Neural population dynamics reveals disruption of spinal circuits' responses to proprioceptive input during electrical stimulation of sensory afferents.

While neurostimulation technologies are rapidly approaching clinical applications for sensorimotor disorders, the impact of electrical stimulation on network dynamics is still unknown. Given the high degree of shared processing in neural structures, it is critical to understand if neurostimulation affects functions that are related to, but not targeted by, the intervention. Here, we approach this question by studying the effects of electrical stimulation of cutaneous afferents on unrelated processing of proprioceptive inputs. We recorded intraspinal neural activity in four monkeys while generating proprioceptive inputs from the radial nerve. We then applied continuous stimulation to the radial nerve cutaneous branch and quantified the impact of the stimulation on spinal processing of proprioceptive inputs via neural population dynamics. Proprioceptive pulses consistently produce neural trajectories that are disrupted by concurrent cutaneous stimulation. This disruption propagates to the somatosensory cortex, suggesting that electrical stimulation can perturb natural information processing across the neural axis.

Supraspinal control of motoneurons after paralysis enabled by spinal cord stimulation.

Spinal cord stimulation (SCS) restores motor control after spinal cord injury (SCI) and stroke. This evidence led to the hypothesis that SCS facilitates residual supraspinal inputs to spinal motoneurons. Instead, here we show that SCS does not facilitate residual supraspinal inputs but directly triggers motoneurons action potentials. However, supraspinal inputs can shape SCS-mediated activity, mimicking volitional control of motoneuron firing. Specifically, by combining simulations, intraspinal electrophysiology in monkeys and single motor unit recordings in humans with motor paralysis, we found that residual supraspinal inputs transform subthreshold SCS-induced excitatory postsynaptic potentials into suprathreshold events. We then demonstrated that only a restricted set of stimulation parameters enables volitional control of motoneuron firing and that lesion severity further restricts the set of effective parameters. Our results explain the facilitation of voluntary motor control during SCS while predicting the limitations of this neurotechnology in cases of severe loss of supraspinal axons.

SUPRASPINAL CONTROL OF MOTONEURONS AFTER PARALYSIS ENABLED BY SPINAL CORD STIMULATION.

Spinal cord stimulation (SCS) restores motor control after spinal cord injury (SCI) and stroke. This evidence led to the hypothesis that SCS facilitates residual supraspinal inputs to spinal motoneurons. Instead, here we show that SCS does not facilitate residual supraspinal inputs but directly triggers motoneurons action potentials. However, supraspinal inputs can shape SCS-mediated activity, mimicking volitional control of motoneuron firing. Specifically, by combining simulations, intraspinal electrophysiology in monkeys and single motor unit recordings in humans with motor paralysis, we found that residual supraspinal inputs transform subthreshold SCS-induced excitatory postsynaptic potentials into suprathreshold events. We then demonstrated that only a restricted set of stimulation parameters enables volitional control of motoneuron firing and that lesion severity further restricts the set of effective parameters. Our results explain the facilitation of voluntary motor control during SCS while predicting the limitations of this neurotechnology in cases of severe loss of supraspinal axons.

POTENTIATION OF CORTICO-SPINAL OUTPUT VIA TARGETED ELECTRICAL STIMULATION OF THE MOTOR THALAMUS.

Cerebral white matter lesions prevent cortico-spinal descending inputs from effectively activating spinal motoneurons, leading to loss of motor control. However, in most cases, the damage to cortico-spinal axons is incomplete offering a potential target for new therapies aimed at improving volitional muscle activation. Here we hypothesized that, by engaging direct excitatory connections to cortico-spinal motoneurons, stimulation of the motor thalamus could facilitate activation of surviving cortico-spinal fibers thereby potentiating motor output. To test this hypothesis, we identified optimal thalamic targets and stimulation parameters that enhanced upper-limb motor evoked potentials and grip forces in anesthetized monkeys. This potentiation persisted after white matter lesions. We replicated these results in humans during intra-operative testing. We then designed a stimulation protocol that immediately improved voluntary grip force control in a patient with a chronic white matter lesion. Our results show that electrical stimulation targeting surviving neural pathways can improve motor control after white matter lesions.

GABA Increases Sensory Transmission In Monkeys.

Sensory input flow is central to voluntary movements. For almost a century, GABA was believed to modulate this flow by inhibiting sensory axons in the spinal cord to sculpt neural inputs into skilled motor output. Instead, here we show that GABA can also facilitate sensory transmission in monkeys and consequently increase spinal and cortical neural responses to sensory inputs challenging our understanding of generation and perception of movement.

Robot Assisted Neurosurgery for High-Accuracy, Minimally-Invasive Deep Brain Electrophysiology in Monkeys.

Traditional methods to access subcortical structures involve the use of anatomical atlases and high precision stereotaxic frames but suffer from significant variations in implantation accuracy. Here, we leveraged the use of the ROSA One(R) Robot Assistance Platform in non-human primates to study electrophysiological interactions of the corticospinal tract with spinal cord circuits. We were able to target and stimulate the corticospinal tract within the internal capsule with high accuracy and efficiency while recording spinal local field potentials and multi-unit spikes. Our method can be extended to any subcortical structure and allows implantation of multiple deep brain stimulation probes at the same time. Clinical Relevance- Our method will allow us to elucidate further roles of the corticospinal tract and its interactions with other processing centers in intact animals and in motor syndromes in the future.

Poststroke arm and hand paresis: should we target the cervical spinal cord?

Despite advances in understanding of corticospinal motor control and stroke pathophysiology, current rehabilitation therapies for poststroke upper limb paresis have limited efficacy at the level of impairment. To address this problem, we make the conceptual case for a new treatment approach. We first summarize current understanding of motor control deficits in the arm and hand after stroke and their shared physiological mechanisms with spinal cord injury (SCI). We then review studies of spinal cord stimulation (SCS) for recovery of locomotion after SCI, which provide convincing evidence for enhancement of residual corticospinal function. By extrapolation, we argue for using cervical SCS to restore upper limb motor control after stroke.

Defining drug and target protein distributions after stent-based drug release: Durable versus deployable coatings.

BACKGROUND: Innovations in drug eluting stent designs make it increasingly important to develop models for differentiating performance through spatial definition of drug, receptor binding and cell state. METHODS: Two designs of sirolimus analog eluting stents were implanted into porcine coronary arteries for 28, 60 or 90 days (n = 9/time point), durable coating (Xience) and deployable absorbable coating (MiStent). Explanted arteries were evaluated for drug content (n = 3/time point) by LC-MS/MS and for drug and target protein (mTOR) distributions by immunofluorescence (IF, n = 6/time point). A computational model was developed to predict drug release and arterial distribution maps. RESULTS: Both stents released the majority of drug load by 28 days, with different tissue retention efficiencies (91.4 ±â€¯4.9% MiStent versus 21.5 ±â€¯1.9% Xience, P < 0.001). Computational modeling of MiStent coating deployment and microcrystal dissolution recapitulated in vivo drug release and net tissue content and predicted that >98.5% of deployed drug remains crystalline through 90 days. Immunofluorescence and computational modeling showed peristrut drug localization for both stents, with similar peaks, but high interstrut levels only at sites of coating deployment from the absorbable coating. Co-localization of mTOR-IF with drug-IF for both devices showed persistent drug effects, though with differential drug-receptor pharmacokinetics. CONCLUSIONS: Immunofluorescence and computational modeling provide insights into drug distribution and binding status that can help differentiate drug delivery technologies. Herein we found that tissue deployment of slow dissolving crystalline drug particles results in temporally and spatially more uniform drug delivery to interstrut zones that might otherwise be under-dosed without excess peristrut drug.

Candidiasis peritoneal: prevalencia y factores de riesgo / Candida peritonitis: prevalence and risk factors

Antecedentes. La obtención de un cultivo positivo de líquido peritoneal para Candida en pacientes con clínica asociada permite establecer el diagnóstico de candidiasis peritoneal (CP), etiología relacionada con mal pronóstico. Es importante conocer sus factores de riesgo y así comenzar un tratamiento empírico precoz. Los pacientes que reciben tratamiento antibiótico prolongado, la infección nosocomial, el género femenino, la afectación del tracto gastrointestinal superior (TGIS) y la existencia de fallo cardiovascular intraoperatorio (FCVI) son los factores de riesgo que se han relacionado con dicha peritonitis. Objetivos. El objetivo principal fue conocer la prevalencia de CP en nuestro hospital y, como objetivos secundarios, relacionar los posibles factores de riesgo asociados. Métodos. Se recoge una muestra de 74 pacientes con diagnóstico de peritonitis, de manera consecutiva, entre 2007 y 2010. Durante el acto quirúrgico se aspira líquido peritoneal libre y se procede a su cultivo. Resultados. La prevalencia de CP obtenida en nuestro hospital es del 17,6%, de la cual el 46,15% de los casos corresponden a Candida albicans. Podemos considerar factores de riesgo para el desarrollo de dicha enfermedad la afectación del TGIS y la aparición de FCVI. La edad, el sexo, la infección nosocomial y el tratamiento antibiótico previo no parecen considerarse factores de riesgo para la misma. Conclusiones. La prevalencia de CP es del 17,6%. Los factores de riesgo que predispondrían son la afectación del TGIS como origen de la peritonitis y el FCVI durante el acto quirúrgico (AU)

Background: A peritoneal fluid with a positive culture for Candida in patients with associated clinical symptoms enables peritoneal candidiasis (PC) to be diagnosed. This etiology is related to a poor prognosis, thus, it is important to know all the risk factors and to start early an empirical treatment. The risk factors associated with this kind of peritonitis are to receive prolonged antibiotic treatment, nosocomial infection, female gender, involvement of the upper gastro-intestinal (UGI) tract, and the ocurrence of an intraoperative cardiovascular failure (CVF). Aims: The principal aim was to determine the prevalence of PC in our hospital, and the secondary aims to determine the associated risk factors. Methods: We obtained samples from 74 patients diagnosed with peritonitis, consecutively from 2007 to 2010. Cultures were performed with the free peritoneal fluid aspirated during surgery. Results: The prevalence of PC obtained in our hospital was 17.6%, from which 46.15% corresponded to Candida albicans. The involvement of the UGI tract and the onset of CVF can be considered risk factors for the development of this pathology. Age, gender, nosocomial infection and previous antibiotic treatment were not related to this pathology. Conclusions: Our prevalence of PC is 17.6%. The risk factors that could predispose are the involvement of the UGI tract as the cause of peritonitis, and CVF during surgical procedure (AU)

[Candida peritonitis: Prevalence and risk factors]. / Candidiasis peritoneal: prevalencia y factores de riesgo.

BACKGROUND: A peritoneal fluid with a positive culture for Candida in patients with associated clinical symptoms enables peritoneal candidiasis (PC) to be diagnosed. This etiology is related to a poor prognosis, thus, it is important to know all the risk factors and to start early an empirical treatment. The risk factors associated with this kind of peritonitis are to receive prolonged antibiotic treatment, nosocomial infection, female gender, involvement of the upper gastro-intestinal (UGI) tract, and the ocurrence of an intraoperative cardiovascular failure (CVF). AIMS: The principal aim was to determine the prevalence of PC in our hospital, and the secondary aims to determine the associated risk factors. METHODS: We obtained samples from 74 patients diagnosed with peritonitis, consecutively from 2007 to 2010. Cultures were performed with the free peritoneal fluid aspirated during surgery. RESULTS: The prevalence of PC obtained in our hospital was 17.6%, from which 46.15% corresponded to Candida albicans. The involvement of the UGI tract and the onset of CVF can be considered risk factors for the development of this pathology. Age, gender, nosocomial infection and previous antibiotic treatment were not related to this pathology. CONCLUSIONS: Our prevalence of PC is 17.6%. The risk factors that could predispose are the involvement of the UGI tract as the cause of peritonitis, and CVF during surgical procedure.

Acute hemodynamic response to beta-blockers and prediction of long-term outcome in primary prophylaxis of variceal bleeding.

BACKGROUND & AIMS: Studies of variceal bleeding have shown that a hemodynamic response to treatment of portal hypertension is appropriate when the hepatic venous pressure gradient (HVPG) decreases below 12 mmHg or by > 20% from baseline. However, in primary prophylaxis, many nonresponders do not bleed and 2 invasive procedures are needed to assess response. We investigated the long-term prognostic value of an acute response to beta-blockers and whether the target reduction in HVPG can be improved in primary prophylaxis. METHODS: An initial hemodynamic study was performed in patients with large varices and without previous bleeding. After baseline measurements were made, propranolol was administered intravenously and measurements were repeated 20 minutes later. Patients were given nadolol daily and a second hemodynamic study was performed. RESULTS: Of 105 patients, 15% had variceal bleeding. Using receiver operating characteristic curve analysis, a decrease of HVPG > or = 10% was the best value to predict bleeding. In the initial study, 75 patients (71%) were responders (HVPG decreased to < or = 12 mmHg or by > or = 10%) and had a lower probability of first bleeding than nonresponders (4% vs 46% at 24 months; P < .001). Acute responders also had a lower risk of developing ascites (P = .001). Chronic responders had a lower probability of bleeding than nonresponders (P < .001). There was a correlation between acute and chronic changes in HVPG (r = 0.62; P = .01). CONCLUSION: The acute hemodynamic response to beta-blockers can be used to predict the long-term risk of first bleeding. An HVPG reduction > 10% from baseline is the best target to define response in primary prophylaxis.

A randomized controlled trial comparing ligation and sclerotherapy as emergency endoscopic treatment added to somatostatin in acute variceal bleeding.

BACKGROUND/AIMS: The currently recommended treatment for acute variceal bleeding is the association of vasoactive drugs and endoscopic therapy. However, which emergency endoscopic treatment combines better with drugs has not been clarified. This study compares the efficacy and safety of variceal ligation and sclerotherapy as emergency endoscopic treatment added to somatostatin. METHODS: Patients admitted with acute gastrointestinal bleeding and with suspected cirrhosis received somatostatin infusion (for 5 days). Endoscopy was performed within 6h and those with esophageal variceal bleeding were randomized to receive either sclerotherapy (N=89) or ligation (N=90). RESULTS: Therapeutic failure occurred in 21 patients treated with sclerotherapy (24%) and in nine treated with ligation (10%) (RR=2.4, 95% CI=1.1-4.9). Failure to control bleeding occurred in 15% vs 4%, respectively (P=0.02). Treatment group, shock and HVPG >16 mmHg were independent predictors of failure. Side-effects occurred in 28% of patients receiving sclerotherapy vs 14% with ligation (RR=1.9, 95% CI=1.1-3.5), being serious in 13% vs 4% (P=0.04). Six-week survival probability without therapeutic failure was better with ligation (P=0.01). CONCLUSIONS: The use of variceal ligation instead of sclerotherapy as emergency endoscopic therapy added to somatostatin for the treatment of acute variceal bleeding significantly improves the efficacy and safety.

Hemodynamic effects of terlipressin and high somatostatin dose during acute variceal bleeding in nonresponders to the usual somatostatin dose.

OBJECTIVES: High dose of somatostatin infusion achieves a greater reduction of hepatic venous pressure gradient (HVPG) than the usual dose, and terlipressin decreases HVPG through mechanisms other than somatostatin. Our aim was to assess the hemodynamic effects of terlipressin and high somatostatin dose during acute variceal bleeding in nonresponders to the usual somatostatin dose. METHODS: Hemodynamic studies were performed in 80 patients with cirrhosis and variceal bleeding during the first 3 days of admission. After baseline measurements, somatostatin was administered (250 microg/h with an initial bolus of 250 microg). Patients were considered responders when the HVPG decreased by >10% from baseline (n = 31). Nonresponders were randomized under double-blind conditions to a control group (n = 7), or to receive terlipressin (2 mg IV bolus, n = 22), or high dose of somatostatin (500 microg/h, n = 20). Final measurements were obtained 30 min later. RESULTS: Terlipressin caused a decrease in HVPG (from 22.2 +/- 5 to 19.1 +/- 5.2, p < 0.01) and heart rate (p < 0.01), while mean arterial pressure increased (p < 0.01). High somatostatin dose also reduced HVPG (from 21.8 +/- 3.4 to 19.6 +/- 3.1, p < 0.01), although this decrease was more pronounced with terlipressin (15%+/- 9%vs 10%+/- 6% from baseline, p= 0.05). Both terlipressin and high somatostatin dose achieved a significantly higher rate of response than that in the control group. A decrease in HVPG >20% was observed in 36% of cases with terlipressin versus 5% with high somatostatin dose (p= 0.02). CONCLUSIONS: In nonresponders to usual somatostatin dose, both terlipressin and high-dose of somatostatin infusion significantly decreased HVPG and increased the rate of hemodynamic responders. Such effects were greater with terlipressin. Both treatments may be an alternative when standard somatostatin fails.

Maintenance of hemodynamic response to treatment for portal hypertension and influence on complications of cirrhosis.

BACKGROUND/AIMS: Following treatment with beta blockers in patients with cirrhosis and portal hypertension, reduction of hepatic venous pressure gradient (HVPG) to <12 mmHg or by >20% of baseline induces an extremely low risk of variceal bleeding. However, several factors such as compliance to therapy or alcohol abstinence may change the initial response after a long follow-up, and the effect of response on other complications of cirrhosis is less clear. The aim of this study was to assess the long-term maintenance of hemodynamic response and its influence on complications of cirrhosis. METHODS: One hundred and thirty two cirrhotic patients received nadolol and isosorbide mononitrate to prevent variceal rebleeding. HVPG was measured at baseline, after 1 to 3 months under treatment and again 12 to 18 months later. RESULTS: Sixty four patients were responders. After a longer follow-up, earlier response did not change in 81% of cases. Changes of response were mainly related to modifications in medication dose or in alcohol intake. As compared with poor-responders, responders had a lower probability of developing ascites (P<0.001) and related conditions, a greater improvement of Child-Pugh score (P=0.03), and a lower likelihood of developing encephalopathy (P=0.001) and of requiring liver transplantation (P=0.002). Eleven responders and 22 poor-responders died (P=0.029). CONCLUSIONS: Hemodynamic response to treatment of portal hypertension is usually sustained after a long-term follow-up. Response decreases the probability of developing complications of cirrhosis and the need for liver transplantation, and significantly improves survival.