Perspectives on the integrative functions of the 'sympatho-adrenomedullary system'

Pupillary Responses to Dot Patterns on a Human Face Background

Dots on natural backgrounds can elicit significant pupillary constrictions within the entire image phase associated with parasympathetic activation, suggesting disgust rather than fear. Although studies have reported that dots on faces elicit stronger disgust than dots on non-face backgrounds, it remains unclear whether dots on a face elicit stronger pupil constrictions than non-face backgrounds. Pupillometry was used while viewing dots on faces and compared with luminance- and spatial frequency-controlled images (dots on phase-scrambled faces) and luminance-controlled images (face only, phase-scrambled faces). Relative pupillary constrictions were elicited when dots were placed on faces and phase-scrambled faces; however, the response to dots on faces did not differ significantly from that to the control stimuli. Approximately 3-5 s after stimulus onset, pupillary responses to dots on faces recovered to baseline faster than those to dots on phase-scrambled faces with a larger pupil size. The initial pupillary constrictions observed are consistent with those in response to dots on natural backgrounds, suggesting that regardless of the background, dots may stimulate parasympathetic activation and elicit disgust rather than fear. The faster recovery from the pupil constriction and larger pupil size in the later phase may be caused by a dynamic balance between the sympathetic and parasympathetic neuronal activities.

Biological testing during acute psychological stress: A hindrance or an opportunity?

All humans deal with acute psychological stress periodically. Some individuals are affected by needle phobia in which a heightened sense of arousal is precipitated by venepuncture. Acute psychological stress invokes a range of physiological changes including activation of the sympathetic-adrenal-medullary and hypothalamic-pituitary-adrenal axes. In this review article, we first examine the human response to acute stress. We then provide an overview of how psychological stress in a subject is likely to be a source of pre-analytical variability for certain measurands, and the major biochemical markers that have been studied in research aiming to quantify stress. As such, we highlight how stress can be a hindrance to the accurate interpretation of certain laboratory results (particularly cortisol, prolactin, metanephrines and growth hormone), and point out the role that biochemical analysis might play in future studies looking at the effects of stress on human behaviour.

Lateralization of autonomic output in response to limb-specific threat

In times of stress or danger, the autonomic nervous system (ANS) signals the fight or flight response. A canonical function of ANS activity is to globally mobilize metabolic resources, preparing the organism to respond to threat. Yet a body of research has demonstrated that, rather than displaying a homogenous pattern across the body, autonomic responses to arousing events - as measured through changes in electrodermal activity (EDA) - can differ between right and left body locations. Surprisingly, an attempt to identify a function of ANS asymmetry consistent with its metabolic role has not been investigated. In the current study, we investigated whether asymmetric autonomic responses could be induced through limb-specific aversive stimulation. Participants were given mild electric stimulation to either the left or right arm while EDA was monitored bilaterally. In a group-level analyses, an ipsilateral EDA response bias was observed, with increased EDA response in the hand adjacent to the stimulation. This effect was observable in ∼50% of individual particpants. These results demonstrate that autonomic output is more complex than canonical interpretations suggest. We suggest that, in stressful situations, autonomic outputs can prepare either the whole-body fight or flight response, or a simply a limb-localized flick, which can effectively neutralize the threat while minimizing global resource consumption. These findings are consistent with recent theories proposing evolutionary leveraging of neural structures organized to mediate sensory responses for processing of cognitive emotional cues.Significance statementThe present study constitutes novel evidence for an autonomic nervous response specific to the side of the body exposed to direct threat. We identify a robust pattern of electrodermal response at the body location that directly receives aversive tactile stimulation. Thus, we demonstrate for the first time in contemporary research that the ANS is capable of location-specific outputs within single effector organs in response to small scale threat. This extends the canonical view of the role of ANS responses in stressful or dangerous stresses - that of provoking a 'fight or flight' response - suggesting a further role of this system: preparation of targeted limb-specific action, i.e., a flick.

Effect of pulmonary vein isolation on the relationship between left atrial reverse remodeling and sympathetic nerve activity in patients with atrial fibrillation

PURPOSE

Catheter ablation (CA) to isolate the pulmonary vein, which is an established treatment for atrial fibrillation (AF), is associated with left atrium reverse remodeling (LARR). The intrinsic cardiac autonomic nervous system includes the ganglion plexi adjacent to the pulmonary vein in the left atrium (LA). However, little is known about the effect of CA on the relationship between LARR and sympathetic nerve activity in patients with AF.

METHODS

This study enrolled 22 AF patients with a normal left ventricular ejection fraction (LVEF) aged 64.6 ± 12.9 years who were scheduled for CA. Sympathetic nerve activity was evaluated by direct recording of muscle sympathetic nerve activity (MSNA) before and 12 weeks after CA. Blood pressure, heart rate (HR), HR variability, and echocardiography were also measured.

RESULTS

The heart rate increased significantly after CA (63 ± 10.9 vs. 70.6 ± 7.7 beats/min, p < 0.01), but blood pressure did not change. A high frequency (HF) and low frequency (LF) of HR variability decreased significantly after ablation, but no significant change in LF/HF was observed. CA significantly decreased MSNA (38.9 ± 9.9 vs. 28 ± 9.1 bursts/min, p < 0.01). Moreover, regression analysis revealed a positive correlation between the percentage change in MSNA and the LA volume index (r = 0.442, p < 0.05).

CONCLUSIONS

Our results show that CA for AF reduced MSNA and the decrease was associated with the LA volume index in AF patients with a normal LVEF. These findings suggest that LARR induced by CA for AF decrease sympathetic nerve activity.

The 2021 Carl Ludwig Lecture. Unsympathetic autonomic regulation in heart failure: patient-inspired insights

Defined as a structural or functional cardiac abnormality accompanied by symptoms, signs, or biomarkers of altered ventricular pressures or volumes, heart failure also is a state of autonomic disequilibrium. A large body of evidence affirms that autonomic disturbances are intrinsic to heart failure; basal or stimulated sympathetic nerve firing or neural norepinephrine (NE) release more often than not exceed homeostatic need, such that an initially adaptive adrenergic or vagal reflex response becomes maladaptive. The magnitude of such maladaptation predicts prognosis. This Ludwig lecture develops two theses: the elucidation and judiciously targeted amelioration of maladaptive autonomic disturbances offers opportunities to complement contemporary guideline-based heart failure therapy, and serendipitous single-participant insights, acquired in the course of experimental protocols with entirely different intent, can generate novel insight, inform mechanisms, and launch entirely new research directions. I précis six elements of our current synthesis of the causes and consequences of maladaptive sympathetic disequilibrium in heart failure, shaped by patient-inspired epiphanies: arterial baroreceptor reflex modulation, excitation stimulated by increased cardiac filling pressure, paradoxical muscle sympathetic activation as a peripheral neurogenic constraint on exercise capacity, renal sympathetic restraint of natriuresis, coexisting sleep apnea, and augmented chemoreceptor reflex sensitivity and then conclude by envisaging translational therapeutic opportunities.

Muscle sympathetic single-unit response patterns during progressive muscle metaboreflex activation in young healthy adults

Muscle sympathetic single units can respond differentially to stress, but whether these responses are linked to the degree of sympathoexcitation is unclear. Fifty-three muscle sympathetic single units (microneurography) were recorded in 17 participants (8 women; 24 ± 3 yr). Five 40-s bouts of 10% static handgrip were performed during a 10-min forearm ischemia to progressively increase metabolite accumulation. Each static handgrip was separated by a 75-s ischemic rest [postexercise circulatory occlusion (PECO)] to assess the isolated action of the muscle metaboreflex. During each set of PECO, individual single units were classified as activated, nonresponsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. From sets 1-5 of PECO, the proportion of single units with activated (34, 45, 68, 87, and 89%), nonresponsive (43, 44, 23, 7, and 9%), or inhibited (23, 11, 9, 6, and 2%) responses changed (P < 0.001) as total muscle sympathoexcitation increased. A total of 51/53 (96%) single units were activated in at least one set of PECO, 16 (31%) initially inhibited before activation. This response pattern delayed the activation onset compared with noninhibited units (set 3 ± 1 vs. 2 ± 1, P < 0.001). Once activated, the spike-frequency rate of rise was similar (8.5 ± 6.5 vs. 7.1 ± 6.0 spikes/min per set, P = 0.48). Muscle sympathetic single-unit firing demonstrated differential control during muscle metaboreflex activation. Single units that were initially inhibited during progressive metaboreflex activation were capable of being activated in later sets. These findings reveal that single-unit activity is influenced by convergent neural inputs (i.e., both inhibitory and excitatory), which yield heterogenous single-unit activation thresholds.NEW & NOTEWORTHY Muscle sympathetic single units respond differentially to sympathoexcitatory stress such that single units can increase firing to contribute to the sympathoexcitatory response or can be nonresponsive or even inhibited. We observed a subgroup of single units that can respond bidirectionally, being first inhibited before activated by progressive increases in forearm muscle metaboreflex activation. These results suggest convergent neural inputs (i.e., inhibitory and excitatory), which yield heterogenous muscle sympathetic single-unit activation thresholds.

Arterial baroreflex regulation of muscle sympathetic single-unit activity in men: influence of resting blood pressure

The arterial baroreflex has dominant control over multiunit muscle sympathetic nerve activity (MSNA) burst occurrence, but whether this extends to all single units or is influenced by resting blood pressure status is unclear. In 22 men (32 ± 8 yr), we assessed 68 MSNA single units during sequential bolus injections of nitroprusside and phenylephrine (modified Oxford). Sympathetic baroreflex sensitivity (sBRS) was quantified as the weighted negative linear regression slope between diastolic blood pressure (DBP) and single-unit spike firing probability and multiple spike firing. Strong negative linear relationships ( r ≥ −0.50) between DBP and spike firing probability were observed in 63/68 (93%) single units (−2.27 ± 1.27%·cardiac cycle−1·mmHg−1 [operating range, 18 ± 8 mmHg]). In contrast, only 45/68 (66%) single units had strong DBP-multiple spike firing relationships (−0.13 ± 0.18 spikes·cardiac cycle−1·mmHg−1 [operating range, 14 ± 7 mmHg]). Participants with higher resting DBP (65 ± 3 vs. 77 ± 3 mmHg, P < 0.001) had similar spike firing probability sBRS (low vs. high, −2.08 ± 1.08 vs. −2.46 ± 1.42%·cardiac cycle−1·mmHg−1, P = 0.33), but a smaller sBRS operating range (20 ± 6 vs. 16 ± 9 mmHg, P = 0.01; 86 ± 24 vs. 52 ± 25% of total range, P < 0.001) and a higher proportion of single units without arterial baroreflex control outside this range [6/31 (19%) vs. 21/32 (66%), P < 0.001]. Participants with higher resting DBP also had fewer single units with arterial baroreflex control of multiple spike firing (79 vs. 53%, P = 0.04). The majority of MSNA single units demonstrate strong arterial baroreflex control over spike firing probability during pharmacological manipulation of blood pressure. Changes in single-unit sBRS operating range and control of multiple spike firing may represent altered sympathetic recruitment patterns associated with the early development of hypertension.

NEW & NOTEWORTHY Muscle sympathetic single units can be differentially controlled during stress. In contrast, we demonstrate that 93% of single units maintain strong arterial baroreflex control during pharmacological manipulation of blood pressure. Interestingly, the operating range and proportion of single units that lose arterial baroreflex control outside of this range are influenced by resting blood pressure levels. Altered single unit, but not multiunit, arterial baroreflex control may represent changes in sympathetic recruitment patterns in early stage development of hypertension.

Implicit Affect and Autonomous Nervous System Reactions: A Review of Research Using the Implicit Positive and Negative Affect Test

In everyday life, affective processes occur spontaneously and typically go along with an automatic activation of action tendencies and physiological responses. Because self-reports of affect are also known to be biased by various factors, including deficits in introspection or impression management strategies, an indirect measure, the Implicit Positive and Negative Affect Test (IPANAT), was developed to assess implicit affect and to circumvent these difficulties. In this review, findings from neurobiological and clinical studies administering the IPANAT are revised, we focus on the link between implicit affect and psychophysiological reactions to affective stimuli and stressors. Specifically, implicit affect as measured by the IPANAT was found to predict cardiovascular, endocrine, and functional neuroimaging correlates of stress or fear beyond explicit affect. The present evidence strongly suggests the usage of implicit affect measures in future research on stress and psychopathology.

Evidence for differential control of muscle sympathetic single units during mild sympathoexcitation in young, healthy humans

Two subpopulations of muscle sympathetic single units with opposite discharge characteristics have been identified during low-level cardiopulmonary baroreflex loading and unloading in middle-aged adults and patients with heart failure. The present study sought to determine whether similar subpopulations are present in young healthy adults during cardiopulmonary baroreflex unloading ( study 1) and rhythmic handgrip exercise ( study 2). Continuous hemodynamic and multiunit and single unit muscle sympathetic nerve activity (MSNA) data were collected at baseline and during nonhypotensive lower body negative pressure (LBNP; n = 12) and 40% maximal voluntary contraction rhythmic handgrip exercise (RHG; n = 24). Single unit MSNA responses were classified as anticipated or paradoxical based on whether changes were concordant or discordant with the multiunit MSNA response, respectively. LBNP and RHG both increased multiunit MSNA burst frequency (∆5 ± 3 bursts/min, P < 0.001; ∆5 ± 8 bursts/min, P = 0.005), burst amplitude (∆5 ± 7%, P = 0.04; ∆13 ± 14%, P < 0.001), and total MSNA (∆302 ± 191 AU/min, P = 0.001; ∆585 ± 556 AU/min, P < 0.001). During LBNP and RHG, 43 and 64 muscle single units were identified, respectively, which increased spike frequency (∆9 ± 11 spikes/min, P < 0.001; ∆10 ± 19 spikes/min, P < 0.001) and the probability of multiple spike firing (∆10 ± 12%, P < 0.001; ∆11 ± 26%, P = 0.001). During LBNP and RHG, 36 (84%) and 39 (61%) single units possessed anticipated firing responses (∆12 ± 10 spikes/min, P < 0.001; ∆19 ± 19 spikes/min, P < 0.001), whereas 7 (16%) and 25 (39%) single units exhibited paradoxical reductions (∆−3 ± 1 spikes/min, P = 0.003; ∆−4 ± 5 spikes/min, P < 0.001). The observation of divergent subpopulations of muscle sympathetic single units in healthy young humans during two mild sympathoexcitatory stressors supports differential control at the fiber level as a fundamental characteristic of human sympathetic regulation.

NEW & NOTEWORTHY The activity of muscle sympathetic single units was recorded during cardiopulmonary baroreceptor unloading and rhythmic handgrip exercise in young healthy humans. During both stressors, the majority of single units (84% and 61%) exhibited anticipated behavior concordant with the integrated muscle sympathetic response, whereas a smaller proportion (16% and 39%) exhibited paradoxical sympathoinhibition. These results support differential control of postganglionic muscle sympathetic fibers as a characteristic of human sympathetic regulation during mild sympathoexcitatory stress.

Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/differential-control-of-sympathetic-outflow-in-young-humans/ .

A Review of Emotion Recognition Using Physiological Signals

Emotion recognition based on physiological signals has been a hot topic and applied in many areas such as safe driving, health care and social security. In this paper, we present a comprehensive review on physiological signal-based emotion recognition, including emotion models, emotion elicitation methods, the published emotional physiological datasets, features, classifiers, and the whole framework for emotion recognition based on the physiological signals. A summary and comparation among the recent studies has been conducted, which reveals the current existing problems and the future work has been discussed.

Pupillometry reveals the physiological underpinnings of the aversion to holes

An unusual, but common, aversion to images with clusters of holes is known as trypophobia. Recent research suggests that trypophobic reactions are caused by visual spectral properties also present in aversive images of evolutionary threatening animals (e.g., snakes and spiders). However, despite similar spectral properties, it remains unknown whether there is a shared emotional response to holes and threatening animals. Whereas snakes and spiders are known to elicit a fear reaction, associated with the sympathetic nervous system, anecdotal reports from self-described trypophobes suggest reactions more consistent with disgust, which is associated with activation of the parasympathetic nervous system. Here we used pupillometry in a novel attempt to uncover the distinct emotional response associated with a trypophobic response to holes. Across two experiments, images of holes elicited greater constriction compared to images of threatening animals and neutral images. Moreover, this effect held when controlling for level of arousal and accounting for the pupil grating response. This pattern of pupillary response is consistent with involvement of the parasympathetic nervous system and suggests a disgust, not a fear, response to images of holes. Although general aversion may be rooted in shared visual-spectral properties, we propose that the specific emotion is determined by cognitive appraisal of the distinct image content.

Insights into the background of autonomic medicine

Knowledge of the physiology underlying the autonomic nervous system is pivotal for understanding autonomic dysfunction in clinical practice. Autonomic dysfunction may result from primary modifications of the autonomic nervous system or be secondary to a wide range of diseases that cause severe morbidity and mortality. Together with a detailed history and physical examination, laboratory assessment of autonomic function is essential for the analysis of various clinical conditions and the establishment of effective, personalized and precise therapeutic schemes. This review summarizes the main aspects of autonomic medicine that constitute the background of cardiovascular autonomic dysfunction.

Cardiorespiratory Regulation in Migraine. Results in Children and Adolescents and Review of the Literature

To investigate autonomic regulation in juvenile migraine we studied 70 children and adolescents with migraine during the headache-free period and 81 healthy controls by cardiorespiratory function tests. Heart rate variability was analysed with time and frequency domain indices during spontaneous breathing at rest and during metronomic breathing. Changes of heart rate and blood pressure were studied during tilt-table test, active standing, Valsalva manoeuvre and sustained handgrip. We found significant differences in metronomic breathing, tilt-table test and Valsalva manoeuvre. We interpret our findings and results reported in the literature as pointing to a restricted ability of the system to rest, which supports therapies intending to further this ability. In autonomic tests, hyperreactivity in juvenile migraineurs changes to hyporeactivity and passive coping in adults. This might be explained by disturbances of raphe nuclei and the periaqueductal grey. It corresponds to psychological findings in juvenile migraineurs reporting hypersensitivity and repressed aggression and claiming learned helplessness.

Emotional Stress as a Risk for Hypertension in Sub-Saharan Africans: Are We Ignoring the Odds?

Globally most interventions focus on improving lifestyle habits and treatment regimens to combat hypertension as a non-communicable disease (NCD). However, despite these interventions and improved medical treatments, blood pressure (BP) values are still on the rise and poorly controlled in sub-Saharan Africa (SSA). Other factors contributing to hypertension prevalence, such as chronic emotional stress, might provide some insight for future health policy approaches.Currently, Hypertension Society guidelines do not mention emotional stress as a probable cause for hypertension. Recently the 2014 World Global Health reports, suggested that African governments should consider using World Health Organization hypertension data as a proxy indicator for social well-being. However, the possibility that a stressful life and taxing environmental factors might disturb central neural control of BP regulation has largely been ignored in SSA.Linking emotional stress to vascular dysregulation is therefore one way to investigate increased cardiometabolic challenges, neurotransmitter depletion and disturbed hemodynamics. Disruption of stress response pathways and subsequent changes in lifestyle habits as ways of coping with a stressful life, and as probable cause for hypertension prevalence in SSA, may be included in future preventive measures. We will provide an overview on emotional stress and central neural control of BP and will include also implications thereof for clinical practice in SSA cohorts.

Salivary α-Amylase Reactivity to Infant Crying in Maltreating Mothers

Deviant physiological reactivity to infant stimuli has been suggested to underlie maladaptive parenting behavior. Our study involved 44 maltreating and 42 non-maltreating mothers. During a standardized cry paradigm, mothers listened to nine cry sounds of varying pitches. Saliva was collected at baseline, after each cry sound, and after a recovery episode. Salivary α-amylase (sAA) as a marker of autonomic nervous system (ANS) activity was assayed from saliva samples. Maltreating mothers showed lower overall sAA levels and an attenuated reactivity pattern to infant crying as compared to non-maltreating mothers. No effect of type of maltreatment (neglect only vs. neglect and abuse) was found. Furthermore, positive correlations between sAA and heart rate (HR) for non-maltreating mothers differed significantly from non-significant correlations between sAA and HR for maltreating mothers. This suggests anomalous asynchrony between different aspects of the ANS in maltreating mothers. Results indicate a lack of functional autonomic (re)activity as a contributing risk factor to child maltreatment.

Paradoxical muscle sympathetic reflex activation in human heart failure

BACKGROUND

Muscle sympathetic activation in heart failure with reduced ejection fraction (HFrEF) has been attributed, on the basis of multiunit recordings, to attenuated inhibitory feedback from stretch-sensitive cardiopulmonary mechanoreceptors. However, such preparations integrate 2 populations of single units exhibiting directionally opposite firing when atrial pressure is perturbed. We tested the hypothesis that the proportion of single units firing paradoxically when filling pressure increases is augmented in HFrEF.

METHODS AND RESULTS

Muscle sympathetic nerve activity and estimated central venous pressure were recorded during nonhypotensive lower body negative pressure (LBNP; -10 mm Hg) and nonhypertensive positive pressure (LBPP; +10 mm Hg) in 11 treated HFrEF (left ventricular ejection fraction 25 ± 6% [mean ± standard deviation]) patients and 14 similarly aged controls. Single-unit muscle sympathetic nerve activity discharge was termed either anticipated, if firing frequency exhibited classic negative-feedback responses, or paradoxical. LBNP and LBPP had no heart rate, stroke volume, or blood pressure effects (P>0.05). Estimated central venous pressure decreased with LBNP (P<0.05), increased with LBPP (P<0.05), and was consistently higher in HFrEF (P<0.05). During LBNP, the ratio of single units with anticipated and paradoxical discharge was similar in HFrEF (18:7) and controls (27:5), whereas LBPP elicited paradoxical reflex excitation in a greater proportion of HFrEF single units (7:18 versus 24:6; P=0.0001). Consequently, LBPP increased mean single-unit firing frequency (P<0.05) and did not inhibit multiunit muscle sympathetic nerve activity of HFrEF subjects (P<0.05 versus controls). Firing of 12/18 HFrEF (but no control) single units increased during both LBPP and LBNP.

CONCLUSION

These findings provide the first evidence in human HFrEF for an augmented excitatory cardiopulmonary-muscle sympathetic nerve activity reflex response to increased preload, incorporating 2 distinct single-unit populations with differing firing properties.

Microneurographic evidence in healthy middle-aged humans for a sympathoexcitatory reflex activated by atrial pressure

Atrial mechanoreceptors, stimulated by increased pressure or volume, elicit in healthy humans a net sympathoinhibitory response. The co-existence of an atrial reflex eliciting muscle sympathoexcitation has been postulated but undetected by conventional multi-unit muscle sympathetic nerve activity (MSNA). We hypothesized that in response to a selective increase in atrial pressure, single-unit MSNA would reveal a subpopulation of efferent sympathetic neurons with firing patterns opposite to the integrated multi-unit MSNA envelope. Multi- and single-unit MSNA recordings were acquired in eight healthy middle-aged subjects (age, 57 ± 8 years; body mass index, 25 ± 2 kg/m2) submitted to selective decreases or increases in atrial pressure by nonhypotensive lower body negative pressure (LBNP; −10 mmHg) or nonhypertensive lower body positive pressure (LBPP; +10 mmHg), respectively. Single-unit MSNA firing responses were classified as anticipated if spike frequency and incidence increased with LBNP or decreased with LBPP and paradoxical if they decreased with LBNP or increased with LBPP. LBNP decreased (3.2 ± 2.8 to 1.4 ± 3.1 mmHg, P < 0.01) and LBPP increased (3.3 ± 2.7 to 4.9 ± 2.8 mmHg, P < 0.01) estimated central venous pressure without affecting stroke volume, systemic pressure, or resistance. Multi-unit MSNA increased with LBNP (31 ± 17 to 38 ± 19 bursts/min, P < 0.01) and diminished with LBPP (33 ± 15 to 28 ± 15 bursts/min, P < 0.01). Of 21 single-units identified, 76% exhibited firing responses to both LBNP and LBPP concordant with multi-unit MSNA, whereas 24% demonstrated discordant or paradoxical responses. The detection of two subpopulations of single-units within the multi-unit MSNA recording, exhibiting opposite firing characteristics, establishes the first evidence in humans for the existence of an excitatory cardiac-muscle sympathetic reflex activated by increasing atrial pressure.

Sympathetic nervous activity, depressive symptoms, and metabolic syndrome in black Africans: the sympathetic activity and ambulatory blood pressure in Africans study

The aim of this study was to examine the association between sympathetic nervous activity, depressive symptoms, and metabolic syndrome in a sample of black and Caucasian Africans. The sample consisted of healthy men and women: 194 blacks (aged, mean ± SD, 44.1 ± 7.9 years) and 206 Caucasians (aged, mean ± SD, 44.7 ± 10.8 years). Salivary 3-methoxy-phenylglycol (MHPG) concentration, the major metabolite of norepinephrine, was measured during the Stroop mental challenge. Depressive symptoms were assessed from the 9-item Patient Health Questionnaire. Metabolic syndrome (defined as central obesity plus any other two risk factors including raised serum triglycerides, reduced serum high-density lipoprotein- cholesterol, raised blood pressure, and raised fasting plasma glucose) was prevalent in 43.0% and 36.4% of blacks and Caucasians, respectively. In blacks there was, on average, a 16.4% increase in salivary MHPG concentration following mental stress, although no significant response was observed in Caucasians. The salivary MHPG response in blacks was associated with risk of metabolic syndrome (odds ratio [OR] = 1.11, 95% CI, 1.00-1.24) after adjusting for age, sex, and baseline salivary MHPG concentration. This association was mainly driven by the central obesity component of the metabolic syndrome. The salivary MHPG response was also related to moderate-severe depressive symptoms (OR = 1.16, 95% CI, 1.04-1.30), and further adjustment for depressive symptoms attenuated the association between salivary MHPG response and metabolic syndrome (OR = 1.07, 95% CI, 0.96-1.20). These data indicate an association between sympathetic activity, depressive symptoms, and metabolic syndrome in a sample of black Africans.

α-Amylase as a reliable and convenient measure of sympathetic activity: don't start salivating just yet!

Recent years have seen a growing interest in salivary α-amylase (sAA) as a non-invasive marker for sympathetic nervous system (SNS) activity. Saliva offers many advantages as a biomarker fluid and sAA is one of its most plentiful components. sAA is a digestive enzyme that breaks down starch, which provides a simple means of quantification by measuring its enzymatic activity. This commentary will address a number of common misconceptions and methodological issues that surround the use of sAA as a marker of SNS activity and limit its utility in biobehavioral research. The usefulness of sAA as an SNS marker is undermined by the fact that the parasympathetic nerves also play a significant role in sAA release. Local parasympathetic nerves regulate sAA activity via: (1) α-amylase release from glands that are solely or mainly parasympathetically innervated; (2) via synergistic sympathetic-parasympathetic effects on protein secretion (known as 'augmented secretion'); and (3) via effects on salivary flow rate. Regarding methodology, we discuss why it is problematic: (1) to ignore the contribution of salivary flow rate; (2) to use absorbent materials for saliva collection, and; (3) to stimulate saliva secretion by chewing. While these methodological problems can be addressed by using standardized and timed collection of unstimulated saliva, the physiological regulation of sAA secretion presents less resolvable issues. We conclude that at present there is insufficient support for the use and interpretation of sAA activity as a valid and reliable measure of SNS activity.

Autonomic nervous system activity in emotion: a review

Autonomic nervous system (ANS) activity is viewed as a major component of the emotion response in many recent theories of emotion. Positions on the degree of specificity of ANS activation in emotion, however, greatly diverge, ranging from undifferentiated arousal, over acknowledgment of strong response idiosyncrasies, to highly specific predictions of autonomic response patterns for certain emotions. A review of 134 publications that report experimental investigations of emotional effects on peripheral physiological responding in healthy individuals suggests considerable ANS response specificity in emotion when considering subtypes of distinct emotions. The importance of sound terminology of investigated affective states as well as of choice of physiological measures in assessing ANS reactivity is discussed.

Specific coping strategies of Africans during urbanization: Comparing cardiovascular responses and perception of health data

Specific coping mechanisms of Africans during urbanization were compared to and correlated with cardiovascular responses and perception of health data. Subjects included men (N=286) and women (N=360). The COPE questionnaire classified subjects as active (AC) or passive (PC) copers and the General Health Questionnaire measured subjective perception of health. The Finapres recorded blood pressure continuously before and during application of a handgrip test. Analyses adjusting for age, body mass index and resting cardiovascular data revealed that AC rural subjects showed predominantly cardiac responses and PC rural subjects predominantly vascular responses. All urbanized African men and women showed higher resting blood pressure, vascular responsiveness and hypertension prevalences than their rural counterparts. All rural AC subjects, especially women, and all urban PC subjects, especially men, reported a poorer perception of health. In conclusion, subjects with a PC style showed a predominantly vascular response in rural and urban areas whereas subjects with an AC style seem to shift from a predominant cardiac output response to a predominant vascular resistance response when moving from a rural to an urban area.

A quantitative approach to recording peristaltic activity from segments of rat small intestine in vivo

We have developed methods that allow correlation of propulsive reflexes of the intestine with measurements of intraluminal pressure, fluid movement and spatio-temporal maps of intestinal wall movements for the first time in vivo. A segment of jejunum was cannulated and set up in a Trendelenburg recording system while remaining connected to the vascular and nerve supply of the anaesthetized rat. The resting intraluminal pressure in intact intestine was 2-4 mmHg. Hydrostatic pressures of 2, 4, 8 and 16 mmHg were imposed. At a baseline pressure of 4 mmHg, propulsive waves generated pressures of 9 +/- 1 mmHg, that progressed oral to anal at 2-5 mm s(-1). Individual propulsive waves propelled 0.8 +/- 0.4 mL of fluid. The frequency of propulsive waves increased with pressure, but peristaltic efficiency (mL per contraction) decreased with pressure increase between 4 and 16 mmHg. Atropine, as a bolus, transiently blocked peristalsis, but caused maintained block when infused. Hexamethonium blocked propulsive contractions. Inhibition of nitrergic transmission converted regular peristalsis to non-propulsive contractions. These studies demonstrate the utility of an adapted Trendelenburg method for quantitative investigation of motility and pharmacology of enteric reflexes in vivo.

A thermodynamic model of the sympathetic and parasympathetic nervous systems

In light of the nonequilibrium thermodynamics by I. Prigogine, the autonomic nervous system as a whole may be viewed as a dissipative structure progressively assembled in the course of evolution, plastically and rhythmically interfaced between forebrain, internal and external environments, to regulate energy, matter and information exchanges. In the present paper, this hypothesis is further pursued to verify whether the two main divisions of the autonomic nervous system, the sympathetic and parasympathetic systems, may support different types of exchange with the external environment. Previous data from hypothalamic stimulation experiments, studies of locus coeruleus function and available data on behavioral functional organization indicate that (1) tight engagement with the external environment, (2) high level of energy mobilization and utilization and (3) information mainly related to exteroceptive sensory stimulation characterize a behavioral prevalence of sympathoadrenal activation. On the other hand, (1) disengagement from the external environment, (2) low levels of internal energy and (3) dominance of proprioceptive information characterize a behavioral prevalence of vagal tone. Behavioral matter exchanges such as feeding, drinking, micturition and defecation are equally absent at the extreme of sympathoadrenal and vagally driven behaviors. The autonomic nervous system as a whole is genetically determined, but the sympathoadrenal system has been mainly designed to organize the visceral apparatus for an action to be performed by the biological system in the external environment and to deal with the novelty of task and of the environment, while the functional role of the parasympathetic is to prepare the visceral apparatus for an action to be performed by the biological system on itself, for recovery and self-protection (homeostasis), and is reinforced by repetition of phylo- and ontogenetically determined patterns. The available clinical data further support this interpretation indicating that an increased sympathetic and a decreased vagal tone may represent a consistent risk factor for cardiovascular diseases.

The visceral nervous system and its environments

Starting from the observation of the relationships of the biological system with its environments and of the genetically determined neuronal properties of plasticity and rhythmicity, it is possible to propose a new hypothesis about the functional role and organization of the visceral nervous system based on the physical model of the Dissipative Structure by I. Prigogine. The similarily between the visceral nervous system function and this model is supported by the following observations: (1) The visceral nervous system is a complex system, composed of many interacting units, which works away from thermodynamic equilibrium; (2) the functional organization of the nervous system is strongly dependent on internal and external environmental stimuli; (3) it is characterized by the presence of rhythms and periodic behaviors and (4) the internal order of the system is maintained in the continuous interplay between function, structure and fluctuations. On the basis of the present hypothesis, a few general principles can be formulated: (1) the higher brain centers, the fluid matrix and the external world, are the visceral nervous system natural environments; (2) with which it is plastically interfaced as a thermodynamic dissipative structure; (3) its main functional role is to regulate, distribute and maintain ordered exchanges of matter, energy and information between these environments. The present is a general interpretation of the operations of the visceral nervous system as a whole. In the frame of this interpretation the hypotheses so far formulated, including the homeostatic theory, can be viewed as the description of discrete and complementary aspects of the visceral nervous system functions.

The relationship between propagated contractions and pseudoaffective changes in blood pressure in response to intestinal distension

We investigated the relationship between changes in small intestinal motility and changes in blood pressure and heart rate in response to intestinal distension. Rats were maintained under stable anaesthesia with alpha-chloralose, and jejunal motility, blood pressure and heart rate were recorded. Pressure changes during propagated contractions of the circular muscle were recorded in the jejunum when the intraluminal pressure was maintained at 10 mmHg. Raising the pressure in 10 mmHg increments from 10 mmHg to 40 mmHg increased the frequency of propagated contractions from 0.30 +/- 0.06 min-1 (mean +/- SEM) to 1.29 +/- 0.09 per min. In contrast, amplitudes of contractions above baseline pressure decreased from 19.5 +/- 0.6 mmHg to 7.8 +/- 0.5 mmHg. Simultaneously, blood pressure and heart rate were both increased. Pretreatment of rats with capsaicin, or severing the mesenteric nerves acutely, prevented these cardiovascular responses, but did not influence the changes in propagated activity caused by distension. Propagated contractions were blocked by hexamethonium (10 mg kg-1, intravenously [i.v.]) and by local application of 2% lidocaine, but propulsion was unchanged by hyoscine (1 mg kg-1, i.v.). Phentolamine (1 mg kg-1, i.v.) increased the frequency of propagated contractions. The methods described in this work allow the effects of drugs on intrinsic intestinal reflexes to be distinguished from their effects on extra-intestinal, pseudoaffective reflexes. In addition, unlike other experiments using anaesthetized rats, blood pressure increased in response to distension, as it does in mammals that are not anaesthetized. The experiments demonstrate that the neural pathways for propagated contractions that rely on intrinsic nerve circuits, including intrinsic primary afferent neurones, and the neural pathways for extrinsic reflexes that signal pain or discomfort in the intestine, which involve capsaicin-sensitive spinal afferent neurones, are independent.