Failure to produce taste‐aversion learning in rats exposed to static electric fields and air ions

Abstract

Taste-aversion (TA) learning was measured to determine whether exposure to high-voltage direct current (HVdc) static electric fields can produce TA learning in male Long Evans rats. Fifty-six rats were randomly distributed into four groups of 14 rats each. All rats were placed on a 20 min/day drinking schedule for 12 consecutive days prior to receiving five conditioning trials. During the conditioning trials, access to 0.1% sodium saccharin-flavored water was given for 20 min, followed 30 min later by one of four treatments. Two groups of 14 rats each were individually exposed to static electric fields and air ions, one group to +75 kV/m (+2 x 10(5) air ions/cm3) and the other group to -75 kV/m (-2 x 10(5) air ions/cm3). Two other groups of 14 rats each served as sham-exposed controls, with the following variation in one of the sham-exposed groups: This group was subdivided into two subsets of seven rats each, so that a positive control group could be included to validate the experimental design. The positive control group (n = 7) was injected with cyclophosphamide 25 mg/kg, i.p., 30 min after access to saccharin-flavored water on conditioning days, whereas the other subset of seven rats was similarly injected with an equivalent volume of saline. Access to saccharin-flavored water on conditioning days was followed by the treatments described above and was alternated daily with water "recovery" sessions in which the rats received access to water for 20 min in the home cage without further treatment. Following the last water-recovery session, a 20 min, two-bottle preference test (between water and saccharin-flavored water) was administered to each group. The positive control group did show TA learning, thus validating the experimental protocol. No saccharin-flavored water was consumed in the two-bottle preference test by the cyclophosphamide-injected, sham-exposed group compared to 74% consumed by the saline-injected sham-exposed controls (P < .0001). Saccharin-preference data for the static field-exposed groups showed no TA learning compared to data for sham-exposed controls. In summary, exposure to intense static electric fields and air ions did not produce TA learning as assessed by this particular design.

Exposure of laboratory animals to small air ions: a systematic review of biological and behavioral studies

“…Some of the same data were reported by these authors in an earlier study [ 63 ]. A third study [ 64 ] tested whether negative and positive air ions (and concurrent static electric-field exposures) administered after drinking sweetened water would suppress later drinking of sweetened water as has been observed for other stimuli that produce gastric distress or other adverse effects. Neither study suggested any effect of air ion exposure, as the SMDs all cluster around zero.…”

“…For this reason, it is also important that the exposures occur in grounded cages to minimize the likelihood of this potential exposure limitation. Of the studies reviewed that generated air ions by corona discharge, only seven [ 48 , 57 , 59 , 64 , 78 , 82 , 109 ] included the proper electric-field-only controls. Several studies from the Krueger laboratory [ 80 , 81 , 99 , 103 , 114 ] and another investigator [ 94 ] also implemented electric-field-only controls, but these studies used a tritium ion generator rather than a corona discharge system for the generation of air ions; the issues associated with this type of ion generation are discussed further below.…”

Biological effects of exposure to static electric fields in humans and vertebrates: a systematic review

“…Seven studies focused on the effects of air ions [38–43, 73]; these studies were included in this review because they also tested a static EF alone. An additional four studies investigated exposures to EF from a HVDC line [44, 45] or a simulated HVDC environment [46, 47]. In these studies, the animals were co-exposed to air ions and static EF.…”

“…Two studies investigated avoidance behavior in rats [46, 47]. Creim et al [47] showed that rats avoided static EF (between 55 and 80 kV/m for 1 h), regardless of the presence of air ions.…”

“…This behavior was found to be dose dependent with higher field strengths inducing greater field avoidance. In a later study, Creim et al [46] failed to induce taste-aversion learning in rats in exposed environments (75 kV/m, 4 h/day for 5 days). The authors speculated that avoidance behavior observed in the earlier study was likely prompted by a response to external sensory stimulation, i.e., the perception of the static EF on the fur.…”