Continuous intravenous infusion of naloxone does not change behavioral, cardiovascular, or inflammatory responses to subcutaneous formalin in the rat

The opioid antagonist, naloxone, produces equivocal effects on the magnitude of nociceptive responses in several animal models of persistent pain, including the formalin test. Hindpaw injection of dilute formalin produces not only inflammation but also phasic (Phase 1) and persistent (Phase 2) behavioral and cardiovascular nociceptive responses in the rat. To test the hypothesis that endogenous opioid systems contribute to the magnitude of responses to intraplantar formalin injection, we evaluated the effects of continuous naloxone administration (0.01-100 mg/kg per h, i.v.) on formalin-evoked hindpaw inflammation, on behavioral indices of pain, flinching and licking pain behavior, and on changes in mean arterial pressure and heart rate. We report that naloxone, at doses less than 100 mg/kg per h, did not change any formalin-evoked response. Although the 100 mg/kg per h dose significantly decreased these responses, it also produced muscle rigidity and profound bradycardia. We conclude that endogenous opioids do not significantly modulate the nociceptive processing induced by subcutaneous formalin.

Differential contribution of the two phases of the formalin test to the pattern of c-fos expression in the rat spinal cord: studies with remifentanil and lidocaine

Injection of formalin in the rat hindpaw produces two phases of nociceptive behavior. Although it is generally agreed that the first phase results from direct chemical activation of nociceptive primary afferent fibers, the factors that contribute to the second phase are not established. In the present study, we monitored the expression of the c-fos protein to evaluate whether the pattern of activity of dorsal horn neurons differs as a result of ongoing afferent activity during the two phases. To selectively block the first or second phase, we respectively used remifentanil, a potent and short acting opiate agonist, and QX-314, a quaternary derivative of lidocaine, which does not cross the blood brain barrier. We also evaluated the effect of eliminating nociceptive behavior in both phases using both remifentanil and lidocaine or a combination of local anesthetics, bupivicaine and quaternary lidocaine. In all groups, formalin (5%, 50 microliters) was injected subcutaneously into the plantar surface of the hindpaw. To assess the nociceptive behavior produced by formalin, we monitored the number of flinches. Injection of remifentanil during the first phase completely blocked the first phase formalin-evoked nociceptive behavior, and had no effect on the second phase. Injection of lidocaine during the interphase completely blocked second phase nociceptive behavior. As expected, when remifentanil was administered during the first phase and lidocaine during the second phase, all formalin-evoked nociceptive behavior was blocked. The same was true for rats that received injections of bupivicaine and lidocaine during phases 1 and 2, respectively. In laminae I-II of the L4-L5 segment, the magnitude of the decrease in Fos expression was comparable for remifentanil (26.5%) and lidocaine (27.3%); the decrease was greater when both remifentanil and lidocaine were administered (50.5%), and even greater when bupivicaine and lidocaine were used (74.2%). In laminae V-VI, remifentanil, by itself, decreased c-fos expression by 39.4%; for lidocaine alone, the decrease was 58.4%. We did not observe further significant decreases when both remifentanil and lidocaine, or bupivacaine and lidocaine were injected (69.7% and 74.6%, respectively). Our results not only provide strong evidence that activity during the second phase is necessary for maintaining the maximal expression of c-fos in the spinal cord, but also reveal significant regional differences in the central patterns of activity generated during the two phases. These results also confirm our previous reports that c-fos expression is not eliminated when the behavioral manifestation of the noxious stimulus is completely blocked.

Theory of deformable substrates for cell motility studies

Linear theory is used to relate the tractions F applied by a cell to the resulting deformation of fluid, viscoelastic, or solid substrates. The theory is used to fit data in which the motion of a fluid surface in the neighborhood of a motile keratocyte is visualized with the aid of embedded beads. The data are best fit by modeling the surface layer as a two-dimensional, nearly incompressible fluid. The data favor this model over another plausible model, the planar free boundary of a three-dimensional fluid. In the resulting diagrams for the distribution of F, it is found that both curl F and div F are concentrated in the lateral extrema of the lamellipodium. In a second investigation, a nonlinear theory of weak wrinkles in a solid substrate is proposed. The in-plane stress tensor plays the role of a metric. Compression wrinkles are found in regions where this metric is negative definite. Tension wrinkles arise, in linear approximation, at points on the boundary between positive definite and indefinite regions, and are conjectured to be stabilized by nonlinear effects. Data for the wrinkles that would be produced by keratocyte traction are computed, and these agree qualitatively with observed keratocyte wrinkles.

Exaggerated cardiovascular and behavioral nociceptive responses to subcutaneous formalin in the spontaneously hypertensive rat

Spontaneously hypertensive rats (SHRs) are typically less responsive to phasic noxious stimuli than are their normotensive controls. Here, we used the formalin test to compare behavioral and cardiovascular responses to persistent noxious stimuli. Hindpaw formalin injection produced exaggerated flinching, arterial pressure and heart rate responses in SHRs, suggesting that abnormalities in blood pressure control systems increase nociceptive responses to persistent noxious stimuli.

Persistent cardiovascular and behavioral nociceptive responses to subcutaneous formalin require peripheral nerve input

Hindpaw injection of formalin produces acute (Phase 1) and persistent (Phase 2) nociceptive behaviors. This model has provided critical evidence supporting a contribution of central sensitization (hyperexcitability of spinal neurons) to the expression of persistent pain. Here, we evaluated the contribution of ongoing peripheral nerve inputs to Phase 2 pain responses. In addition to pain behavior (flinching), we measured formalin-evoked increases in arterial pressure and heart rate; these cardiovascular responses were also biphasic in nature. The arterial pressure response correlated highly with behavior, and was dependent on formalin concentration (0.625-5.0%), indicating that it was largely driven by noxious input. Lightly anesthetized (0.7% halothane) rats exhibited robust increases in blood pressure in the absence of pain behavior, indicating cardiovascular responses did not reflect somatomotor-cardiovascular coupling. Animals obtained from Charles River exhibited slightly larger Phase 2 flinching and heart rate responses compared to those obtained from Bantin and Kingman, suggesting cardiovascular-related pain responses can vary with the source of animal. We next evaluated the contribution of ongoing peripheral nerve activity to the expression of the Phase 2 pressor, tachycardia, and flinch responses. After Phase 1 subsided, but before Phase 2 began, we locally anesthetized the ipsilateral or contralateral (control) hindpaw with a hydrophilic lidocaine derivative, QX-314 (2%). Intraplantar QX-314 blocked Phase 2 pressor, tachycardia and behavioral responses only when injected into the paw that received formalin (2.5% or 10.0%). We conclude that persistent ongoing activity in peripheral afferent fibers during Phase 2 is required for the persistent pain evoked by formalin.

Object recognition contributions to figure-ground organization: operations on outlines and subjective contours

In previous research, replicated here, we found that some object recognition processes influence figure-ground organization. We have proposed that these object recognition processes operate on edges (or contours) detected early in visual processing, rather than on regions. Consistent with this proposal, influences from object recognition on figure-ground organization were previously observed in both pictures and stereograms depicting regions of different luminance, but not in random-dot stereograms, where edges arise late in processing (Peterson & Gibson, 1993). In the present experiments, we examined whether or not two other types of contours--outlines and subjective contours--enable object recognition influences on figure-ground organization. For both types of contours we observed a pattern of effects similar to that originally obtained with luminance edges. The results of these experiments are valuable for distinguishing between alternative views of the mechanisms mediating object recognition influences on figure-ground organization. In addition, in both Experiments 1 and 2, fixated regions were seen as figure longer than nonfixated regions, suggesting that fixation location must be included among the variables relevant to figure-ground organization.

Does orientation-independent object recognition precede orientation-dependent recognition? Evidence from a cuing paradigm

Object recognition may entail an incremental normalization process before access to canonical orientation representations, but is this process guided by prior access to object-centered representations? In Experiment 1, the authors showed observers figure-ground stimuli known to reflect access to, and output from, stored shape representations. The stimuli appeared in each of 6 different orientations, preceded by cues providing either (a) no information, (b) upright shape information only, (c) upright shape information plus orientation information (separately), or (d) shape information in the same orientation as the upcoming figure-ground test stimulus. Contrary to predictions by a postaccess account, the cues failed to eliminate orientation dependency in shape recognition. The results favor a preaccess account of the normalization process within the context of canonical orientation representations.

Does orientation-independent object recognition precede orientation-dependent recognition? Evidence from a cuing paradigm

Object recognition may entail an incremental normalization process before access to canonical orientation representations, but is this process guided by prior access to object-centered representations? In Experiment 1, the authors showed observers figure-ground stimuli known to reflect access to, and output from, stored shape representations. The stimuli appeared in each of 6 different orientations, preceded by cues providing either (a) no information, (b) upright shape information only, (c) upright shape information plus orientation information (separately), or (d) shape information in the same orientation as the upcoming figure-ground test stimulus. Contrary to predictions by a postaccess account, the cues failed to eliminate orientation dependency in shape recognition. The results favor a preaccess account of the normalization process within the context of canonical orientation representations.

Sexual function does not change when serum testosterone levels are pharmacologically varied within the normal male range

OBJECTIVE

To examine the relationship between serum T levels and sexual function when T levels are varied in the normal male range by pharmacological means. Two groups of healthy men were treated with a depot form of GnRH agonist leuprolide acetate (Lupron depot; TAP Pharmaceuticals, Chicago, IL) on days 1 and 31 to suppress endogenous T production and either 4 (n = 6) or 8 (n = 5) mg/d T replacement by a sustained release, long-acting T microcapsule formulation on day 1.

OUTCOME MEASURES

Sexual function was evaluated by daily logs of sexual activity and electroencephalogram-coupled nocturnal penile tumescence recording before and after 9 weeks of treatment.

RESULTS

Serum T levels in 4 and 8 mg/d groups were at low and high ends of the normal male range, respectively (10.5 +/- 1.7 versus 26.5 +/- 3.4 nmol/L). The number and duration of rapid eye movement (REM) periods, latency to REM sleep, erections/REM period, magnitude, and duration of tumescence were not significantly different between the 4 and 8 mg groups. Sexual logs also did not show significant differences in overall scores or in subcategories of intensity of sexual feelings (libido) and sexual activity between the two doses.

CONCLUSIONS

These data indicate that erectile function and sexual activity and feelings are restored by relatively low T levels. These data may help explain why some partially hypogonadal men continue to have normal sexual function and the absence of good correlation between serum T levels in the normal range and sexual function.

Political influence in the 1990s: from iron triangles to policy networks

To assess the prospects of comprehensive health care reform during the Clinton administration, we must examine the changes that have occurred in the political and structural contexts in which reform is debated. The political context includes the status of the health care system itself as well as public attitudes and voting patterns associated with health care reform; it may be friendlier now to reform than it has been in any previous period, but it cannot on its own produce policy change. The structural context, the representational community of organized interests and government institutions, is the means by which politics is either thwarted or translated into action. Changes in these organized interests and in Congress have transformed the health care reform policy community from an "iron triangle" dominated by an antireform alliance of medicine, insurance, and business to a more loosely bound policy network in which a reform coalition may now be able to prevail, especially under the direction of an activist president like Bill Clinton. I consider three hypotheses: The first claims that, despite the apparent structural changes, the core power relationships will remain the same as in the past, and the antireform alliance either will continue to block policy change or will push through a reform program that protects its constituent interests. According to the second, the structural changes produce an atomization of power, making coalition building in support of reform impossible. The third and most plausible hypothesis proposes that the structural changes, in combination with the shift in politics and Clinton's election, have generated new opportunities for fundamental reform.

Mental images can be ambiguous: reconstruals and reference-frame reversals

Philosophers and psychologists have debated whether or not mental images of ambiguous figures are reversible as pictures of such figures are. Previously, empirical evidence both pro (Finke, Pinker, & Farah, 1989) and con (Chambers & Reisberg, 1985) has been obtained. In a series of four experiments, we identify the conditions under which images of classic ambiguous figures like the duck/rabbit and the snail/elephant are reversible. We distinguish between two types of reversal: those that entail a change in reference-frame specification as well as a reconstrual of image components (reference-frame realignments) and those that entail reconstruals only (reconstruals). We show that reference-frame realignments can occur in imagery, particularly if observers are given an explicit or an implicit suggestion; and that reconstruals of images occur commonly, regardless of experimental conditions. In addition, we show that images constructed from good parts are more likely to reverse than images constructed from poor parts. On the basis of these results, we propose a functional organization of shape memory that is consistent with shape recognition findings as well as with our reversal findings.

A biodegradable testosterone microcapsule formulation provides uniform eugonadal levels of testosterone for 10-11 weeks in hypogonadal men

Limitations of presently available testosterone esters (enanthate and cypionate) include the fluctuating serum testosterone levels and the need for relatively frequent injections (every 10-21 days). These limitations of testosterone esters have prompted the development of more physiological and longer acting systems for androgen delivery. This paper reports pharmacokinetic and pharmacodynamic data with a second generation long-acting testosterone microcapsule formulation in hypogonadal men. This was a single dose, open label, nonrandomized study. Ten hypogonadal men with primary (n = 6) or secondary (n = 4) hypogonadism, otherwise in good health, received 630 mg microencapsulated testosterone in dextran solution (IM) on day 1. Serum total and free testosterone; LH; FSH; dihydrotesterone; estradiol; sex hormone-binding globulin; total cholesterol; high, low, and very low density lipoprotein cholesterol; triglycerides; and apoprotein-AII and -B were measured on multiple occasions during the 2-week control period and the 16-week treatment period. In addition, on days 0, 1, 28, 56, and 84, subjects were hospitalized for detailed hormone analyses over the 24-h period. Serum total and free testosterone levels rose quickly into the midnormal range and stayed uniformly in the eugonadal range for about 70-77 days, after which serum testosterone levels declined gradually into the hypogonadal range. Testosterone release from the microcapsule formulation over the first 10 weeks approximated zero order kinetics. Serum dihydrotestosterone levels rose into the normal range, and testosterone to dihydrotestosterone ratios remained in the physiological range. Serum estradiol levels rose and stayed in the midnormal male range. Serum sex hormone-binding globulin levels decreased significantly during treatment. Serum LH and FSH levels also significantly decreased in the six hypergonadotropic men. Total cholesterol low and very low density lipoprotein cholesterol and triglyceride levels did not change, but plasma high density lipoprotein cholesterol levels decreased significantly during treatment. These data indicate that testosterone microcapsule formulation provides uniform eugonadal levels of testosterone for about 10 weeks. The long duration and zero order kinetics make it an attractive alternative to existing methods of androgen replacement.

Contouring structures for 3-dimensional treatment planning

Three-dimensional (3-D) treatment planning is a labor-intensive process with contouring of the target volume and critical normal tissues being a significant time-consuming component. The use of 3-D treatment planning on a routine basis may be limited by the time required to complete treatment plans. Despite the need to increase the efficiency of the process, there is little literature addressing the speed and accuracy of contouring systems. In an attempt to initiate systematic analysis of the contouring process, data sets consisting of 10 CT images each were developed on two patients with esophageal carcinoma. Nine different operators manually contoured structures (target volume, spinal canal, lungs) on the data sets using four different contouring systems present in our department. These included both commercially available systems and those developed by the authors. There was a wide variation in the hardware and software characteristics of these systems. The time required to contour the CT data sets was recorded and analyzed. The contouring accuracy was assessed by comparison with a standard template derived from the CT data set for each image. The contouring time was found to be dependent on the system design, previous contouring experience, and the type of drawing instrument (lightpen vs mouse). The mean contouring time ranged from 26 minutes per patient for the fastest system to 41 minutes for the slowest. Potential clinically significant errors in contouring were rare for the spinal canal and lungs but present at a greater rate for the target volume (30.3%). The implications of this finding are discussed.

Shape recognition contributions to figure-ground reversal: which route counts?

Observers viewed upright and inverted versions of figure-ground stimuli, in which Gestalt variables specified that the center was figure. In upright versions, the surround was high in denotivity, in that most viewers agreed it depicted the same shape; in inverted versions, the surround was low in denotivity. The surround was maintained as figure longer and was more likely to be obtained as figure when the stimuli were upright rather than inverted. In four experiments, these effects reflected inputs to figure-ground computations from orientation-specific shape representations only. To account for these findings, a nonratiomorphic mechanism is proposed that enables shape recognition processes before figure-ground relationships are determined.

Dose-response evaluation of oral labetalol in patients presenting to the emergency department with accelerated hypertension

STUDY OBJECTIVE

Dose-response evaluation of oral labetalol (100, 200, or 300 mg) on heart rate and systemic blood pressure in emergency department patients with hypertensive urgency (diastolic blood pressure, 110 to 140 mm Hg, and no end-organ evidence of hypertensive emergency).

METHODS

This acute-treatment, dose-ranging study used a randomized, double-blind, parallel design. Patients with supine diastolic blood pressure of 110 to 140 mm Hg after 30 minutes of bedrest received an oral dose of labetalol. Supine blood pressure and heart rate were measured manually and recorded hourly for four hours after dose. Diastolic blood pressure of 100 mm Hg or less or a 30-mm Hg reduction in diastolic blood pressure was considered a treatment success.

RESULTS

Two hundred fifty-five patients were evaluated for inclusion, and 36 patients (19 women and 17 men; mean age, 44 years; age range, 23 to 67 years) were studied. The most frequent reason for exclusion was a spontaneous decrease in diastolic blood pressure to less than 110 mm Hg (31%) with bedrest. There were 12 patients in each treatment group. Compared with baseline, the 100-mg dose significantly (P less than .05) reduced heart rate at three and four hours after dose, and the 300-mg dose significantly (P less than .05) reduced heart rate at one, two, and three hours after dose; the 200-mg dose did not significantly affect heart rate. All doses produced a significant decrease in systolic and diastolic blood pressures at one, two, three, and four hours after dose compared with baseline. There were no statistically significant differences between treatment groups with regard to systolic or diastolic blood pressure or heart rate at baseline or one, two, three, or four hours after dose. At two hours after dose, diastolic blood pressure control was observed in 75%, 58%, and 67% of patients receiving 100, 200, and 300 mg, respectively (P = .903). At four hours after dose, diastolic blood pressure control was observed in 50%, 64%, and 67% of patients receiving 100, 200, and 300 mg, respectively (P = .755). A comparison of treatment success rates between the two time periods showed a waning of response with the 100-mg dose of labetalol at hour 4 compared with hour 2 (P less than .05). No adverse effects were observed.

CONCLUSION

Labetalol provides safe and effective treatment for hypertensive urgencies when administered orally in doses of 100 to 300 mg.