J phys chem

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Smokers j phys chem instructed not to smoke for 12 h and avoid taking nonprescription medications for 24 h before the PET study. To prevent j phys chem withdrawal, caffeine users were instructed to drink only one-half cup of a caffeine-containing beverage no less than 2 h before the study.

Before each test session (20 min), subjects received two pieces of polacrilex gum to chew for 15 min at a rate of one j phys chem every 3 j phys chem. Each piece of gum contained either nicotine (2 mg Nicorette) or taste-matched placebo.

Peak plasma concentrations of nicotine using this procedure are similar to j phys chem achieved by smoking a typical American cigarette (11). Expired-air CO levels were recorded on arrival at the PET center. Of the 32 items of the STESS, four symptoms were selected on the basis of previous reports of side effects from nicotine gum: difficulty paying attention, stomachaches, dizziness, and shakiness.

Blood samples were collected before and 30 min after the 15-min period of chewing the gum for assays of plasma cotinine and nicotine concentration. Assays were performed by liquid extraction and gas chromatography (Labstat, Ontario, Canada). The 2BT required subjects to keep in memory a series of three letters that were being updated constantly.

The letters were 2. They appeared for 500 msec at intervals of 1,000 msec. This way, the number j phys chem finger movements remained constant, independent of performance. The button was always pressed with the right hand.

Scans were acquired under three conditions: resting (eyes fixated on a dot at the center of the screen), active task (2BT), and control task. The resting condition was included for use in a future protocol that would measure absolute rCBF but was not used in the present data analysis. In each J phys chem session, six 1-min scans were acquired. The order of conditions was: rest, 2BT, control, 2BT, control, rest or rest, control, 2BT, control, 2BT, and rest.

This order was counterbalanced across subjects but kept constant for each subject. Each task began 30 sec before an i. The determination of rCBF by PET involves the administration of a freely diffusible positron-emitting radiotracer such as O-15-labeled water. Because of the j phys chem half-life of 15O (2. H215O is administered by i. The relationship between radioactivity counts in brain and rCBF is almost linear, and the PET j phys chem closely reflects perfusion differences between brain regions, providing a measure of relative rCBF.

This instrument produces images of 15 contiguous transaxial slices 6. The within-plane resolution (full width at half maximum) is 6. A thermoplastic mask, custom-made for each subject, was used to minimize head movement. Radioactive counts were recorded for 1 min after brain activity reached a threshold value of 8,000 counts. Scan data were reconstructed with corrections for attenuation (measured with transmission j phys chem. Because arterial blood was not sampled, absolute rates of rCBF were not j phys chem. Demographic and subjective variables were compared between smokers and ex-smokers by using Student's t test.

Plasma nicotine and cotinine concentrations at baseline and 30 min after gum administration were analyzed by two ANOVAs with group and time as between-subjects and within-subjects factors, respectively. For the j phys chem, three different sets of performance scores were analyzed: accuracy (percentage of correct j phys chem and percentage of incorrect responses), reaction time (RT to all stimuli and RT to correct responses), and RT variability (RT variability to all stimuli and RT variability to correct j phys chem. The standard deviation of the mean RT for each subject was used as a measure of variability.

This measure tracks sustained attention and reflects consistency in psychomotor speed. Multivariate ANOVA was used to estimate the effect split personality group and drug on cognitive performance.

The mean of the counts of all voxels common to all registered j phys chem of an individual (i. By using statistical parametric mapping (18), the registered data were resized and reshaped to a stereotaxic atlas (19) to facilitate interscan analysis.

Data were then smoothed with a three-dimensional Gaussian filter (10 mm, 10 mm, and 10 mm in the x, y, euflexxa z planes) to reduce high-frequency noise and the effects of individual differences in gyral anatomy. Finally, a voxel-by-voxel analysis was performed for all planes common to j phys chem subjects (from 28 mm below to 54 mm above the intercommissural line).

Activations were analyzed by testing the rCBF differences between the 2BT and the control task for each drug condition in each group. For each planned analysis, the value of t for each voxel was calculated and transformed to a normal standard distribution.

Prefrontal, cingulate, and parietal areas were predicted to be activated by the glyburide (20, 21). Correlation analyses were performed between activated pixels and clinical variables (performance scores, anxiety and nicotine-withdrawal ratings, and plasma concentration of nicotine and cotinine).

For j phys chem subject, four mean images of the two repeated scans of each condition (placebo-control task, placebo 2BT, nicotine-control task, and nicotine 2BT) were computed by using the statistical parametric mapping adjusted-mean module. Finally, maps j phys chem Pearson coefficient correlation (r) and their corresponding z maps were computed for each j phys chem in each drug condition by using MEDx correlation-analysis module.

Maxima of peak correlations were collected only in the regions that were activated by the 2BT (prefrontal, cingulate, and parietal cortices). Because of the relatively small sample sizes and the absence of corrections for the number of voxels tested, these correlations are exploratory and must be interpreted with caution.

The 11 smokers (age 31. Smokers reported smoking, on average, 33. Ex-smokers had smoked previously an average of 3. Plasma concentrations of nicotine and cotinine were in the expected range for 12-h nicotine-abstinent j phys chem (nicotine 4.

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