Spatiotemporally Precise Optical Manipulation of Intracellular Molecular Activities

Controlling chemical processes in live cells is a challenging task. The spatial heterogeneity of biochemical reactions in cells is often overlooked by conventional means of incubating cells with desired chemicals. A comprehensive understanding of spatially diverse biochemical processes requires precise control over molecular activities at the subcellular level. Herein, a closed-loop optoelectronic control system is developed that allows the manipulation of biomolecular activities in live cells at high spatiotemporal precision. Chemical-selective fluorescence signals are utilized to command lasers that trigger specific chemical processes or control the activation of photoswitchable inhibitors at desired targets. This technology is fully compatible with laser scanning confocal fluorescence microscopes. The authors demonstrate selective interactions of a 405 nm laser with targeted organelles and simultaneous monitoring of cell responses by fluorescent protein signals. Notably, blue laser interaction with the endoplasmic reticulum leads to a more pronounced reduction in cytosolic green fluorescent protein signals in comparison to that with nuclei and lipid droplets. Moreover, when combined with a photoswitchable inhibitor, microtubule polymerization is selectively inhibited within the subcellular compartments. This technology enables subcellular spatiotemporal optical manipulation over chemical processes and drug activities, exclusively at desired targets, while minimizing undesired effects on non-targeted locations.

Hybrid Thrombectomy and Central Extracorporeal Membrane Oxygenation for Massive Pulmonary Embolism in a Child

We describe a hybrid thrombectomy and central extracorporeal membrane oxygenation for a child in cardiogenic shock due to a massive pulmonary embolism.

Central Extracorporeal Membrane Oxygenation Support Following Calcium Channel Blocker Overdose in Children

Refractory vasodilatory shock (RVS) following massive calcium channel blocker (CCB) overdose remains a challenging clinical entity. Peripheral venoarterial extracorporeal membrane oxygenation (ECMO) has proven useful in several cases of CCB intoxication, however, its use in the pediatric population poses unique challenges given the generally small size of pediatric peripheral vasculature in comparison to the high flow rates necessary for adequate mechanical circulatory support. As a result of these challenges, our group has adopted a "primary" central ECMO cannulation approach to the treatment of children and adolescents admitted to our center with profound RVS after CCB ingestion. We present four cases within the last year using this approach. All patients were successfully discharged from the hospital with no late morbidity at most recent follow-up. Central ECMO support in cases of massive vasodilatory shock following CCB overdose is safe and effective and should be considered early in the clinical course of these critically ill patients.

Amyloid β Induces Lipid Droplet-Mediated Microglial Dysfunction in Alzheimer's Disease

Several microglia-expressed genes have emerged as top risk variants for Alzheimer's disease (AD). Impaired microglial phagocytosis is one of the main proposed outcomes by which these AD-risk genes may contribute to neurodegeneration, but the mechanisms translating genetic association to cellular dysfunction remain unknown. Here we show that microglia form lipid droplets (LDs) upon exposure to amyloid-beta (Aβ), and that their LD load increases with proximity to amyloid plaques in brains from human patients and the AD mouse model 5xFAD. LD formation is dependent upon age and disease progression and is more prominent in the hippocampus in mice and humans. Despite variability in LD load between microglia from male versus female animals and between cells from different brain regions, LD-laden microglia exhibited a deficit in Aβ phagocytosis. Unbiased lipidomic analysis identified a substantial decrease in free fatty acids (FFAs) and a parallel increase in triacylglycerols (TAGs) as the key metabolic transition underlying LD formation. We demonstrate that DGAT2, a key enzyme for the conversion of FFAs to TAGs, promotes microglial LD formation, is increased in microglia from 5xFAD and human AD brains, and that inhibiting DGAT2 improved microglial uptake of Aβ. These findings identify a new lipid-mediated mechanism underlying microglial dysfunction that could become a novel therapeutic target for AD.

Chemical-imaging-guided optical manipulation of biomolecules

Chemical imaging via advanced optical microscopy technologies has revealed remarkable details of biomolecules in living specimens. However, the ways to control chemical processes in biological samples remain preliminary. The lack of appropriate methods to spatially regulate chemical reactions in live cells in real-time prevents investigation of site-specific molecular behaviors and biological functions. Chemical- and site-specific control of biomolecules requires the detection of chemicals with high specificity and spatially precise modulation of chemical reactions. Laser-scanning optical microscopes offer great platforms for high-speed chemical detection. A closed-loop feedback control system, when paired with a laser scanning microscope, allows real-time precision opto-control (RPOC) of chemical processes for dynamic molecular targets in live cells. In this perspective, we briefly review recent advancements in chemical imaging based on laser scanning microscopy, summarize methods developed for precise optical manipulation, and highlight a recently developed RPOC technology. Furthermore, we discuss future directions of precision opto-control of biomolecules.

Real-time precision opto-control of chemical processes in live cells

Precision control of molecular activities and chemical reactions in live cells is a long-sought capability by life scientists. No existing technology can probe molecular targets in cells and simultaneously control the activities of only these targets at high spatial precision. We develop a real-time precision opto-control (RPOC) technology that detects a chemical-specific optical response from molecular targets during laser scanning and uses the optical signal to couple a separate laser to only interact with these molecules without affecting other sample locations. We demonstrate precision control of molecular states of a photochromic molecule in different regions of the cells. We also synthesize a photoswitchable compound and use it with RPOC to achieve site-specific inhibition of microtubule polymerization and control of organelle dynamics in live cells. RPOC can automatically detect and control biomolecular activities and chemical processes in dynamic living samples with submicron spatial accuracy, fast response time, and high chemical specificity.

There is a need to control molecular activities at high spatial precision. Here the authors report a real-time precision opto-control technology that detects a chemical-specific optical response from molecular targets, and precisely control photoswitchable microtubule polymerization inhibitors in cells.

Early Versus Late Sternal Closure in Infants-Perioperative Associations and Outcomes

BACKGROUND

Delayed sternal closure (DSC) has been used for patients who develop bleeding, chest wall edema, and malignant arrhythmia following cardiopulmonary bypass. Multiple factors can influence the timing of when to perform DSC. We aimed to describe our DSC experience in neonates and infants by comparing outcomes between patients undergoing early (<48 hours) versus late DSC (> 48 hours). We explored the associations between specific clinical and laboratory variables and the timing of DSC.

METHODS

Retrospective chart review of neonates and infants (<one-year-old) with DSC after heart surgery from December 2012 to December 2018. Patients requiring extracorporeal membrane oxygenation were excluded.

RESULTS

A total of 121 patients were included in the analysis, 34% (n = 41) met late DSC criteria. The overall cohort had a 75% survival rate and a median time for open sternum of 42.5 hours (Q1:23-Q3:65). The median time for open sternum in the early and late DSC groups was 24 hours (Q1:21-Q3:43) and 93 hours (Q1:65-Q3:141), respectively (P < .01). There was no statistical difference in mortality rate between groups. Patients with late DSC endured longer intensive care unit stays (median 24.3 days [Q1:13-Q3:35.3] vs 36.8 [Q1:23.9, 73.6]; P< .01) and a two-fold longer hospital stay compared to the early DSC group (multivariable analysis: relative risk = 2, 95% CI: 1.5-2.7; P < .01). Univariate analysis revealed patients with late DSC had higher median lactates both intraoperatively (7.6 [Q1:5.9-Q3:10.7] vs 9.3 [Q1:7.5-Q3:12.1]; P < .01) and 24 hours postoperatively (6.5 [Q1:4.3-Q3:10.3] vs 8.7 [Q1:5.7-Q3:14.70]; P = .03). A higher vasoactive inotrope score at 36 hours was associated with late DSC (odds ratio = 1.1, 95% CI: 1.01-1.2; P = .02).

CONCLUSIONS

Future research that explores additional clinical and laboratory variables that can help guide DSC decision-making and timing is needed.

Pediatric Donor Management Goals in Use by US Organ Procurement Organizations

INTRODUCTION

A recent study of pediatric organ donation after the neurologic determination of death (DNDD) demonstrated an association between the use of donor management goals (DMGs) by organ procurement organizations (OPOs) and organ yield.

OBJECTIVE

To describe the pediatric DMGs used by OPOs and any association between specific DMGs and organ yield.

DESIGN

Query of US OPOs who utilized DMGs in the care of pediatric DNDD organ donors from 2010 to 2013.

RESULTS

All 23 OPOs using DMGs for pediatric DNDD organ donors during the study period participated (100%). The OPOs pursued an average 9.6 goals (standard deviation: 3.9; range: 5-22) with 113 unique definitions that targeted 33 aspects of donor hemodynamics, gas exchange/mechanical ventilation, electrolytes/renal function, blood products, thermoregulation, and infection control. The DMGs used by >50% of OPOs included blood pressure, oxygenation (partial pressure of arterial oxygen (PaO₂), oxygen saturation of hemoglobin by pulse oximetry, or PaO₂/fractional concentration of inspired oxygen [FiO₂] ratio), pH, central venous pressure, serum sodium, urine output, limitations on inotropic support, and serum glucose. There was no significant correlation between the number of DMGs pursued by OPOs and organ yield. There was a difference in the observed/expected organs transplanted in the 0- to 10-year age-group for OPOs that included serum creatinine among their DMGs ( P = .046).

CONCLUSIONS

The pediatric DMGs used by OPOs were generally measurable but diverse in definition and the number of goals pursued. There was no benefit in organ yield from larger DMG bundles. There may be a benefit in organ yield through the use of serum creatinine as a DMG in pediatric donors aged 0 to 10 years.

Variability of DKA Management Among Pediatric Emergency Room and Critical Care Providers: A Call for More Evidence-Based and Cost-Effective Care?

Management protocols have been shown to be effective in the pediatric emergency medicine (PEM) and pediatric critical care (PCC) settings. Treatment protocols define clear goals which are achieved with consistency in implementation. Over the last decade, many new recommendations have been proposed on managing diabetic ketoacidosis (DKA). Although no perfect set of guidelines exist, many institutions are developing DKA treatment protocols. We sought to determine the variability between institutions in implementation of these protocols.

Effects of central administration of insulin or l-NMMA on rat skeletal muscle microvascular perfusion

AIM

Intracerebroventricular (ICV) administration of a nitric oxide synthase (NOS) inhibitor to rats has been reported to raise blood pressure (BP) and cause insulin resistance, suggestive of a central effect of insulin that is NO dependent. Herein we test whether ICV insulin has peripheral haemodynamic and metabolic effects and whether peripheral effects of systemic insulin are affected by the ICV administration of the NOS inhibitor N(G) -methyl-l-arginine (l-NMMA).

METHODS

Anaesthetized rats were fitted with an ICV cannula for insulin, artificial cerebrospinal fluid (aCSF) or l-NMMA infusion. Rats receiving ICV l-NMMA (500 µg) underwent systemic insulin clamp (10 mU/min/kg) or saline treatment for 70 min and were compared with animals receiving an equal amount of l-NMMA infused systemically.

RESULTS

ICV aCSF or insulin (135 mU/min/kg brain) for 70 min or systemic l-NMMA (500 µg) had no effect on BP, heart rate (HR), femoral blood flow (FBF), glucose infusion rate, muscle 2-deoxyglucose uptake, microvascular perfusion or plasma insulin. However, ICV l-NMMA reduced systemic insulin-mediated increases in FBF (2.05 ± 0.08 to 1.55 ± 0.15 ml/min), 2-deoxyglucose uptake (17.7 ± 0.15 to 10.0 ± 0.03 µg/g/min) and microvascular perfusion (10.5 ± 0.5 to 6.6 ± 1.1 mol/min) (each mean ± SE, p < 0.05); plasma insulin, HR and BP were unaffected.

CONCLUSIONS

Central insulin administration had no effect on skeletal muscle haemodynamics or glucose metabolism. However, systemic insulin-mediated increases in limb blood flow, muscle microvascular perfusion and glucose uptake may be regulated by a central pathway that is NO dependent.

Estimation of the fructose diphosphatase-phosphofructokinase substrate cycle in the flight muscle of Bombus affinis

1. Substrate cycling of fructose 6-phosphate through reactions catalysed by phosphofructokinase and fructose diphosphatase was estimated in bumble-bee (Bombus affinis) flight muscle in vivo. 2. Estimations of substrate cycling of fructose 6-phosphate and of glycolysis were made from the equilibrium value of the (3)H/(14)C ratio in glucose 6-phosphate as well as the rate of (3)H release to water after the metabolism of [5-(3)H,U-(14)C]glucose. 3. In flight, the metabolism of glucose proceeded exclusively through glycolysis (20.4mumol/min per g fresh wt.) and there was no evidence for substrate cycling. 4. In the resting bumble-bee exposed to low temperatures (5 degrees C), the pattern of glucose metabolism in the flight muscle was altered so that substrate cycling was high (10.4mumol/min per g fresh wt.) and glycolysis was decreased (5.8mumol/min per g fresh wt.). 5. The rate of substrate cycling in the resting bumble-bee flight muscle was inversely related to the ambient temperature, since at 27 degrees , 21 degrees and 5 degrees C the rates of substrate cycling were 0, 0.48 and 10.4mumol/min per g fresh wt. respectively. 6. Calcium ions inhibited fructose diphosphatase of the bumble-bee flight muscle at concentrations that were without effect on phosphofructokinase. The inhibition was reversed by the presence of a Ca(2+)-chelating compound. It is proposed that the rate of fructose 6-phosphate substrate cycling could be regulated by changes in the sarcoplasmic Ca(2+) concentration associated with the contractile process.

A model study of the fructose diphosphatase-phosphofructokinase substrate cycle

A fructose diphosphatase-phosphofructokinase substrate cycle has been reconstructed in vitro to provide a system that recycles fructose 6-phosphate and hydrolyses ATP to ADP and P(i). The concerted actions of glucose phosphate isomerase, phosphofructokinase, aldolase and triose phosphate isomerase catalysed the loss of (3)H from [5-(3)H,U-(14)C]glucose 6-phosphate. This was used as the basis of a method for the estimation of the fructose diphosphatase-phosphofructokinase substrate cycle. For the reconstructed cycle, the rate of decrease of the (3)H/(14)C ratio in [5-(3)H,U-(14)C]hexose 6-phosphate was proportional to the rate of fructose 6-phosphate substrate cycling. A detailed theoretical treatment of this relationship is developed, which enables the rate of substrate cycling to be determined in vivo.

Systemic administration of the potential countermeasure huperzine reversibly inhibits central and peripheral acetylcholinesterase activity without adverse cognitive-behavioral effects

Huperzine A is potentially superior to pyridostigmine bromide as a pretreatment for nerve agent intoxication because it inhibits acetylcholinesterase both peripherally and centrally, unlike pyridostigmine, which acts only peripherally. Using rhesus monkeys, we evaluated the time course of acetylcholinesterase and butyrylcholinesterase inhibition following four different doses of -(-)huperzine A: 5, 10, 20, and 40 microg/kg. Acetylcholinesterase inhibition peaked 30 min after intramuscular injection and varied dose dependently, ranging from about 30% to 75%. Subsequently, cognitive-behavioral functioning was also evaluated at each dose of huperzine A using a six-item serial-probe recognition task that assessed attention, motivation, and working memory. Huperzine did not impair performance, but physostigmine did. The results demonstrate that huperzine A can selectively and reversibly inhibit acetylcholinesterase without cognitive-behavioral side effects, thus warranting further study.

Galantamine is a novel post-exposure therapeutic against lethal VX challenge

The ability of galantamine hydrobromide (GAL HBr) treatment to antagonize O-ethyl-S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX)-induced lethality, impairment of muscle tension, and electroencephalographic (EEG) changes was assessed in guinea pigs. Guinea pigs were challenged with 16.8 microg/kg VX (2LD50). One min after challenge, animals were administered 0.5 mg/kg atropine sulfate (ATR) and 25 mg/kg pyridine-2-aldoxime methochloride (2-PAM). In addition, guinea pigs were given 0, 1, 2, 4, 8 or 10 mg/kg GAL as a post-exposure treatment immediately prior to ATR and 2-PAM. Animals were either monitored for 24-h survival, scheduled for electroencephalography (EEG) recording, or euthanized 60 min later for measurement of indirectly-elicited muscle tension in the hemidiaphragm. Post-exposure GAL therapy produced a dose-dependent increase in survival from lethal VX challenge. Optimal clinical benefits were observed in the presence of 10 mg/kg GAL, which led to 100% survival of VX-challenged guinea pigs. Based on muscle physiology studies, GAL post-exposure treatment protected the guinea pig diaphragm, the major effector muscle of respiration, from fatigue, tetanic fade, and muscular paralysis. Protection against the paralyzing effects of VX was dose-dependent. In EEG studies, GAL did not alter seizure onset for all doses tested. At the highest dose tested (10 mg/kg), GAL decreased seizure duration when administered as a post-exposure treatment 1 min after VX. GAL also reduced the high correlation associated between seizure activity and lethality after 2LD50 VX challenge. GAL may have additional benefits both centrally and peripherally that are unrelated to its established mechanism as a reversible acetylcholinesterase inhibitor (AChEI).

Acute blockade by endothelin-1 of haemodynamic insulin action in rats

AIMS/HYPOTHESIS

Plasma levels of endothelin-1 are frequently elevated in patients with hypertension, obesity and type 2 diabetes. We hypothesise that this vasoconstrictor may prevent full perfusion of muscle, thereby limiting delivery of insulin and glucose and contributing to insulin resistance.

MATERIALS AND METHODS

The acute effects of endothelin-1 on insulin-mediated haemodynamic and metabolic effects were examined in rats in vivo. Endothelin-1 (50 pmol min(-1) kg(-1) for 2.5 h) was infused alone, or 30 min prior to a hyperinsulinaemic-euglycaemic insulin clamp (10 mU min(-1) kg(-1) for 2 h). Insulin clamps (10 or 15 mU min(-1) kg(-1)) were performed after 30 min of saline infusion.

RESULTS

Endothelin-1 infusion alone increased plasma endothelin-1 11-fold (p < 0.05) and blood pressure by 20% (p < 0.05). Endothelin-1 alone had no effect on femoral blood flow, capillary recruitment or glucose uptake, but endothelin-1 with 10 mU min(-1) kg(-1) insulin caused a decrease in insulin clearance from 0.35 +/- 0.6 to 0.19 +/- 0.02 ml/min (p = 0.02), resulting in significantly higher plasma insulin levels (10 mU min(-1) kg(-1) insulin: 2,120 +/- 190 pmol/l; endothelin-1 + 10 mU min(-1)kg(-1) insulin: 4,740 +/- 910 pmol/l), equivalent to 15 mU min(-1) kg(-1) insulin alone (4,920 +/- 190 pmol/l). The stimulatory effects of equivalent doses of insulin on femoral blood flow, capillary recruitment and glucose uptake were blocked by endothelin-1.

CONCLUSIONS/INTERPRETATION

Endothelin-1 blocks insulin's haemodynamic effects, particularly capillary recruitment, and is associated with decreased muscle glucose uptake and glucose infusion rate. These findings suggest that elevated endothelin-1 levels may contribute to insulin resistance of muscle by increasing vascular resistance and limiting insulin and glucose delivery.

Serial-probe recognition in rhesus macaques: effects of midazolam

A serial-probe recognition task was used to assess the effects of midazolam on visual attention and short-term memory in three rhesus monkeys. On each trial, six unique alphanumeric sample stimuli (list items) were presented sequentially followed by a choice period. Choosing the 'probe' stimulus was correct if the probe matched one of the list items; otherwise, choosing the 'default' stimulus (a white square) was correct. Behavior was examined under a range of doses of midazolam (0.065, 0.13, 0.26, and 0.52 mg/kg IM). Midazolam did not significantly reduce choice accuracy or change the shape of the serial position function and did not significantly reduce choice responding. However, choice reaction time was significantly increased by the two highest doses of midazolam. Responding directed at the sample stimuli was reduced at the two highest doses of midazolam. Furthermore, 0.52 mg/kg midazolam significantly increased sample-stimulus reaction time at all six serial positions. Overall, these data suggest that the two highest doses of midazolam tested increase reaction time, but do not directly impair short-term visual recognition memory. This is noteworthy because such doses appear capable of protecting against nerve agent-induced seizures.

Vascular and metabolic effects of methacholine in relation to insulin action in muscle

AIMS/HYPOTHESIS

Methacholine (MC) is a nitric oxide vasodilator, but unlike other vasodilators, it potentiates insulin-mediated glucose uptake by muscle. The present study aimed to resolve whether this action was the result of a vascular effect of MC leading to increased muscle perfusion or a direct effect of MC on the myocytes. We hypothesise that vascular-mediated insulin-stimulated glucose uptake responses to MC occur at lower doses than direct myocyte MC-mediated increases in glucose uptake.

METHODS

The vascular and metabolic effects of this vasodilator were examined in rats in vivo using a novel local infusion technique, and in the pump-perfused rat hindlimb under conditions of constant flow.

RESULTS

Local infusion of low-dose MC (0.3 micromol/l) into the epigastric artery of one leg (test) in vivo markedly increased femoral blood flow and decreased vascular resistance, without effects in the contra-lateral leg. Capillary recruitment, but not glucose uptake, was increased in the test leg. All increases caused by MC were confined to the test leg and blocked by local infusion into the test leg of N-nitro-L-arginine methyl ester (L-NAME), but not by infusion of N-nitro-D-arginine methyl ester (D-NAME). In the constant-flow pump-perfused rat hindlimb, infusion of 0.6 micromol/l MC vasodilated the pre-constriction effected by 70 nmol/l noradrenaline or 300 nmol/l serotonin, and this was blocked by 10 micromol/l L-NAME. 2-Deoxyglucose in muscle was increased by 30 micromol/l MC (p<0.05), but was unaffected by 3 micromol/l MC. All increases in 2-deoxyglucose uptake by 30 micromol/l MC were blocked by 10 micromol/l L-NAME.

CONCLUSIONS/INTERPRETATION

MC has dose-dependent effects both on the vasculature and on muscle metabolism. At low dose (0.3-3 micromol/l), MC is a potent vasodilator in muscle, both in vivo and in vitro, without metabolic effects; at higher doses (> or =30 micromol/l) MC has a direct metabolic effect leading to increased glucose uptake. Both the vascular and metabolic effects are sensitive to L-NAME. The low-dose enhancement of insulin action in vivo by MC, which has been reported previously, thus seems to be attributable to vascular effects.

Endothelial Na+-D-glucose cotransporter: no role in insulin-mediated glucose uptake

A recent report indicates that the Na+-D-glucose cotransporter SGLT1 is present in capillaries of skeletal muscle and is required for insulin-mediated glucose uptake in myocytes. This result is based on the complete inhibition of insulin-mediated muscle glucose uptake by phlorizin, an inhibitor of SGLT1. Using the pump-perfused rat hind limb, we measured glucose uptake, lactate efflux, and radioactive 2-deoxyglucose uptake into individual muscles with saline (control), phlorizin, insulin, and insulin plus phlorizin, as well as with saline and insulin using normal and low Na+ perfusion buffer. Insulin-mediated glucose uptake was not inhibited after correction for phlorizin interference in the glucose assay. Lactate efflux and 2-deoxyglucose uptake by individual muscles were unaffected by phlorizin. Low Na+ buffer did not affect insulin-mediated glucose uptake, lactate efflux, or 2-deoxyglucose uptake. We conclude that endothelial SGLT1 exerts no barrier for glucose delivery to myocytes.

Acute glucosamine-induced insulin resistance in muscle in vivo is associated with impaired capillary recruitment

AIMS/HYPOTHESIS

Glucose toxicity and glucosamine-induced insulin resistance have been attributed to products of glucosamine metabolism. In addition, endothelial cell nitric oxide synthase is inhibited by glucosamine. Since insulin has endothelial nitric-oxide-dependent vasodilatory effects in muscle, we hypothesise that glucosamine-induced insulin resistance in muscle in vivo is associated with impaired vascular responses including capillary recruitment.

MATERIALS AND METHODS

Glucosamine (6.48 mg kg(-1) min(-1) for 3 h) was infused with or without insulin (10 mU kg(-1) min(-1)) into anaesthetised rats under euglycaemic conditions.

RESULTS

Glucosamine infusion alone increased blood glucosamine (1.9+/-0.1 mmol/l) and glucose (5.4+/-0.2 to 7.7+/-0.3 mmol/l) (p<0.05) but not insulin. Glucosamine induced both hepatic and muscle insulin resistance as evident from measures of glucose appearance and disposal as well as hind-leg glucose uptake, which was inhibited by approx. 50% (p<0.05). Insulin-mediated increases in femoral arterial blood flow and capillary recruitment were completely blocked by glucosamine.

CONCLUSION/INTERPRETATION

Glucosamine mediates a major impairment of insulin action in muscle vasculature associated with the insulin resistance of muscle. Further studies will be required to assess whether the impaired capillary recruitment contributes to insulin resistance.

Effects of physostigmine and human butyrylcholinesterase on acoustic startle reflex and prepulse inhibition in C57BL/6J mice

The use of exogenously administered cholinesterases as bioscavengers of highly toxic organophosphorus nerve agents is a viable prophylactic against this threat. To use this strategy, cholinesterases must provide protection without disrupting behavior when administered alone. To assess behavioral safety, the acoustic startle reflex and prepulse inhibition (PPI) of C57BL/6J mice were investigated following administration of human plasma-derived butyrylcholinesterase (HuBChE). Two hours before testing, four groups of mice (n=10 per group) were pretreated with saline or HuBChE (2000 U, ip). Fifteen minutes before testing, subjects received either saline or the carbamate physostigmine (0.4 mg/kg, sc). Mice exposed to physostigmine exhibited a significant attenuation of the startle reflex, an increased time to peak startle amplitude, and significantly increased PPI. This effect was partially mitigated in mice pretreated with HuBChE. HuBChE alone did not change startle behavior or PPI significantly compared to saline controls. The circulatory time-course of butyrylcholinesterase was assessed in a separate group of mice and revealed levels approximately 600 times the physiological norm 2-4 h post administration. Thus, HuBChE does not appear to significantly alter startle or PPI behavior at a dose 30-fold higher than that estimated to be necessary for protection against 2LD50 of soman in humans.

Local methacholine but not bradykinin potentiates insulin-mediated glucose uptake in muscle in vivo by augmenting capillary recruitment

AIMS/HYPOTHESIS

Insulin has nitric-oxide-dependent vasodilatory effects in muscle, including capillary recruitment, that enhance access for itself and glucose. However, nitric-oxide-dependent vasodilators other than methacholine do not enhance insulin action. Our hypothesis is that methacholine, unlike bradykinin, enhances insulin-mediated glucose uptake in muscle by augmenting capillary recruitment.

METHODS

Local infusion of either methacholine or bradykinin into one leg of the anaesthetised rat was made during physiological insulin (3 mU.kg(-1).min(-1)) infusion under euglycaemic conditions and without affecting systemic blood pressure. Whole-body glucose infusion was determined, as was femoral blood flow, 2-deoxyglucose uptake into calf muscles and the metabolism of infused 1-methylxanthine, a measure of capillary recruitment for each leg.

RESULTS

Methacholine alone (0.3 micromol.l(-1)) increased femoral arterial blood flow, increased capillary recruitment but had no effect on 2-deoxyglucose uptake of the test leg relative to the contra-lateral control leg. Insulin alone (systemically) required a glucose infusion rate of 8.7 mg.kg(-1).min(-1) to maintain euglycaemia, increased 2-deoxyglucose uptake and capillary recruitment, but was without effect on femoral blood flow in either leg. Local methacholine with systemic insulin infusion increased femoral blood flow, 2-deoxyglucose uptake and capillary recruitment in the test leg only. Bradykinin (0.07 micromol.l(-1)), alone or with insulin, administered in a manner that increased femoral blood flow similarly to methacholine, did not affect 2-deoxyglucose uptake or capillary recruitment.

CONCLUSIONS/INTERPRETATION

Methacholine but not bradykinin enhances insulin-mediated muscle glucose uptake in vivo. We conclude that methacholine acts at specific sites in the vasculature of muscle to stimulate capillary recruitment and thereby enhance insulin access.

Age and experience-related improvements in gap detection in the rat

The ability to accurately process brief, successive acoustic signals rapidly presented to the central nervous system is believed to underlie successful language development. The limits of temporal resolution of the auditory system, often assessed using gap detection tasks, has been widely studied in relation to developing and decoding speech. In the present study, a reflex modification paradigm was used to investigate potential shifts in gap detection thresholds in rats across development, with test sessions beginning on postnatal day (P) 15, P35 and P64. We found that thresholds decreased over the course of development. These thresholds were determined to lie between 10 and 20 ms for the P15 and P35 groups, and between 5 and 10 ms for the P64 group. Moreover, we observed improvements in gap detection thresholds in all age groups over 5 days of testing, including the youngest age group (P15). These later results suggest that experience-dependent plasticity mechanisms at the level of sensory processing are operational and observable both very early in development, and also in adult animals. The present findings also demonstrate maturational improvements in silent gap detection using a pre-pulse inhibition paradigm.

Inhibiting NOS blocks microvascular recruitment and blunts muscle glucose uptake in response to insulin

We examined the effects of inhibiting nitric oxide synthase with Nomega-nitro-l-arginine-methyl ester (l-NAME) on total hindlimb blood flow, muscle microvascular recruitment, and hindlimb glucose uptake during euglycemic hyperinsulinemia in vivo in the rat. We used two independent methods to measure microvascular perfusion. In one group of animals, microvascular recruitment was measured using the metabolism of exogenously infused 1-methylxanthine (1-MX), and in a second group contrast-enhanced ultrasound (CEU) was used. Limb glucose uptake was measured by arterial-venous concentration differences after 2 h of insulin infusion. Saline alone did not alter femoral artery flow, glucose uptake, or 1-MX metabolism. Insulin (10 mU.min-1.kg-1) significantly increased hindlimb total blood flow (0.69 +/- 0.02 to 1.22 +/- 0.11 ml/min, P < 0.05), glucose uptake (0.27 +/- 0.05 to 0.95 +/- 0.08 micromol/min, P < 0.05), 1-MX uptake (5.0 +/- 0.5 to 8.5 +/- 1.0 nmol/min, P < 0.05), and skeletal muscle microvascular volume measured by CEU (10.0 +/- 1.6 to 15.0 +/- 1.2 video intensity units, P < 0.05). Addition of l-NAME to insulin completely blocked the effect of insulin on both total limb flow and microvascular recruitment (measured using either 1-MX or CEU) and blunted glucose uptake by 40% (P < 0.05). We conclude that insulin specifically recruits flow to the microvasculture in skeletal muscle via a nitric oxide-dependent pathway and that this may be important to insulin's overall action to regulate glucose disposal.

Nonnutritive flow impairs uptake of fatty acid by white muscles of the perfused rat hindlimb

Triglyceride hydrolysis by the perfused rat hindlimb is enhanced with serotonin-induced nonnutritive flow (NNF) and may be due to the presence of nonnutritive route-associated connective tissue fat cells. Here, we assess whether NNF influences muscle uptake of 0.55 mM palmitate in the perfused hindlimb. Comparisons were made with insulin-mediated glucose uptake. NNF induced during 60 nM insulin infusion inhibited hindlimb oxygen uptake from 22.0 +/- 0.5 to 9.7 +/- 0.8 micromol x g(-1) x h(-1) (P < 0.001), 1-methylxanthine metabolism (indicator of nutritive flow) from 5.8 +/- 0.4 to 3.8 +/- 0.4 nmol x min(-1) x g(-1) (P = 0.004), glucose uptake from 29.2 +/- 1.7 to 23.1 +/- 1.8 micromol x g(-1) x h(-1) (P = 0.005) and muscle 2-deoxyglucose uptake from 82.1 +/- 4.6 to 41.6 +/- 6.7 micromol x g(-1) x h(-1) (P < 0.001). Palmitate uptake, unaffected by insulin alone, was inhibited by NNF in extensor digitorum longus, white gastrocnemius, and tibialis anterior muscles; average inhibition was from 13.9 +/- 1.2 to 6.9 +/- 1.4 micromol x g(-1) x h(-1) (P = 0.02). Thus NNF impairs both fatty acid and glucose uptake by muscle by restricting flow to myocytes but, as shown previously, favors triglyceride hydrolysis and uptake into nearby connective tissue fat cells. The findings have implications for lipid partitioning in limb muscles between myocytes and attendant adipocytes.

Air and shock two-way shuttlebox avoidance in C57BL/6J and 129X1/SvJ mice

Despite multiple advantages of the use of electric shock as an aversive stimulus, reasons exist for considering alternative aversive stimuli. In the present study, we examined and compared the acquisition of two-way shuttlebox avoidance with 275.8-kPa (40-psi) pulsed air and continuous 0.4-mA shock in two strains of mice commonly employed in targeted gene mutation research, C57BL/6J and 129X1/SvJ. Each trial consisted of a 5-s warning stimulus (WS, light) during which shuttling to the other side cancelled delivery of the aversive stimulus. Once initiated, the aversive stimulus remained active for 20 s or until an escape response occurred. For C57BL/6J mice, air and shock were equally and highly effective aversive stimuli. In contrast, air was less effective than shock for 129X1/SvJ mice. C57BL/6J mice outperformed 129X1/SvJ mice for both stimulus types. For 129X1/SvJ mice, longer escape latencies were observed initially for air, suggesting that shock is more effective. However, these differences in latency dissipated within the first seven sessions. Nevertheless, by the end of the 17-day study, asymptotic levels of avoidance proficiency were substantially lower for air than for shock in 129X1/SvJ mice. These results indicate that air is a suitable substitute for shock as an aversive stimulus in shuttlebox active avoidance; however, the relative efficacies of these aversive stimuli appear to depend upon the strain chosen for study.

Effects of anticholinergics on serial-probe recognition accuracy of rhesus macaques (Macaca mulatta)

Potential deleterious behavioral effects of the anticholinergics biperiden and scopolamine were examined via the performance of rhesus monkeys on a serial-probe recognition (SPR) procedure. On each trial, six unique stimuli (list items) were presented sequentially followed by a choice phase. In the choice phase, two stimuli were presented, a standard or 'default' stimulus (a white rectangle) and a 'probe' stimulus that differed with each choice trial. Choosing the probe stimulus was considered correct if the probe matched one of the list items; otherwise, choosing the default stimulus was considered correct. Behavior was examined under a range of doses of biperiden (0.001-1.0 mg/kg) and scopolamine (0.0056-0.03 mg/kg). Scopolamine (0.01-0.03 mg/kg) and biperiden (0.3-1.0 mg/kg) reduced overall accuracy. At the highest dose, scopolamine, but not biperiden, reduced the number of trials completed per session. The results suggest that doses of scopolamine and biperiden necessary to prevent or eliminate organophosphate induced seizures may affect performance adversely. However, because the degree of impairment from biperiden was modest, further examination of this anticonvulsant may be warranted.

Skeletal muscle microvascular recruitment by physiological hyperinsulinemia precedes increases in total blood flow

Supraphysiological doses of insulin enhance total limb blood flow and recruit capillaries in skeletal muscle. Whether these processes change in response to physiological hyperinsulinemia is uncertain. To examine this, we infused either saline (n = 6) or insulin (euglycemic clamp, 3.0 mU x min(-1) x kg(-1), n = 9) into anesthetized rats for 120 min. Femoral artery flow was monitored continuously using a Doppler flow probe, and muscle microvascular recruitment was assessed by metabolism of infused 1-methylxanthine (1-MX) and by contrast-enhanced ultrasound (CEU). Insulin infusion raised plasma insulin concentrations by approximately 10-fold. Compared with saline, physiological hyperinsulinemia increased femoral artery flow (1.02 +/- 0.10 vs. 0.68 +/- 0.09 ml/min; P < 0.05), microvascular recruitment (measured by 1-MX metabolism [6.6 +/- 0.5 vs. 4.5 +/- 0.48 nmol/min; P < 0.05] as well as by CEU [167.0 +/- 39.8 vs. 28.2 +/- 13.8%; P < 0.01]), and microvascular flow velocity (beta, 0.14 +/- 0.02 vs. 0.09 +/- 0.02 s(-1)). Subsequently, we studied the time dependency of insulin's vascular action in a second group (n = 5) of animals. Using CEU, microvascular volume was measured at 0, 30, and 90 min of insulin infusion. Insulin augmented microvascular perfusion within 30 min (52.8 +/- 14.8%), and this persisted at 90 min (64.6 +/- 9.9%). Microvascular recruitment occurred without changes to femoral artery flow or beta. We conclude that insulin increases tissue perfusion by recruiting microvascular beds, and at physiological concentrations this precedes increases in total muscle blood flow by 60-90 min.

Exercise training improves insulin-mediated capillary recruitment in association with glucose uptake in rat hindlimb

Exercise training is considered to be beneficial in the treatment and prevention of insulin insensitivity, and much of the effect occurs in muscle. We have recently shown that capillary recruitment by insulin in vivo is associated with and may facilitate insulin action to increase muscle glucose uptake. In the present study, we examined the effect of 14 days of voluntary exercise training on euglycemic-hyperinsulinemic clamped (10 mU. min(-1). kg(-1) for 2 h), anesthetized rats. Whole-body glucose infusion rate (GIR), hindleg glucose uptake, femoral blood flow (FBF), vascular resistance, and capillary recruitment, as measured by metabolism of infused 1-methylxanthine (1-MX), were assessed. In sedentary animals, insulin caused a significant (P < 0.05) increase in FBF (1.6-fold) and capillary recruitment (1.7-fold) but a significant decrease in vascular resistance. In addition, hindleg glucose uptake was increased (4.3-fold). Exercise training increased insulin-mediated GIR (24%), hindleg glucose uptake (93%), and capillary recruitment (62%) relative to sedentary animals. Neither capillary density nor total xanthine-oxidase activity in skeletal muscle were increased as a result of the training regimen used. We concluded that exercise training improves insulin-mediated increases in capillary recruitment in combination with augmented muscle glucose uptake. Increased insulin-mediated glucose uptake may in part result from the improved hemodynamic control attributable to exercise training.

Nutritive blood flow affects microdialysis O/I ratio for [(14)C]ethanol and (3)H(2)O in perfused rat hindlimb

Changes in the microdialysis outflow-to-inflow (O/I) ratio for [(14)C]ethanol and (3)H(2)O were determined in the perfused rat hindlimb after increases and decreases in nutritive flow mediated by the vasoconstrictors norepinephrine (NE) and serotonin (5-HT), respectively. Microdialysis probes (containing 10 mM [(14)C]ethanol and (3)H(2)O pumped at 1 or 2 microl/min) were inserted through the calf of the rat. Hindlimb perfusion flow rate was varied from 6 to 56 ml x min(-1) x 100 g(-1) in the presence of NE, 5-HT, or saline vehicle. The O/I ratios for both tracers were determined at each perfusion flow rate, as was perfusion pressure, oxygen uptake (a surrogate indicator of nutritive flow), and lactate release. Both tracers showed a decreased O/I ratio as hindlimb perfusion flow was increased, with [(14)C]ethanol being higher than (3)H(2)O. NE decreased the O/I ratio compared with vehicle, and 5-HT increased it for both tracers and both microdialysis flow rates. We conclude that the microdialysis O/I ratio, while able to detect changes in total flow, is also sensitive to changes in nutritive and nonnutritive flow, where the latter still extracts tracer, but less than the former.

Size-dependent effects of microspheres on vasoconstrictor-mediated change in oxygen uptake by perfused rat hindlimb

There are two vascular flow routes in skeletal muscle that can be accessed by different vasoconstrictors acting at selective sites in the vascular tree. Thus, angiotensin II (AII) and serotonin (5-HT), which stimulate and inhibit metabolism, do so by directing flow to nutritive and nonnutritive routes, respectively. In the present study the association between vascular flow route recruitment and metabolism was assessed by embolism with microspheres of different sizes. Latex microspheres (MS) of four sizes, 5.4 (MS5), 11.8 (MS12), 23.4 (MS23), and 93.6 microm (MS94), were injected during AII- or 5-HT-mediated constriction or under basal conditions and the effects on hindlimb oxygen uptake (VO2), perfusion pressure, and venous flow rate were determined. MS5 or MS12 partially reversed 5-HT-mediated inhibition of VO2 by 39 and 55%, respectively (P < 0.05), fully reversed AII-mediated stimulation of VO2 (P < 0.05), stimulated basal VO2 (P < 0.05), and increased pressure while only marginally (<10%) decreasing venous flow. MS23 or MS94 dose-dependently increased pressure and inhibited VO2, during basal or 5HT- and AII-mediated constriction, while only marginally decreasing venous flow. In conclusion, microspheres of less than 12 microm when injected into the constant flow perfused rat hindlimb can alter metabolism by altering flow distribution between nutritive and nonnutritive routes. Larger MS (> or =24 microm) are nondiscriminating possibly because they exceed the size of vessels in which branch points to the two vascular routes are located. Overall the findings provide further evidence for two microvascular routes in muscle, one nutritive and the other nonnutritive.

Heterogeneity of laser Doppler flowmetry in perfused muscle indicative of nutritive and nonnutritive flow

Laser Doppler flowmetry (LDF) signal responses have been compared with metabolic changes using both a surface macroprobe and randomly placed implantable microprobes in muscles of the constant-flow-perfused rat hindlimb. Changes in response to total flow and to vasoconstrictors that are known to increase (norepinephrine, NE) or decrease (serotonin, 5-HT) hindlimb oxygen uptake were assessed. The surface macroprobe (anterior end of biceps femoris) identified only one type of LDF response characterized by increased signal in response to NE and decreased signal in response to 5-HT. Implanted microprobes (tibialis, gastrocnemius, vastus, or bicep femoris) identified sites that gave three LDF responses of differing character. These responses were where the LDF signal increased with NE and decreased with 5-HT (56.7%), where the LDF signal decreased with NE and increased with 5-HT (16.5%), or where there was no net response to either vasoconstrictor (24.7%). The data are consistent with discrete regions of nutritive and nonnutritive flow in muscle where flow in each as controlled by vasoconstrictors relates directly to the metabolic behavior of the tissue.

Insulin stimulates laser Doppler signal by rat muscle in vivo, consistent with nutritive flow recruitment

Insulin-mediated increases in limb blood flow are thought to enhance glucose uptake by skeletal muscle. Using the perfused rat hindlimb, we report that macro laser Doppler flowmetry (LDF) probes positioned on the surface of muscle detect changes in muscle capillary (nutritive) flow. With this as background, we examined the effects of insulin and adrenaline (epinephrine), which are both known to increase total leg blood flow, on the LDF signals from scanning and stationary probes on the muscle surface in vivo. The aim is to assess the relationship between capillary recruitment, total limb blood flow and glucose metabolism. Glucose infusion rate, femoral arterial blood flow (FBF) and muscle LDF, using either scanning or a stationary probe positioned over the biceps femoris muscle, were measured. With scanning LDF, animals received insulin (10 m-units x min(-1) x kg(-1)), adrenaline (0.125 microg.min(-1) x kg(-1)) or saline. By 1 h, insulin had increased the glucose infusion rate from 0 to 128 micromol.min(-1) x kg(-1) and the scanning LDF had increased by 62+/-8% (P<0.05), but FBF was unaffected. Adrenaline increased FBF by 49% at 15 min, but LDF was unchanged. With saline at 1 h, neither FBF nor LDF had changed. With the stationary LDF surface probe, insulin at 1 h had increased FBF by 47% (P<0.05) and LDF by 47% (P<0.05) relative to saline controls. Adrenaline increased FBF (39%), but LDF was unaltered. The stimulation of LDF by insulin is consistent with capillary recruitment (nutritive flow) as part of the action of this hormone in vivo. The recruitment may be independent of changes in total flow, as adrenaline, which also increased FBF, did not increase LDF. The time of onset suggests that LDF closely parallels glucose uptake. Thus, depending on probe design, measurement of muscle haemodynamic effects mediated by insulin in normally responsive and insulin-resistant patients should be possible.

Spatial distribution of nutritive and nonnutritive vascular routes in perfused rat hindlimb muscle using microspheres

Skeletal muscle appears to have two vascular flow routes, nutritive and nonnutritive, where the balance of flow is controlled by vasoconstrictors. In the present study, spatial distributions of the two flow routes in muscles of the perfused rat hindlimb were attempted using fluorescent microspheres (15 microm in diameter). Microspheres were injected during steady-state perfusion with norepinephrine (proposed recruiter of nutritive flow), serotonin (proposed recruiter of nonnutritive flow), or vehicle. The three-dimensional location of individual microspheres in representative muscles was determined using a Fluorescent Imaging CryoMicrotome. Norepinephrine and serotonin each increased perfusion pressure (P < 0.05) but stimulated and inhibited oxygen consumption (P < 0.05), respectively. The distribution of microspheres lodged in muscle was independent of the agent used. Spatial perfusion indices for norepinephrine, serotonin, and vehicle did not differ from each other. Similarly, there was no difference in these indices for a theoretical distribution where microspheres were deliberately positioned in muscle bundle capillaries or interfibrillar connective tissue vessels. We conclude that the nutritive and nonnutritive flow routes are distributed throughout muscle sections consistent with their locations in muscle bundle capillaries and interfibrillar connective tissue, respectively.

Interaction between metabolism and flow in tendon and muscle

Blood vessels supplying the musculotendinous region of tendons, including interfibrillar connective tissue, represent a parallel vascular network to that supplying muscle fibers. Reciprocal control by vasomodulators and neural input determines relative flow in each network, and therefore relative supply of nutrients and hormones. Vessels supplying the tendon support fat cells and may function as a non-nutritive network within muscle groups to regulate resting muscle energy metabolism and to act as a flow reservoir for nutrient delivery in exercise.

Failure of laser Doppler signal to correlate with total flow in muscle: is this a question of vessel architecture?

The signal strength from LDF probes positioned in perfused muscle can be altered by vasoconstrictors despite total flow being maintained constant. Apart from redistribution of flow via collateral channels outside the region of measurement, the change in LDF signal may arise because the vasoconstrictors have switched flow to vessels of different architecture or altered the architecture of the blood vessels being perfused. Thus we have examined the effect of tube architecture on LDF signal using polymer tubes of 250, 100, and 50 microm internal diameter. At 3% hematocrit the LDF signal was linear for each of the three tube sizes from 10 to 80 microl/h. The signal strength was greatest from the smallest tube and least from the largest tube. For a single tube (100 microm) that doubled back on itself twice to cross the field of measurement three times, the LDF signal at any flow (10-80 microl/h, hematocrit 3%) was approx threefold greater than that for the same tube crossing the field of measurement once. The effect of progressively switching flow (constant at 120 microl/h, hematocrit 9%) from five to one tube in a manifold of five tubes (100 microm) gave rise to a progressive increase in signal. It is concluded that LDF signal derives predominantly from nonvectorial cell speed and less from cell number. Thus any agent that alters the architecture has the potential to alter the LDF signal.

Acute impairment of insulin-mediated capillary recruitment and glucose uptake in rat skeletal muscle in vivo by TNF-alpha

The vascular actions of insulin may contribute to the increase in glucose uptake by skeletal muscle. We have recently shown that when capillary recruitment by insulin is blocked in vivo, an acute state of insulin resistance is induced. Another agent that may have vascular effects is the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha), which has been reported to play an important role in the insulin resistance of obesity, type 2 diabetes, and sepsis in both animals and humans. Thus, in the present study, we have investigated the effect of an intravenous 3-h TNF treatment (0.5 microg x h(1) x kg(-1)) in control and euglycemic-hyperinsulinemic-clamped (10 mU x min(-1) x kg(-1) for 2 h) anesthetized rats. Hind-leg glucose uptake, muscle uptake of 2-deoxyglucose (2-DG), femoral blood flow (FBF), vascular resistance (VR), and capillary recruitment as measured by metabolism of infused 1-methylxanthine (1-MX) were assessed. Insulin alone caused a significant (P < 0.05) increase in FBF (1.7-fold) and capillary recruitment (2.5-fold), with a significant decrease in VR. In addition, hind-leg glucose uptake was increased (fourfold), as was 2-DG uptake in the soleus and plantaris muscles. TNF completely prevented the insulin-mediated changes in FBF, VR, and capillary recruitment and significantly reduced (P < 0.05) the insulin-mediated increase in total hind-leg glucose uptake (by 61%) and muscle 2-DG uptake (by at least 50%). TNF alone had no significant effect on any of these variables. It is concluded that acute administration in vivo of TNF completely blocks the hemodynamic actions of insulin on rat skeletal muscle vasculature and blocks approximately half of the glucose uptake by muscle. It remains to be determined whether these two effects are interdependent.

Relationship of MTT reduction to stimulants of muscle metabolism

MTT, a positively charged tetrazolium salt, is widely used as an indicator of cell viability and metabolism and has potential for histochemical identification of tissue regions of hypermetabolism. In the present study, MTT was infused in the constant-flow perfused rat hindlimb to assess the effect of various agents and particularly vasoconstrictors that increase muscle metabolism. Reduction of MTT to the insoluble formazan in muscles assessed at the end of experiments was linear over a 30 min period and production rates were greater in red fibre types than white fibre types. The vasoconstrictors, norepinephrine (100 nM) and angiotensin (10 nM) decreased MTT formazan production in all muscles but increased hindlimb oxygen uptake and lactate efflux. Veratridine, a Na(+) channel opener that increases hindlimb oxygen uptake and lactate efflux without increases in perfusion pressure, also decreased MTT formazan production. Membrane stabilizing doses (100 microM) of (+/-)-propranolol reversed the inhibitory effects of angiotensin and veratridine on MTT formazan production. Muscle contractions elicited by stimulation of the sciatic nerve, reversed the norepinephrine-mediated inhibitory effects on MTT formazan production, even though oxygen consumption and lactate efflux were further stimulated. Stimulation of hindlimb muscle oxygen uptake by pentachlorophenol, a mitochondrial uncoupler, was not associated with alterations in MTT formazan production. It is concluded that apart from muscle contractions MTT formazan production does not increase with increased muscle metabolism. Since the vasoconstrictors angiotensin and norepinephrine as well as veratridine activate Na(+) channels and the Na(+)/K(+) pump, energy required for Na(+) pumping may be required for MTT reduction. It is unlikely that vasoconstrictors that stimulate oxygen uptake do so by uncoupling respiration.

Impaired processing of complex auditory stimuli in rats with induced cerebrocortical microgyria: An animal model of developmental language disabilities

Individuals with developmental language disabilities, including developmental dyslexia and specific language impairment (SLI), exhibit impairments in processing rapidly presented auditory stimuli. It has been hypothesized that these deficits are associated with concurrent deficits in speech perception and, in turn, impaired language development. Additionally, postmortem analyses of human dyslexic brains have revealed the presence of focal neocortical malformations such as cerebrocortical microgyria. In an initial study bridging these research domains, we found that male rats with induced microgyria were impaired in discriminating rapidly presented auditory stimuli. In order to further assess this anatomical- behavioral association, we designed two experiments using auditory-reflex modification. These studies were intended to assess whether auditory processing deficits in microgyric male rats would be seen in threshold detection of a silent gap in white noise, and in oddball detection of a two-tone stimulus of variable duration. Results showed no differences between sham and microgyric subjects on gap detection, but did show that microgyric subjects were impaired in the discrimination of two-tone stimuli presented in an oddball paradigm. This impairment was evident for stimuli with total duration of 64 msec or less, while both groups were able to discriminate stimuli with duration of 89 msec or greater. The current results further support the relationship between malformations of the cerebral cortex and deficits in rapid auditory processing. They also suggest that the parameters characterizing rapid auditory processing deficits for a specific task may be influenced by stimulus features and/or cognitive demand of that particular task.

Impaired two-tone processing at rapid rates in male rats with induced microgyria

We previously reported that adult male rats with bilateral induced microgyria exhibit deficits in rapid auditory processing, which appear similar to auditory processing deficits seen in individuals with developmental language disabilities. The current study was designed to further elaborate that finding using an improved paradigm in which stimulus duration was uncoupled from testing experience and learning effects. Specifically, two-tone stimuli with durations of 540, 390, 332 and 249 ms were all presented within a single test session in a modified operant conditioning paradigm. Subjects were tested over a period of 12 days using this variable-stimulus format. Results confirmed microgyric male rats were impaired only in processing two-tone stimuli presented at rapid rates (i.e., 249 ms duration). Thus the current results support the previously observed link between focal malformations and deficits in rapid auditory processing.

Nutritive and non-nutritive blood flow: rest and exercise

There is growing evidence to support the notion of two vascular routes within, or closely associated with skeletal muscle. One route is in intimate contact with muscle cells (hence is known as 'nutritive') and the other functions as a vascular shunt (and has had the interesting misnomer of 'non-nutritive'). Recent findings suggest that the 'non-nutritive' route may, in part, be those vessels in closely associated (interlacing?) connective tissue that nourishes attached fat cells, and may form the basis of 'marbling' of muscle in obesity. In addition, embolism studies using various size microspheres indicate that the 'non-nutritive' vessels are likely to be capillaries fed by terminal arterioles that branch from the same transverse arterioles as those supplying terminal arterioles of the muscle capillaries (i.e. two vascular systems operating in parallel). The proportion of flow distributed between the two routes is tightly regulated and controls muscle metabolism and contraction by regulating hormone and substrate delivery as well as product removal. Because a high proportion of nutritive flow may elevate the set point for basal metabolism, a low proportion of nutritive flow in muscle at rest confers an evolutionary advantage, particularly when food is scarce. In addition, the proportion of flow that is carried by the non-nutritive routes at rest affords a flow reserve that can be switched to the nutritive route to amplify nutrient supply during exercise. Alternatively the non-nutritive route may allow flow to escape when active muscle contraction compresses its nutritive capillaries. Thus rhythmic oscillation of blood flow between the non-nutritive and nutritive networks may aid the muscle pump.

Perceptual auditory gap detection deficits in male BXSB mice with cerebrocortical ectopias

Underlying impairments in rapid auditory processing may contribute to disrupted phonological processing, which in turn characterizes developmental language impairment (LI). Identification of a neurobiological feature of LI that is associated with auditory deficits would further support this model. Accordingly, we found that adult male rats with induced cortical malformations were impaired in rapid auditory processing. Since 40-60% of BXSB mice exhibit spontaneous focal cerebrocortical ectopias (as seen in dyslexics brains), we assessed auditory gap detection in adult male BXSB mice. Ectopic mice were significantly worse than non-ectopics in detecting a 5 ms silent gap, but were not significantly impaired at longer gap durations (10-100 ms). Our results confirm that focal cortical malformations are associated with impairments in rapid auditory processing.