These findings indicate that nerve injury-induced electrical instability is restricted to axotomized neurons and is absent in adjacent intact neurons.

Key points• The peripheral terminals of sensory neurons encode physical and chemical signals into trains of action potentials (APs) and transmit these trains to the CNS.• Although modulation of this process is thought to predominantly reside at synapses, there are also indications that AP trains are incompletely propagated past points at which axons branch. One such site is the T-junction, where the single sensory neuron axon branches into peripheral and central processes.• In recordings from sensory neurons of dorsal root ganglia excised from adult rats, we identified use-dependent failure of AP propagation between the peripheral and central processes that results in filtering of rapid AP trains, especially in C-type neurons.• Propagation failure was regulated by membrane input resistance and Ca 2+ -sensitive K + and Cl − currents. Following peripheral nerve injury, T-junction filtering is reduced in C-type neurons, which may possibly contribute to pain generation.Abstract The T-junction of sensory neurons in the dorsal root ganglion (DRG) is a potential impediment to action potential (AP) propagation towards the CNS. Using intracellular recordings from rat DRG neuronal somata during stimulation of the dorsal root, we determined that the maximal rate at which all of 20 APs in a train could successfully transit the T-junction (following frequency) was lowest in C-type units, followed by A-type units with inflected descending limbs of the AP, and highest in A-type units without inflections. In C-type units, following frequency was slower than the rate at which AP trains could be produced in either dorsal root axonal segments or in the soma alone, indicating that the T-junction is a site that acts as a low-pass filter for AP propagation. Following frequency was slower for a train of 20 APs than for two, indicating that a cumulative process leads to propagation failure. Propagation failure was accompanied by diminished somatic membrane input resistance, and was enhanced when Ca 2+ -sensitive K + currents were augmented or when Ca 2+ -sensitive Cl − currents were blocked. After peripheral nerve injury, following frequencies were increased in axotomized C-type neurons and decreased in axotomized non-inflected A-type neurons. These findings reveal that the T-junction in sensory neurons is a regulator of afferent impulse traffic. Diminished filtering of AP trains at the T-junction of C-type neurons with axotomized peripheral processes could enhance the transmission of activity that is ectopically triggered in a neuroma or the neuronal soma, possibly contributing to pain generation.

Ischemic cardiac injury can be substantially alleviated by exposing the heart to pharmacological agents such as volatile anesthetics before occurrence of ischemia-reperfusion. A hallmark of this preconditioning phenomenon is its memory, when cardioprotective effects persist even after removal of preconditioning stimulus. Since numerous studies pinpoint mitochondria as crucial players in protective pathways of preconditioning, the aim of this study was to investigate the effects of preconditioning agent isoflurane on the mitochondrial bioenergetic phenotype. Endogenous flavoprotein fluorescence, an indicator of mitochondrial redox state, was elevated to 195 +/- 16% of baseline upon isoflurane application in intact cardiomyocytes, indicating more oxidized state of mitochondria. Isoflurane treatment also elicited partial dissipation of mitochondrial transmembrane potential, which remained depolarized even after anesthetic withdrawal (tetramethylrhodamine fluorescence intensity declined to 83 +/- 3 and 81 +/- 7% of baseline during isoflurane exposure and washout, respectively). Mild uncoupling, with preserved ATP synthesis, was also detected in mitochondria that were isolated from animals that had been previously preconditioned by isoflurane in vivo, revealing its memory nature. These mitochondria, after exposure to hypoxia and reoxygenation, exhibited better preserved respiration and ATP synthesis compared with mitochondria from nonpreconditioned animals. Partial mitochondrial depolarization was paralleled by a diminished Ca(2+) uptake into isoflurane-treated mitochondria, as indicated by the reduced increment in rhod-2 fluorescence when mitochondria were challenged with increased Ca(2+) (180 +/- 24 vs. 258 +/- 14% for the control). In conclusion, isoflurane preconditioning elicits partial mitochondrial uncoupling and reduces mitochondrial Ca(2+) uptake. These effects are likely to reduce the extent of the mitochondrial damage after the hypoxic stress.

The goal of this study was to evaluate annexin V-positive microparticles (MPs) and neutrophil activation in humans following decompression from open-water SCUBA diving with the hypothesis that changes are related to intravascular bubble formation. Sixteen male volunteer divers followed a uniform profile of four daily SCUBA dives to 18 m of sea water for 47 min. Blood was obtained prior to and at 80 min following the first and fourth dives to evaluate the impact of repetitive diving, and intravascular bubbles were quantified by trans-thoracic echocardiography carried out at 20-min intervals for 2 h after each dive. MPs increased by 3.4-fold after each dive, neutrophil activation occurred as assessed by surface expression of myeloperoxidase and the CD18 component of β2-integrins, and there was an increased presence of the platelet-derived CD41 protein on the neutrophil surface indicating interactions with platelet membranes. Intravascular bubbles were detected in all divers. Surprisingly, significant inverse correlations were found among postdiving bubble scores and MPs, most consistently at 80 min or more after the dive on the fourth day. There were significant positive correlations between MPs and platelet-neutrophil interactions after the first dive and between platelet-neutrophil interactions and neutrophil activation documented as an elevation in β2-integrin expression after the fourth dive. We conclude that MPs- and neutrophil-related events in humans are consistent with findings in an animal decompression model. Whether there are causal relationships among bubbles, MPs, platelet-neutrophil interactions, and neutrophil activation remains obscure and requires additional study.

The study goal was to evaluate responses in humans following decompression from open-water SCUBA diving with the hypothesis that exertion underwater and use of a breathing mixture containing more oxygen and less nitrogen (enriched air nitrox) would alter annexin V-positive microparticle (MP) production and size changes and neutrophil activation, as well as their relationships to intravascular bubble formation. Twenty-four divers followed a uniform dive profile to 18 m of sea water breathing air or 22.5 m breathing 32% oxygen/68% nitrogen for 47 min, either swimming with moderately heavy exertion underwater or remaining stationary at depth. Blood was obtained pre- and at 15 and 120 min postdive. Intravascular bubbles were quantified by transthoracic echocardiography postdive at 20-min intervals for 2 h. There were no significant differences in maximum bubble scores among the dives. MP number increased 2.7-fold, on average, within 15 min after each dive; only the air-exertion dive resulted in a significant further increase to 5-fold over baseline at 2 h postdive. Neutrophil activation occurred after all dives. For the enriched air nitrox stationary at depth dive, but not for other conditions, the numbers of postdive annexin V-positive particles above 1 μm in diameter were correlated with intravascular bubble scores (correlation coefficients ∼0.9, P < 0.05). We conclude that postdecompression relationships among bubbles, MPs, platelet-neutrophil interactions, and neutrophil activation appear to exist, but more study is required to improve confidence in the associations.

Background Signal transduction cascade of anesthetic-induced preconditioning has been extensively studied, yet many aspects of it remain unsolved. Here we investigated the roles of reactive oxygen species (ROS) and mitochondrial uncoupling in cardiomyocyte preconditioning by 2 modern volatile anesthetics: desflurane and sevoflurane. Methods Adult rat ventricular cardiomyocytes were isolated enzymatically. The preconditioning potency of desflurane and sevoflurane was assessed in cell survival experiments by evaluating myocyte protection from the oxidative stress-induced cell death. ROS production and flavoprotein fluorescence, an indicator of flavoprotein oxidation and mitochondrial uncoupling, were monitored in real-time by confocal microscopy. The functional aspect of enhanced ROS generation by the anesthetics was assessed in cell survival and confocal experiments using the ROS scavenger Trolox. Results Preconditioning of cardiomyocytes with desflurane or sevoflurane significantly decreased oxidative stress-induced cell death. That effect coincided with increased ROS production and increased flavoprotein oxidation detected during acute myocyte exposure to the anesthetics. Desflurane induced significantly greater ROS production and flavoprotein oxidation than sevoflurane. ROS scavenging with Trolox abrogated preconditioning potency of anesthetics and attenuated flavoprotein oxidation. Conclusion Preconditioning with desflurane or sevoflurane protects isolated rat cardiomyocytes from oxidative stress-induced cell death. Scavenging of ROS abolishes the preconditioning effect of both anesthetics and attenuates anesthetic-induced mitochondrial uncoupling, suggesting a crucial role for ROS in anesthetic-induced preconditioning and implying that ROS act upstream of mitochondrial uncoupling. Desflurane exhibits greater effect on stimulation of ROS production and mitochondrial uncoupling than sevoflurane.

Exercise reduces LV contractile deterioration in post-infarction heart failure and alleviates the extent of mitochondrial dysfunction, which is paralleled with preserved complex I activity.

Background Chronic neuropathic pain resulting from neuronal damage remains difficult to treat, in part due to incomplete understanding of underlying cellular mechanisms. We have previously shown that inward Ca2+ flux (ICa) across the sensory neuron plasmalemma is decreased in a rodent model of chronic neuropathic pain, but the direct consequence of this loss of ICa on function of the sensory neuron has not been defined. We therefore examined the extent to which altered membrane properties after nerve injury, especially increased excitability that may contribute to chronic pain, are attributable to diminished Ca2+ entry. Methods Intracellular microelectrode measurements were obtained from A-type neurons of dorsal root ganglia excised from control rats and those with neuropathic pain behavior following spinal nerve ligation. Recording conditions were varied to suppress or promote ICa while biophysical parameters and excitability were determined. Results Both lowered external bath Ca2+ concentration and blockade of ICa with bath cadmium diminished the duration and area of the afterhyperpolarization (AHP), accompanied by decreased current threshold for action potential (AP) initiation and increased repetitive firing during sustained depolarization. Reciprocally, elevated bath Ca2+ increased the AHP and suppressed repetitive firing. Voltage sag during neuronal hyperpolarization, indicative of the cation-nonselective H-current, diminished with lowered bath Ca2+, cadmium application, or chelation of intracellular Ca2+. Additional recordings with selective blockers of ICa subtypes showed that N-, P/Q, L-, and R-type currents each contribute to generation of the AHP, and that blockade of any of these as well as the T-type current slows the AP upstroke, prolongs the AP duration, and (except for L-type current) decreases the current threshold for AP initiation. Conclusions Taken together, our findings show that suppression of ICa decreases the AHP, reduces the hyperpolarization-induced voltage sag, and increases excitability in sensory neurons, replicating changes that follow peripheral nerve trauma. This suggests that the loss of ICa previously demonstrated in injured sensory neurons contributes to their dysfunction and hyperexcitability, and may lead to neuropathic pain. Implications Statement Loss of inward Ca2+ current in A-type neurons, such as follows peripheral nerve injury, contributes to increased sensory neuron excitability. Measures that increase inward Ca2+ flux may potentially be therapeutic for painful peripheral neuropathy.