The human nucleus of the solitary tract: visceral pathways revealed with an "in vitro" postmortem tracing method

Intrathecal Baclofen Pump Refill-Related Cardiac Arrest: A Case Report

We present the case of a 45-year-old male with a history of multiple sclerosis complicated by spasticity and paraplegia, who developed altered mental status and type II respiratory failure requiring intubation on the same day his intrathecal baclofen pump was refilled by his pain physician. Shortly after admission, the patient experienced cardiac arrest four times within two hours until the pump contents were aspirated, and the patient was stabilized. This case report emphasizes the significance of vigilance and prompt recognition of intrathecal baclofen poisoning, which can lead to life-threatening toxicities and withdrawals.

Is Postoperative Nausea and Vomiting Associated With Increased Postoperative Pain in Patients Undergoing Minor Oral and Maxillofacial Surgery Under General Anesthesia?

BACKGROUND

Whether postoperative nausea and vomiting (PONV) contributes to increased postoperative pain (POP) remains unclear, although POP is reported to cause PONV.

PURPOSE

This study aimed to determine whether PONV following minor oral and maxillofacial surgery (OMS) under general anesthesia increases POP.

STUDY DESIGN, SETTING, SAMPLE

The researchers implemented a retrospective cohort study. Patients who presented to Saitama Medical University Hospital between January 2021 and August 2022 and who required minor OMS under general anesthesia were identified from a review of electronic records. The inclusion criteria were patients aged between 16 and 65 years and nasal intubation via inhalational or propofol-based total intravenous general anesthesia. The exclusion criterion was patients who had diseases affecting POP or PONV.

PREDICTOR VARIABLES

The primary predictor variable was the occurrence of PONV (yes/no) at 2 hours postoperatively.

MAIN OUTCOME VARIABLES

The main outcome variable was POP measured on a 100 mm visual analog scale (VAS) at 2 hours postoperatively. The secondary outcome was the timing of POP, which was measured at 6 hours.

COVARIATES

Covariates included patient-related factors (age, body mass index, American Society of Anesthesiologists Physical Status, smoking status, and history of PONV or motion sickness), anesthesia-related factors (intraoperative analgesics, intraoperative antiemetics, duration of anesthesia, and anesthesia type), and surgery-related factors (surgery type and duration of surgery).

ANALYSES

Analyses were used for ordinal, categorical, and continuous variables. The POP VAS values were compared between each measurement time with repeated-measures analysis of variance. A P value < .05 indicated statistical significance.

RESULTS

The sample included 148 patients with a mean age of 40 ± 16.5 years, 66 (44.6%) of whom were male. The incidence of PONV was 31 (20.9%) at 0 to 2 hours, 7 (4.7%) at 2 to 6 hours, and 0 (0%) at 6 to 24 hours. POP VAS scores were significantly higher in the PONV group than in the non-PONV group at 2 hours. The mean VAS score at 2 hours was 40.5 ± 29.2 (PONV group) versus 29.8 ± 23.7 (non-PONV group) (P = .03); the VAS score at 6 hours was 41.0 ± 29.4 (PONV group) compared with 25.4 ± 26.4 (non-PONV group) (P = .13).

CONCLUSION

Our present study revealed that PONV is associated with increased POP in patients undergoing minor OMS under general anesthesia.

Brainstem neuronal responses to transcutaneous auricular and cervical vagus nerve stimulation in rats

Transcutaneous auricular vagus nerve stimulation (taVNS) targets subcutaneous axons in the auricular branch of the vagus nerve at the outer ear. Its non-invasive nature makes it a potential treatment for various disorders. taVNS induces neuromodulatory effects within the nucleus of the solitary tract (NTS), and due to its widespread connectivity, the NTS acts as a gateway to elicit neuromodulation in both higher-order brain regions and other brainstem nuclei (e.g. spinal trigeminal nucleus; Sp5). Our objective was to examine stimulation parameters on single-neuron electrophysiological responses in α-chloralose-anaesthetized Sprague-Dawley rats within NTS and Sp5. taVNS was also compared to traditional cervical VNS (cVNS) on single neuronal activation. Specifically, electrophysiological extracellular recordings were evaluated for a range of frequency and intensity parameters (20-250 Hz, 0.5-1.0 mA). Neurons were classified as positive, negative or non-responders based on increased activity, decreased activity or no response during stimulation, respectively. Frequency-dependent analysis showed that 20 and 100 Hz generated the highest proportion of positive responders in NTS and Sp5 with 1.0 mA intensities eliciting the greatest magnitude of response. Comparisons between taVNS and cVNS revealed similar parameter-specific activation for caudal NTS neuronal populations; however, individual neurons showed different activation profiles. The latter suggests that cVNS and taVNS send afferent input to NTS via different neuronal pathways. This study demonstrates differential parameter-specific taVNS responses and begins an investigation of the mechanisms responsible for taVNS modulation. Understanding the neuronal pathways responsible for eliciting neuromodulatory effects will enable more tailored taVNS treatments in various clinical disorders. KEY POINTS: Transcutaneous auricular vagus nerve stimulation (taVNS) offers a non-invasive alternative to invasive cervical vagus nerve stimulation (cVNS) by activating vagal afferents in the ear to induce neuromodulation. Our study evaluated taVNS effects on neuronal firing patterns in the nucleus of the solitary tract (NTS) and spinal trigeminal nucleus (Sp5) and found that 20 and 100 Hz notably increased neuronal activity during stimulation in both nuclei. Increasing taVNS intensity not only increased the number of neurons responding in Sp5 but also increased the magnitude of response, suggesting a heightened sensitivity to taVNS compared to NTS. Comparisons between cVNS and taVNS revealed similar overall activation but different responses on individual neurons, indicating distinct neural pathways. These results show parameter-specific and nuclei-specific responses to taVNS and confirm that taVNS can elicit responses comparable to cVNS at the neuronal level, but it does so through different neuronal pathways.

Closed-loop transcutaneous auricular vagus nerve stimulation for the improvement of upper extremity motor function in stroke patients: a study protocol

Background

Transcutaneous auricular vagus nerve stimulation (taVNS) has garnered attention for stroke rehabilitation, with studies demonstrating its benefits when combined with motor rehabilitative training or delivered before motor training. The necessity of concurrently applying taVNS with motor training for post-stroke motor rehabilitation remains unclear. We aimed to investigate the necessity and advantages of applying the taVNS concurrently with motor training by an electromyography (EMG)-triggered closed-loop system for post-stroke rehabilitation.

Methods

We propose a double-blinded, randomized clinical trial involving 150 stroke patients assigned to one of three groups: concurrent taVNS, sequential taVNS, or sham control condition. In the concurrent group, taVNS bursts will synchronize with upper extremity motor movements with EMG-triggered closed-loop system during the rehabilitative training, while in the sequential group, a taVNS session will precede the motor rehabilitative training. TaVNS intensity will be set below the pain threshold for both concurrent and sequential conditions and at zero for the control condition. The primary outcome measure is the Fugl-Meyer Assessment of Upper Extremity (FMA-UE). Secondary measures include standard upper limb function assessments, as well as EMG and electrocardiogram (ECG) features.

Ethics and dissemination

Ethical approval has been granted by the Medical Ethics Committee, affiliated with Zhujiang Hospital of Southern Medical University for Clinical Studies (2023-QX-012-01). This study has been registered on ClinicalTrials (NCT05943431). Signed informed consent will be obtained from all included participants. The findings will be published in peer-reviewed journals and presented at relevant stakeholder conferences and meetings.

Discussion

This study represents a pioneering effort in directly comparing the impact of concurrent taVNS with motor training to that of sequential taVNS with motor training on stroke rehabilitation. Secondly, the incorporation of an EMG-triggered closed-loop taVNS system has enabled the automation and individualization of both taVNS and diverse motor training tasks-a novel approach not explored in previous research. This technological advancement holds promise for delivering more precise and tailored training interventions for stroke patients. However, it is essential to acknowledge a limitation of this study, as it does not delve into examining the neural mechanisms underlying taVNS in the context of post-stroke rehabilitation.

Tonic and phasic transcutaneous auricular vagus nerve stimulation (taVNS) both evoke rapid and transient pupil dilation

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (tVNS or taVNS) is a non-invasive method of electrical stimulation of the afferent pathway of the vagus nerve, suggested to drive changes in putative physiological markers of noradrenergic activity, including pupil dilation.

OBJECTIVE

However, it is unknown whether different taVNS modes can map onto the phasic and tonic modes of noradrenergic activity. The effects of taVNS on pupil dilation in humans are inconsistent, largely due to differences in stimulation protocols. Here, we attempted to address these issues.

METHODS

We investigated pupil dilation under phasic (1 s) and tonic (30 s) taVNS, in a pre-registered, single-blind, sham-controlled, within-subject cross-over design, in the absence of a behavioural task.

RESULTS

Phasic taVNS induced a rapid increase in pupil size over baseline, significantly greater than under sham stimulation, which rapidly declined after stimulation offset. Tonic taVNS induced a similarly rapid (and larger than sham) increase in pupil size over baseline, returning to baseline within 5 s, despite the ongoing stimulation. Thus, both active and sham tonic modes closely resembled the phasic effect. There were no differences in tonic baseline pupil size, and no sustained effects of stimulation on tonic baseline pupil size.

CONCLUSIONS

These results suggest that both phasic- and tonic-like taVNS under the standard stimulation parameters may modulate primarily the phasic mode of noradrenergic activity, as indexed by evoked pupil dilation, over and above somatosensory effects. This result sheds light on the temporal profile of phasic and tonic stimulation, with implications for their applicability in further research.

Non-invasive neuromodulation of the cervical vagus nerve in rare primary headaches

Primary headache disorders can be remarkably disabling and the therapeutic options available are usually limited to medication with a high rate of adverse events. Here, we discuss the mechanism of action of non-invasive vagal nerve stimulation, as well as the findings of the main studies involving patients with primary headaches other than migraine or cluster headache, such as hemicrania continua, paroxysmal hemicrania, cough headache, or short-lasting neuralgiform headache attacks (SUNCT/SUNA), in a narrative analysis. A bibliographical search of low-prevalence disorders such as rare primary headaches retrieves a moderate number of studies, usually underpowered. Headache intensity, severity, and duration showed a clinically significant reduction in the majority, especially those involving indomethacin-responsive headaches. The lack of response of some patients with a similar diagnosis could be due to a different stimulation pattern, technique, or total dose. The use of non-invasive vagal nerve stimulation for the treatment of primary headache disorders represents an excellent option for patients with these debilitating and otherwise refractory conditions, or that cannot tolerate several lines of preventive medication, and should always be considered before contemplating invasive, non-reversible stimulation techniques.

The Solitary Nucleus Connectivity to Key Autonomic Regions in Humans MRI and Literature based Considerations

The nucleus tractus solitarius (NTS), is a key brainstem structure relaying interoceptive peripheral information to the interrelated brain centers for eliciting rapid autonomic responses and for shaping longer-term neuroendocrine and motor patterns. Structural and functional NTS' connectivity has been extensively investigated in laboratory animals. But there is limited information about NTS' connectome in humans. Using MRI, we examined diffusion and resting state data from 20 healthy participants in the Human Connectome Project. The regions within the brainstem (n=8), subcortical (n=6), cerebellar (n=2) and cortical (n=5) parts of the brain were selected via a systematic review of the literature and their white matter NTS connections were evaluated via probabilistic tractography along with functional and directional (i.e., Granger-causality) analyses. The underlying study confirms previous results from animal models and provides novel aspects on NTS integration in humans. Two key findings can be summarized: (i) the NTS predominantly processes afferent input and (ii) a lateralization towards a predominantly left-sided NTS processing. Our results lay the foundations for future investigations into the NTS' tripartite role comprised of interoreceptors' input integration, the resultant neurochemical outflow and cognitive/affective processing. The implications of these data add to the understanding of NTS' role in specific aspects of autonomic functions.

Arousal States as a Key Source of Variability in Speech Perception and Learning

The human brain exhibits the remarkable ability to categorize speech sounds into distinct, meaningful percepts, even in challenging tasks like learning non-native speech categories in adulthood and hearing speech in noisy listening conditions. In these scenarios, there is substantial variability in perception and behavior, both across individual listeners and individual trials. While there has been extensive work characterizing stimulus-related and contextual factors that contribute to variability, recent advances in neuroscience are beginning to shed light on another potential source of variability that has not been explored in speech processing. Specifically, there are task-independent, moment-to-moment variations in neural activity in broadly-distributed cortical and subcortical networks that affect how a stimulus is perceived on a trial-by-trial basis. In this review, we discuss factors that affect speech sound learning and moment-to-moment variability in perception, particularly arousal states—neurotransmitter-dependent modulations of cortical activity. We propose that a more complete model of speech perception and learning should incorporate subcortically-mediated arousal states that alter behavior in ways that are distinct from, yet complementary to, top-down cognitive modulations. Finally, we discuss a novel neuromodulation technique, transcutaneous auricular vagus nerve stimulation (taVNS), which is particularly well-suited to investigating causal relationships between arousal mechanisms and performance in a variety of perceptual tasks. Together, these approaches provide novel testable hypotheses for explaining variability in classically challenging tasks, including non-native speech sound learning.

Vagus nerve afferent stimulation: Projection into the brain, reflexive physiological, perceptual, and behavioral responses, and clinical relevance

The afferent vagus nerves project to diverse neural networks within the brainstem and forebrain, based on neuroanatomical, neurophysiological, and functional (fMRI) brain imaging evidence. In response to afferent vagal stimulation, multiple homeostatic visceral reflexes are elicited. Physiological stimuli and both invasive and non-invasive electrical stimulation that activate the afferent vagus elicit perceptual and behavioral responses that are of physiological and clinical significance. In the present review, we address these multiple roles of the afferent vagus under normal and pathological conditions, based on both animal and human evidence.

Potential of Electrical Neuromodulation for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a common chronic inflammatory disease of the digestive tract that is often debilitating. It affects patients' quality of life and imposes a financial burden. Despite advances in treatment with medications such as biologics, a large proportion of patients do not respond to medical therapy or develop adverse events. Therefore, alternative treatment options such as electrical neuromodulation are currently being investigated. Electrical neuromodulation, also called bioelectronic medicine, is emerging as a potential new treatment for IBD. Over the past decade, advancements have been made in electrical neuromodulation. A number of electrical neuromodulation methods, such as vagus nerve stimulation, sacral nerve stimulation, and tibial nerve stimulation, have been tested to treat IBD. A series of animal and clinical trials have been performed to evaluate efficacy with promising results. Although the exact underlying mechanisms of action for electrical neuromodulation remain to be explored, this modality is promising. Further randomized controlled trials and basic experiments are needed to investigate efficacy and clarify intrinsic mechanisms.

The Evolution of Neuromodulation in the Treatment of Chronic Pain: Forward-Looking Perspectives

Background

The field of neuromodulation is continually evolving, with the past decade showing significant advancement in the therapeutic efficacy of neuromodulation procedures. The continued evolution of neuromodulation technology brings with it the promise of addressing the needs of both patients and physicians, as current technology improves and clinical applications expand.

Design

This review highlights the current state of the art of neuromodulation for treating chronic pain, describes key areas of development including stimulation patterns and neural targets, expanding indications and applications, feedback-controlled systems, noninvasive approaches, and biomarkers for neuromodulation and technology miniaturization.

Results and Conclusions

The field of neuromodulation is undergoing a renaissance of technology development with potential for profoundly improving the care of chronic pain patients. New and emerging targets like the dorsal root ganglion, as well as high-frequency and patterned stimulation methodologies such as burst stimulation, are paving the way for better clinical outcomes. As we look forward to the future, neural sensing, novel target-specific stimulation patterns, and approaches combining neuromodulation therapies are likely to significantly impact how neuromodulation is used. Moreover, select biomarkers may influence and guide the use of neuromodulation and help objectively demonstrate efficacy and outcomes.

The anatomical basis for transcutaneous auricular vagus nerve stimulation

The array of end organ innervations of the vagus nerve, coupled with increased basic science evidence, has led to vagus nerve stimulation (VNS) being explored as a management option in a number of clinical disorders, such as heart failure, migraine and inflammatory bowel disease. Both invasive (surgically implanted) and non-invasive (transcutaneous) techniques of VNS exist. Transcutaneous VNS (tVNS) delivery systems rely on the cutaneous distribution of vagal afferents, either at the external ear (auricular branch of the vagus nerve) or at the neck (cervical branch of the vagus nerve), thus obviating the need for surgical implantation of a VNS delivery device and facilitating further investigations across a wide range of uses. The concept of electrically stimulating the auricular branch of the vagus nerve (ABVN), which provides somatosensory innervation to several aspects of the external ear, is relatively more recent compared with cervical VNS; thus, there is a relative paucity of literature surrounding its operation and functionality. Despite the increasing body of research exploring the therapeutic uses of auricular transcutaneous VNS (tVNS), a comprehensive review of the cutaneous, intracranial and central distribution of ABVN fibres has not been conducted to date. A review of the literature exploring the neuroanatomical basis of this neuromodulatory therapy is therefore timely. Our review article explores the neuroanatomy of the ABVN with reference to (1) clinical surveys examining Arnold's reflex, (2) cadaveric studies, (3) fMRI studies, (4) electrophysiological studies, (5) acupuncture studies, (6) retrograde tracing studies and (7) studies measuring changes in autonomic (cardiovascular) parameters in response to auricular tVNS. We also provide an overview of the fibre composition of the ABVN and the effects of auricular tVNS on the central nervous system. Cadaveric studies, of which a limited number exist in the literature, would be the 'gold-standard' approach to studying the cutaneous map of the ABVN; thus, there is a need for more such studies to be conducted. Functional magnetic resonance imaging (fMRI) represents a useful surrogate modality for discerning the auricular sites most likely innervated by the ABVN and the most promising locations for auricular tVNS. However, given the heterogeneity in the results of such investigations and the various limitations of using fMRI, the current literature lacks a clear consensus on the auricular sites that are most densely innervated by the ABVN and whether the brain regions secondarily activated by electrical auricular tVNS depend on specific parameters. At present, it is reasonable to surmise that the concha and inner tragus are suitable locations for vagal modulation. Given the therapeutic potential of auricular tVNS, there remains a need for the cutaneous map of the ABVN to be further refined and the effects of various stimulation parameters and stimulation sites to be determined.

Vagus nerve stimulation for primary headache disorders: An anatomical review to explain a clinical phenomenon

BACKGROUND

Non-invasive stimulation of the vagus nerve has been proposed as a new neuromodulation therapy to treat primary headache disorders, as the vagus nerve is hypothesized to modulate the headache pain pathways in the brain. Vagus nerve stimulation can be performed by placing an electrode on the ear to stimulate the tragus nerve, which contains about 1% of the vagus fibers. Non-invasive vagus nerve stimulation (nVNS) conventionally refers to stimulation of the cervical branch of the vagus nerve, which is made up entirely of vagal nerve fibers. While used interchangeably, most of the research to date has been performed with nVNS or an implanted vagus nerve stimulation device. However, the exact mechanism of action of nVNS remains hypothetical and no clear overview of the effectiveness of nVNS in primary headache disorders is available.

METHODS

In the present study, the clinical trials that investigated the effectiveness, tolerability and safety of nVNS in primary headache disorders were systematically reviewed. The second part of this study reviewed the central connections of the vagus nerve. Papers on the clinical use of nVNS and the anatomical investigations were included based on predefined criteria, evaluated, and results were reported in a narrative way.

RESULTS

The first part of this review shows that nVNS in primary headache disorders is moderately effective, safe and well-tolerated. Regarding the anatomical review, it was reported that fibers from the vagus nerve intertwine with fibers from the trigeminal, facial, glossopharyngeal and hypoglossal nerves, mostly in the trigeminal spinal tract. Second, the four nuclei of the vagus nerve (nuclei of the solitary tract, nucleus ambiguus, spinal nucleus of the trigeminal nerve and dorsal motor nucleus (DMX)) show extensive interconnections. Third, the efferents from the vagal nuclei that receive sensory and visceral input (i.e. nuclei of the solitary tract and spinal nucleus of the trigeminal nerve) mainly course towards the main parts of the neural pain matrix directly or indirectly via other vagal nuclei.

CONCLUSION

The moderate effectiveness of nVNS in treating primary headache disorders can possibly be linked to the connections between the trigeminal and vagal systems as described in animals.

Treating Chronic Migraine With Neuromodulation: The Role of Neurophysiological Abnormalities and Maladaptive Plasticity

Chronic migraine (CM) is the most disabling form of migraine, because pharmacological treatments have low efficacy and cumbersome side effects. New evidence has shown that migraine is primarily a disorder of brain plasticity and migraine chronification depends on a maladaptive process favoring the development of a brain state of hyperexcitability. Due to the ability to induce plastic changes in the brain, researchers started to look at Non-Invasive Brain Stimulation (NIBS) as a possible therapeutic option in migraine field. On one side, NIBS techniques induce changes of neural plasticity that outlast the period of the stimulation (a fundamental prerequisite of a prophylactic migraine treatment, concurrently they allow targeting neurophysiological abnormalities that contribute to the transition from episodic to CM. The action may thus influence not only the cortex but also brainstem and diencephalic structures. Plus, NIBS is not burdened by serious medication side effects and drug–drug interactions. Although the majority of the studies reported somewhat beneficial effects in migraine patients, no standard intervention has been defined. This may be due to methodological differences regarding the used techniques (e.g., transcranial magnetic stimulation, transcranial direct current stimulation), the brain regions chosen as targets, and the stimulation types (e.g., the use of inhibitory and excitatory stimulations on the basis of opposite rationales), and an intrinsic variability of stimulation effect. Hence, it is difficult to draw a conclusion on the real effect of neuromodulation in migraine. In this article, we first will review the definition and mechanisms of brain plasticity, some neurophysiological hallmarks of migraine, and migraine chronification-related (dys)plasticity. Secondly, we will review available results from therapeutic and physiological studies using neuromodulation in CM. Lastly we will discuss the results obtained in these preventive trials in the light of a possible effect on brain plasticity.

Non-invasive High Frequency Median Nerve Stimulation Effectively Suppresses Olfactory Intensity Perception in Healthy Males

Median nerve stimulation (MNS) had been performed in the existing literature to alleviate symptoms of nausea and vomiting. The observed facilitative effects are thought to be mediated by the vagal pathways, particularly the vagus nerve (VN) brainstem nuclei of the dorsal motor nucleus of vagus and nucleus tractus solitarius (DMV-NTS). Sense of smell is one of the major sensory modalities for inducing vomiting and nausea as a primary defense against potentially harmful intake of material. This study aimed to test effects of non-invasive, high and low frequency MNS on human olfactory functioning, with supplementary exploration of the orbitofrontal cortex (OFC) using near-infrared spectroscopy (NIRS). Twenty healthy, male, adults performed supra-threshold odor intensity tests (labeled magnitude scale, LMS) for four food-related odorant samples (presented in three different concentrations) before and after receiving high-, low frequency MNS and placebo (no stimulation), while cortical activities in the OFC was monitored by the NIRS. Data of the NIRS and LMS test of separate stimulation parameters were statistically analyzed using mixed-model analysis of variance (ANOVA). Only the high frequency MNS showed effects for suppressing the intensity perception of the moderate concentration of Amyl Acetate (p:0.042) and strong concentration of Isovaleric Acid (p:0.004) and 1-Octen-3-ol (p:0.006). These behavioral changes were coupled with significant changes in the NIRS recordings of the left (p:0.000) and right (p:0.003) hemispheric orbitofrontal cortices. This is the first study that applied non-invasive, high frequency MNS to suppress the supra-threshold odor ratings of specific concentrations of odors. The vagal networks are potential relays of MNS to influence OFC. Results from the current article implore further research into non-invasive, high frequency MNS in the investigation of its modulatory effects on olfactory function, given its potential to be used for ameliorating nausea and malnutrition associated with various health conditions.

Shared Autonomic Pathways Connect Bone Marrow and Peripheral Adipose Tissues Across the Central Neuraxis

Bone marrow adipose tissue (BMAT) is increased in both obesity and anorexia. This is unique relative to white adipose tissue (WAT), which is generally more attuned to metabolic demand. It suggests that there may be regulatory pathways that are common to both BMAT and WAT and also those that are specific to BMAT alone. The central nervous system (CNS) is a key mediator of adipose tissue function through sympathetic adrenergic neurons. Thus, we hypothesized that central autonomic pathways may be involved in BMAT regulation. To test this, we first quantified the innervation of BMAT by tyrosine hydroxylase (TH) positive nerves within the metaphysis and diaphysis of the tibia of B6 and C3H mice. We found that many of the TH+ axons were concentrated around central blood vessels in the bone marrow. However, there were also areas of free nerve endings which terminated in regions of BMAT adipocytes. Overall, the proportion of nerve-associated BMAT adipocytes increased from proximal to distal along the length of the tibia (from ~3-5 to ~14-24%), regardless of mouse strain. To identify the central pathways involved in BMAT innervation and compare to peripheral WAT, we then performed retrograde viral tract tracing with an attenuated pseudorabies virus (PRV) to infect efferent nerves from the tibial metaphysis (inclusive of BMAT) and inguinal WAT (iWAT) of C3H mice. PRV positive neurons were identified consistently from both injection sites in the intermediolateral horn of the spinal cord, reticular formation, rostroventral medulla, solitary tract, periaqueductal gray, locus coeruleus, subcoeruleus, Barrington's nucleus, and hypothalamus. We also observed dual-PRV infected neurons within the majority of these regions. Similar tracings were observed in pons, midbrain, and hypothalamic regions from B6 femur and tibia, demonstrating that these results persist across mouse strains and between skeletal sites. Altogether, this is the first quantitative report of BMAT autonomic innervation and reveals common central neuroanatomic pathways, including putative "command" neurons, involved in coordinating multiple aspects of sympathetic output and facilitation of parallel processing between bone marrow/BMAT and peripheral adipose tissue.

Cortical stimulation in conscious rats controls joint inflammation

The neuronal control of the immune system is fundamental to the development of new therapeutic strategies for inflammatory disorders. Recent studies reported that afferent vagal stimulation attenuates peripheral inflammation by activating specific sympathetic central and peripheral networks, but only few subcortical brain areas were investigated. In the present study, we report that afferent vagal stimulation also activates specific cortical areas, as the parietal and cingulate cortex. Since these cortical structures innervate sympathetic-related areas, we investigate whether electrical stimulation of parietal cortex can attenuate knee joint inflammation in non-anesthetized rats. Our results show that cortical stimulation in rats increased sympathetic activity and improved joint inflammatory parameters, such as local neutrophil infiltration and pro-inflammatory cytokine levels, without causing behavioral disturbance, brain epileptiform activity or neural damage. In addition, we superposed the areas activated by afferent vagal or cortical stimulation to map common central structures to depict a brain immunological homunculus that can allow novel therapeutic approaches against inflammatory joint diseases, such as rheumatoid arthritis.

Improvement of Olfactory Function With High Frequency Non-invasive Auricular Electrostimulation in Healthy Humans

In past literature on animal models, invasive vagal nerve stimulation using high frequencies has shown to be effective at modulating the activity of the olfactory bulb (OB). Recent advances in invasive vagal nerve stimulation in humans, despite previous findings in animal models, used low frequency stimulation and found no effect on the olfactory functioning. The present article aimed to test potential effects of non-invasive, high and low frequency vagal nerve stimulation in humans, with supplementary exploration of the orbitofrontal cortex using near-infrared spectroscopy (NIRS). Healthy, male adult participants (n = 18) performed two olfactory tests [odor threshold test (OTT) and supra-threshold test (STT)] before and after receiving high-, low frequency vagal nerve stimulation and placebo (no stimulation). Participant's olfactory functioning was monitored using NIRS, and assessed with two behavioral olfactory tests. NIRS data of separate stimulation parameters were statistically analyzed using repeated-measures ANOVA across different stages. Data from olfactory tests were analyzed using paired parametric and non-parametric statistical tests. Only high frequency, non-invasive vagal nerve stimulation was able to positively modulate the performance of the healthy participants in the STT (p = 0.021, Wilcoxon sign-ranked test), with significant differences in NIRS (p = 0.014, post-hoc with Bonferroni correction) recordings of the right hemispheric, orbitofrontal cortex. The results from the current article implore further exploration of the neurocircuitry involved under vagal nerve stimulation and the effects of non-invasive, high frequency, vagal nerve stimulation toward olfactory dysfunction which showcase in Parkinson's and Alzheimer's Diseases. Despite the sufficient effect size (moderate effect, correlation coefficient (r): 0.39 for the STT) of the current study, future research should replicate the current findings with a larger cohort.

Clinical characteristics of menstrually related and non-menstrual migraine

Migraine attacks increase during the perimenstrual period in approximately half of female migraineurs. There are differences in the pathogenesis and clinical features of menstrually related and non-menstrual migraine attacks. The objective of this study was to compare the characteristics of migraine in patients with menstrually related and non-menstrual migraine, and to investigate the differences between premenstrual, menstrual, and late-menstrual migraine attacks. Three-hundred and thirty-two women with migraine without aura were evaluated using questionnaires and diaries to determine the characteristics of headache, preceding and accompanying symptoms, and the relation of migraine attacks and menstruation. One-hundred and sixty-three women had menstrually related migraine without aura (49.1%). Duration of disease and duration of headache were longer (p = 0.002 and p < 0.001, respectively), and nausea, vomiting, phonophobia, and aggravation of headache with physical activity were more frequent in patients with menstrually related migraine (p = 0.005, p = 0.006, p < 0.001 and p = 0.006, respectively). Premonitory symptoms and allodynia were observed more frequently in the menstrually related migraine group (p = 0.012 and p = 0.004, respectively). Perimenstrual migraine attacks occurred premenstrually (days -2 and -1) in 46 patients (25.3%), menstrually (days 1 to 3) in 90 patients (49.4%), and late menstrually (days 4 to 7) in 19 patients (10.4%). Our results showed that the duration of headache was longer and accompanying symptoms were more frequent and diverse in patients with menstrually related migraine without aura, suggesting that these findings may reflect the increase in excitability or susceptibility of the brain in these patients.

Vagus nerve stimulation: a new promising therapeutic tool in inflammatory bowel disease

Inflammatory bowel disease (IBD), that is Crohn's disease (CD) and ulcerative colitis, affects about 1.5 million persons in the USA and 2.2 million in Europe. The pathophysiology of IBD involves immunological, genetic and environmental factors. The treatment is medico-surgical but suspensive. Anti-TNFα agents have revolutionized the treatment of IBD but have side effects. In addition, a non-negligible percentage of patients with IBD stop or take episodically their treatment. Consequently, a nondrug therapy targeting TNFα through a physiological pathway, devoid of major side effects and with a good cost-effectiveness ratio, would be of interest. The vagus nerve has dual anti-inflammatory properties through its afferent (i.e. hypothalamic-pituitary-adrenal axis) and efferent (i.e. the anti-TNFα effect of the cholinergic anti-inflammatory pathway) fibres. We have shown that there is an inverse relationship between vagal tone and plasma TNFα level in patients with CD, and have reported, for the first time, that chronic vagus nerve stimulation has anti-inflammatory properties in a rat model of colitis and in a pilot study performed in seven patients with moderate CD. Two of these patients failed to improve after 3 months of vagus nerve stimulation but five were in deep remission (clinical, biological and endoscopic) at 6 months of follow-up and vagal tone was restored. No major side effects were observed. Thus, vagus nerve stimulation provides a new therapeutic option in the treatment of CD.

An Update on Non-Pharmacological Neuromodulation for the Acute and Preventive Treatment of Migraine

OBJECTIVE

To review current neuromodulation treatments available for migraine therapy, both in the acute and preventive setting.

METHODS

The published literature was reviewed for studies reporting the effects of different neuromodulation strategies in migraine with and without aura. The use of non-invasive: single pulse transcranial magnetic stimulation, non-invasive vagal nerve stimulation, supraorbital nerve stimulation, and transcranial direct current stimulation, as well as invasive methods such as occipital nerve stimulation and sphenopalatine ganglion stimulation, are assessed.

RESULTS

The available evidence shows that non-invasive techniques represent promising treatment strategies, whereas an invasive approach should only be used where patients are refractory to other preventives, including non-invasive methods.

CONCLUSIONS

Neuromodulation is emerging as an exciting approach to migraine therapy, especially in the context of failure of commonly used medicines or for patients who do not tolerate common side effects. More studies with appropriate blinding strategies are needed to confirm the results of these new treatment opportunities.

Current Approaches to Neuromodulation in Primary Headaches: Focus on Vagal Nerve and Sphenopalatine Ganglion Stimulation

Neuromodulation is a promising, novel approach for the treatment of primary headache disorders. Neuromodulation offers a new dimension in the treatment that is both easily reversible and tends to be very well tolerated. The autonomic nervous system is a logical target given the neurobiology of common primary headache disorders, such as migraine and the trigeminal autonomic cephalalgias (TACs). This article will review new encouraging results of studies from the most recent literature on neuromodulation as acute and preventive treatment in primary headache disorders, and cover some possible underlying mechanisms. We will especially focus on vagus nerve stimulation (VNS) and sphenopalatine ganglion (SPG) since they have targeted autonomic pathways that are cranial and can modulate relevant pathophysiological mechanisms. The initial data suggests these approaches will find an important role in headache disorder management going forward.

Painful Stimulation of the Temple Induces Nausea, Headache and Extracranial Vasodilation in Migraine Sufferers

To determine whether painful stimulation of the temple would induce nausea, ice was applied to the temple for 30 s, three times at 4-min intervals in 23 migraine sufferers and 22 age- and sex-matched controls. On one occasion, the ice was applied in the presence of residual motion sickness induced by optokinetic stimulation. On another occasion, the ice application was not preceded by optokinetic stimulation (the baseline condition). In the baseline condition, nausea had developed in migraine sufferers but not controls by the third application of ice. In the presence of residual motion sickness, each painful stimulus intensified nausea and headache in migraine sufferers whereas symptoms were minimal in controls. Changes in frontotemporal pulse amplitude were monitored with photoelectric pulse transducers. The extracranial blood vessels dilated in migraine sufferers but not controls before the first application of ice in the baseline condition, presumably due to anticipatory anxiety. In contrast, the ice application did not provoke extra-cranial vasodilation in either group after optokinetic stimulation. The findings show that susceptibility to nausea and stress-induced extracranial vascular hyper-reactivity are associated with the migraine predisposition. They also suggest that head pain might intensify gastrointestinal disturbances during attacks of migraine.

Non-invasive Access to the Vagus Nerve Central Projections via Electrical Stimulation of the External Ear: fMRI Evidence in Humans

BACKGROUND

Tract-tracing studies in cats and rats demonstrated that the auricular branch of the vagus nerve (ABVN) projects to the nucleus tractus solitarii (NTS); it has remained unclear as to whether or not the ABVN projects to the NTS in humans.

OBJECTIVE

To ascertain whether non-invasive electrical stimulation of the cymba conchae, a region of the external ear exclusively innervated by the ABVN, activates the NTS and the "classical" central vagal projections in humans.

METHODS

Twelve healthy adults underwent two fMRI scans in the same session. Electrical stimulation (continuous 0.25ms pulses, 25Hz) was applied to the earlobe (control, scan #1) and left cymba conchae (scan #2). Statistical analyses were performed with FSL. Two region-of-interest analyses were performed to test the effects of cymba conchae stimulation (compared to baseline and control, earlobe, stimulation) on the central vagal projections (corrected; brainstem P < 0.01, forebrain P < 0.05), followed by a whole-brain analysis (corrected, P < 0.05).

RESULTS

Cymba conchae stimulation, compared to earlobe (control) stimulation, produced significant activation of the "classical" central vagal projections, e.g., widespread activity in the ipsilateral NTS, bilateral spinal trigeminal nucleus, dorsal raphe, locus coeruleus, and contralateral parabrachial area, amygdala, and nucleus accumbens. Bilateral activation of the paracentral lobule was also observed. Deactivations were observed bilaterally in the hippocampus and hypothalamus.

CONCLUSION

These findings provide evidence in humans that the central projections of the ABVN are consistent with the "classical" central vagal projections and can be accessed non-invasively via the external ear.

Vestibulo-sympathetic responses

Evidence accumulated over 30 years, from experiments on animals and human subjects, has conclusively demonstrated that inputs from the vestibular otolith organs contribute to the control of blood pressure during movement and changes in posture. This review considers the effects of gravity on the body axis, and the consequences of postural changes on blood distribution in the body. It then separately considers findings collected in experiments on animals and human subjects demonstrating that the vestibular system regulates blood distribution in the body during movement. Vestibulosympathetic reflexes differ from responses triggered by unloading of cardiovascular receptors such as baroreceptors and cardiopulmonary receptors, as they can be elicited before a change in blood distribution occurs in the body. Dissimilarities in the expression of vestibulosympathetic reflexes in humans and animals are also described. In particular, there is evidence from experiments in animals, but not humans, that vestibulosympathetic reflexes are patterned, and differ between body regions. Results from neurophysiological and neuroanatomical studies in animals are discussed that identify the neurons that mediate vestibulosympathetic responses, which include cells in the caudal aspect of the vestibular nucleus complex, interneurons in the lateral medullary reticular formation, and bulbospinal neurons in the rostral ventrolateral medulla. Recent findings showing that cognition can modify the gain of vestibulosympathetic responses are also presented, and neural pathways that could mediate adaptive plasticity in the responses are proposed, including connections of the posterior cerebellar vermis with the vestibular nuclei and brainstem nuclei that regulate blood pressure.

Cutaneous allodynia in patients with episodic migraine

Cutaneous allodynia may be observed in patients with migraine and this reflects the central sensitization of the trigeminal neurons. We aimed to investigate the frequency of cutaneous allodynia in patients with episodic migraine and to compare clinical characteristics of migraine patients with and without allodynia. One hundred and eighty-six consecutive patients with episodic migraine attacks were prospectively included in the study. The cutaneous allodynia symptoms that occurred during headache attacks were documented using a questionnaire for assessing cephalic and extracephalic cutaneous allodynia. One hundred and fourteen patients (61.3 %) were observed to develop allodynia during migraine attacks and the ratio of the female gender was found higher among the patients with allodynia (p < 0.001). Migraine disease duration was longer (p = 0.004) and accompanying nausea and phonophobia were more common (p = 0.003 and p = 0.005, respectively) in the patients with allodynia. Menstrually related migraine was found to be associated with both allodynia (p = 0.049) and its severity (p = 0.003). The results of present study revealed that cutaneous allodynia was rather frequent in episodic migraine, particularly in patients having longer disease duration. Higher frequency of allodynia in women and its association with menstrually related migraine may be related to the effects of hormonal factors on cutaneous pain thresholds and central sensitization. Association of nausea and phonophobia with allodynia may be interpreted as the common pathways are shared in the development of these symptoms.

Vagal afferent modulation of spinal trigeminal neuronal responses to dural electrical stimulation in rats

Vagus nerve stimulation (VNS) is an approved antiepileptic and antidepressant treatment, which has recently shown promise as a therapy for drug-resistant primary headaches. Specific neurobiological mechanisms underlying its anticephalgic action are not elucidated, partly because of the deficiency of research-related findings. The spinal trigeminal nucleus (STN) plays a prominent role in pathophysiology of headaches by modulating pain transmission from intracranial structures to higher centers of the brain. To determine whether vagal stimulation may affect trigeminovascular nociception, we investigated the effects of VNS on the STN neuronal activity in the animal model of headache. In anesthetized rats the spike activity of the STN neurons with convergent orofacial and meningeal inputs was monitored, and the changes in neuronal responses to electrical stimulation of the dura mater under preconditioning or under continuous electrical stimulation of the left cervical vagus nerve were studied. Preconditioning vagal afferent stimulation (200-ms train of pulses at 30 Hz applied before each dural stimulus) did not produce substantial changes in the STN spike activity. However, continuous VNS with frequency of 10 Hz in 48% of cases significantly suppressed trigeminal neuronal responses to dural electrical stimulation. In line with the decrease in evoked activity, the VNS-induced depression of ongoing neuronal firing was observed. Although the inhibitory effect was prevailing, 29.5% of STN neurons were facilitated by VNS, whereas 22.5% were unresponsive to the stimulation. These results provide an evidence of VNS-induced modulation of trigeminovascular nociception, and therefore contribute to a deeper understanding of neurophysiological mechanisms underlying effects of vagal stimulation in chronic drug-resistant headaches.

The brainstem preproglucagon system in a non-human primate (Macaca mulatta)

The nucleus of the solitary tract (NTS) contains a small population of neurons expressing preproglucagon. In these neurons preproglucagon is processed to the glucagon-like-peptides 1 and 2 (GLP-1 and GLP-2) and oxyntomodulin. Whereas the neuroanatomy of these neurons is well characterized in rodents the location and projection of preproglucagon neurons have never been described in primates. The purpose of the present study was to characterize the location of preproglucagon neurons and their projections in the non-human primate using radioactive in situ hybridization and immunohistochemistry. In situ hybridization revealed preproglucagon mRNA expressing neurons in the caudal nucleus of the solitary tract extending laterally through the intermediate reticular nucleus into the A1 area. Using an antibody raised against rat GLP-2, GLP-2-immunoreactive (-ir) cell bodies were found in the same areas as the preproglucagon mRNA. Only very few GLP-2-ir nerve fibers were observed in the caudal brainstem and mostly in the same areas as the GLP-2-ir cell bodies. The most prominent GLP-2-ir terminal fields were detected in the hypothalamus and rostrally in the bed nucleus of the stria terminalis complex. In the hypothalamus, GLP-2-ir fibers arborized extensively in the paraventricular nucleus of the hypothalamus (PVN), the dorsomedial hypothalamic nucleus (DMH) and the arcuate nucleus (Arc), the latter containing the densest fiber-plexus. The findings indicate that the brainstem preproglucagon neuronal system is highly conserved between rat and non-human primate with the exception of a much denser innervation of the mediobasal hypothalamus in the primate brain.

The chemical neuroanatomy of vagus nerve stimulation

In this short overview a reappraisal of the anatomical connections of vagal afferents is reported. The manuscript moves from classic neuroanatomy to review details of vagus nerve anatomy which are now becoming more and more relevant for clinical outcomes (i.e. the therapeutic use of vagus nerve stimulation). In drawing such an updated odology of central vagal connections the anatomical basis subserving the neurochemical effects of vagal stimulation are addressed. In detail, apart from the thalamic projection of central vagal afferents, the monoaminergic systems appear to play a pivotal role. Stemming from the chemical neuroanatomy of monoamines such as serotonin and norepinephrine the widespread effects of vagal stimulation on cerebral cortical activity are better elucidated. This refers both to the antiepileptic effects and most recently to the beneficial effects of vagal stimulation in mood and cognitive disorders.

Vestibular and pulse-related modulation of skin sympathetic nerve activity during sinusoidal galvanic vestibular stimulation in human subjects

We have previously shown that sinusoidal galvanic vestibular stimulation (sGVS), a means of a selectively modulating vestibular afferent input without affecting other inputs, can cause partial entrainment of muscle sympathetic nerve activity (MSNA). Given that motion sickness causes sweating and pallor, we tested the hypothesis that sGVS also entrains skin sympathetic nerve activity (SSNA), but that the optimal frequencies are closer to those associated with slow postural changes (0.2 Hz). SSNA was recorded via tungsten microelectrodes inserted into the common peroneal nerve in 11 awake-seated subjects. Bipolar binaural sinusoidal GVS (+/-2 mA, 200 cycles) was applied to the mastoid processes at frequencies of 0.2, 0.5, 0.8, 1.1, 1.4, 1.7 and 2.0 Hz. All subjects reported strong postural illusions of 'rocking in a boat' or 'swaying in a hammock'. Sinusoidal GVS caused a marked entrainment of SSNA at all frequencies. Measured as the modulation index, vestibular modulation ranged from 81.5 +/- 4.0% at 0.2 Hz to 76.6 +/- 3.6% at 1.7 Hz; it was significantly weaker at 2.0 Hz (63.2 +/- 5.4%). Interestingly, pulse-related modulation of SSNA, which is normally weak, increased significantly during sGVS but was stronger at 0.8 Hz (86.2 +/- 2.0%) than at 0.2 Hz (69.3 +/- 8.3%), the opposite of the pattern seen with vestibular modulation of MSNA. We conclude that vestibular inputs can entrain the firing of cutaneous sympathetic neurones and increase their normally weak pulse-related rhythmicity.

Epilepsy, electroacupuncture and the nucleus of the solitary tract

Vagal nerve stimulation and electroacupuncture have some promise as neuroprotective therapies for patients with poorly controlled epilepsy. It has been demonstrated that stimulation of acupuncture points on the extremities results in stimulation of the vagus nerve. It is possible that the antiepileptic effects of these two applications might be targeting the same centre in the brain. The nucleus of the solitary tract, which is a primary site at which vagal afferents terminate, is also the site for afferent pathways of facial, scalp and auricular acupuncture via trigeminal, cervical spinal and glossopharyngeal nerves. Taken together with laboratory findings, the neuroprotective pathways of electroacupuncture in epileptic models may stem from the collaboration of its anti-inflammatory and neurotrophic actions through the nucleus of the solitary tract via vagus nerve stimulation.

The relationship between migraine pain and other associated symptoms

This study explores the relationship of the pain of the migraine headache and the associated features of migraine. Migraineurs (n=1025) (ICHD-2, 1.1-1.2 and 1.5.1) were evaluated retrospectively using a detailed database (daily unremitting excluded). Variables studied included headache intensity and duration, associated symptoms and pain characteristics. Non-parametric correlations were used to evaluate relationships among variables. Headache intensity correlated with nausea, vomiting, photophobia, phonophobia, dizziness (all P=0.000), running of the nose/tearing of the eyes (P=0.007), and osmophobia (P=0.044), but not with diarrhoea or taste abnormality. Headache duration correlated only with osmophobia (P=0.002) and taste abnormality (P=0.005). Throbbing, pressure and stabbing pain correlated with most of the associated symptoms. Aching correlated only with taste abnormality. This correlational study demonstrates that migraine pain is clearly related to nausea, but is also correlated with other associated migraine symptoms. Taste abnormality and osmophobia are better correlated with headache duration rather than headache intensity.

The falcine trigeminocardiac reflex: case report and review of the literature

BACKGROUND

Trigeminocardiac reflex (TCR), the reproducible hypotension and bradycardia upon stimulation of the trigeminal nerve, has been reported during craniofacial surgery and during surgery within the cerebellopontine angle, petrosal sinus, orbit, and trigeminal ganglion. Whereas the falx cerebri is known to be innervated by the nervus tentorii, a recurrent branch of V1, there have been no reports to date of this response upon mechanical stimulation of the falx.

CASE DESCRIPTION

We report a case of immediate, reproducible, and reflexive response of asystole upon stimulation of the falx cerebri during operative resection of a parafalcine meningioma in a 53-year-old woman. Upon recognition of the reproducible relationship between falcine stimulation and increased vagal tone, the patient was given glycopyrrolate in an effort to block cholinergic hyperactivity. After glycopyrrolate was given, no further dysrhythmias occurred.

CONCLUSION

In this patient, mechanical stimulation of the falx likely resulted in the hyperactivity of the trigeminal ganglion, thereby triggering TCR. The dorsal region of the spinal trigeminal tract includes neurons from hypoglossal and vagus nerves, and projections have been seen between the vagus and trigeminal nuclei. The vagus provides parasympathetic innervation to the heart, vascular smooth muscle, and abdominal viscera. Vagal stimulation via these connections after trigeminal nerve activation likely accounts for the reflexive response of asystole seen in this patient. This is confirmed by the observation that the reflex was inhibited by the anticholinergic effects of glycopyrrolate. Awareness of TCR allows for early detection and appropriate treatment.

The insular lobe of Reil--its anatamico-functional, behavioural and neuropsychiatric attributes in humans--a review

There is considerable clinical and experimental research to explore the anatamico-functional correlations of the limbic lobe to establish its relevance in modern neuroscience. The insula being a pivotal structure in the concept of the greater limbic lobe, we have attempted to highlight in this review the topographical anatomy and development, the remarkable heterogeneity of the insular cortical architecture, the widespread multifaceted spectrum of functional connectivity patterns and how this is translated to its behavioural specialisation in humans. The insula serves as an intergration cortex for multimodal convergence of distributed neural networks such as the somesthetic-limbic, insulo-limbic, insulo-orbito-temporal and the prefrontal-striato-pallidal-basal forebrain. This provides the conceptual framework to facilitate functional and clinical considerations relevant to the various behavioural and neuropsychiatric disorders outlined in this review. The functional role of the insula in these disorders with particular reference to the current functional neuroimaging data has been also reviewed in this article.

Human cardiovascular and gustatory brainstem sites observed by functional magnetic resonance imaging

The reflex control and relay to higher brain sites of visceral sensory information within the central nervous system is mediated via discrete sites in the brainstem. Anatomical characterization of these sites in humans has been limited due to the invasive nature of such research. The present study employed 4 Tesla functional magnetic resonance imaging (fMRI) to characterize brainstem sites involved in autonomic control in the human. Eight subjects performed tasks that activate the general visceral (the isometric hand-grip, maximal inspiration, Valsalva maneuver) or special visceral sensory systems (sucrose administration to the tongue). Activation of the nucleus of the solitary tract and parabrachial nucleus was consistently observed with all general visceral tasks. Periaqueductal gray area activation was observed during the maximal inspiration and Valsalva maneuver conditions and raphe activation was present in response to isometric hand-grip and maximal inspiration tasks. The activation in the nucleus of the solitary tract was consistently more rostral in the medulla during sucrose administration than during performance of the other experimental tasks. This finding is consistent with what has been previously demonstrated in animals. This is the first study to image the human brainstem with respect to visceral control and demonstrates the feasibility of using high-resolution fMRI to study the functional organization of the human brainstem.

Anatomic relationships of the human nucleus of the solitary tract in the medulla oblongata: a DiI labeling study

The nucleus of the solitary tract (nTS) is a major site of brainstem control of vital functions (e.g., cardiovascular reflexes and respiration). We examined anatomic relationships of the human nucleus of the solitary tract, using a bidirectional lipophilic fluorescent tracer 1-1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) in 10 postmortem human fetal midgestational medullae oblongatae. Labeling by diffusion of DiI from the nucleus of the solitary tract included: (1) neuropil of all future subdivisions of the nucleus of the solitary tract ipsilateral to the DiI crystal; (2) stellate cells in the caudal raphe at the junction of the nucleus raphe pallidus and the arcuate nucleus at the ventral medullary surface, as well as single fibers along the caudal raphe and the arcuate nucleus; (3) cells and fibers in other medullary areas related to autonomic and respiratory control, including the dorsal motor nucleus of the vagus, nucleus ambiguus complex/ventral respiratory group, rostral ventrolateral medulla (RVLM) and caudal ventrolateral medulla (CVLM), and medullary reticular formation. The pattern of connections of the nucleus of the solitary tract already established by midgestation in the human fetus is consistent with the pattern previously demonstrated in adult experimental animals. A major finding of the study is that of the stellate cells at the junction of nucleus raphe pallidus and the arcuate nucleus at the ventral medullary surface, which project to the nucleus of the solitary tract, and could be homologous to chemosensitive serotonergic neurons at the midline ventral medullary surface of experimental animals. This connection between the ventral caudal raphe and the nucleus of the solitary tract may participate in chemoreception and central regulation of cardiorespiratory reflexes during human perinatal development; it is, therefore, relevant to the study of sudden infant death syndrome (SIDS).

Motion sickness and migraine: optokinetic stimulation increases scalp tenderness, pain sensitivity in the fingers and photophobia

The aim of this study was to determine whether scalp tenderness and photophobia, two well-recognized symptoms of migraine, develop during the motion sickness induced by optokinetic stimulation. To investigate whether motion sickness has a general influence on pain perception, pain was also assessed in the fingertips. After optokinetic stimulation, nausea increased more and headache persisted longer in 21 migraine sufferers than in 15 non-headache controls. Scalp tenderness increased during optokinetic stimulation in nauseated subjects, and pain in the fingertips increased more and photophobia persisted longer in migraine sufferers than controls. These findings suggest that the disturbance responsible for nausea also sensitizes trigeminal nociceptive neurones or releases inhibitory controls on their discharge. A low nausea threshold and a propensity for sensitization to develop rapidly in nociceptive pathways may increase susceptibility to migraine.

Anterior insular cortex: linking intestinal pathology and brain function in autism-spectrum subgroups

Autism includes deficits in communications skills and is associated with intestinal pathology. Numerous parents and some physicians report that an autistic child's attention and language improve in response to treatments which eliminate certain dietary antigens and/or which improve intestinal health. For at least some autism-spectrum children, the link between intestinal pathology, attention, and language may derive from shared neuroanatomic pathways within the anterior insular cortex (aIC); from a neurotrophic virus such as herpes simplex (HSV) migrating within afferents to the insular cortex; and/or from synaptic exhaustion in the aIC as induced by chronically inappropriate neuronal activity in the enteric nervous system and/or its vagal efferents.

Anatomic relationships of the human nucleus paragigantocellularis lateralis: a DiI labeling study

The nucleus paragigantocellularis lateralis (PGL) is located in the rostral ventrolateral medulla (RVLM), a brainstem region that regulates homeostatic functions, such as blood pressure and cardiovascular reflexes, respiration. central chemosensitivity and pain. In the present study, we examined anatomic relationships of the human nucleus paragigantocellularis lateralis using a bidirectional lipophilic fluorescent tracer, 1,1'-dioctadecyl-3,3.3',3'-tetramethylindocarbocyanine perchlorate (DiI), in nine postmortem human fetal midgestational brainstems. The areas which were labeled by diffusion of DiI from the nucleus paragigantocellularis lateralis included the arcuate nucleus (ARC) of the medulla, caudal raphe (nucleus raphe obscurus and pallidus), hilum and amiculum of the inferior olive, bilateral "reticular formation" (including the nucleus paragigantocellularis lateralis, nucleus gigantocellular-is and the intermediate reticular zone (IRZ)). vestibular and cochlear nuclei, cells and fibers at the floor of the fourth ventricle with morphologic features of tanycytes, parabrachial nuclei (PBN), medial lemniscus, lateral lemniscus, inferior cerebellar peduncle and cerebellar white matter, central tegmental tract, and the capsule of the red nucleus. This pattern of DiI labeling bears many similarities with the pattern of connections of the nucleus paragigantocellularis lateralis previously demonstrated by tract-tracing methods in experimental animals, and is consistent with the role of the nucleus paragigantocellularis lateralis in central regulation of homeostatic functions. In contrast to the animal studies, however, we did not demonstrate connections of the nucleus paragigantocellularis lateralis with the nucleus of the tractus solitarius (nTS) (only connections with the rostral subdivision were examined), locus coeruleus, or the periaqueductal gray (PAG) in the human midgestational brainstem. In our previous studies, six medullary areas showed reduced serotonin receptor binding in a subset of victims of sudden infant death syndrome (SIDS). The present study demonstrated DiI labeling in all of these six areas, suggesting that they are interconnected.