Asymmetric sympathetic output: The dorsomedial hypothalamus as a potential link between emotional stress and cardiac arrhythmias

Emotional and behavioral problems accelerate hypothalamic development from childhood to adolescence: Findings from a longitudinal cohort study

BACKGROUND

Despite the pivotal role of the hypothalamus in regulating various physiological processes, our understanding of its developmental trajectory and subregional organization during childhood and adolescence remains limited, as well as how emotional and behavioral problems can impact hypothalamic development, potentially leading to neurodevelopmental disorders.

METHODS

This population-based longitudinal cohort study utilized data from a representative sample of 702 children, who were followed two to five times. Emotional and behavioral problems were assessed using the Strengths and Difficulties Questionnaire (SDQ). Linear mixed models were employed to delineate developmental trajectories and behavioral regulation.

RESULTS

Using an automated segmentation technique, we quantified the volumes and asymmetries of the hypothalamus and its subregions in a large longitudinal sample of 702 subjects aged 6-15 years with 1371 MRI scans, and mapped their developmental trajectories. Our findings indicate that while the anterior and posterior regions of the hypothalamus exhibit a tendency toward decline, the tubular region demonstrates a linear increase which is influenced by lateralization, sex, and intracranial volume. Furthermore, emotional and behavioral problems - particularly emotional symptoms and peer relationship problems - accelerate development in superior tubular and anterior-superior regions.

CONCLUSIONS

In this study, we initially delineated the developmental trajectories of the hypothalamus and its subregions from childhood to adolescence based on a longitudinal cohort study. Our findings revealed that the development of hypothalamus followed the pattern of "lateral early to medial late, and dorsomedial early to ventromedial late", and the emotional and behavioral problems accelerate hypothalamic development. This study provides preliminary evidence regarding the impact of emotional and behavioral problems on the dynamic development of the hypothalamus, offering a crucial foundation for future prevention and intervention strategies targeting cognitive and emotional behavioral problems.

Clinical features of autonomic dysfunction in children with anti-N-methyl-D aspartic receptor encephalitis

BACKGROUND

Anti-N-methyl-D-aspartic receptor encephalitis (Anti-NMDAR encephalitis) is the most prevalent form of autoimmune encephalitis in pediatric patients. Autonomic dysfunction is a frequent symptom of Anti-NMDAR encephalitis, yet it often goes unnoticed by pediatricians. Studies have indicated that pediatric patients with autonomic dysfunction exhibit a poorer prognosis compared to those without. To date, research on autonomic dysfunction in encephalitis has predominantly focused on adults, with no studies conducted on pediatric populations. This analysis examines the clinical features of pediatric patients with Anti-NMDAR encephalitis complicated by autonomic dysfunction.

METHODS

We performed a retrospective analysis of patients diagnosed with Anti-NMDAR encephalitis at the Department of Neurology, Children's Hospital affiliated to the Capital Institute of Pediatrics, from June 2017 to June 2023. Patients were categorized based on the presence or absence of autonomic dysfunction during their illness. We summarized and compared the clinical features of children with autonomic dysfunction and analyzed the risk factors for its development in pediatric Anti-NMDAR encephalitis patients.

RESULTS

A total of 56 children were included in this study. Twenty-two (39.3%) exhibited autonomic nervous dysfunction. The most prevalent symptom of autonomic dysfunction was cardiovascular autonomic dysfunction(21/22, 95%),with the specific manifestations being sinus tachycardia (8 cases), ventricular premature beats (2 cases), atrioventricular block (2 cases), atrial premature beats (3 cases), and sinus bradycardia (4 cases),hypertension(1 case) and cardiac arrest(1 case). Other symptoms included gland secretion dysfunction (19/22, 86%),ventilate dysfunction(3/22,14%), thermoregulatory dysfunction (3/22,14%), bladder dysfunction(2/22,9%). Compared to the group without autonomic dysfunction, the group with dysfunction showed significantly higher rates of prodrome infection, tumor complications (all ovarian teratoma), consciousness disturbance, elevated cerebrospinal fluid protein, initiation of second-line and long-term immunotherapy, length of hospital stay, and hospitalization costs (P < 0.05).

CONCLUSION

Among pediatric patients with Anti-NMDAR encephalitis, cardiovascular autonomic dysfunction is the most common form of autonomic dysfunction. Those with autonomic dysfunction have a worse prognosis and longer hospital stays. Active initiation of second-line and long-term immunotherapy is recommended.

The insular cortex, autonomic asymmetry and cardiovascular control: looking at the right side of stroke

PURPOSE

Evidence from animal and human studies demonstrates that cortical regions play a key role in autonomic modulation with a differential role for some brain regions located in the left and right brain hemispheres. Known as autonomic asymmetry, this phenomenon has been demonstrated by clinical observations, by experimental models, and currently by combined neuroimaging and direct recordings of sympathetic nerve activity. Previous studies report peculiar autonomic-mediated cardiovascular alterations following unilateral damage to the left or right insula, a multifunctional key cortical region involved in emotional processing linked to autonomic cardiovascular control and featuring asymmetric characteristics.

METHODS

Based on clinical studies reporting specific damage to the insular cortex, this review aims to provide an overview of the prognostic significance of unilateral (left or right hemisphere) post-insular stroke cardiac alterations. In addition, we review experimental data aiming to unravel the central mechanisms involved in post-insular stroke cardiovascular complications.

RESULTS AND CONCLUSION

Current clinical and experimental data suggest that stroke of the right insula  can present a worse cardiovascular prognosis.

Hypothalamic Regulation of Cardiorespiratory Functions: Insights into the Dorsomedial and Perifornical Pathways

The dorsomedial hypothalamus nucleus (DMH) plays a pivotal role in the orchestration of sympathetic nervous system activities. Through its projections to the brainstem and pontomedullary nuclei, it controls heart rate, contractility, blood pressure, and respiratory activity, such as timing and volumes. The DMH integrates inputs from higher brain centers and processes these signals in order to modulate autonomic outflow accordingly. It has been demonstrated to be of particular significance in the context of stress responses, where it orchestrates the physiological adaptations that are necessary for all adaptative responses. The perifornical region (PeF), which is closely associated with the DMH, also makes a contribution to autonomic regulation. The involvement of the PeF region in autonomic control is evidenced by its function in coordinating the autonomic and endocrine responses to stress, frequently in conjunction with the DMH. The DMH and the PeF do not function in an isolated manner; rather, they are components of a comprehensive hypothalamic network that integrates several autonomic responses. This neural network could serve as a target for developing therapeutic strategies in cardiovascular diseases.

The proarrhythmogenic role of autonomics and emerging neuromodulation approaches to prevent sudden death in cardiac ion channelopathies

Ventricular arrhythmias in cardiac channelopathies are linked to autonomic triggers, which are sub-optimally targeted in current management strategies. Improved molecular understanding of cardiac channelopathies and cellular autonomic signalling could refine autonomic therapies to target the specific signalling pathways relevant to the specific aetiologies as well as the central nervous system centres involved in the cardiac autonomic regulation. This review summarizes key anatomical and physiological aspects of the cardiac autonomic nervous system and its impact on ventricular arrhythmias in primary inherited arrhythmia syndromes. Proarrhythmogenic autonomic effects and potential therapeutic targets in defined conditions including the Brugada syndrome, early repolarization syndrome, long QT syndrome, and catecholaminergic polymorphic ventricular tachycardia will be examined. Pharmacological and interventional neuromodulation options for these cardiac channelopathies are discussed. Promising new targets for cardiac neuromodulation include inhibitory and excitatory G-protein coupled receptors, neuropeptides, chemorepellents/attractants as well as the vagal and sympathetic nuclei in the central nervous system. Novel therapeutic strategies utilizing invasive and non-invasive deep brain/brain stem stimulation as well as the rapidly growing field of chemo-, opto-, or sonogenetics allowing cell-specific targeting to reduce ventricular arrhythmias are presented.

Central stress pathways in the development of cardiovascular disease

PURPOSE

Mental stress is of essential consideration when assessing cardiovascular pathophysiology in all patient populations. Substantial evidence indicates associations among stress, cardiovascular disease and aberrant brain-body communication. However, our understanding of the flow of stress information in humans, is limited, despite the crucial insights this area may offer into future therapeutic targets for clinical intervention.

METHODS

Key terms including mental stress, cardiovascular disease and central control, were searched in PubMed, ScienceDirect and Scopus databases. Articles indicative of heart rate and blood pressure regulation, or central control of cardiovascular disease through direct neural innervation of the cardiac, splanchnic and vascular regions were included. Focus on human neuroimaging research and the flow of stress information is described, before brain-body connectivity, via pre-motor brainstem intermediates is discussed. Lastly, we review current understandings of pathophysiological stress and cardiovascular disease aetiology.

RESULTS

Structural and functional changes to corticolimbic circuitry encode stress information, integrated by the hypothalamus and amygdala. Pre-autonomic brain-body relays to brainstem and spinal cord nuclei establish dysautonomia and lead to alterations in baroreflex functioning, firing of the sympathetic fibres, cellular reuptake of norepinephrine and withdrawal of the parasympathetic reflex. The combined result is profoundly adrenergic and increases the likelihood of cardiac myopathy, arrhythmogenesis, coronary ischaemia, hypertension and the overall risk of future sudden stress-induced heart failure.

CONCLUSIONS

There is undeniable support that mental stress contributes to the development of cardiovascular disease. The emerging accumulation of large-scale multimodal neuroimaging data analytics to assess this relationship promises exciting novel therapeutic targets for future cardiovascular disease detection and prevention.

Electrical stimulation of the ventromedial prefrontal cortex modulates muscle sympathetic nerve activity and blood pressure

We recently showed that transcranial alternating current stimulation of the dorsolateral prefrontal cortex modulates spontaneous bursts of muscle sympathetic nerve activity, heart rate, and blood pressure (Sesa-Ashton G, Wong R, McCarthy B, Datta S, Henderson LA, Dawood T, Macefield VG. Stimulation of the dorsolateral prefrontal cortex modulates muscle sympathetic nerve activity and blood pressure in humans. Cereb Cortex Comm. 2022:3:2tgac017.). Stimulation was delivered between scalp electrodes placed over the nasion and electroencephalogram (EEG) electrode site F3 (left dorsolateral prefrontal cortex) or F4 (right dorsolateral prefrontal cortex), and therefore the current passed within the anatomical locations underlying the left and right ventromedial prefrontal cortices. Accordingly, we tested the hypothesis that stimulation of the left and right ventromedial prefrontal cortices would also modulate muscle sympathetic nerve activity, although we predicted that this would be weaker than that seen during dorsolateral prefrontal cortex stimulation. We further tested whether stimulation of the right ventromedial prefrontal cortices would cause greater modulation of muscle sympathetic nerve activity, than stimulation of the left ventromedial prefrontal cortices. In 11 individuals, muscle sympathetic nerve activity was recorded via microelectrodes inserted into the right common peroneal nerve, together with continuous blood pressure, electrocardiogram, and respiration. Stimulation was achieved using transcranial alternating current stimulation, +2 to -2 mA, 0.08 Hz, 100 cycles, applied between electrodes placed over the nasion, and EEG electrode site FP1, (left ventromedial prefrontal cortices) or FP2 (right ventromedial prefrontal cortices); for comparison, stimulation was also applied over F4 (right dorsolateral prefrontal cortex). Stimulation of all three cortical sites caused partial entrainment of muscle sympathetic nerve activity to the sinusoidal stimulation, together with modulation of blood pressure and heart rate. We found a significant fall in mean blood pressure of ~6 mmHg (P = 0.039) during stimulation of the left ventromedial prefrontal cortices, as compared with stimulation of the right. We have shown, for the first time, that transcranial alternating current stimulation of the ventromedial prefrontal cortices modulates muscle sympathetic nerve activity and blood pressure in awake humans at rest. However, it is unclear if this modulation occurred through the same brain pathways activated during transcranial alternating current stimulation of the dorsolateral prefrontal cortex.

Interleukin 6 (IL-6) Regulates GABAA Receptors in the Dorsomedial Hypothalamus Nucleus (DMH) through Activation of the JAK/STAT Pathway to Affect Heart Rate Variability in Stressed Rats

The dorsomedial hypothalamus nucleus (DMH) is an important component of the autonomic nervous system and plays a critical role in regulating the sympathetic outputs of the heart. Stress alters the neuronal activity of the DMH, affecting sympathetic outputs and triggering heart rate variability. However, the specific molecular mechanisms behind stress leading to abnormal DMH neuronal activity have still not been fully elucidated. Therefore, in the present study, we successfully constructed a stressed rat model and used it to investigate the potential molecular mechanisms by which IL-6 regulates GABAA receptors in the DMH through activation of the JAK/STAT pathway and thus affects heart rate variability in rats. By detecting the c-Fos expression of neurons in the DMH and electrocardiogram (ECG) changes in rats, we clarified the relationship between abnormal DMH neuronal activity and heart rate variability in stressed rats. Then, using ELISA, immunohistochemical staining, Western blotting, RT-qPCR, and RNAscope, we further explored the correlation between the IL-6/JAK/STAT signaling pathway and GABAA receptors. The data showed that an increase in IL-6 induced by stress inhibited GABAA receptors in DMH neurons by activating the JAK/STAT signaling pathway, while specific inhibition of the JAK/STAT signaling pathway using AG490 obviously reduced DMH neuronal activity and improved heart rate variability in rats. These findings suggest that IL-6 regulates the expression of GABAA receptors via the activation of the JAK/STAT pathway in the DMH, which may be an important cause of heart rate variability in stressed rats.

Neurogenic Background for Emotional Stress-Associated Hypertension

PURPOSE OF REVIEW

The response to natural stressors involves both cardiac stimulation and vascular changes, primarily triggered by increases in sympathetic activity. These effects lead to immediate flow redistribution that provides metabolic support to priority target organs combined with other key physiological responses and cognitive strategies, against stressor challenges. This extremely well-orchestrated response that was developed over millions of years of evolution is presently being challenged, over a short period of time. In this short review, we discuss the neurogenic background for the origin of emotional stress-induced hypertension, focusing on sympathetic pathways from related findings in humans and animals.

RECENT FINDINGS

The urban environment offers a variety of psychological stressors. Real or anticipatory, emotional stressors may increase baseline sympathetic activity. From routine day-to-day traffic stress to job-related anxiety, chronic or abnormal increases in sympathetic activity caused by emotional stressors can lead to cardiovascular events, including cardiac arrhythmias, increases in blood pressure and even sudden death. Among the various alterations proposed, chronic stress could modify neuroglial circuits or compromise antioxidant systems that may alter the responsiveness of neurons to stressful stimuli. These phenomena lead to increases in sympathetic activity, hypertension and consequent cardiovascular diseases. The link between anxiety, emotional stress, and hypertension may result from an altered neuronal firing rate in central pathways controlling sympathetic activity. The participation of neuroglial and oxidative mechanisms in altered neuronal function is primarily involved in enhanced sympathetic outflow. The significance of the insular cortex-dorsomedial hypothalamic pathway in the evolution of enhanced overall sympathetic outflow is discussed.

[Manual spinal therapy techniques to stimulate the autonomic nervous system: a scoping review]

BACKGROUND

Physical interventions or manual therapeutic techniques (MTTe) such as mobilisation, manipulation or soft tissue techniques not only have an influence on the target tissue with improvement of metabolism or reduction of hypertonic muscles. They are also used for balance regulation in central nervous changes of the autonomic nervous system (ANS). To date, there is a lack of empirical evidence on impact mechanisms and target locations of MTTe on the ANS. This scoping review aims to provide an overview of the evidence on the application of MTTe at diverse levels of the spine with a view to the ANS.

METHOD

A systematic literature search was conducted on CENTRAL, Google Scholar, Osteopathic Research Web, PEDro and PubMed. The scope and content of the literature were documented. The results of the included and referenced studies were summarised in a narrative approach with the focus being on the most significant clinical aspects.

RESULTS

MTTe was described as manipulations, mobilisations, myofascial techniques and cervical traction. In 27 out of 35 studies, therapeutic treatments were carried out on healthy volunteers. Ten studies analysed immediate effects in patients, while two studies were designed as longitudinal studies in patients with hypertension. Over a period of four to eight weeks, the frequency of intervention was between one and three MTTe sessions a week.

CONCLUSION

The study results proved to be heterogeneous. For this reason, it is not possible to draw definitive, explicit and generally valid statements regarding the type and intensity as well as the segmental level at which MTTe should be applied in order to trigger specific positive ANS response mechanisms. Consequently, longitudinal studies with follow-up are recommended for future studies. In addition, comprehensive effects of MTTe should be evaluated in groups of patients with different characteristics.

Regional hypothalamic, amygdala, and midbrain periaqueductal gray matter recruitment during acute pain in awake humans: A 7-Tesla functional magnetic resonance imaging study

Over the past two decades, magnetic resonance imaging (MRI) studies have explored brain activation patterns during acute noxious stimuli. Whilst these human investigations have detailed changes in primarily cortical regions, they have generally not explored discrete changes within small brain areas that are critical in driving behavioural, autonomic, and endocrine responses to pain, such as within subregions of the hypothalamus, amygdala, and midbrain periaqueductal gray matter (PAG). Ultra-high field (7-Tesla) MRI provides enough signal-to-noise at high spatial resolutions to investigate activation patterns within these small brain regions during acute noxious stimulation in awake humans. In this study we used 7T functional MRI to concentrate on hypothalamic, amygdala, and PAG signal changes during acute noxious orofacial stimuli. Noxious heat stimuli were applied in three separate fMRI scans to three adjacent sites on the face in 16 healthy control participants (7 females). Images were processed using SPM12 and custom software, and blood oxygen level dependent signal changes within the hypothalamus, amygdala, and PAG assessed. We identified altered activity within eight unique subregions of the hypothalamus, four unique subregions of the amygdala, and a single region in the lateral PAG. Specifically, within the hypothalamus and amygdala, signal intensity largely decreased during noxious stimulation, and increased in the lateral PAG. Furthermore, we found sex-related differences in discrete regions of the hypothalamus and amygdala. This study reveals that the activity of discrete nuclei during acute noxious thermal stimulation in awake humans.

Altered cardiac structure and function is related to seizure frequency in a rat model of chronic acquired temporal lobe epilepsy

OBJECTIVE

This study aimed to prospectively examine cardiac structure and function in the kainic acid-induced post-status epilepticus (post-KA SE) model of chronic acquired temporal lobe epilepsy (TLE), specifically to examine for changes between the pre-epileptic, early epileptogenesis and the chronic epilepsy stages. We also aimed to examine whether any changes related to the seizure frequency in individual animals.

METHODS

Four hours of SE was induced in 9 male Wistar rats at 10 weeks of age, with 8 saline treated matched control rats. Echocardiography was performed prior to the induction of SE, two- and 10-weeks post-SE. Two weeks of continuous video-EEG and simultaneous ECG recordings were acquired for two weeks from 11 weeks post-KA SE. The video-EEG recordings were analyzed blindly to quantify the number and severity of spontaneous seizures, and the ECG recordings analyzed for measures of heart rate variability (HRV). PicroSirius red histology was performed to assess cardiac fibrosis, and intracellular Ca²⁺ levels and cell contractility were measured by microfluorimetry.

RESULTS

All 9 post-KA SE rats were demonstrated to have spontaneous recurrent seizures on the two-week video-EEG recording acquired from 11 weeks SE (seizure frequency ranging from 0.3 to 10.6 seizures/day with the seizure durations from 11 to 62 s), and none of the 8 control rats. Left ventricular wall thickness was thinner, left ventricular internal dimension was shorter, and ejection fraction was significantly decreased in chronically epileptic rats, and was negatively correlated to seizure frequency in individual rats. Diastolic dysfunction was evident in chronically epileptic rats by a decrease in mitral valve deceleration time and an increase in E/E` ratio. Measures of HRV were reduced in the chronically epileptic rats, indicating abnormalities of cardiac autonomic function. Cardiac fibrosis was significantly increased in epileptic rats, positively correlated to seizure frequency, and negatively correlated to ejection fraction. The cardiac fibrosis was not a consequence of direct effect of KA toxicity, as it was not seen in the 6/10 rats from separate cohort that received similar doses of KA but did not go into SE. Cardiomyocyte length, width, volume, and rate of cell lengthening and shortening were significantly reduced in epileptic rats.

SIGNIFICANCE

The results from this study demonstrate that chronic epilepsy in the post-KA SE rat model of TLE is associated with a progressive deterioration in cardiac structure and function, with a restrictive cardiomyopathy associated with myocardial fibrosis. Positive correlations between seizure frequency and the severity of the cardiac changes were identified. These results provide new insights into the pathophysiology of cardiac disease in chronic epilepsy, and may have relevance for the heterogeneous mechanisms that place these people at risk of sudden unexplained death.

Stress and central autonomic network

The central autonomic network (CAN) plays a critical role in the stress response, which is triggered by challenges on the homeostasis (physiological stressors) or unpleasant social or environmental situations. This review focuses on the role of areas of the CAN including the insular and anterior cingulate cortices, extended amygdala, hypothalamus, periaqueductal gray and locus coeruleus in the stress response. These areas are interconnected and affect sympathetic or parasympathetic output via their influence on premotor or preganglionic autonomic neurons in the lower brainstem and spinal cord. The insula integrates multiple inputs to create a sense of the physiological state of the body, whereas the anterior cingulate initiates predictive visceromotor commands. The amygdala and bed nucleus of the stria terminalis provide automatic emotional tagging and trigger automatic survival responses to threat via their outputs to the hypothalamus, periaqueductal gray, and lower brainstem. Several regions of the hypothalamus, including the paraventricular nucleus, dorsomedial nucleus and lateral hypothalamic area participate in different patterns of stress response according to the type of stimulus and projections to premotor and preganglionic autonomic neurons. The periaqueductal gray initiates different patterns of autonomic, pain modulatory, and motor responses, including the "fight or flight" or "playing dead" responses. The locus coeruleus promotes emotional learning in the amygdala associated with states of anxiety. Neurons of the C1 area of the rostral ventrolateral medulla elicit sympathoexcitatory responses to internal stressors such as hypoxia and inflammation. The ventromedial medulla, including the nucleus raphe pallidus, initiates sympathoexcitatory responses to social and other external stressors.

Tachycardia evoked from insular stroke in rats is dependent on glutamatergic neurotransmission in the dorsomedial hypothalamus

BACKGROUND AND PURPOSE

Damage to the insula results in cardiovascular complications. In rats, activation of N-methyl-d-aspartate receptors (NMDARs) in the intermediate region of the posterior insular cortex (iIC) results in sympathoexcitation, tachycardia and arterial pressure increases. Similarly, focal experimental hemorrhage at the iIC results in a marked sympathetic-mediated increase in baseline heart rate. The dorsomedial hypothalamic region (DMH) is critical for the integration of sympathetic-mediated tachycardic responses. Here, whether responses evoked from the iIC are dependent on a synaptic relay in the DMH was evaluated.

METHODS

Wistar rats were prepared for injections into the iIC and DMH. Anatomical (tracing combined with immunofluorescence) and functional experiments (cardiovascular and sympathetic recordings) were performed.

RESULTS

The iIC sends dense projections to the DMH. Approximately 50% of iIC neurons projecting to the DMH express NMDARs, NR1 subunit. Blockade of glutamatergic receptors in the DMH abolishes the cardiovascular and autonomic responses evoked by the activation of NMDARs in the iIC (change in mean arterial pressure 7 ± 1 vs. 1 ± 1 mmHg after DMH blockade; change in heart rate 28 ± 3 vs. 0 ± 3 bpm after DMH blockade; change in renal sympathetic nerve activity 23% ± 1% vs. -1% ± 4% after DMH blockade). Experimental hemorrhage at the iIC resulted in a marked tachycardia (change 89 ± 14 bpm) that was attenuated by 65% ± 5% (p = 0.0009) after glutamatergic blockade at the DMH.

CONCLUSIONS

The iIC-induced tachycardia is largely dependent upon a glutamatergic relay in the DMH. Our study reveals the presence of an excitatory glutamatergic pathway from the iIC to the DMH that may be involved in the cardiovascular alterations observed after insular stroke.

Centrally acting antihypertensives change the psychogenic cardiovascular reactivity

Clonidine (CL) and Rilmenidine (RI) are among the most frequently prescribed centrally acting antihypertensives. Here, we compared CL and RI effects on psychogenic cardiovascular reactivity to sonant, luminous, motosensory, and vibrotactile stimuli during neurogenic hypertension. The femoral artery and vein of Wistar (WT - normotensive) and spontaneously hypertensive rats (SHR) were catheterized before (24 h interval) i.p. injection of vehicle (NaCl 0.9%, control - CT group), CL (10 µg/kg), or RI (10 µg/kg) and acute exposure to luminous (5000 lm), sonant (75 dB sudden tap), motor (180° cage twist), and air-jet (10 L/min - restraint and vibrotactile). Findings showed that: (i) CL or RI reduced the arterial pressure of SHR, without affecting basal heart rate in WT and SHR; (ii) different stimuli evoked pressor and tachycardic responses; (iii) CL and RI reduced pressor response to sound; (iv) CL or RI reduced pressor responses to luminous stimulus without a change in peak tachycardia in SHR; (v) cage twist increased blood pressure in SHR, which was attenuated by CL or RI; (vi) air-jet increased pressure and heart rate; (vii) CL or RI attenuated the pressor responses to air-jet in SHR while RI reduced the chronotropic reactivity in both strains. Altogether, both antihypertensives relieved the psychogenic cardiovascular responses to different stimuli. The RI elicited higher cardioprotective effects through a reduction in air-jet-induced tachycardia.

The role of the dorsomedial and ventromedial hypothalamus in regulating behaviorally coupled and resting autonomic drive

Nearly a century ago it was reported that stimulation of the hypothalamus could evoke profound behavioral state changes coupled with altered autonomic function. Since these initial observations, further studies in animals have revealed that two hypothalamic regions-the dorsomedial and ventromedial hypothalamic nuclei-are critical for numerous behaviors, including those in response to psychological stressors. These behaviors are coupled with changes in autonomic functions, such as altered blood pressure, heart rate, sympathetic nerve activity, resetting of the baroreflex and changes in pituitary function. There is also growing evidence that these two hypothalamic regions play a critical role in thermogenesis, and suggestions they could also be responsible for the hypertension associated with obesity. The aim of this chapter is to review the anatomy, projection patterns, and function of the dorsomedial and ventromedial hypothalamus with a particular focus on their role in autonomic regulation. While most of what is known about these two hypothalamic regions is derived from laboratory animal experiments, recent human studies will also be explored. Finally, we will describe recent human brain imaging studies that provide evidence of a role for these hypothalamic regions in setting resting sympathetic drive and their potential role in conditions such as hypertension.

Physiology and Pathophysiology of the Autonomic Nervous System

PURPOSE OF THE REVIEW

This article reviews the anatomic, functional, and neurochemical organization of the sympathetic and parasympathetic outputs; the effects on target organs; the central mechanisms controlling autonomic function; and the pathophysiologic basis for core symptoms of autonomic failure.

RECENT FINDINGS

Functional neuroimaging studies have elucidated the areas involved in central control of autonomic function in humans. Optogenetic and other novel approaches in animal experiments have provided new insights into the role of these areas in autonomic control across behavioral states, including stress and the sleep-wake cycle.

SUMMARY

Control of the function of the sympathetic, parasympathetic, and enteric nervous system functions depends on complex interactions at all levels of the neuraxis. Peripheral sympathetic outputs are critical for maintenance of blood pressure, thermoregulation, and response to stress. Parasympathetic reflexes control lacrimation, salivation, pupil response to light, beat-to-beat control of the heart rate, gastrointestinal motility, micturition, and erectile function. The insular cortex, anterior and midcingulate cortex, and amygdala generate autonomic responses to behaviorally relevant stimuli. Several nuclei of the hypothalamus generate coordinated patterns of autonomic responses to internal or social stressors. Several brainstem nuclei participate in integrated control of autonomic function in relationship to respiration and the sleep-wake cycle. Disorders affecting the central or peripheral autonomic pathways, or both, manifest with autonomic failure (including orthostatic hypotension, anhidrosis, gastrointestinal dysmotility, and neurogenic bladder or erectile dysfunction) or autonomic hyperactivity, primary hypertension, tachycardia, and hyperhidrosis.

Ventromedial medullary pathway mediating cardiac responses evoked from periaqueductal gray

Periaqueductal gray (PAG) is a midbrain region that projects to areas controlling behavioral and autonomic outputs and is involved in the behavioral and physiological components of defense reactions. Since Raphe Pallidus (RPa) is a medial medullary region comprising sympathetic premotor neurons governing heart function, it is worth considering the PAG-RPa path. We assessed: i) whether PAG projects to RPa; ii) the amplitude of cardiac responses evoked from PAG; iii) whether cardiovascular responses evoked from PAG rely on RPa. Experiments conducted in Wistar rats (±300 g) were approved by Ethics Committee CEUA-UFG (092/18). Firstly, (n = 3), monosynaptic retrograde tracer Retrobeads was injected into RPa; PAG slices were analyzed. Other two groups (n = 6 each) were anesthetized with urethane (1.4 g/kg) and chloralose (120 mg/kg) and underwent craniotomy, tracheostomy, catheterization of femoral artery and vein and of cardiac left ventricle. In one group, we injected the GABA_A receptor antagonist, bicuculline methiodide (BMI - 40 pmol/100 nL) into lateral/dorsolateral PAG. Another group was injected (100 nL) with the GABA_A receptor agonist muscimol (20 mM) into RPa, 20 min before BMI into PAG. The results were: i) retrogradely labelled neurons were found in PAG; ii) PAG activation by BMI caused positive chronotropism and inotropism, which were accompanied by afterload increases; iii) RPa inhibition with Muscimol reduced heart rate, arterial and ventricular pressures; iv) the subsequent PAG activation still increased arterial pressure, cardiac chronotropy and inotropy, but these responses were significantly attenuated. In conclusion, PAG activation increases cardiac chronotropy and inotropy, and these responses seem to rely on a direct pathway reaching ventromedial medullary RPa neurons.

Autonomic and cardiovascular consequences resulting from experimental hemorrhagic stroke in the left or right intermediate insular cortex in rats

Damage to the insular cortex (IC) results in serious cardiovascular consequences and evidence indicates that the characteristics are lateralized. However, a study comparing the effects of focal experimental hemorrhage between IC sides was never performed. We compared the cardiovascular, autonomic and cardiac changes produced by focal experimental hemorrhage (ICH) into the left (L) or right (R) IC. Wistar rats were submitted to microinjection of autologous blood (ICH) or saline (n = 6 each side/group) into the R or L IC. Blood pressure (BP), heart rate (HR) and renal sympathetic activity (RSNA) were recorded. Measurements of calcium transient and sarcoplasmic Ca²⁺ ATPase expression in cardiomyocytes were performed. ICH increased baseline HR (Δ:L-ICH 452 ± 13 vs saline 407 ± 11 bpm; R-ICH 450 ± 7 vs saline 406 ± 8 bpm, P < 0.05) without changing BP. HR was restored to baseline levels after i.v. atenolol. Strikingly, ICH rats presented a reduced baseline RSNA (Δ:L-ICH 122 ± 4 vs saline 148 ± 11 spikes/s; R-ICH 112 ± 5 vs saline 148 ± 7 spikes/s, P < 0.05). After 24 h of ICH we observed a marked increase in cardiac ectopies and this number was greater after ICH R-IC. Heart weight, calcium amplitude and SERCA expression were reduced only in ICH R-IC. Focal stroke into IC can alter the cardiac and renal autonomic control. Damage to the R-IC produces a greater number of arrhythmias and changes in calcium dynamics in cardiac cells indicating that the cardiovascular consequences are hemisphere-dependent. These findings confirm asymmetry for cardiac autonomic control at the IC and help to understand the cardiac and renal implications observed after specific side cortical damage.

Identifying Increases in Activity of the Human RVLM Through MSNA-Coupled fMRI

AIM

We initially developed concurrent recording of muscle sympathetic nerve activity (MSNA) and functional magnetic resonance imaging (fMRI) of the brain to functionally identify the human homolog of the rostral ventrolateral medulla (RVLM). Here we summarize the cortical and subcortical connections to the RVLM, as identified using MSNA-coupled fMRI.

METHODS

MSNA was recorded via tungsten microelectrodes inserted into the peroneal nerve. Gradient echo, echo-planar fMRI was performed at 3T (Philips Achieva). 200 volumes (46 axial slices (TR = 8 s, TE = 4 s, flip angle = 90°, raw voxel size = 1.5 × 1.5 × 2.75 mm) were collected in a 4 s-ON, 4 s-OFF sparse sampling protocol and MSNA measured in each 1 s epoch in the 4-s period between scans. Blood oxygen level dependent (BOLD) signal intensity was measured in the corresponding 1 s epoch 4 s later to account for peripheral neural conduction and central neurovascular coupling delays.

RESULTS

BOLD signal intensity was positively related to bursts of MSNA in the RVLM, dorsomedial hypothalamus (DMH), ventromedial hypothalamus (VMH), insula, dorsolateral prefrontal cortex (dlPFC), posterior cingulate cortex (PCC), and precuneus, and negatively related in the caudal ventrolateral medulla (CVLM), nucleus tractus solitarius (NTS), and the midbrain periaqueductal gray (PAG). During physiological increases in MSNA (tonic muscle pain), MSNA-coupled BOLD signal intensity was greater in RVLM, NTS, PAG, DMH, dlPFC, medial prefrontal cortex (mPFC), precuneus, and anterior cingulate cortex (ACC) than at rest. During pathophysiological increases in MSNA [obstructive sleep apnoea (OSA)] signal intensity was also higher in dlPFC, mPFC, ACC, and precuneus than in controls. Conversely, signal intensity was lower in RVLM in OSA than in controls, which we interpret as reflecting a withdrawal of active inhibition of the RVLM.

CONCLUSION

These results suggest that multiple cortical and subcortical areas are functionally coupled to the RVLM, which in turn is functionally coupled to the generation of spontaneous bursts of MSNA and their augmentation during physiological and pathophysiological increase in vasoconstrictor drive.

A time to fight: Circadian control of aggression and associated autonomic support

The central circadian clock, located in the suprachiasmatic nucleus of the mammalian hypothalamus (SCN), regulates daily behavioral rhythms including the temporal propensity for aggressive behavior. Such aggression propensity rhythms are regulated by a functional circuit from the SCN to neurons that drive attack behavior in the ventromedial hypothalamus (VMH), via a relay in the subparaventricular zone (SPZ). In addition to this pathway, the SCN also regulates sleep-wake and locomotor activity rhythms, via the SPZ, in a circuit to the dorsomedial hypothalamus (DMH), a structure that is also known to play a key role in autonomic function and the sympathetic "fight-or-flight" response (which prepares the body for action in stressful situations such as an agonistic encounter). While the autonomic nervous system is known to be under pronounced circadian control, it is less apparent how such autonomic rhythms and their underlying circuitry may support the temporal propensity for aggressive behavior. Additionally, it is unclear how circadian and autonomic dysfunction may contribute to aberrant social and emotional behavior, such as agitation and aggression. Here we review the literature concerning interactions between the circadian and autonomic systems and aggression, and we discuss the implications of these relationships for human neural and behavioral pathologies.

Brs3 neurons in the mouse dorsomedial hypothalamus regulate body temperature, energy expenditure, and heart rate, but not food intake

Bombesin-like receptor 3 (BRS3) is an orphan G protein-coupled receptor that regulates energy homeostasis and heart rate. We report that acute activation of Brs3-expressing neurons in the dorsomedial hypothalamus (DMH^Brs3) increased body temperature (Tb), brown adipose tissue temperature, energy expenditure, heart rate and blood pressure, with no effect on food intake or physical activity. Conversely, activation of Brs3 neurons in the paraventricular nucleus of the hypothalamus (PVH^Brs3) had no effect on Tb or energy expenditure, but suppressed food intake. Inhibition of DMH^Brs3 neurons decreased Tb and energy expenditure, suggesting a necessary role in Tb regulation. We found that the preoptic area provides major input (excitatory and inhibitory) to DMH^Brs3 neurons. Optogenetic stimulation of DMH^Brs3 projections to the raphe pallidus (RPa) increased Tb. Thus, DMH^Brs3→RPa neurons regulate Tb, energy expenditure and heart rate, and PVH^Brs3 neurons regulate food intake. Brs3 expression is a useful marker for delineating energy metabolism regulatory circuitry.