The midbrain periaqueductal gray control of respiration

Nucleus of the solitary tract neuronal degeneration and impaired hypoxia response in a model of Parkinson's disease

Parkinson's disease (PD) involves the degeneration of dopaminergic neurons in the substantia nigra (SNpc) and manifests with both classic and non-classic motor symptoms, including respiratory failure. Our study aims to investigate the involvement of the commissural and intermediate nucleus of the solitary tract (cNTS and iNTS) in the attenuated respiratory response to hypoxia in PD. Using a PD rat model induced by bilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum of male Wistar rats, we explored potential alterations in the population of Phox2b neurons or hypoxia-activated neurons in the NTS projecting to the retrotrapezoid nucleus (RTN). Additionally, we explored neuronal connectivity between SNpc and cNTS. Projections pathways were assessed using unilateral injection of the retrograde tracer Fluorogold (FG) in the cNTS and RTN. Neuronal activation was evaluated by analyzing fos expression in rats exposed to hypoxia. In the PD model, the ventilatory response, measured through whole-body plethysmography, was impaired at both baseline and in response to hypoxia. A reduction in Phox2b-expressing neurons or hypoxia-activated neurons projecting to the RTN was observed. Additionally, we identified an indirect pathway linking the SNpc and cNTS, which passes through the periaqueductal gray (PAG). In conclusion, our findings suggest impairment in the SNpc-PAG-cNTS pathway in the PD model, explaining the loss of Phox2b-expressing neurons or hypoxia-activated neurons in the cNTS and subsequent respiratory impairment during hypoxic stimulation. We propose that the reduced population of Phox2b-expressing neurons in the NTS may include the same neurons activated by hypoxia and projecting to the RTN.

A descending pathway from the lateral/ventrolateral PAG to the rostroventral medulla mediating the vasomotor response evoked by social defeat stress in rats

The stress-induced cardiovascular response is based on the defensive reaction in mammals. It has been shown that the sympathetic vasomotor pathway of acute psychological stress is indirectly mediated via neurons in the rostroventral medulla (RVM) from the hypothalamic stress center. In this study, direct projections to the RVM and distribution of neuroexcitatory marker c-Fos-expressed neurons were investigated during social defeat stress (SDS) in conscious rats. The experimental rat that was injected with a neural tracer, FluoroGold (FG) into the unilateral RVM, was exposed to the SDS. Double-positive neurons of both c-Fos and FG were locally distributed in the lateral/ventrolateral periaqueductal gray matter (l/vl PAG) in the midbrain. These results suggest that the neurons in the l/vl PAG contribute to the defensive reaction evoked by acute psychological stress, such as the SDS. During the SDS period, arterial pressure (AP) and heart rate (HR) showed sustained increases in the rat. Therefore, we performed chemical stimulation by excitatory amino acid microinjection within the l/vl PAG and measured cardiovascular response and sympathetic nerve activity in some anesthetized rats. The chemical stimulation of neurons in the l/vl PAG caused significant increases in arterial pressure and renal sympathetic nerve activity. Taken together, our results suggest that neurons in the l/vl PAG are a possible candidate for the cardiovascular descending pathway that modulates sympathetic vascular resistance evoked by acute psychological stress, like the SDS.NEW & NOTEWORTHY The sympathetic vasomotor pathway of an acute psychological stress-induced cardiovascular response is mediated via neurons in the RVM indirectly from the hypothalamus. In this study, we showed the relaying area of the efferent sympathetic vasomotor pathway from the hypothalamus to the RVM. The results suggested that the pressor response during psychological stress is mediated via neurons in the lateral/ventrolateral PAG to the RVM.

Seven Tesla Evidence for Columnar and Rostral-Caudal Organization of the Human Periaqueductal Gray Response in the Absence of Threat: A Working Memory Study

The periaqueductal gray (PAG) is a small midbrain structure that surrounds the cerebral aqueduct, regulates brain-body communication, and is often studied for its role in "fight-or-flight" and "freezing" responses to threat. We used ultra-high-field 7 T fMRI to resolve the PAG in humans and distinguish it from the cerebral aqueduct, examining its in vivo function during a working memory task (N = 87). Both mild and moderate cognitive demands elicited spatially similar patterns of whole-brain blood oxygenation level-dependent (BOLD) response, and moderate cognitive demand elicited widespread BOLD increases above baseline in the brainstem. Notably, these brainstem increases were not significantly greater than those in the mild demand condition, suggesting that a subthreshold brainstem BOLD increase occurred for mild cognitive demand as well. Subject-specific masks were group aligned to examine PAG response. In PAG, both mild and moderate demands elicited a well-defined response in ventrolateral PAG, a region thought to be functionally related to anticipated painful threat in humans and nonhuman animals-yet, the present task posed only the most minimal (if any) "threat," with the cognitive tasks used being approximately as challenging as remembering a phone number. These findings suggest that the PAG may play a more general role in visceromotor regulation, even in the absence of threat.

Neuroanatomical frameworks for volitional control of breathing and orofacial behaviors

Breathing is the only vital function that can be volitionally controlled. However, a detailed understanding how volitional (cortical) motor commands can transform vital breathing activity into adaptive breathing patterns that accommodate orofacial behaviors such as swallowing, vocalization or sniffing remains to be developed. Recent neuroanatomical tract tracing studies have identified patterns and origins of descending forebrain projections that target brain nuclei involved in laryngeal adductor function which is critically involved in orofacial behavior. These nuclei include the midbrain periaqueductal gray and nuclei of the respiratory rhythm and pattern generating network in the brainstem, specifically including the pontine Kölliker-Fuse nucleus and the pre-Bötzinger complex in the medulla oblongata. This review discusses the functional implications of the forebrain-brainstem anatomical connectivity that could underlie the volitional control and coordination of orofacial behaviors with breathing.

The contribution of periaqueductal gray in the regulation of physiological and pathological behaviors

Periaqueductal gray (PAG), an integration center for neuronal signals, is located in the midbrain and regulates multiple physiological and pathological behaviors, including pain, defensive and aggressive behaviors, anxiety and depression, cardiovascular response, respiration, and sleep-wake behaviors. Due to the different neuroanatomical connections and functional characteristics of the four functional columns of PAG, different subregions of PAG synergistically regulate various instinctual behaviors. In the current review, we summarized the role and possible neurobiological mechanism of different subregions of PAG in the regulation of pain, defensive and aggressive behaviors, anxiety, and depression from the perspective of the up-down neuronal circuits of PAG. Furthermore, we proposed the potential clinical applications of PAG. Knowledge of these aspects will give us a better understanding of the key role of PAG in physiological and pathological behaviors and provide directions for future clinical treatments.

Deep Diaphragmatic Breathing-Anatomical and Biomechanical Consideration

Background: Deep diaphragmatic breathing (DDB) involves slow and fully contraction of the diaphragm with expansion of the belly during inhalation, and slow and fully contraction of the abdominal muscles with reduction of the belly during exhalation. It is the key component of the holistic mind-body exercises commonly used for patients with multimorbidity. Purpose: The purpose of this study was to re-visit and address the fundamental anatomical and biomechanical consideration of the DDB with the relevant literature. Method: Peer-reviewed publications from last the 15 years were retrieved, reviewed, and analyzed. Findings: In this article, we described the updated morphological and anatomical characteristics of the diaphragm. Then, we elucidated in a biomechanical approach how and why the DDB can work on the gastrointestinal, cardiopulmonary, and nervous systems as well as on regulating the intra-abdominopelvic pressure and mind-body interaction to coordinate the diaphragm-pelvic floor-abdominal complex for a variety of physical and physiological activities. Conclusion: Understanding of this updated DDB knowledge may help holistic healthcare professionals including holistic nurses provide better patient education and care management during the DDB or DDB-based mind-body intervention time.

A Systematic Review of Direct Outputs from the Cerebellum to the Brainstem and Diencephalon in Mammals

The cerebellum is involved in many motor, autonomic and cognitive functions, and new tasks that have a cerebellar contribution are discovered on a regular basis. Simultaneously, our insight into the functional compartmentalization of the cerebellum has markedly improved. Additionally, studies on cerebellar output pathways have seen a renaissance due to the development of viral tracing techniques. To create an overview of the current state of our understanding of cerebellar efferents, we undertook a systematic review of all studies on monosynaptic projections from the cerebellum to the brainstem and the diencephalon in mammals. This revealed that important projections from the cerebellum, to the motor nuclei, cerebral cortex, and basal ganglia, are predominantly di- or polysynaptic, rather than monosynaptic. Strikingly, most target areas receive cerebellar input from all three cerebellar nuclei, showing a convergence of cerebellar information at the output level. Overall, there appeared to be a large level of agreement between studies on different species as well as on the use of different types of neural tracers, making the emerging picture of the cerebellar output areas a solid one. Finally, we discuss how this cerebellar output network is affected by a range of diseases and syndromes, with also non-cerebellar diseases having impact on cerebellar output areas.

Whole-brain monosynaptic inputs to lateral periaqueductal gray glutamatergic neurons in mice

OBJECTIVE

The lateral periaqueductal gray (LPAG), which mainly contains glutamatergic neurons, plays an important role in social responses, pain, and offensive and defensive behaviors. Currently, the whole-brain monosynaptic inputs to LPAG glutamatergic neurons are unknown. This study aims to explore the structural framework of the underlying neural mechanisms of LPAG glutamatergic neurons.

METHODS

This study used retrograde tracing systems based on the rabies virus, Cre-LoxP technology, and immunofluorescence analysis.

RESULTS

We found that 59 nuclei projected monosynaptic inputs to the LPAG glutamatergic neurons. In addition, seven hypothalamic nuclei, namely the lateral hypothalamic area (LH), lateral preoptic area (LPO), substantia innominata (SI), medial preoptic area, ventral pallidum, posterior hypothalamic area, and lateral globus pallidus, projected most densely to the LPAG glutamatergic neurons. Notably, we discovered through further immunofluorescence analysis that the inputs to the LPAG glutamatergic neurons were colocalized with several markers related to important neurological functions associated with physiological behaviors.

CONCLUSION

The LPAG glutamatergic neurons received dense projections from the hypothalamus, especially nuclei such as LH, LPO, and SI. The input neurons were colocalized with several markers of physiological behaviors, which show the pivotal role of glutamatergic neurons in the physiological behaviors regulation by LPAG.

Cerebellar mutism is linked to midbrain volatility and desynchronization from speech cortices

Cerebellar mutism syndrome is a disorder of speech, movement and affect that can occur after tumour removal from the posterior fossa. Projections from the fastigial nuclei to the periaqueductal grey area were recently implicated in its pathogenesis, but the functional consequences of damaging these projections remain poorly understood. Here, we examine functional MRI data from patients treated for medulloblastoma to identify functional changes in key brain areas that comprise the motor system for speech, which occur along the timeline of acute speech impairment in cerebellar mutism syndrome. One hundred and twenty-four participants, all with medulloblastoma, contributed to the study: 45 with cerebellar mutism syndrome, 11 patients with severe postoperative deficits other than mutism, and 68 without either (asymptomatic). We first performed a data-driven parcellation to spatially define functional nodes relevant to the cohort that align with brain regions critical for the motor control of speech. We then estimated functional connectivity between these nodes during the initial postoperative imaging sessions to identify functional deficits associated with the acute phase of the disorder. We further analysed how functional connectivity changed over time within a subset of participants that had suitable imaging acquired over the course of recovery. Signal dispersion was also measured in the periaqueductal grey area and red nuclei to estimate activity in midbrain regions considered key targets of the cerebellum with suspected involvement in cerebellar mutism pathogenesis. We found evidence of periaqueductal grey dysfunction in the acute phase of the disorder, with abnormal volatility and desynchronization with neocortical language nodes. Functional connectivity with periaqueductal grey was restored in imaging sessions that occurred after speech recovery and was further shown to be increased with left dorsolateral prefrontal cortex. The amygdalae were also broadly hyperconnected with neocortical nodes in the acute phase. Stable connectivity differences between groups were broadly present throughout the cerebrum, and one of the most substantial differences-between Broca's area and the supplementary motor area-was found to be inversely related to cerebellar outflow pathway damage in the mutism group. These results reveal systemic changes in the speech motor system of patients with mutism, centred on limbic areas tasked with the control of phonation. These findings provide further support for the hypothesis that periaqueductal grey dysfunction (following cerebellar surgical injury) contributes to the transient postoperative non-verbal episode commonly observed in cerebellar mutism syndrome but highlights a potential role of intact cerebellocortical projections in chronic features of the disorder.

Pedunculopontine Chx10+ neurons control global motor arrest in mice

Arrest of ongoing movements is an integral part of executing motor programs. Behavioral arrest may happen upon termination of a variety of goal-directed movements or as a global motor arrest either in the context of fear or in response to salient environmental cues. The neuronal circuits that bridge with the executive motor circuits to implement a global motor arrest are poorly understood. We report the discovery that the activation of glutamatergic Chx10-derived neurons in the pedunculopontine nucleus (PPN) in mice arrests all ongoing movements while simultaneously causing apnea and bradycardia. This global motor arrest has a pause-and-play pattern with an instantaneous interruption of movement followed by a short-latency continuation from where it was paused. Mice naturally perform arrest bouts with the same combination of motor and autonomic features. The Chx10-PPN-evoked arrest is different to ventrolateral periaqueductal gray-induced freezing. Our study defines a motor command that induces a global motor arrest, which may be recruited in response to salient environmental cues to allow for a preparatory or arousal state, and identifies a locomotor-opposing role for rostrally biased glutamatergic neurons in the PPN.

The integrated brain network that controls respiration

Respiration is a brain function on which our lives essentially depend. Control of respiration ensures that the frequency and depth of breathing adapt continuously to metabolic needs. In addition, the respiratory control network of the brain has to organize muscular synergies that integrate ventilation with posture and body movement. Finally, respiration is coupled to cardiovascular function and emotion. Here, we argue that the brain can handle this all by integrating a brainstem central pattern generator circuit in a larger network that also comprises the cerebellum. Although currently not generally recognized as a respiratory control center, the cerebellum is well known for its coordinating and modulating role in motor behavior, as well as for its role in the autonomic nervous system. In this review, we discuss the role of brain regions involved in the control of respiration, and their anatomical and functional interactions. We discuss how sensory feedback can result in adaptation of respiration, and how these mechanisms can be compromised by various neurological and psychological disorders. Finally, we demonstrate how the respiratory pattern generators are part of a larger and integrated network of respiratory brain regions.

Effect of Dynamic Neuromuscular Stabilization on Balance, Trunk Function, Falling, and Spasticity in People With Multiple Sclerosis: A Randomized Controlled Trial

OBJECTIVE

To compare the effects of core stabilization (CS) and dynamic neuromuscular stabilization (DNS) on balance, trunk function, mobility, falling, and spasticity, in people with multiple sclerosis (PWMS).

DESIGN

Two-group randomized controlled trial.

SETTING

General community and referral center.

PARTICIPANTS

A total of 64 PWMS, between 30 and 50 years old, and an expanded disability status scale between 2 and 5, participated in this study (N=64).

INTERVENTIONS

Participants were randomly assigned to CS (n=32) and DNS (n=32) groups. Both groups received a total of 15 sessions of CS or DNS exercises, 60 minutes per session, 3 times a week during the 5 weeks.

OUTCOME MEASURES

Balance function was measured as the primary outcome measure. Trunk function, postural stability, falling rate, fear of falling, falling index, mobility, and spasticity were measured as secondary outcomes.

RESULTS

DNS group had significant improvement in Berg balance scale, trunk impairment scale, postural stability, activities-specific balance confidence, reduced falling rate, the timed Up and Go (TUG), multiple sclerosis walking scale-12, and multiple sclerosis spasticity scale in PWMS compared with the CS group, (P<.0001) after 5 weeks of intervention and 17 weeks of follow-up. Except for the modified Ashworth scale (MAS), significant improvements were seen in all outcome measures in both groups after 5 weeks of intervention.

CONCLUSION

This is the first clinical evidence to support the importance of DNS exercise in improving balance, trunk function, and fall prevention in PWMS. This study provides clinical evidence that DNS may be more effective for PWMS than CS.

Effect of the cholinergic system of the lateral periaqueductal gray (lPAG) on blood pressure and heart rate in normal and hydralazine hypotensive rats

Objectives

Due to the presence of the cholinergic system in the lateral periaqueductal gray (lPAG) column, the cardiovascular effects of acetylcholine (ACH) and its receptors in normotensive and hydralazine (HYD) hypotensive rats in this area were evaluated.

Materials and Methods

After anesthesia, the femoral artery was cannulated and systolic blood pressure (SBP), mean arterial pressure (MAP), heart rate (HR), and also electrocardiogram for evaluation of low frequency (LF) and high frequency (HF) bands, important components of heart rate variability (HRV), were recorded. ACH, atropine (Atr, a muscarinic antagonist), and hexamethonium (Hex, an antagonist nicotinic) alone and together microinjected into lPAG, changes (Δ) of cardiovascular responses and normalized (n) LF, HF, and LF/HF ratio were analyzed.

Results

In normotensive rats, ACH decreased SBP and MAP, and enhanced HR while Atr and Hex did had no effects. In co-injection of Atr and Hex with ACH, only ACH+Atr significantly attenuated parameters. In HYD hypotension, ACH had no affect but Atr and Hex significantly improved the hypotensive effect. Co-injection of Atr and Hex with ACH decreased the hypotensive effect but the effect of Atr+ACH was higher. In normotensive rats, ACH decreased nLF, nHF, and nLF/nHF ratio. These parameters in the Atr +ACH group were significantly higher than in ACH group. In HYD hypotension nLF and nLF/nHF ratio increased which was attenuated by ACH. Also, Atr+ACH decreased nLF and nLF/nHF ratio and increased nHF.

Conclusion

The cholinergic system of lPAG mainly via muscarinic receptors has an inhibitory effect on the cardiovascular system. Based on HRV assessment, peripheral cardiovascular effects are mostly mediated by the parasympathetic system.

Pathophysiology and Therapy of Associated Features of Migraine

Migraine is a complex and debilitating disorder that is broadly recognised by its characteristic headache. However, given the wide array of clinical presentations in migraineurs, the headache might not represent the main troublesome symptom and it can even go unnoticed. Understanding migraines exclusively as a pain process is simplistic and certainly hinders management. We describe the mechanisms behind some of the most disabling associated symptoms of migraine, including the relationship between the central and peripheral processes that take part in nausea, osmophobia, phonophobia, vertigo and allodynia. The rationale for the efficacy of the current therapeutic arsenal is also depicted in this article. The associated symptoms to migraine, apart from the painful component, are frequent, under-recognised and can be more deleterious than the headache itself. The clinical anamnesis of a headache patient should enquire about the associated symptoms, and treatment should be considered and individualised. Acknowledging the associated symptoms as a fundamental part of migraine has permitted a deeper and more coherent comprehension of the pathophysiology of migraine.

Functional MRI Correlates of Carbon Dioxide Chemosensing in Persons With Epilepsy

Objectives

Sudden unexpected death in epilepsy (SUDEP) is a catastrophic epilepsy outcome for which there are no reliable premortem imaging biomarkers of risk. Percival respiratory depression is seen in monitored SUDEP and near SUDEP cases, and abnormal chemosensing of raised blood carbon dioxide (CO2) is thought to contribute. Damage to brainstem respiratory control and chemosensing structures has been demonstrated in structural imaging and neuropathological studies of SUDEP. We hypothesized that functional MRI (fMRI) correlates of abnormal chemosensing are detectable in brainstems of persons with epilepsy (PWE) and are different from healthy controls (HC).

Methods

We analyzed fMRI BOLD activation and brain connectivity in 10 PWE and 10 age- and sex-matched HCs during precisely metered iso-oxic, hypercapnic breathing challenges. Segmented brainstem responses were of particular interest, along with characterization of functional connectivity metrics between these structures. Regional BOLD activations during hypercapnic challenges were convolved with hemodynamic responses, and the resulting activation maps were passed on to group-level analyses. For the functional connectivity analysis, significant clusters from BOLD results were used as seeds. Each individual seed time-series activation map was extracted for bivariate correlation coefficient analyses to study changes in brain connectivity between PWE and HCs.

Results

(1) Greater brainstem BOLD activations in PWE were observed compared to HC during hypercapnic challenges in several structures with respiratory/chemosensing properties. Group comparison between PWE vs. HC showed significantly greater activation in the dorsal raphe among PWE (p < 0.05) compared to HCs. (2) PWE had significantly greater seed-seed connectivity and recruited more structures during hypercapnia compared to HC.

Significance

The results of this study show that BOLD responses to hypercapnia in human brainstem are detectable and different in PWE compared to HC. Increased dorsal raphe BOLD activation in PWE and increased seed-seed connectivity between brainstem and adjacent subcortical areas may indicate abnormal chemosensing in these individuals. Imaging investigation of brainstem respiratory centers involved in respiratory regulation in PWE is an important step toward identifying suspected dysfunction of brainstem breathing control that culminates in SUDEP and deserve further study as potential imaging SUDEP biomarkers.

Proposing a neural framework for the evolution of elaborate courtship displays

In many vertebrates, courtship occurs through the performance of elaborate behavioral displays that are as spectacular as they are complex. The question of how sexual selection acts upon these animals' neuromuscular systems to transform a repertoire of pre-existing movements into such remarkable (if not unusual) display routines has received relatively little research attention. This is a surprising gap in knowledge, given that unraveling this extraordinary process is central to understanding the evolution of behavioral diversity and its neural control. In many vertebrates, courtship displays often push the limits of neuromuscular performance, and often in a ritualized manner. These displays can range from songs that require rapid switching between two independently controlled 'voice boxes' to precisely choreographed acrobatics. Here, we propose a framework for thinking about how the brain might not only control these displays, but also shape their evolution. Our framework focuses specifically on a major midbrain area, which we view as a likely important node in the orchestration of the complex neural control of behavior used in the courtship process. This area is the periaqueductal grey (PAG), as studies suggest that it is both necessary and sufficient for the production of many instinctive survival behaviors, including courtship vocalizations. Thus, we speculate about why the PAG, as well as its key inputs, might serve as targets of sexual selection for display behavior. In doing so, we attempt to combine core ideas about the neural control of behavior with principles of display evolution. Our intent is to spur research in this area and bring together neurobiologists and behavioral ecologists to more fully understand the role that the brain might play in behavioral innovation and diversification.

The PV2 cluster of parvalbumin neurons in the murine periaqueductal gray: connections and gene expression

The PV2 (Celio 1990), a cluster of parvalbumin-positive neurons located in the ventromedial region of the distal periaqueductal gray (PAG) has not been previously described as its own entity, leading us to study its extent, connections, and gene expression. It is an oval, bilateral, elongated cluster composed of approximately 475 parvalbumin-expressing neurons in a single mouse hemisphere. In its anterior portion it impinges upon the paratrochlear nucleus (Par4) and in its distal portion it is harbored in the posterodorsal raphe nucleus (PDR). It is known to receive inputs from the orbitofrontal cortex and from the parvafox nucleus in the ventrolateral hypothalamus. Using anterograde tracing methods in parvalbumin-Cre mice, the main projections of the PV2 cluster innervate the supraoculomotor periaqueductal gray (Su3) of the PAG, the parvafox nucleus of the lateral hypothalamus, the gemini nuclei of the posterior hypothalamus, the septal regions, and the diagonal band in the forebrain, as well as various nuclei within the reticular formation in the midbrain and brainstem. Within the brainstem, projections were discrete, but involved areas implicated in autonomic control. The PV2 cluster expressed various peptides and receptors, including the receptor for Adcyap1, a peptide secreted by one of its main afferences, namely, the parvafox nucleus. The expression of GAD1 and GAD2 in the region of the PV2, the presence of Vgat-1 in a subpopulation of PV2-neurons as well as the coexistence of GAD67 immunoreactivity with parvalbumin in terminal endings indicates the inhibitory nature of a subpopulation of PV2-neurons. The PV2 cluster may be part of a feedback controlling the activity of the hypothalamic parvafox and the Su3 nuclei in the periaqueductal gray.

Ventrolateral periaqueductal gray matter integrative system of defense and antinociception

Defensive responses are neurophysiological processes crucial for survival during threatening situations. Defensive immobility is a common adaptive response, in rodents, elaborated by ventrolateral periaqueductal gray matter (vlPAG) when threat is unavoidable. It is associated with somatosensory and autonomic reactions such as alteration in the sensation of pain and rate of respiration. In this study, defensive immobility was assessed by chemical stimulation of vlPAG with different doses of NMDA (0.1, 0.3, and 0.6 nmol). After elicitation of defensive immobility, antinociceptive and respiratory response tests were also performed. Results revealed that defensive immobility was followed by a decrease in the nociceptive perception. Furthermore, the lowest dose of NMDA induced antinociceptive response without eliciting defensive immobility. During defensive immobility, respiratory responses were also disturbed. Interestingly, respiratory rate was increased and interspersed with prolonged expiratory phase of breathing. These findings suggest that vlPAG integrates three different defensive behavioral responses, contributing to the most effective defensive strategies during threatening situations.

Potential Circumstances Associated With Moral Injury and Moral Distress in Healthcare Workers and Public Safety Personnel Across the Globe During COVID-19: A Scoping Review

Healthcare workers (HCWs) and public safety personnel (PSP) across the globe have continued to face ethically and morally challenging situations during the COVID-19 pandemic that increase their risk for the development of moral distress (MD) and moral injury (MI). To date, however, the global circumstances that confer risk for MD and MI in these cohorts have not been systematically explored, nor have the unique circumstances that may exist across countries been explored. Here, we sought to identify and compare, across the globe, potentially morally injurious or distressful events (PMIDEs) in HCWs and PSP during the COVID-19 pandemic. A scoping review was conducted to identify and synthesize global knowledge on PMIDEs in HCWs and select PSP. Six databases were searched, including MEDLINE, EMBASE, Web of Science, PsychInfo, CINAHL, and Global Health. A total of 1,412 articles were retrieved, of which 57 articles were included in this review. These articles collectively described the experiences of samples from 19 different countries, which were comprised almost exclusively of HCWs. Given the lack of PSP data, the following results should not be generalized to PSP populations without further research. Using qualitative content analysis, six themes describing circumstances associated with PMIDEs were identified: (1) Risk of contracting or transmitting COVID-19; (2) Inability to work on the frontlines; (3) Provision of suboptimal care; (4) Care prioritization and resource allocation; (5) Perceived lack of support and unfair treatment by their organization; and (6) Stigma, discrimination, and abuse. HCWs described a range of emotions related to these PMIDEs, including anxiety, fear, guilt, shame, burnout, anger, and helplessness. Most PMIDE themes appeared to be shared globally, particularly the 'Risk of contracting or transmitting COVID-19' and the 'Perceived lack of support and unfair treatment by their organization.' Articles included within the theme of 'Stigma, discrimination, and abuse' represented the smallest global distribution of all PMIDE themes. Overall, the present review provides insight into PMIDEs encountered by HCWs across the globe during COVID-19. Further research is required to differentiate the experience of PSP from HCWs, and to explore the impact of social and cultural factors on the experience of MD and MI.

Critical roles for breathing in the genesis and modulation of emotional states

Breathing can be classified into metabolic and behavioral categories. Metabolic breathing and voluntary behavioral breathing are controlled in the brainstem and in the cerebral motor cortex, respectively. This chapter places special emphasis on the reciprocal influences between breathing and emotional processes. As is the case with neural control of breathing, emotions are generated by multiple control networks, located primarily in the forebrain. For several decades, a respiratory rhythm generator has been investigated in the limbic system. The amygdala receives respiratory-related input from the piriform cortex. Excitatory recurrent branches are located in the piriform cortex and have tight reciprocal synaptic connections, which produce periodic oscillations, similar to those recorded in the hippocampus during slow-wave sleep. The relationship between olfactory breathing rhythm and emotion is seen as the gateway to interpreting the relationship between breathing and emotion. In this chapter, we describe roles of breathing in the genesis of emotion, neural structures common to breathing and emotion, and mutual importance of breathing and emotion. We also describe the central roles of conscious awareness and voluntary control of breathing, as effective methods for stabilizing attention and the contents in the stream of consciousness. Voluntary control of breathing is seen as an essential practice for achieving emotional well-being.

Human threat circuits: Threats of pain, aggressive conspecific, and predator elicit distinct BOLD activations in the amygdala and hypothalamus

INTRODUCTION

Threat processing, enabled by threat circuits, is supported by a remarkably conserved neural architecture across mammals. Threatening stimuli relevant for most species include the threat of being attacked by a predator or an aggressive conspecific and the threat of pain. Extensive studies in rodents have associated the threats of pain, predator attack and aggressive conspecific attack with distinct neural circuits in subregions of the amygdala, the hypothalamus and the periaqueductal gray. Bearing in mind the considerable conservation of both the anatomy of these regions and defensive behaviors across mammalian species, we hypothesized that distinct brain activity corresponding to the threats of pain, predator attack and aggressive conspecific attack would also exist in human subcortical brain regions.

METHODS

Forty healthy female subjects underwent fMRI scanning during aversive classical conditioning. In close analogy to rodent studies, threat stimuli consisted of painful electric shocks, a short video clip of an attacking bear and a short video clip of an attacking man. Threat processing was conceptualized as the expectation of the aversive stimulus during the presentation of the conditioned stimulus.

RESULTS

Our results demonstrate differential brain activations in the left and right amygdala as well as in the left hypothalamus for the threats of pain, predator attack and aggressive conspecific attack, for the first time showing distinct threat-related brain activity within the human subcortical brain. Specifically, the threat of pain showed an increase of activity in the left and right amygdala and the left hypothalamus compared to the threat of conspecific attack (pain > conspecific), and increased activity in the left amygdala compared to the threat of predator attack (pain > predator). Threat of conspecific attack revealed heightened activity in the right amygdala, both in comparison to threat of pain (conspecific > pain) and threat of predator attack (conspecific > predator). Finally, for the condition threat of predator attack we found increased activity in the bilateral amygdala and the hypothalamus when compared to threat of conspecific attack (predator > conspecific). No significant clusters were found for the contrast predator attack > pain.

CONCLUSION

Results suggest that threat type-specific circuits identified in rodents might be conserved in the human brain.

The pathophysiology of opioid-induced respiratory depression

Opiates, such as morphine, and synthetic opioids, such as fentanyl, constitute a class of drugs acting on opioid receptors which have been used therapeutically and recreationally for centuries. Opioid drugs have strong analgesic properties and are used to treat moderate to severe pain, but also present side effects including opioid dependence, tolerance, addiction, and respiratory depression, which can lead to lethal overdose if not treated. This chapter explores the pathophysiology, the neural circuits, and the cellular mechanisms underlying opioid-induced respiratory depression and provides a translational perspective of the most recent research. The pathophysiology discussed includes the effects of opioid drugs on the respiratory system in patients, as well as the animal models used to identify underlying mechanisms. Using a combination of gene editing and pharmacology, the neural circuits and molecular pathways mediating neuronal inhibition by opioids are examined. By using pharmacology and neuroscience approaches, new therapies to prevent or reverse respiratory depression by opioid drugs have been identified and are currently being developed. Considering the health and economic burden associated with the current opioid epidemic, innovative research is needed to better understand the side effects of opioid drugs and to discover new therapeutic solutions to reduce the incidence of lethal overdoses.

Respiratory function modulated during execution, observation, and imagination of walking via SII

The Mirror Neurons System (MNS) consists of brain areas active during actions execution, as well as observation-imagination of the same actions. MNS represents a potential mechanism by which we understand other's action goals. We investigated MNS activation for legs actions, and its interaction with the autonomic nervous system. We performed a physiological and fMRI investigation on the common neural structures recruited during the execution, observation, and imagination of walking, and their effects on respiratory activity. Bilateral SMA were activated by all three tasks, suggesting that these areas are responsible for the core of the MNS effect for walking. Moreover, we observed in bilateral parietal opercula (OP1, secondary somatosensory cortex-SII) evidence of an MNS subtending walking execution-observation-imagination that also modulated the respiratory function. We suggest that SII, in modulating the vegetative response during motor activity but also during observation-imagination, consists of a re-enacting function which facilitates the understanding of motor actions.

The Mesencephalic Periaqueductal Gray, a Further Structure Involved in Breathing Failure Underlying Sudden Infant Death Syndrome

The aim of this study was to investigate the involvement of the periaqueductal gray (PAG), an area of gray matter surrounding the cerebral aqueduct of Sylvius, in the pathogenetic mechanism of SIDS, a syndrome frequently ascribed to arousal failure from sleep. We reconsidered the same samples of brainstem, more precisely midbrain specimens, taken from a large series of sudden infant deaths, namely 46 cases aged from 1 to about 7 months, among which 26 SIDS and 20 controls, in which we already highlighted significant developmental alterations of the substantia nigra, another mesencephalic structure with a critical role in breath and awakening regulation. Specific histological and immunohistochemical methods were applied to examine the PAG cytoarchitecture and the expression of the tyrosine hydroxylase, a marker of catecholaminergic neurons. Hypoplasia of the PAG subnucleus medialis was observed in 65% of SIDS but never in controls; tyrosine hydroxylase expression was significantly higher in controls than in SIDS. A significant correlation was found between these findings and those related to the substantia nigra, demonstrating a link between these neuronal centers and the brainstem respiratory network and a common involvement in the sleep-arousal phase failure leading to SIDS.

Multi-Level Regulation of Opioid-Induced Respiratory Depression

Opioids depress minute ventilation primarily by reducing respiratory rate. This results from direct effects on the preBötzinger Complex as well as from depression of the Parabrachial/Kölliker-Fuse Complex, which provides excitatory drive to preBötzinger Complex neurons mediating respiratory phase-switch. Opioids also depress awake drive from the forebrain and chemodrive.

Conservation and dimorphism in androgen receptor distribution in Alston's singing mouse (Scotinomys teguina)

Because of their roles in courtship and intrasexual competition, sexual displays are often sexually dimorphic, but we know little about the mechanisms that produce such dimorphism. Among mammals, one example is the vocalization of Alston's singing mouse (Scotinomys teguina), which consists of a series of rapidly repeated, frequency-modulated notes. The rate and duration of songs is sexually dimorphic and androgen responsive. To understand the neuronal mechanisms underlying this sexual dimorphism, we map the sites of androgen sensitivity throughout the brain, focusing analysis along a pathway that spans from limbic structures to vocal motor regions. We find widespread expression of AR immunoreactivity (AR-ir) throughout limbic structures important for social behavior and vocalization, including the lateral septum, extended amygdala, preoptic area and hypothalamus. We also find extensive AR staining along previously documented vocal motor pathways, including the periaqueductal gray, parabrachial nucleus, and nucleus ambiguus, the last of which innervates intrinsic laryngeal muscles. Lastly, AR-ir is also evident in sensory areas such as the medial geniculate, inferior, and superior colliculi. A quantitative analysis revealed that males exhibited more AR-ir than females, a pattern that was most pronounced in the hypothalamus. Despite the elaboration of vocalization in singing mice, comparison with prior literature suggests that the broad pattern of AR-ir may be conserved across a wide range of rodents. Together these data identify brain nuclei well positioned to shape the sexually dimorphic vocalization of S. teguina and suggest that such androgen modulation of vocalization is evolutionary conserved among rodents.

Reciprocal connectivity of the periaqueductal gray with the ponto-medullary respiratory network in rat

Synaptic activities of the periaqueductal gray (PAG) can modulate or appropriate the respiratory motor activities in the context of behavior and emotion via descending projections to nucleus retroambiguus. However, alternative anatomical pathways for the mediation of PAG-evoked respiratory modulation via core nuclei of the brainstem respiratory network remains only partially described. We injected the retrograde tracer Cholera toxin subunit B (CT-B) in the pontine Kölliker-Fuse nucleus (KFn, n = 5), medullary Bötzinger (BötC, n = 3) and pre-Bötzinger complexes (pre-BötC; n = 3), and the caudal raphé nuclei (n = 3), and quantified the descending connectivity of the PAG targeting these brainstem respiratory regions. CT-B injections in the KFn, pre-BötC, and caudal raphé, but not in the BötC, resulted in CT-B-labeled neurons that were predominantly located in the lateral and ventrolateral PAG columns. In turn, CT-B injections in the lateral and ventrolateral PAG columns (n = 4) produced the highest numbers of CT-B-labeled neurons in the KFn and far fewer numbers of labeled neurons in the pre-BötC, BötC, and caudal raphé. Analysis of the relative projection strength revealed that the KFn shares the densest reciprocal connectivity with the PAG (ventrolateral and lateral columns, in particular). Overall, our data imply that the PAG may engage a distributed respiratory rhythm and pattern generating network beyond the nucleus retroambiguus to mediate downstream modulation of breathing. However, the reciprocal connectivity of the KFn and PAG suggests specific roles for synaptic interaction between these two nuclei that are most likely related to the regulation of upper airway patency during vocalization or other volitional orofacial behaviors.

Expectation and dyspnea: The neurobiological basis of respiratory nocebo effects

Cues such as odours that do not per se evoke bronchoconstriction can become triggers of asthma exacerbations. Despite its clinical significance, the neural basis of this respiratory nocebo effect is unknown. We investigated this effect in a functional magnetic resonance imaging (fMRI) study involving 36 healthy volunteers. The experiment consisted of an Experience phase in which volunteers experienced dyspnea while being exposed to an odorous gas ("Histarinol"). Volunteers were told that "Histarinol" induces dyspnea by bronchoconstriction. This was compared to another odorous gas which did not evoke dyspnea. Actually, dyspnea was induced by a concealed, resistive load inserted into the breathing system. In a second, Expectation phase, Histarinol and the control gas were both followed by an identical, very mild load. Respiration parameters were continuously recorded and after each trial participants rated dyspnea intensity. Dyspnea ratings were significantly higher in Histarinol compared to control conditions, both in the Experience and in the Expectation phase, despite identical physical resistance in the Expectation phase. Insula fMRI signal matched the actual load, i.e. a significant difference between Histarinol and Control in the Experience phase, but no difference in the Expectation phase. The periaqueductal gray showed a significantly higher fMRI signal during the expectation of dyspnea. Finally, Histarinol related deactivations during the Expectation phase in the rostral anterior cingulate cortex mirror similar responses for nocebo effects in pain. These findings highlight the neural basis of expectation effects associated with dyspnea, which has important consequences for our understanding of the perception of respiratory symptoms.

Research Advances on Therapeutic Approaches to Congenital Central Hypoventilation Syndrome (CCHS)

Congenital central hypoventilation syndrome (CCHS) is a genetic disorder of neurodevelopment, with an autosomal dominant transmission, caused by heterozygous mutations in the PHOX2B gene. CCHS is a rare disorder characterized by hypoventilation due to the failure of autonomic control of breathing. Until now no curative treatment has been found. PHOX2B is a transcription factor that plays a crucial role in the development (and maintenance) of the autonomic nervous system, and in particular the neuronal structures involved in respiratory reflexes. The underlying pathogenetic mechanism is still unclear, although studies in vivo and in CCHS patients indicate that some neuronal structures may be damaged. Moreover, in vitro experimental data suggest that transcriptional dysregulation and protein misfolding may be key pathogenic mechanisms. This review summarizes latest researches that improved the comprehension of the molecular pathogenetic mechanisms responsible for CCHS and discusses the search for therapeutic intervention in light of the current knowledge about PHOX2B function.

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.

Association of Peri-ictal Brainstem Posturing With Seizure Severity and Breathing Compromise in Patients With Generalized Convulsive Seizures

OBJECTIVE

To analyze the association between peri-ictal brainstem posturing semiologies with postictal generalized electroencephalographic suppression (PGES) and breathing dysfunction in generalized convulsive seizures (GCS).

METHODS

In this prospective, multicenter analysis of GCS, ictal brainstem semiology was classified as (1) decerebration (bilateral symmetric tonic arm extension), (2) decortication (bilateral symmetric tonic arm flexion only), (3) hemi-decerebration (unilateral tonic arm extension with contralateral flexion) and (4) absence of ictal tonic phase. Postictal posturing was also assessed. Respiration was monitored with thoracoabdominal belts, video, and pulse oximetry.

RESULTS

Two hundred ninety-five seizures (180 patients) were analyzed. Ictal decerebration was observed in 122 of 295 (41.4%), decortication in 47 of 295 (15.9%), and hemi-decerebration in 28 of 295 (9.5%) seizures. Tonic phase was absent in 98 of 295 (33.2%) seizures. Postictal posturing occurred in 18 of 295 (6.1%) seizures. PGES risk increased with ictal decerebration (odds ratio [OR] 14.79, 95% confidence interval [CI] 6.18-35.39, p < 0.001), decortication (OR 11.26, 95% CI 2.96-42.93, p < 0.001), or hemi-decerebration (OR 48.56, 95% CI 6.07-388.78, p < 0.001). Ictal decerebration was associated with longer PGES (p = 0.011). Postictal posturing was associated with postconvulsive central apnea (PCCA) (p = 0.004), longer hypoxemia (p < 0.001), and Spo₂ recovery (p = 0.035).

CONCLUSIONS

Ictal brainstem semiology is associated with increased PGES risk. Ictal decerebration is associated with longer PGES. Postictal posturing is associated with a 6-fold increased risk of PCCA, longer hypoxemia, and Spo₂ recovery. Peri-ictal brainstem posturing may be a surrogate biomarker for GCS severity identifiable without in-hospital monitoring.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that peri-ictal brainstem posturing is associated with the GCS with more prolonged PGES and more severe breathing dysfunction.

Respiratory dysfunction in Parkinson's disease: a narrative review

The presence of respiratory symptoms in Parkinson's disease (PD) has been known since the first description of the disease, even though the prevalence and incidence of these disturbances are not well defined. Several causes have been reported, comprising obstructive and restrictive pulmonary disease and changes in the central ventilatory control, and different pathogenetic mechanisms have been postulated accordingly. In our review, we encompass the current knowledge about respiratory abnormalities in PD, as well as the impact of anti-Parkinsonian drugs as either risk or protective factors. A description of putative pathogenetic mechanisms is also provided, and possible treatments are discussed, focusing on the importance of recognising and treating respiratory symptoms as a key manifestation of the disease itself. A brief description of respiratory dysfunctions in atypical Parkinsonism, especially α-synucleinopathies, is also provided.

This review addresses current knowledge about respiratory dysfunctions in Parkinson's disease, from the aetiopathology to pharmacological and invasive treatments, describing the different clinical phenotypeshttps://bit.ly/2X7OLtN

Midbrain control of breathing and blood pressure: The role of periaqueductal gray matter and mesencephalic collicular neuronal microcircuit oscillators

Neural circuitry residing within the medullary ventral respiratory column nuclei and dorsal respiratory group interact with the Kölliker-Fuse and medial parabrachial nuclei to generate the core breathing rhythm and pattern during resting conditions. Triphasic eupnea consists of inspiratory [I], post-inspiratory [post-I], and late-expiratory [E2] phases. Mesencephalic zones exert modulatory influences upon respiratory rhythm-generating circuitry, sympathetic oscillators, and parasympathetic nuclei. The earliest evidence supporting the existence of midbrain control of breathing derives from studies conducted by Martin and Booker in 1878. These authors demonstrated electrical stimulation of the deep layers of the mesencephalic colliculi in the rabbit augmented ventilation and sequentially elicited chest wall tremors and tetany. Investigations performed during the past several decades would demonstrate stimlation of distributed zones within the midbrain reticular formation elicits starkly disparate effects upon respiratory phase switching. Schmid, Böhmer, and Fallert demonstrated electrical stimulation of the nucleus rubre and emanating axon bundles alternately elicits or inhibits the activity of medullary expiratory- or inspiratory-related units and phrenic nerve discharge with differential latency. A series of studies would later indicate the red nucleus mediates hypoxic ventilatory depression. Periaqueductal gray matter neurons exhibit extensive afferent and efferent interconnectivity with suprabulbar, brainstem, and spinal cord zones aptly positioning these units to modulate breathing, autonomic outflow, nociception locomotion, micturtion, and sexual behavior. Experimental stimulatory activation of the tectal colliculi and periaqueductal gray matter via electrical current or glutamate, D,L-homocysteinic acid, or bicuculline microinjections coordinately modulates neuromotor inspiratory bursting frequency and amplitude and discharge of pre-Bötzinger complex, ventrolateral medullary late-I and post-I, and ventrolateral nucleus tractus solitarius decrementing early-I and augmenting and decrementing late-I neurons, elicits expiratory outflow and vocalization, and blunt the Hering-Breuer reflex in unanesthetzed decerebrate and anesthetized preprations of the cat and rat. Stimulation of the mesencephalic colliuli or dorsal divisions of the PAG potently amplifes renal sympathetic neural efferent activity, dynamic arterial pressure magnitude, and myocardial contraction frequency and elicits various behavioral defense responses. Elicited physiological effects exhibit extensive locoregional heterogeneity and variably enlist requisite contributions from the dorsomedial hypothalamus and/or lateral parabrachial nuclei. Stimulation of the dorsal mesencephalon occasionally elicits dynamic increases of arterial pressure magnitude exhibiting prominent oscillatory variability coherent with phrenic nerve discharge, perhaps by generating intra-neuraxial hysteresis, serving to intermittently deliver blood to organ vascular beds under high pressure in order to prevent organ edema, microcirculatory dysfunction, and downregulation of vascular smooth muscle alpha adrenergic receptors. Chemosensitive mesencephalic caudal raphé units and projections of hypoxia-sensitive units in the caudal hypothalamus to the periaqueductal gray matter may imply the existence of a diencephalo-smesencephalic chemosensitive network modulating breathing and sympathetic discharge.

A human amygdala site that inhibits respiration and elicits apnea in pediatric epilepsy

BACKGROUNDSeizure-induced inhibition of respiration plays a critical role in sudden unexpected death in epilepsy (SUDEP). However, the mechanisms underlying seizure-induced central apnea in pediatric epilepsy are unknown.METHODSWe studied 8 pediatric patients with intractable epilepsy undergoing intracranial electroencephalography. We recorded respiration during seizures and during electrical stimulation mapping of 174 forebrain sites. A machine-learning algorithm was used to delineate brain regions that inhibit respiration.RESULTSIn 2 patients, apnea coincided with seizure spread to the amygdala. Supporting a role for the amygdala in breathing inhibition in children, electrically stimulating the amygdala produced apnea in all 8 subjects (3-17 years old). These effects did not depend on epilepsy type and were relatively specific to the amygdala, as no other site affected breathing. Remarkably, patients were unaware that they had stopped breathing, and none reported dyspnea or arousal, findings critical for SUDEP. Finally, a machine-learning algorithm based on 45 stimulation sites and 210 stimulation trials identified a focal subregion in the human amygdala that consistently produced apnea. This site, which we refer to as the amygdala inhibition of respiration (AIR) site includes the medial subregion of the basal nuclei, cortical and medial nuclei, amygdala transition areas, and intercalated neurons.CONCLUSIONSA focal site in the amygdala inhibits respiration and induces apnea (AIR site) when electrically stimulated and during seizures in children with epilepsy. This site may prove valuable for determining those at greatest risk for SUDEP and as a therapeutic target.FUNDINGNational Institute of Neurological Disorders and Stroke - Congress of Neurological Surgeons, National Institute of General Medical Sciences, Roy J. Carver Charitable Trust.

Microstimulation in Different Parts of the Periaqueductal Gray Generates Different Types of Vocalizations in the Cat

In the cat four different types of vocalization, mews, howls, cries, and hisses were generated by microstimulation in different parts of the periaqueductal gray (PAG). While mews imply positive vocal expressions, howls, hisses, and cries represent negative vocal expressions. In the intermediate PAG, mews were generated in the lateral column, howls, and hisses in the ventrolateral column. Cries were generated in two other regions, the lateral column of the rostral PAG and the ventrolateral column of the caudal PAG. In order to define the specific motor patterns of the mews, howls, and cries, the following muscles were recorded during these vocalizations; larynx (cricothyroid, thyroarytenoid, and posterior cricoarytenoid), tongue (genioglossus), jaw (digastric), and respiration muscles (diaphragm, internal intercostal, external, and internal abdominal oblique). During these mews, howls, and cries we analyzed the frequency, intensity, activation cascades power density, turns, and amplitude analysis of the electromyograms (EMGs). It appeared that each type of vocalization consists of a specific circumscribed motor coordination. The nucleus retroambiguus (NRA) in the caudal medulla is known to serve as the final premotor interneuronal output system for vocalization. Although neurochemical microstimulation in the NRA itself also generated vocalizations, they only consisted of guttural sounds, the EMGs of which involved only small parts of the EMGs of the mews, howls, and cries generated by neurochemical stimulation in the PAG. These results demonstrate that positive and negative vocalizations are generated in different parts of the PAG. These parts have access to different groups of premotoneurons in the NRA, that, in turn, have access to different groups of motoneurons in the brainstem and spinal cord, resulting in different vocalizations. The findings would serve a valuable model for diagnostic assessment of voice disorders in humans.

Incidence, Recurrence, and Risk Factors for Peri-ictal Central Apnea and Sudden Unexpected Death in Epilepsy

Introduction: Peri-ictal breathing dysfunction was proposed as a potential mechanism for SUDEP. We examined the incidence and risk factors for both ictal (ICA) and post-convulsive central apnea (PCCA) and their relationship with potential seizure severity biomarkers (i. e., post-ictal generalized EEG suppression (PGES) and recurrence.

Methods: Prospective, multi-center seizure monitoring study of autonomic, and breathing biomarkers of SUDEP in adults with intractable epilepsy and monitored seizures. Video EEG, thoraco-abdominal excursions, capillary oxygen saturation, and electrocardiography were analyzed. A subgroup analysis determined the incidences of recurrent ICA and PCCA in patients with ≥2 recorded seizures. We excluded status epilepticus and obscured/unavailable video. Central apnea (absence of thoracic-abdominal breathing movements) was defined as ≥1 missed breath, and ≥5 s. ICA referred to apnea preceding or occurring along with non-convulsive seizures (NCS) or apnea before generalized convulsive seizures (GCS).

Results: We analyzed 558 seizures in 218 patients (130 female); 321 seizures were NCS and 237 were GCS. ICA occurred in 180/487 (36.9%) seizures in 83/192 (43.2%) patients, all with focal epilepsy. Sleep state was related to presence of ICA [RR 1.33, CI 95% (1.08–1.64), p = 0.008] whereas extratemporal epilepsy was related to lower incidence of ICA [RR 0.58, CI 95% (0.37–0.90), p = 0.015]. ICA recurred in 45/60 (75%) patients. PCCA occurred in 41/228 (18%) of GCS in 30/134 (22.4%) patients, regardless of epilepsy type. Female sex [RR 11.30, CI 95% (4.50–28.34), p < 0.001] and ICA duration [RR 1.14 CI 95% (1.05–1.25), p = 0.001] were related to PCCA presence, whereas absence of PGES was related to absence of PCCA [0.27, CI 95% (0.16–0.47), p < 0.001]. PCCA duration was longer in males [HR 1.84, CI 95% (1.06–3.19), p = 0.003]. In 9/17 (52.9%) patients, PCCA was recurrent.

Conclusion: ICA incidence is almost twice the incidence of PCCA and is only seen in focal epilepsies, as opposed to PCCA, suggesting different pathophysiologies. ICA is likely to be a recurrent semiological phenomenon of cortical seizure discharge, whereas PCCA may be a reflection of brainstem dysfunction after GCS. Prolonged ICA or PCCA may, respectively, contribute to SUDEP, as evidenced by two cases we report. Further prospective cohort studies are needed to validate these hypotheses.

Postconvulsive central apnea as a biomarker for sudden unexpected death in epilepsy (SUDEP)

OBJECTIVE

To characterize peri-ictal apnea and postictal asystole in generalized convulsive seizures (GCS) of intractable epilepsy.

METHODS

This was a prospective, multicenter epilepsy monitoring study of autonomic and breathing biomarkers of sudden unexpected death in epilepsy (SUDEP) in patients ≥18 years old with intractable epilepsy and monitored GCS. Video-EEG, thoracoabdominal excursions, nasal airflow, capillary oxygen saturation, and ECG were analyzed.

RESULTS

We studied 148 GCS in 87 patients. Nineteen patients had generalized epilepsy; 65 had focal epilepsy; 1 had both; and the epileptogenic zone was unknown in 2. Ictal central apnea (ICA) preceded GCS in 49 of 121 (40.4%) seizures in 23 patients, all with focal epilepsy. Postconvulsive central apnea (PCCA) occurred in 31 of 140 (22.1%) seizures in 22 patients, with generalized, focal, or unknown epileptogenic zones. In 2 patients, PCCA occurred concurrently with asystole (near-SUDEP), with an incidence rate of 10.2 per 1,000 patient-years. One patient with PCCA died of probable SUDEP during follow-up, suggesting a SUDEP incidence rate 5.1 per 1,000 patient-years. No cases of laryngospasm were detected. Rhythmic muscle artifact synchronous with breathing was present in 75 of 147 seizures and related to stertorous breathing (odds ratio 3.856, 95% confidence interval 1.395-10.663, p = 0.009).

CONCLUSIONS

PCCA occurred in both focal and generalized epilepsies, suggesting a different pathophysiology from ICA, which occurred only in focal epilepsy. PCCA was seen in 2 near-SUDEP cases and 1 probable SUDEP case, suggesting that this phenomenon may serve as a clinical biomarker of SUDEP. Larger studies are needed to validate this observation. Rhythmic postictal muscle artifact is suggestive of post-GCS breathing effort rather than a specific biomarker of laryngospasm.

The midbrain periaqueductal gray as an integrative and interoceptive neural structure for breathing

The periaqueductal gray (PAG) plays a critical role in autonomic function and behavioural responses to threatening stimuli. Recent evidence has revealed the PAG's potential involvement in the perception of breathlessness, a highly threatening respiratory symptom. In this review, we outline the current evidence in animals and humans on the role of the PAG in respiratory control and in the perception of breathlessness. While recent work has unveiled dissociable brain activity within the lateral PAG during perception of breathlessness and ventrolateral PAG during conditioned anticipation in healthy humans, this is yet to be translated into diseases dominated by breathlessness symptomology, such as chronic obstructive pulmonary disease. Understanding how the sub-structures of the PAG differentially interact with interoceptive brain networks involved in the perception of breathlessness will help towards understanding discordant symptomology, and may reveal treatment targets for those debilitated by chronic and pervasive breathlessness.

Functional connectivity of PAG with core limbic system and laryngeal cortico-motor structures during human phonation

Previous studies in animals and humans suggest the periaqueductal grey region (PAG) is a final integration station between the brain and laryngeal musculature during phonation. To date, a limited number of functional magnetic neuroimaging (fMRI) studies have examined the functional connectivity of the PAG during volitional human phonation. An event-related, stimulus-induced, volitional movement paradigm was used to examine neural activity during sustained vocalization in neurologically healthy adults and was compared to controlled exhalation through the nose. The contrast of vocalization greater than controlled expiration revealed activation of bilateral auditory cortex, dorsal and ventral laryngeal motor areas (dLMA and vLMA) (p < 0.05, corrected), and suggested activation of the cerbellum, insula, dorsomedial prefrontal cortex (dmPFC), amygdala, and PAG. The functionally defined PAG cluster was used as a seed region for psychophysiological interaction analysis (PPI) to identify regions with greater functional connectivity with PAG during volitional vocalization, while the above functionally defined amygdala cluster was used in an ROI PPI analysis. Whole-brain results revealed increased functional connectivity of the PAG with left vLMA during voicing, relative to controlled expiration, while trend-level evidence was observed for increased PAG/amygdala coupling during voicing (p = 0.07, uncorrected). Diffusion tensor imaging (DTI) analysis confirmed structural connectivity between PAG and vLMA. The present study sheds further light on neural mechanisms of volitional vocalization that include multiple inputs from both limbic and motor structures to PAG. Future studies should include investigation of how these neural mechanisms are affected in individuals with voice disorders during volitional vocalization.

Periaqueductal gray and emotions: the complexity of the problem and the light at the end of the tunnel, the magnetic resonance imaging

The periaqueductal gray (PAG) is less referred in relationship with emotions than other parts of the brain (e.g. cortex, thalamus, amygdala), most probably because of the difficulty to reach and manipulate this small and deeply lying structure. After defining how to evaluate emotions, we have reviewed the literature and summarized data of the PAG contribution to the feeling of emotions focusing on the behavioral and neurochemical considerations. In humans, emotions can be characterized by three main domains: the physiological changes, the communicative expressions, and the subjective experiences. In animals, the physiological changes can mainly be studied. Indeed, early studies have considered the PAG as an important center of the emotions-related autonomic and motoric processes. However, in vivo imaging have changed our view by highlighting the PAG as a significant player in emotions-related cognitive processes. The PAG lies on the crossroad of networks important in the regulation of emotions and therefore it should not be neglected. In vivo imaging represents a good tool for studying this structure in living organism and may reveal new information about its role beyond its importance in the neurovegetative regulation.

Deficient post-ictal cardiorespiratory compensatory mechanisms mediated by the periaqueductal gray may lead to death in a mouse model of SUDEP

Post-ictal cardiorespiratory failure is implicated as a major cause of sudden unexpected death in epilepsy (SUDEP) in patients. The DBA/1 mouse model of SUDEP is abnormally susceptible to fatal seizure-induced cardiorespiratory failure (S-CRF) induced by convulsant drug, hyperthermia, electroshock, and acoustic stimulation. Clinical and pre-clinical studies have implicated periaqueductal gray (PAG) abnormalities in SUDEP. Recent functional neuroimaging studies observed that S-CRF resulted in selective changes in PAG neuronal activity in DBA/1 mice. The PAG plays a critical compensatory role for respiratory distress caused by numerous physiological challenges in non-epileptic individuals. These observations suggest that abnormalities in PAG-mediated cardiorespiratory modulation may contribute to S-CRF in DBA/1 mice. To evaluate this, electrical stimulation (20 Hz, 20-100 μA, 10 s) was presented in the PAG of anesthetized DBA/1 and C57BL/6 (non-epileptic) control mice, and post-stimulus changes in respiration [inter-breath interval (IBI)] and heart rate variability (HRV) were examined. The post-stimulus period was considered analogous to the post-ictal period when S-CRF occurred in previous DBA/1 mouse studies. PAG stimulation caused significant intensity-related decreases in IBI in both mouse strains. However, this effect was significantly reduced in DBA/1 vis-a-vis C57BL/6 mice. These changes began immediately following cessation of stimulation and remained significant for 10 s. This time period is critical for initiating resuscitation to successfully prevent seizure-induced death in previous DBA/1 mouse experiments. Significant post-stimulus increases in HRV were also seen at ≥60 μA in the PAG in C57BL/6 mice, which were absent in DBA/1 mice. These data along with previous neuroimaging findings suggest that compensatory cardiorespiratory modulation mediated by PAG is deficient, which may be important to the susceptibility of DBA/1 mice to S-CRF. These observations suggest that correcting this deficit pharmacologically or by electrical stimulation may help to prevent S-CRF. These findings further support the potential importance of PAG abnormalities to human SUDEP.

The involvement of the pathway connecting the substantia nigra, the periaqueductal gray matter and the retrotrapezoid nucleus in breathing control in a rat model of Parkinson's disease

Parkinson's disease (PD) is characterized by a reduction in the number of dopaminergic neurons of the substantia nigra (SNpc), accompanied by motor and non-motor deficiencies such as respiratory failure. Here, our aim was to investigate possible neuronal communications between the SNpc and chemoreceptor neurons within the retrotrapezoid nucleus (RTN), in order to explain neurodegeneration and the loss of breathing function in the 6-OHDA PD animal model. Male Wistar rats received tracer injections in the SNpc, RTN and periaqueductal gray (PAG) regions to investigate the projections between those regions. The results showed that neurons of the SNpc project to the RTN by an indirect pathway that goes through the PAG region. In different groups of rats, reductions in the density of neuronal markers (NeuN) and the number of catecholaminergic varicosities in PAG, as well as reductions in the number of CO₂-activated PAG neurons with RTN projections, were observed in a 6-OHDA model of PD. Physiological experiments showed that inhibition of the PAG by bilateral injection of muscimol did not produce resting breathing disturbances but instead reduced genioglossus (GG_EMG) and abdominal (Abd_EMG) muscle activity amplitude induced by hypercapnia in control rats that were urethane-anesthetized, vagotomized, and artificially ventilated. However, in a model of PD, we found reductions in resting diaphragm muscle activity (Dia_EMG) and GG_EMG frequencies, as well as in hypercapnia-induced Dia_EMG, GG_EMG and Abd_EMG frequencies and GG_EMG and Abd_EMG amplitudes. Therefore, we can conclude that there is an indirect pathway between neurons of the SNpc and RTN that goes through the PAG and that there is a defect of this pathway in an animal model of PD.