Validation of frontal near-infrared spectroscopy as noninvasive bedside monitoring for regional cerebral blood flow in brain-injured patients.

OBJECT: Near-infrared spectroscopy (NIRS) offers noninvasive bedside measurement of direct regional cerebral arteriovenous (mixed) brain oxygenation. To validate the accuracy of this monitoring technique, the authors analyzed the statistical correlation of NIRS and CT perfusion with respect to regional cerebral blood flow (CBF) measurements. METHODS: The authors retrospectively reviewed all cases in which NIRS measurements were obtained at a single, academic neurointensive care unit from February 2008 to June 2011 in which CT perfusion was performed at the same time as NIRS data was collected. Regions of interest were obtained 2.5 cm below the NIRS bifrontal scalp probe on CT perfusion with an average volume between 2 and 4 ml, with mean CBF values used for purposes of analysis. Linear regression analysis was performed for NIRS and CBF values. RESULTS: The study included 8 patients (2 men, 6 women), 6 of whom suffered subarachnoid hemorrhage, 1 ischemic stroke, and 1 intracerebral hemorrhage and brain edema. Mean CBF measured by CT perfusion was 61 ml/100 g/min for the left side and 60 ml/100 g/min for the right side, while mean NIRS values were 75 on the right and 74 on the left. Linear regression analysis demonstrated a statistically significant probability value (p<0.0001) comparing NIRS frontal oximetry and CT perfusion-obtained CBF values. CONCLUSIONS: The authors demonstrated a linear correlation for frontal NIRS cerebral oxygenation measurements compared with regional CBF on CT perfusion imaging. Thus, frontal NIRS cerebral oxygenation measurement may serve as a useful, noninvasive, bedside intensive care unit monitoring tool to assess brain oxygenation in a direct manner.

Intracranial phosphaturic mesenchymal tumor, mixed connective tissue variant presenting without oncogenic osteomalacia.

BACKGROUND: Phosphaturic mesenchymal tumor, mixed connective tissue variant (PMTMCT) is a rare tumor typically occurring in soft tissues and bone, causing oncogenic (tumor-induced) osteomalacia (TIO) through secretion of the phosphaturic hormone, fibroblast growth factor-23 (FGF-23). Rare tumors identical to PMTMCT occur without known TIO. Intracranial localization of PMTMCT is extremely rare, with only two cases reported in the literature. We present a very unusual case of a patient with an intracranial PMTMCT that presented with neurologic changes without osteomalacia. CASE DESCRIPTION: A 67-year-old woman presented with progressive incontinence, apathy, and abulia after having undergone a total knee replacement 1 month earlier. Imaging disclosed a large left frontal anterior fossa mass. She underwent uncomplicated surgical resection of this tumor. Surprisingly, histopathology suggested PMTMCT. Reverse transcription polymerase chain reaction (RT-PCR) assay demonstrating FGF-23 expression in the tumor confirmed the diagnosis. Serum FGF-23 levels postoperatively were normal and she had no clinical or laboratory evidence of osteomalacia or phosphaturia. CONCLUSION: This report should serve to alert clinicians to the possibility that PMTMCT can be included in the differential diagnosis of intracranial masses even in the absence of tumor-induced osteomalacia.

Medical therapy for ischemic stroke: review of intravenous and intra-arterial treatment options.

BACKGROUND: Thrombolytic therapy is of proven and substantial benefit for select patients with acute cerebral ischemia. Diagnostic options and medical treatment options for acute stroke ischemia have undergone enormous changes in the past decades. Whereas initially stroke treatment was reduced to prevention, management of symptoms, and rehabilitation, nowadays a multitude of different fibrinolytic drugs are available. The wide availability of computed tomography in the late 1980s made thrombolysis a real therapeutic option because it allowed a fast and accurate differentiation between ischemic and hemorrhagic stroke. METHODS: This study reviews these developments and how they have shaped our current use and understanding of thrombolytics in the treatment of acute ischemic stroke. RESULTS: Patient selection remains a central aspect of thrombolytic treatment, and to date, the use of different fibrinolytics has been studied in over 20 large randomized trials for different clinical settings, time windows, and routes of administration. These studies included over 7000 patients, and led to our current understanding of the use of thrombolysis in acute stroke. CONCLUSIONS: Intravenous fibrinolytic therapy within the first 3 hours of ischemic stroke onset offers substantial benefits for virtually all patients with potentially disabling deficits. In the 3- to 4.5-hour treatment window, intravenous fibrinolytic therapy has been shown to offer moderate net benefits when applied to all patients with potentially disabling deficits. Intra-arterial fibrinolytic therapy in the 3- to 6-hour window offers moderate net benefits when applied to all patients with potentially disabling deficits and large-artery cerebral thrombotic occlusions.

Angiographic reversed flow ratio as an indicator of high-grade internal carotid stenosis.

PURPOSE: To examine differential flow through internal carotid artery (ICA) and external carotid artery (ECA) circulations on digital subtraction angiography (DSA) as an indicator of carotid stenosis. MATERIALS AND METHODS: Carotid and cerebral angiograms (N = 148) were retrospectively evaluated, with flow through ICA and ECA circulations scored on a five-point flow scale ratio: a score of 1 indicated ICA flow arrived at the vertex at least 1 second before ECA flow, a score of 3 indicated ICA and ECA flow arrived at the same time, and a score of 5 indicated ECA flow reached the vertex at least 1 second before ICA flow. Sensitivities and specificities for ICA stenosis detection were determined for flow ratios. RESULTS: Sensitivity and specificity varied with stenosis severity and flow grade. In general, deranged flow was an insensitive marker for stenosis; however, flow ratio equalization or frank ratio reversal was a highly specific indicator of ICA stenosis. A flow grade of 3-5 was 88% specific (95% CI, 79%-94%) and 66% sensitive (95% CI, 53%-77%) for stenosis of 70% or greater. A grade of 4 or 5 was 99% specific (95% CI, 93%-99%) and 24% sensitive (95% CI, 15%-37%) and a grade of 5 was 100% specific (95% CI, 94%-100%) and 18% sensitive (95% CI, 9%-29%) for carotid stenosis of 70% or greater. CONCLUSIONS: Identification of deranged differential flow between the ICA and ECA circulations is an insensitive but highly specific marker for high-grade stenosis. Therefore, if flow reversal is identified but the apparent carotid stenosis is mild, further angiographic projections should be used to uncover a highly probable severe carotid stenosis.

MicroNester coils as an adjunct to endovascular embolization.

OBJECTIVES/BACKGROUND: In June 2003, detachable balloons were removed from the US market and were supplanted with coil embolization for parent artery sacrifice in difficult or nonsurgical aneurysms and other vascular pathologies. The current series examines the use of MicroNester pushable coils (Cook Medical, Bloomington, IN) as a low-cost and effective adjunct to detachable coils in the treatment of selected neurovascular pathologies. METHODS: A retrospective analysis of all patients undergoing neurointerventional procedures from November 2003 through May 2008 was performed to identify patients in whom MicroNester coils were used as part of treatment. Analysis of coil type and number as well as pathology was performed. RESULTS: MicroNesters were used in 26 cases, of which 21 were for arterial sacrifice--19 for the internal carotid artery and 2 for the vertebral artery. Fourteen were performed for intracranial aneurysms, 3 for pseudoaneurysms, 2 for carotid cavernous fistulae, 1 for a carotid blowout, and 1 for an arteriovenous malformation. Five additional procedures were transvenous, for treatment of dural arterial venous fistulae. The mean number of coils for artery sacrifice was 13, with an average of 10 MicroNesters. For transvenous embolizations, the means were 30 and 6, respectively. CONCLUSION: MicroNesters are not the coil of choice for most neurointerventional procedures because they are not retrievable. However, when parent artery sacrifice or transvenous occlusion of dural arteriovenous fistulas is the goal, MicroNesters are a relatively inexpensive and equally effective alternative to more expensive, detachable coils and can reduce the procedural costs by $3600 to $6000 for the current series.

Safety of early ambulation after diagnostic and therapeutic neuroendovascular procedures without use of closure devices.

OBJECTIVE: To evaluate the safety of manual compression and early ambulation after diagnostic and therapeutic neuroendovascular procedures. METHODS: Data were prospectively collected and retrospectively analyzed for consecutive patients undergoing diagnostic or therapeutic neuroendovascular procedures. Manual compression at the femoral access site was applied. The target for early ambulation was 2 hours after compression. RESULTS: Three hundred forty-three patients were enrolled, of whom 295 were eligible for early ambulation. Diagnostic procedures totaled 214 (72.5%); therapeutic procedures, 81 (27.5%). Ambulation occurred at 2 hours for 82 patients who underwent a diagnostic and 11 patients who underwent a therapeutic procedure. Overall, 142 patients (66.4%) after a diagnostic and 21 patients (25.9%) after a therapeutic procedure ambulated within 3 hours; 94% of outpatients ambulated within 2 to 3 hours and were dismissed shortly thereafter. Delayed ambulation was related to nursing staff delays, recovery from general anesthesia, or patient preference. Fourteen patients (4.7%)--9 (4.2%) who had a diagnostic and 5 (6.2%) who had a therapeutic procedure--required delayed ambulation because of local oozing (8 patients), a hematoma of less than 5 cm (3 patients), a pseudoaneurysm (2 patients), or a large hematoma requiring surgical evacuation (1 patient). CONCLUSION: Early ambulation is feasible and safe after diagnostic and therapeutic procedures and manual compression. A longer period of bed rest or the routine use of closure devices is often not required; thereby avoiding the costs associated with bed rest and the complications associated with closure devices.

Going viral: fusiform vertebrobasilar and internal carotid aneurysms with varicella angiitis and common variable immunodeficiency.

Intracranial aneurysms in the pediatric population are relatively rare entities. Immunocompromised patients (often from HIV/AIDS or pharmacological immunosuppression) represent a significant fraction of children with cerebral aneurysms. One proposed mechanism of aneurysm formation in these patients is from direct infection of the affected arteries. In this study, the authors report on a case of a 14-year-old girl with common variable immunodeficiency with T-cell dysfunction and a CSF polymerase chain reaction test positive for varicella-zoster virus who underwent evaluation for carotid and basilar artery fusiform aneurysms.

Real-time myocardial perfusion contrast echocardiography and regional wall motion abnormalities after aneurysmal subarachnoid hemorrhage. Clinical article.

OBJECT: The pathophysiology of myocardial dysfunction after subarachnoid hemorrhage (SAH) remains unclear. Using myocardial real-time perfusion contrast echocardiography (RTP-CE), the authors evaluated microvascular function in patients with acute SAH. METHODS: Over a 15-month period, 10 patients with acute SAH and evidence of cardiac dysfunction were prospectively enrolled. The authors performed RTP-CE within 48 hours of SAH diagnosis. Wall motion and myocardial perfusion were evaluated in 16 left ventricle segments. Qualitative and quantitative RTP-CE analyses were conducted to compare patients with and without regional wall motion abnormalities (RWMAs). Follow-up RTP-CE at a mean of 53.7 +/- 43 days was undertaken in patients with baseline RWMAs. RESULTS: Ten patients with SAH and evidence of cardiac dysfunction were prospectively enrolled. There were 3 men and 7 women whose mean age was 63.5 +/- 10.1 years. The authors documented evidence of RWMAs in 6 patients. Normal perfusion was demonstrated by RTP-CE in all patients at baseline and follow-up, despite the presence of RWMAs. Compared with patients presenting with normal wall motion, in patients with RWMAs there was a trend for higher quantitative RTP-CE parameters, suggesting hyperemia with mean myocardial blood flow velocity (beta, s(-1)) of 1.08 +/- 0.61 (95% CI 0-2.61) compared with 1.62 +/- 0.64 (95% CI 0.94-2.29) and myocardial blood flow (A x beta, dB/s) of 0.99 +/- 0.41 (95% CI 0-2.0) versus 1.63 +/- 0.86 (95% CI 0.72-2.53). Follow-up RTP-CE was feasible in 3 patients with RWMAs. Regional systolic function was restored in those who completed follow-up. CONCLUSIONS: The authors found that RTP-CE readily evaluates microvascular function in patients with SAH. Wall motion and perfusion dissociation were observed. Quantitative RTP-CE showed a trend for microvascular hyperemia in patients with RWMAs, suggesting that post-SAH myocardial dysfunction could occur in the absence of microvascular dysfunction.

Myocardial contrast echocardiography in subarachnoid hemorrhage-induced cardiac dysfunction: case report.

OBJECTIVE: Cardiac dysfunction is a well-known complication of aneurysmal subarachnoid hemorrhage (SAH) that is generally regarded as secondary to catecholamine excess rather than overt ischemia. Myocardial contrast echocardiography (MCE) is a novel method of evaluating cardiac function and perfusion. We report the use of MCE in a patient with SAH and correlate the results to coronary angiography. METHODS: Bedside MCE using Definity contrast agent (Bristol-Myers Squibb/Sanofi Pharmaceuticals, New York, NY) was performed at the onset of SAH and at the 1-week and 4-month follow-up evaluations. RESULTS: A 64-year-old woman presented with aneurysmal SAH. She developed transient ST elevation on lateral electrocardiographic leads and elevated cardiac enzymes with creatine-kinase MB isoenzyme of 44.3 ng/ml and troponin of 0.62 ng/ml. An emergent coronary angiogram performed at the outside facility revealed normal coronary anatomy, ejection fraction of 30%, and midventricular akinesis. On transfer to our facility, MCE demonstrated an ejection fraction of 45% with normal coronary perfusion in the akinetic midventricular segments and normally contracting basal and apical segments. At the 4-month follow-up examination, her ejection fraction normalized to 67% and regional wall motion had improved. CONCLUSION: To our knowledge, our case represents the first reported use of MCE in a patient with SAH. MCE demonstrating normal myocardium perfusion in the setting of normal coronary arteries on coronary angiogram and midventricular akinetic segments is compatible with nonischemic injury, which further supports the "catecholamine hypothesis" of neurogenic cardiac stunning. MCE may be a feasible noninvasive method to evaluate myocardial perfusion in the SAH population.

Protection of mitochondrial function and improvement in cognitive recovery in rats treated with hyperbaric oxygen following lateral fluid-percussion injury.

OBJECT: Hyperbaric oxygen (HBO2) has been shown to improve outcome after severe traumatic brain injury, but its underlying mechanisms are unknown. Following lateral fluid-percussion injury (FPI), the authors tested the effects of HBO2 treatment as well as enhanced normobaric oxygenation on mitochondrial function, as measured by both cognitive recovery and cellular adenosine triphosphate (ATP) levels. METHODS: Adult male Sprague-Dawley rats were subjected to moderate lateral FPI or sham injury and were allocated to one of four treatment groups: 1) FPI treated with 4 hours of normobaric 30% O2; 2) FPI treated with 4 hours of normobaric 100% O2; 3) FPI treated with 1 hour of HBO2 plus 3 hours of normobaric 100% O2; and 4) sham-injured treated with normobaric 30% O2. Cognitive outcome was assessed using the Morris water maze (MWM) on Days 11 to 15 after injury. Animals were then killed 21 days postinjury to assess hippocampal neuronal loss. Adenosine triphosphate was extracted from the neocortex and measured using high-performance liquid chromatography. The results showed that injured animals treated with HBO2 or normobaric 100% O2 alone had significantly higher levels of cerebral ATP as compared with animals treated using normobaric 30% O2 (p < or = 0.05). The injured animals treated with HBO2 had significant improvements in cognitive recovery, as characterized by a shorter latency in MWM performance (p < or = 0.05), and decreased neuronal loss in the CA2/3 and hilar regions as compared with those treated with 30% or 100% O2, (p < or = 0.05). CONCLUSIONS: Both hyperbaric and normobaric hyperoxia increased cerebral ATP levels after lateral FPI. In addition, HBO2 treatment improved cognitive recovery and reduced hippocampal neuronal cell loss after brain injury in the rat.

Effect of perfluorocarbons on brain oxygenation and ischemic damage in an acute subdural hematoma model in rats.

OBJECT: This study was conducted to determine whether perfluorocarbons (PFCs) improve brain oxygenation and reduce ischemic brain damage in an acute subdural hematoma (SDH) model in rats. METHODS: Forty adult male Sprague-Dawley rats were allocated to four groups: (1) controls, acute SDH treated with saline and 30% O2; (2) 30-PFC group, acute SDH treated with PFC infusion in 30% O2; (3) 100-O2 group, acute SDH treated with 100% O2; and (4) 100-PFC group, acute SDH treated with PFC plus 100% O2. Ten minutes after the induction of acute SDH, a single dose of PFC was infused and 30% or 100% O2 was administered simultaneously. Four hours later, half of the rats were killed by perfusion for histological study to assess the extent of ischemic brain damage. The other half were used to measure brain tissue oxygen tension (PO2). The volume of ischemic brain damage was 162.4 +/- 7.6 mm3 in controls, 165.3 +/- 11.3 mm3 in the 30-PFC group, 153.4 +/- 17.3 mm3 in the 100-O2 group, and 95.9 +/- 12.8 mm3 in the 100-PFC group (41% reduction compared with controls, p = 0.002). Baseline brain tissue PO2 values were approximately 20 mm Hg, and after induction of acute SDH, PO2 rapidly decreased and remained at 1 to 2 mm Hg. Treatment with either PFC or 100% O2 improved brain tissue PO2, with final values of 5.14 and 7.02 mm Hg, respectively. Infusion of PFC with 100% O2 improved brain tissue PO2 the most, with a final value of 15.16 mm Hg. CONCLUSIONS: Data from the current study demonstrated that PFC infusion along with 100% O2 can significantly improve brain oxygenation and reduce ischemic brain damage in acute SDH.

Cell proliferation and neuronal differentiation in the dentate gyrus in juvenile and adult rats following traumatic brain injury.

It is well known that the cognitive functions of juveniles recover to a greater extent than adult patients following traumatic brain injury (TBI). The exact mechanisms underlying this age-related disparity are unknown; however, we speculate that this improved recovery in juveniles following TBI may be associated with an endogenous neurogenic response in the hippocampus. We, therefore, examined the effects of TBI on cellular proliferation and differentiation in the dentate gyrus (DG) of the hippocampus in juvenile and adult rats following lateral fluid percussion injury (FPI). The temporal profile of the injury-induced proliferative response was determined using BrdU labeling at varying survival times. The differentiation of these newly generated cells was investigated using cell-type specific markers. We found that, following injury, there was a significant increase in cell proliferation in the DG in both injured juveniles and adults at 2 days post injury when compared to shams. When comparing the extent of cell proliferation between juveniles and adults following TBI, the absolute number of cells generated in the subgranular zone (SGZ) was far greater in the juveniles. Moreover, the percentage of newly generated cells in the SGZ that differentiated into neurons was nearly two times higher in the juveniles as compared to adults. Conversely, more glial differentiation was observed in the DG of adult rats. These findings provide compelling evidence that age-related differences in the neurogenic response to injury may underlie the differences observed in cognitive recovery in juvenile mammals as compared to adults following TBI.

Effects of hyperbaric oxygen therapy on cerebral oxygenation and mitochondrial function following moderate lateral fluid-percussion injury in rats.

OBJECT: In the current study, the authors examined the effects of hyperbaric O2 (HBO) following fluid-percussion brain injury and its implications on brain tissue oxygenation (PO2) and O2 consumption (VO2) and mitochondrial function (redox potential). METHODS: Cerebral tissue PO2 was measured following induction of a lateral fluid-percussion brain injury in rats. Hyperbaric O2 treatment (100% O2 at 1.5 ata) significantly increased brain tissue PO2 in both injured and sham-injured animals. For VO2 and redox potential experiments, animals were treated using 30% O2 or HBO therapy for 1 or 4 hours (that is, 4 hours 30% O2 or 1 hour HBO and 3 hours 100% O2). Microrespirometer measurements of VO2 demonstrated significant increases following HBO treatment in both injured and sham-injured animals when compared with animals that underwent 30% O2 treatment. Mitochondrial redox potential, as measured by Alamar blue fluorescence, demonstrated injury-induced reductions at 1 hour postinjury. These reductions were partially reversed at 4 hours postinjury in animals treated with 30% O2 and completely reversed at 4 hours postinjury in animals on HBO therapy when compared with animals treated for only 1 hour. CONCLUSIONS: Analysis of data in the current study demonstrates that HBO significantly increases brain tissue PO2 after injury. Nonetheless, treatment with HBO was insufficient to overcome injury-induced reductions in mitochondrial redox potential at 1 hour postinjury but was able to restore redox potential by 4 hours postinjury. Furthermore, HBO induced an increase in VO2 in both injured and sham-injured animals. Taken together, these data demonstrate that mitochondrial function is depressed by injury and that the recovery of aerobic metabolic function may be enhanced by treatment with HBO.

Perfluorocarbon emulsion improves cerebral oxygenation and mitochondrial function after fluid percussion brain injury in rats.

OBJECTIVE: Cerebral ischemia is a common secondary sequela of traumatic brain injury (TBI). Experimental models of stroke have demonstrated reductions in ischemia after perfluorocarbon (PFC) administration; however, there are no published reports of PFC efficacy after TBI. The current study analyzed the effect of the PFC emulsion Oxygent (AF0144; Alliance Pharmaceutical Corp., San Diego, CA) on cerebral oxygenation, mitochondrial redox potential, and free radical formation after lateral fluid percussion injury. METHODS: After fluid percussion injury, five 2.25 ml/kg doses of PFC or saline were administered to rats breathing 100% O(2), and oxygen tension was recorded. In a second experiment, a single bolus (11.25 ml/kg) of PFC or saline was given after injury, and redox potential and free radical formation were measured at 1 or 4 hours with Alamar blue dye and dihydrorhodamine 123, respectively. RESULTS: Cerebral oxygen tension was significantly increased in both injured and sham animals treated with 11.25 ml/kg of PFC as compared with saline (P < 0.05). Likewise, PFC significantly increased mitochondrial redox potential as compared with saline at 4 hours after injury (P < 0.01). Mitochondrial peroxynitrite and peroxide production also increased with the administration of PFC (P < 0.05). CONCLUSION: The current study demonstrates that a PFC emulsion can significantly increase cerebral oxygenation after TBI and enhance mitochondrial function at 4 hours after injury as compared with saline. This study demonstrates a new therapeutic potential for PFC to enhance cerebral oxygenation and aerobic metabolism after TBI. However, the increased free radical formation with high-dose PFCs suggests the need for further studies combining PFCs with free radical scavengers.

Brain oxygenation and energy metabolism: part I-biological function and pathophysiology.

CONTINUOUS OXYGEN DELIVERY and CO(2) clearance are paramount in the maintenance of normal brain function and tissue integrity. Under normal conditions, aerobic metabolism is the major source of energy in the brain, but this system may be compromised by the interruption of substrate delivery and disturbances in cerebral metabolism. These disruptions are major factors contributing to ischemic and hypoxic brain damage resulting from traumatic brain injury, stroke, and subarachnoid hemorrhage. There is evidence that mitochondrial function also is reduced after injury. Furthermore, early impairment of cerebral blood flow in patients with severe injury correlates with poor tissue oxygenation and may be an important parameter in secondary damage. Recent advances in brain tissue monitoring in the intensive care unit and operating room have made it possible to continuously measure tissue oxygen tension and temperature, as well as certain aspects of brain metabolism and neurochemistry. Therefore, it is important to understand the physiological process and the pathophysiology produced by these events. This is Part I of a two-part review that analyzes the physiology of cerebral oxygenation and metabolism as well as some of the pathological mechanisms involved in ischemic and traumatic brain injuries. Brain tissue monitoring techniques will be examined in the second article of this two-part series. To understand cerebral oxygenation, it is important to understand cerebral blood flow, energy production, ischemia, acidosis, generation of reactive oxygen species, and mitochondrial failure. These issues provide the basis of knowledge regarding brain bioenergetics and are important topics to understand when developing new approaches to patient care.

Stress-induced activation of median raphe serotonergic neurons in rats is potentiated by the neurotensin antagonist, SR 48692.

The activation of rostrally projecting serotonergic (5-HT) neurons by acute sound stress is blocked by exogenous administration of the tridecapeptide neurotensin (NT). 5-HT neurons respond to acute sound stress within the median raphe nucleus (MRN), but not within the dorsal raphe nucleus or hindbrain regions. By use of the NT antagonist, SR 48692, the present study examines the involvement of endogenous NT in modulating the preferential activation of MRN 5-HT neurons by sound stress, and extends the findings with sound stress to two other stressors (swim and tail shock). Activation is determined from the enhanced accumulation of 5-hydroxytryptophan (5-HTP) from various brain regions over basal after inhibition of aromatic amino acid decarboxylase. The NT antagonist, SR 48692, enhances the stress activation of MRN 5-HT neurons and its projections without changing 5-HTP accumulation under basal conditions. Thus, the antagonist, SR 48692, unmasks the action of endogenous NT-containing neurons indicating that they become activated by stress and serve to attenuate the stress-induced response of MRN 5-HT neurons.