Dual role of mitochondria in producing melatonin and driving GPCR signaling to block cytochrome c release.

G protein-coupled receptors (GPCRs) are classically characterized as cell-surface receptors transmitting extracellular signals into cells. Here we show that central components of a GPCR signaling system comprised of the melatonin type 1 receptor (MT1), its associated G protein, and ß-arrestins are on and within neuronal mitochondria. We discovered that the ligand melatonin is exclusively synthesized in the mitochondrial matrix and released by the organelle activating the mitochondrial MT1 signal-transduction pathway inhibiting stress-mediated cytochrome c release and caspase activation. These findings coupled with our observation that mitochondrial MT1 overexpression reduces ischemic brain injury in mice delineate a mitochondrial GPCR mechanism contributing to the neuroprotective action of melatonin. We propose a new term, "automitocrine," analogous to "autocrine" when a similar phenomenon occurs at the cellular level, to describe this unexpected intracellular organelle ligand-receptor pathway that opens a new research avenue investigating mitochondrial GPCR biology.

Perioperative stroke after carotid endarterectomy: etiology and implications.

BACKGROUND: Carotid endarterectomy (CEA) is the procedure of choice for reducing the risk of stroke in both symptomatic and asymptomatic carotid artery stenoses. Stroke is associated with significant morbidity and mortality peri-operatively (2-3 %). Our primary aim is to evaluate the etiology of these strokes after CEA and their impact on morbidity by comparing the length of stay in the hospital. METHODS: A total of 584 patients with documented neurological status evaluations who underwent CEAs were included in the study. Neurophysiological monitoring data was obtained during CEA for carotid stenosis included eight-channel electroencephalography (EEG) and upper extremity somatosensory evoked potentials (SSEPs). RESULTS: Twenty-one (3.595 %) patients had strokes in the perioperative period and they were more likely to have left-sided surgery (p = 0.008), intraoperative monitoring (IOM) changes (p < 0.001), an intraoperative shunt placed (p = 0.0002) or a hospital stay longer than 5 days (p = 0.0042). Unilateral anterior circulation ischemic stroke were the most common in our series. In a logistic regression model, left-sided surgery was shown to be 4.78 times more likely to be associated with perioperative stroke (1.50-15.27; p = 0.008) while intraoperative shunts were 11.85 times more likely to have strokes (3.97-35.34; p < 0.0001). Patients with stenosis greater than 70 % were 6.67 times less likely to have a stroke (0.04-0.59; p = 0.007). CONCLUSIONS: Ischemic anterior circulation strokes are the most common type of post-operative neurological changes in patients undergoing CEA. Intraoperative shunt placement was a strong predictor of perioperative strokes. Since shunts are only placed following intraoperative monitoring changes, SSEPs and EEG can therefore function as a biomarker of cerebral hypo-perfusion.

Total Hip Arthroplasty Complicated by a Gluteal Hematoma Resulting in Acute Foot Drop.

Total hip arthroplasty is a prevalent orthopedic intervention in the United States. Massive postoperative hematomas are a rare albeit serious complication of the procedure. Sequelae of these hematomas can include lower extremity paralysis from compression of the sciatic nerve. A 66-year-old woman taking aspirin and clopidogrel for coronary stents presented with a complete foot drop, paresthesias, and lower extremity pain 10 days after a total hip arthroplasty. The patient was initially seen by a neurology service at another hospital and thought to have lateral recess stenosis. At the authors' center, magnetic resonance imaging of the lumbar spine failed to show lateral recess stenosis. Urgent pelvic computed tomography showed a large hematoma and raised suspicion of sciatic nerve compression. Hip magnetic resonance imaging showed a right gluteal hematoma compressing the sciatic nerve. The patient was then taken to the operating room for the clot to be evacuated and was later referred for rehabilitation. Massive hematomas after total hip arthroplasty are an important consideration in the differential diagnosis of nontraumatic acute foot drop. Prompt diagnosis may correlate with improved neurological outcome and help reduce overall morbidity.

Isolation of functionally active and highly purified neuronal mitochondria from human cortex.

BACKGROUND: Functional and structural properties of mitochondria are highly tissue and cell dependent, but isolation of highly purified human neuronal mitochondria is not currently available. NEW METHOD: We developed and validated a procedure to isolate purified neuronal mitochondria from brain tissue. The method combines Percoll gradient centrifugation to obtain synaptosomal fraction with nitrogen cavitation mediated synaptosome disruption and extraction of mitochondria using anti mitochondrial outer membrane protein antibodies conjugated to magnetic beads. The final products of isolation are non-synaptosomal mitochondria, which are a mixture of mitochondria isolated from different brain cells (i.e. neurons, astrocytes, oligodendrocytes, microglia) and synaptic mitochondria, which are of neuronal origin. This method is well suited for preparing functional mitochondria from human cortex tissue that is surgically extracted. RESULTS: The procedure produces mitochondria with minimal cytoplasmic contaminations that are functionally active based on measurements of mitochondrial respiration as well as mitochondrial protein import. The procedure requires approximately four hours for the isolation of human neuronal mitochondria and can also be used to isolate mitochondria from mouse/rat/monkey brains. COMPARISON WITH EXISTING METHODS AND CONCLUSIONS: This method will allow researchers to study highly enriched neuronal mitochondria without the confounding effect of cellular and organelle contaminants.