ID Number		563
Study Type		In Vivo
Model		750, 900 MHz (CW), 9.2, 40-52 GHz (AM 0.5-10 Hz) exposure to rat hippocampal slices and isolated frog sciatic nerves and analysis of conduction
Details		Hippocampal tissue slices from Sprague Dawley rats were given a brief tetanic stimulation to induce long term potentiation (LTP) in the evoked potential recordings from CA1 neurons, and exposed either before, during, or after stimulation to 9.2 GHz at high peak power (PW 0.5-2 usec pulse width, 0.5 - 10 Hz pulse repetition rate) at SARs of 0.7, 1.8, and 3.6 W/kg average (up to 500 kW/g peak). These SARs resulted in temperature increases of 1.4, 3.0, and 5.8 degrees. Exposure decreased the LTP population spikes (PS), but in a manner directly related to the temperature increase. The decreases in PS subsided as the temperature returned to normal. Similar effects could be triggered by either 9.2 GHz (CW) exposure or conventional heating, suggesting that the effect was completely thermal. In similar studies, 9.2 GHz (AM at 16 Hz) RF was used to expose hippocampal slices for ~ 15 minutes at 0.36, 1.2, or 6 W/kg. Exposures resulted in heating of 0.8 degrees at 1.2 W/kg and 4 degrees at 6 W/kg. Hippocampal slices were also superfused with a glutamate solution which effectively decreased population spikes by ~50% until it was washed out. RF exposure at 6 W/kg enhanced glutamate suppression and prevented recovery of population spikes in the slices, possibly due to a temperature effect. No repeatable and statistically significant effects on population spikes were observed from exposure at 1.2 W/kg or 0.36 W/kg. In ongoing studies, hippocampal slices were exposed to 9.6 GHz following epileptiform bursts triggered by 4-aminopyridine (4-AP) administration (somewhat addressing the earlier reports of Tattersal et al of effects in a similar system exposed at 750 & 900 MHz). RF exposure was ramped up in 5-minute intervals to 0 (sham), 0.024, 0.12, 0.6, and 3 W/g estimated average SAR, followed by no exposure and a drug wash for 20 minutes. No significant heating was found at 0.024 and 0.12 W/g, but 0.6 W/g resulted in a temperature increase from 34 to 34.7 C, and 3 W/g resulted in a temperature increase from 34 to 38 C. No effects were reported at non-heating levels, and effects reported at higher SAR levels were consistent with conventional heating. In earlier studies performed in isolated frog sciatic neurons exposed to microwaves, the authors reported thermal but no non-thermal effects. Studies using mm waves (40-52 GHz) and exposures of 10-60 minutes at power densities of ~3 mW/cm2 showed frequency dependent and transient reduction of compound action potential (CAP) latency and peak latency along with a rise of the test CAP amplitude  the effects were reversed shortly after cessation of exposure and were qualitatively and quantitatively similar to the effect of conventional heating of 0.30.4 degrees C.
Findings		Effects (only at thermal levels)
Status		Completed With Publication
Principal Investigator		USAF Research Lab, Brooks AF Base, USA - andrei.pakhomov@brooks.af.mil
Funding Agency		AF, USA
Country		UNITED STATES
References		Pakhomov, AG et al. Bioelectromagnetics, (2003) 24:174-181 Pakhomov, AG et al. Electro-Magnetobiol., (1998) 17:115-125 Pakhomov, AG et al. Bioelectromagnetics, (1998) 19:393-413 Pakhomov, AG et al. Electro- and Magnetobiology, (1997) 16:43-57 Pakhomov, AG et al. Bioelectromagnetics, (1997) 18:324-334 Pakhomov, AG et al. Electro. Magnetobiol., (1993) 12:1-15 Pakhomov, AG et al. J. Bioelectricity, (1991) 10:185-203 Doyle, J et al. Bioelectromagnetics: Current Concepts (Ayrapetyan SN, Markov MS, eds.), (2006) :123-133 Pakhomov, AG et al. Bioelectrochem. Bioenerg., (1997) 43:27-33
Comments		LTP in hippocampal neurons is generally thought to be the mechanism involved in memory development, although admittedly such extrapolation from the results of an experiment using an in situ rat hippocampal system to human memory function or a human provocation study is weak at best. The results of this study are in contrast to Tattersal, although those studies were performed using 700 MHz (CW). The present results, however, suggest the Tattersal study may have been the result of heating.