ID Number		112
Study Type		In Vitro
Model		400, 700, 900, 1800, 2100 MHz (CW, GSM, UMTS, Tetra) exposure to rat hippocampal slices and analysis of evoked & spontaneous potentials
Details		Rat (Porton) hippocampal slices (400 uM thick) were initially exposed to 700 MHz (CW) signals and analyzed for changes in evoked, spontaneous, and long term potentials. Exposure of hippocampal slices to RF for 5 minutes at 1.41 W/kg at slice surface (1.27 W/kg at slice bottom) in a stirpline waveguide system reduced the evoked and spontaneous population spikes from the CA1 region of the hippocampus to ~50% of control (ANOVA, p<0.001). In contrast, lower exposure levels increased these population spikes up to 20% of controls (Wood et al 1997, Soc. Neurosci. Abstr. 23:2205). Further studies showed both 700 & 900 MHz (CW) RF could modify long term potentiation (LTP) also (Scott et al., 20th BEMS Meeting). In other studies, 700 & 900 MHz (CW) exposure at 0.19 W/kg and 900 & 1800 MHz (GSM) exposure at 0.036 W/kg (given before electrical induction of LTP) produced increases in the population spike amplitude of the CA1 neurons. RF exposure given during treatment of the slices with 100 uM 4- aminopyridine (a Ca++ channel blocker that induces a seizure response) reduced the rate and amplitude of spontaneous epileptiform bursting. No detectable temperature increases in any of these studies were reported. A presentation at BEMS (2001) in St. Paul MN reported that modeling of the SAR around the probe tips used in these studies indicated SAR values may have been 10-20 times higher than the reported values. The effects of 16 Hz modulation to the 700 MHz RF exposure had no effect on these results. However in subsequent studies supported by the UK Home Office, hippocampal slices from C57BL mice were evaluated following exposure to 400 MHz (Tetra) at 20 W/kg (peak average SAR), 900 MHz (GSM) at 36 W/kg (peak average SAR), or 2.2 GHz (UMTS / W-CDMA) at 20 W/kg (peak average SAR) for 1 hour using a head-first loop antenna under well controlled conditions. Immediately following exposure, hippocampal slices were prepared and analyzed. The authors report no significant effects on electrophysiology, consistent with the absence of behavioral effects in mice reported by Bottomley et al (2004 BEMS). In a recent (2008) the authors exposed rat hippocampal slices to 380 MHz (Tetra) at 10-100 watts of power to deterimine the duration of temperature elevation needed to abolish evoked potential measurements in the CA1 nucleus following a stimulatory pulse. The authors report the potentials were abolished with very rapid pulses (20 msec at 100 watts, 2 seconds for 10 watts) that resulted in a locally observable elevation in tissue temperature (~58 degrees C via IR thermography). The exposure correlated with an SAR of 5.54 MW/kg.
Findings		Effects (only at thermal levels)
Status		Completed With Publication
Principal Investigator		DERA, UK
Funding Agency		DOH, UK, Home Office, UK
Country		UNITED KINGDOM
References		Tattersall, JE et al. Brain Res., (2001) 904:43-53
Comments		In the initial studies, reference electrode + recording electrode + recording system form a closed loop of conductors concatenated with the H field from the stripline, and could have generated spurious responses. An appropriate control would have been to include poisoned tissue plus exposure to the same RF fields. Earlier studies by Wachtel (1983, Bioelectromagnetics Society, 5th Annual Meeting, 12-17 June, Boulder, CO, p. 27), however, did show that wide (0.1 to 100 msec) pulsed 2450 MHz microwaves at 0.02 to 0.06 W/kg (average SAR) could modulate neuronal activity in Aplysia neurons and excitatory potentials in mouse hippocampal brain slices.