Cervical Epidural Electrical Stimulation Increases Respiratory Activity through Somatostatin-Expressing Neurons in the Dorsal Cervical Spinal Cord in Rats.

We tested the hypothesis that dorsal cervical epidural electrical stimulation (CEES) increases respiratory activity in male and female anesthetized rats. Respiratory frequency and minute ventilation were significantly increased when CEES was applied dorsally to the C2-C6 region of the cervical spinal cord. By injecting pseudorabies virus into the diaphragm and using c-Fos activity to identify neurons activated during CEES, we found neurons in the dorsal horn of the cervical spinal cord in which c-Fos and pseudorabies were co-localized, and these neurons expressed somatostatin (SST). Using dual viral infection to express the inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADD), hM4D(Gi), selectively in SST-positive cells, we inhibited SST-expressing neurons by administering Clozapine N-oxide (CNO). During CNO-mediated inhibition of SST-expressing cervical spinal neurons, the respiratory excitation elicited by CEES was diminished. Thus, dorsal cervical epidural stimulation activated SST-expressing neurons in the cervical spinal cord, likely interneurons, that communicated with the respiratory pattern generating network to effect changes in ventilation.SIGNIFICANCE STATEMENT A network of pontomedullary neurons within the brainstem generates respiratory behaviors that are susceptible to modulation by a variety of inputs; spinal sensory and motor circuits modulate and adapt this output to meet the demands placed on the respiratory system. We explored dorsal cervical epidural electrical stimulation (CEES) excitation of spinal circuits to increase ventilation in rats. We identified dorsal somatostatin (SST)-expressing neurons in the cervical spinal cord that were activated (c-Fos-positive) by CEES. CEES no longer stimulated ventilation during inhibition of SST-expressing spinal neuronal activity, thereby demonstrating that spinal SST neurons participate in the activation of respiratory circuits affected by CEES. This work establishes a mechanistic foundation to repurpose a clinically accessible neuromodulatory therapy to activate respiratory circuits and stimulate ventilation.

Epidural electrical stimulation of the cervical spinal cord opposes opioid-induced respiratory depression.

Opioid overdose suppresses brainstem respiratory circuits, causes apnoea and may result in death. Epidural electrical stimulation (EES) at the cervical spinal cord facilitated motor activity in rodents and humans, and we hypothesized that EES of the cervical spinal cord could antagonize opioid-induced respiratory depression in humans. Eighteen patients requiring surgical access to the dorsal surface of the spinal cord between C2 and C7 received EES or sham stimulation for up to 90 s at 5 or 30 Hz during complete (OFF-State) or partial suppression (ON-State) of respiration induced by remifentanil. During the ON-State, 30 Hz EES at C4 and 5 Hz EES at C3/4 increased tidal volume and decreased the end-tidal carbon dioxide level compared to pre-stimulation control levels. EES of 5 Hz at C5 and C7 increased respiratory frequency compared to pre-stimulation control levels. In the OFF-State, 30 Hz cervical EES at C3/4 terminated apnoea and induced rhythmic breathing. In cadaveric tissue obtained from a brain bank, more neurons expressed both the neurokinin 1 receptor (NK1R) and somatostatin (SST) in the cervical spinal levels responsive to EES (C3/4, C6 and C7) compared to a region non-responsive to EES (C2). Thus, the capacity of cervical EES to oppose opioid depression of respiration may be mediated by NK1R+/SST+ neurons in the dorsal cervical spinal cord. This study provides proof of principle that cervical EES may provide a novel therapeutic approach to augment respiratory activity when the neural function of the central respiratory circuits is compromised by opioids or other pathological conditions. KEY POINTS: Epidural electrical stimulation (EES) using an implanted spinal cord stimulator (SCS) is an FDA-approved method to manage chronic pain. We tested the hypothesis that cervical EES facilitates respiration during administration of opioids in 18 human subjects who were treated with low-dose remifentanil that suppressed respiration (ON-State) or high-dose remifentanil that completely inhibited breathing (OFF-State) during the course of cervical surgery. Dorsal cervical EES of the spinal cord augmented the respiratory tidal volume or increased the respiratory frequency, and the response to EES varied as a function of the stimulation frequency (5 or 30 Hz) and the cervical level stimulated (C2-C7). Short, continuous cervical EES restored a cyclic breathing pattern (eupnoea) in the OFF-State, suggesting that cervical EES reversed the opioid-induced respiratory depression. These findings add to our understanding of respiratory pattern modulation and suggest a novel mechanism to oppose the respiratory depression caused by opioids.

Platinum-doped ceria based biosensor for in vitro and in vivo monitoring of lactate during hypoxia.

Measurements of lactate concentrations in blood and tissues are an important indication of the adequacy of tissue oxygenation and could be useful for monitoring the state and progress of a variety of diseases. This paper describes the fabrication, analytical characterization, and physiological application of an amperometric microbiosensor based on lactate oxidase and oxygen-rich platinum doped ceria (Pt-ceria) nanoparticles for monitoring lactate levels during hypoxic conditions. The Pt-ceria nanoparticles provided electrocatalytic amplification for the detection of the enzymatically produced hydrogen peroxide and acted as an internal oxygen source for the enzyme, enabling lactate monitoring in an oxygen depleted tissue. In vitro evaluation of the biosensor demonstrated high selectivity against physiological levels of ascorbic acid, a storage stability of 3 weeks, a fast response time of 6 s, and good, linear sensitivity over a wide concentration range. In vivo experiments performed by placing the biosensor in the hippocampus of anesthetized rats demonstrated the feasibility of continuous lactate monitoring over 2 h ischemia and reperfusion. The results demonstrate that Pt-ceria is a versatile material for use in implantable enzyme bioelectrodes, which may be used to assess the pathophysiology of tissue hypoxia. In addition to measurements in hypoxic conditions, the detection limit of this biosensor was low, 100 pM, and the materials used to fabricate this biosensor can be particularly useful in ultrasensitive devices for monitoring lactate levels in a variety of conditions.

Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part II. Age-associated alterations in serotonin receptor binding profiles within medullary nuclei supporting cardiorespiratory homeostasis.

The failure of chemoreflexes, arousal, and/or autoresuscitation to asphyxia may underlie some sudden infant death syndrome (SIDS) cases. In Part I, we showed that some SIDS infants had altered 5-hydroxytryptamine (5-HT)2A/C receptor binding in medullary nuclei supporting chemoreflexes, arousal, and autoresuscitation. Here, using the same dataset, we tested the hypotheses that the prevalence of low 5-HT1A and/or 5-HT2A/C receptor binding (defined as levels below the 95% confidence interval of controls-a new approach), and the percentages of nuclei affected are greater in SIDS versus controls, and that the distribution of low binding varied with age of death. The prevalence and percentage of nuclei with low 5-HT1A and 5-HT2A/C binding in SIDS were twice that of controls. The percentage of nuclei with low 5-HT2A/C binding was greater in older SIDS infants. In >80% of older SIDS infants, low 5-HT2A/C binding characterized the hypoglossal nucleus, vagal dorsal nucleus, nucleus of solitary tract, and nuclei of the olivocerebellar subnetwork (important for blood pressure regulation). Together, our findings from SIDS infants and from animal models of serotonergic dysfunction suggest that some SIDS cases represent a serotonopathy. We present new hypotheses, yet to be tested, about how defects within serotonergic subnetworks may lead to SIDS.

In Search of a Feedback Signal for Closed-Loop Deep Brain Stimulation: Stimulation of the Subthalamic Nucleus Reveals Altered Glutamate Dynamics in the Globus Pallidus in Anesthetized, 6-Hydroxydopamine-Treated Rats.

Deep Brain Stimulation (DBS) of the subthalamic nucleus (STN) is a surgical procedure for alleviating motor symptoms of Parkinson's Disease (PD). The pattern of DBS (e.g., the electrode pairs used and the intensity of stimulation) is usually optimized by trial and error based on a subjective evaluation of motor function. We tested the hypotheses that DBS releases glutamate in selected basal ganglia nuclei and that the creation of 6-hydroxydopamine (6-OHDA)-induced nigrostriatal lesions alters glutamate release during DBS in those basal ganglia nuclei. We studied the relationship between a pseudo-random binary sequence of DBS and glutamate levels in the STN itself or in the globus pallidus (GP) in anesthetized, control, and 6-OHDA-treated rats. We characterized the stimulus-response relationships between DBS and glutamate levels using a transfer function estimated using System Identification. Stimulation of the STN elevated glutamate levels in the GP and in the STN. Although the 6-OHDA treatment did not affect glutamate dynamics in the STN during DBS in the STN, the transfer function between DBS in the STN and glutamate levels in the GP was significantly altered by the presence or absence of 6-OHDA-induced lesions. Thus, glutamate responses in the GP in the 6-OHDA-treated animals (but not in the STN) depended on dopaminergic inputs. For this reason, measuring glutamate levels in the GP may provide a useful feedback target in a closed-loop DBS device in patients with PD since the dynamics of glutamate release in the GP during DBS seem to reflect the loss of dopaminergic neurons in the SNc.

Minimal handgrip force is needed for transcutaneous electrical stimulation to improve hand functions of patients with severe spinal cord injury.

Spinal cord stimulation enhanced restoration of motor function following spinal cord injury (SCI) in unblinded studies. To determine whether training combined with transcutaneous electrical spinal cord stimulation (tSCS), with or without systemic serotonergic treatment with buspirone (busp), could improve hand function in individuals with severe hand paralysis following SCI, we assessed ten subjects in a double-blind, sham-controlled, crossover study. All treatments-busp, tSCS, and the busp plus tSCS-reduced muscle tone and spasm frequency. Buspirone did not have any discernible impact on grip force or manual dexterity when administered alone or in combination with tSCS. In contrast, grip force, sinusoidal force generation and grip-release rate improved significantly after 6 weeks of tSCS in 5 out of 10 subjects who had residual grip force within the range of 0.1-1.5 N at the baseline evaluation. Improved hand function was sustained in subjects with residual grip force 2-5 months after the tSCS and buspirone treatment. We conclude that tSCS combined with training improves hand strength and manual dexterity in subjects with SCI who have residual grip strength greater than 0.1 N. Buspirone did not significantly improve the hand function nor add to the effect of stimulation.

Complexity of the Nano-Bio Interface and the Tortuous Path of Metal Oxides in Biological Systems.

Metal oxide nanoparticles (NPs) have received a great deal of attention as potential theranostic agents. Despite extensive work on a wide variety of metal oxide NPs, few chemically active metal oxide NPs have received Food and Drug Administration (FDA) clearance. The clinical translation of metal oxide NP activity, which often looks so promising in preclinical studies, has not progressed as rapidly as one might expect. The lack of FDA approval for metal oxide NPs appears to be a consequence of the complex transformation of NP chemistry as any given NP passes through multiple extra- and intracellular environments and interacts with a variety of proteins and transport processes that may degrade or transform the chemical properties of the metal oxide NP. Moreover, the translational models frequently used to study these materials do not represent the final therapeutic environment well, and studies in reduced preparations have, all too frequently, predicted fundamentally different physico-chemical properties from the biological activity observed in intact organisms. Understanding the evolving pharmacology of metal oxide NPs as they interact with biological systems is critical to establish translational test systems that effectively predict future theranostic activity.

Deep brain stimulation of the nucleus accumbens reduces alcohol intake in alcohol-preferring rats.

OBJECT: The authors tested the hypothesis that deep brain stimulation (DBS) in the nucleus accumbens (NAcc) decreases alcohol intake in alcohol-preferring (P) rats after each animal has established a stable, large alcohol intake and after P rats with an established intake have been deprived of alcohol for 4-6 weeks. METHODS: Bipolar stimulating electrodes were bilaterally placed in the NAcc using stereotactic coordinates. In the first study, P rats (9 animals) were allowed to establish a stable pattern of alcohol intake (about 5-7 g/day) over approximately 2 weeks, and the acute effects of DBS in the NAcc (140-150 Hz, 60-microsec pulse width, and 200-microA current intensity) on alcohol intake and alcohol preference were studied. Each animal acted as its own control and received 1 hour of DBS followed by 1 hour of sham-DBS or vice versa on each of 2 sequential days. The order of testing (sham-DBS vs DBS) was randomized. In the second study, each animal was allowed to establish a stable alcohol intake and then the animal was deprived of alcohol for 4-6 weeks. Animals received DBS (6 rats) or sham-DBS (5 rats) in the NAcc for 24 hours starting when alcohol was reintroduced to each animal. RESULTS: Deep brain stimulation in the NAcc, as compared with a period of sham-DBS treatment in the same animals, acutely decreased alcohol preference. Furthermore, alcohol consumption and preference were significantly reduced in the DBS group compared with the sham treatment group during the first 24 hours that alcohol was made available after a period of forced abstinence. CONCLUSIONS: The NAcc plays a key role in the rewarding and subsequent addictive properties of drugs of abuse in general and of alcohol in particular. Deep brain stimulation in the NAcc reduced alcohol consumption in P rats both acutely and after a period of alcohol deprivation. Therefore, DBS in the NAcc coupled with other neurophysiological measurements may be a useful tool in determining the role of the NAcc in the mesocorticolimbic reward circuit. Deep brain stimulation in the NAcc may also be an effective treatment for reducing alcohol consumption in patients who abuse alcohol and have not responded to other forms of therapy.

Optical recording of intracellular pH in respiratory chemoreceptors.

We studied the spontaneously active in vitro tadpole brainstem and recorded whole nerve respiratory activity while simultaneously visualizing intracellular pH (pHi) dynamics using the pH-sensitive dye, 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF, AM). The isolated, superfused tadpole brainstem is well oxygenated and retains synaptic connectivity among respiratory central pattern generators, central respiratory chemoreceptors, and respiratory motor neurons. We generated a calibration curve to correlate the emitted fluorescence of BCECF to pHi. In addition, we demonstrated that the dye loading protocol that we established labeled an adequate number of cells and did not disrupt spontaneous respiratory rhythmogenesis or the respiratory response to central chemoreceptor stimulation. Validation of the use of the pH sensitive dye BCECF in this preparation will permit further characterization of the pH regulatory responses of central respiratory chemoreceptors and allow correlation between the changes in pHi in central chemoreceptors and respiratory motor output recorded from cranial nerves.

Serotonergic modulation of respiratory rhythmogenesis and central chemoreception.

In addition to evidence supporting serotonergic modulation of respiratory rhythmogenesis, serotonergic mechanisms play a role in central respiratory chemoreception. We examined the role of serotonin 5HT1A receptors in respiratory rhythmicity and central respiratory chemosensitivity in in vitro brainstem preparations of the bullfrog tadpole, Rana catesbeiana. Spontaneous respiratory motor output was recorded from cranial nerve 7 at control bath pH (7.8) and hypercapnic bath pH (7.4) as bath concentrations of a 5HT1A receptor agonist were steadily increased from 0.5 to 25 microM. Activation of the 5HT1A receptor significantly altered the respiratory burst cycle. Significant increases in both gill and lung burst cycle were observed in response to bath application of 8-OH-DPAT; gill burst cycle in response to 8-OH-DPAT was influenced by bath pH, as gill burst cycle at bath pH 7.8 was not significantly increased at 0.5 or 5.0 microM 8-OH-DPAT. However, when the pH was reduced to 7.4 gill burst cycle was significantly increased at these same bath concentrations of 8-OH-DPAT. Gill burst amplitude was not altered in response to bath application of 8-OH-DPAT; however, lung burst amplitude was significantly decreased at 25.0 microM 8-OH-DPAT at bath pH 7.8. These data indicate that 5HT1A receptors are involved in neural respiratory rhythmogenic and chemoreceptive circuits in the bullfrog tadpole, and support the hypothesis that abnormalities in serotonergic systems may be an underlying component of Sudden Infant Death Syndrome.

Take a deep breath and wake up: The protean role of serotonin preventing sudden death in infancy.

Recordings from infants who died suddenly and unexpectedly demonstrate the occurrence of recurring apneas, ineffective gasping, and finally, failure to restore eupnea and arouse prior to death. Immunohistochemical and autoradiographic data demonstrate a constellation of serotonergic defects in the caudal raphe nuclei in infants who died of Sudden Infant Death Syndrome (SIDS). The purpose of this review is to synthesize what is known about adaptive responses of the infant to severely hypoxic conditions, which unleash a flood of neuromodulators that inhibit cardiorespiratory function, thermogenesis, and arousal and the emerging role of serotonin, which combats this cardiorespiratory inhibition to foster autoresuscitation, eupnea, and arousal to ensure survival following an hypoxic episode. The laryngeal and carotid body chemoreflexes are potent in newborns and infants, and both reflexes can induce apnea and bradycardia, which may be adaptive initially, but must be terminated if an infant is to survive. Serotonin has a unique ability to touch on each of the processes that may be required to recover from hypoxic reflex apnea: gasping, the restoration of heart rate and blood pressure, termination of apneas and, eventually, stimulation of eupnea and arousal. Recurrent apneic events, bradycardia, ineffective gasping and a failure to terminate apneas and restore eupnea are observed in animals harboring defects in the caudal serotonergic system models - all of these phenotypes are reminiscent of and compatible with the cardiorespiratory recordings made in infants who subsequently died of SIDS. The caudal serotonergic system provides an organized, multi-pronged defense against reflex cardiorespiratory inhibition and the hypoxia that accompanies prolonged apnea, bradycardia and hypotension, and any deficiency of caudal serotonergic function will increase the propensity for sudden unexplained infant death.

Inhibition of monocarboxylate transporter 2 in the retrotrapezoid nucleus in rats: a test of the astrocyte-neuron lactate-shuttle hypothesis.

The astrocyte-neuronal lactate-shuttle hypothesis posits that lactate released from astrocytes into the extracellular space is metabolized by neurons. The lactate released should alter extracellular pH (pHe), and changes in pH in central chemosensory regions of the brainstem stimulate ventilation. Therefore, we assessed the impact of disrupting the lactate shuttle by administering 100 microM alpha-cyano-4-hydroxy-cinnamate (4-CIN), a dose that blocks the neuronal monocarboxylate transporter (MCT) 2 but not the astrocytic MCTs (MCT1 and MCT4). Administration of 4-CIN focally in the retrotrapezoid nucleus (RTN), a medullary central chemosensory nucleus, increased ventilation and decreased pHe in intact animals. In medullary brain slices, 4-CIN reduced astrocytic intracellular pH (pHi) slightly but alkalinized neuronal pHi. Nonetheless, pHi fell significantly in both cell types when they were treated with exogenous lactate, although 100 microM 4-CIN significantly reduced the magnitude of the acidosis in neurons but not astrocytes. Finally, 4-CIN treatment increased the uptake of a fluorescent 2-deoxy-D-glucose analog in neurons but did not alter the uptake rate of this 2-deoxy-D-glucose analog in astrocytes. These data confirm the existence of an astrocyte to neuron lactate shuttle in intact animals in the RTN, and lactate derived from astrocytes forms part of the central chemosensory stimulus for ventilation in this nucleus. When the lactate shuttle was disrupted by treatment with 4-CIN, neurons increased the uptake of glucose. Therefore, neurons seem to metabolize a combination of glucose and lactate (and other substances such as pyruvate) depending, in part, on the availability of each of these particular substrates.

Gestational cigarette smoke exposure and hyperthermic enhancement of laryngeal chemoreflex in rat pups.

Laryngeal chemoreflex (LCR) apnea occurs in infant mammals of many species in response to water or other liquids in the laryngeal lumen. The apnea can last for many seconds, sometimes leading to dangerous hypoxemia, and has therefore been considered as a possible mechanism in the Sudden Infant Death Syndrome (SIDS). We have found recently that this reflex is markedly prolonged in decerebrate piglets and anesthetized rat pups that are warmed 1-3 degrees C above their normal body temperatures. We intermittently exposed pregnant rats to cigarette smoke and examined the LCR in their four- to fifteen-day-old offspring under general anesthesia, with and without whole body warming. During warming, pups of gestationally smoke-exposed dams had significantly longer LCR-induced respiratory disruption than similarly warmed control pups. The results may be significant for the pathogenesis and/or prevention of SIDS as maternal cigarette smoking during human pregnancy and heat stress in infants are known risk factors for SIDS.

Muscles of Breathing: Development, Function, and Patterns of Activation.

This review is a comprehensive description of all muscles that assist lung inflation or deflation in any way. The developmental origin, anatomical orientation, mechanical action, innervation, and pattern of activation are described for each respiratory muscle fulfilling this broad definition. In addition, the circumstances in which each muscle is called upon to assist ventilation are discussed. The number of "respiratory" muscles is large, and the coordination of respiratory muscles with "nonrespiratory" muscles and in nonrespiratory activities is complex-commensurate with the diversity of activities that humans pursue, including sleep (8.27). The capacity for speech and adoption of the bipedal posture in human evolution has resulted in patterns of respiratory muscle activation that differ significantly from most other animals. A disproportionate number of respiratory muscles affect the nose, mouth, pharynx, and larynx, reflecting the vital importance of coordinated muscle activity to control upper airway patency during both wakefulness and sleep. The upright posture has freed the hands from locomotor functions, but the evolutionary history and ontogeny of forelimb muscles pervades the patterns of activation and the forces generated by these muscles during breathing. The distinction between respiratory and nonrespiratory muscles is artificial, as many "nonrespiratory" muscles can augment breathing under conditions of high ventilator demand. Understanding the ontogeny, innervation, activation patterns, and functions of respiratory muscles is clinically useful, particularly in sleep medicine. Detailed explorations of how the nervous system controls the multiple muscles required for successful completion of respiratory behaviors will continue to be a fruitful area of investigation. © 2019 American Physiological Society. Compr Physiol 9:1025-1080, 2019.

Clinical measurements obtained from point-of-care ultrasound images to assess acquisition skills.

BACKGROUND: Current methods of assessing competence in acquiring point-of-care ultrasound images are inadequate. They rely upon cumbersome rating systems that do not depend on the actual outcome measured and lack evidence of validity. We describe a new method that uses a rigorous statistical model to assess performance of individual trainees based on the actual task, image acquisition. Measurements obtained from the images acquired (the actual desired outcome) are themselves used to validate effective training and competence acquiring ultrasound images. We enrolled a convenience sample of 21 spontaneously breathing adults from a general medicine ward. In random order, two trainees (A and B) and an instructor contemporaneously acquired point-of-care ultrasound images of the inferior vena cava and the right internal jugular vein from the same patients. Blinded diameter measurements from each ultrasound were analyzed quantitatively using a multilevel model. Consistent mean differences between each trainee's and the instructor's images were ascribed to systematic acquisition errors, indicative of poor measurement technique and a need for further training. Wider variances were attributed to sporadic errors, indicative of inconsistent application of measurement technique across patients. In addition, the instructor recorded qualitative observations of each trainee's performance during image acquisition. RESULTS: For all four diameters, the means and variances of measurements from trainee A's images differed significantly from the instructor's, whereas those from trainee B's images were comparable. Techniques directly observed by the instructor supported these model-derived findings. For example, mean anteroposterior diameters of the internal jugular vein obtained from trainee A's images were 3.8 mm (90% CI 2.3-5.4) smaller than from the instructor's; this model-derived finding matched the instructor's observation that trainee A compressed the vein during acquisition. Instructor summative assessments agreed with model-derived findings, providing internal validation of the descriptive and quantitative assessments of competence acquiring ultrasound images. CONCLUSIONS: Clinical measurements obtained from point-of-care ultrasound images acquired contemporaneously by trainees and an instructor can be used to quantitatively assess the image acquisition competence of specific trainees. This method may obviate resource-intensive qualitative rating systems that are based on ultrasound image quality and direct observation, while also helping instructors guide remediation.

Antioxidant Enzyme-Mimetic Activity and Neuroprotective Effects of Cerium Oxide Nanoparticles Stabilized with Various Ratios of Citric Acid and EDTA.

Cerium oxide (CeO2) nanoparticles (CeNPs) are potent antioxidants that are being explored as potential therapies for diseases in which oxidative stress plays an important pathological role. However, both beneficial and toxic effects of CeNPs have been reported, and the method of synthesis as well as physico-chemical, biological, and environmental factors can impact the ultimate biological effects of CeNPs. In the present study, we explored the effect of different ratios of citric acid (CA) and EDTA (CA/EDTA), which are used as stabilizers during synthesis of CeNPs, on the antioxidant enzyme-mimetic and biological activity of the CeNPs. We separated the CeNPs into supernatant and pellet fractions and used commercially available enzymatic assays to measure the catalase-, superoxide dismutase (SOD)-, and oxidase-mimetic activity of each fraction. We tested the effects of these CeNPs in a mouse hippocampal brain slice model of ischemia to induce oxidative stress where the fluorescence indicator SYTOX green was used to assess cell death. Our results demonstrate that CeNPs stabilized with various ratios of CA/EDTA display different enzyme-mimetic activities. CeNPs with intermediate CA/EDTA stabilization ratios demonstrated greater neuroprotection in ischemic mouse brain slices, and the neuroprotective activity resides in the pellet fraction of the CeNPs. The neuroprotective effects of CeNPs stabilized with equal proportions of CA/EDTA (50/50) were also demonstrated in two other models of ischemia/reperfusion in mice and rats. Thus, CeNPs merit further development as a neuroprotective therapy for use in diseases associated with oxidative stress in the nervous system.

Laryngeal apnea in rat pups: effects of age and body temperature.

In neonatal mammals of many species, including human infants, apnea and other reflex responses frequently arise from stimulation of laryngeal receptors by ingested or regurgitated liquids. These reflexes, mediated by afferents in the superior laryngeal nerves (SLNs), are collectively known as the laryngeal chemoreflex (LCR) and are suspected to be responsible for some cases of the sudden infant death syndrome (SIDS). The LCR is strongly enhanced by mild increases in body temperature in decerebrate piglets, a finding that is of interest because SIDS victims are often found in overheated environments. Because of the experimental advantages of studying reflex development and mechanisms in neonatal rodents, we have developed methods for eliciting laryngeal apnea in anesthetized rat pups and have examined the influence of mild hyperthermia in animals ranging in age from 3 to 21 days. We found that apnea and respiratory disruption, elicited either by intralaryngeal water or by electrical stimulation of the SLN, occurred at all ages studied. Raising body temperature by 2-3 degrees C prolonged the respiratory disturbance in response to either stimulus. This effect of hyperthermia was prominent in the youngest animals and diminished with age. We conclude that many studies of the LCR restricted to larger neonatal animals in the past can be performed in infant rodents using appropriate methods. Moreover, the developmental changes in the LCR and in the thermal modulation of the LCR seem to follow different temporal profiles, implying that distinct neurophysiological processes may mediate the LCR and thermal prolongation of the LCR.

A prospective randomized controlled blinded study of three bronchodilators in infants with respiratory syncytial virus bronchiolitis on mechanical ventilation.

OBJECTIVE: To study patients with respiratory syncytial virus bronchiolitis in respiratory failure to make specific measurements reflecting airway resistance before and after treatment with commonly used agents. We hypothesized that racemic epinephrine would decrease airways resistance more effectively than levalbuterol, and levalbuterol would decrease airways resistance more effectively than racemic albuterol. Normal saline was used as a control. DESIGN: Prospective, randomized, controlled, blinded study. SETTING: Tertiary Pediatric Intensive Care Unit in a University affiliated hospital in the northeastern United States. PATIENTS: Twenty-two patients with respiratory syncytial virus bronchiolitis and in respiratory failure were enrolled. All were intubated and ventilated in a volume control mode and sedated. INTERVENTIONS: In a randomized, blinded fashion patients were given four agents: norepinephrine, levalbuterol, racemic albuterol, and normal saline at 6 hr intervals. MEASUREMENTS: As indicators of bronchodilation, peak inspiratory pressure and inspiratory respiratory system resistance were measured before and 20 mins after each agent was given. Thus, each patient acted as his/her own control. MAIN RESULTS: There were small but statistically significant decreases in peak inspiratory pressure after racemic epinephrine treatment, levalbuterol, and racemic albuterol. There was no change in peak inspiratory pressure after inhaled normal saline. Inspiratory respiratory system resistance fell significantly after all treatments, including saline. Heart rate rose significantly after inhaled bronchodilator treatments (p < 0.05 for all treatments). CONCLUSIONS: Similar statistically significant bronchodilation occurred after all three bronchodilators as indicated by a decrease in peak inspiratory pressure and respiratory system resistance, but these changes were small and probably clinically insignificant. However, side effects of bronchodilators, such as tachycardia, also occurred, and these may be clinically significant. Thus the benefit of bronchodilator treatment in these patients is small, does not differ among the drugs we studied and of questionable value.

The effects of environmentally relevant mixtures of estrogens on Japanese medaka (Oryzias latipes) reproduction.

Wastewater effluent contains a variety of estrogenic compounds that vary in potency, but each of which contributes to the overall estrogenicity of the effluent. We hypothesized that the effects of mixtures of estrogens on reproduction in pair breeding medaka (Oryzias latipes) could be predicted by their relative estrogenicity. Relative estrogenicity was defined by the ability of estrogenic compounds to induce vitellogenesis in various species of male fish. We exposed reproducing pairs of medaka to mixtures of the environmental estrogens nonylphenol (NP), 17alpha-ethinylestradiol (EE(2)), and natural 17beta-estradiol (E(2)), as well as treatments of equivalent estrogenicity that were composed of E(2) alone. Reproducing medaka exposed to mixtures of estrogenic compounds and equipotent treatments of estradiol alone had very similar responses in mortality and reproduction (fecundity, number of spawns). However, mixtures of NP, E(2), and EE(2) elicited lower vitellogenic induction than equipotent concentrations of E(2) alone. Therefore, relative estrogenicity was a good model for predicting some, but not all, reproductive responses, and simple additive mixture models may not predict all relevant physiological responses.

Electrocardiogram-synchronized pulsatile extracorporeal life support preserves left ventricular function and coronary flow in a porcine model of cardiogenic shock.

INTRODUCTION: Veno-arterial extracorporeal life support (ECLS) is increasingly being used to treat rapidly progressing or severe cardiogenic shock. However, it has been repeatedly shown that increased afterload associated with ECLS significantly diminishes left ventricular (LV) performance. The objective of the present study was to compare LV function and coronary flow during standard continuous-flow ECLS support and electrocardiogram (ECG)-synchronized pulsatile ECLS flow in a porcine model of cardiogenic shock. METHODS: Sixteen female swine (mean body weight 45 kg) underwent ECLS implantation under general anesthesia and artificial ventilation. Subsequently, acute cardiogenic shock, with documented signs of tissue hypoperfusion, was induced by initiating global myocardial hypoxia. Hemodynamic cardiac performance variables and coronary flow were then measured at different rates of continuous or pulsatile ECLS flow (ranging from 1 L/min to 4 L/min) using arterial and venous catheters, a pulmonary artery catheter, an LV pressure-volume loop catheter, and a Doppler coronary guide-wire. RESULTS: Myocardial hypoxia resulted in declines in mean cardiac output to 1.7±0.7 L/min, systolic blood pressure to 64±22 mmHg, and LV ejection fraction (LVEF) to 22±7%. Synchronized pulsatile flow was associated with a significant reduction in LV end-systolic volume by 6.2 mL (6.7%), an increase in LV stroke volume by 5.0 mL (17.4%), higher LVEF by 4.5% (18.8% relative), cardiac output by 0.37 L/min (17.1%), and mean arterial pressure by 3.0 mmHg (5.5%) when compared with continuous ECLS flow at all ECLS flow rates (P<0.05). At selected ECLS flow rates, pulsatile flow also reduced LV end-diastolic pressure, end-diastolic volume, and systolic pressure. ECG-synchronized pulsatile flow was also associated with significantly increased (7% to 22%) coronary flow at all ECLS flow rates. CONCLUSION: ECG-synchronized pulsatile ECLS flow preserved LV function and coronary flow compared with standard continuous-flow ECLS in a porcine model of cardiogenic shock.