Seizure-Induced Sympathoexcitation Is Caused by Activation of Glutamatergic Receptors in RVLM That Also Causes Proarrhythmogenic Changes Mediated by PACAP and Microglia in Rats.

Cardiovascular autonomic dysfunction in seizure is a major cause of sudden unexpected death in epilepsy. The catecholaminergic neurons in the rostral ventrolateral medulla (RVLM) maintain sympathetic vasomotor tone and blood pressure through their direct excitatory projections to the intermediolateral (IML) cell column. Glutamate, the principal excitatory neurotransmitter in brain, is increased in seizures. Pituitary adenylate cyclase activating polypeptide (PACAP) is an excitatory neuropeptide with neuroprotective properties, whereas microglia are key players in inflammatory responses in CNS. We investigated the roles of glutamate, PACAP, and microglia on RVLM catecholaminergic neurons during the cardiovascular responses to 2 mg/kg kainic acid (KA)-induced seizures in urethane anesthetized, male Sprague Dawley rats. Microinjection of the glutamate antagonist, kynurenic acid (50 nl; 100 mM) into RVLM, blocked the seizure-induced 43.2 ± 12.6% sympathoexcitation (p ≤ 0.05), and abolished the pressor responses, tachycardia, and QT interval prolongation. PACAP or microglia antagonists (50 nl) (PACAP(6-38), 15 pmol; minocycline 10 mg/ml) microinjected bilaterally into RVLM had no effect on seizure-induced sympathoexcitation, pressor responses, or tachycardia but abolished the prolongation of QT interval. The actions of PACAP or microglia on RVLM neurons do not cause sympathoexcitation, but they do elicit proarrhythmogenic changes. An immunohistochemical analysis in 2 and 10 mg/kg KA-induced seizure rats revealed that microglia surrounding catecholaminergic neurons are in a "surveillance" state with no change in the number of M2 microglia (anti-inflammatory). In conclusion, seizure-induced sympathoexcitation is caused by activation of glutamatergic receptors in RVLM that also cause proarrhythmogenic changes mediated by PACAP and microglia. SIGNIFICANCE STATEMENT: Sudden unexpected death in epilepsy is a major cause of death in epilepsy. Generally, seizures are accompanied by changes in brain function leading to uncontrolled nerve activity causing high blood pressure, rapid heart rate, and abnormal heart rhythm. Nevertheless, the brain chemicals causing these cardiovascular changes are unknown. Chemicals, such as glutamate and pituitary adenylate cyclase activating polypeptide, whose expression is increased after seizures, act on specific cardiovascular nuclei in the brain and influence the activity of the heart, and blood vessels. Microglia, which manage excitation in the brain, are commonly activated after seizure and produce pro- and/or anti-inflammatory factors. Hence, we aimed to determine the effects of blocking glutamate, pituitary adenylate cyclase activating polypeptide, and microglia in the RVLM and their contribution to cardiovascular autonomic dysfunction in seizure.

Inhibition of microglial activation with minocycline at the intrathecal level attenuates sympathoexcitatory and proarrhythmogenic changes in rats with chronic temporal lobe epilepsy.

The incidence of sudden unexpected death in epilepsy (SUDEP) is highest in people with chronic and drug-resistant epilepsy. Chronic spontaneous recurrent seizures cause cardiorespiratory autonomic dysfunctions. Pituitary adenylate cyclase-activating polypeptide (PACAP) is neuroprotective, whereas microglia produce both pro- and anti-inflammatory effects in the CNS. During acute seizures in rats, PACAP and microglia produce sympathoprotective effect at the intermediolateral cell column (IML), whereas their action on the presympathetic rostral ventrolateral medulla (RVLM) neurons mediates proarrhythmogenic changes. We evaluated the effect of PACAP and microglia at the IML on sympathetic nerve activity (SNA), cardiovascular reflex responses, and electrocardiographic changes in the post-status epilepticus (SE) model of acquired epilepsy, and control rats. Chronic spontaneous seizures in rats produced tachycardia with profound proarrhythmogenic effects (prolongation of QT interval). Antagonism of microglia, but not PACAP, significantly reduced the SNA and the corrected QT interval in post-SE rats. PACAP and microglia antagonists did not change baroreflex and peripheral or central chemoreflex responses with varied effect on somatosympathetic responses in post-SE and control rats. We did not notice changes in microglial morphology or changes in a number of M2 phenotype in epileptic nor control rats in the vicinity of RVLM neurons. Our findings establish that microglial activation, and not PACAP, at the IML accounts for higher SNA and proarrhythmogenic changes during chronic epilepsy in rats. This is the first experimental evidence to support a neurotoxic effect of microglia during chronic epilepsy, in contrast to their neuroprotective action during acute seizures.

Microglia PACAP and glutamate: Friends or foes in seizure-induced autonomic dysfunction and SUDEP?

Seizure-induced cardiorespiratory autonomic dysfunction is a major cause of sudden unexpected death in epilepsy (SUDEP), and the underlying mechanism is unclear. Seizures lead to increased synthesis, and release of glutamate, pituitary adenylate cyclase activating polypeptide (PACAP), and other neurotransmitters, and cause extensive activation of microglia at multiple regions in the brain including central autonomic cardiorespiratory brainstem nuclei. Glutamate contributes to neurodegeneration, and inflammation in epilepsy. PACAP has neuroprotective, and anti-inflammatory properties, whereas microglia are key players in inflammatory responses in CNS. Seizure-induced increase in PACAP is neuroprotective. PACAP produces neuroprotective effects acting on microglial PAC1 and VPAC1 receptors. Microglia also express glutamate transporters, and their expression can be increased by PACAP in response to harmful or stressful situations such as seizures. Here we discuss the mechanism of autonomic cardiorespiratory dysfunction in seizure, and the role of PACAP, glutamate and microglia in regulating cardiorespiratory brainstem neurons in their physiological state that could provide future therapeutic options for SUDEP.

Alerted microglia and the sympathetic nervous system: A novel form of microglia in the development of hypertension.

Microglia, commonly known as the tissue resident macrophages of the central nervous system (CNS), are ubiquitously expressed in the CNS. Microglia, in their resting, or surveilling, stage, play a critical role in the maintenance of normal neuronal physiology and homeostasis. On activation, microglia can acquire either a neurotoxic (M1) or a neuroprotective (M2) phenotype. Prior to development of the M1 or M2 phenotype, little was known about changes in microglial activity, when subjected to stimuli. It is postulated, that an inability of microglia to maintain neuronal physiology within a normal working range can contribute to the development of cardiovascular disorders (CVDs) such as hypertension, but clear evidence supporting this hypothesis is missing. Even though our understanding of microglial function in a state of CNS injury/inflammation is extensive, the literature concerning role of microglia in the healthy CNS, is limited. Involvement of microglia in the pathophysiology of CVDs, in a neuroprotective/neurotoxic manner, is a key area that requires further investigation.

Dynamic changes in the relationship of microglia to cardiovascular neurons in response to increases and decreases in blood pressure.

Microglia are present throughout the central nervous system (CNS) and express receptors for every known neurotransmitter. During inflammation, microglia change into a state that either promotes removal of debris (M1), or into a state that promotes soothing (M2). Caudal- and rostral- ventrolateral medullary regions (CVLM and RVLM, respectively) of the brainstem are key nuclei involved in all aspects of the cardiovascular system. In this study, we investigate a novel role for microglia in cardiovascular control in the brainstem of adult male Sprague-Dawley (SD) rat. Here we show, that increases and decreases in blood pressure (BP) triggers alertness in the physiology of microglia in the brainstem region; inducing changes in microglial spatial distribution and the number of synapses in contact with microglial end processes. Following 6h of acute hypertension, the number of synapses in contact with microglia increased by ≈30% in both regions of the brainstem, CVLM and RVLM. Induction of acute hypotension for 6h causes microglia to reduce the number of synaptic contacts by >20% in both, CVLM and RVLM, nuclei of the brainstem. Our analysis of the morphological characteristics of microglia, and expression levels of M1 and M2, reveals that the changes induced in microglial behavior do not require any obvious dramatic changes in their morphology. Taken together, our findings suggest that microglia play a novel, unexpected, physiological role in the uninjured autonomic nuclei of CNS; we therefore speculate that microglia act cooperatively with brainstem cardiovascular neurons to maintain them in a physiologically receptive state.

Microglial number is related to the number of tyrosine hydroxylase neurons in SHR and normotensive rats.

Microglia are ubiquitously distributed throughout the central nervous system (CNS) and play a critical role in the maintenance of neuronal homeostasis. Recent advances have shown that microglia, never resting cells of the CNS, continuously monitor and influence neuronal/synaptic activity levels, by communicating with neurons with the aid of their dynamic processes. The brainstem contains many catecholaminergic nuclei that are key to many aspects of brain function. This includes C1 neurons of the ventrolateral medulla that are thought to play a critical role in control of the circulation. Despite the role of catecholaminergic brainstem neurons in normal physiology, the presence of microglia that surrounds them is poorly understood. Here, we investigate the spatial distribution and morphology of microglia in catecholaminergic nuclei of the brainstem in 3 strains of rat: Sprague-Dawley (SD), Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Our data reveal that microglia are heterogeneously distributed within and across different strains of rats. Interestingly, intra-strain comparison of tyrosine hydroxylase-immunoreactive (TH-ir) neuronal and microglial number reveals that microglial number varies with the TH-ir neuronal number in the brainstem. Even though microglial spatial distribution varies across brainstem nuclei, microglial morphology (% area covered, number of end point processes and branch length) does not differ significantly. This work provides the first evidence that even though microglia, in their surveilling state, do not vary appreciably in their morphology across brainstem areas, they do have a heterogeneous pattern of distribution that may be influenced by their local environment.

Thromboembolic disease prophylaxis in patients with hip fracture: a multimodal approach.

OBJECTIVES: To assess if pneumatic compression in conjunction with chemoprophylaxis is an effective way to reduce the incidence of deep vein thrombosis in orthopedic trauma patients sustaining fragility hip fractures. DESIGN: Two hundred patients admitted to the authors' institution between May 1998 and June 2002 for fractures of the hip were prospectively studied. All patients were treated operatively and received the VenaFlow calf compression device on both lower extremities immediately following surgery. Chemical prophylaxis of either aspirin (n = 67) or warfarin (n = 133) was administered in addition to mechanical compression. A noninvasive serial color flow duplex scan was performed 1 to 11 days postoperatively (mean 4.5 days) to determine the presence or absence of deep vein thrombosis. All patients were followed clinically 3 months postoperatively for a clinical evaluation of symptomatic deep vein thrombosis or pulmonary embolism. RESULTS: Overall, the incidence of deep vein thrombosis was 3.5% (7 of 200) and included only 1 proximal thrombosis (1 out of 200, or 0.5%) and no pulmonary embolism. Five of the 7 patients positive for deep vein thrombosis were in the mechanical compression and warfarin prophylaxis group and 2 were in the aspirin arm of the study. For patients with deep vein thrombosis, the average number of risk factors was 3.71, whereas patients without clots averaged 1.75 clinical risk factors (P < or = 0.05). Three patients in the warfarin group developed bleeding complications (1 with a gastrointestinal bleed and 2 with minor bleeding not at the operative site). No evidence of a symptomatic deep vein thrombosis or pulmonary embolism was reported within a 3-month period following hospitalization. CONCLUSIONS: Our findings suggest mechanical compression with the VenaFlow calf compression device in conjunction with chemoprophylaxis is an effective means of reducing thromboembolic disease in this high-risk population.

Correlations between community structure and link formation in complex networks.

BACKGROUND: Links in complex networks commonly represent specific ties between pairs of nodes, such as protein-protein interactions in biological networks or friendships in social networks. However, understanding the mechanism of link formation in complex networks is a long standing challenge for network analysis and data mining. METHODOLOGY/PRINCIPAL FINDINGS: Links in complex networks have a tendency to cluster locally and form so-called communities. This widely existed phenomenon reflects some underlying mechanism of link formation. To study the correlations between community structure and link formation, we present a general computational framework including a theory for network partitioning and link probability estimation. Our approach enables us to accurately identify missing links in partially observed networks in an efficient way. The links having high connection likelihoods in the communities reveal that links are formed preferentially to create cliques and accordingly promote the clustering level of the communities. The experimental results verify that such a mechanism can be well captured by our approach. CONCLUSIONS/SIGNIFICANCE: Our findings provide a new insight into understanding how links are created in the communities. The computational framework opens a wide range of possibilities to develop new approaches and applications, such as community detection and missing link prediction.

Operative treatment of tibial plateau fractures in patients older than 55 years.

Surgical treatment of tibial plateau fractures in the older patient poses an additional challenge because of the underlying condition of the bone and articular surface. We sought to identify risk factors for poorer outcomes in the operative treatment of displaced tibial plateau fractures in older patients. Thirty-nine displaced tibial plateau fractures in patients 55 years and older were treated operatively. Patients were evaluated objectively with Rasmussen clinical and radiologic scoring techniques, and the Short Musculoskeletal Function Assessment and the Short-Form 36 self-assessment instruments. The Rasmussen clinical and radiologic scoring systems, used on average 2.54 years postoperatively, found acceptable results in 87.2% and 82.1% of patients, respectively. The fracture classification of Schatzker was not predictive of results. External fixation was associated with significantly poorer results. Increasing age was associated with poorer clinical and self-assessment scores, although preexisting degenerative joint disease was not. The results from the Short-Form 36 indices were not significantly worse for our study patients. The average Short Musculoskeletal Function Assessment score of our study patients indicated poorer function for mobility than a normative group. Operative treatment of this injury in this population can result in favorable outcomes as evaluated by clinical, radiographic, and self-assessment criteria.