RATS AVOID EXPOSURE TO HVDC ELECTRIC-FIELDS - A DOSE-RESPONSE STUDY

Rats, given the choice, avoid exposure to alternating current (ac) 60- Hz electric fields at intensities greater-than-or-equal-to 75 kV/m. Th is study investigated the generality of this behavior by studying the response of rats when exposed to high voltage direct current (HVdc) el ectric fields. Three hundred eighty male Long Evans rats were studied in 9 experiments with 40 rats per experiment and in one experiment wit h 20 rats to determine 1) if rats avoid exposure to HVdc electric fiel ds of varying field strengths, and 2) if avoidance did occur, what rol e, if any, the concentration of air ions would have on the avoidance b ehavior. In all experiments a three-compartment glass shuttlebox was u sed; either the left or right compartment could be exposed to a combin ation of HVdc electric fields and air ions while the other compartment remained sham-exposed. The third, center compartment was a transition zone between exposure and sham-exposure. In each experiment, the rats were individually assessed in 1-h sessions where half of the rats (n = 20) had the choice to locomote between the two sides being exposed o r sham-exposed, while the other half of the rats (n = 20) were sham-ex posed regardless of their location, except in one experiment where the re was no sham-exposed group. The exposure levels for the first six ex periments were 80, 55, 42.5, 30, -36, and -55 kV/m, respectively. The air ion concentration was constant at 1.4 x 10(6) ions/cc for the four positive exposure levels and -1.4 x 10(6) ions/cc for the two negativ e exposure levels. Rats having a choice between exposure and non-expos ure relative to always sham-exposed control animals significantly redu ced the amount of time spent on the exposed side at 80kV/m (P < .002) as they did at both 55 and -55 kV/m (P < .005). No significant differe nces between groups were observed at 42.5, 30, or -36 kV/m. To determi ne what role the air ion concentration might have had on the avoidance behavior at field strengths of 55 kV/m or greater, four additional ex periments were conducted. The HVdc exposure level was held constant at either -55 kV/m (for three experiments) or -55 kV/m (for 1 experiment ) while the air ion concentration was varied between experiments at 2. 5 x 10(5) ions/cc, 1.0 x 10(4) for two of the experiments and was belo w the measurement limit (< +/- 2 x 10(3) ions/cc) for the other two ex periments at 55 and -55 kV/m. The exposed rats significantly reduced t he amount of time spent on the exposed side at 55 and -55 kV/m, relati ve to the sham-exposed rats regardless of air ion concentration (all a t P <.005). Thus, HVdc electric fields of greater-than-or-equal-to + o r -55 kV/m are sufficient to produce avoidance behavior in rats. Posit ive or negative air ion concentrations were not significant factors in these avoidance outcomes. (C) 1993 Wiley-Liss, Inc.