Kelly Baylor

Peripheral nerve at extreme low temperatures 1: effects of temperature on the action potential.

Hypothermia is an important means of neuroprotection. Understanding the effects of temperature on a physiologic measurement such as the nerve action potential (NAP) is important in monitoring its effects. The effects of hypothermia on the NAP amplitude, conduction velocity, and response to paired pulse stimulation were quantified in a rat sciatic nerve preparation from 37 to 10 degrees C. The time course of temperature related changes and the effect of repeated cycles of cooling and rewarming are explored using the following measures of the NAP: peak-to-peak amplitude, conduction velocity, duration, area under the curve and response to paired pulse stimuli. The NAP amplitude initially increases as temperature is reduced to 27 degrees C and then drops to roughly 50% of its baseline value by 16 degrees C while the area under the curve increases gradually until it begins to decline at 16 degrees C. Permanent loss of the NAP appears only after cooling below 10 degrees C for extended periods. Although the dependence of amplitude on temperature is approximately sigmoidal, the conduction velocity declines linearly at a rate of 2.8m/s/ degrees C. The response to paired pulse stimulation is strongly dependent on both temperature and the interstimulus interval with the responses at shorter interstimulus intervals being more temperature sensitive. With repetitive cycles of cooling and rewarming, the NAP amplitude declines by roughly 4% with every cycle without changes in the temperature at which the NAP amplitude reaches 50% of baseline. Only minor differences in conduction velocity are seen during cooling and rewarming.

The sarcoglycan complex in Schwann cells and its role in myelin stability.

Sarcoglycans are originally identified in muscle for their involvement in limb-girdle muscular dystrophies. They form a multi-meric complex (alpha-, beta-, gamma-, delta-sarcoglycan) that associates with dystrophin, dystroglycan and other proteins to constitute the larger dystrophin-glycoprotein complex at the muscle membrane. Three sarcoglycan subunits (epsilon-, beta-, delta-sarcoglycan) were previously identified in Schwann cells and shown to associate with dystroglycan and a Schwann cell-specific dystrophin isoform (Dp116) at the outermost Schwann cell membrane. Currently, little is known about the exact composition and function of the sarcoglycan complex in the peripheral nervous system. In this study, we showed that the Schwann cell sarcoglycan complex consists of epsilon-, beta-, delta-sarcoglycan and the newly identified zeta-sarcoglycan subunit. The expression of sarcoglycans precedes the onset of myelination and is induced by neurons. In sarcoglycan-deficient BIO14.6 hamsters, loss of the Schwann cell sarcoglycan complex reduces the steady state levels of alpha-dystroglycan and Dp116. Ultrastructural analysis of sciatic nerves from the mutant animals revealed altered myelin sheaths and disorganized Schmidt-Lanterman incisures indicative of myelin instability. The disruption in myelin structure increased in severity with age. Nerve conduction studies also showed subtle electrophysiological abnormalities in the BIO14.6 hamsters consistent with reduced myelin stability. Together, these findings suggest an important role of sarcoglycans in the stability of peripheral nerve myelin.

Synergistic Roles for G-protein γ3 and γ7 Subtypes in Seizure Susceptibility as Revealed in Double Knock-out Mice

Background: Specificity of G-protein function may be determined by a specific αβγ composition. Results: Combinatorial disruption of γ3 and γ7 produces a severe seizure phenotype not observed with either gene alone. Conclusion: This reflects distinct roles for γ3 and γ7 in Gi/o- and Golf-signaling pathways that modulate seizure susceptibility. Significance: The γ subunits direct the assembly of distinct G-protein αβγ heterotrimers that specify diverse receptor actions. The functions of different G-protein αβγ subunit combinations are traditionally ascribed to their various α components. However, the discovery of similarly diverse γ subtypes raises the possibility that they may also contribute to specificity. To test this possibility, we used a gene targeting approach to determine whether the closely related γ3 and γ7 subunits can perform functionally interchangeable roles in mice. In contrast to single knock-out mice that show normal survival, Gng3−/−Gng7−/− double knock-out mice display a progressive seizure disorder that dramatically reduces their median life span to only 75 days. Biochemical analyses reveal that the severe phenotype is not due to redundant roles for the two γ subunits in the same signaling pathway but rather is attributed to their unique actions in different signaling pathways. The results suggest that the γ3 subunit is a component of a Gi/o protein that is required for γ-aminobutyric acid, type B, receptor-regulated neuronal excitability, whereas the γ7 subunit is a component of a Golf protein that is responsible for A2A adenosine or D1 dopamine receptor-induced neuro-protective response. The development of this mouse model offers a novel experimental framework for exploring how signaling pathways integrate to produce normal brain function and how their combined dysfunction leads to spontaneous seizures and premature death. The results underscore the critical role of the γ subunit in this process.

Peripheral nerve at extreme low temperatures 2: pharmacologic modulation of temperature effects.

Changes in temperature have profound and clinically important effects on the peripheral nerve. In a previous paper, the effects of temperature on many properties of the peripheral nerve action potential (NAP) were explored including the NAP amplitude, conduction velocity and response to paired pulse stimulation. In this paper, the effects of pharmacologic manipulations on these parameters were explored in order to further understand the mechanisms of these effects. The reduction in conduction velocity with temperature was shown to be independent of the ionic composition of the perfusate and was unaffected by potassium or sodium channel blockade. This implies that the phenomenon of reduced conduction velocities at low temperature may be related to changes in the passive properties of the axon with temperature. Blockade of sodium channels and chronic membrane depolarization produced by high perfusate potassium concentrations or high dose 4-aminopyridine impair the resistance of the nerve to hypothermia and enhance the injury to the nerve produced by cycles of cooling and rewarming. This suggests the possibility that changes in the sodium inactivation channel may be responsible for the changes in the NAP amplitude with temperature and that prolonged sodium inactivation may lead more permanent changes in excitability.

Acute nerve compression and the compound muscle action potential

Detecting acute nerve compression using neurophysiologic studies is an important part of the practice of clinical intra-operative neurophysiology. The goal of this paper was to study the changes in the compound muscle action potential (CMAP) during acute mechanical compression. This is the type of injury most likely to occur during surgery. Thus, understanding the changes in the CMAP during this type of injury will be useful in the detection and prevention using intra-operative neurophysiologic monitoring. The model involved compression of the hamster sciatic nerve over a region of 1.3 mm with pressures up to 2000 mmHg for times on the order of 3 minutes. In this model CMAP amplitude dropped to 50% of its baseline value when a pressure of roughly 1000 mmHg is applied while, at the same time, nerve conduction velocities decline by only 5%. The ability to detect statistically significant changes in the CMAP at low force levels using other descriptors of the CMAP including duration, latency variation, etc alone or in conjunction with amplitude and velocity measures was investigated. However, these other parameters did not allow for earlier detection of significant changes. This study focused on a model in which nerve injury on a short time scale is purely mechanical in origin. It demonstrated that a pure compression injury produced large changes in CMAP amplitude prior to large changes in conduction velocity. On the other hand, ischemic and stretch injuries are associated with larger changes in conduction velocity for a given value of CMAP amplitude reduction.

Acute nerve stretch and the compound motor action potential

In this paper, the acute changes in the compound motor action potential (CMAP) during mechanical stretch were studied in hamster sciatic nerve and compared to the changes that occur during compression. In response to stretch, the nerve physically broke when a mean force of 331 gm (3.3 N) was applied while the CMAP disappeared at an average stretch force of 73 gm (0.73 N). There were 5 primary measures of the CMAP used to describe the changes during the experiment: the normalized peak to peak amplitude, the normalized area under the curve (AUC), the normalized duration, the normalized velocity and the normalized velocity corrected for the additional path length the impulses travel when the nerve is stretched. Each of these measures was shown to contain information not available in the others. During stretch, the earliest change is a reduction in conduction velocity followed at higher stretch forces by declines in the amplitude of the CMAP. This is associated with the appearance of spontaneous EMG activity. With stretch forces < 40 gm (0.40 N), there is evidence of increased excitability since the corrected velocities increase above baseline values. In addition, there is a remarkable increase in the peak to peak amplitude of the CMAP after recovery from stretch < 40 gm, often to 20% above baseline. Multiple means of predicting when a change in the CMAP suggests a significant stretch are discussed and it is clear that a multifactorial approach using both velocity and amplitude parameters is important. In the case of pure compression, it is only the amplitude of the CMAP that is critical in predicting which changes in the CMAP are associated with significant compression.

Fibrillin-2 is dispensable for peripheral nerve development, myelination and regeneration

The extracellular matrix of peripheral nerve is formed from a diverse set of macromolecules, including glycoproteins, collagens and proteoglycans. Recent studies using knockout animal models have demonstrated that individual components of the extracellular matrix play a vital role in peripheral nerve development and regeneration. In this study we identified fibrillin-1 and fibrillin-2, large modular structural glycoproteins, as components of the extracellular matrix of peripheral nerve. Previously it was found that fibrillin-2 null mice display joint contractures, suggesting a possible defect of the peripheral nervous system in these animals. Close examination of the peripheral nerves of fibrillin-2 deficient animals described here revealed some structural abnormalities in the perineurium, while general structure of the nerve and molecular composition of nerve extracellular matrix remained unchanged. We also found that in spite of the obvious motor function impairment, fibrillin-2 null mice failed to display changes of nerve conduction properties or nerve regeneration capacity. Based on the data obtained we can conclude that peripheral neuropathy should be excluded as the cause of the impairment of locomotory function and joint contractures observed in fibrillin-2 deficient animals.

In-vitro stability of peripheral nerve preparations: Relation to ischemic responses

Although in-vitro peripheral nerve preparations are useful tools in studying the physiology of axons, their function invariably declines gradually over time. This study investigates the effects of age and temperature on both the in-vitro stability of rat sciatic nerve and the response of the nerve to acute hypoxia. Comparison of the effects of age and temperature in these two models can clarify a possible connection between the hypoxic response and the stability of in-vitro preparations. In in-vitro preparations, the amplitude of the nerve action potential (NAP) declines more rapidly at high temperatures than low temperatures. At high temperatures, the decline in NAP amplitude is faster in nerves taken from younger animals while at low temperatures, the NAP amplitude is the same in both young and old animals. This dependence is similar to that of the time required for the NAP to reach 50% of its baseline value after recovery from hypoxia and the NAP amplitude after a 1.5-h period of hypoxia. It is different from the behavior of the time required for the NAP to drop to 50% of its initial value during hypoxia since the effects of temperature and age on this parameter are independent. This provides evidence of a relationship between the injury caused by hypoxia and the changes that occur after transection. However, since the effect of age on the changes in conduction velocity after transection and after hypoxia are different, the two processes must differ in the response of myelin to the metabolic changes in these conditions.

Impact of a multidisciplinary pain management program on patient care utilization and cost of care

Objective Chronic pain is a highly prevalent and costly condition with few proven treatment options. Since 2014, Geisinger’s Department of Pain Medicine has implemented the Multidisciplinary Pain Program (MPP), which consists of a 3-day educational seminar followed by 12 months of comprehensive care. This study examines the impact of MPP on care utilization and cost between 2014 and 2016. Methods A retrospective health insurance claims data analysis covering a 3-year period between January 2013 and December 2016. Among all patients referred to MPP during the period, a subset of those who were Geisinger Health Plan (GHP) members was identified (113 patients). Those who were GHP members and were referred to MPP after December 2016 served as the contemporaneous comparison group (69 patients). GHP’s claims data for the corresponding period were analyzed on a per-member-per-month (PMPM) basis. Results MPP was associated with US

Electrical Stimulation and Electrode Properties. Part 2: Pure Metal Electrodes

754 PMPM reduction in total cost of care including prescription drug costs (P=0.014) and US