Plasma and organ catecholamine levels following stimulation of the rat insular cortex

Sex Hormone-Specific Neuroanatomy of Takotsubo Syndrome: Is the Insular Cortex a Moderator?

Takotsubo syndrome (TTS), a transient form of dysfunction in the heart’s left ventricle, occurs predominantly in postmenopausal women who have emotional stress. Earlier studies support the concept that the human circulatory system is modulated by a cortical network (consisting of the anterior cingulate gyrus, amygdala, and insular cortex (Ic)) that plays a pivotal role in the central autonomic nervous system in relation to emotional stressors. The Ic plays a crucial role in the sympathovagal balance, and decreased levels of female sex hormones have been speculated to change functional cerebral asymmetry, with a possible link to autonomic instability. In this review, we focus on the Ic as an important moderator of the human brain–heart axis in association with sex hormones. We also summarize the current knowledge regarding the sex-specific neuroanatomy in TTS.

Functional organization of the insula in men and women with obstructive sleep apnea during Valsalva

STUDY OBJECTIVES

Obstructive sleep apnea (OSA) patients show impaired autonomic regulation, perhaps related to functional reorganization of the insula, which in healthy individuals shows sex-specific anterior and right dominance during sympathetic activation. We examined insular organization of responses to a Valsalva maneuver in OSA with functional magnetic resonance imaging (fMRI).

METHODS

We studied 43 newly diagnosed OSA (age mean ± SD: 46.8 ± 8.7 years; apnea-hypopnea index (AHI) ± SD: 32.1 ± 20.1 events/hour; 34 males) and 63 healthy (47.2 ± 8.8 years; 40 males) participants. Participants performed four 18-second Valsalva maneuvers (1-minute intervals, pressure ≥ 30 mmHg) during scanning. fMRI time trends from five insular gyri-anterior short (ASG); mid short (MSG); posterior short (PSG); anterior long (ALG); and posterior long (PLG)-were assessed for within-group responses and between-group differences with repeated measures ANOVA (p < 0.05); age and resting heart rate (HR) influences were also assessed.

RESULTS

Right and anterior fMRI signal dominance appeared in OSA and controls, with no between-group differences. Separation by sex revealed group differences. Left ASG anterior signal dominance was lower in OSA versus control males. Left ASG and ALG anterior dominance was higher in OSA versus control females. In all right gyri, only OSA females showed greater anterior dominance than controls. Right dominance was apparent in PSG and ALG in all groups; females showed right dominance in MSG and PLG. OSA males did not show PLG right dominance. Responses were influenced substantially by HR but modestly by age.

CONCLUSIONS

Anterior and right insular fMRI dominance appears similar in OSA versus control participants during the sympathetic phase of the Valsalva maneuver. OSA and control similarities were present in just males, but not necessarily females, which may reflect sex-specific neural injury.

Insula stroke: the weird and the worrisome

Infarction of the insula is a common scenario with large tissue-volume strokes in the middle cerebral artery territory. Considered to be part of the central autonomic network, infarction of this region is associated with autonomic disturbances, in particular cardiovascular dysregulation. Risk of aspiration following stroke is also associated with involvement of the insula, consistent with its purported participation in complex functions of the mouth and pharynx. Strokes restricted to the insula are rare and present with a broad range of symptoms that offer a window of insight into the diverse functionality of the insular cortex. Chemosensory, autonomic, vestibular, auditory, somatosensory, language and oropharyngeal functional deficits are all recognised, among others. Long-term sequelae are unknown but profound symptoms, such as hemiparesis, are usually transient. Understanding the patterns of dysfunction highlighted provides the basis for future strategies to optimise stroke management on the discovery of insula involvement.

Forebrain neurocircuitry associated with human reflex cardiovascular control

Physiological homeostasis depends upon adequate integration and responsiveness of sensory information with the autonomic nervous system to affect rapid and effective adjustments in end organ control. Dysregulation of the autonomic nervous system leads to cardiovascular disability with consequences as severe as sudden death. The neural pathways involved in reflexive autonomic control are dependent upon brainstem nuclei but these receive modulatory inputs from higher centers in the midbrain and cortex. Neuroimaging technologies have allowed closer study of the cortical circuitry related to autonomic cardiovascular adjustments to many stressors in awake humans and have exposed many forebrain sites that associate strongly with cardiovascular arousal during stress including the medial prefrontal cortex, insula cortex, anterior cingulate, amygdala and hippocampus. Using a comparative approach, this review will consider the cortical autonomic circuitry in rodents and primates with a major emphasis on more recent neuroimaging studies in awake humans. A challenge with neuroimaging studies is their interpretation in view of multiple sensory, perceptual, emotive and/or reflexive components of autonomic responses. This review will focus on those responses related to non-volitional baroreflex control of blood pressure and also on the coordinated responses to non-fatiguing, non-painful volitional exercise with particular emphasis on the medial prefrontal cortex and the insula cortex.

[Cardiac complications of acute brain injury]

The clinical importance of cardiovascular consequences resulting from cerebral injury has long been recognized. However, interactions between the brain and the cardiovascular system remain poorly defined and their importance for the management of patients suffering from acute brain injury is largely underestimated. This should have profound consequences on treatment strategies during anaesthesia and intensive cares of these patients, taking into account not only brain perfusion, but also cardiovascular optimisation. This report summarizes the main data available regarding the cardiovascular consequences of brain death, traumatic brain injury, stroke and epilepsy.

Calcineurin inhibition in splenocytes induced by pavlovian conditioning

Pavlovian conditioning is one of the major neurobiological mechanisms of placebo effects, potentially influencing the course of specific diseases and the response to a pharmacological therapy, such as immunosuppression. In our study with behaviorally conditioned rats, a relevant taste (0.2% saccharin) preceded the application of the immunosuppressive drug cyclosporin A (CsA), a specific calcineurin (CaN) inhibitor. Our results demonstrate that through pavlovian conditioning the particular pharmacological properties of CsA can be transferred to a neutral taste, i.e., CaN activity was inhibited in splenocytes from conditioned rats after reexposure to the gustatory stimulus. Concomitant immune consequences were observed on ex vivo mitogenic challenge (anti-CD3). Particularly, Th1-cytokine, but not Th2-cytokine, production and cell proliferation were impeded. Appropriate pharmacological and behavioral controls certify that all these changes in T-lymphocyte reactivity are attributable to mere taste reexposure. Furthermore, the underlying sympathetic-lymphocyte interaction was revealed modeling the conditioned response in vitro. CaN activity in CD4(+) T lymphocytes is reduced by beta-adrenergic stimulation (terbutaline), with these effects antagonized by the beta-adrenoreceptor antagonist nadolol. In summary, CaN was identified as the intracellular target for inducing conditioned immunosuppression by CsA, contributing to our understanding of the intracellular mechanisms behind "learned placebo effects."

Stroke location and association with fatal cardiac outcomes: Northern Manhattan Study (NOMAS)

BACKGROUND AND PURPOSE

Cardiac mortality after stroke is common, and small studies have suggested an association of short-term cardiac mortality with insular location of cerebral infarction. Few population-based studies with long-term follow-up have evaluated the effect of stroke location on the long-term risk of cardiac death or myocardial infarction (MI) after first ischemic stroke. We sought to determine the association between stroke location and cardiac death or MI in a multiethnic community-based cohort.

METHODS

The Northern Manhattan Study is a population-based study designed to determine stroke incidence, risk factors, and prognosis in a multiethnic urban population. First ischemic stroke patients age 40 or older were prospectively followed up for cardiac death defined as fatal MI, fatal congestive heart failure, or sudden death/arrhythmia and for nonfatal MI. Primary brain anatomic site was determined by consensus of research neurologists. Hazard ratios (HRs) and 95% CIs were calculated by Cox proportional-hazards models and adjusted for vascular risk factors (age, sex, history of coronary disease, hypertension, diabetes, cholesterol, and smoking), stroke severity, infarct size, and stroke etiology.

RESULTS

The study population consisted of 655 patients whose mean age was 69.7+/-12.7 years; 44.6% were men and 51.3% were Hispanic. During a median follow-up of 4.0 years, 44 patients (6.7%) had fatal cardiac events. Of these, fatal MI occurred in 38.6%, fatal congestive heart failure in 18.2%, and sudden death in 43.2%. In multivariate models, clinical diagnosis of left parietal lobe infarction was associated with cardiac death (adjusted HR=4.45; 95% CI, 1.83 to 10.83) and cardiac death or MI (adjusted HR=3.30; 95% CI, 1.45 to 7.51). When analysis of anatomic location was restricted to neuroimaging (computed tomography, magnetic resonance imaging, or both [n=447]), left parietal lobe infarction was associated with cardiac death (adjusted HR=3.37; 95% CI, 1.26 to 8.97), and both left (adjusted HR=3.49; 95% CI, 1.38 to 8.80) and right (adjusted HR=3.13; 95% CI, 1.04 to 9.45) parietal lobe infarctions were associated with cardiac death or MI. We did not find an association between frontal, temporal, or insular stroke and fatal cardiac events, although the number of purely insular strokes was small.

CONCLUSIONS

Parietal lobe infarction is an independent predictor of long-term cardiac death or MI in this population. Further studies are needed to confirm whether parietal lobe infarction is an independent predictor of cardiac events and death. Surveillance for cardiac disease and implementation of cardioprotective therapies may reduce cardiac mortality in patients with parietal stroke.

Neurophysiology of the neurogenic lower urinary tract disorders

The nervous system structures involved in the control of the lower urinary tract (LUT) are usually divided using a neuroanatomical classification system into suprapontine, pontine, spinal and sacral. In all patients with LUT symptoms, after exclusion of local causes, a nervous system disorder needs to be considered. For the diagnosis of neurogenic LUT disorders, in addition to clinical assessment, neurophysiologic testing might be useful. Imaging and other laboratory studies (e.g., cystometry) often provide relevant additional information. Neurophysiologic tests are more useful in patients with sacral compared with suprasacral disorders. Although in patients with LUT disorders external urethral sphincter (EUS) electromyography (EMG) would seem the most appropriate, anal sphincter EMG is the single most useful diagnostic test, particularly for focal sacral lesions, and atypical parkinsonism. Another clinically useful method that tests the sacral segments, and complements EMG, is the sacral (penilo/clitoro-cavernosus) reflex. Kinesiologic EMG is useful to demonstrate detrusor sphincter dyssynergia (i.e., increased EUS activity during bladder contraction), which is particularly common in spinal cord disease. Somatosensory evoked potential (SEP) and motor evoked potential (MEP) studies (cortical and lumbar) may be useful to diagnose clinically silent central lesions. MEP, in addition, seems to be very promising in research into cortical excitability. Theoretically, cortical SEP on bladder/urethra stimulation would be much more useful than pudendal SEP because it tests thin nerve afferents from the pelvic viscera. However, the utility of this technique is limited by technical difficulties, which can be partially overcome by the concomitant recording of a palmar sympathetic skin response (SSR). SSR recorded from the saddle region is also useful for testing the lumbosacral sympathetic system. Although the technique of detrusor EMG has been recently described in humans, a clinically useful test for evaluating the sacral parasympathetic system, which is crucial for LUT functioning, is still lacking.

Role of limbic peptidergic circuits in regulation of arterial pressure, relevant to development of essential hypertension

It is generally accepted that the essential hypertension (EH) is caused by interactions among congenital gene, multiple pathogenetic pressor factors, and disorder of physiologic depressor factors. The central nervous system may play a key role in the development of EH. The underlying mechanisms, however, are not well understood. Studies show that peptidergic transmitters in the limbic forebrain are involved in long-term regulation of arterial pressure and in the pathogenesis of EH. In the limbic forebrain there are peptidergic pressor and depressor circuits. The former includes corticotropin releasing factor-, substance P-, and angiotensin II-circuits; and the latter includes beta-endorphin- and atrial natriuretic peptide-circuits. These circuits extensively interconnect and interact with each other. The altered functions of them may be the pathogenesis of EH. In this review, we focus on the roles of limbic peptidergic circuits in regulation of arterial pressure, relevant to the neurogenetic mechanisms in developing EH.

Power spectrum analysis and cardiovascular morbidity in anxiety disorders

Spectral analysis of heart rate variability (HRV) and related measures has been shown to be a reliable noninvasive technique enabling quantitative assessment of cardiovascular autonomic regulatory responses to autonomic regulatory mechanisms; it provides a dynamic probe of sympathetic and parasympathetic tone, reflecting the interactions between the two. Over 20 studies reported abnormalities of HRV in anxiety, and patients with heart disease and anxiety are at increased risk for morbidity and mortality. Psychiatric drugs partly correct abnormalities of HRV and, recently, autonomic drugs (beta-blockers) have been studied in anxiety disorders. The authors call for further studies, especially in patients with co-existing anxiety disorders and heart disease, incorporating assessment of HRV.

Neural substrates for behaviorally conditioned immunosuppression in the rat

We have previously demonstrated behaviorally conditioned immunosuppression using cyclosporin A as an unconditioned stimulus and saccharin as a conditioned stimulus. In the current study, we examined the central processing of this phenomenon generating excitotoxic lesions before and after acquisition to discriminate between learning and memory processes. Three different brain areas were analyzed: insular cortex (IC), amygdala (Am), and ventromedial nucleus of the hypothalamus (VMH). The results demonstrate that IC lesions performed before and after acquisition disrupted the behavioral component of the conditioned response (taste aversion). In contrast, Am and VMH lesions did not affect conditioned taste aversion. The behaviorally conditioned suppression of splenocyte proliferation and cytokine production (interleukin-2 and interferon-gamma) was differentially affected by the excitotoxic lesions, showing that the IC is essential to acquire and evoke this conditioned response of the immune system. In contrast, the Am seems to mediate the input of visceral information necessary at the acquisition time, whereas the VMH appears to participate within the output pathway to the immune system necessary to evoke the behavioral conditioned immune response. The present data reveal relevant neural mechanisms underlying the learning and memory processes of behaviorally conditioned immunosuppression.

Lateralization in autononic dysfunction in ischemic stroke involving the insular cortex

Autonomic nervous system dysfunction is a common complication of ischemic stroke. Clinical and experimental data indicate hemispheric lateralization in the control of autonomic activity. The insular cortex has also been shown to play a crucial role in the central autonomic network. The aim of this study was to assess cardio-autonomic dysfunction in patients with ischemic insular versus non-insular cortex infarction, and to demonstrate a possible lateralization in autonomic activity mediated by the insular cortex. Sympathetic function was prospectively assessed by determining plasma norepinephrine and epinephrine in 15 patients with left-hemisphere (LH; four insular infarction), and 14 with right-hemisphere (RH) middle cerebral artery (MCA) stroke (five insular infarction). Systolic and diastolic blood pressure and heart rate were recorded during the first 5 days after stroke. Sympathetic activity was significantly higher in insular than in non-insular infarction (p < 0.05) with concomitantly elevated cardiovascular parameters in insular stroke patients. The pathological activation of the sympathetic nervous system was most excessive in RH-stroke involving the insular cortex (p < 0.05). Our data indicate a hemispheric lateralization in autonomic activity which is mediated by the right-sided insular cortex. Patients with RH stroke involving the insular cortex are most susceptible to develop cardio-autonomic dysfunction.

Location-dependent patterns in cardio-autonomic dysfunction in ischaemic stroke

BACKGROUND AND STUDY PURPOSE

Autonomic nervous system dysfunction is a common complication of acute cerebrovascular disorders. The aim of this study was to investigate a possible location-dependent difference in cardio-autonomic function in patients with ischaemic stroke.

PATIENTS AND METHODS

Sympathetic function was prospectively assessed by determining plasma norepinephrine and epinephrine in 19 patients with left-hemisphere (LH), 14 with right-hemisphere (RH) and 6 with brainstem/cerebellar (BS) stroke. Blood pressure, heart rate, cardiac output and transcranial flow velocity in the middle cerebral artery were recorded during the first 5 days after stroke.

RESULTS

Stroke caused an initial increase in sympathetic function in all 3 groups with a spontaneous decrease in norepinephrine in LH (p < 0.01) and BS stroke (p < 0.05) only. Norepinephrine was significantly higher in RH than in BS stroke (p < 0.05). The alterations in autonomic function were paralleled by a sustained elevation in cardiovascular parameters mainly in RH stroke.

CONCLUSIONS

Plasma catecholamines are feasible in monitoring location-dependent autonomic dysfunction in ischaemic stroke. Hemispheric lateralization in autonomic control should be taken into account in the management of stroke because of an increased susceptibility to cardio-autonomic dysfunction in patients with RH stroke.

Impaired heart rate variability in euthymic bipolar patients

BACKGROUND

Power spectral analysis of heart rate variability (HRV) has recently been shown to be a reliable non-invasive test for quantitative assessment of the central sympathovagal interaction that modulates cardiovascular autonomic function.

METHODS

We studied 39 euthymic bipolar patients and 39 controls, matched for age and sex. A high-resolution electrocardiogram was obtained during complete rest. Spectral analysis of R-R intervals was performed by the fast Fourier transform algorithm.

RESULTS

Euthymic bipolar patients at rest are characterized by markedly low HRV, independent of specific drug treatments.

CONCLUSION

While these results of autonomic stability in euthymic bipolar patients are counter-intuitive, the findings may be important in understanding pathophysiology of bipolar affective illness.

Central representation of the sympathetic nervous system in the cerebral cortex

The sympathetic-related regions of the cerebral cortex were identified in rats after pseudorabies virus injections were made in functionally different targets: adrenal gland, stellate ganglion which regulates the heart, or celiac ganglion which innervates the gastrointestinal tract. Extensive transneuronal labeling was found in limbic system areas: (1) extended amygdaloid complex, (2) lateral septum, and (3) infralimbic, insular, and ventromedial temporal cortical regions (viz., ectorhinal cortex=Brodmann's area 36, perirhinal cortex=area 35, lateral entorhinal=area 28, and ventral temporal association cortex=Te3 region). Deep temporal lobe structures were prominently labeled, including the amygdalopiriform and amygdalohippocampal transition areas, ventral hippocampus and ventral subiculum. The cortical circuits mediating emotional-autonomic changes (i.e., mind-body control) are discussed.

Periaqueductal gray matter projections to midline and intralaminar thalamic nuclei of the rat

The periaqueductal gray matter (PAG) projections to the intralaminar and midline thalamic nuclei were examined in rats. Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected in discrete regions of the PAG, and axonal labeling was examined in the thalamus. PHA-L was also placed into the dorsal raphe nuclei or nucleus of Darkschewitsch and interstitial nucleus of Cajal as controls. In a separate group of rats, the retrograde tracer cholera toxin beta-subunit (CTb) was injected into one of the intralaminar thalamic nuclei-lateral parafascicular, medial parafascicular, central lateral (CL), paracentral (PC), or central medial nucleus-or one of the midline thalamic nuclei-paraventricular (PVT), intermediodorsal (IMD), mediodorsal, paratenial, rhomboid (Rh), reuniens (Re), or caudal ventral medial (VMc) nucleus. The distribution of CTb labeled neurons in the PAG was then mapped. All PAG regions (the four columns of the caudal two-thirds of the PAG plus rostral PAG) and the precommissural nucleus projected to the rostral PVT, IMD, and CL. The ventrolateral, lateral, and rostral PAG provided additional inputs to most of the other intralaminar and midline thalamic nuclei. PAG inputs to the VMc originated from the rostral and ventrolateral PAG areas. In addition, the lateral and rostral PAG projected to the zona incerta. No evidence was found for a PAG input to the ventroposterior lateral parvicellular, ventroposterior medial parvicellular, caudal PC, oval paracentral, and reticular thalamic nuclei. PAG --> thalamic circuits may modulate autonomic-, nociceptive-, and behavior-related forebrain circuits associated with defense and emotional responses.

Neurogenic ST depression in stroke

BACKGROUND

Stroke is occasionally associated with ECG repolarization changes including ST depression. Recent evidence suggests a neurogenic contribution to these abnormalities in stroke patients. Animal studies implicate the insular cortex in cardiovascular control. We describe a patient with a left insular infarct and without cardiac or coronary artery disease, who developed ST depression indicating a neurogenic etiology.

CASE DESCRIPTION

A 48 year-old female, with no risk factors for stroke, developed sudden expressive aphasia. MRI brain showed an infarct in the left insular cortex. Twenty-four hour Holter monitoring on the third day revealed transient ST depression more than 1.5 mm, which was not reproducible on subsequent monitoring. Transesophageal echo-cardiography (TEE) was normal. She had no cardiac symptoms and serial ECGs, cardiac enzymes (CKMB) and adenosine thallium scan were normal. To-date, there had been no cardiac events like congestive heart failure or myocardial ischemia.

CONCLUSION

These findings suggest neurogenic ST depression is related to the left insular infarct in view of the normal adenosine thallium scan, non-reproducibility and evanescence of the ST segment changes and lack of associated cardiac symptoms. When neurogenic ST depression is combined with underlying coronary artery disease, it may adversely influence cardiac outcome after stroke.

Altered muscle metabolism associated with vasoconstriction in spontaneously hypertensive rats

In the rat muscle vascular bed, vasoconstrictors either increase or decrease oxygen consumption (VO2). The present study compared the effects of norepinephrine (NE), angiotensin II (ANG II), and 5-hydroxytryptamine (5-HT) on vasoconstriction-associated metabolism in the constant-flow perfused hindlimb of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) in the absence of insulin. Basal perfusion pressure, VO2, glucose uptake, and lactate production were increased by 21.4, 11.9, 46.4, and 44.9% (P < 0.05 for all), respectively, in SHR, which also had higher blood pressure and metabolic rate (P < 0.05) in vivo. Dose-response curves for NE-induced perfusion pressure, VO2, and lactate production in SHR were shifted to the left compared with WKY. Associated with the increased perfusion pressure, NE-induced VO2 and glucose uptake were both decreased (P < 0.01), particularly at high concentrations. These differences were unaffected by 10 microM propranolol but were all diminished by further addition of prazosin (2.5 nM). ANG II stimulated VO2, glucose uptake, and lactate production in both strains, but the increased lactate production was smaller in SHR (P < 0.05) with a proportional decrease (P < 0.05) in glucose uptake. Conversely, 5-HT decreased VO2 in both strains (P < 0.01), and this effect was greater in SHR (P < 0.01). These data suggest that SHR muscle thermogenesis and glucose uptake are impaired during vasoconstriction, especially in response to NE.

The parabrachial nucleus mediates the decreased cardiac baroreflex sensitivity observed following short-term visceral afferent activation

Previous investigations have provided evidence demonstrating that the extracellular release of glutamate into the parabrachial nucleus was significantly enhanced following visceral afferent activation. This period of enhanced glutamate release into the parabrachial nucleus corresponded to a time during which the pressor response to a bolus phenylephrine injection was significantly enhanced, and the reflex bradycardia was attenuated. This decrease in the sensitivity of the baroreflex is suggestive of an enhanced sympathetic tone as a result of the vagal stimulation. The present investigation was done to determine if the decreased baroreflex sensitivity observed following short-term vagal stimulation is mediated by an increase in sympathetic activity and was dependent on the parabrachial synapse. Male Sprague-Dawley rats were anaesthetized with sodium thiobutabarbitol and instrumented to monitor blood pressure and heart rate and for the placement of a stimulating electrode on the left cervical vagus nerve. Femoral arterial blood samples were taken before, during and after 2 h of vagal stimulation which were later assayed for plasma catecholamines. The results showed that plasma norepinephrine levels decreased during, and were significantly elevated immediately following termination of the vagal stimulation, indicative of an increase in sympathetic tone. To determine if the parabrachial nucleus is involved in mediating an enhanced sympathetic activity following vagal stimulation, a second group of animals underwent an identical surgical preparation, vagal stimulation and blood sampling protocol with the addition of bilateral microinjections of either the reversible anaesthetic, lidocaine, or saline into the parabrachial nucleus. The results showed that reversible blockade of the parabrachial nucleus prior to the onset of the vagal stimulation was effective in blocking both the elevation in plasma norepinephrine levels and the depressed baroreflex sensitivity previously observed following 2 h of vagal stimulation. These results suggest that the parabrachial nucleus mediated the sympathoexcitation and consequent depression in baroreflex sensitivity observed following visceral afferent activation.

Role of the insular cortex in the modulation of baroreflex sensitivity

Cervical vagal stimulation for 2 h results in a depressed baroreflex sensitivity produced by an enhanced sympathetic output, as indicated by increased plasma norepinephrine levels. The current study examined the role of the insular cortex in modulating the vagal stimulation-induced changes in baroreflex sensitivity. Male Sprague-Dawley rats were anesthetized with thiobutabarbitol sodium and instrumented for recording blood pressure, heart rate, intravenous drug administration, and vagal afferent nerve stimulation. Stereotaxic microinjections (300 nl) of either 5% lidocaine or 0.9% saline were made bilaterally into the insula. Thirty minutes after 2 h of vagal stimulation, the baroreflex was significantly depressed and plasma norepinephrine levels were significantly elevated in both groups. The baroreflex was also significantly depressed after bilateral lidocaine injections into the insula, independent of vagal stimulation. However, no significant change in plasma norepinephrine was observed, suggesting that an attenuated parasympathetic output contributed to the altered baroreflex. Taken together, the results suggest that the insular cortex modulates the cardiac baroreflex through a modulation of parasympathetic output.

Characterization, distribution and lateralization of baroreceptor-related neurons in the rat insular cortex

The insular cortex contains a site of cardiovascular representation. Stimulation experiments suggest a discrete localization within the rostral posterior insula. In 34 urethane-anesthetized male Sprague-Dawley rats, we investigated whether cells responsive to baroreceptor stimulation with phenylephrine and sodium nitroprusside were selectively clustered within the insula compared with the surrounding frontoparietal cortex, the extent of distribution of these responsive cells within the insula, and whether there was any lateralization of response. In addition, we characterized the cells as SE (sympathoexcitatory), SI (sympathoinhibitory) or null cells using the criteria of Barman. Of the 128 insular cells investigated with extracellular recording techniques, 70% responded to baroreceptor manipulations compared to 32% of the 57 cells investigated outside the insula (P < 0.0001). The majority of the responsive cells were SE units and were distributed widely throughout the insular cortex including anterior areas not previously thought to be involved in cardiovascular control. Within the rostral posterior insula from which cardiovascular effects are mainly obtained in stimulation experiments, lateralization was identified, with significantly more cells responding to blood pressure changes being found within the right posterior insula than the left (P < 0.003). These data confirm the importance of the right posterior insula in the rat as a site of cardiovascular representation; identify a more extensive distribution of cells responsive to blood pressure changes within the insula than previous studies and imply more widespread convergence of visceral afferent information within the insula.

Prognostic significance of ST-segment depression on continuous electrocardiography in patients with acute ischemic neurologic events

Patients with a history of ischemic stroke or transient ischemic attack (TIA) are at significant risk of cardiac death. This study reports the prognostic significance of ST-segment depression and ventricular tachycardia on continuous electrocardiography in 48 consecutive patients hospitalized with an acute ischemic stroke or TIA. Thirty-one percent of patients had episodes of asymptomatic ST-segment depression and 6% had transient ventricular tachycardia on continuous electrocardiographic monitoring. At a mean follow-up of 13 months, 19% had experienced a cardiac outcome, and 19% met criteria for a neurologic outcome. Cardiac and neurologic outcomes, including death, were not significantly different in patients with and without ST-segment depression on continuous electrocardiography. Cardiac outcomes occurred in 13% of patients with ST-segment depression and in 21% of patient without ST-segment depression (p = 0.52). However, ventricular tachycardia was associated with a higher rate of cardiac death (33% vs. 2%, p < 0.01). Only 27% of patients subsequently found to have coronary artery disease had ST-segment depression by continuous electrocardiography. In contrast to patients with coronary artery disease, ST-segment depression on continuous electrocardiography is not associated with poorer outcome among patients with acute ischemic stroke or TIA.

Identification of a cortical site for stress-induced cardiovascular dysfunction

The evidence indicating that the insular cortex is a likely candidate to mediate stress-induced cardiovascular responses is reviewed. Both neuroanatomical and electrophysiological investigations demonstrate that the insular cortex receives an organized representation of visceral information. In addition, the insular cortex also receives highly processed association cortex information. The insular cortex is also highly interconnected with many subcortical limbic and autonomic regions. This combination of sensory input and limbic/autonomic connectivity would be necessary to permit the insular cortex to be a critical site for the integration of emotional and autonomic responses. Stimulation of the insular cortex elicits specific cardiovascular and autonomic responses from discrete sites. Phasic stimulation entrained to the cardiac cycle is even capable of causing severe arrhythmias. The efferent pathways and some of the neurotransmitter mechanisms have determined. It appears that the lateral hypothalamic area is the primary site of synapse for responses originating in the insular cortex and this information is relayed by NMDA glutamatergic receptors and modulated by neuropeptides including neuropeptide Y, neurotensin, leu-enkephalin and dynorphin. Finally, a rat stroke model, which includes the insular cortex in the infarct region indicates that disruption of the insula can produce substantial cardiac and autonomic abnormalities, which might be similar to those produced by stress. Some of the chronic neurochemical changes, including increases in opioids, neuropeptide Y and neurotensin in the central nucleus of the amygdala, which might be mediating these cardiovascular disturbances, have been determined.

ST segment depression detected by continuous electrocardiography in patients with acute ischemic stroke or transient ischemic attack

BACKGROUND AND PURPOSE

Forty percent of patients with a history of ischemic stroke or transient ischemic attack (TIA) have concomitant coronary artery disease. ST segment depression, detected by continuous electrocardiography, is associated with increased cardiac morbidity and mortality in patients with known coronary artery disease. While electrocardiographic changes have been associated with acute stroke, the etiology and significance of these changes remain unclear. In this pilot study we report the prevalence of ST segment depression and ventricular arrhythmias in patients with acute ischemic stroke or TIA monitored by continuous electrocardiography. Clinical predictors of ST segment depression and ventricular arrhythmia are also identified.

METHODS

Consecutive patients presenting with acute ischemic stroke or TIA were enrolled within 72 hours of hospital admission and monitored by continuous electrocardiography for 48 hours. The electrocardiographic results were analyzed for periods of ST segment depression and ventricular arrhythmias.

RESULTS

Of 51 patients with ischemic stroke or TIA, 15 (29%) had episodes of ST segment depression (95% confidence interval, 15% to 43%), and 18 (35%) had ventricular arrhythmias (95% confidence interval, 21% to 49%). In logistic regression analysis, increasing age (P < .02) and a left-sided neurological event (P < .01) were significant predictors of ST segment depression. Increasing numbers of atherosclerotic risk factors, a history of cardiac disease, and increasing or decreasing mean arterial pressure were not predictive of ST segment depression.

CONCLUSIONS

Patients with acute ischemic stroke or TIA have a 29% prevalence of ST segment depression within the first 5 days after their event. In comparison, the prevalence of ST depression is 2.5% to 8% in asymptomatic adults and 43% to 60% in patients with symptomatic coronary artery disease. The association of ST segment depression with left-sided neurological events suggests that the electrocardiographic changes are in part neurologically mediated. Further study is necessary to better define the brain-heart interaction and to determine whether ST segment depression in patients with ischemic stroke or TIA reflects underlying coronary artery disease.

Lateral hypothalamic area neurotransmission and neuromodulation of the specific cardiac effects of insular cortex stimulation

Microstimulation of the rat posterior insular cortex in phase with the ECG R wave elicits pure cardiac effects unaccompanied by changes in blood pressure or respiration. This technique has successfully demonstrated cardiac chronotropic organisation and arrhythmogenesis within the insula. Pathways exist linking the insular cortex with the lateral hypothalamic area (LHA). Similarly, the LHA has previously been shown to mediate the sympathetic and blood pressure effects of insular cortex stimulation. Therefore it was anticipated that the tachycardia elicited by insular phasic microstimulation would be responsive to LHA manipulations. Insular tachycardia sites in 28 chloralose-anesthetised male Wistar rats were phasically stimulated once with each cardiac cycle using 500 microA for 1 min before and after microinfusions (390 nl) into the LHA. The insular tachycardia response was abolished by LHA microinfusions of the synaptic blocker cobaltous chloride (4 mM). LHA microinjection of kynurenic acid (250 mM) attenuated insular tachycardia by 95%. Microinjection of naloxone (30 mM) similarly attenuated the tachycardia by 95%. Met-enkephalin (3.5 mM) was without effect on this response whereas Leu-enkephalin (3.5 mM) and neuropeptide Y (0.01 mM) (NPY) doubled the magnitude of the tachycardia. Dynorphin (0.12 mM), a specific kappa opioid receptor agonist, augmented the response to stimulation of insular tachycardia sites 8-fold. Consequently, it is suggested that the LHA contains an obligatory synapse mediating insular tachycardia and that glutamate is the likely neurotransmitter at this site. Neuromodulation of insular tachycardia may be effected by opiate kappa and NPY receptors, a finding of considerable clinical relevance.