Quantification of perfusion fMRI using a numerical model of arterial spin labeling that accounts for dynamic transit time effects.

A new approach to modeling the signal observed in arterial spin labeling (ASL) experiments during changing perfusion conditions is presented in this article. The new model uses numerical methods to extend first-order kinetic principles to include the changes in arrival time of the arterial tag that occur during neuronal activation. Estimation of the perfusion function from the ASL signal using this model is also demonstrated. The estimation algorithm uses a roughness penalty as well as prior information. The approach is demonstrated in numerical simulations and human experiments. The approach presented here is particularly suitable for fast ASL acquisition schemes, such as turbo continuous ASL (Turbo-CASL), which allows subtraction pairs to be acquired in less than 3 s but is sensitive to arrival time changes. This modeling approach can also be extended to other acquisition schemes.     

Effects of chelating agents on the rheological property of cervical mucus

As an ongoing effort to elucidate the mechanisms involved in the calcium-dependent fertility regulation process, the viscoelastic properties of the mucus obtained from lamb cervix and human semen, as well as their water and total protein contents after exposure to EDTA, a chelating agent, or Nonoxynol-9 (N-9), a spermicidal agent, were examined. The viscosity was measured using a Cone Plate Digital Viscometer, while the water and total protein contents were determined by the lyophilization process and the Lowry method, respectively. The significant changes in the rheological properties of mucus, such as its viscosity and the water content, upon exposure to EDTA were demonstrated. The viscosity of cervical mucus and human semen were significantly increased by EDTA treatment (as compared to the controls): lamb cervical mucus (2.9 ± 0.3 vs. 2.2 ± 0.3 cps) and human semen (5.0 ± 0.3 vs. 4.3 ± 0.3 cps), respectively. The hydration rate was decreased by EDTA treatment as compared with the control (93.6 ± 0.7 vs. 96.8 ± 0.8%). Among tested samples, the reduction in the percentage of sperm penetration through the cervical mucus was the highest in the mucus containing EDTA, which had the lowest water content (93.6 ± 0.7%), indicating that there is a positive relationship between the hydration rate of the cervical mucus and its ability to permit the penetration of spermatozoa. This result indicates that spermicidal activity exerted by high concentrations of EDTA is in part due to its effect on the rheological properties of cervical mucus or semen.     

Pharmacological evidence, using in vivo dialysis, that substances additional to ascorbic acid, uric acid and homovanillic acid contribute to the voltammetric signals obtained in unrestrained rats from chronically implanted carbon paste electrodes

In vivo voltammetry at chronically implanted carbon paste electrodes in unrestrained rats is a particularly useful technique for evaluating neurochemical changes during spontaneous behaviour, or behaviour under experimental control. A 3 peak signal is observed in the striatum; most recently the consensus view has attributed these peaks to ascorbic acid (AA), uric acid (UA) and homovanillic acid (HVA) in ascending order of oxidation potential. We have used a pharmacological approach, combined with in vivo dialysis, to further elucidate the nature of the contributing species. Allopurinol, an inhibitor of xanthine oxidase, and thus of uric acid production, has previously been reported to abolish peak 2. We now report, using dialysis, that it selectively depletes UA in the extracellular fluid (ECF). Pargyline, a monoamine oxidase inhibitor, reduces peak 3 transiently (max. 60%) as expected, however it results in a more sustained reduction in ECF HVA (max. 100%). It also increases peak 1 (max. 75%) and decreases peak 2 (max. 40%), although changes in ECF AA and UA measured by dialysis and HPLC are minimal. Pargyline does however reduce ECF 5-hydroxyindoleacetic acid by 65%. We conclude that, using linear sweep voltammetry at chronically implanted paste electrodes: (a) one or more substances in addition to AA can contribute to peak 1; dopamine can do so in some situations; (b) 5-hydroxyindoleacetic acid, as well as UA, contributes to peak 2; its contribution is about one third that of the latter; and (c) one or more substances in addition to HVA can contribute to peak 3. 3-Methoxytyramine can do so. Since this is another methylated metabolite of dopamine, this does not prevent the use of peak 3 as an index of dopamine metabolism, and may extend its usefulness to situations where monoamine oxidase is inhibited.     

Sleep apnea--an overview

Though distressing and potentially dangerous, sleep apnea may be an under-recognized disease in many countries. The obstructive type, which usually presents with loud snoring and excessive daytime sleepiness, is by far the commonest form. It causes a great deal of medical, social and psychological morbidity as well as an increased mortality. Doctors of different specialties have an important role in detecting and referring suspected patients for early assessment and treatment. Multidisciplinary management in a general hospital and accurate assessment with polysomnography are essential as modern and sometimes effective methods of treatment are becoming available.