Biomedical subjects

Andrei G Pakhomov

Publications and source records attributed to Andrei G Pakhomov.

4 recordsLinked to original sources

PubMed2006

Hydraulically coupled microejection technique for precise local solution delivery in tissues.

Hydraulically coupled volume microejection (HCVM) was employed to overcome known drawbacks of conventional pressure ejection of drugs in isolated brain slices and other tissues. For HCVM, a solution-filled glass micropipette is connected to a motor-driven, liquid-filled syringe by low-compliance, liquid-filled tubing, and the system is sealed leaving no gaps or air bubbles. The volume ejected from the micropipette is the same as the volume displaced by movement of the syringe plunger (it is not much influenced by the diameter of the micropipette tip or its clogging by tissue debris), so the ejection rate and duration can be precisely controlled. The HCVM performance was characterized by fluorescent imaging of ejected dyes, its combination with infrared/differential interference contrast (IR/DIC) imaging in brain slices, and by concurrent patch-clamp recording of ejected drug effects in individual neurons. Ejection of varied volumes into a brain slice (1.6-400 nl) formed a globular shape that transiently displaced the tissue adjacent to the micropipette tip. The radial penetration of the ejected dye correlated well with the electrophysiological responses to a concurrently ejected drug, at least for brief (100-200 ms) intervals after the ejection. The penetration distance could be increased by increasing either the ejection volume, or the ejection rate, or both. However, at higher ejection volumes (100-400 nl), a notable fraction of the ejectate was "pushed" out of the slice by tissue resiliency, and escaped to the outside by a back-flow along the ejection pipette. The use of HCVM enabled us to achieve a concentration rise time (10-90%) on the order of 20-40 ms. These and other measurements demonstrated principal capabilities and limitations of HCVM and provided guidance for its practical use, including some potentially unique applications.

Animals↗

PubMed2006

Oxygen enhances lethal effect of high-intensity, ultrashort electrical pulses.

The study explored the effect of ambient oxygen on mammalian cell survival after exposure to 10 ns duration, high voltage electrical pulses (nsEP, 80-90 or 120-130 kV/cm; 200-400 pulses per exposure). Cell samples were equilibrated with pure nitrogen, atmospheric air, or pure oxygen prior to the nsEP treatment and were returned to the incubator (air + 5% CO2) shortly after the exposure. The experiments established that survival of hypoxic Jurkat and U937 cells exceeded that of air-equilibrated controls about twofold (P < .01). Conversely, saturation of the medium with oxygen prior to exposure decreased Jurkat cell survival about 1.5 times, P < .01. Attenuation of the cytotoxic effect under hypoxic conditions resembled a well-known effect of oxygen on cell killing by sparsely ionizing radiations and may be indicative of the similarity of underlying cell damage mechanisms.

Apoptosis↗

PubMed2003

Effects of high power microwave pulses on synaptic transmission and long term potentiation in hippocampus.

Effects of short, extremely high power microwave pulses (EHPP) on neuronal network function were explored by electrophysiological techniques in the isolated rat hippocampal slice model. Population spikes (PS) in the CA1 area were evoked by repeated stimulation (1 per 30 s) of the Schaffer collateral pathway. A brief tetanus (2 s at 50 Hz) was used to induce long term potentiation (LTP) of synaptic transmission. In three different series of experiments with a total of 160 brain slices, the EHPP irradiation was performed before, during, or after the tetanus. The EHPP carrier frequency was 9.3 GHz, the pulse width and repetition rate were from 0.5 to 2 micros and from 0.5 to 10 Hz, respectively, and the peak specific absorption rate (SAR) in brain slices reached up to 500 MW/kg. Microwave heating of the preparation ranged from 0.5 degrees C (at 0.3 kW/kg time average SAR) to 6 degrees C (at 3.6 kW/kg). The experiments established that the only effect caused by EHPP exposure within the studied range of parameters was a transient and fully reversible decrease in the PS amplitude. Recovery took no more than a few minutes after the cessation of exposure and return to the initial temperature. This effect's features were characteristic of an ordinary thermal response: it was proportional to the temperature rise but not to any specific parameter of EHPP, and it could also be induced by a continuous wave (CW) irradiation or conventional heating. Irradiation did not affect the ability of neurons to develop LTP in response to tetanus or to retain the potentiated state that was induced before irradiation. No lasting or delayed effects of EHPP were observed. The results are consistent with the thermal mechanism of EHPP action and thus far provided no indication of EHPP-specific effects on neuronal function.

Animals↗

PubMed2002

Comparison of dose dependences for bioeffects of continuous-wave and high-peak power microwave emissions using gel-suspended cell cultures.

The study compared bioeffects of continuous wave (CW) microwaves and short, extremely high power pulses (EHPP) at the same carrier frequency (9.3 GHz) and average power (1.25 W). The peak transmitted power for EHPP was 250 kW (0.5-micro s pulse width, 10 p.p.s.), producing the E field of 1.57 MV/m in the waveguide. A biological endpoint was the density of yeast cells, achieved after a 6 h growth period in a solid nutrient medium (agarose gel) during EHPP or CW exposure. Owing to power losses in the medium, the specific absorption rate (SAR) ranged from 3.2 kW/kg at the exposed surface of the sample to 0.6 mW/kg at 24 mm depth. Absorption and penetration of EHPP was identical to CW, producing peak SAR values 200 000 times higher than the average SAR, as high as 650 MW/kg at the surface. CW and EHPP exposures produced highly nonuniform but identical heating patterns in exposed samples. Following the exposure, the samples were sliced in a plane perpendicular to the wave propagation, in order to separate cell masses exposed at different SAR levels. Cell density in the slices was determined by nephelometry and compared to unexposed parallel control samples. Cell density was strongly affected by irradiation, and the changes correlated well with the local temperature rise. However, the data revealed no statistically significant difference between CW and EHPP samples across the entire studied range of SAR levels (over six orders of magnitude). A trend (P<0.1) for such a difference was observed in slices that were exposed at a time average SAR of 100 W/kg and higher, which corresponded to peak SAR above 20 MW/kg for the EHPP condition. These numbers could be indicative of a threshold for a specific (not merely thermal) exposure effect if the trend is confirmed by future studies.

Cell Count↗