Prenatal Exposures to LTP-Patterned Magnetic Fields: Quantitative Effects on Specific Limbic Structures and Acquisition of Contextually Conditioned Fear

Abstract

Weak (<1 microT) complex magnetic fields (CMFs) may exert their behavioral influences through the hippocampus by resonating by accident or design with intrinsic electrical patterns. Rats were exposed prenatally to one of four intensities of a CMF (either <5 nanoTesla [nT], 10-50 nT, 50-500 nT, or 500-1000 nT) designed to interact with the process of Long-Term Potentiation (LTP) in the hippocampus. Rats then underwent testing in the forced swim, open field, and fear-conditioning procedures. The cell densities of all amygdaloid nuclei, specific hypothalamic structures, and the major regions of the hippocampus were quantified. Results showed that acquisition of conditioned fear was strongly inhibited in animals exposed to LTP-CMFs. Rats exposed to intensities above 10 nT showed decreased cell density in the CA2 fields of the hippocampus; more neurons were present in the CA1 fields of rats exposed to the 10-50 nT intensities compared to all other groups. A decrease in cell density in the medial preoptic nucleus was linearly dependent on field intensity. In the forced-swim test, swimming was decreased in rats that had been exposed to low (10-50 nT) and medium intensity (50-500 nT) LTP-CMFs in a manner consistent with monoamine modulation. In the open field, exposed rats were indistinguishable from controls. These findings support the hypothesis that continuous exposure during prenatal development to CMFs designed to simulate intrinsic LTP within the hippocampus can affect adult behaviors specific to this structure and produce quantitative alterations in neuronal density.

Neurodevelopmental anomalies of the hippocampus in rats exposed to weak intensity complex magnetic fields throughout gestation

“…The temporal structures of the complex magnetic fields used in this study (composite, LTP‐like, and non‐sinusoidal 50 Hz) have shown empirical effectiveness in influencing brain development and behavior when individually applied (Persinger and Koren, 2007; St‐Pierre et al, 2008; St‐Pierre and Persinger, 2003, 2008; Whissell et al, 2009). In summary, the composite pattern was composed of 40, 250 ms signatures that involved various frequency‐modulated patterns as well as those derived from mathematical relationships (Persinger, 2010; Persinger and Koren, 2007).…”

“…This was the same timing previously shown to be effective in producing long‐term potentiation in hippocampal slices when induced by electric current (Diamond et al, 1988). The 50 Hz pattern was designed from theoretical assumptions (Persinger and Koren, 2007; Whissell et al, 2009) that considered the importance of increments of 20 ms. For example the replication forks in DNA are estimated to move at about 50 nucleotides s −1 , that is 20 ms per nucleotide. The 50 Hz pattern was designed with a rise time and fall time of 1 ms and a plateau and trough of 20 ms.…”

“…For instance, sinusoidal or square‐wave pulses can be harmful to CNS growth and development but typically require field strengths on the order of a millitesla or higher to produce reliable effects (Gona et al, 1993; Juutilainen et al, 1986; Lahijani et al, 2011; Sikov et al, 1984; Ubeda et al, 1983). In contrast, we have found that wave‐form patterns whose intrinsic shapes (often asymmetric or irregular pulse patterns) and interstimulus intervals have been designed to simulate common physiological or naturalistic phenomena can also be effective in altering the development of the rat brain even when applied at flux densities several magnitudes lower (<1 μT) (McKay and Persinger, 1999; McKay et al, 2003; St‐Pierre et al, 2008; St‐Pierre and Persinger, 2003, 2008; Whissell et al, 2009). In one study, St‐Pierre et al (2008) reported that continuous prenatal exposure to a complex composite magnetic field containing 50 sequential 200 ms intervals of specific patterns produced non‐linear, intensity‐dependent elevations in adult serum aminotransaminase, glucose, and uric acid.…”

Electromagnetic Field and Γ Aminobutyric Acid a Receptors Interaction in the Fear Response

“…Several studies indicate the effect of electromagnetic field on fear response. It has been shown that acquisition of conditioned fear was strongly inhibited in animals exposed to complex magnetic fields (Whissell et al, 2009). Prenatal exposure to physiologically-patterned magnetic fields within a specific "window" of intensities that overlap with values found in many human habitats may produce long-term changes in fear behaviors (St-Pierre and Persinger, 2008).…”

Developmental Effects of 7 Hz, Square Wave Magnetic Fields and Nitric Oxide Modulation on Organ Systems

“…Examples of physiologically-relevant patterns include waveforms modeled after hippocampal theta rhythms [16] and waveforms modeled after geomagnetic micropulsations [17] as they are both naturally occurring patterns of magnetic activity. Brain structure appears sensitive to these fields: reductions in the density of the medial preoptic nucleus in males [18,19] and parasolitary nucleus in both sexes [17] have been reported as have alterations in the gross [20] and fine structure of the hippocampus [16]. Changes in testicular weight [19] and thyroid weight [21] might also occur.…”