Multistage electrophoresis system for the separation of cells, particles and solutes.

It is common to operate equilibrium-based separation methods, such as distillation and extraction, as multistage unit operations, in which equilibrium is presumably achieved within each stage. Two rate-based separation processes, free electrophoresis and magnetic particle separation, have now been operated in multistage mode. Preparative free electrophoresis of particles and solutes has resisted scale-up and is confined to a narrow range of ionic compositions. Natural convection induced in electrophoresis buffers by Ohmic heating has been a strong deterrent and has led to such measures as radial electrophoresis in Couette flow, free-flow electrophoresis, low-gravity electrophoresis, density gradient electrophoresis, and reorienting density gradient electrophoresis, to name a few. The short vertical electrophoresis path exploited in the last-mentioned forms the basis for multistage electrophoresis. A thin-layer countercurrent distribution apparatus was designed and constructed so that up to 20 fractions could be collected on the basis of electrophoretic mobility by applying an electric field. The mixture to be separated starts in a bottom cavity, and successive top cavities collect fractions as separand particles or molecules are electrophoresed upward out of the bottom cavity. Mathematical models of this process were developed, and experiments were performed to verify the predictions of the models by collecting and counting particles in each cavity after fractionation.

Advantages of percutaneous hollow needle technique for iliac bone harvest in alveolar cleft grafting.

OBJECTIVE: To evaluate the percutaneous hollow needle technique for bone harvest to determine if morbidity from the bone donor site can be reduced significantly. METHODS: A retrospective chart review was performed evaluating all patients undergoing alveolar bone grafting at our institution from January 1992 through December 1996. Patients who underwent additional major procedures were excluded. Group I consisted of 12 patients in whom the percutaneous technique was utilized. The patients had an average age of 11.1 years (range: 8 to 15 years). Six were male and six were female. One had a bilateral cleft. Group II consisted of 15 patients in whom the conventional open technique for iliac crest bone harvest was used. They had an average age of 13.1 years (range: 7 to 31 years). Six were male and nine were female. Two had bilateral clefts. Minimum follow-up was 6 months. We evaluated intraoperative blood loss, total postoperative analgesia requirement, and length of hospital stay based on a retrospective hospital chart review. RESULTS: A significant difference was found between the two groups regarding intraoperative blood loss (group I: 83.3 cm3, group II: 208 cm3; p = .0015), postoperative total analgesia requirement (group I: 0.04 mg/kg, range: 0 to 0.17 mg/kg; group II: 0.34 mg/kg, range: 0.03 to 0.74 mg/kg; p = .0002), and length of hospital stay (group I: 1.0 days, group II: 2.13 days; p = .0001). There was no significant change in these results when bilateral clefts were excluded. CONCLUSION: Iliac bone graft harvest using the percutaneous hollow needle technique results in less blood loss, decreased postoperative pain, and shorter hospital stays compared with the open technique.

Differential expression of hyperpolarization-activated currents reveals distinct classes of visual cortical projection neurons.

Combining in vivo retrograde labeling and in vitro electrophysiological recording techniques, we examined the distributions, densities, and biophysical properties of hyperpolarization-activated inward currents in two types of isolated, identified visual cortical projection neurons, superior colliculus-projecting (SCP) and callosal-projecting (CP) cells. In SCP cells, two kinetically distinct time-dependent hyperpolarization-activated inward current components are present. We have termed these Ih,f and Ih,s to denote the fast and slow components, respectively, of Ih activation. In CP cells, in contrast, Ih,f and Ih,s are differentially expressed. In 59% of the CP cells examined, for example, both Ih,f and Ih,s were present. The properties of the currents are indistinguishable from those recorded from SCP cells, although both Ih,f and Ih,s are expressed at significantly lower densities in this subset of CP cells (as compared to the current densities in SCP cells). Of the remaining 41% of the CP cells studied, 26% were found to express only Ih,s, and 12% of the cells expressed neither Ih,f nor Ih,s. Taken together, these results reveal that the electrical properties of CP visual cortical neurons are considerably more heterogeneous than those of SCP cells. The differential expression of Ih,f and Ih,s is expected to influence the integrated responses of different types of cortical projection neurons to excitatory and inhibitory synaptic inputs.