The effects of intense exercise on pain perception, mood, and plasma endocrine levels in man were studied under naloxone and saline conditions. Twelve long-distance runners (mean weekly mileage = 41.5) were evaluated on thermal, ischemic, and cold pressor pain tests and on mood visual analogue scales (VAS). Blood was drawn for determination of plasma levels of beta-endorphin-like immunoreactivity (BEir), growth hormone (GH), adrenocorticotrophic hormone (ACTH), and prolactin (PRL). These procedures were undertaken before and after a 6.3 mile run at 85% of maximal aerobic capacity. Subjects participated on two occasions in a double-blind procedure counterbalanced for drug order: on one day they received 2 i.v. injections of naloxone (0.8 mg in 2 ml vehicle each) at 20 min intervals following the run; on the other day, 2 equal volume injections of normal saline (2 ml). Sensory decision theory analysis of the responses to thermal stimulation showed that discriminability, P(A), was significantly reduced post-run under the saline condition, a hypoalgesic effect; response bias, B, was unaffected. Ischemic pain reports were significantly reduced post-run on the saline day, also a hypoalgesic effect. Naloxone reversed the post-run ischemic but not thermal hypoalgesic effects. Joy, euphoria, cooperation, and conscientiousness VAS ratings were elevated post-run; naloxone attenuated the elevation of joy and euphoria ratings only. Plasma levels of BEir, ACTH, GH, and PRL were significantly increased post-run. The results show that long-distance running produces hypoalgesia and mood elevation in man. The effects of naloxone implicate endogenous opioid neural systems as mechanisms of some but not all of the run-induced alterations in mood and pain perception.

Objective: The aim was to determine whether lower visceral pain thresholds in irritable bowel syndrome (IBS) primarily reflect physiological or psychological factors. Methods: Firstly, 121 IBS patients and 28 controls underwent balloon distensions in the descending colon using the ascending methods of limits (AML) to assess pain and urge thresholds. Secondly, sensory decision theory analysis was used to separate physiological from psychological components of perception: neurosensory sensitivity (p(A)) was measured by the ability to discriminate between 30 mm Hg vs 34 mm Hg distensions; psychological influences were measured by the report criterion-that is, the overall tendency to report pain, indexed by the median intensity rating for all distensions, independent of intensity. Psychological symptoms were assessed using the Brief Symptom Inventory (BSI). Results: IBS patients had lower AML pain thresholds (median: 28 mm Hg vs 40 mm Hg; p,0.001), but similar neurosensory sensitivity (median p(A): 0.5 vs 0.5; p = 0.69; 42.6% vs 42.9% were able to discriminate between the stimuli better than chance) and a greater tendency to report pain (median report criterion: 4.0 (''mild'' pain) vs 5.2 (''weak'' pain); p = 0.003). AML pain thresholds were not correlated with neurosensory sensitivity (r = 20.13; p = 0.14), but were strongly correlated with report criterion (r = 0.67; p,0.0001). Report criterion was inversely correlated with BSI somatisation (r = 20.26; p = 0.001) and BSI global score (r = 20.18; p = 0.035). Similar results were seen for the non-painful sensation of urgency. Conclusion: Increased colonic sensitivity in IBS is strongly influenced by a psychological tendency to report pain and urge rather than increased neurosensory sensitivity.

Glassy carbon (GC) surfaces modified with monolayers of biphenyl and nitrobiphenyl molecules were examined as voltammetric electrodes for ferrocene, benzoquinone, and tetracyanoquinodimethane electrochemistry in acetonitrile. The modified electrodes exhibited slower electron transfer than unmodified GC, by factors that varied with the monolayer and redox system. However, after a negative potential excursion to approximately -2.0 V versus Ag+/Ag, the modified electrodes exhibited much faster electron-transfer kinetics, approaching those observed on unmodified GC. The effect is attributed to an apparently irreversible structural change in the biphenyl or nitrobiphenyl monolayer, which increases the rate of electron tunneling. The transition to the "ON" state is associated with electron injection into the monolayer similar to that observed in previous spectroscopic investigations and causes a significant decrease in the calculated HOMO-LUMO gap for the monolayer molecule. Once the monolayer is switched ON, it supports rapid electron exchange with outer-sphere redox systems, but not with dopamine, which requires adsorption to the GC surface. The increase in electron-transfer rate with electron injection is consistent with an increase in electron tunneling rate through the monolayer, caused by a significant decrease in tunneling barrier height. The ON electrode can reduce biphenyl- or nitrobiphenyldiazonium reagent in solution to permit formation of a second modification layer of biphenyl or nitrobiphenyl molecules. This "double derivatization" procedure was used to prepare tetraphenyl- and nitrotetraphenyl-modified electrodes, which exhibit significantly slower electron transfer than their biphenyl and nitrobiphenyl counterparts. A "switching" electrode may have useful properties for electroanalytical applications and possibly in electrocatalysis. In addition, the ON state represents an "organic electrode" in which electron transfer occurs at an interface between an organic conductor and a solution rather than an interface between a solution and a metal or carbon electrode.

The effects of chromate treatment on the corrosion of an aluminum/copper aircraft alloy were examined with a galvanic corrosion apparatus composed of two electrodes and a zero resistance ammeter. Combinations of pure Al, pure Cu, and AA2024-T3 electrodes were immersed in 0.1 M NaCl solution, which was saturated with air, O 2 , or argon. Selection of electrode material or differential aeration resulted in partial segregation of corrosion reactions, with one electrode becoming a net cathode and the other a net anode. For the case of an Al/Cu galvanic cell, chromate significantly reduced the observed cathodic current on Cu but had little effect when added to the Al cell. For an AA2024/AA2024 couple, chromate decreased the observed current when present in either the net anode or net cathode compartments. The results indicate that Cr VI in solution, or Cr VI pretreatment, inhibits O 2 reduction on Cu sites. Inhibition is preceded by a spike in the reduction current, implying that Cr III is formed at approximately a monolayer level on Cu. The results for Cr VI effects on the AA2024/AA2024 galvanic couple are consistent with observed polarization curves. Considering the results in their entirety, Cr VI acts as a strong irreversible cathodic inhibitor on Cu and AA2024, but the results do not exclude the action of Cr VI as an anodic inhibitor on AA2024-T3.Aluminum alloy 2024-T3 (AA2024-T3) has been well documented to be highly susceptible to corrosion, particularly localized pitting corrosion, and intergranular corrosion. AA2024-T3 is an in-homogeneous alloy (nominal composition Al, 3.8-4.9% Cu, 1.2-1.8% Mg, 0.3-0.9% Mn, 0.5% Fe, 0.5% Si, 0.25% Zn, 0.1% Cr, 0.05% Ti) containing several types of secondary-phase intermetallic particles that are enriched in alloying elements vs. the alloy matrix.

The oxygen reduction reaction ͑ORR͒ was examined on copper, platinum, and glassy carbon electrodes, with regard to its inhibition by exposure of the electrode to chromate ion (Cr VI ) in NaCl solution. All three electrode materials exhibited a mass transport limited current for the ORR at sufficiently negative potentials, but this current was strongly inhibited in the presence of Cr VI . Inhibition persisted in Cr VI -free solution after the electrode was rinsed thoroughly, indicating that Cr VI formed an irreversibly adsorbed inhibiting layer. A reduction peak observed in Cr VI solution had an area of 1.1-2.5 mC/cm 2 , and the area varied little with Cr VI concentration, electrode material, and potential in the range of ϩ0.2 to Ϫ0.6 V vs. Ag/AgCl. This reduction peak is attributed to Cr III formation, and corresponds to formation of approximately a monolayer of Cr III oxyhydroxide. Once formed, this Cr III monolayer inhibits both O 2 reduction and further reduction of Cr VI . The onset of monolayer formation at about ϩ0.25 V vs. Ag/AgCl is the same as the potential of the onset of ORR inhbition in dilute Cr VI . The monolayer also decreases the electron transfer rate to ferrocene and Ru(NH 3 ) 6 ϩ3 , which are known to be outer sphere redox systems that do not require adsorption to the electrode surface. The results indicate that the adsorbed Cr III film formed by Cr VI reduction is a powerful inhibitor of oxygen reduction, due both to occupation of active chemisorption sites and to inhibition of electron transfer. In the context of corrosion protection, Cr VI acts as a ''site-directed'' irreversible inhibitor which migrates to active sites for the ORR, then is reduced to Cr III , and forms a permanent inhibiting monolayer.Continuing efforts to reduce exposure to materials containing hexavalent chromium have necessitated the drive to eliminate chromium as a corrosion inhibitor for aluminum alloys. Better understanding of the inhibition mechanism of chromium potentially will enable better design of replacements. The investigations of chromium oxyanion protection of aluminum alloys have been dominated by studies of the inhibition of the dissolution half-reaction ͑anodic inhibition͒ of the corrosion process. More recently, the issues of cathodic inhibition such as the role of chromium in the inhibition of the reduction of oxygen have started to be investigated. 1-3 The kinetics of the oxygen reduction reaction ͑ORR͒ on copper-bearing intermetallic compounds present in aluminum alloy AA2024-T3 have been examined in the presence of a chromate conversion coating. 1 The oxygen reduction reaction rate was reduced for conversion coated electrodes made of these intermetallics, although the role of the conversion coating was unclear. Inhibition of cathodic reactions on Cu-containing aluminides was attributed to hexavalent chromium adsorption in another recent study. 2 Further, separation of anodic and cathodic portions of the corrosion process was achieved by the use of a split-cell with various combinations of aluminum, c...