Effect of acute hypoxic preconditioning on qEEG and functional recovery after cardiac arrest in rats

Acute hypoxic preconditioning (AHPC) can confer neuroprotection from global cerebral ischemia such as cardiac arrest. We hypothesize that acute neuroprotection by AHPC will be detected early by quantitative EEG (qEEG) entropy analysis after asphyxial cardiac arrest (aCA). Cerebral ischemia lowers EEG signal randomness leading to low entropy. A qEEG entropy index defined as the duration when the entropy measure is 15% below uninjured baseline entropy is used as a measure of injury. We compared 3 groups of adult Wistar rats: (1) untreated controls that were subjected to 5 min of aCA and were resuscitated (n = 5); (2) AHPC-treated group with 10% FI O2 for 30 min, then 25 min of room air, 5 min of aCA followed by resuscitation (n = 5); and (3) a surgical sham group (no aCA) (n = 3). Functional outcome was assessed by neurodeficit score (NDS) which consisted of level of consciousness, cranial nerve, motor-sensory function, and simple behavioral tests (best = 100 and brain dead = 0). We found that increasing entropy index of injury at 0-5 h from return of spontaneous circulation (ROSC) is associated with worsening NDS at 24 h (linear regression: r = 0.81, P < 0.001). The NDS of the group sham (84.7 +/- 2.8) (mean +/- SEM) and AHPC group (84.6 +/- 2.9, P > 0.05) was better than control injury group (52.2 +/- 8.4, P < 0.05) (ANOVA with Tukey test). We therefore conclude that AHPC confers acute neuroprotection at 24 h, which was detected by qEEG entropy during the first 5 h after injury.     

The role of calcitonin gene-related Peptide in the in vivo pituitary-adrenocortical response to acute hypoxemia in the late-gestation sheep fetus

This study tested the hypothesis that calcitonin gene-related peptide (CGRP) has a role in mediating the in vivo fetal adrenal glucocorticoid response to acute stress. The hypothesis was tested by investigating the effects of fetal treatment with a selective CGRP antagonist on plasma ACTH and cortisol responses to acute hypoxemia in the late-gestation sheep fetus. Under anesthesia, six fetuses at 0.8 of gestation were surgically instrumented with vascular catheters. Five days later, fetuses were subjected to 0.5-h hypoxemia during treatment with either iv saline or a CGRP antagonist, in randomized order, on different days. Treatment started 30 min before hypoxemia and ran continuously until the end of the challenge. Arterial blood samples were collected for plasma ACTH and cortisol measurements (RIA) and blood gas monitoring. CGRP antagonism did not alter basal arterial blood gas or endocrine status. During hypoxemia, similar falls in arterial partial pressure of oxygen occurred in all fetuses. During saline infusion, acute hypoxemia induced significant increases in fetal ACTH and cortisol concentrations. During CGRP antagonism, the pituitary-adrenal responses were markedly attenuated. Correlation of paired plasma ACTH and cortisol values from all individual fetuses during normoxia and hypoxemia showed positive linear relationships; however, neither the slope nor the intercept of the peptide-steroid relationship was affected by CGRP antagonism. These data support the hypothesis that CGRP is involved in the in vivo regulation of fetal adrenocortical steroidogenesis during acute hypoxemia. In addition, the data reveal that CGRP may have a role in the control of other components of the hypothalamo-pituitary-adrenal axis during stimulated conditions in fetal life.     

Ectopic Activity in Ventricular Cells Induced by Early Afterdepolarizations Developed in Purkinje Cells

The development of early afterdepolarizations (EADs) in Purkinje fibers and their propagation to ventricular muscle cells are studied by computer modeling. The Purkinje-ventricular system has been simulated by a two-dimensional model of a Purkinje fiber (PF) connected to a thin sheet of ventricular muscle tissue (VMT). EADs are induced in the PF by enhancing the fast second inward current, i _Ca,f and blocking the delayed K⁺ current, i _K while the VMT is kept under physiological conditions. Different phenomena are observed depending on the EAD conditions applied. For 70% i _K blockade and i _Ca,f enhancement greater than 60%, a single phase 3 EAD developed in the PF propagates to the VMT generating an ectopic beat. For 80% i _K blockade and i _Ca,f enhancement in the range from 0% to 70%, multiple ectopic beats appear in the VMT. However, for i _K blockades over 80%, action potentials in PF cells do not repolarize and the ectopic activity in the VMT disappears. In our simulations, the ionic mechanism underlying phase 3 EAD development is the reactivation of the fast sodium current in the PF. Our results demonstrate that there exists a critical range of EAD conditions that favor the development of EADs in the PF and their propagation to the VMT as ectopic activity. This phenomenon could underlie the genesis of some triggered arrhythmias. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8716Uv, 8719Hh, 8719Ff, 8717Nn     

Optogenetic-guided cortical plasticity after nerve injury

Peripheral nerve injury causes sensory dysfunctions that are thought to be attributable to changes in neuronal activity occurring in somatosensory cortices both contralateral and ipsilateral to the injury. Recent studies suggest that distorted functional response observed in deprived primary somatosensory cortex (S1) may be the result of an increase in inhibitory interneuron activity and is mediated by the transcallosal pathway. The goal of this study was to develop a strategy to manipulate and control the transcallosal activity to facilitate appropriate plasticity by guiding the cortical reorganization in a rat model of sensory deprivation. Since transcallosal fibers originate mainly from excitatory pyramidal neurons somata situated in laminae III and V, the excitatory neurons in rat S1 were engineered to express halorhodopsin, a light-sensitive chloride pump that triggers neuronal hyperpolarization. Results from electrophysiology, optical imaging, and functional MRI measurements are concordant with that within the deprived S1, activity in response to intact forepaw electrical stimulation was significantly increased by concurrent illumination of halorhodopsin over the healthy S1. Optogenetic manipulations effectively decreased the adverse inhibition of deprived cortex and revealed the major contribution of the transcallosal projections, showing interhemispheric neuroplasticity and thus, setting a foundation to develop improved rehabilitation strategies to restore cortical functions.     

Time jitter of somatosensory evoked potentials in recovery from hypoxic-ischemic brain injury

Impaired neural conductivity shown by delayed latency and reduced amplitude of characteristic peaks in somatosensory evoked potentials (SSEPs), has been used to monitor hypoxic-ischemic brain injury after cardiac arrest (CA). However, rather than characteristic peak deferral and suppression, the time jitter of the peak in SSEP related with time-variant neurological abnormalities is diminished by the commonly used ensemble average method. This paper utilizes the second order blind identification (SOBI) technique to extract characteristic peak information from one trial of SSEPs. Sixteen male Wistar rats were subjected to 7 or 9 min of asphyxial CA (n = 8 per group). The SSEPs from median nerve stimulation were recorded for 4 h after CA and then for 15 min periods at 24, 48 and 72 h. Neurological outcomes were evaluated by neurologic deficit score (NDS) at 72 h post-CA. The SSEP signal was analyzed offline with SOBI processing in Matlab. The N10 feature of SSEP was compared between good (NDS ≥ 50) and bad (NDS < 50) outcomes. After processed by SOBI, the N10 detection rate was significantly increased (p < 0.001) from 90 min post-CA. Statistical difference of the latency variance of the N10 between good and bad outcome groups existed at 24, 48 and 72 h post-CA (p ≤ 0.001). Our study is the first application using SOBI detecting variance in neural signals like SSEP. N10 latency variance, related with neurophysiological dysfunction, increased after hypoxic-ischemic injury. The SOBI technique is an efficient method in the identification of peak detection and offers a favorable alternative to reveal the neural transmission variation.     

Neuronal gene delivery by negatively charged pullulan–spermine/DNA anioplexes

Nonviral gene transfer to neurons remains unreliable due to a lack of effective and nontoxic vectors. Here, we achieved effective neuronal gene delivery through salt-free complexation of plasmid DNA and pullulan–spermine, a conjugate prepared from a naturally derived polysaccharide and polyamine. Specifically, at low spermine nitrogen:DNA phosphate (N:P) ratios, complexes formed with ζ-potential and diameter of approximately?40 mV and 350 nm, respectively. Higher N:P ratios increased the ζ-potential to approximately +10 mV. All complexes were stable for at least 1 week and protected DNA from degradation. In vitro transfection of rat sensory neurons occurred at all N:P ratios, but uniquely, efficiency was highest for anionic complexes (anioplexes). Subsequent analyses revealed the inhibition of reporter gene expression by asialofetuin (1 mg/ml) and methyl-beta-cyclodextrin (5 mm), indicating utilization of glycoprotein-specific interactions and lipid rafts for uptake and intracellular trafficking. In marked contrast to a commercial cationic lipid reagent, anioplexes did not exhibit measurable cytotoxicity at up to 20 μg/ml DNA. Additionally, transfection efficiency was maintained in the presence of serum and antibiotics. Based on these favorable properties, we successfully established two transfection methods for cultured adult sensory neurons and tissue explants. Collectively, these data suggest that negatively charged pullulan–spermine/DNA anioplexes could represent an effective gene delivery technology, particularly for neurons.     

Population pharmacokinetics of enfuvirtide in HIV-1-infected pediatric patients over 48 weeks of treatment

The objective of this study was to characterize the population pharmacokinetics of enfuvirtide in HIV-1-infected children and adolescents. HIV-infected patients received combination antiretroviral therapy, including enfuvirtide 2.0 mg/kg subcutaneously, twice daily. Serial and trough blood samples were collected up to 48 weeks. NONMEM was used for population pharmacokinetic analysis. Enfuvirtide exposure was calculated from individual parameter estimates derived from the final model. A total of 218 samples from 43 patients were included in the analysis. Enfuvirtide plasma concentration-time data were described by a 1-compartment model with first-order absorption and elimination. The addition of each subject's actual body weight as a covariate affected CL/F but not V/F or K(a). The population CL/F, V/F, and K(a) for a 33-kg reference patient was 1.31 L/h, 2.31 L, and 0.105 h(-1), respectively. The final model was CL/F (L/h) = 1.31 . (body weight/33 [kg])(0.721). Age did not affect enfuvirtide exposure. These results confirm the appropriateness of body weight-based pediatric enfuvirtide dosing.