Immune Reconstitution Inflammatory Syndrome Associated With Kaposi's Sarcoma

Purpose

A proportion of patients with HIV infection who subsequently receive highly active antiretroviral therapy (HAART) exhibit a deterioration in their clinical status, despite control of virologic and immunologic parameters. This clinical response, known as the immune reconstitution inflammatory syndrome (IRIS), occurs secondary to an immune response against previously diagnosed pathogens.

Patients and Methods

From our cohort of 5,832 patients treated in the HAART era, we identified 150 therapy-naive patients with a first presentation of Kaposi's sarcoma (KS). Their clinicopathologic features and progress were recorded prospectively.

Results

After commencing HAART, ten patients (6.6%) developed progressive KS, which we identify as IRIS-associated KS. In a comparison of these individuals with those whose KS did not progress, we found that IRIS-KS occurred in patients with higher CD4 counts (P = .03), KS-associated edema (P = .01), and therapy with both protease inhibitors and non-nucleosides together (P = .03). Time to treatment failure was similar for both groups, although the CD4 count declined more rapidly at first, in those patients with IRIS-associated KS. Despite this initial decline, in our clinical experience HAART could be successfully continued in those with IRIS-associated KS.

Conclusion

We have identified IRIS-KS in a cohort of HIV patients with KS who start HAART.

FTIR investigation of monomer polymerisation and polyacid neutralisation kinetics and mechanisms in various aesthetic dental restorative materials

Diamond ATR FTIR has been used to quantify light catalysed polymerisation and polyacid neutralisation rates in various glass ionomer cements (GIC), resin-modified GICs (RMGIC) and compomers. At 150s after the start of light exposure, levels of methacrylate polymerisation on the lower surfaces of 1mm thick specimens were 97% and 98% for the RMGIC, Vitremer and Fuji II LC and 47% and 37% for the compomers, Compoglass and Dyract. After light exposure, polymerisation rates for the compomers decreased linearly with inverse time. By 50,000s Compoglass and Dyract were 62% and 51% polymerised. Initial rate of polyacid neutralisation in the GIC Shofu HIFI was 0.32 times that of Fuji IX GIC. Those in Vitremer, Fuji II LC, Compoglass and Dyract were 0.16, 0.09, 0.004 and 0.004 times that of Fuji IX. Excluding short initial periods, log of neutralisation rates decreased linearly with log-time. Average gradients were -1.35 for the GIC, -0.80 for the RMGIC and -0.59 for the compomers. By 50,000s, polyacid salt concentrations for the RMGIC and compomers were 0.41 and 0.016 times that of the GIC. Reaction mechanisms have been discussed and used to help interpret material mechanical properties, fluoride release rates and adhesion to tooth structure.

FTIR investigation of polymerisation and polyacid neutralisation kinetics in resin-modified glass-ionomer dental cements

A new diamond ATR FTIR method has been developed to quantify the processes occurring in the resin-modified glass-ionomer cement (RMGIC). Fuji II LC (Improved), at 1 mm depth from the cement/water interface. With Fuji II LC (Improved) various changes in the spectra due to 90% monomer polymerisation were observed within 1 min after 20 s exposure to a dental light. Following polymerisation further different peak shifts with time were detected. Comparison with spectral changes seen during setting of the conventional glass-ionomer cement, Fuji IX, showed these could be assigned to water sorption and/or polyacid neutralisation. Any absorbance change due to the acid/glass reaction alone exhibited 2 linear regions when plotted against square root of time. Such behaviour suggests two separate diffusion mechanisms for acid neutralisation. The first faster one ceases at 30 or 150 min after mixing in Fuji IX and Fuji II LC (Improved), respectively. It was proposed that these were the times at which all the water (a required component of the reaction) in the original formulation is used up. The slower process was the same acid/glass reaction but initiated by water sorption. The initial rates of absorbance change due to acid neutralisation were 17 times faster for Fuji IX than Fuji II LC (Improved). By 4 days however, the total absorbance change due to acid neutralisation for Fuji IX was only 4 times that for Fuji II LC (Improved). Such results can help to explain changes in cement properties with time.

Prospective randomized comparison of dacarbazine (DTIC) versus DTIC plus interferon-alpha (IFN-alpha) in metastatic melanoma

Dacarbazine (DTIC) has been the mainstay of chemotherapy for metastatic melanoma for over two decades, but only 15%-20% of patients respond and benefit is usually transient. Randomized studies combining DTIC with interferon-alpha (IFN-alpha) in advanced disease have so far been inconclusive in terms of response and survival. We report a randomized prospective pilot Phase III trial of DTIC +IFN-alpha in patients with metastatic melanoma. The primary endpoint was death. A total of 61 patients were randomized between April 1995 and April 1998. Differences in survival between groups were assessed using log-rank analysis. Quality of life was measured using the European Organization for Research on Treatment of Cancer QLQ C30 (+3) questionnaire. Fifty-seven patients died during the study. The median survival for patients receiving DTIC was 7.2 months (95% confidence interval (CI) 4.4-9.0); it was 4.8 months for DTIC + IFN-alpha (95% CI 2.0-8.0). There was no significant difference in survival between the two treatment arms (chi2 unadjusted = 0.15, P = 0.70; chi2 adjusted = 0.01, P = 0.91). The 6-month survival of those patients randomized to DTIC alone was 58% compared with 40% for those patients randomized to DTIC + IFN-alpha. There were no differences in quality of life between treatment groups. This study failed to demonstrate a survival benefit for patients receiving IFN-alpha in combination with DTIC. These results are inconclusive primarily owing to the small size of the trial. A meta-analysis is required to determine whether there is a role for the addition of IFN-alpha to DTIC in the treatment of this disease.

Dealing with daily hassles: smoking and African-American adolescent girls

PURPOSE

To examine cigarette use and its relationship to daily life hassles in an urban sample of African-American adolescent girls.

METHODS

A sample of 105 African-American adolescent girls (mean age of 15.45 years) derived from a larger cross-sectional research project titled "Female Adolescent Substance Experience Study" funded by the National Institute of Drug Abuse comprised the sample. The sample was divided into adolescents who had ever smoked in their lifetime and adolescents who had never smoked before. Student's t-tests were conducted to determine whether there were differences between these groups on demographic characteristics and the number of daily life hassles. Pearson product moment correlations were also conducted to examine the association between age of smoking initiation and number of hassles.

RESULTS

Less than 50% of the teenagers had ever smoked cigarettes in their lifetime, and of those who had ever smoked, the average age of initiation was 12.55 years (SD = 2.63). Furthermore, girls who had ever smoked, in contrast to girls who had never smoked, had a significantly greater number of daily life hassles, in general, and within the school/academic and family/economic domains in particular. Age of smoking initiation was negatively related to the number of hassles, indicating that girls who started to smoke at a younger age reported more hassles.

CONCLUSIONS

These findings are discussed in terms of developing an understanding of gender and ethnic-specific correlates of smoking that can be used to better delineate the developmental smoking trajectory of African-American girls.

Social Isolation & Sexual Abuse Among Women Who Smoke Crack

The purpose of this study was to explore the prevalence of social isolation and its relationship to sexual trauma in a sample of Black women who smoke crack cocaine. Using a convenience sample of 115 Black women with a history of smoking crack cocaine, participants were interviewed for 2 to 4 hours and asked a variety of questions about their health, relationships, sexuality, and drug use. Bivariate and multivariate logistical regressions were used to predict whether the women reported being socially isolated. While social isolation was not necessarily a common experience among the sample, it was found that women who had been sexually abused were three times more likely to report being socially isolated than women who had not been sexually abused. In addition, social isolation was more common among women who had been abused by a family member, who had been abused when they were young, and who had been abused for a long period of time. However, multivariate analyses revealed that the age at which the sexual trauma occurred was the most salient predictor of social isolation in adulthood. Implications for drug treatment are discussed.

Presynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor-mediated stimulation of glutamate and GABA release in the rat striatum in vivo: a dual-label microdialysis study

The existence of presynaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate autoreceptors on glutamate nerve terminals in vitro has recently been demonstrated using synaptosomal and brain slice preparations. In the present study we have used a modification of a rapid dual-label intracerebral microdialysis method, previously developed by Young and co-workers(80,81) for the study of presynaptic mechanisms of neurotransmitter release, to investigate whether presynaptic AMPA receptors also play a role in the control of striatal glutamate release in vivo. For comparative purposes, the action of locally applied AMPA on striatal GABA release in vivo was also monitored. Local application of AMPA (0.01-100 microM), by reverse dialysis, into the striatum resulted in concentration-dependent increases in the Ca(2+)-dependent efflux of both [3H]L-glutamate and [14C]GABA. Maximum responses reached 142.0+/-6.5% and 166.8+/-7.7% of basal efflux for [3H]L-glutamate and [14C]GABA, respectively. No marked behavioural changes were observed at any dose of the agonist. Unexpectedly, the AMPA-evoked responses were not potentiated by the AMPA receptor desensitization inhibitors cyclothiazide (10-100microM) or aniracetam (1mM). Consistent with this finding, AMPA-stimulated [3H]L-glutamate and [14C]GABA efflux were significantly attenuated by co-perfusion with the selective, competitive AMPA receptor antagonist 6-nitro-7-sulphamoylbenzo(F)quinoxaline-2,3-dione (100microM) but not 1-(aminophenyl)-4-methyl-7,8-methylendioxy-5H-2,3-benzodiazepine (100microM), a non-competitive AMPA receptor antagonist known to interact with the cyclothiazide site to control AMPA receptor function. The broad spectrum ionotropic glutamate receptor antagonist, kynurenic acid (100-1000microM) also markedly inhibited the AMPA-evoked responses in the striatum in vivo. None of the antagonists, when given alone, influenced basal efflux of [3H]L-glutamate suggesting a lack of tonic regulatory control of glutamate release via presynaptic AMPA-type autoreceptors in the rat striatum. These results demonstrate the presence of presynaptic AMPA receptors, of a novel cyclothiazide- and aniracetam-insensitive subtype, on presynaptic nerve terminals in the rat striatum in vivo, acting to enhance glutamate and GABA release. Our data support the concept of AMPA receptor heterogeneity in vivo, a finding which may facilitate the development of novel, more selective drugs for the treatment of a range of neurological disorders associated with abnormal cerebral glutamate release. The pharmacological profile of these novel presynaptic receptors is currently under investigation.

Access conditions are crucial: comment on Lynch and Carroll (2001)

W. J. Lynch and M. E. Carroll (2001) sought to identify factors that control drug intake, that is, factors that decrease the avidity of drug seeking and drug taking while drug is obviously available. The review provides updated information about factors that regulate drug intake and a heuristic framework for future studies of regulatory processes throughout the natural history of a substance abuse disorder. In particular, the review suggests a productive framework for studies of transitions from early drug use to later abusive use. Forceful identification of factors that control the avidity of drug seeking and drug taking under the controlled conditions of the laboratory may encourage development of therapeutic interventions that capitalize on these factors for successful treatment of human drug abuse. Extending the analysis of regulation of intake to include factors that can be manipulated to reorganize behavior may improve the design of interventions to treat drug abuse.

Effect of radiographic quality on computer-assisted head penetration measurements

Even the most sophisticated computer-assisted radiographic techniques of measuring femoral head penetration into the polyethylene liner depend on the quality of the radiograph being evaluated, which varies greatly in clinical settings. The authors of this study sought to determine how the accuracy and reproducibility of three commercially available computer-assisted measurement systems differed when measuring optimal radiographs (with sharply defined component edges) and suboptimal radiographs (with less well defined edges). Using three computer-assisted measurement systems, the authors measured head penetration on simulated and clinical hip radiographs. All systems calculated head penetration as the movement of the head center relative to the cup center. To define the periphery of the prosthetic head and cup, one method (System One) used the human eye and a digitizing tablet, whereas the other two methods (System Two and System Three) used digital edge detection algorithms. For simulated hip radiographs, error was calculated as the absolute value of the difference between the known amount of head penetration, determined by a coordinate measuring machine, and the amount of penetration determined by the software. Three way analysis of variance showed a significant difference in absolute error among the three measurement techniques. System One had a significantly smaller absolute error (0.11 +/- 0.06 mm) than did System Two (0.25 +/- 0.25 mm) and System Three (0.19 +/- 0.13 mm). In addition, three-way analysis of variance showed that optimal radiographs were associated with a significantly lower absolute error (0.14 +/- 0.09 mm) than were suboptimal radiographs (0.23 +/- 0.22 mm). For optimal radiographs, there was no significant difference in error among the three measurement methods; all systems were accurate and reproducible. However, for suboptimal radiographs absolute error increased and varied widely, and a significant difference among the methods existed. These data show the susceptibility of head penetration measurements to radiographic technique and underscore the importance of good quality radiographs for all analyses of head penetration.

Modulation of latent inhibition in the rat by altered dopamine transmission in the nucleus accumbens at the time of conditioning

Latent inhibition describes a process by which pre-exposure of a stimulus without consequence retards the learning of subsequent conditioned associations with that stimulus. It is well established that latent inhibition in rats is impaired by increased dopamine function and potentiated by reduced dopamine function. Previous evidence has suggested that these effects are modulated via the meso-accumbens dopamine projections. We have now undertaken three experiments to examine this issue directly, especially in the light of one study in which latent inhibition was reported to be unaffected by direct injection of amphetamine into the accumbens. Latent inhibition was studied using the effect of pre-exposure of a tone stimulus on the subsequent formation of a conditioned emotional response to the tone. 6-Hydroxydopamine-induced lesions of dopamine terminals in the nucleus accumbens resulted in potentiation of latent inhibition. Bilateral local injections of the dopamine antagonist haloperidol into the nucleus accumbens (0.5 microg/side) before conditioning also potentiated latent inhibition. Moreover, such injections were able to reverse the disruptive effect of systemic amphetamine (1mg/kg, i.p.) on latent inhibition. Bilateral local injection of amphetamine (5 microg/side) into the nucleus accumbens before conditioning was able to disrupt latent inhibition, provided that it was preceded by a systemic injection of amphetamine (1mg/kg) 24h earlier.We conclude that the attenuation of latent inhibition by increased dopamine function in the nucleus accumbens is brought about by impulse-dependent release of the neurotransmitter occurring at the time of conditioning. The previously reported failure to disrupt latent inhibition with intra-accumbens amphetamine is probably due to impulse-independent release of dopamine. The implications of these conclusions for theories linking disrupted latent inhibition to the attentional deficits in schizophrenia, and to the dopamine theory of this disorder, are discussed.

Reflections on validity and epistemology in a study of working relations between deaf and hearing professionals

In this article, a research study that examined the working relationships between Deaf and hearing professionals in health and educational services in the United Kingdom is addressed. These service providers worked in bilingual organizations where both British Sign Language and English were used and in which Deaf people's identity as a cultural-linguistic minority was accepted. The focus of this article is on issues of validity and epistemology that arose for the Deaf and hearing research team in the course of this study. In particular, it examines the influence of identity attributions on the research process for researchers operating within a context of historical oppression, minority language use and legitimization of research knowledge, and challenges to the interpretative analysis used in the study that arose from the dynamics of majority-minority power relations in the wider social world.

Differential tolerance to antinociceptive effects of mu opioids during repeated treatment with etonitazene, morphine, or buprenorphine in rats

RATIONALE

Repeated treatment experiments with high and low efficacy agonists provide critical insight into possible mechanisms underlying development of opioid tolerance.

OBJECTIVE

Experiments in a tail-withdrawal assay tested the hypothesis that magnitude of tolerance to antinociceptive effects is inversely related to agonist relative efficacy in rats intermittently treated with etonitazene. morphine, or buprenorphine.

METHODS

The antinociceptive effects of five mu opioid agonists were tested in male, Sprague-Dawley rats in a warm-water tail-withdrawal assay. To induce tolerance, escalating doses of the higher efficacy agonist etonitazene, the high efficacy agonist morphine, or the lower efficacy agonist buprenorphine were administered twice daily for 2-8 weeks.

RESULTS

Etonitazene, etorphine, morphine, buprenorphine, and GPA 1657 [(1)-beta-2'-hydroxy-2,9-dimethyl-5-phenyl-6,7-benzomorphan] produced dose-dependent increases in tail-withdrawal latency until 100% maximum possible effect (%MPE) was obtained. Treatment with escalating doses of etonitazene, morphine, or buprenorphine produced greater tolerance to the lower efficacy agonists buprenorphine and GPA 1657 than to the higher efficacy agonists etonitazene, etorphine, and morphine. Treatment with buprenorphine, a lower efficacy agonist, produced greater tolerance than did treatment with equivalent doses of the higher efficacy agonists morphine or etonitazene.

CONCLUSIONS

Taken together, these data suggest that magnitude of antinociceptive tolerance is inversely related to relative efficacy of mu agonists, with lower efficacy agonists being more susceptible to tolerance than are higher efficacy agonists under these intermittent dosing conditions.

Pre-clinical and clinical study of QC12, a water-soluble, pro-drug of quercetin

BACKGROUND

Quercetin is a naturally occurring flavonoid with many biological activities including inhibition of a number of tyrosine kinases. A phase I, dose-escalation trial of quercetin defined the maximum tolerated dose (MTD) as 1700 mg/m2 three weekly, but the vehicle, dimethyl sulphoxide (DMSO) is unsuitable for further clinical development of quercetin.

PATIENTS AND METHODS

A water-soluble, pro-drug of quercetin (3'(N-carboxymethyl)carbomyl-3,4',5,7-tetrahydroxyflavone), QC12 has been synthesised. Six cancer patients received 400 mg of QC12 (equivalent to 298 mg of quercetin), orally on day 1 and intravenously (i.v.) in normal saline on day 14.

RESULTS

Following oral administration of QC12 we were unable to detect QC12 or quercetin in plasma. After i.v. administration, we detected peak plasma concentrations of QC12 of 108.7 +/- 41.67 microMolar (microM). A two-compartment model with mean t(1/2)alpha of 0.31 +/- 0.27 hours and mean t(1/2)beta of 0.86 +/- 0.78 hours best described the concentration-time curves for QC12. The mean AUC was 44.54 +/- 13.0 microM.hour and mean volume of distribution (Vd) of 10.0 +/- 6.2 litres (l). Quercetin was found in all patients following i.v. infusion of QC12, with peak levels of quercetin 19.9 +/- 11.8 microM. The relative bioavailability of quercetin was estimated to be 20%-25% quercetin released from QC12.

CONCLUSIONS

QC12 is not orally bioavailable. This water-soluble pro-drug warrants further clinical investigation; starting with a formal phase I, IV, dose-escalation study.

Use of Raman spectroscopy in the characterisation of the acid-base reaction in glass-ionomer cements

Raman spectra of various combinations of glass-ionomer cement components have been compared with those of the reactants and the salts of polyacrylic and tartaric acids. The components consisted of a fast-setting acid-degradable dental glass (containing, inter alia, oxides of Si, Al, Ca, Ba and Na), polyacrylic acid (PAA) and/or tartaric acid (TA). On the addition of water to the glass and tartaric acid, Raman spectroscopy indicated loss of acid and production of tartrate salts within seconds of mixing. Mixtures containing the glass, PAA and water in mass ratios 2:1:(0.1-4) reacted to form polyacrylate salts. The maximum fraction of unreacted PAA was found to decrease linearly with initial water/PAA mass ratio to a minimum of approximately 20% when this ratio exceeds 1.5. The data are consistent with 5.6 moles of water being required when each mole of acidic groups is neutralised. In newly prepared cements containing glass, water, polyacrylic and tartaric acids, polyacrylic acid and its salts, in both ionised and solid state form, can be detected. After about 1 h, however, Raman peaks associated with ionised species disappear.

Comparison of in vivo wear between polyethylene liners articulating with ceramic and cobalt-chrome femoral heads

At yearly intervals we compared the radiological wear characteristics of 81 alumina ceramic femoral heads with a well-matched group of 43 cobalt-chrome femoral heads. Using a computer-assisted measurement system we assessed two-dimensional penetration of the head into the polyethylene liner. We used linear regression analysis of temporal data of the penetration of the head to calculate the true rates of polyethylene wear for both groups. At a mean of seven years the true rate of wear of the ceramic group was slightly greater (0.09 mm/year, SD 0.07) than that of the cobalt-chrome group (0.07 mm/year, SD 0.04). Despite the numerous theoretical advantages of ceramic over cobalt-chrome femoral heads, the wear performance in vivo of these components was similar.

A phase II study of the 5-lipoxygenase inhibitor, CV6504, in advanced pancreatic cancer: correlation of clinical data with pharmacokinetic and pharmacodynamic endpoints

PURPOSE

Primary objective was to determine response rate of patients with advanced pancreatic cancer to a novel lipoxygenase and thromboxane A2 synthetase inhibitor (CV6504); secondary objectives included estimation of pharmacokinetics of CV6504, target-enzyme inhibition, safety and tolerance, quality of life and survival.

PATIENTS AND METHODS

Thirty-one patients with advanced pancreatic cancer were planned to receive CV6504, 100 mg TDS, orally for three months, at which point CT scans were performed to assess therapeutic response rates. Steady state concentrations of CV6504 and thromboxane B2 (an indirect measure of thromboxane A2 synthetase (TA2S) inhibition) were made. Of the 31 patients entered into the study, 23 were considered fully evaluable for response.

RESULTS

The drug was well tolerated with few side effects; no partial or complete responses were seen, but 10 patients had stable disease at 3 months; quality of life was maintained during therapy; mean CV6504 steady state plasma concentrations of 14 +/- 6 ng/ml resulting in 75 +/- 18% inhibition of TA2S were achieved; median-survival time for all patients considered eligible for assessment of efficacy was 36.6 weeks after the initial dose of study medication. The actuarial one-year survival was approximately 25%.

CONCLUSION

CV6504 inhibits its target enzyme in vivo, maintains stable disease in 32% of evaluable patients and is well tolerated.

Characterization of long-term femoral-head-penetration rates. Association with and prediction of osteolysis

BACKGROUND

We examined the relationship between long-term femoral-head-penetration patterns and osteolysis in a ten-year follow-up study of a well controlled patient population. The purposes of this study were to characterize the linearity of long-term head-penetration patterns over time, to describe the relationship between ten-year true wear rates and osteolysis, and to determine whether the occurrence of osteolysis at ten years could be predicted by penetration data obtained prior to five years.

METHODS

Temporal femoral-head-penetration patterns were examined at a minimum of ten years after forty-eight primary total hip arthroplasties. The arthroplasties were performed with the use of an Arthropor acetabular cup (Joint Medical Products) and a thirty-two-millimeter-diameter cobalt-chromium femoral head (DePuy). Using a computer-assisted radiographic technique, we evaluated two-dimensional head penetration on serial annual radiographs. Linear regression analysis modeled penetration-versus-time data as a line for each patient. The slope of the regression line indicated the true wear rate for each patient. In a subgroup of thirty-four hips for which three annual radiographs had been made less than five years after the arthroplasty, we compared early head-penetration patterns with the later occurrence of osteolysis.

RESULTS

For all forty-eight hips, the true wear rate averaged 0.18 millimeter per year (range, 0.01 to 0.44 millimeter per year) and temporal head-penetration patterns tended to be linear (mean r2 = 0.91 +/- 0.16). Osteolysis at ten years was strongly associated with increasing true wear rates (p < 0.001). Osteolysis did not develop in any of the nine hips with a true wear rate of less than 0.1 millimeter per year. However, osteolysis developed in nine (43 percent) of twenty-one hips with a rate between 0.1 and less than 0.2 millimeter per year, in eight of ten hips with a rate between 0.2 and 0.3 millimeter per year, and in all eight hips with a rate of greater than 0.3 millimeter per year. Evaluation of early true wear rates as a predictor of late osteolysis showed a similar relationship.

CONCLUSIONS

This study demonstrates that true wear rates tend to be constant and that increased true wear is significantly associated with osteolysis at ten years after the operation. A similar relationship was also found at the early follow-up interval, indicating that early true wear rates (determined from serial radiographs) might enable orthopaedists to predict if patients are at risk for the development of osteolysis.

CLINICAL RELEVANCE

On the basis of these findings, we use temporal femoral-head-penetration data in our practice to evaluate polyethylene inserts in asymptomatic patients, to estimate the time to component wear-through, and to adjust the frequency of follow-up evaluations for monitoring the development of osteolytic lesions in at-risk patients.

Discriminative stimulus effects of two doses of fentanyl in rats: pharmacological selectivity and effect of training dose on agonist and antagonist effects of mu opioids

RATIONALE

Discriminative stimulus effects of mu opioids vary systematically as a function of training dose. Differences among training doses may arise from multiple mechanisms.

OBJECTIVES

In vivo apparent pA(2) analyses were used to examine the contributions of opioid mechanisms to stimulus control by low and high training doses of the mu opioid fentanyl.

METHODS

Saline and one of two doses of fentanyl, administered s.c., were established as discriminative stimuli in two groups of rats (low training dose group: 0.01 mg/kg; high training dose group: 0.04 mg/kg). Generalization tests and in vivo apparent pA(2) analyses were used to evaluate receptor mechanisms of stimulus control.

RESULTS

Fentanyl, etonitazene, methadone, and morphine evoked full fentanyl generalization in both groups but were more potent in the low-dose group. Spiradoline and d-amphetamine did not evoke generalization in either group. Naltrexone antagonized stimulus and rate-altering effects of fentanyl in both groups, with apparent pA(2) values of 7. 6 in the low-dose group and 7.5 in the high-dose group. Nalbuphine and nalorphine evoked full generalization in the low-dose group but less than 40% generalization in the high-dose group. In the high-dose group, nalbuphine and nalorphine antagonized the stimulus and rate-altering effects of fentanyl with apparent pA(2) values of 5.3 and 6.1, respectively, demonstrating lower efficacy mu actions.

CONCLUSIONS

Changes in fentanyl training dose preserved the mu opioid selectivity of stimulus control but altered the intensity of the transduced mu opioid stimulus required for generalization. These differences in intensity of the fentanyl stimulus determined whether low efficacy mu opioids would evoke or antagonize fentanyl generalization.

On creating a workable signing environment: deaf and hearing perspectives

This article studies teams of service providers in education and psychiatric services, in which a substantial number of both deaf and hearing people work together as colleagues. It focuses specifically on the challenges involved in cooperatively creating a signing work environment. Using a methodology that draws on the principles of ethnography, it identifies and explores the meaning constructions associated with signing at work, from deaf and hearing perspectives. Data were collected through interviews in three organizations all in the United Kingdom: two specialist psychiatric units for deaf adults and a school for deaf children. Forty-one informants participated (20 deaf, 21 hearing). Results show that from a deaf perspective, hearing people's use of sign language in their presence at work is closely associated with demonstrating personal respect, value, and confidence, and hearing colleagues' willingness to sign is more significant than their fluency. From a hearing perspective, results demonstrate that sign language use at work is closely associated with change, pressure, and the questioning of professional competence. The challenges involved in improving deaf/hearing relations are perceived from a deaf perspective as largely person-centered, and from a hearing perspective as primarily language-centered. The significance of organizational factors such as imbalances in power and status between deaf and hearing colleagues is explored in relation to the findings.

Can pharmacokinetic monitoring improve clinical use of fluorouracil?

Fluorouracil is used clinically against a variety of solid tumors. It is a prodrug that undergoes a series of intracellular conversions to active cytotoxic species. There is wide interindividual variability in fluorouracil metabolism; furthermore, it has nonlinear kinetics that make it relatively more difficult to predict plasma concentrations after brief infusions compared with prolonged infusions. There is an increasing body of evidence that relates plasma fluorouracil concentrations to toxicity and effectiveness, and consequently there may be a definable mathematical relationship that describes a 'therapeutic window'. Dose nomograms and pharmacokinetic models based on limited sampling strategies have been developed, as have empirical dose escalation schedules based on multivariate analysis of the determinants of toxicity, The utility of these approaches should be tested in properly powered, prospective, randomised trials.

Preliminary clinical study of the distribution of HPMA copolymers bearing doxorubicin and galactosamine

Galactose-targeted delivery of macromolecules and drug conjugates to asialoglycoprotein receptor (ASGPR) positive cells has been widely documented in animals, although targeting in humans has never been demonstrated. In this study we report the pharmacokinetics and imaging determined in the first patient enrolled in a phase I clinical study of the poly[N-(2-hydroxypropyl)methacrylamide] copolymer bearing doxorubicin and galactosamine, known as PK2. Gradient high performance liquid chromatography (HPLC) evaluation of plasma and urine has been combined with 123I-based imaging to show biphasic clearance of the drug from the plasma (half-lives of 78+/-1 and 990+/-15), and approximately 30% delivery of the drug to the hepatic region, as determined by planar whole body imaging at 24 h. This patient has a multifocal hepatoma, and single photon emission computed tomography (SPECT) analysis showed a ratio of tumour tissue to normal liver uptake of approximately 1:3, at 24 h. On the basis of this patient, effective hepatic targeting can be achieved following an intravenous dose of 20 mg/m2 doxorubicin as PK2, however the therapeutic usefulness of this targeted drug has yet to be established.

Contoured elastic-membrane microvalves for microfluidic network integration

A contoured elastic-membrane microvalve is presented that enables integrated microfluidic processing at the network level. This method takes advantage of two ideas to improve performance: flexible elastic membranes (which enable high-performance shutoff and reduced footprint), and three-dimensionally contoured valve geometries (which reduce dead volume, improve fluidic priming, and reduce susceptibility to cavitation at high fluid velocities). We describe the use of laser-induced etching for microfluidic manifold fabrication, discuss the nonlinear load-deflection behavior of elastic membranes that can occur below 30 psi, and present flow-rate data for microvalves under inlet pressures of 0-20 psi with zero applied membrane pressure. Valve-closure data for inlet pressures of 0-30 psi are presented for fully assembled microvalve structures. The microvalve structures under test were capable of turning off flows of > 20 microL/s. These flow rates were shown to be limited by inlet and outlet flow resistances and not by the valve structure itself, so that higher maximum flow rate capabilities should be readily achieved.

Dopamine release in the amygdaloid complex of the rat, studied by brain microdialysis

The dopaminergic projection from the ventral tegmental area to the amygdaloid complex may be modulatory on the processes of associative learning in the latter region. We measured dopamine in four different amygdaloid subfields in the rat, using brain microdialysis. Extracellular levels of dopamine in two sites in the lateral nucleus were not consistently measurable, even after treatment with amphetamine. However, basal dopamine levels were measurable in more medial locations (basolateral and central nuclei), with higher concentrations in the caudal than in the rostral probe placement, and were increased around 3-fold by systemic amphetamine. Similarly, dopamine levels in caudal-medial amygdala were increased by local potassium stimulation and by mild footshock in a calcium-dependent manner, indicating a neurotransmitter origin.

Establishing morphine and U-50,488H as discriminative stimuli in a three-choice assay with pigeons

Pigeons were trained in a 3-choice assay to discriminate among injections of 5.6 mg/kg U-50,488H, 5.6 mg/kg morphine, and vehicle solution. In dose-response tests, subjects rarely responded on the U-50,488H-appropriate key when morphine was administered or on the morphine-appropriate key when they received U-50,488H. A high dose of naltrexone (1.0 mg/kg) completely blocked the morphine cue but failed to block completely the U-50,488H cue. In generalization tests, d-amphetamine primarily engendered saline-appropriate responding. Ethylketazocine produced mixed results, in that moderate doses produced responding on both the morphine- and U-50,488H-appropriate keys, but 3.2 mg/kg engendered primarily morphine-appropriate responding. These results demonstrate the feasibility, but not necessarily the value, of 3-choice discrimination procedures involving mu and kappa agonists and vehicle.

Increased extracellular dopamine in the nucleus accumbens of the rat during associative learning of neutral stimuli

Brain microdialysis was used to study changes in dopamine in the nucleus accumbens and the dorsal striatum during associative learning between two neutral stimuli, flashing light and tone, presented on a paired schedule during stage 1 of a sensory preconditioning paradigm. The tone was subsequently paired with mild footshock using standard aversive conditioning procedures and the formation of a conditioned association between the flashing light and the tone in stage 1 was assessed by measuring the ability of the flashing light to elicit the same conditioned response as the tone when presented at test. The first experiment used behavioural monitoring only, to establish stimulus parameters for subsequent microdialysis experiments. Animals receiving paired presentation of the light and tone in stage 1 showed a conditioned suppression of licking to the light as well as to the tone, indicating that associative learning between the flashing light and the tone had occurred during stage 1, whilst in a separate group of animals given the same stimuli over the same time period but on an explicitly non-paired schedule, the conditioned emotional response was seen to the tone, but not to the light, showing that no association had been formed between the two stimuli during stage 1. In dialysis experiments using the same procedure, we measured a two-fold rise in dopamine in the nucleus accumbens during paired presentation of flashing light and tone, but not during non-paired presentation of the two stimuli. On subsequent test presentation of the two stimuli, we saw increases in accumbal dopamine on presentation of the tone in both groups, reflecting the formation of an association with the footshock in both. However the flashing light elicited an increase in dopamine only in the group which had received paired presentation at stage 1. Thus accumbal dopamine release at test is correlated to the ability of the stimulus to evoke a conditioned response measured behaviourally. Hypotheses of the behavioural function of the mesolimbic dopamine system centre on its role in mediating the effects of biological reinforcers, both rewarding and aversive, conditioned and unconditioned. The present results, showing increases in extracellular dopamine in the nucleus accumbens when an association is formed between two stimuli of which neither is a biological reinforcer nor, prior to formation of the association, affects dopamine levels, suggest a role for accumbal dopamine in the modulation of associative learning in general, not only that involving reinforcement.

In vivo apparent affinity and efficacy estimates for mu opiates in a rat tail-withdrawal assay

Experiments in a rat tail-withdrawal assay tested the hypothesis that the magnitude and pattern of antagonism of mu opiate agonists by the insurmountable mu opioid antagonist clocinnamox are inversely related to agonist efficacy. In addition, these experiments examined whether this antagonism could be quantified to yield apparent affinity and efficacy estimates for the pharmacological characterization of five opiate agonists. Etonitazene, etorphine, morphine, buprenorphine, and GPA 1657 produced dose-dependent increases in tail-withdrawal latency until 100% maximum possible effect (%MPE) was obtained. Morphine required a higher dose of clocinnamox for a 50% reduction in maximal antinociceptive effect than did buprenorphine or GPA 1657. In contrast, no dose of clocinnamox tested decreased the %MPE for etonitazene or etorphine. These data suggest a rank order of relative efficacy of etonitazene > or = etorphine > morphine > or = GPA 1657 > or = buprenorphine. Similarly, numerical analysis of these data yielded the following apparent affinity and efficacy estimates: etonitazene (0.38 mg/kg, 128); etorphine (0.68 mg/kg, 125); morphine (50 mg/kg, 38), GPA 1657 (6.6, 39); and buprenorphine (0.042 mg/kg, 2.2). These data illustrate that in vivo affinity and efficacy estimates for a number of agonists are remarkably similar across different methods of analysis and are useful for drug classification.

Latent inhibition: the nucleus accumbens connection revisited

It has been proposed that dopaminergic transmission in the nucleus accumbens plays a key role in regulating latent inhibition (LI), i.e. the retardation of conditioning that occurs if a to-be-conditioned stimulus is first presented a number of times ('preexposure') without other consequence. New evidence in support of this hypothesis is presented or reviewed here, showing that: (1) intra-accumbens injection of haloperidol at the time of conditioning potentiates LI; (2) destruction of dopaminergic terminals in the nucleus accumbens potentiates LI; (3) intra-accumbens haloperidol reverses the blockade of LI caused by systemic nicotine; (4) intra-accumbens haloperidol reverses the blockade of LI caused by systemic amphetamine; (5) after a single systemic injection of amphetamine (insufficient on its own to block LI), a subsequent intra-accumbens injection of amphetamine at the time of conditioning blocks LI; and (6) intra-accumbens (like systemic) amphetamine administered 15 min before conditioning, without prior systemic amphetamine, failed to block LI. The difference between the effects on LI of one and two administrations of amphetamine, respectively, is interpreted in terms of the need for sensitisation of the response to amphetamine, with the result that the response to the second administration includes a component of impulse-dependent dopamine release in the nucleus accumbens that is otherwise lacking. Data from dialysis experiments suggest that such impulse-dependent accumbens dopamine release also occurs at relatively long delays after a single systemic administration of amphetamine. It was accordingly predicted, and found, that, although LI is intact 15 min after an i.p. injection (confirming previous results), it is abolished at 90 min after the injection of amphetamine. This finding is consistent with the effects of amphetamine in human subjects, in whom LI is blocked 90 min after a single oral administration. Overall, these results strengthen the case that the blockade of LI by elevated, and potentiation of LI by decreased, dopaminergic transmission are both due specifically to actions in the nucleus accumbens; and also add to the similarities between LI studied in animal and human subjects, respectively.

Tolerance and cross-tolerance to morphine-like stimulus effects of mu opioids in rats

The purpose of these experiments was to examine the relationship of agonist relative efficacy to the pattern of tolerance and cross-tolerance to the morphine-like stimulus effects of three opioid agonists. Rats were trained to discriminate 3.2 mg/kg morphine from saline under fixed-ratio 15 schedule of food reinforcement. Morphine, nalbuphine, and fentanyl produced dose-dependent increases in morphine-like stimulus effects and decreases in response rates. Repeated treatment with 20 mg/kg per day morphine increased the ED50 for stimulus control by fentanyl, morphine, or nalbuphine two-, four-, or 40-fold, respectively. Repeated treatment with 64 mg/kg per day nalbuphine increased the ED50 for stimulus control for morphine by two-fold, but lower or higher treatment doses had no significant effect. Treatment with 100 mg/kg per day nalbuphine increased the ED50 for nalbuphine by six-fold. Repeated treatment with 0.22 mg/kg per day fentanyl increased the ED50 for stimulus control by fentanyl or morphine by approximately two-fold. Comparisons among treatment conditions suggested that magnitude of tolerance to morphine-like stimulus effects did not vary as an inverse function of the relative efficacy of the agonist used for repeated treatment. Rather repeated morphine and fentanyl treatments produced comparable tolerance, whereas repeated nalbuphine treatment did not evoke substantial tolerance. Comparisons within treatment conditions, however, suggested that magnitude of tolerance may vary inversely with relative efficacy of the agonist tested for morphine-like stimulus effects. During treatment with morphine or fentanyl, greater tolerance was observed to the morphine-like stimulus effects of the lower efficacy agonist relative to the higher efficacy agonist.

Determining priorities for change in primary care: the value of practice-based needs assessment

BACKGROUND

Primary care is being expected to expand the range of services it provides, and to take on many of the tasks traditionally provided in secondary care. At the same time, general practitioners (GPs) will become increasingly responsible for assessing their patients' health care needs and commissioning care from other providers. This article describes an approach taken in one general practice to meet these difficult challenges.

AIM

To examine whether information on health and health care needs, when used as the basis for a priority setting exercise, can provide a useful first step in planning primary care provision within a practice.

METHOD

A three-stage process of information-gathering from a number of sources, including continuous data recording of patient contacts and a postal survey of all adults registered with the practice, identification of key findings and discussion of associated issues, and priority setting of proposals for practice development using the nominal group technique.

RESULTS

Continuous data recording of patient contacts with GPs and the practice nurse provided data on 4489 GP contacts with 2027 patients, 1000 district nurse contacts with 101 patients, and 361 health visitor contacts with 172 clients. More than 70% of patient records had been computerized, with 600 diagnostic READ codes identified and 11,500 separate entries made. The socioeconomic and health survey questionnaire achieved an 84% response rate. Following the priority-setting exercise, 28 proposed practice developments were identified. These were reduced to a final list of eight.

CONCLUSION

A comprehensive method of practice-based needs assessment, when used as the basis for some form of priority setting, has great potential in helping to plan primary care services within a practice. The success of such initiatives will require a substantial investment of resources in primary care and fundamental changes to the way in which primary care is funded.

Prolonged intraperitoneal infusion of 5-fluorouracil using a novel carrier solution

A novel peritoneal carrier solution, Icodextrin 20 (7.5%), has allowed exploration of prolonged, intraperitoneal (i.p.) infusion of the cytotoxic drug 5-fluorouracil (5-FU). A phase I and pharmacokinetic study was performed to determine the toxicities and maximum tolerated dose of prolonged and continuous intraperitoneal 5-FU in patients with peritoneal carcinomatosis. Seventeen patients were entered into this study. Each patient had a Tenckhoff catheter placed into the peritoneal cavity under general anaesthetic. After initial flushing and gradual increase in exchange volumes with Icodextrin 20, 5-FU was administered daily from Monday to Friday, 50% as a bolus in the exchange bag and 50% in an elastomeric infusor device delivering continuous 5-FU to the peritoneal cavity at 2 ml h-1. Treatment was continued for 12 weeks or until intolerable toxicity developed. Abdominal pain and infective peritonitis proved to be the main dose-limiting toxicities. Initial problems with infective peritonitis were overcome by redesign of the delivery system, and it proved possible to deliver 300 mg m-2 5-FU daily (5 days per week) for 12 weeks. Pharmacokinetic studies showed i.p. steady-state 5-FU concentrations (mean 47 500 ng ml-1) that were > 1000-fold higher than systemic venous levels (mean 30 ng ml-1).

Behavioral contingencies modulate tolerance to discriminative stimulus effects of morphine

Experiments examined how learning processes modulate tolerance to discriminative stimulus effects of morphine. Rats were trained to discriminate saline and 3.2 mg/kg morphine, and the doses of morphine required to mimic the training dose were determined before, during and after repeated treatment with saline or high doses of morphine (10 mg/kg, b.i.d.). In one set of experiments, training was either suspended or continued with saline and the original training dose during a 2-week treatment regimen. When training was suspended, high-dose morphine treatment increased the dose of morphine required for stimulus effects approximately 3-fold. Tolerance persisted 2 days after treatment ended, but disappeared within 7 days. In contrast, continued training with saline and 3.2 mg/kg morphine during high-dose treatment both attenuated development of tolerance and transferred control to lower doses. Transfer of control to lower doses appeared conditional upon recent termination of high-dose treatment, as it disappeared within 7 days. Treatment with saline did not change the doses of morphine required for stimulus effects under either training condition. A final experiment examined whether high-dose treatment could transfer control to higher doses of morphine. The treatment dose of 10 mg/kg morphine itself was used as the training dose during a 2-week treatment regimen. The dose of morphine required for stimulus effects increased 2- to 4-fold during treatment, but quickly returned to control values when treatment ended. These results extend previous findings that conditioning and pharmacodynamic processes jointly regulate development of tolerance to discriminative effects of morphine.

In vivo apparent pA2 analysis in rats treated with either clocinnamox or morphine

Experiments tested the hypothesis that loss of agonist potency or effectiveness following irreversible antagonist or chronic agonist treatment may result from affinity changes at mu opioid receptors. Apparent affinity of naltrexone or nalbuphine for mu opioid receptors was measured in vivo in rats treated with either a single dose of the irreversible antagonist clocinnamox or repeated doses of morphine. Apparent affinity of each antagonist was estimated from its potency as an antagonist of discriminative stimulus or rate-decreasing effects of morphine in rats trained to discriminate 3.2 mg/kg morphine and saline. In control rats, apparent pA2 values for naltrexone and nalbuphine were 7.5-7.6 and 5.3, respectively. In clocinnamox-treated rats, apparent pA2 values for naltrexone were 7.2-7.7, suggesting that clocinnamox treatment did not alter affinity of naltrexone for sites through which morphine exerts behavioral effects. In rats treated repeatedly with morphine, apparent pA2 values for nalbuphine were 5.1-5.3, suggesting that repeated morphine treatment did not alter affinity of nalbuphine for these sites. The observation that neither clocinnamox nor repeated morphine treatment altered in vivo affinity estimates for naltrexone or nalbuphine, respectively, suggests that the reductions in agonist potency produced by these treatments do not result from changes in affinity at mu opioid receptors.

Photolysis of retinol in liposomes and its protection with tocopherol and oxybenzone

In this work the stabilities of retinol in methanolic solutions and liposomal suspensions exposed to UV light were compared using absorbance spectroscopy and the ability of alpha-tocopherol and the sunscreen additive, oxybenzone, to reduce the rate of retinol decomposition assessed. Retinol in methanol decolorized almost completely within a few minutes of exposure to a 6 W 350 nm wavelength lamp. From the concentration dependence of the reaction rates it appears that retinol activated by light can decomposed either directly or after collision with a second retinol molecule. Several reaction products are formed. alpha-Tocopherol solutions were unaffected by 350 nm light but they did darken when irradiated with 250 nm wavelength light. Addition of alpha-tocopherol or removal of oxygen from the retinol in methanol solutions reduced only slightly the rates of retinol photolysis. When dispersed in water within liposomes made of equimolar egg phosphatidylcholine (PC) and cholesterol, up to six-fold increases in the decomposition rate of the retinol were observed. The reaction rate could be reduced but only slightly by increasing the ratio of PC to retinol. A mechanism that explains the concentration dependence of the retinol photolysis is that the reduction in reaction rate on diluting the retinol concentration within a given liposome was due to the prevention of the reaction between one light-activated retinol molecule with another within the same liposome. Incorporation of oxybenzone into the liposomes reduced the reaction rates. The results suggested that most of the protection in this case arises through the oxybenzone closet to the light source absorbing the light, thereby preventing it reaching retinol much further into the sample. Incorporation of alpha-tocopherol into the liposomes could also reduce substantially the photolysis rate of co-entrapped retinol. The mechanism of protection in this case appears to be via the tocopherol quenching activated retinol molecules. The close proximity of the tocopherol to the retinol within a single liposome has shown to be important in this case. Only slight protection of retinol in one liposome by tocopherol in another was observed under the conditions studied. This means that the protection by tocopherol will still be observed if the liposome dispersions are diluted considerably or if only thin samples are exposed to light.

The role of mesolimbic dopaminergic and retrohippocampal afferents to the nucleus accumbens in latent inhibition: implications for schizophrenia

Latent inhibition (LI) consists in a retardation of conditioning seen when the to-be-conditioned stimulus is first presented a number of times without other consequence. Disruption of LI has been proposed as a possible model of the cognitive abnormality that underlies the positive psychotic symptoms of acute schizophrenia. We review here evidence in support of the model, including experiments tending to show that: (1) disruption of LI is characteristic of acute, positively-symptomatic schizophrenia; (2) LI depends upon dopaminergic activity; (3) LI depends specifically upon dopamine release in n. accumbens; (4) LI depends upon the integrity of the hippocampal formation and the retrohippocampal region reciprocally connected to the hippocampal formation; (5) the roles of n. accumbens and the hippocampal system in LI are interconnected.

Effect of amygdaloid kindling on the content and release of amino acids from the amygdaloid complex: in vivo and in vitro studies

The tissue content and the interstitial fluid levels of glutamate, aspartate, GABA, glutamine, glycine, and serine were studied in amygdaloid-kindled rat brain. Interstitial levels were studied in vivo before and during stage 5 full limbic seizures using microdialysis. Slices of amygdala from kindled and sham-operated animals were used to study baseline and KCl-evoked release in vitro. The contents of these amino acids were measured in slices of amygdala, hippocampus, and cerebral cortex from kindled and sham-operated animals. Kindled brains showed two- to threefold higher levels of glutamate, aspartate, and GABA and 12-fold higher levels of glutamine than sham-operated controls. Correlating with this, interstitial fluid levels of glutamate were two- to threefold higher from kindled amygdala than from control both in vivo (microdialysis) and in vitro (superfusion). GABA levels in interstitial fluid from kindled amygdala were reduced by 67% compared with control amygdala.

In vivo apparent pA2 analysis for naltrexone antagonism of discriminative stimulus and analgesic effects of opiate agonists in rats

Six opiate agonists were characterized by in vivo apparent pA2 analysis with respect to their discriminative stimulus, rate-decreasing and analgesic effects, by using the antagonist naltrexone. In drug discrimination experiments, rats were trained to discriminate 3.2 mg/kg of morphine from saline under a fixed-ratio 15 schedule of food reinforcement. In analgesia experiments, rat's tails were immersed into 55 degrees C water and latency for tail withdrawal was measured. Naltrexone (0.01-1.0 mg/kg) antagonized discriminative stimulus effects of all agonists, rate-decreasing effects of etorphine, morphine, fentanyl, buprenorphine and GPA 1657 [(1)-B-2'-hydroxy-2,9-dimethyl-5-phenyl-6,7-benzomorphan] and analgesic effects of etorphine, morphine, buprenorphine and GPA 1657. Analgesic effects of fentanyl and nalbuphine were not tested. Naltrexone apparent pA2 values across the three behavioral measures were etorphine (7.2-7.4 mol/kg), fentanyl (7.3-7.4 mol/kg), morphine (7.5-8.4 mol/kg), GPA 1657 (7.0-7.3 mol/kg), buprenorphine (7.5-7.7 mol/kg) and nalbuphine (7.7 mol/kg). Apparent pA2 values averaged 7.5 mol/kg and slopes of the naltrexone Schild regressions were not different from unity, suggesting that the measured behavioral effects of these agonists are mediated by mu opioid receptors. Nalbuphine also was used as an antagonist in the tail-withdrawal assay. The apparent pA2 values for nalbuphine were etorphine (4.9 mol/kg), morphine (5.9 mol/kg), GPA 1657 (5.7 mol/kg) and buprenorphine (5.5 mol/kg). Slopes of the Schild regressions differed, suggesting that nalbuphine's modest analgesic effects may have prevented proper conditions for an accurate Schild analysis.

Intracerebral microdialysis in the study of physiology and behaviour

In the past, studies relating neurotransmitter function to behaviour have involved looking at the behavioural effects of specific drugs or lesions, or using post-mortem biochemistry in animals killed after undertaking the behaviour. Whilst these methods still play an important part in behavioural pharmacology research, recent advances in the technology of in vivo methods have enabled direct measurements of neurotransmitter function to be made in conscious and unrestrained animals. Among the more important of these methods are voltammetry and brain wash methods (e.g. push-pull perfusion, cortical cup) /116/. However, perhaps the greatest impact on this field of research has been made by microdialysis. This article reviews the contribution made by microdialysis to the understanding of neurotransmitter systems underlying normal physiological function and behaviour, and points to possible future directions for this work.

Discriminative-stimulus effects of the low efficacy mu agonist nalbuphine

The discriminative stimulus effects of nalbuphine were studied in 15 male Sprague-Dawley rats trained to discriminate 3.2 mg/kg of nalbuphine from saline under a fixed-ratio 15 schedule of food delivery. Cumulative doses of nalbuphine produced nalbuphine lever responding at doses of 1.0 to 10 mg/kg and rate-suppressing effects at doses of 3.2 to 32 mg/kg. Experiments to evaluate the contribution of opioid receptor activity suggested that the stimulus effects of nalbuphine were mediated through mu systems, inasmuch as mu agonists (etorphine, fentanyl, morphine, buprenorphine, GPA 1657 and nalorphine) produced nalbuphine lever responding, whereas kappa agonists [EKC and U-50,488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl] benzeneacetamide methanesulfonate hydrate)] and nonopioids (d-pentazocine, d-amphetamine and ketamine) produced saline lever responding. dl-Pentazocine produced nalbuphine lever responding in one-half the rats tested. Both high and low efficacy agonists produced nalbuphine lever responding, but the antagonist naltrexone produced predominantly saline lever responding. Increasing the training dose of nalbuphine by a 0.50 log unit failed to alter the potency of nalbuphine or any other compound to produce nalbuphine lever responding, suggesting that these training doses produce a maximum amount of stimulation at the mu receptor. Naltrexone antagonized the discriminative stimulus but not the rate-decreasing effects of nalbuphine, suggesting that only the discriminative stimulus effects of nalbuphine are mediated by a mu opioid mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Latent inhibition of conditioned dopamine release in rat nucleus accumbens

Classical conditioning both to rewarding and to aversive stimuli is sensitive to drugs which act on the dopaminergic system: amphetamine enhances conditioning and neuroleptics attenuate it. Many lines of evidence point to the nucleus accumbens as being part of an anatomical substrate for reward. We have examined the release of dopamine in the nucleus accumbens during classical aversive conditioning using microdialysis in the unrestrained rat. Two mild footshocks caused a release of dopamine, which was potentiated when each footshock was immediately preceded by a novel tone or light stimulus. Presentation of either of these stimuli after conditioning elicited an increase in dopamine, only to that stimulus which had been conditioned; presentation of either stimulus after footshock alone without conditioning produced no dopamine response. Latent inhibition is a process whereby pre-exposure to a stimulus without consequence impairs learning about that stimulus at subsequent conditioning. This process too is believed to be under the control of dopaminergic systems, particularly in nucleus accumbens. Pre-exposure to the tone stimulus both markedly attenuated the potentiation of dopamine release at conditioning and abolished the conditioned release of dopamine at subsequent tone presentation. This is the first report of direct measurement of potentiated dopamine release during conditioning, and may provide a neurochemical basis for the effects of dopaminergic drugs on conditioning and latent inhibition. The results also support the hypothesis that disrupted latent inhibition in schizophrenia reflects increased mesolimbic dopamine function.

N-methyl-D-aspartate releases gamma-aminobutyric acid from rat striatum in vivo: a microdialysis study using a novel preloading method

In vivo microdialysis was used in conjunction with a novel dual-label preloading method to monitor changes in extracellular levels of gamma-aminobutyric acid (GABA) and glutamate due to N-methyl-D-aspartate (NMDA) infusion in the striatum of conscious, unrestrained rats. [14C]GABA and [3H]glutamate were applied in the dialysis stream for a preloading period of 30 min, after which dialysis perfusion was continued for up to 6 h and dialysate samples were collected for analysis by liquid scintillation spectrometry. NMDA (300 microM in the dialysate) caused significant rises in both 14C and 3H content measured in the dialysates, the majority of which remained associated with the preloaded GABA and glutamate, respectively. The NMDA-evoked release of both GABA and glutamate was blocked by the specific NMDA receptor antagonist 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (CPP), indicating that the response was receptor mediated. The NMDA-stimulated release of glutamate was also totally abolished by concomitant application of the adenosine agonist 2-chloroadenosine or by prior frontal decortication. However, these two treatments caused little change in NMDA-evoked GABA release. These results show that NMDA causes release of GABA from the striatum in vivo by an NMDA receptor-mediated mechanism and that the majority of this release is not secondary to glutamate release from terminals of the corticostriate pathway. In addition, they confirm the results of previous studies investigating the effect of NMDA on endogenous glutamate release.

Increased dopamine release in vivo in nucleus accumbens and caudate nucleus of the rat during drinking: a microdialysis study

Changes in dopamine release and metabolism during drinking in thirsty rats were studied using in vivo microdialysis. Animals were maintained on controlled water (1 h per day) and trained to lick for water in a behavioural box. Microdialysis probes were then inserted into the left nucleus accumbens and right caudate nucleus through previously implanted guide cannulae, and the following day animals were connected for dialysis perfusion, during which they were allowed 1 h free access to water. Dopamine, and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, increased in both nucleus accumbens and caudate nucleus in association with drinking, but the 5-hydroxytryptamine metabolite, 5-hydroxyindoleacetic acid, only increased in the caudate nucleus. There was a direct correlation between the maximum dopamine release in nucleus accumbens and the maximum licking rate per 10-min period, but the maximum increase in dopamine did not occur until after the period of maximum licking. Increases in 3,4-dihydroxyphenylacetic acid and homovanillic acid were further delayed (by 20 and 30 min, respectively). In the caudate, changes in 5-hydroxyindoleacetic acid showed a very similar time-course to those of 3,4-dihydroxyphenylacetic acid. These data show that dopamine systems in both nucleus accumbens and caudate nucleus are activated in relation to drinking in thirsty rats. In addition, they indicate that 5-hydroxytryptamine systems in the caudate nucleus, but not in nucleus accumbens, may also be involved. The support that the results provide for the hypothesized connection between reward and limbic dopamine is discussed.

Discriminative stimulus effects of morphine: effects of training dose on agonist and antagonist effects of mu opioids

Experiments examined how training dose of morphine modulates the agonist and antagonist effects of selected mu opioids. Saline and either 3.2 or 5.6 mg/kg morphine were established as discriminative stimuli for food-reinforced responses in two groups of rats. Etorphine and morphine evoked full morphine lever responding in both groups, but were more potent in subjects trained with 3.2 mg/kg morphine. Methadone, dezocine and dl-pentazocine were equieffective and equipotent in evoking full morphine-like stimulus effects in both groups. Nalbuphine evoked full morphine-like stimulus effects and decreased the dose of morphine required for stimulus effects in rats trained with 3.2 mg/kg morphine. In contrast, nalbuphine antagonized stimulus effects of morphine in rats trained with 5.6 mg/kg morphine, and antagonized rate-altering effects of morphine in both groups, with an apparent pA2 of 5.4 mol/kg. Nalorphine and naltrexone antagonized stimulus and rate-altering effects of morphine in both groups, with an apparent pA2 of 6.0 mol/kg for nalorphine and 7.8 mol/kg for naltrexone. For both compounds, apparent pA2 values did not discriminate between stimulus or rate-altering effects of morphine, or between training conditions. d-Amphetamine and ketamine enhanced the rate-suppressing effects of morphine. However, whereas d-amphetamine prevented stimulus effects of 3.2 mg/kg, but not 5.6 mg/kg morphine, ketamine increased sensitivity to stimulus effects of morphine in rats trained with 3.2 mg/kg morphine without altering sensitivity in rats trained with 5.6 mg/kg. These results demonstrate that training dose of morphine can modulate the likelihood that certain opioids will reproduce or antagonize discriminative stimulus effects of morphine. Furthermore, for nalbuphine and nalorphine, diminished morphine-like stimulus effects in subjects trained with the higher dose of morphine appeared to result from low efficacy mu agonist actions.

Onset of tolerance to discriminative stimulus effects of morphine

Experiments assessed the onset of tolerance to discriminative stimulus effects of morphine in rats treated repeatedly with twice daily doses of 10 mg/kg morphine. Saline and 3.2 mg/kg morphine were established as discriminative stimuli for food-reinforced fixed-ratio performances in several groups of rats, and initial ED50 values were determined for stimulus and rate-altering effects of morphine. To assess onset of tolerance, training was halted and 10 mg/kg doses of morphine were administered repeatedly at 12-h intervals. In separate experiments, ED50 values were redetermined after various treatment periods. One treatment with 10 mg/kg morphine did not alter the ED50 for stimulus effects of morphine, whereas treatment for one or three days increased the ED50 by approximately 2-fold. Comparisons with published data showed even greater tolerance when treatment lasted one or two weeks. Tolerance to stimulus effects of morphine generally was accompanied by tolerance to its rate-decreasing effects. Repeated treatment with morphine also produced cross-tolerance to morphine-like stimulus effects of methadone and buprenorphine. As with morphine itself, greater tolerance developed with longer treatment. These results suggest that tolerance to discriminative stimulus effects of morphine develops gradually, with magnitude of tolerance increasing as a function of treatment duration.

Tolerance to morphine-like stimulus effects of mu opioid agonists

Experiments assessed the ability of repeated treatment with morphine to produce tolerance to morphine-like discriminative stimulus effects of buprenorphine, etorphine, methadone, morphine, and nalbuphine. Before treatment, each compound evoked full morphine-like stimulus effects in rats trained to discriminate saline and 3.2 mg/kg morphine. During treatment, training was halted and a dose of 10 mg/kg morphine administered every 12 h for 14-18 days. Repeated treatment with morphine increased the ED50 for stimulus control by etorphine, methadone or buprenorphine 2- to 4-fold and that for morphine 4.5-fold. Repeated treatment produced an insurmountable tolerance to the morphine-like stimulus effects of nalbuphine, so that a dose 150-fold higher than the initial ED50 evoked only 40% generalization. Treatment with a lower dose of morphine (10 mg/kg every 24 h) produced a short-lived surmountable tolerance to stimulus effects of nalbuphine. For etorphine, methadone and morphine, tolerance to morphine-like stimulus effects was accompanied by tolerance to rate suppressing effects. After treatment ended, the ED50 for stimulus control by etorphine, methadone or nalbuphine returned to initial values within 3 days; that for morphine, within 5 days; that for buprenorphine, within 10 days. These results demonstrate that repeated treatment with morphine produces cross-tolerance to compounds that exert morphine-like stimulus effects. Additionally, the results suggest that differences among these compounds in agonist efficacy may be revealed as differences in the degree of tolerance produced by morphine treatment.