Malaria in a nonimmune population after extended chloroquine or primaquine prophylaxis

Extended chemoprophylaxis against endemic malaria raises concern with regard to susceptibility after ceasing use of the drug. In this study, we measured attack rates of malaria among adult men for 28 weeks after they ended one year of prophylaxis using either weekly chloroquine (5 mg base/kg, n = 20), daily primaquine (0.5 mg base/kg, n = 30), or a placebo of primaquine (n = 41). The 28-week incidence densities, times to parasitemia, parasite densities, and symptoms of primary post-prophylaxis infections were not significantly different among the former primaquine, chloroquine, and placebo groups. However, the incidence of Plasmodium falciparum infection in the post-chloroquine group was significantly greater than in the post-primaquine group during the first (P = 0.03) and second (P = 0.02) months post-prophylaxis. Six of 10 primary P. falciparum and three of 10 P. vivax infections occurred in the former chloroquine group within one month after ending prophylaxis and the mean time to infection was 30-35 days. In contrast, only one P. falciparum and no P. vivax infections occurred during the first month after ending primaquine prophylaxis. The mean time to first parasitemia by either species of malaria parasite in this group was 72-77 days. There was no indication that daily use of primaquine for one year placed subjects at greater risk of malaria infection or to more severe clinical symptoms of malaria than subjects who had taken placebo or chloroquine, despite the potential for some degree of immunity to have been acquired in these latter two groups during the year-long prophylaxis period. The results do suggest that chloroquine suppressed P.falciparum infections until drug levels decreased, and that primaquine had effectively prevented the establishment of liver-stage parasites.

A systems approach to asthma care

This two-year asthma intervention focuses on provider education emphasizing early diagnosis of asthma, early use of oral steroids, proper use of inhalation devices, objective monitoring of patient status, and use of daily preventive treatment. Patient education is an integral part of treatment. This approach supports the primary care physician as the provider and coordinator of care by supplying monitoring and treatment devices, books, diaries, home care services, and allergy consultation. It also manifests a systems approach to asthma care in its reliance on a nurse case manager who oversees patient and family support network.

Three-dimensional performance of a small-diameter positron emission tomograph

Recently, the initial 2D physical characterization of a small-diameter positron emission tomograph, designed specifically for scanning of small laboratory animals, was reported. The physical characteristics of the tomograph operating in 3D mode have now been measured and compared to those obtained in 2D mode. In 3D, the transaxial resolution was measured as 2.4 +/- 0.1 mm full width at half maximum (FWHM) and 6.7 +/- 1.1 mm full width at tenth maximum (FWTM) at the centre of the transaxial field of view (FOV). These values degraded to 4.5 +/- 0.3 mm (tangential) and 6.6 +/- 0.3 mm (radial) FWHM and 10.6 +/- 1.6 mm (tangential) and 11.2 +/- 2.1 mm (radial) FWTM, respectively, at a distance of 40 mm from the centre of the transaxial FOV. The axial resolution was measured as 4.6 +/- 0.1 mm FWHM and 15.0 +/- 0.5 mm FWTM at the centre of the transaxial FOV, increasing to 5.0 +/- 0.1 mm FWHM and 18.8 +/- 3.7 mm FWTM at a radial distance of 40 mm from the centre of the transaxial FOV. These resolutions are similar to those obtained for the tomograph operating in 2D mode. The sensitivity of the tomograph operating in 3D was 4.31 x 10(4) counts s-1 MBq-1 at 250-850 keV compared to 0.995 x 10(4) counts s-1 MBQ-1 in 2D at the same energy thresholds. In this energy window the noise equivalent count rate peaked at 4.1 x 10(4) counts s-1, compared to 1.03 x 10(4) counts s-1 in 2D. A scatter fraction of 30.2% at 250-850 keV was measured for a 18F line source centered in a 60 mm diameter water filled phantom in 3D, compared to 31.0% in 2D for the same scanning geometry and energy thresholds. A comparison was made between 2D and 3D kinetic analyses for a group of five anaesthetized rats scanned using [11C] SCH 23390, a marker of dopamine D1 receptors. The integrity of the results was maintained between 2D and 3D data sets, though in 3D there was a significant reduction in the standard error of the fitted parameter. The results demonstrate that, with regard to sensitivity, there are significant gains in the physical performance of this tomograph when operating in 3D compared to 2D mode and that the quantification of PET studies of small animals using the 3D data reflects this.

One-week therapy with twice-daily butenafine 1% cream versus vehicle in the treatment of tinea pedis: a multicenter, double-blind trial

BACKGROUND

Butenafine hydrochloride, a benzylamine derivative with potent antifungal activity, has been used in Japan to treat superficial fungal diseases.

OBJECTIVE

We evaluated the safety and efficacy of twice-daily butenafine versus its vehicle in the treatment of interdigital tinea pedis in a multicenter, randomized, double-blind, parallel-group trial.

METHODS

A total of 402 patients with interdigital tinea pedis and a positive potassium hydroxide examination were enrolled. Of the 271 patients who had culture-confirmed tinea pedis and were assessed for efficacy, 132 applied butenafine and 139 applied vehicle twice daily for 1 week. Patients were assessed for mycologic cure, effective treatment, overall cure, and mycologic/clinical cure.

RESULTS

The rates of all four end points were significantly higher with butenafine than with vehicle 5 weeks after treatment ended. Rates of mycologic cure and effective treatment with butenafine were significantly higher than with vehicle at cessation of treatment. Adverse events to treatment occurred in less than 1% of patients treated with butenafine and 2% of patients who applied vehicle.

CONCLUSION

Butenafine applied twice daily for 1 week is highly effective in treating interdigital tinea pedis.

Analysis of dynamic radioligand displacement or "activation" studies

We present a simple way of assessing dynamic or time-dependent changes in displacement during single-subject radioligand positron emission tomography (PET) activation studies. The approach is designed to facilitate dynamic activation studies using selective radioligands. These studies are, in principle, capable of characterising functional neurochemistry by analogy with the study of functional neuroanatomy using rCBF activation studies. The proposed approach combines time-dependent compartmental models of tracer kinetics and the general linear model used in statistical parametric mapping. This provides for a comprehensive, voxel-based and data-led assessment of regionally specific effects. The statistical model proposed in this paper is predicated on a single-compartment model extended to allow for time-dependent changes in kinetics. We have addressed the sensitivity and specificity of the analysis, as it would be used operationally, by applying the analysis to 11C-Flumazenil dynamic displacement studies. The activation used in this demonstration study was a pharmacological (i.v. midazolam) challenge, 30 min after administration of the tracer. We were able to demonstrate, and make statistical inferences about, regional increases in k2 (or decreases in the volume of distribution) in prefrontal and other cortical areas.

The ecology of echo

Echo is a generic ecosystem model in which evolving agents are situated in a resource-limited environment. The Echo model is described, and the behavior of Echo is evaluated on two well-studied measures of ecological diversity: relative species abundance and the species-area scaling relation. In simulation experiments, these measures are used to compare the behavior of Echo with that of a neutral model, in which selection on agent genotypes is random. These simulations show that the evolutionary component of Echo makes a significant contribution to its behavior and that Echo shows good qualitative agreement with naturally occurring species abundance distributions and species-area scaling relations.

ECAT ART - a continuously rotating PET camera: performance characteristics, initial clinical studies, and installation considerations in a nuclear medicine department

Advances in fully three-dimensional (3D) image reconstruction techniques have permitted the development of a commercial, rotating, partial ring, fully 3D positron emission tomographic (PET) scanner, the ECAT ART. The system has less than one-half the number of bismuth germanate detectors compared with a full ring scanner with the equivalent field of view, resulting in reduced capital cost. The performance characteristics, implications for installation in a nuclear medicine department, and clinical utility of the scanner are presented in this report. The sensitivity (20 cm diameterx20 cm long cylindrical phantom, no scatter correction) is 11400 cps.kBq-1.ml-1. This compares with 5800 and 40500 cps.kBq-1.ml-1 in 2D and 3D respectively for the equivalent full ring scanner (ECAT EXACT). With an energy window of 350-650 keV the maximum noise equivalent count (NEC) rate was 27 kcps at a radioactivity concentration of approximately 15 kBq.ml-1 in the cylinder. Spatial resolution is approximately 6 mm full width at half maximum on axis degrading to just under 8 mm at a distance of 20 cm off axis. Installation and use within the nuclear medicine department does not appreciably increase background levels of radiation on gamma cameras in adjacent rooms and the dose rate to an operator in the same room is 2 microSv. h-1 for a typical fluorine-18 fluorodeoxyglucose (18F-FDG) study with an initial injected activity of 370 MBq. The scanner has been used for clinical imaging with18F-FDG for neurological and oncological applications. Its novel use for imaging iron-52 transferrin for localising erythropoietic activity demonstrates its sensitivity and resolution advantages over a conventional dual-headed gamma camera. The ECAT ART provides a viable alternative to conventional full ring PET scanners without compromising the performance required for clinical PET imaging.

Mutual interaction between remacemide hydrochloride and phenytoin

A randomised, double-blind, placebo-controlled crossover study of add-on remacemide hydrochloride was carried out in epilepsy patients being treated with phenytoin (PHT) monotherapy. Eleven patients were recruited, ten of whom completed the study. Plasma concentration profiles of PHT, remacemide, and its active desglycinyl metabolite (ARL12495XX) were determined following single and multiple dosing with remacemide hydrochloride. Following 14 days' treatment with remacemide hydrochloride 300 mg twice daily, the mean AUC of PHT was increased by 11.5% (P = 0.33), Cmax by 13.7% (P = 0.32) and Cmin by 22.2% (P = 0.12) over placebo. There was an increase in trough concentrations of PHT averaging 20% during active treatment compared with placebo (P = 0.01). No symptoms of PHT toxicity were reported by any patient. There was no evidence of autoinduction of remacemide metabolism. However, average concentrations of remacemide and its active metabolite in PHT-treated patients were around 40 and 30% lower, respectively than in healthy volunteers previously receiving the same dose of remacemide hydrochloride. Thus, remacemide hydrochloride has a small inhibitory effect on PHT metabolism, which itself induces that of remacemide and its active metabolite. This mutual interaction is predictable and modest and should not present a barrier to their clinical use in combination.

Correction for scatter in 3D brain PET using a dual energy window method

A method for scatter correction using dual energy window acquisition has been developed and implemented on data collected with a brain-PET tomograph operated in the septa retracted, 3D mode. Coincidence events are assigned to (i) an upper energy window where both photons deposit energy between 380 keV and 850 keV or (ii) a lower energy window where one or both photons deposit within 200 keV and 380 keV. Scaling parameters are derived from measurements of the ratios of counts from line sources due to scattered and unscattered events in the two energy windows in head-sized phantoms. A scaled subtraction of the two energy windows produces a distribution of scatter which is smoothed prior to subtraction from the upper energy window. In phantoms, the correction was found to restore the uniformity, contrast and linearity of activity concentration. Relative activity concentrations were restored to within 7% of their true values in a multicompartment phantom. The method was found to provide accurate correction for scattered events arising from activity outside the direct detector field of view. In a three-compartment phantom containing water, 18F and 11C scanned in dynamic, multiframe mode, the half-lives of the two isotopes were restored to within 2% of their true value.

Accessory human cytomegalovirus glycoprotein US9 in the unique short component of the viral genome promotes cell-to-cell transmission of virus in polarized epithelial cells

Human cytomegalovirus (CMV) encodes accessory glycoproteins that are dispensable for virus growth in nonpolarized cells in culture. We report that CMV deletion mutants lacking the gene for accessory glycoprotein US9 in the unique short component of the viral genome are impaired in plaque formation in polarized human retinal pigment epithelial (ARPE-19) cells. Comparison of CMV deletion mutants in US9 with herpes simplex virus type 1 deletion mutants lacking glycoproteins gE and gI showed that both of these mutants are impaired in altering junctional complexes and increasing paracellular permeability in polarized ARPE-19 cells cultured on permeable filter supports. Results of functional studies indicate that CMV US9 and homologs of gE have analogous roles in promoting virus spread across lateral membranes of polarized epithelial cells.

Impact of complementary parathyroid scintigraphy and ultrasonography on the surgical management of hyperparathyroidism

BACKGROUND

An ongoing debate exists regarding the relative merits of full versus limited neck exploration in the surgical management of parathyroid adenomata. The aim of this study was to assess the impact of localization studies on the subsequent surgical management of hyperparathyroidism.

METHODS

The accuracy of complementary ultrasonography and 201TI/99mTc parathyroid subtraction scintigraphy in hyperparathyroidism was evaluated retrospectively during a 10-year period in patients referred for localization studies. Surgical and pathologic confirmation of the diagnosis was possible in 121 patients, and these data formed the basis of this study. Operative procedure, times, outcome, and complications were recorded.

RESULTS

The sensitivity, specificity, and accuracy for combined scintigraphy and ultrasonography were 86%, 98%, and 96%, respectively. Limited neck exploration was performed in 61 of 121 patients, and 60 patients underwent full neck exploration. In primary hyperparathyroidism 59 of 105 patients underwent limited and 46 underwent full neck exploration with average operative times of 70 and 109 minutes, respectively. (p < 0.0001). Complications developed in five patients who underwent full neck exploration.

CONCLUSIONS

Confident localization of parathyroid adenomata facilitated successful limited neck exploration in most of the patients, questioning the need for full neck exploration in all patients with primary hyperparathyroidism.

In vivo quantification of human pulmonary beta-adrenoceptors: effect of beta-agonist therapy

In human subjects, chronic beta2-agonist dosing reduces mononuclear leukocyte (MNL) beta-adrenoceptor numbers. The aim of this study was to investigate whether this downregulation also occurs in the lung. Seven healthy male subjects were treated for 2 wk with oral (up to 16 mg/d) and inhaled (up to 1.6 mg/d) albuterol (salbutamol in Europe). Pulmonary maximal beta-adrenoceptor binding capacity (Bmax) was determined in vivo using positron emission tomography (PET) and the beta-receptor antagonist ligand, 11C-labeled CGP-12177, before and after the 2-wk chronic dosing. MNL Bmax was also measured, using a radioligand binding assay and 3H-labeled CGP-12177. Bronchodilator responses to the beta2-agonist were determined after each PET scan by measuring the change in specific airway conductance (SGaw) after increasing doses of inhaled albuterol. Pulmonary and MNL Bmax fell by 22% +/- 14% (p < 0.05) and 42% +/- 19% (p < 0.05) respectively. The changes in pulmonary and MNL Bmax were correlated (r = 0.9, p < 0.05). There was also a reduction in the bronchodilator response to inhaled albuterol. In a further six subjects, pulmonary and MNL Bmax did not change during an acute infusion of albuterol (2 to 4 microg/kg/h). The reduction in pulmonary beta-adrenoceptor numbers after chronic albuterol dosing may be predictable from the changes observed in circulating MNL cells.

Mutual interaction between remacemide hydrochloride and carbamazepine: two drugs with active metabolites

PURPOSE

We wished to determine mutual interaction of two drugs with active metabolism: remacemide, hydrochloride and carbamazepine (CBZ).

METHODS

A randomized, double-blind, placebo-controlled cross-over study of add-on remacemide hydrochloride was performed in 10 of 14 recruited patients being treated with CBZ monotherapy. Forty-eight-hour concentration profiles of CBZ, its active epoxide metabolite (CBZ-E), remacemide, and its desglycinyl metabolite (ARL12495XX) were assayed after single and multiple dosing.

RESULTS

After patients were treated with 300 mg remacemide hydrochloride twice daily for 14 days, the mean area under the concentration-time curve (AUC) of CBZ was increased by 22% (p = 0.12), Cmax was increased by 27% (p = 0.07), and Cmin was increased by 22% (p = 0.29). Trough concentrations of CBZ were higher (p = 0.0037) during active treatment as compared with placebo treatment. CBZ-E levels were unaffected. No symptoms of CBZ toxicity were reported. There was no evidence of autoinduction of remacemide metabolism. However, in CBZ-treated patients, the AUC of remacemide and its active metabolite was 60 and 30%, respectively, of values observed in healthy volunteers treated previously with the same dose.

CONCLUSIONS

Remacemide hydrochloride inhibits CBZ metabolism, which itself induces that of remacemide hydrochloride and its active metabolite. This mutual interaction between remacemide hydrochloride and CBZ is predictable and modest and should not present a barrier to their clinical use in combination.

Comparison of an antifungal agent used alone with an antifungal used with a topical steroid in inflammatory tinea pedis

The efficacy and safety of monotherapy with oxiconazole nitrate cream, 1 percent, a topical broadspectrum antifungal agent, were compared with those of combination therapy with oxiconazole nitrate cream, 1 percent, and fluticasone propionate cream, 0.05 percent, in a multicenter, randomized, double-blind, vehicle-controlled, parallel-group study of patients with inflammatory tinea pedis. Both combination therapy and monotherapy were associated with significantly greater proportions of mycologic and clinical cure, and a better global response than vehicle. An unexpected finding in this study was that more than 70 percent of patients with interdigital tinea pedis also had plantar or plantar plus vesiculobullous infection.

Guided bone regeneration to facilitate implant and prosthodontic therapy: three case reports

In some patients, lack of bone at a desired fixture site has resulted, by necessity, in the placement of endosseous implants in less than favorable locations. The principles of guided bone regeneration can be used to restore lost alveolar bone and permit the placement of implants at more ideal locations, or to provide a more favorable ridge form to support a removable prosthesis. The advantages of a two-stage technique involving bone grafting followed by a healing period prior to implant placement are discussed. Different methods of membrane tenting to provide space for bone growth are illustrated by three case reports. Evidence of bone augmentation is provided by computed tomography.

In vitro lymphocyte proliferative responses and gamma-interferon production as measures of cell-mediated immunity of cattle exposed to Pasteurella haemolytica

Cell-mediated immune mechanisms may play a role in the pathogenesis and prevention of pneumonia in cattle caused by Pasteurella haemolytica serotype A1. To determine the circumstances required to stimulate and identify cell-mediated immune responses, calves were vaccinated with a commercial P. haemolytica bacterin or a live commercial P. haemolytica vaccine, or were infected intratracheally with virulent P. haemolytica. All calves were challenge-exposed intratracheally with P. haemolytica 31 d after vaccination or prior infection. Peripheral blood mononuclear cells and mediastinal and superficial cervical lymph node cells were stimulated with antigens prepared from P. haemolytica to evaluate in vitro proliferative responses and gamma-interferon production as measures of cell-mediated immunity. Strong proliferative responses and gamma-interferon production were detected in lymph node cells from calves vaccinated with the live vaccine and from infected calves, especially in response to stimulation with an outer membrane protein preparation from P. haemolytica. Greater proliferative responses and gamma-interferon production were associated with the lymph node nearer the site of bacterin administration (superficial cervical lymph node) or the site of infection (mediastinal lymph node), whereas greater proliferative responses and gamma-interferon production were associated with the more distant lymph node (mediastinal lymph node) in calves vaccinated with the live vaccine. Neither proliferative responses nor gamma-interferon production were detected in peripheral blood mononuclear cells from calves that were vaccinated for or infected with P. haemolytica. Antileukotoxin antibody titers were determined by a serum neutralization assay, and protection against pneumonic lesions was more closely correlated with antileukotoxin antibody responses than with lymphocyte proliferation or gamma-interferon responses.

Noninvasive quantification of regional myocardial metabolic rate for oxygen by use of 15O2 inhalation and positron emission tomography. Theory, error analysis, and application in humans

BACKGROUND

A method has been developed to measure the regional myocardial metabolic rate of oxygen consumption (rMMRO2) and oxygen extraction fraction (rOEF) quantitatively and noninvasively in humans by use of 15O2 inhalation and positron emission tomography. This article describes the theory, an error analysis of the technique, and procedures of the method used in a human feasibility study.

METHODS AND RESULTS

Inhaled 15O2 is transported to peripheral tissues, where it is converted to 15O-labeled water of metabolism, which exchanges with the relatively large extravascular tissue space. Quantification of this buildup of radioactivity allows the calculation of rMMRO2 and rOEF. However, a correction for the spillover of the pulmonary gas radioactivity signal into myocardial regions is required and has been made by use of a gas volume distribution estimated from the transmission scan. This was validated by comparative measurements using the inert gas [11C]CH4 in four greyhounds. Spillover of the cardiac chamber radioactivity has been corrected for with an inhaled [13O]CO (blood volume) scan. The underestimation of myocardial radioactivity due to wall motion and thickness has been corrected for by use of values of tissue fraction obtained from the flow measurement [15OKCO2 scan). Values of rOEF were similar (within 4%) whether obtained from gas volume measurements determined from the transmission or [11C]CH4 scan data. 15O2 scan information from six healthy volunteers showed a clear distribution of myocardial radioactivity after the vascular and pulmonary gas 15O background was subtracted. Subsequent compartmental analysis resulted in values for rOEF and rMMRO2 of 0.60 +/- 0.11 and 0.10 +/- 0.03 mL.min-1.g-1 in the human myocardium at rest.

CONCLUSIONS

The results of this study are in good agreement with established values. This is the first known approach to allow the direct quantitative determination of rOEF and oxygen metabolism to be made noninvasively on a regional basis.

Noninvasive quantification of regional myocardial metabolic rate of oxygen by 15O2 inhalation and positron emission tomography. Experimental validation

BACKGROUND

The purpose of this study was to validate a novel method for noninvasive quantification of regional myocardial oxygen consumption (MMRO2, mL.min-1 x 100 g-1) and oxygen extraction fraction (OEF) by use of positron emission tomography (PET) and inhalation of 15O-labeled molecular oxygen gas (15O2).

METHODS AND RESULTS

Twenty-four measurements were performed in eight closed-chest anesthetized greyhounds at baseline and during infusions of adenosine (100 to 200 micrograms.kg-1.min-1), isoproterenol (1 to 10 microgram/min), and propranolol (5 mg botus +0.2 to 1 mg/min) with morphine (5 mg slow infusion +0.2 to 0.5 mg/ min) to obtain a wide range of oxidative metabolism. The PET imaging protocol consisted of 15O2 emission (OEF and MMRO2), transmission, [15O]CO emission (blood pool), and [15O]CO2 emission (myocardial blood flow: MBF(pets) mL.min-1.g-1) scans. OEF was calculated from the PET data (OEFpet) by three different analytical techniques: steady-state, 5-minute, and 8-minute autoradiographic analyses. Reference measurements of MBF (MBFref) and OEF (OEFref) were obtained during 15O2 inhalation with radiolabeled microspheres and paired arterial and coronary sinus blood sampling, respectively. MMRO2 was calculated from the PET (MMRO2pet) and the reference (MMRO2ref) data as follows: MMRO2 = OEF x MBF x (O2 content of arterial blood). OEF measured by the steady-state PET method was well correlated with the reference data over the range 0.16 to 0.73 (OEFpet = 1.03 OEFref -0.01, r = .97), as was MMRO2 over the range 2.4 to 27.5 mL.min-1 x 100 g-1 (MMRO2pet = 0.98 MMRO2ref +0.91, r = .94). OEFpet calculated by use of the 5-minute and 8-minute autoradiographic analyses were equally well correlated with the reference measurements (r = .95 and r = .97, respectively). There were no significant differences between values of MMRO2pet calculated by use of the steady-state, 5-minute, and 8-minute autoradiographic analyses (P = NS by ANOVA). Regional values of MBFpet, OEFpet, and MMRO2pet were homogeneously distributed and similar to the whole-heart values both at baseline and during the various pharmacological interventions.

CONCLUSIONS

Accurate quantification of OEF and MMRO2 is feasible with 15O2 inhalation and PET imaging using both the steady-state and autoradiographic analytical approaches. These studies suggest the applicability of this method for quantitative assessments of regional cardiac oxidative metabolism in clinical studies.

In vivo quantification of human pulmonary beta-adrenoceptor density using PET: comparison with in vitro radioligand binding

A new method has recently been developed to quantify pulmonary beta-adrenergic receptors in vivo using PET. This study used in vitro radioligand binding assay (RLBA) as the gold standard to validate in vivo PET measurements.

METHODS

Five male patients with lung cancer aged 57 yr (range 42-67 yr) were studied. PET scanning was performed the day before thoracotomy to determine regional pulmonary beta-receptor density. RLBA was carried out on cell membranes prepared from specimens of lung tissue obtained at the thoracotomy to measure beta-receptor density in vitro. In both cases, the hydrophilic nonselective beta-antagonist radioligand (S)-CGP-12177 was used. For PET studies, this was labeled with 11C and for RLBA with 3H.

RESULTS

In the PET study, beta-receptor density (Bmax) was 9.43 +/- 1.32 pmole g-1 tissue. In the RLBA study, Bmax was 99.0 +/- 15.5 fmole mg-1 protein, equivalent to 9.90 +/- 1.55 pmole mg-1 tissue. These values are in good agreement with previously reported in vitro measurements on human lung membranes using 125I-iodocyanopindolol. A correlation was found between beta-adrenergic density obtained using PET and beta-adrenergic density obtained using RLBA (r = 0.92; p < 0.05).

CONCLUSION

The results support the use of PET as a new method for imaging and the way for studies of physiological and pharmacological regulation of beta-adrenergic receptors through noninvasive serial measurements.

The potential of high-resolution positron emission tomography to monitor striatal dopaminergic function in rat models of disease

The use of a recently commissioned small-diameter, high-resolution positron emission tomography (PET) to obtain a measure of specific binding of 3 carbon-11 labelled ligands in rat striatum is described. Using cerebellum as a reference tissue, compartmental modelling was used to obtain individual estimates of striatal binding potential (defined as the ratio of rate constants to and from the specifically bound compartment) for [11C]raclopride (D2 receptors), [11C]SCH 23390 (D1 receptors) and [11C]RTI-121 (dopamine transporter). The coefficients of variation in control, anaesthetized rats were of the order of 10%. Using two models of human disease, namely striatal injection of ibotenic acid to produce postsynaptic cell loss as in Huntington's disease, and 6-hydroxydopamine injection into substantia nigra pars compacta to mimic dopaminergic terminal loss in Parkinson's disease, marked reductions in binding potential were observed for the corresponding pre- or postsynaptic markers. When the regions of interest are so small as to be of the order of the spatial resolution of the system, factor such as spill over and partial volume negate absolute quantification of tissue radioactivity. Nevertheless, the use of PET to monitor relative changes in dopaminergic integrity should be considered as a viable complement to established in vivo microdialysis and post mortem techniques.