Biomedical subjects

S R Akers

Publications and source records attributed to S R Akers.

4 recordsLinked to original sources

PubMed1999

Ontogenetic expression of trk neurotrophin receptors in the chick auditory system.

Neurotrophins and their cognate receptors are critical to normal nervous system development. Trk receptors are high-affinity receptors for nerve-growth factor (trkA), brain-derived neurotrophic factor and neurotrophin-4/5 (trkB), and neurotrophin-3 (trkC). We examine the expression of these three neurotrophin tyrosine kinase receptors in the chick auditory system throughout most of development. Trks were localized in the auditory brainstem, the cochlear ganglion, and the basilar papilla of chicks from embryonic (E) day 5 to E21, by using antibodies and standard immunocytochemical methods. TrkB mRNA was localized in brainstem nuclei by in situ hybridization. TrkB and trkC are highly expressed in the embryonic auditory brainstem, and their patterns of expression are both spatially and temporally dynamic. During early brainstem development, trkB and trkC are localized in the neuronal cell bodies and in the surrounding neuropil of nucleus magnocellularis (NM) and nucleus laminaris (NL). During later development, trkC is expressed in the cell bodies of NM and NL, whereas trkB is expressed in the nerve calyces surrounding NM neurons and in the ventral, but not the dorsal, dendrites of NL. In the periphery, trkB and trkC are located in the cochlear ganglion neurons and in peripheral fibers innervating the basilar papilla and synapsing at the base of hair cells. The protracted expression of trks seen in our materials is consistent with the hypothesis that the neurotrophins/tyrosine kinase receptors play one or several roles in the development of auditory circuitry. In particular, the polarized expression of trkB in NL is coincident with refinement of NM terminal arborizations on NL.

Animals↗

PubMed1997

Load to failure of common meniscal repair techniques: effects of suture technique and suture material.

Success of meniscal repair with early or immediate motion depends on the ability of the suture fixation to withstand the loads applied. Vertical and horizontal mattress suture techniques were tested using 2-0 Ethibond, and 0-PDS and 1-PDS sutures (Ethicon, Somerville, NJ). Mulberry knot technique was tested with 0-PDS and 1-PDS sutures. Twenty menisci (60 sutures) were tested for each suture material. Sutures were placed 3 to 4 mm from the peripheral edge of the meniscus with double barreled cannulas for vertical and horizontal mattress techniques or a spinal needle for the mulberry knot technique, reproducing clinical techniques of meniscal repair. Mechanical testing of suture fixation was performed to failure at a rate of 10 mm/min on a MTS material testing system (MTS Systems Corp, Minneapolis, MN). Suture pullouts were reported as the load displacement to failure from the inner fragment only, because clinical failure would ensue should a suture pull through the inner fragment of a tear. Vertical mattress technique with 1-PDS suture had significantly greater load to failure than any other combination (P < .05). Analysis of variance showed that the vertical mattress technique had statistically superior pullout strength (P < .0001) compared with the horizontal mattress and mulberry knot techniques, which were statistically similar. There were significant differences (P < .0001) between suture types, with 1-PDS proving best compared with 0-PDS, which was stronger than 2-0 Ethibond. Selection of suture material had the greatest impact on vertical mattress load to failure and was not important to the strength of the other techniques.

Analysis of Variance↗

PubMed1987

Extracorporeal shock wave lithotripsy: the use of chemical treatments for improved stone comminution.

Extracorporeal shock wave lithotripsy (ESWL) can require more than two thousand acoustic shocks to achieve an adequate degree of renal calculus comminution. A decrease in the number of shocks necessary for effective treatment offers both technical and clinical benefits. The results presented here demonstrate that it is possible in particular cases to increase substantially the degree of comminution produced using a fixed number of acoustic impulses by exposing the stones to solutions of controlled pH and chemical composition during acoustic shock treatment. The largest increase in comminution was observed for magnesium ammonium phosphate hexahydrate/apatite stones exposed to citrate solutions. The smaller particle sizes are shown to result not only from stone dissolution but also from an increase in the ease of stone fracture during acoustic shocking. The degree of comminution of the largest fragment sizes was also found to be slightly increased for calcium oxalate stones by exposure to synthetic urine of elevated pH. These chemical methods of increased stone comminution appear to be directly applicable to particular cases and may have general clinical utility if suitable conditions affecting all stones can be found.

Calcium Oxalate↗

PubMedDate not supplied

Experimental laboratory lithotripter: design, construction, and operation.

A laboratory lithotripter has been constructed and used to comminute (crush to a powder) both kidney stones and gallstones. The stones are placed in the second focus (f2) of an ellipse of revolution whose linear eccentricity is 4.7 cm and then acoustically shocked an average of 200 times by an underwater spark discharge at the first focus (f1). The energy levels available from the capacitors (3 to 52 joules) of this unit extend below and above the range of commercially available clinical devices. The electrical and mechanical design of this unit is presented. At a relatively low cost (approximately $15,000) the unit appears to have considerable application in non-clinical research in lithotripsy. Quantitative results of the application of this device to the comminution of human kidney stones are presented.

Cholelithiasis↗