as speech. Additionally, we describe novel anatomic projections providing cholinergic input to the MNTB. Together, these findings shed new light on the contribution of neuromodulation to fundamental computational processes in auditory brainstem circuitry and to a more holistic understanding of modulatory influences in sensory processing.

Brain biomarkers and neuropsychological outcomes of pediatric posterior fossa brain tumor survivors treated with surgical resection with or without adjuvant chemotherapy.

PURPOSE: Children with brain tumors experience cognitive late effects, often related to cranial radiation. We sought to determine differential effects of surgery and chemotherapy on brain structure and neuropsychological outcomes in children who did not receive cranial radiation therapy (CRT). METHODS: Twenty-eight children with a history of posterior fossa tumor (17 treated with surgery, 11 treated with surgery and chemotherapy) underwent neuroimaging and neuropsychological assessment a mean of 4.5 years (surgery group) to 9 years (surgery + chemotherapy group) posttreatment, along with 18 healthy sibling controls. Psychometric measures assessed IQ, language, executive functions, processing speed, memory, and social-emotional functioning. Group differences and correlations between diffusion tensor imaging findings and psychometric scores were examined. RESULTS: The z-score mapping demonstrated fractional anisotropy (FA) values were ≥2 standard deviations lower in white matter tracts, prefrontal cortex gray matter, hippocampus, thalamus, basal ganglia, and pons between patient groups, indicating microstructural damage associated with chemotherapy. Patients scored lower than controls on visuoconstructional reasoning and memory (P ≤ .02). Lower FA in the uncinate fasciculus (R = -0.82 to -0.91) and higher FA in the thalamus (R = 0.73-0.91) associated with higher IQ scores, and higher FA in the thalamus associated with higher scores on spatial working memory (R = 0.82). CONCLUSIONS: Posterior fossa brain tumor treatment with surgery and chemotherapy affects brain microstructure and neuropsychological functioning years into survivorship, with spatial processes the most vulnerable. Biomarkers indicating cellular changes in the thalamus, hippocampus, pons, prefrontal cortex, and white matter tracts associate with lower psychometric scores.

Forebrain projection neurons target functionally diverse respiratory control areas in the midbrain, pons, and medulla oblongata.

Eupnea is generated by neural circuits located in the ponto-medullary brainstem, but can be modulated by higher brain inputs which contribute to volitional control of breathing and the expression of orofacial behaviors, such as vocalization, sniffing, coughing, and swallowing. Surprisingly, the anatomical organization of descending inputs that connect the forebrain with the brainstem respiratory network remains poorly defined. We hypothesized that descending forebrain projections target multiple distributed respiratory control nuclei across the neuroaxis. To test our hypothesis, we made discrete unilateral microinjections of the retrograde tracer cholera toxin subunit B in the midbrain periaqueductal gray (PAG), the pontine Kölliker-Fuse nucleus (KFn), the medullary Bötzinger complex (BötC), pre-BötC, or caudal midline raphé nuclei. We quantified the regional distribution of retrogradely labeled neurons in the forebrain 12-14 days postinjection. Overall, our data reveal that descending inputs from cortical areas predominantly target the PAG and KFn. Differential forebrain regions innervating the PAG (prefrontal, cingulate cortices, and lateral septum) and KFn (rhinal, piriform, and somatosensory cortices) imply that volitional motor commands for vocalization are specifically relayed via the PAG, while the KFn may receive commands to coordinate breathing with other orofacial behaviors (e.g., sniffing, swallowing). Additionally, we observed that the limbic or autonomic (interoceptive) systems are connected to broadly distributed downstream bulbar respiratory networks. Collectively, these data provide a neural substrate to explain how volitional, state-dependent, and emotional modulation of breathing is regulated by the forebrain.

Coupling of hippocampal theta and ripples with pontogeniculooccipital waves.

The hippocampus has a major role in encoding and consolidating long-term memories, and undergoes plastic changes during sleep1. These changes require precise homeostatic control by subcortical neuromodulatory structures2. The underlying mechanisms of this phenomenon, however, remain unknown. Here, using multi-structure recordings in macaque monkeys, we show that the brainstem transiently modulates hippocampal network events through phasic pontine waves known as pontogeniculooccipital waves (PGO waves). Two physiologically distinct types of PGO wave appear to occur sequentially, selectively influencing high-frequency ripples and low-frequency theta events, respectively. The two types of PGO wave are associated with opposite hippocampal spike-field coupling, prompting periods of high neural synchrony of neural populations during periods of ripple and theta instances. The coupling between PGO waves and ripples, classically associated with distinct sleep stages, supports the notion that a global coordination mechanism of hippocampal sleep dynamics by cholinergic pontine transients may promote systems and synaptic memory consolidation as well as synaptic homeostasis.