Central circuits mediating patterned autonomic activity during active vs. passive emotional coping

Periaqueductal Gray Sheds Light on Dark Areas of Psychopathology

Neurons in the periaqueductal gray (PAG) integrate negative emotions with the autonomic, neuroendocrine, and immune systems to facilitate responses to threat. Modern functional track tracing in animals and optogenetic and chemogenetic techniques show that the PAG is a rich substrate for the integration of active and passive responses to threat. In humans, the same regions of the PAG that give rise to adaptive anger/fight, fear/panic, depression/shutdown, pain, and predatory behaviors in response to challenging situations or overwhelming threats can become activated pathologically, resulting in symptoms that resemble those of psychiatric disorders. This review coalesces human and animal studies to link PAG neuropathways to specific elements of psychiatric diagnoses. The insights gained from this overview may eventually lead to new therapeutic interventions.

Neural Dynamics of Shooting Decisions and the Switch from Freeze to Fight

Real-life shooting decisions typically occur under acute threat and require fast switching between vigilant situational assessment and immediate fight-or-flight actions. Recent studies suggested that freezing facilitates action preparation and decision-making but the neurocognitive mechanisms remain unclear. We applied functional magnetic resonance imaging, posturographic and autonomic measurements while participants performed a shooting task under threat of shock. Two independent studies, in unselected civilians (N = 22) and police recruits (N = 54), revealed that preparation for shooting decisions under threat is associated with postural freezing, bradycardia, midbrain activity (including the periaqueductal gray-PAG) and PAG-amygdala connectivity. Crucially, stronger activity in the midbrain/PAG during this preparatory stage of freezing predicted faster subsequent accurate shooting. Finally, the switch from preparation to active shooting was associated with tachycardia, perigenual anterior cingulate cortex (pgACC) activity and pgACC-amygdala connectivity. These findings suggest that threat-anticipatory midbrain activity centred around the PAG supports decision-making by facilitating action preparation and highlight the role of the pgACC when switching from preparation to action. These results translate animal models of the neural switch from freeze-to-action. In addition, they reveal a core neural circuit for shooting performance under threat and provide empirical evidence for the role of defensive reactions such as freezing in subsequent action decision-making.

Racial/ethnic differences in 12-month prevalence and persistence of mood, anxiety, and substance use disorders: Variation by nativity and socioeconomic status

BACKGROUND

Despite equivalent or lower lifetime and past-year prevalence of mental disorder among racial/ethnic minorities compared to non-Latino Whites in the United States, evidence suggests that mental disorders are more persistent among minorities than non-Latino Whites. But, it is unclear how nativity and socioeconomic status contribute to observed racial/ethnic differences in prevalence and persistence of mood, anxiety, and substance disorders.

METHOD

Data were examined from a coordinated series of four national surveys that together assessed 21,024 Asian, non-Latino Black, Latino, and non-Latino White adults between 2001 and 2003. Common DSM-IV mood, anxiety, and substance disorders were assessed using the Composite International Diagnostic Interview. Logistic regression analyses examined how several predictors (e.g., race/ethnicity, nativity, education, income) and the interactions between those predictors were associated with both 12-month disorder prevalence and 12-month prevalence among lifetime cases. For the second series of analyses, age of onset and time since onset were used as additional control variables to indirectly estimate disorder persistence.

RESULTS

Non-Latino Whites demonstrated the highest unadjusted 12-month prevalence of all disorder types (p < 0.001), though differences were also observed across minority groups. In contrast, Asian, Latino, and Black adults demonstrated higher 12-month prevalence of mood disorders among lifetime cases than Whites (p < 0.001) prior to adjustments Once we introduced nativity and other relevant controls (e.g., age, sex, urbanicity), US-born Whites with at least one US-born parent demonstrated higher 12-month mood disorder prevalence than foreign-born Whites or US-born Whites with two foreign parents (OR = 0.51, 95% CI = [0.36, 0.73]); this group also demonstrated higher odds of past-year mood disorder than Asian (OR = 0.59, 95% CI = [0.42, 0.82]) and Black (OR = 0.70, 95% CI = [0.58, 0.83]) adults, but not Latino adults (OR = 0.89, 95% CI = [0.74, 1.06]). Racial/ethnic differences in 12-month mood and substance disorder prevalence were moderated by educational attainment, especially among adults without a college education. Additionally, racial/ethnic minority groups with no more than a high school education demonstrated more persistent mood and substance disorders than non-Latino Whites; these relationships reversed or disappeared at higher education levels.

CONCLUSION

Nativity may be a particularly relevant consideration for diagnosing mood disorder among non-Latino Whites; additionally, lower education appears to be associated with increased relative risk of persistent mood and substance use disorders among racial/ethnic minorities compared to non-Latino Whites.

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.

The Innate Alarm System and Subliminal Threat Presentation in Posttraumatic Stress Disorder: Neuroimaging of the Midbrain and Cerebellum

BACKGROUND

The innate alarm system, a network of interconnected midbrain, other brainstem, and thalamic structures, serves to rapidly detect stimuli in the environment prior to the onset of conscious awareness. This system is sensitive to threatening stimuli and has evolved to process these stimuli subliminally for hastened responding. Despite the conscious unawareness, the presentation of subliminal threat stimuli generates increased activation of limbic structures, including the amygdala and insula, as well as emotionally evaluative structures, including the cerebellum and orbitofrontal cortex. Posttraumatic stress disorder (PTSD) is associated with an increased startle response and decreased extinction learning to conditioned threat. The role of the innate alarm system in the clinical presentation of PTSD, however, remains poorly understood.

METHODS

Here, we compare midbrain, brainstem, and cerebellar activation in persons with PTSD (n = 26) and matched controls (n = 20) during subliminal threat presentation. Subjects were presented with masked trauma-related and neutral stimuli below conscious threshold. Contrasts of subliminal brain activation for the presentation of neutral stimuli were subtracted from trauma-related brain activation. Group differences in activation, as well as correlations between clinical scores and PTSD activation, were examined. Imaging data were preprocessed utilizing the spatially unbiased infratentorial template toolbox within SPM12.

RESULTS

Analyses revealed increased midbrain activation in PTSD as compared to controls in the superior colliculus, periaqueductal gray, and midbrain reticular formation during subliminal threat as compared to neutral stimulus presentation. Controls showed increased activation in the right cerebellar lobule V during subliminal threat presentation as compared to PTSD. Finally, a negative correlation emerged between PTSD patient scores on the Multiscale Dissociation Inventory for the Depersonalization/Derealization subscale and activation in the right lobule V of the cerebellum during the presentation of subliminal threat as compared to neutral stimuli.

CONCLUSION

We interpret these findings as evidence of innate alarm system overactivation in PTSD and of the prominent role of the cerebellum in the undermodulation of emotion observed in PTSD.

Basics of autonomic nervous system function

The autonomic nervous system has widespread innervation to nearly every organ system in the body. In order to understand the basics of autonomic function, knowledge of the neuroanatomy of the autonomic nervous system is necessary. Frequently considered to control the "fight or flight" and "rest and digest" functions, the autonomic nervous system has an intricate network of connections to finely tune the systemic response to nearly any situation. Although traditionally considered two discrete systems (sympathetic and parasympathetic), the enteric nervous system is now considered a third component of the autonomic nervous system. This chapter reviews the background of the neuroanatomical distribution of the autonomic nervous system in order to facilitate understanding the basics of autonomic function.

Prefrontal-Bed Nucleus Circuit Modulation of a Passive Coping Response Set

One of the challenges facing neuroscience entails localization of circuits and mechanisms accounting for how multiple features of stress responses are organized to promote survival during adverse experiences. The rodent medial prefrontal cortex (mPFC) is generally regarded as a key site for cognitive and affective information processing, and the anteroventral bed nuclei of the stria terminalis (avBST) integrates homeostatic information from a variety of sources, including the mPFC. Thus, we proposed that the mPFC is capable of generating multiple features (endocrine, behavioral) of adaptive responses via its influence over the avBST. To address this possibility, we first optogenetically inhibited input to avBST from the rostral prelimbic cortical region of mPFC and observed concurrent increases in immobility and hypothalamo-pituitary-adrenal (HPA) output in male rats during tail suspension, whereas photostimulation of this pathway decreased immobility during the same challenge. Anatomical tracing experiments confirmed projections from the rostral prelimbic subfield to separate populations of avBST neurons, and from these to HPA effector neurons in the paraventricular hypothalamic nucleus, and to aspects of the midbrain periaqueductal gray that coordinate passive defensive behaviors. Finally, stimulation and inhibition of the prelimbic-avBST pathway, respectively, decreased and increased passive coping in the shock-probe defensive burying test, without having any direct effect on active coping (burying) behavior. These results define a new neural substrate in the coordination of a response set that involves the gating of passive, rather than active, coping behaviors while restraining neuroendocrine activation to optimize adaptation during threat exposure.SIGNIFICANCE STATEMENT The circuits and mechanisms accounting for how multiple features of responses are organized to promote adaptation have yet to be elucidated. Our report identifies a prefrontal-bed nucleus pathway that organizes a response set capable of gating passive coping behaviors while concurrently restraining neuroendocrine activation during exposure to inescapable stressors. These data provide insight into the central organization of how multiple features of responses are integrated to promote adaptation during adverse experiences, and how disruption in one neural pathway may underlie a broad array of maladaptive responses in stress-related psychiatric disorders.

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.

A Review of the Neurobiological Basis of Trauma-Related Dissociation and Its Relation to Cannabinoid- and Opioid-Mediated Stress Response: a Transdiagnostic, Translational Approach

Dissociative experiences have been associated with increased disease severity, chronicity, and, in some cases, reduced treatment response across trauma-related and other psychiatric disorders. A better understanding of the neurobiological mechanisms through which dissociative experiences occur may assist in identifying novel pharmacological and non-pharmacological treatment approaches. Here, we review emerging work on the dissociative subtype of posttraumatic stress disorder (PTSD), and other trauma-related disorders providing evidence for two related overarching neurobiological models of dissociation, the defense cascade model of dissociation and Mobb's threat detection model. In particular, we review neuroimaging studies highlighting alterations in functional connectivity of key brain regions associated with these models, including connectivity between the prefrontal cortex, the amygdala and its complexes, the insula, and the periaqueductal gray. Work implicating the kappa-opioid and endocannabinoid systems in trauma-related dissociative experiences is also reviewed. Finally, we hypothesize mechanisms by which pharmacological modulation of these neurochemical systems may serve as promising transdiagnostic treatment modalities for individuals experiencing clinically significant levels of dissociation. Specifically, whereas kappa-opioid receptor antagonists may serve as a pharmacological vehicle for the selective targeting of dissociative symptoms and associated emotion overmodulation in the dissociative subtype of posttraumatic stress disorder and transdiagnostically, modulation of the endocannabinoid system may reduce symptoms associated with emotional undermodulation of the fight or flight components of the defense cascade model.

The central amygdala to periaqueductal gray pathway comprises intrinsically distinct neurons differentially affected in a model of inflammatory pain

KEY POINTS

The central nucleus of the amygdala (CeA) encompasses the main output pathways of the amygdala, a temporal lobe structure essential in affective and cognitive dimensions of pain. A major population of neurons in the CeA send projections to the periaqueductal gray (PAG), a key midbrain structure that mediates coping strategies in response to threat or stress. CeA-PAG neurons are topographically organized based on their targeted subregion within the PAG. PAG-projecting neurons in the central medial (CeM) and central lateral (CeL) regions of CeA are intrinsically distinct. CeL-PAG neurons are a homogeneous population of intrinsically distinct neurons while CeM-PAG neurons are intrinsically heterogeneous. Membrane properties of distinct CeM-PAG subtypes are altered in the complete Freund's adjuvant model of inflammatory pain.

ABSTRACT

A major population of neurons in the central nucleus of amygdala (CeA) send projections to the periaqueductal gray (PAG), a key midbrain structure that mediates coping strategies in response to threat or stress. While the CeA-PAG pathway has proved to be a component of descending anti-nociceptive circuitry, the functional organization of CeA-PAG neurons remains unclear. We identified CeA-PAG neurons in C57BL/6 mice of both sexes using intracranial injection of a fluorescent retrograde tracer into the PAG. In acute brain slices, we investigated the topographical and intrinsic characteristics of retrogradely labelled CeA-PAG neurons using epifluorescence and whole-cell electrophysiology. We also measured changes to CeA-PAG neurons in the complete Freund's adjuvant (CFA) model of inflammatory pain. Neurons in the central lateral (CeL) and central medial (CeM) amygdala project primarily to different regions of the PAG. CeL-PAG neurons consist of a relatively homogeneous population of intrinsically distinct neurons while CeM-PAG neurons are intrinsically heterogeneous. Membrane properties of distinct CeM-PAG subtypes are altered 1 day after induction of the CFA inflammatory pain model. Collectively, our results provide insight into pain-induced changes to a specific population of CeA neurons that probably play a key role in the integration of noxious input with endogenous analgesia and behavioural coping response.

What, If Anything, Is Rodent Prefrontal Cortex?

Prefrontal cortex (PFC) means different things to different people. In recent years, there has been a major increase in publications on the PFC, especially using mice. However, inconsistencies in the nomenclature and anatomical boundaries of PFC areas has made it difficult for researchers to compare data and interpret findings across species. We conducted a meta-analysis of publications on the PFC of humans and rodents and found dramatic differences in the focus of research on these species. In addition, we compared anatomical terms and criteria across several common rodent brain atlases and found inconsistencies among, and even within, leading atlases. To assess the impact of these issues on the research community, we conducted a survey of established PFC researchers on their use of anatomical terms and found little consensus. We report on the results of the survey and propose an alternative scheme for interpreting data from rodent studies, based on structural analysis of the corpus callosum and nomenclature used in research on the anterior cingulate cortex (ACC) of primates.

Supraspinal interaction between HIV-1-gp120 and cannabinoid analgesic effectiveness

The growing therapeutic use (self-medication) of cannabinoids by HIV-1 infected people and the recent interest in the possible medicinal use of cannabinoids, particularly in pain management, create an urgent need to identify their potential interactions with HIV-1. The goal here is to determine any interaction between proteins of HIV-1 and the analgesic effectiveness of cannabinoid at supraspinal level. Young adult male rats (Sprague-Dawley) were stereotaxically pretreated with HIV-1 envelope glycoprotein 120 (gp120) into the periaqueductal gray (PAG) area, the primary control center of pain modulation. Then, we examined its effect on cannabinoid receptor agonist WIN55,212-2-induced analgesia. Our results demonstrated that gp120 in PAG diminished the analgesic effectiveness of this cannabinoid agonist. These results suggest that gp120 may interact with the cannabinoid system through the descending modulatory pain pathways centered in the PAG to impair the analgesic effectiveness of cannabinoids.

A Bayesian Account of Psychopathy: A Model of Lacks Remorse and Self-Aggrandizing

This article proposes a formal model that integrates cognitive and psychodynamic psychotherapeutic models of psychopathy to show how two major psychopathic traits called lacks remorse and self-aggrandizing can be understood as a form of abnormal Bayesian inference about the self. This model draws on the predictive coding (i.e., active inference) framework, a neurobiologically plausible explanatory framework for message passing in the brain that is formalized in terms of hierarchical Bayesian inference. In summary, this model proposes that these two cardinal psychopathic traits reflect entrenched maladaptive Bayesian inferences about the self, which defend against the experience of deep-seated, self-related negative emotions, specifically shame and worthlessness. Support for the model in extant research on the neurobiology of psychopathy and quantitative simulations are provided. Finally, we offer a preliminary overview of a novel treatment for psychopathy that rests on our Bayesian formulation.

Contradictory effects of erythropoietin on inhibitory synaptic transmission in left and right prelimbic cortex of mice

Erythropoietin (EPO) has been shown to improve cognitive function in mammals as well as in patients of psychiatric diseases by directly acting on the brain. In addition, EPO attenuates the synaptic transmission and enhances short- and long-term synaptic plasticity in hippocampus of mice, although there are still many discrepancies between different studies. It has been suggested that the divergences of different studies take root in different in-vivo application schemata or in long-term trophic effects of EPO. In the current study, we investigated the direct effects of EPO in slices of prelimbic cortex (PrL) by acute ex-vivo application of EPO, so that the erythropoietic or other trophic effects could be entirely excluded. Our results showed that the EPO effects were contradictory between the left and the right PrL. It enhanced the inhibitory transmission in the left and depressed the inhibitory transmission in the right PrL. Strikingly, this lateralized effect of EPO could be consistently found in individual bi-lateral PrL of all tested mice. Thus, our data suggest that EPO differentially modulates the inhibitory synaptic transmission of neuronal networks in the left and the right PrL. We hypothesize that such lateralized effects of EPO contribute to the development of the lateralization of stress reaction in PFC and underlie the altered bilateral GAGAergic synaptic transmission and oscillation patterns under stress that impact the central emotional and cognitive control in physiology as well as in pathophysiology.

•

EPO showed fast effects on inhibitory transmission in the prefrontal cortex of mice.

•

EPO enhanced the inhibitory transmission in the left and depressed it in the right prelimbic cortex of mice.

•

The expression of EPOR in GAD⁺-neurons is different between the left and right PFC.

Eliminating the VGlut2-Dependent Glutamatergic Transmission of Parvalbumin-Expressing Neurons Leads to Deficits in Locomotion and Vocalization, Decreased Pain Sensitivity, and Increased Dominance

The calcium-binding protein parvalbumin (PV) is a recognized marker of short-axon GABA-ergic neurons in the cortex and the hippocampus. However in addition, PV is expressed by excitatory, glutamatergic neurons in various areas of the brain and spinal cord. Depending on the location of these neurons, loading of their synaptic vesicles with glutamate is mediated by either of three vesicular glutamate transporters (VGlut): VGlut1, VGlut2, or VGlut3. Driven by our interest in one of these glutamatergic/PV-expressing cell clusters-the lateral hypothalamic parvafox nucleus-we investigated the functions of this population of neurons by the selective deletion of VGlut2 expression in PV-expressing cells according to the Cre/Lox-approach. PV-Cre;VGlut2-Lox mutant mice are phenotypically characterized by deficits in locomotion and vocalization, by a decreased thermal nociception, and by an increased social dominance. We conducted a search of the Allen Brain Atlas for regions that might co-express the genes encoding PV and VGlut2, and that might thus contribute to the manifestation of the observed phenotypes. Our survey revealed several structures that could contribute to the deficits in locomotion and vocalization, such as the red, the subthalamic and the deep cerebellar nuclei. It also disclosed that a shift in the balance of afferental glutamatergic neurotransmission to the periaqueductal gray matter might be accountable for the decrease in sensitivity to pain and for the increase in social dominance. As a whole, this study broadens the state of knowledge about PV-expressing excitatory neurons.

Intrinsic connectivity network dynamics in PTSD during amygdala downregulation using real-time fMRI neurofeedback: A preliminary analysis

Posttraumatic stress disorder (PTSD) has been associated with a disturbance in neural intrinsic connectivity networks (ICN), including the central executive network (CEN), default mode network (DMN), and salience network (SN). Here, we conducted a preliminary investigation examining potential changes in ICN recruitment as a function of real-time fMRI neurofeedback (rt-fMRI-NFB) during symptom provocation where we targeted the downregulation of neural response within the amygdala-a key region-of-interest in PTSD neuropathophysiology. Patients with PTSD (n = 14) completed three sessions of rt-fMRI-NFB with the following conditions: (a) regulate: decrease activation in the amygdala while processing personalized trauma words; (b) view: process trauma words while not attempting to regulate the amygdala; and (c) neutral: process neutral words. We found that recruitment of the left CEN increased over neurofeedback runs during the regulate condition, a finding supported by increased dlPFC activation during the regulate as compared to the view condition. In contrast, DMN task-negative recruitment was stable during neurofeedback runs, albeit was the highest during view conditions and increased (normalized) during rest periods. Critically, SN recruitment was high for both the regulate and the view conditions, a finding potentially indicative of CEN modality switching, adaptive learning, and increasing threat/defense processing in PTSD. In conclusion, this study provides provocative, preliminary evidence that downregulation of the amygdala using rt-fMRI-NFB in PTSD is associated with dynamic changes in ICN, an effect similar to those observed using EEG modalities of neurofeedback.

Emotion and the Cardiovascular System: Postulated Role of Inputs From the Medial Prefrontal Cortex to the Dorsolateral Periaqueductal Gray

The midbrain periaqueductal gray (PAG) plays a major role in generating different types of behavioral responses to emotional stressors. This review focuses on the role of the dorsolateral (dl) portion of the PAG, which on the basis of anatomical and functional studies, appears to have a unique and distinctive role in generating behavioral, cardiovascular and respiratory responses to real and perceived emotional stressors. In particular, the dlPAG, but not other parts of the PAG, receives direct inputs from the primary auditory cortex and from the secondary visual cortex. In addition, there are strong direct inputs to the dlPAG, but not other parts of the PAG, from regions within the medial prefrontal cortex that in primates correspond to cortical areas 10 m, 25 and 32. I first summarise the evidence that the inputs to the dlPAG arising from visual, auditory and olfactory signals trigger defensive behavioral responses supported by appropriate cardiovascular and respiratory effects, when such signals indicate the presence of a real external threat, such as the presence of a predator. I then consider the functional roles of the direct inputs from the medial prefrontal cortex, and propose the hypothesis that these inputs are activated by perceived threats, that are generated as a consequence of complex cognitive processes. I further propose that the inputs from areas 10 m, 25 and 32 are activated under different circumstances. The input from cortical area 10 m is of special interest, because this cortical area exists only in primates and is much larger in the brain of humans than in all other primates.

Affective neuroscience of self-generated thought

Despite increasing scientific interest in self-generated thought-mental content largely independent of the immediate environment-there has yet to be any comprehensive synthesis of the subjective experience and neural correlates of affect in these forms of thinking. Here, we aim to develop an integrated affective neuroscience encompassing many forms of self-generated thought-normal and pathological, moderate and excessive, in waking and in sleep. In synthesizing existing literature on this topic, we reveal consistent findings pertaining to the prevalence, valence, and variability of emotion in self-generated thought, and highlight how these factors might interact with self-generated thought to influence general well-being. We integrate these psychological findings with recent neuroimaging research, bringing attention to the neural correlates of affect in self-generated thought. We show that affect in self-generated thought is prevalent, positively biased, highly variable (both within and across individuals), and consistently recruits many brain areas implicated in emotional processing, including the orbitofrontal cortex, amygdala, insula, and medial prefrontal cortex. Many factors modulate these typical psychological and neural patterns, however; the emerging affective neuroscience of self-generated thought must endeavor to link brain function and subjective experience in both everyday self-generated thought as well as its dysfunctions in mental illness.

The effects of audiovisual distraction on the muscle sympathetic responses to experimental muscle pain

Pain elicited by intramuscular infusion of hypertonic saline solution causes muscle sympathetic nerve activity (MSNA) to increase in some subjects, yet decrease in others. Although the direction of the response is not predictable based on baseline physiological and psychological parameters, we know that it results from sustained functional changes in specific brain regions that are responsible for the behavioral and cardiovascular responses to psychological stressors, as well as those involved in attention. The aim of this study was to investigate whether MSNA responses to experimental muscle pain in humans could be altered with an audiovisual stimulus that served to distract them from the pain. MSNA was recorded from the left common peroneal nerve of 20 young healthy individuals during a 45-min intramuscular infusion of hypertonic saline solution into the ipsilateral tibialis anterior muscle. The distracting stimulus commenced 15 min after the start of the infusion and lasted for 15 min. Fifteen subjects showed an increase in mean burst amplitude of MSNA (to 176.4 ± 7.9% of baseline), while five showed a decrease (to 73.1 ± 5.2% of baseline); distraction had no effect on these profiles. These results indicate that even though the subjects were attending to the audiovisual stimulus, and were presumably distracted from the pain, it failed to alter the MSNA responses to muscle pain.

Evaluation of Autonomic Nervous System Function Using Heart Rate Variability Analysis During Transient Heart Rate Reduction Caused by Acupuncture

Objective: Human studies have demonstrated that heart rate (HR) decreases during acupuncture stimulation, and pharmacologic studies have shown that this autonomic nervous system (ANS) response is parasympathetic-dominant. It has become clear that significant changes occur in the ANS after acupuncture, based on HR variability (HRV). However, it is inconclusive, according to HRV analysis, if acupuncture induces a significant change in autonomic function during stimulation. The aim of this study was to investigate ANS function using HRV analysis during HR reduction induced by manual acupuncture stimulation to the muscles. Materials and Methods: In this study, electrocardiograms of 25 adult men were analyzed. After resting for 20 minutes, participants underwent 15-20-mm deep acupuncture stimulation at the Shousanli (LI 10) point at 1 Hz for 2 minutes. Instantaneous HR was recorded. The index of parasympathetic nervous activity high-frequency (HF) normalized units (HFnu) and the ratio of sympathovagal balance (low frequency [LF]/HF) were calculated by HRV analysis. Results: HR during acupuncture was significantly lower, compared to HR both before and after acupuncture. HFnu during acupuncture were significantly higher, compared to HFnu both before and after acupuncture. The LF/HF ratio during acupuncture was significantly lower, compared to the ratio before acupuncture, and remained low after acupuncture, compared to before acupuncture. Conclusions: Acupuncture stimulation to the muscle can effectively reduce HR, increase HFnu, and decrease LF/HF that depends on autonomic regulation of both sympathovagal balances.

Hippocampal modulation of cardiorespiratory function

Changes in cardiorespiratory control accompany the expression of complex emotions, indicative of limbic brain inputs onto bulbar autonomic pathways. Previous studies have focussed on the role of the prefrontal cortex in autonomic regulation. However, the role of the hippocampus, also important in limbic processing, has not been addressed in detail. Anaesthetised, instrumented rats were used to map the location of hippocampal sites capable of evoking changes in cardiorespiratory control showing that stimulation of discrete regions within the CA1 fields of both the dorsal and ventral hippocampus potently alter breathing and cardiovascular activity. Additionally, tracing of the neuroanatomical tracts and pharmacological inactivation studies were used to demonstrate a role of the basomedial amygdala in hippocampal evoked responses. Collectively, these data support the existence of a hippocampal-amygdala neural circuit capable of modulating bulbar cardiorespiratory control networks and may suggest a role for this circuit in the top-down regulation of breathing and autonomic outflow necessary for the expression of complex emotions.

Muscle sympathetic nerve activity-coupled changes in brain activity during sustained muscle pain

INTRODUCTION

Long-lasting experimental muscle pain elicits divergent muscle sympathetic responses, with some individuals exhibiting a persistent increase in muscle sympathetic nerve activity (MSNA), and others a decrease. These divergent responses are thought to result from sustained functional changes in specific brain regions that modulate the cardiovascular responses to pain.

AIM

The aim of this study was to investigate brain regions that are functionally coupled to the generation of an MSNA burst at rest and to determine their behavior during tonic muscle pain.

METHODS

Functional magnetic resonance imaging of the brain was performed concurrently with microelectrode recording of MSNA from the common peroneal nerve during a 40 min infusion of hypertonic saline into the ipsilateral tibialis anterior muscle of 37 healthy human subjects.

RESULTS

At rest, blood oxygen level-dependent signal intensity coupled to bursts of MSNA increased in the rostral ventrolateral medulla, insula, dorsolateral prefrontal cortex, posterior cingulate cortex, and precuneus and decreased in the region of the midbrain periaqueductal gray. During pain, MSNA-coupled signal intensity was greater in the region of the nucleus tractus solitarius, midbrain periaqueductal gray, dorsolateral prefrontal, medial prefrontal, and anterior cingulate cortices, than at rest. Conversely, MSNA-coupled signal intensity decreased during pain in parts of the prefrontal cortex.

CONCLUSIONS

These results suggest that multiple brain regions are recruited in a burst-to-burst manner, and the magnitude of these signal changes is correlated to the overall change in MSNA amplitude during tonic muscle pain.

Intrinsic functional connectivity of the central nucleus of the amygdala and bed nucleus of the stria terminalis

The central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST), two nuclei within the central extended amygdala, function as critical relays within the distributed neural networks that coordinate sensory, emotional, and cognitive responses to threat. These structures have overlapping anatomical projections to downstream targets that initiate defensive responses. Despite these commonalities, researchers have also proposed a functional dissociation between the CeA and BNST, with the CeA promoting responses to discrete stimuli and the BNST promoting responses to diffuse threat. Intrinsic functional connectivity (iFC) provides a means to investigate the functional architecture of the brain, unbiased by task demands. Using ultra-high field neuroimaging (7-Tesla fMRI), which provides increased spatial resolution, this study compared the iFC networks of the CeA and BNST in 27 healthy individuals. Both structures were coupled with areas of the medial prefrontal cortex, hippocampus, thalamus, and periaqueductal gray matter. Compared to the BNST, the bilateral CeA was more strongly coupled with the insula and regions that support sensory processing, including thalamus and fusiform gyrus. In contrast, the bilateral BNST was more strongly coupled with regions involved in cognitive and motivational processes, including the dorsal paracingulate gyrus, posterior cingulate cortex, and striatum. Collectively, these findings suggest that responses to sensory stimulation are preferentially coordinated by the CeA and cognitive and motivational responses are preferentially coordinated by the BNST.

Brain Regions Involved in Arousal and Reward Processing are Associated with Apathy in Alzheimer's Disease and Frontotemporal Dementia

BACKGROUND

Apathy is a common and problematic symptom of several neurodegenerative illnesses, but its neuroanatomical bases are not understood.

OBJECTIVE

To determine the regions associated with apathy in subjects with mild Alzheimer's disease (AD) using a method that accounts for the significant co-linearity of regional atrophy and neuropsychiatric symptoms.

METHODS

We identified 57 subjects with mild AD (CDR = 1) and neuropsychiatric symptoms in the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. We performed a multivariate multiple regression with LASSO regularization on all symptom subscales of the Neuropsychiatric Inventory and the whole-brain ROI volumes calculated from their baseline MRIs with FreeSurfer. We compared our results to those from a previous study using the same method in patients with frontotemporal dementia (FTD) and corticobasal syndrome (CBS).

RESULTS

Of neuropsychiatric symptoms, apathy showed the most robust neuroanatomical associations in the AD subjects. Atrophy of the following regions were independently associated with apathy: the ventromedial prefrontal cortex; ventrolateral prefrontal cortex; posterior cingulate cortex and adjacent lateral cortex; and the bank of the superior temporal sulcus. These results replicate previous studies using FTD and CBS patients, mostly agree with the previous literature on apathy in AD, and correspond to the Medial and Orbital Prefrontal Cortex networks identified in non-human primates.

CONCLUSION

The current study, previous studies from our laboratory, and the previous literature suggest that impairment of the same brain networks involved in arousal, threat response, and reward processing are associated with apathy in AD and FTD.

Orbital and Medial Prefrontal Cortex Functional Connectivity of Major Depression Vulnerability and Disease

BACKGROUND

Pathophysiology models of major depression (MD) center on the dysfunction of various cortical areas within the orbital and medial prefrontal cortex. While independent structural and functional abnormalities in these areas are consistent findings in MD, the complex interactions among them and the rest of the cortex remain largely unexplored.

METHODS

We used resting-state functional magnetic resonance imaging connectivity to systematically map alterations in the communication between orbital and medial prefrontal cortex fields and the rest of the brain in MD. Functional connectivity (FC) maps from participants with current MD (n = 35), unaffected first-degree relatives (n = 36), and healthy control subjects (n = 38) were subjected to conjunction analyses to distinguish FC markers of MD vulnerability and FC markers of MD disease.

RESULTS

FC abnormalities in MD vulnerability were found for dorsal medial wall regions and the anterior insula and concerned altered communication of these areas with the inferior parietal cortex and dorsal posterior cingulate, occipital areas and the brainstem. FC aberrations in current MD included the anterior insula, rostral and dorsal anterior cingulate cortex, and lateral orbitofrontal areas and concerned altered communication with the dorsal striatum, the cerebellum, the precuneus, the anterior prefrontal cortex, somatomotor cortex, dorsolateral prefrontal cortex, and visual areas in the occipital and inferior temporal lobes.

CONCLUSIONS

Functionally delineated parcellation maps can be used to identify putative connectivity markers in extended cortical regions such as the orbital and medial prefrontal cortex. The anterior insula and the rostral anterior cingulate cortex play a central role in the pathophysiology of MD, being consistently implicated both in the MD vulnerability and MD disease states.

Transforming Pain With Prosocial Meaning: A Functional Magnetic Resonance Imaging Study

OBJECTIVE

Contextual factors can transform how we experience pain, particularly if pain is associated with other positive outcomes. Here, we test a novel meaning-based intervention. Participants were given the opportunity to choose to receive pain on behalf of their romantic partners, situating pain experience in a positive, prosocial meaning context. We predicted that the ventromedial prefrontal cortex (vmPFC), a key structure for pain regulation and generation of affective meaning, would mediate the transformation of pain experience by this prosocial interpersonal context.

METHODS

We studied fMRI activity and behavioral responses in 29 heterosexual female participants during (1) a baseline pain challenge and (2) a task in which participants decided to accept a self-selected number of additional pain trials to reduce pain in their male romantic partners ("accept-partner-pain" condition).

RESULTS

Enduring extra pain for the benefit of the romantic partner reduced pain-related unpleasantness (t = -2.54, p = .016) but not intensity, and increased positive thoughts (t = 3.60, p = .001) and pleasant feelings (t = 5.39, p < .0005). Greater willingness to accept the pain of one's partner predicted greater unpleasantness reductions (t = 3.94, p = .001) and increases in positive thoughts (r = .457, p = .013). The vmPFC showed significant increases (q < .05 FDR-corrected) in activation during accept-partner-pain, especially for women with greater willingness to relieve their partner's pain (t = 2.63, p = .014). Reductions in brain regions processing pain and aversive emotion significantly mediated reductions in pain unpleasantness (q < .05 FDR-corrected).

CONCLUSIONS

The vmPFC has a key role in transforming the meaning of pain, which is associated with a cascade of positive psychological and brain effects, including changes in affective meaning, value, and pain-specific neural circuits.

Resting State Functional Connectivity of the Lateral and Medial Hypothalamus in Cocaine Dependence: An Exploratory Study

The role of dopamine in cocaine misuse has been extensively documented for the mesocorticolimbic circuit. Preclinical work from earlier lesion studies to recent multidisciplinary investigations has suggested that the hypothalamus is critically involved in motivated behavior, with the lateral and medial hypothalamus each involved in waking/feeding and resting/satiety. However, little is known of hypothalamus function and dysfunction in cocaine misuse. Here, we examined resting state functional connectivity of the lateral and medial hypothalamus in 70 individuals with cocaine dependence (CD) and 70 age as well as gender matched healthy controls (HC). Image pre-processing and analyses followed published work. Compared to HC, CD showed increased lateral hypothalamic connectivity with dorsolateral prefrontal cortex and decreased functional connectivity with the ventral precuneus. CD showed increased medial hypothalamic connectivity with the inferior parietal lobule and decreased connectivity with the ventromedial prefrontal cortex, temporal gyrus, fusiform gyrus, and ventral striatum. Further, at trend level significance, the connectivity strength between lateral hypothalamus and dorsolateral prefrontal cortex was positively correlated with total amount of cocaine use in the past month (p = 0.004, r = 0.35) and the connectivity strength between medial hypothalamus and ventral striatum was negatively correlated with cocaine craving as assessed by the Tiffany Cocaine Craving Questionnaire (p = 0.008, r = -0.33). Together, the findings demonstrated altered resting state functional connectivity of the hypothalamus and may provide new insight on circuit level deficits in cocaine dependence.

Larger Numbers of Glial and Neuronal Cells in the Periaqueductal Gray Matter of μ-Opioid Receptor Knockout Mice

Background: μ-opioid receptor knockout (MOP-KO) mice display baseline hyperalgesia. We have recently identified changes in tissue volume in the periaqueductal gray matter (PAG) using magnetic resonance imaging voxel-based morphometry. Changes in the structure and connectivity of this region might account for some behavior phenotypes in MOP-KO mice, including hyperalgesia. Methods: Adult male MOP-KO and wild-type (WT) mice were studied. Immunohistochemistry was performed to detect microglia, astrocytes, and neurons in the PAG using specific markers: ionized calcium-binding adaptor molecule 1 (Iba-1) for microglia, glial fibrillary acidic protein (GFAP) for astrocytes, and the neuronal nuclei antigen (NeuN; product of the Rbfox3 gene) for neurons, respectively. Cell counting was performed in the four parallel longitudinal columns of the PAG (dorsomedial, dorsolateral, lateral, and ventrolateral) at three different locations from bregma (-3.5, -4.0, and -4.5 mm). Results: The quantitative analysis showed larger numbers of well-distributed Iba1-IR cells (microglia), NeuN-IR cells (neurons), and GFAP-IR areas (astrocytes) at all the anatomically distinct regions examined, namely, the dorsomedial (DM) PAG, dorsolateral (DL) PAG, lateral (L) PAG, and ventrolateral (VL) PAG, in MOP-KO mice than in control mice. Conclusions: The cellular changes in the PAG identified in this paper may underlie aspects of the behavioral alterations produced by MOP receptor deletion, and suggest that alterations in the cellular structure of the PAG may contribute to hyperalgesic states.

In vivo structural imaging in rats reveals neuroanatomical correlates of behavioral sub-dimensions of cocaine addiction

Cocaine addiction is a multi-dimensional behavioral disorder characterized by a loss of control over cocaine taking despite of detrimental consequences. Structural MRI studies have revealed association between cocaine consumption and gray matter volume (GMV) in cocaine-addicted patients. However, the behavioral correlates of GMV in cocaine addiction are poorly understood. Here, we used a DSM-IV-based rat model of cocaine addiction with high face validity for structural imaging. According to three behavioral sub-dimensions of addiction, rats were separated into two groups showing either addict-like or non-addict-like behavior. These behavioral sub-dimensions were (1) the inability to refrain from drug-seeking and taking, (2) high motivation for the drug, and (3) maintained drug use despite negative consequences. In these rats, we performed structural MRI with voxel-based morphometry and analyzed the interaction of GMV with behavioral sub-dimensions in cocaine-addicted rats. Our major findings are that GMV differentially correlate with the inability to refrain from drug-seeking and taking in addict-like and non-addict-like rats within the somatosensory cortices and the amygdala. High motivation for the drug differentially correlates with GMV in addict-like and non-addict-like rats within the medial prefrontal cortex, and maintained drug use despite negative consequences differentially correlates with GMV in these two groups of rats within the periaqueductal gray. Our results demonstrate that the behavioral differences characterizing addict-like and non-addict-like rats in each behavioral sub-dimension of addiction are reflected by divergent covariance with GMV. We conclude that structural imaging provides specific neuroanatomical correlates of behavioral sub-dimensions of addiction.

Ventromedial Hypothalamus and the Generation of Aggression

Aggression is a costly behavior, sometimes with severe consequences including death. Yet aggression is prevalent across animal species ranging from insects to humans, demonstrating its essential role in the survival of individuals and groups. The question of how the brain decides when to generate this costly behavior has intrigued neuroscientists for over a century and has led to the identification of relevant neural substrates. Various lesion and electric stimulation experiments have revealed that the hypothalamus, an ancient structure situated deep in the brain, is essential for expressing aggressive behaviors. More recently, studies using precise circuit manipulation tools have identified a small subnucleus in the medial hypothalamus, the ventrolateral part of the ventromedial hypothalamus (VMHvl), as a key structure for driving both aggression and aggression-seeking behaviors. Here, we provide an updated summary of the evidence that supports a role of the VMHvl in aggressive behaviors. We will consider our recent findings detailing the physiological response properties of populations of VMHvl cells during aggressive behaviors and provide new understanding regarding the role of the VMHvl embedded within the larger whole-brain circuit for social sensation and action.

Brainstem Pain-Control Circuitry Connectivity in Chronic Neuropathic Pain

Preclinical investigations have suggested that altered functioning of brainstem pain-modulation circuits may be crucial for the maintenance of some chronic pain conditions. While some human psychophysical studies show that patients with chronic pain display altered pain-modulation efficacy, it remains unknown whether brainstem pain-modulation circuits are altered in individuals with chronic pain. The aim of the present investigation was to determine whether, in humans, chronic pain following nerve injury is associated with altered ongoing functioning of the brainstem descending modulation systems. Using resting-state functional magnetic resonance imaging, we found that male and female patients with chronic neuropathic orofacial pain show increased functional connectivity between the rostral ventromedial medulla (RVM) and other brainstem pain-modulatory regions, including the ventrolateral periaqueductal gray (vlPAG) and locus ceruleus (LC). We also identified an increase in RVM functional connectivity with the region that receives orofacial nociceptor afferents, the spinal trigeminal nucleus. In addition, the vlPAG and LC displayed increased functional connectivity strengths with higher brain regions, including the hippocampus, nucleus accumbens, and anterior cingulate cortex, in individuals with chronic pain. These data reveal that chronic pain is associated with altered ongoing functioning within the endogenous pain-modulation network. These changes may underlie enhanced descending facilitation of processing at the primary synapse, resulting in increased nociceptive transmission to higher brain centers. Further, our findings show that higher brain regions interact with the brainstem modulation system differently in chronic pain, possibly reflecting top-down engagement of the circuitry alongside altered reward processing in pain conditions.SIGNIFICANCE STATEMENT Experimental animal models and human psychophysical studies suggest that altered functioning of brainstem pain-modulation systems contributes to the maintenance of chronic pain. However, the function of this circuitry has not yet been explored in humans with chronic pain. In this study, we report that individuals with orofacial neuropathic pain show altered functional connectivity between regions within the brainstem pain-modulation network. We suggest that these changes reflect largely central mechanisms that feed back onto the primary nociceptive synapse and enhance the transfer of noxious information to higher brain regions, thus contributing to the constant perception of pain. Identifying the mechanisms responsible for the maintenance of neuropathic pain is imperative for the development of more efficacious therapies.

Dynamic causal modeling in PTSD and its dissociative subtype: Bottom-up versus top-down processing within fear and emotion regulation circuitry

OBJECTIVE

Posttraumatic stress disorder (PTSD) is associated with decreased top-down emotion modulation from medial prefrontal cortex (mPFC) regions, a pathophysiology accompanied by hyperarousal and hyperactivation of the amygdala. By contrast, PTSD patients with the dissociative subtype (PTSD + DS) often exhibit increased mPFC top-down modulation and decreased amygdala activation associated with emotional detachment and hypoarousal. Crucially, PTSD and PTSD + DS display distinct functional connectivity within the PFC, amygdala complexes, and the periaqueductal gray (PAG), a region related to defensive responses/emotional coping. However, differences in directed connectivity between these regions have not been established in PTSD, PTSD + DS, or controls.

METHODS

To examine directed (effective) connectivity among these nodes, as well as group differences, we conducted resting-state stochastic dynamic causal modeling (sDCM) pairwise analyses of coupling between the ventromedial (vm)PFC, the bilateral basolateral and centromedial (CMA) amygdala complexes, and the PAG, in 155 participants (PTSD [n = 62]; PTSD + DS [n = 41]; age-matched healthy trauma-unexposed controls [n = 52]).

RESULTS

PTSD was characterized by a pattern of predominant bottom-up connectivity from the amygdala to the vmPFC and from the PAG to the vmPFC and amygdala. Conversely, PTSD + DS exhibited predominant top-down connectivity between all node pairs (from the vmPFC to the amygdala and PAG, and from the amygdala to the PAG). Interestingly, the PTSD + DS group displayed the strongest intrinsic inhibitory connections within the vmPFC.

CONCLUSIONS

These results suggest the contrasting symptom profiles of PTSD and its dissociative subtype (hyper- vs. hypo-emotionality, respectively) may be driven by complementary changes in directed connectivity corresponding to bottom-up defensive fear processing versus enhanced top-down regulation. Hum Brain Mapp 38:5551-5561, 2017. © 2017 Wiley Periodicals, Inc.

A hypothalamo-midbrain-medullary pathway involved in the inhibition of the respiratory chemoreflex response induced by potassium cyanide in rodents

Recent studies have demonstrated that a mild stimulation of the dorsomedian nucleus of the hypothalamus (DMH), a defense area, induces the inhibition of the carotid chemoreflex tachypnea. DMH activation reduces the cardiac chemoreflex response via the dorsolateral part of the periaqueductal grey matter (dlPAG) and serotonin receptors (5-HT₃ subtype) in the nucleus tractus solitarius (NTS). The objectives of this study were to assess whether dlPAG and subsequent NTS 5-HT₃ receptors are involved in chemoreflex tachypnea inhibition during mild activation of the DMH. For this purpose, peripheral chemoreflex was activated with potassium cyanide (KCN, 40 μg/rat, i.v.) during electrical and chemical minimal supra-threshold (mild) stimulation of the dlPAG or DMH. In both situations, changes in respiratory frequency (RF) following KCN administration were reduced. Moreover, pharmacological blockade of the dlPAG prevented DMH-induced KCN tachypnea inhibition. Activation of NTS 5-HT₃ receptors also reduced chemoreflex tachypnea in a dose-dependent manner. In addition, blockade of NTS 5-HT₃ receptors with granisetron (2.5 but not 1.25 mM), or the use of mice lacking the 5-HT_3a receptor (5-HT_3a KO), prevented dlPAG-induced KCN reductions in RF. A respiratory hypothalamo-midbrain-medullary pathway (HMM) therefore plays a crucial role in the inhibition of the hyperventilatory response to carotid chemoreflex.

Central Sensitization-Based Classification for Temporomandibular Disorders: A Pathogenetic Hypothesis

Dysregulation of Autonomic Nervous System (ANS) and central pain pathways in temporomandibular disorders (TMD) is a growing evidence. Authors include some forms of TMD among central sensitization syndromes (CSS), a group of pathologies characterized by central morphofunctional alterations. Central Sensitization Inventory (CSI) is useful for clinical diagnosis. Clinical examination and CSI cannot identify the central site(s) affected in these diseases. Ultralow frequency transcutaneous electrical nerve stimulation (ULFTENS) is extensively used in TMD and in dental clinical practice, because of its effects on descending pain modulation pathways. The Diagnostic Criteria for TMD (DC/TMD) are the most accurate tool for diagnosis and classification of TMD. However, it includes CSI to investigate central aspects of TMD. Preliminary data on sensory ULFTENS show it is a reliable tool for the study of central and autonomic pathways in TMD. An alternative classification based on the presence of Central Sensitization and on individual response to sensory ULFTENS is proposed. TMD may be classified into 4 groups: (a) TMD with Central Sensitization ULFTENS Responders; (b) TMD with Central Sensitization ULFTENS Nonresponders; (c) TMD without Central Sensitization ULFTENS Responders; (d) TMD without Central Sensitization ULFTENS Nonresponders. This pathogenic classification of TMD may help to differentiate therapy and aetiology.

An Emotional Call to Action: Integrating Affective Neuroscience in Models of Motor Control

Intimate relationships between emotion and action have long been acknowledged, yet contemporary theories and experimental research within affective and movement neuroscience have not been linked into a coherent framework bridging these two fields. Accumulating psychological and neuroimaging evidence has, however, brought new insights regarding how emotions affect the preparation, execution, and control of voluntary movement. Here we review main approaches and findings on such emotion–action interactions. To assimilate key emotion concepts of action tendencies and motive states with fundamental constructs of the motor system, we underscore the need for integrating an information-processing approach of motor control into affective neuroscience. This should provide a rich foundation to bridge the two fields, allowing further refinement and empirical testing of emotion theories and better understanding of affective influences in movement disorders.

The initial fall in arterial pressure evoked by endotoxin is mediated by the ventrolateral periaqueductal gray

This study tested the hypothesis that the initial fall in arterial pressure evoked by lipopolysaccharide (LPS) is mediated by the ventrolateral column of the midbrain periaqueductal gray region (vlPAG). To test this hypothesis, the local anaesthetic lidocaine (2%; 0.1 μL, 0.2 μL or 1.0 μL), the delta opioid receptor antagonist naltrindole (2 nmol) or saline was microinjected into the vlPAG of isoflurane-anaesthetized rats bilaterally and LPS (1 mg/kg) or saline was administered intravenously 2 min later. Both lidocaine and naltrindole inhibited LPS-evoked hypotension significantly but did not affect arterial pressure in saline-treated control animals. Neither lidocaine nor naltrindole altered heart rate significantly in either LPS-treated or control animals. Microinjection of lidocaine or naltrindole into the dorsolateral PAG was ineffective. These data indicate that the vlPAG plays an important role in the initiation of endotoxic hypotension and further show that delta opioid receptors in the vlPAG participate in the response.

A leptin-regulated circuit controls glucose mobilization during noxious stimuli

Adipocytes secrete the hormone leptin to signal the sufficiency of energy stores. Reductions in circulating leptin concentrations reflect a negative energy balance, which augments sympathetic nervous system (SNS) activation in response to metabolically demanding emergencies. This process ensures adequate glucose mobilization despite low energy stores. We report that leptin receptor-expressing neurons (LepRb neurons) in the periaqueductal gray (PAG), the largest population of LepRb neurons in the brain stem, mediate this process. Application of noxious stimuli, which often signal the need to mobilize glucose to support an appropriate response, activated PAG LepRb neurons, which project to and activate parabrachial nucleus (PBN) neurons that control SNS activation and glucose mobilization. Furthermore, activating PAG LepRb neurons increased SNS activity and blood glucose concentrations, while ablating LepRb in PAG neurons augmented glucose mobilization in response to noxious stimuli. Thus, decreased leptin action on PAG LepRb neurons augments the autonomic response to noxious stimuli, ensuring sufficient glucose mobilization during periods of acute demand in the face of diminished energy stores.

Left Habenular Activity Attenuates Fear Responses in Larval Zebrafish

Fear responses are defensive states that ensure survival of an organism in the presence of a threat. Perception of an aversive cue causes changes in behavior and physiology, such as freezing and elevated cortisol, followed by a return to the baseline state when the threat is evaded [1]. Neural systems that elicit fear behaviors include the amygdala, hippocampus, and medial prefrontal cortex. However, aside from a few examples, little is known about brain regions that promote recovery from an aversive event [2]. Previous studies had implicated the dorsal habenular nuclei in regulating fear responses and boldness in zebrafish [3-7]. We now show, through perturbation of its inherent left-right (L-R) asymmetry at larval stages, that the dorsal habenulo-interpeduncular (dHb-IPN) pathway expedites the return of locomotor activity following an unexpected negative stimulus, electric shock. Severing habenular efferents to the IPN, or only those from the left dHb, prolongs the freezing behavior that follows shock. Individuals with a symmetric, right-isomerized dHb also exhibit increased freezing. In contrast, larvae that have a symmetric, left-isomerized dHb, or in which just the left dHb-IPN projection is optogenetically activated, rapidly resume swimming post shock. In vivo calcium imaging reveals a neuronal subset, predominantly in the left dHb, whose activation is correlated with resumption of swimming. The results demonstrate functional specialization of the left dHb-IPN pathway in attenuating the response to fear.

A Basal Forebrain Site Coordinates the Modulation of Endocrine and Behavioral Stress Responses via Divergent Neural Pathways

The bed nuclei of the stria terminalis (BST) are critically important for integrating stress-related signals between the limbic forebrain and hypothalamo-pituitary-adrenal (HPA) effector neurons in the paraventricular hypothalamus (PVH). Nevertheless, the circuitry underlying BST control over the stress axis and its role in depression-related behaviors has remained obscure. Utilizing optogenetic approaches in rats, we have identified a novel role for the anteroventral subdivision of BST in the coordinated inhibition of both HPA output and passive coping behaviors during acute inescapable (tail suspension, TS) stress. Follow-up experiments probed axonal pathways emanating from the anteroventral BST which accounted for separable endocrine and behavioral functions subserved by this cell group. The PVH and ventrolateral periaqueductal gray were recipients of GABAergic outputs from the anteroventral BST that were necessary to restrain stress-induced HPA activation and passive coping behavior, respectively, during TS and forced swim tests. In contrast to other BST subdivisions implicated in anxiety-like responses, these results direct attention to the anteroventral BST as a nodal point in a stress-modulatory network for coordinating neuroendocrine and behavioral coping responses, wherein impairment could account for core features of stress-related mood disorders.

SIGNIFICANCE STATEMENT

Dysregulation of the neural pathways modulating stress-adaptive behaviors is implicated in stress-related psychiatric illness. While aversive situations activate a network of limbic forebrain regions thought to mediate such changes, little is known about how this information is integrated to orchestrate complex stress responses. Here we identify novel roles for the anteroventral bed nuclei of the stria terminalis in inhibiting both stress hormone output and passive coping behavior via divergent projections to regions of the hypothalamus and midbrain. Inhibition of these projections produced features observed with rodent models of depression, namely stress hormone hypersecretion and increased passive coping behavior, suggesting that dysfunction in these networks may contribute to expression of pathological changes in stress-related disorders.

Top down control of spinal sensorimotor circuits essential for survival

The ability to interact with challenging environments requires coordination of sensory and motor systems that underpin appropriate survival behaviours. All animals, including humans, use active and passive coping strategies to react to escapable or inescapable threats, respectively. Across species the neural pathways involved in survival behaviours are highly conserved and there is a consensus that knowledge of such pathways is a fundamental step towards understanding the neural circuits underpinning emotion in humans and treating anxiety or other prevalent emotional disorders. The midbrain periaqueductal grey (PAG) lies at the heart of the defence-arousal system and its integrity is paramount to the expression of survival behaviours. To date, studies of 'top down control' components of defence behaviours have focused largely on the sensory and autonomic consequences of PAG activation. In this context, effects on motor activity have received comparatively little attention, despite overwhelming evidence of a pivotal role for the PAG in coordinating motor responses essential to survival (e.g. such as freezing in response to fear). In this article we provide an overview of top down control of sensory functions from the PAG, including selective control of different modalities of sensory, including proprioceptive, information forwarded to a major supsraspinal motor control centre, the cerebellum. Next, evidence from our own and other laboratories of PAG control of motor outflow is also discussed. Finally, the integration of sensorimotor functions by the PAG is considered, as part of coordinated defence behaviours that prepare an animal to be ready and able to react to danger.

Active avoidance and attentive freezing in the face of approaching threat

Defensive behaviors in animals and humans vary dynamically with increasing proximity of a threat and depending upon the behavioral repertoire at hand. The current study investigated physiological and behavioral adjustments and associated brain activation when participants were exposed to dynamically approaching threat that was either inevitable or could be avoided by motor action. When the approaching threat was inevitable, attentive freezing was observed as indicated by fear bradycardia, startle potentiation, and a dynamic increase in activation of the anterior insula and the periaqueductal grey. In preparation for active avoidance a switch in defensive behavior was observed characterized by startle inhibition and heart rate acceleration along with potentiated activation of the amygdala and the periaqueductal grey. Importantly, the modulation of defensive behavior according to threat imminence and the behavioral option at hand was associated with activity changes in the ventromedial prefrontal cortex. These findings improve our understanding of brain mechanisms guiding human behavior during approaching threat depending on available resources.

Lower Functional Connectivity of the Periaqueductal Gray Is Related to Negative Affect and Clinical Manifestations of Fibromyalgia

Fibromyalgia (FM) syndrome is characterized by chronic widespread pain, muscle tenderness and emotional distress. Previous studies found reduced endogenous pain modulation in FM. This deficiency of pain modulation may be related to the attributes of chronic pain and other clinical symptoms experienced in patients with FM. Thus, we tested whether there is a link between the clinical symptoms of FM and functional connectivity (FC) of the periaqueductal gray (PAG), a key node of pain modulation. We acquired resting state 3T functional MRI (rsfMRI) data from 23 female patients with FM and 16 age- and sex- matched healthy controls (HC) and assessed FM symptoms with the Brief Pain Inventory (BPI), Fibromyalgia Impact Questionnaire (FIQ), Hospital Anxiety and Depression Scale (HADS) and Pain Catastrophizing Scale (PCS). We found that patients with FM exhibit statistically significant disruptions in PAG FC, particularly with brain regions implicated in negative affect, self-awareness and saliency. Specifically, we found that, compared to HCs, the FM patients had stronger PAG FC with the lingual gyrus and hippocampus but weaker PAG FC with regions associated with motor/executive functions, the salience (SN) and default mode networks (DMN). The attenuated PAG FC was also negatively correlated with FIQ scores, and positively correlated with the magnification subscale of the PCS. These alterations were correlated with emotional and behavioral symptoms of FM. Our study implicates the PAG as a site of dysfunction contributing to the clinical manifestations and pain in FM.

Cardiovascular and autonomic reactivity to psychological stress: Neurophysiological substrates and links to cardiovascular disease

Psychologically stressful experiences evoke changes in cardiovascular physiology that may influence risk for cardiovascular disease (CVD). But what are the neural circuits and intermediate physiological pathways that link stressful experiences to cardiovascular changes that might in turn confer disease risk? This question is important because it has broader implications for our understanding of the neurophysiological pathways that link stressful and other psychological experiences to physical health. This review highlights selected findings from brain imaging studies of stressor-evoked cardiovascular reactivity and CVD risk. Converging evidence across these studies complements animal models and patient lesion studies to suggest that a network of cortical, limbic, and brainstem areas for central autonomic and physiological control are important for generating and regulating stressor-evoked cardiovascular reactivity via visceromotor and viscerosensory mechanisms. Emerging evidence further suggests that these brain areas may play a role in stress-related CVD risk, specifically by their involvement in mediating metabolically-dysregulated or extreme stressor-evoked cardiovascular reactions. Contextually, the research reviewed here offers an example of how brain imaging and health neuroscience methods can be integrated to address open and mechanistic questions about the neurophysiological pathways linking psychological stress and physical health.