Surfactant chain length and concentration influence on the interfacial tension of two immiscible model liquids: a coarse-grained approach.

The interfacial tension between immiscible liquids is studied as a function of a model linear surfactant length and concentration using coarse-grained, dissipative particle dynamics numerical simulations. The adsorption isotherms obtained from the simulations are found to be in agreement with Langmuir's model. The reduction of the interfacial tension with increasing surfactant concentration is found to display some common characteristics for all the values of chain length modeled, with our predictions being in agreement with Szyszkowski's equation. Lastly, the critical micelle concentration is predicted for all surfactant lengths, finding exponentially decaying behavior, in agreement with Kleven's model. It is argued that these findings can be helpful guiding tools in the interpretation of available experiments and in the design of new ones with new surfactants and polymers.

Development of a radiofrequency based thermal therapy technique in an in vivo porcine model for the treatment of small renal masses.

PURPOSE: Incidentally detected small renal tumors appear to grow slowly and be localized to the kidney. Minimally invasive therapies are being investigated as alternatives to standard surgical techniques. Radiofrequency ablation has been reported for the treatment of small renal cell carcinomas. We developed a radiofrequency technique and established its efficacy and safety in a large animal model. METHODS AND METHODS: A total of 22 lesions were created in normal kidneys of 7 pigs. Radiofrequency energy was administered during open exposure of the kidneys or percutaneously under ultrasound guidance. Lesion development was monitored with gray-scale and power Doppler ultrasound. To avoid heating surrounding tissues new hydro-dissection and gas-dissection techniques were developed. Lesion sizes and characteristics were assessed by ultrasound and pathological examination. RESULTS: No complications were observed due to probe insertion and removal. Perirenal structures were thermally damaged before the development and application of the dissection techniques. Lesion size was accurately predicted by gray-scale ultrasound on day 7. Loss of perfusion in the ablated volume was confirmed by power Doppler ultrasound. Lesions were wedge-shaped, presumably due to the effects of heating on segmental blood flow distribution. Pathological examination revealed changes consistent with thermal injury and ischemic type infarction. CONCLUSIONS: Radiofrequency thermal therapy is an effective and efficient method for ablating normal renal tissue in the pig. It may be applied percutaneously under ultrasound guidance with minimal complications provided that vital adjacent structures are protected from thermal damage. Further studies are required in humans before adopting this technique as definitive treatment for small renal cell carcinoma.

The effect of the NMDA receptor blocker, dextromethorphan, on cribbing in horses.

Stereotypic cribbing in horses is thought to involve excess dopaminergic activity within the striatum. Various models of stress-induced stereotypies including cribbing in horses postulate that stress stimulates the release of endorphins, triggering the release of striatal dopamine. Dopamine in turn activates basal ganglia motor programs, reinforcing behavior via a reward mechanism. Furthermore, the release of dopamine by endorphins has been shown to depend on activation of NMDA receptors. In the present study, horses identified as cribbers and volunteered by their owners were treated with the NMDA receptor antagonist dextromethorphan (DM). When DM was administered via jugular injection (1 mg/kg), eight of nine horses responded with reductions in cribbing rate (CR) compared to baseline, and cribbing was suppressed completely for a period of time in almost half of the horses tested.

The natural history of small renal masses.

PURPOSE: Ultrasound, computerized tomography and magnetic resonance imaging are widely available. Incidentally discovered small renal masses are reported more frequently. Most of these masses are low stage renal cell carcinomas. To understand better the natural history of these lesions and offer appropriate management, we followed prospectively a series of patients with this type of lesion. MATERIALS AND METHODS: A total of 13 patients with radiologically detected solitary small renal masses who were unfit for or refused surgery were followed with abdominal imaging for a median of 42 months. Median patient age was 69 years and mean lesion volume at diagnosis was 13.6 cm.3 or 2.95 cm. in diameter. Growth rate was calculated based on tumor volume rather than bi-dimensional diameter. Individual slopes of tumor size in time were calculated. RESULTS: Of the 13 patients 5 underwent surgery following a period of surveillance because of apparent tumor enlargement or new onset of symptoms. Pathological evaluation revealed renal cell carcinoma in all 5. No patient had metastases. Only 2 tumors were fast growing and these were the only 2 cases in which symptoms developed. When these patients were excluded from analysis, average growth rate was 1.32 cm.3 per year (p = 0.5, 95% confidence interval -3.00 to 5.76 cm.3 per year), which was not statistically significantly different from 0 slope or no growth. CONCLUSIONS: These results demonstrate that the growth rate of small renal tumors is variable, tumors that are destined to grow and possibly metastasize do so early and most small tumors grow at a low rate or not at all.

Neuropeptide Y phase shifts the circadian clock in vitro via a Y2 receptor.

The suprachiasmatic nuclei (SCN) contain a circadian clock whose activity can be recorded in vitro for several days. This clock can be reset by the application of neuropeptide Y. In this study, we focused on determination of the receptor responsible for neuropeptide Y phase shifts of the hamster circadian clock in vitro. Coronal hypothalamic slices containing the SCN were prepared from Syrian hamsters housed under a 14 h:10 h light:dark cycle. Tissue was bathed in artificial cerebrospinal fluid (ACSF), and the firing rates of individual cells were sampled throughout a 12 h period. Control slices received either no application or application of 200 nl ACSF to the SCN at zeitgeber time 6 (ZT6; ZT12 was defined as the time of lights off). Application of 200 ng/200 nl of neuropeptide Y at ZT6 resulted in a phase advance of 3.4 h. Application of the Y2 receptor agonist, neuropeptide Y (3-36), induced a similar phase advance in the rhythm, while the Y1 receptor agonist, [Leu31, Pro34]-neuropeptide Y had no effect. Pancreatic polypeptide (rat or avian) also had no measurable phase-shifting effect. Neuropeptide Y applied at ZT20 or 22 had no detectable phase-shifting effect. These results suggest that the phase-shifting effects of neuropeptide Y are mediated through a Y2 receptor, similar to results found in vivo.