Field tourniquets in an austere military environment: A prospective case series.

OBJECTIVE: Field tourniquets are often used for battlefield extremity injuries. Their effectiveness has been documented by a large combat theater trauma center. However, their use and effectiveness by an austere forward surgical team has not been reported. Aims of this study were to determine: Whether field tourniquets: (1) Were placed for appropriate indications; (2) significantly reduced hemorrhage as measured by transfusion requirements; (3) influenced vital signs and injury severity scores; and (4) did they cause limb amputation, changed amputation level, or other complications. METHODS: Twenty-five patients with 30 involved extremities presenting to a forward surgical team in Iraq met the inclusion criteria. We prospectively collected data regarding the presence, indications for, and effectiveness of field tourniquets based on the need for blood transfusion. We recorded any complications associated with their use. RESULTS: Tourniquets significantly reduced hemorrhage from penetrating injuries as measured by transfusion requirements. Those having major vascular injuries with effective tourniquets, a total of 12 units of blood were transfused (1.7 units/vascular injury; 2 units/patient). However, 19 units were transfused in patients (3.3 units/vascular injury; 3.8 units/patient) who had an ineffective or no tourniquet (p = 0.0006). Transfusion requirements were related the presence of an effective tourniquet regardless of concomitant injuries. The group with effective tourniquets and compressed hemorrhage presented with higher mean systolic (p = 0.003) and diastolic (p = 0.023) blood pressures than the group with no tourniquets or ineffective ones. Complications included one peroneal nerve palsy and no amputations resulted from tourniquet application. CONCLUSION: Field tourniquets applied for penetrating injuries with severe bleeding can significantly reduce transfusion requirements and help maintain adequate blood pressure. Tourniquets were not the proximate cause of amputation and did not determine the choice of immediate amputation level.

Subacute High-Energy Traumatic Knee Dislocation in an Ambulatory Patient: A Case Report.

CASE: A 62-year-old man presented with a posterolateral knee dislocation sustained in a motorcycle collision initially managed nonsurgically. His treatment was complicated by recurrent dislocation from noncompliance with bracing and weight-bearing restrictions and by comorbidities including peripheral artery disease, type 2 diabetes, and heavy smoking and drinking. He was treated with a multiplanar knee-spanning external fixator and patellar tendon repair without further ligamentous reconstruction. This treatment provided a stable, functional knee with minimal pain. CONCLUSIONS: In this complex, noncompliant patient with a subacute knee dislocation, knee-spanning biplanar external fixation and patellar tendon repair without ligament reconstruction were crucial in achieving a satisfactory outcome.

A neurosteroid analogue with T-type calcium channel blocking properties is an effective hypnotic, but is not harmful to neonatal rat brain.

BACKGROUND: More than 4 million children are exposed annually to sedatives and general anaesthetics (GAs) in the USA alone. Recent data suggest that common GAs can be detrimental to brain development causing neurodegeneration and long-term cognitive impairments. Challenged by a recent US Food and Drug Administration (FDA) warning about potentially neurotoxic effects of GAs in children, there is an urgent need to develop safer GAs. METHODS: Postnatal Day 7 (P7) rat pups of both sexes were exposed to six (repeated every 2 h) injections of equipotent hypnotic doses of ketamine or the neuroactive steroid (3ß,5ß,17ß)-3-hydroxyandrostane-17-carbonitrile (3ß-OH) for 12 h. Loss of righting reflex was used to assess hypnotic properties and therapeutic index; quantitative caspase-3 immunohistochemistry was used to assess developmental neuroapoptosis; patch-clamp recordings in acute brain slices were used to assess the effects of 3ß-OH on neuronal excitability and synaptic transmission. Cognitive abilities of rats exposed to ketamine, 3ß-OH, or vehicle at P7 were assessed in young adulthood using the radial arm maze. RESULTS: The neuroactive steroid 3ß-OH has a therapeutic index similar to ketamine, a commonly used clinical GA. We report that 3ß-OH is safe and, unlike ketamine, does not cause neuroapoptosis or impair cognitive development when administered to P7 rat pups. Interestingly, 3ß-OH blocks T-type calcium channels and presynaptically dampens synaptic transmission at hypnotically-relevant brain concentrations, but it lacks a direct effect on γ-aminobutyric acid A or glutamate-gated ion channels. CONCLUSIONS: The neurosteroid 3ß-OH is a relatively safe hypnotic that warrants further consideration for paediatric anaesthesia.

In vitro evaluation of surface properties of Pro Seal® and Opal® SealTM in preventing white spot lesions.

OBJECTIVES: To evaluate the surface properties of two commercially available sealants (Pro Seal® (PS) and Opal® SealTM (OS)) in terms of fluoride(F) release, biofilm formation of Streptococcus mutans and Lactobacillus and the ability to resist acid penetration. SETTING: University of Nebraska Medical Center. MATERIAL & METHODS: Discs of similar diameter and thickness were made from OS and PS. Discs were soaked in double-distilled water, and F released was measured with fluoride meter daily for 14 consecutive days, then at 21 and 28 days. Biofilm formation was evaluated with Streptococcus mutans and Lactobacilli grown on sealant discs using confocal microscopy. Extracted human teeth (n=8) with sealant-coated buccal surfaces and untreated lingual surfaces were exposed to 0.1M lactic acid(pH=4.5) to test the acid penetration. After 1-4 weeks of exposure, teeth were subjected to microhardness testing and SEM microscopy. RESULTS: PS released significantly higher levels of F than OS. PS showed more S. mutans adherence than OS, whereas Lactobacillus did not show any differences in adherence. Both sealants protected enamel surfaces, showing statistically significant difference in the depth of acid penetration compared to their unsealed control sides. CONCLUSION: F release was adequate to aid in remineralization, although clinically it would not likely aid in preventing demineralization as there was no prolonged release of F by both sealants tested. S. mutans adherence to OS surface was less compared to PS surface, which could be of relevance in biofilm formation and white spot lesions. Both sealants protected enamel surfaces from acid penetration.

Conversion From Limb Salvage to Late Amputation: Lessons Learned From Recent Battlefields With Application to Civilian Trauma.

Battlefield injuries and high-energy civilian trauma present orthopaedic surgeons with treatment challenges. Despite efforts at limb salvage, some patients elect late amputation. This article reviews risk factors that predispose to late amputation. Using a MEDLINE search, English language peer-reviewed articles from 1993 to 2013 having data on late amputation following limb salvage were included. Late lower extremity amputation after limb salvage varied from 3.9% to 40% in civilian patients and from 5.2% to 15.2% in military patients. Factors influencing a patient's decision to undergo late amputation included a combination of complex pain symptoms with neurologic dysfunction, infection, a desire for improved limb functionality, and unwillingness to endure an often complicated and lengthy course of treatment. In military patients, rank was a significant risk factor since officers were 2.5 times more likely to elect late amputation (p < .05) than enlisted personnel. Despite often extraordinary efforts towardlimb salvage, results maybe disappointing.

Structural requirements of steroidal agonists of transient receptor potential melastatin 3 (TRPM3) cation channels.

BACKGROUND AND PURPOSE: Transient receptor potential melastatin 3 (TRPM3) proteins form non-selective but calcium-permeable membrane channels, rapidly activated by extracellular application of the steroid pregnenolone sulphate and the dihydropyridine nifedipine. Our aim was to characterize the steroid binding site by analysing the structural chemical requirements for TRPM3 activation. EXPERIMENTAL APPROACH: Whole-cell patch-clamp recordings and measurements of intracellular calcium concentrations were performed on HEK293 cells transfected with TRPM3 (or untransfected controls) during superfusion with pharmacological substances. KEY RESULTS: Pregnenolone sulphate and nifedipine activated TRPM3 channels supra-additively over a wide concentration range. Other dihydropyridines inhibited TRPM3 channels. The natural enantiomer of pregnenolone sulphate was more efficient in activating TRPM3 channels than its synthetic mirror image. However, both enantiomers exerted very similar inhibitory effects on proton-activated outwardly rectifying anion channels. Epiallopregnanolone sulphate activated TRPM3 almost equally as well as pregnenolone sulphate. Exchanging the sulphate for other chemical moieties showed that a negative charge at this position is required for activating TRPM3 channels. CONCLUSIONS AND IMPLICATIONS: Our data demonstrate that nifedipine and pregnenolone sulphate act at different binding sites when activating TRPM3. The latter activates TRPM3 by binding to a chiral and thus proteinaceous binding site, as inferred from the differential effects of the enantiomers. The double bond between position C5 and C6 of pregnenolone sulphate is not strictly necessary for the activation of TRPM3 channels, but a negative charge at position C3 of the steroid is highly important. These results provide a solid basis for understanding mechanistically the rapid chemical activation of TRPM3 channels.

A Wireless IC for Wide-Range Neurochemical Monitoring Using Amperometry and Fast-Scan Cyclic Voltammetry.

An integrated circuit for real-time wireless monitoring of neurochemical activity in the nervous system is described. The chip is capable of conducting measurements in both fast-scan cyclic voltammetry (FSCV) and amperometry modes for a wide input current range. The chip architecture employs a second-order DeltaSigma modulator (DeltaSigmaM) and a frequency-shift-keyed transmitter operating near 433 MHz. It is fabricated using the AMI 0.5-mum double-poly triple-metal n-well CMOS process, and requires only one off-chip component for operation. A measured current resolution of 12 pA at a sampling rate of 100 Hz and 132 pA at a sampling rate of 10 kHz is achieved in amperometry and 300-V/s FSCV modes, respectively, for any input current in the range of plusmn430 nA. The modulator core and the transmitter draw 22 and 400 muA from a 2.6-V power supply, respectively. The chip has been externally interfaced with a carbon-fiber microelectrode implanted acutely in the caudate-putamen of an anesthetized rat, and, for the first time, extracellular levels of dopamine elicited by electrical stimulation of the medial forebrain bundle have been successfully recorded wirelessly using 300-V/s FSCV.

The effects of sequential sectioning of defined posterior cruciate ligament fiber regions on translational knee motion.

BACKGROUND: Recent studies have shown that the posterior cruciate ligament (PCL) is composed of a continuum of fiber regions that display characteristic mechanical behavior under different motion and loading conditions. HYPOTHESIS: The anterior, central, and posterior fiber regions of the PCL differentially contribute to control of posterior translation of the tibia. STUDY DESIGN: Controlled laboratory study. METHODS: Nine intact, fresh-frozen cadaveric knees were instrumented with excursion wires implanted within the anterior, central, and posterior fiber regions of the PCL. In groups of 3, patterns of incremental posterior tibial translation using a 74-N posterior force were analyzed as a function of the variable linear separation distance between tibial and femoral fiber region attachment sites during posterior drawer testing at knee flexion angles of 20 degrees and 90 degrees before and after sequential fiber region section. RESULTS: At 20 degrees of knee flexion, there was no statistical difference in the relatively small amount of posterior tibial translation, regardless of whether the anterior, central, or posterior fibers were alone transected (P = .350). At 90 degrees of knee flexion, whether the posterior fibers were cut first, second, or third (order of section), the incremental difference in posterior tibial translation this produced was significantly different (P = .039). For the fiber regions combined, the third fiber region section resulted in a significantly larger incremental translation than did either the first or second section with the knee flexed 90 degrees (P = .001). After transection of all fiber regions, significantly more total posterior tibial translation occurred at 90 degrees versus 20 degrees of flexion (P = .002). CONCLUSIONS: This study shows that fiber regions within the PCL have unique characteristics and behave differently in response to posterior drawer forces. CLINICAL RELEVANCE: This study provides additional information on the complex mechanical behavior of the PCL and suggests that some partial tears (ie, those involving 1 or 2 fiber regions) may only result in minimal posterior translation during drawer testing at 90 degrees .

Cyclodextrins sequester neuroactive steroids and differentiate mechanisms that rate limit steroid actions.

BACKGROUND AND PURPOSE: Neuroactive steroids are potent modulators of GABA(A) receptors and are thus of interest for their sedative, anxiolytic, anticonvulsant and anaesthetic properties. Cyclodextrins may be useful tools to manipulate neuroactive effects of steroids on GABA(A) receptors because cyclodextrins form inclusion complexes with at least some steroids that are active at the GABA(A) receptor, such as (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha5alphaP, allopregnanolone). EXPERIMENTAL APPROACH: To assess the versatility of cyclodextrins as steroid modulators, we investigated interactions between gamma-cyclodextrin and neuroactive steroids of different structural classes. KEY RESULTS: Both a bioassay based on electrophysiological assessment of GABA(A) receptor function and optical measurements of cellular accumulation of a fluorescent steroid analogue suggest that gamma-cyclodextrin sequesters steroids rather than directly influencing GABA(A) receptor function. Neither a 5beta-reduced A/B ring fusion nor a sulphate group at carbon 3 affected the presumed inclusion complex formation between steroid and gamma-cyclodextrin. Apparent dissociation constants for interactions between natural steroids and gamma-cyclodexrin ranged from 10-60 microM. Although gamma-cyclodextrin accommodates a range of natural and synthetic steroids, C(11) substitutions reduced inclusion complex formation. Using gamma-cyclodextrin to remove steroid not directly bound to GABA(A) receptors, we found that cellular retention of receptor-unbound steroid rate limits potentiation by 3alpha- hydroxysteroids but not inhibition by sulphated steroids. CONCLUSIONS AND IMPLICATIONS: We conclude that gamma-cyclodextrins can be useful, albeit non-specific, tools for terminating the actions of multiple classes of naturally occurring neuroactive steroids.

5alpha-reduced neuroactive steroids alleviate thermal and mechanical hyperalgesia in rats with neuropathic pain.

5alpha-reduced neuroactive steroids with selective modulatory action in vitro on T or combined modulatory action on T and GABA(A) currents present in peripheral sensory neurons have been shown to induce potent peripheral analgesia in vivo in intact animals. Although the role of T and GABA(A) currents in pathophysiology of neuropathic pain (NPP) is not established, it appears that blockade of T currents and/or potentiation of GABA(A) currents could be beneficial in the management of NPP. To study the potential usefulness of 5alpha-reduced neuroactive steroids in alleviating NPP, we selected two newly synthesized steroids-ECN and CDNC24-with a selective blocking effect on T currents and a selective potentiating effect on GABA(A) currents, respectively, and commercial analogs-alphaxalone and 3alpha5alphaP-with the effects on both ion channels. We used a sciatic nerve ligation model to induce thermal and mechanical hyperalgesia in adult rats and tested peripheral thermal and mechanical nociception following local injection of neuroactive steroids into the peripheral receptive fields of a ligated hind paw. We found that 5alpha-reduced neuroactive steroids alleviate thermal and mechanical hyperalgesia in NPP rats. ECN and CDNC24 were more selective in alleviating thermal nociception in NPP than in sham animals when compared to 3alpha5alphaP and alphaxalone although the anti-nociceptive effect induced by 3alpha5alphaP and alphaxalone was more profound. CDNC24 was most selective since it had very minimal anti-nociceptive effect in sham animals but a very profound anti-nociceptive effect in NPP animals suggesting that, under pathological conditions, peripheral GABA(A) receptors might be an attractive therapeutic target.

Epipregnanolone and a novel synthetic neuroactive steroid reduce alcohol self-administration in rats.

This study was designed to compare the effects of several neuroactive steroids with varying patterns of modulation of gamma-aminobutyric acid (GABA)(A) and NMDA receptors on operant self-administration of ethanol or water. Once stable responding for 10% (w/v) ethanol was achieved, separate test sessions were conducted in which male Wistar rats were allowed to self-administer ethanol or water following pre-treatment with vehicle or one of the following neuroactive steroids: (3beta,5beta)-3-hydroxypregnan-20-one (epipregnanolone; 5, 10, 20 mg/kg; n=12), (3alpha,5beta)-20-oxo-pregnane-3-carboxylic acid (PCA; 10, 20, 30 mg/kg n=10), (3alpha,5beta)-3-hydroxypregnan-20-one hemisuccinate (pregnanolone hemisuccinate; 5, 10, 20 mg/kg; n=12) and (3alpha,5alpha)-3-hydroxyandrostan-17-one hemisuccinate (androsterone hemisuccinate; 5, 10, 20 mg/kg; n=11). The effect of the 3beta-epimer of PCA, (3beta,5beta)-20-oxo-pregnane-3-carboxylic acid (10, 20, 30 mg/kg; n=9), on ethanol self-administration was also examined. The compounds were administered using a Latin-square design 45 min prior to the weekly test sessions. The effects of the 30 mg/kg dose of the steroidal hemisuccinates on ethanol intake were also examined 5 min after administration of these drugs. Both epipregnanolone and PCA attenuated ethanol self-administration. However, neither of the hemisuccinate compounds significantly altered this behavior. The steroidal hemisuccinates (30 mg/kg; n=7) were also tested 5 min before behavior testing and had no effect on ethanol intake 5 min after administration. The 3beta-epimer of PCA also failed to alter ethanol intake. None of the test compounds altered water intake. In electrophysiological studies, the effects of PCA and androsterone hemisuccinate on evoked GABA(A) receptor-mediated inhibitory postsynaptic currents (GABA(A)-IPSCs) was examined in brain slices of the amygdala. PCA had a stimulatory effect at concentrations of 5 and 25 muM. Androsterone hemisuccinate had no agonist activity. The ability of epipregnanolone and PCA to alter ethanol intake appears to be related to different inhibitory actions of these compounds on either GABA(A) or NMDA receptors, respectively. Thus, dual modulation of these systems by selected neuroactive steroids may offer potential for modifying the reinforcing effects of alcohol.

Percentage of canals filled in apical cross sections - an in vitro study of seven obturation techniques.

AIM: To compare the apical density of several obturation techniques when used in palatal roots of extracted maxillary molars. METHODOLOGY: Seventy extracted molars were randomly divided into seven groups with 10 teeth each. The palatal root canals were instrumented to size 60 MAF, coated with Kerr's Pulp Canal Sealer, and obturated using one of seven techniques. The palatal roots were separated from the crowns, decalcified, and sectioned horizontally at 2 and 4 mm from the apex. The cross-sections were photographed through a microscope, the photos were analysed, and the amount of area in the canal that was obturated with gutta-percha was measured. The means for the 20 sections per group were calculated and the means were compared using mixed analysis of variance test. RESULTS: Simplifill used in accordance with the manufacturer's directions and Thermafil had the greatest mean obturated area, but neither were statistically better than mechanical lateral or warm vertical compaction (WVC; Schilder Technique). Simplifill as recommended and Thermafil were statistically better than cold lateral (P = 0.0210 and 0.0433, respectively), WVC (continuous wave) (P = 0.0006 and 0.0015), and the modified Simplifill group (P = 0.0010 and 0.0012). In addition, mechanical lateral and WVC (Schilder) had statistically more obturated area than WVC (continuous wave) (P = 0.0054 and 0.0073) and modified Simplifill (P = 0.0015 and 0.0016). Cold lateral and WVC (continuous wave) had significantly more obturated area than modified Simplifill (P = 0.0040 and 0.0087). CONCLUSIONS: Simplifill as recommended, Thermafil, mechanical lateral and WVC (Schilder) obturation techniques created more complete obturation using gutta-percha at the 2 and 4 mm levels than cold lateral, WVC (continuous wave), and Simplifill not used as directed.

Inhibition of type A GABA receptors by L-type calcium channel blockers.

Modulation of type A GABA receptors (GABAA) by L-type Ca++ channel blockers was investigated. The dihydropyridines nifedipine and nitrendipine, and the phenylalkylamine verapamil inhibited recombinant rat alpha1beta2gamma2 receptors recorded from human embryonic kidney (HEK) 293 cells; nifedipine at low concentrations also elicited modest stimulatory effects on GABA-gated current. The IC50 for GABA current inhibition was lowest for nitrendipine (17.3 +/- 1.3 microM), so subsequent studies were focused on further exploring its mechanism and possible site of action. When co-applied with GABA, nitrendipine had minimal effects on initial current amplitude, but significantly enhanced current decay rate. Nitrendipine-mediated inhibition was subunit-selective, as its IC50 was 10-fold lower in alpha1beta2 receptors. Nitrendipine's effect in recombinant human alpha1beta2gamma2 receptors was similar (IC50=23.0 +/- 1.3 microM) to that observed in rat receptors of the same configuration, indicating the site of action is conserved in the two species. The inhibitory effects were dependent on channel gating, were independent of transmembrane voltage, and were also observed in GABAA receptors recorded from hypothalamic brain slices. The pharmacologic mechanism of inhibition by nitrendipine was non-competitive, indicating it does not act at the GABA binding site. Nitrendipine block was retained in the presence of the benzodiazepine antagonist flumazenil, indicating it does not interact at the benzodiazepine site. The actions of nitrendipine were not affected by a mutation (beta2T246F) that confers resistance to the channel blocker picrotoxin, and they were not altered in the presence of the picrotoxin site antagonist alpha-isopropyl-alpha-methyl-gamma-butyrolactone, demonstrating nitrendipine does not act at the picrotoxin site of the GABAA receptor. Possible interaction of nitrendipine with the Zn++ site was also eliminated, as mutation of beta2 H267 to A, which confers resistance to Zn++, had no effect on nitrendipine-mediated inhibition. Our data suggest some of the central effects of dihydropyridines may be due to actions at GABAA receptors. Moreover, the effects may be mediated through interaction with a novel modulatory site on the GABAA receptor.

The enantiomer of cholesterol.

Cholesterol plays a variety of significant roles in biological systems. However, the mechanisms by which cholesterol functions remain largely unclear. The enantiomer of cholesterol (ent-cholesterol)--which has identical physical properties, but opposite three-dimensional configuration compared to cholesterol--is a unique tool that can be used to better understand the mechanisms of cholesterol function. We review the literature pertaining to ent-cholesterol, focusing in particular on its use in biological studies.

Neuroprotective agent riluzole potentiates postsynaptic GABA(A) receptor function.

The antiepileptic drug riluzole is a use-dependent blocker of voltage-gated Na(+) channels and selectively depresses action potential-driven glutamate over gamma-aminobutyric acid (GABA) release. Here we report that in addition to its presynaptic effect, riluzole at higher concentrations also strongly potentiates postsynaptic GABA(A) responses both in cultured hippocampal neurons and in Xenopus oocytes expressing recombinant receptors. Although peak inhibitory postsynaptic currents (IPSCs) of autaptic hippocampal neurons were inhibited, 20-100 microM riluzole significantly prolonged the decay of IPSCs, resulting in little change in total charge transfer. The effect was dose-dependent and reversible. Riluzole selectively increased miniature IPSC fast and slow decay time constants, without affecting their relative proportions. Miniature IPSC peak amplitude, rise time and frequency were unaffected, indicating a postsynaptic mechanism. In the Xenopus oocyte expression system, riluzole potentiated GABA responses by lowering the EC(50) for GABA activation. Riluzole directly gated a GABA(A) current that was partially blocked by bicuculline and gabazine. Pharmacological experiments suggest that the action of riluzole did not involve a benzodiazepine, barbiturate, or neurosteroid site. Instead, riluzole-induced potentiation was inhibited by the lactone antagonist alpha-isopropyl-alpha-methyl-gamma-butyrolatone (alpha-IMGBL). While most anticonvulsants either block voltage-gated Na(+) channels or potentiate GABA(A) receptors, our results suggest that riluzole may define an advantageous class of anticonvulsants with both effects.

Recent developments in structure-activity relationships for steroid modulators of GABA(A) receptors.

GABAergic neurotransmission can be both positively and negatively modulated by steroids. The steroid effects are thought to be mediated by binding of steroids to specific sites on GABA(A) receptors. It appears that the receptor sites for positive and negative modulatory steroids are different. Thus far, the location and number of binding sites for steroids on these receptors have not been established. In this brief review, we concentrate largely on results from our own structure-activity studies. Novel analogues have been studied to further delineate the structural features required for compounds to modulate receptor function via steroid binding sites. Non-naturally occurring enantiomers of both positive and negative modulators have been studied to provide further evidence for the existence of specific steroid binding sites on the receptors.

The synthetic enantiomer of pregnenolone sulfate is very active on memory in rats and mice, even more so than its physiological neurosteroid counterpart: distinct mechanisms?

The demonstration that the neurosteroid pregnenolone sulfate (PREGS) is active on memory function at both the physiological and pharmacological levels led to us examining in detail the effects of the steroid on spatial working memory by using a two-trial recognition task in a Y-maze, a paradigm based on the natural drive in rodents to explore a novel environment. Dose-response studies in young male adult Sprague-Dawley rats and Swiss mice, after the postacquisition intracerebroventricular injection of steroid, showed an U-inverted curve for memory performance and indicated a greater responsiveness in rats compared with mice. Remarkably, the synthetic (-) enantiomer of PREGS not only also displayed promnesiant activity, but its potency was 10 times higher than that of the natural steroid. Intracerebroventricular coadministration experiments with DL-2-amino-5-phosphonovaleric acid, a competitive selective antagonist of the N-methyl-D-aspartate receptor, abolished the memory-enhancing effect of PREGS, but not that of the PREGS enantiomer, evoking enantiomeric selectivity at the N-methyl-d-aspartate receptor and/or different mechanisms for the promnestic function of the two enantiomers.

Porosity in manually and machine mixed resin-modified glass ionomer cements.

The powder and liquid components of resin-modified glass ionomer cements are available in manual and machine mixed forms. This study quantified the effect mixing methods have on the porosity and shear strength of a resin-modified glass ionomer cement (RMGIC). A RMGIC (Fuji II LC) was manually or machined mixed according to manufacturer's instructions. Thin, disc-shaped specimens (n = 5) were made by compressing the cement between glass platens to a thickness of approximately 76 microns. The specimens were light cured for 120 seconds. Digital images of the specimens were recorded using a measuring microscope and slide film scanner. Digital imaging software was used to determine the number and volume of the cement's pores. Shear test specimens of manual and machine mixed cements (n = 10) of each group (approximately 800 microns thickness) were made as previously described. Shear punch tests were conducted using a 3.75 mm diameter punch mounted on a universal testing machine. The mean number and total volume of pores in the manually mixed specimens was considerably greater than that of the machine mixed group (p < 0.05). The shear punch test results of the machine mixed group was significantly higher than the manual mixed group, (p < 0.05).

Enantiospecificity of cholesterol function in vivo.

The importance of the absolute configuration of cholesterol for its function in vivo is unknown. To directly test this question in vivo, we synthesized the enantiomer of cholesterol (ent-cholesterol) and tested its ability to substitute for natural cholesterol (nat-cholesterol) in the growth, viability, and behavior of Caenorhabditis elegans, a cholesterol auxotroph. First-generation animals grown on ent-cholesterol were viable with only mild behavioral defects. However, ent-cholesterol produced 100% lethality/arrest of their second generation progeny. Isotopically labeled ent-cholesterol incorporated into animals, indicating that its lethality was not secondary to cholesterol starvation. When mixed with nat-cholesterol, ent-cholesterol was not inert; rather, it antagonized the activity of nat-cholesterol. These results demonstrate for the first time that the absolute configuration of cholesterol, not just its physical properties, is essential for its functions in vivo.