Anil Maybhate

Multiscale Entropy Analysis of EEG for Assessment of Post-Cardiac Arrest Neurological Recovery Under Hypothermia in Rats

Neurological complications after cardiac arrest (CA) can be fatal. Although hypothermia has been shown to be beneficial, understanding the mechanism and establishing neurological outcomes remains challenging because effects of CA and hypothermia are not well characterized. This paper aims to analyze EEG (and the alpha-rhythms) using multiscale entropy (MSE) to demonstrate the ability of MSE in tracking changes due to hypothermia and compare MSE during early recovery with long-term neurological examinations. Ten Wistar rats, upon post-CA resuscitation, were randomly subjected to hypothermia (32degC-34degC, N = 5) or normothermia (36.5degC-37.5degC, N = 5). EEG was recorded and analyzed using MSE during seven recovery phases for each experiment: baseline, CA, and five early recovery phases (R1-R5). Postresuscitation neurological examination was performed at 6, 24, 48, and 72 h to obtain neurological deficit scores (NDSs). Results showed MSE to be a sensitive marker of changes in alpha-rhythms. Significant difference (p < 0.05) was found between the MSE for two groups during recovery, suggesting that MSE can successfully reflect temperature modulation. A comparison of short-term MSE and long-term NDS suggested that MSE could be used for predicting favorability of long-term outcome. These experiments point to the role of cortical rhythms in reporting early neurological response to ischemia and therapeutic hypothermia.

Potential long-term benefits of acute hypothermia after spinal cord injury: Assessments with somatosensory-evoked potentials*

Objective: Neuroprotection by hypothermia has been an important research topic over last two decades. In animal models of spinal cord injury, the primary focus has been assessing the effects of hypothermia on behavioral and histologic outcomes. Although a few studies have investigated electrophysiological changes in descending motor pathways with motor-evoked potentials recorded during cooling, we report here hypothermia induced increased electrical conduction in the ascending spinal cord pathways with somatosensory-evoked potentials in injured rats. In our experiments, these effects lasted long after the acute hypothermia and were accompanied by potential long-term improvements in motor movement. Design: Laboratory investigation. Setting: University medical school. Subjects: Twenty-one female Lewis rats. Interventions: Hypothermia. Measurements and Main Results: All animals underwent spinal cord contusion with the NYU-Impactor by a 12.5-mm weight drop at thoracic vertebra T8. A group (n = 10) was randomly assigned for a systemic 2-hr hypothermia episode (32 ± 0.5°C) initiated approximately 2.0 hrs postinjury. Eleven rats were controls with postinjury temperature maintained at 37 ± 0.5°C for 2 hrs. The two groups underwent preinjury, weekly postinjury (up to 4 wks) somatosensory-evoked potential recordings and standard motor behavioral tests (BBB). Three randomly selected rats from each group were euthanized for histologic analysis at postinjury day 3 and day 28. Compared with controls, the hypothermia group showed significantly higher postinjury somatosensory-evoked potential amplitudes with longer latencies. The BBB scores were also higher immediately after injury and 4 wks later in the hypothermia group. Importantly, specific changes in the Basso, Beattie, Bresnahan scores in the hypothermia group (not seen in controls) indicated regained functions critical for motor control. Histologic evaluations showed more tissue preservation in the hypothermia group. Conclusions: After spinal cord injury, early systemic hypothermia provided significant neuroprotection weeks after injury through improved sensory electrophysiological signals in rats. This was accompanied by higher motor behavioral scores and more spared tissue in acute and postacute periods after injury.

Human Glial-Restricted Progenitors Survive, Proliferate, and Preserve Electrophysiological Function in Rats with Focal Inflammatory Spinal Cord Demyelination

Transplantation of glial progenitor cells results in transplant‐derived myelination and improved function in rodents with genetic dysmyelination or chemical demyelination. However, glial cell transplantation in adult CNS inflammatory demyelinating models has not been well studied. Here we transplanted human glial‐restricted progenitor (hGRP) cells into the spinal cord of adult rats with inflammatory demyelination, and monitored cell fate in chemically immunosuppressed animals. We found that hGRPs migrate extensively, expand within inflammatory spinal cord lesions, do not form tumors, and adopt a mature glial phenotype, albeit at a low rate. Human GRP‐transplanted rats, but not controls, exhibited preserved electrophysiological conduction across the spinal cord, though no differences in behavioral improvement were noted between the two groups. Although these hGRPs myelinated extensively after implantation into neonatal shiverer mouse brain, only marginal remyelination was observed in the inflammatory spinal cord demyelination model. The low rate of transplant‐derived myelination in adult rat spinal cord may reflect host age, species, transplant environment/location, and/or immune suppression regime differences. We conclude that hGRPs have the capacity to myelinate dysmyelinated neonatal rodent brain and preserve conduction in the inflammatory demyelinated adult rodent spinal cord. The latter benefit is likely dependent on trophic support and suggests further exploration of potential of glial progenitors in animal models of chronic inflammatory demyelination.

Quantitative assessment of somatosensory-evoked potentials after cardiac arrest in rats: Prognostication of functional outcomes

Objective:High incidence of poor neurologic sequelae after resuscitation from cardiac arrest underscores the need for objective electrophysiological markers for assessment and prognosis. This study aims to develop a novel marker based on somatosensory evoked potentials (SSEPs). Normal SSEPs involve thalamocortical circuits suggested to play a role in arousal. Due to the vulnerability of these circuits to hypoxic-ischemic insults, we hypothesize that quantitative SSEP markers may indicate future neurologic status. Design:Laboratory investigation. Setting:University Medical School and Animal Research Facility. Subjects:Sixteen adult male Wistar rats. Interventions:None. Measurements and Main Results:SSEPs were recorded during baseline, during the first 4 hrs, and at 24, 48, and 72 hrs postasphyxia from animals subjected to asphyxia-induced cardiac arrest for 7 or 9 mins (n = 8/group). Functional evaluation was performed using the Neurologic Deficit Score (NDS). For quantitative analysis, the phase space representation of the SSEPs—a plot of the signal vs. its slope—was used to compute the phase space area bounded by the waveforms recorded after injury and recovery. Phase space areas during the first 85–190 mins postasphyxia were significantly different between rats with good (72 hr NDS ≥50) and poor (72 hr NDS <50) outcomes (p = .02). Phase space area not only had a high outcome prediction accuracy (80–93%, p < .05) during 85–190 mins postasphyxia but also offered 78% sensitivity to good outcomes without compromising specificity (83–100%). A very early peak of SSEPs that precedes the primary somatosensory response was found to have a modest correlation with the 72 hr NDS subscores for thalamic and brainstem function (p = .066) and not with sensory-motor function (p = .30). Conclusions:Phase space area, a quantitative measure of the entire SSEP morphology, was shown to robustly track neurologic recovery after cardiac arrest. SSEPs are among the most reliable predictors of poor outcome after cardiac arrest; however, phase space area values early after resuscitation can enhance the ability to prognosticate not only poor but also good long-term neurologic outcomes.

Electrophysiological evaluation of sensory and motor pathways after incomplete unilateral spinal cord contusion.

OBJECT Unilateral contusions represent an increasingly popular model for studying the pathways and recovery mechanisms of spinal cord injury (SCI). Current studies rely heavily on motor behavior scoring and histological evidence to make assessments. Electrophysiology represents one way to reliably quantify the functionality of motor pathways. The authors sought to quantify the functional integrity of the bilateral motor and sensory pathways following unilateral SCI by using measurements of motor and somatosensory evoked potentials (MEPs and SSEPs, respectively). METHODS Eighteen rats were randomly divided into 3 groups receiving a mild unilateral contusion, a mild midline contusion, or a laminectomy only (control). Contusions were induced at T-8 using a MASCIS impactor. Electrophysiological analysis, motor behavior scoring, and histological quantifications were then performed to identify relationships among pathway conductivity, motor function, and tissue preservation. RESULTS Hindlimb MEPs ipsilateral to the injury showed recovery by Day 28 after injury and corresponded to approximately 61% of spared corticospinal tract (CST) tissue. In contrast, MEPs of the midline-injured group did not recover, and correspondingly > 90% of the CST tissue was damaged. Somatosensory evoked potentials showed only a moderate reduction in amplitude, with no difference in latency for the pathways ipsilateral to injury. Furthermore, these SSEPs were significantly better than those of the midline-injured rats for the same amount of white matter damage. CONCLUSIONS Motor evoked potential recovery corresponded to the amount of spared CST in unilateral and midline injuries, but motor behavior consistently recovered independent of MEPs. These data support the idea that spared contralateral pathways aid in reducing the functional deficits of injured ipsilateral pathways and further support the idea of CNS plasticity.

Slope analysis of somatosensory evoked potentials in spinal cord injury for detecting contusion injury and focal demyelination

In spinal cord injury (SCI) research there is a need for reliable measures to determine the extent of injury and assess progress due to natural recovery, drug therapy, surgical intervention or rehabilitation. Somatosensory evoked potentials (SEP) can be used to quantitatively examine the functionality of the ascending sensory pathways in the spinal cord. A reduction of more than 50% in peak amplitude or an increase of more than 10% in latency are threshold indicators of injury. However, in the context of injury, SEP peaks are often obscured by noise. We have developed a new technique to investigate the morphology of the SEP waveform, rather than focusing on a small number of peaks. In this study, we compare SEP signals before and after SCI using two rat models: a contusion injury model and a focal experimental autoimmune encephalomyelitis model. Based on mean slope changes over the signal, we were able to effectively differentiate pre-injury and post-injury SEP values with high levels of sensitivity (83.3%) and specificity (79.2%).

Enhancement of Bilateral Cortical Somatosensory Evoked Potentials to Intact Forelimb Stimulation Following Thoracic Contusion Spinal Cord Injury in Rats

The adult central nervous system is capable of significant reorganization and adaptation following neurotrauma. After a thoracic contusive spinal cord injury (SCI) neuropathways that innervate the cord below the epicenter of injury are damaged, with minimal prospects for functional recovery. In contrast, pathways above the site of injury remain intact and may undergo adaptive changes in response to injury. We used cortical somatosensory evoked potentials (SSEPs) to evaluate changes in intact forelimb pathways. Rats received a midline contusion SCI, unilateral contusion SCI, or laminectomy with no contusion at the T8 level and were monitored for 28 days post-injury. In the midline injury group, SSEPs recorded from the contralateral forelimb region of the primary somatosensory cortex were 59.7% (CI 34.7%, 84.8%; c2 = 21.9; dof = 1; p = 2.9 ×10-6) greater than the laminectomy group; SSEPs from the ipsilateral somatosensory cortex were 47.6% (CI 18.3%, 77%; c2 = 10.1; dof = 1; p = 0.001) greater. Activation of the ipsilateral somatosensory cortex was further supported by BOLD-fMRI, which showed increased oxygenation at the ipsilateral hemisphere at day seven post-injury. In the unilateral injury group, ipsilesional side was compared to the contralesional side. SSEPs on day 14 (148%; CI 111%, 185%) and day 21 (137%; CI 110%, 163%) for ipsilesional forelimb stimulation were significantly increased over baseline (100%). SSEPs recorded from the hindlimb sensory cortex upon ipsilesional stimulation were 33.9% (CI 14.3%, 53.4%; c2 = 11.6; dof = 1; p = 0.0007) greater than contralesional stimulation. Therefore, these results demonstrate the ability of SSEPs to detect significant enhancements in the activation of forelimb sensory pathways following both midline and unilateral contusive SCI at T8. Reorganization of forelimb pathways may occur after thoracic SCI, which SSEPs can monitor to aid the development of future therapies.

Multi-limb acquisition of motor evoked potentials and its application in spinal cord injury.

The motor evoked potential (MEP) is an electrical response of peripheral neuro-muscular pathways to stimulation of the motor cortex. MEPs provide objective assessment of electrical conduction through the associated neural pathways, and therefore detect disruption due to a nervous system injury such as spinal cord injury (SCI). In our studies of SCI, we developed a novel, multi-channel set-up for MEP acquisition in rat models. Unlike existing electrophysiological systems for SCI assessment, the set-up allows for multi-channel MEP acquisition from all limbs of rats and enables longitudinal monitoring of injury and treatment for in vivo models of experimental SCI. The article describes the development of the set-up and discusses its capabilities to acquire MEPs in rat models of SCI. We demonstrate its use for MEP acquisition under two types of anesthesia as well as a range of cortical stimulation parameters, identifying parameters yielding consistent and reliable MEPs. To validate our set-up, MEPs were recorded from a group of 10 rats before and after contusive SCI. Upon contusion with moderate severity (12.5mm impact height), MEP amplitude decreased by 91.36±6.03%. A corresponding decline of 93.8±11.4% was seen in the motor behavioral score (BBB), a gold standard in rodent models of SCI.

Evoked potential and behavioral outcomes for experimental autoimmune encephalomyelitis in Lewis rats

A reliable outcome measurement is needed to assess the effects of experimental lesions in the rat spinal cord as well as to assess the benefits of therapies designed to modulate them. The Basso, Beattie, and Bresnahan (BBB) behavioral scores can be indicative of the functionality in motor pathways. However, since lesions are often induced in the more accessible dorsal parts associated with the sensory pathways, the BBB scores may not be ideal measure of the disability. We propose somatosensory evoked potential (SEP) as a complementary measure to assess the integrity of sensory pathways. We used the focal experimental autoimmune encephalomyelitis (EAE) model, in which focal demyelinating lesions were induced by injecting cytokine-ethidium bromide into dorsal white matter after MOG-IFA immunization. Both the SEP and BBB measures reflected injury; however, the SEP was uniformly and consistently altered after the injury whereas the BBB varied widely. The results suggest that the SEP measures are more sensitive and reliable markers of focal spinal cord demyelination compared to the behavioral measures like the BBB score.

Plasticity associated changes in cortical somatosensory evoked potentials following spinal cord injury in rats

Spinal cord injury (SCI) causes a number of physiological and neurological changes resulting in loss of sensorimotor function. Recent work has shown that the central nervous system is capable of plastic behaviors post-injury, including axonal regrowth and cortical remapping. Functional integrity of afferent sensory pathways can be quantified using cortical somatosensory evoked potentials (SSEPs) recorded upon peripheral limb stimulation. We implanted 15 rats with transcranial screw electrodes and recorded SSEPs from cortical regions corresponding to each limb before and after a mild or moderate contusion injury. We report a post-injury increase in the mean amplitude of cortical SSEPs upon forelimb stimulation. SSEP amplitudes for mild and moderate SCI groups increased by 183%±95% and 107%±38% over baseline, respectively, while hindlimb SSEPs decreased by 58%±14% and 79%±4%. In addition, we report increased SSEP amplitude measured from the anatomically adjacent hindlimb region upon forelimb stimulation (increase of 90%±19%). Our results show that previously allocated hindlimb cortical regions are now activated by forelimb stimulation, suggesting an expansion in the area of cortical forelimb representation into hindlimb regions after an injury. This result is indicative of adaptive plasticity in undamaged areas of the CNS following SCI.