Time-gated fluorescence lifetime imaging and microvolume spectroscopy using two-photon excitation

A scanning microscope utilizing two-photon excitation in combination with fluorescence lifetime contrast is presented. The microscope makes use of a tunable femtosecond titanium:sapphire laser enabling the two-photon excitation of a broad range of fluorescent molecules, including UV probes. Importantly, the penetration depth of the two-photon exciting (infra)red light is substantially greater than for the corresponding single-photon wavelength while photobleaching is significantly reduced. The time structure of the Ti:Sa laser can be employed in a straightforward way for the realization of fluorescence lifetime imaging. The fluorescence lifetime is sensitive to the local environment of the fluorescent molecule. This behaviour can be used for example to quantify concentrations of ions, such as pH and Ca²⁺, or pO₂ and pCO₂. In the set-up presented here the fluorescence lifetime imaging is accomplished by time-gated single photon counting. The performance and optical properties of the microscope are investigated by a number of test measurements on fluorescent test beads. Point-spread functions calculated from measurements on 230-nm beads using an iterative restoration procedure compare well with theoretical expectations. Lifetime imaging experiments on a test target containing two different types of test bead in a fluorescent buffer all with different lifetimes (2.15 ns, 2.56 ns and 3.34 ns) show excellent quantitative agreement with reference values obtained from time correlated single photon counting measurements. Moreover, the standard deviation in the results can be wholly ascribed to the photon statistics. Measurements of acridine orange stained biofilms are presented as an example of the potential of two-photon excitation combined with fluorescence lifetime contrast. Fluorescence lifetime and intensity images were recorded over the whole sample depth of 100 μm. Fluorescence intensity imaging is seriously hampered by the rapid decrease of the fluorescence signal as a function of the depth into the sample. Fluorescence lifetime imaging on the other hand is not affected by the decrease of the fluorescence intensity.     

Automatic feedback control of relative blood volume changes during hemodialysis improves blood pressure stability during and after dialysis

Automatic feedback systems have been designed to control relative blood volume changes during hemodialysis (HD) as hypovolemia plays a major role in the development of dialysis hypotension. Of these systems, one is based on the concept of blood volume tracking (BVT). BVT has been shown to improve intra-HD hemodynamic stability. We first questioned whether BVT also improves post-HD blood pressure stability in hypotension-prone patients and second, whether BVT is effective in reducing the post-HD weight as many hypotension-prone patients are overhydrated because of an inability to reach dry weight. After a 3-week period on standard HD, 12 hypotension-prone patients were treated with two consecutive BVT treatment protocols. During the first BVT period of 3 weeks, the post-HD target weight was kept identical compared with the standard HD period (BVT-constant weight; BVT-cw). During the second BVT period of 6 weeks, we gradually tried to lower the post-HD target weight (BVT-reduced weight; BVT-rw). In the last week of each period, we studied intra-HD and 24 hr post-HD blood pressure behavior by ambulatory blood pressure measurement (ABPM). Pre- and post-HD weight did not differ between standard HD and either BVT-cw or BVT-rw. Heart size on a standing pre-dialysis chest X-ray did not change significantly throughout the study. There were less episodes of dialysis hypotension during BVT compared with standard HD (both BVT periods: p<0.01). ABPM data were complete in 10 patients. During the first 16 hr post-HD, systolic blood pressure was significantly higher with BVT in comparison with standard HD (both BVT periods: p<0.05). The use of BVT in hypotension-prone patients is associated with higher systolic blood pressures for as long as 16 hr post-HD. BVT was not effective in reducing the post-HD target weight in this patient group.     

42-month preliminary follow-up of the silastic ring vertical banded gastroplasty

BACKGROUND: The authors review preliminary experience with silastic ring vertical gastroplasty (SRVG). METHODS: Of 202 patients who underwent SRVG, 191 are more than 3 months postoperation and of these 165 were accessible for review. RESULTS: Pouch volume could not be readily measured. The TA90BN stapler was occasionally difficult to apply exactly at the angle of His. There was one subphrenic abscess, one gastric bleed, and one dehiscence. Vomiting occurred in eight patients who required reoperation: ring removal, three; cholecystectomy, one; conversion to vertical banded gastroplasty, one; conversion to Roux-en-Y gastric bypass, three. There was no mortality. Weight loss has been satisfactory to 42 months. CONCLUSION: SRVG has been a relatively simple operation, with acceptable morbidity and weight loss thus far.     

Effects of varied reward schedules on generalized persistence of rats.

Gave concurrent acquisition training to 4 groups of male albino rats (N = 70) in 2 parallel runways, such that continuous reward (CR) occurred in 1 alley and varied reward (VR) occurred in the other. The varied reward conditions were partial reward (PR), partial delay (PD), variable magnitude (VM), and constant delay (CD). A CR control group received CR in both alleys. All Ss were extinguished in the alley which had previously been associated with CR. Using resistance to extinction in the CR runway as the index of generalized persistence, the groups were ordered from greatest to least persistence as follows: PR, PD, VM, CD, and CR. This specific ordering is most easily accommodated by an elaboration of stimulus-aftereffects theory. (27 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Language police running amok.

In this article I critique Kathleen Slaney and Michael Maraun's (see record 2006-12348-004) addition to the ongoing philosophical charge that neuroscientific writing often transgresses the bounds of sense. While they sometimes suggest a minimal, cautious thesis--that certain usage can generate confusion and in some cases has--they also bandy about charges of meaninglessness, conceptual confusion, and nonsense freely. These charges rest on the premise that the offending terms have specific correct usages that correspond with Slaney and Maraun's sense of everyday linguistic practice. I challenge this premise. I argue that they have not shown that there are such specific correct usages; and, further, that even if they had, they fail to justify that their definitions are the correct ones. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Watersheds and stream networks viewed longitudinally: Example insights from novel spatial portrayals of watershed characteristics

Longitudinal depictions of watershed structure and characteristics, including topography, stream networks, wetlands, ground water levels, and land use, can provide watershed knowledge and understanding unavailable from standard plan view maps. Three case studies provide examples of knowledge gained by applying longitudinal views of stream networks, watershed hydrologic behavior, and land use distributions. Longitudinal views of mountain stream networks show extreme variability in the slope-area relationships of low Strahler order streams, large discontinuities in drainage area (large parts of drainage area space are absent in networks), and large variations in network curvature. Longitudinal views of a groundwater-dominated headwater watershed increase the inference available from limited groundwater observations and clearly reveal how groundwater connections affect the permanence of surface water features and the distribution of vadose zone storage in the landscape. Plotting land uses longitudinally illuminates and allows a quantitative analysis of how land uses are distributed relative to topographic position. Viewing watersheds and stream networks longitudinally can provide new insights into watershed forms and processes and motivate new questions and research.