Light alters nociceptive effects of magnetic field shielding in mice: intensity and wavelength considerations

Abstract

Previous experiments with mice have shown that repeated 1 hour daily exposure to an ambient magnetic field-shielded environment induces analgesia (antinociception). The exposures were carried out in the dark (less than 2.0!10 16 photons s K1 m K2 ) during the midlight phase of the diurnal cycle. However, if the mice were exposed in the presence of visible light (2.0!10 18 photons s K1 m K2 , 400-750 nm), then the analgesic effects of shielding were eliminated. Here, we show that this effect of light is intensity and wavelength dependent. Introduction of red light (peak at 635 nm) had little or no effect, presumably because mice do not have photoreceptors sensitive to red light above 600 nm in their eyes. By contrast, introduction of ultraviolet light (peak at 405 nm) abolished the effect, presumably because mice do have ultraviolet A receptors. Blue light exposures (peak at 465 nm) of different intensities demonstrate that the effect has an intensity threshold of approximately 12% of the blue light in the housing facility, corresponding to 5!10 16 photons s K1 m K2 (integral). This intensity is similar to that associated with photoreceptor-based magnetoreception in birds and in mice stimulates photopic/cone vision. Could the detection mechanism that senses ambient magnetic fields in mice be similar to that in bird navigation?

The detection threshold for extremely low frequency magnetic fields may be below 1000 nT‐Hz in mice

“…Recently, we have shown that the presence of light can also attenuate the analgesia induced by repeated ELF-MF shielding in a wavelength and intensity dependence similar to that associated with geomagnetic orientation of birds and newts [Prato et al, 2009]. At that time we argued that a similar mechanism may explain both animal orientation and animal nociception effects of magnetic field exposure.…”

“…Also, inspection of Figure 3a and b indicates that the 25 nT exposures at 30 and 120 Hz give very different results, contrary to predictions if detection is dependent on an RPM. It is worth noting that to date, except for a recent publication from our laboratory [Prato et al, 2009], there is little evidence of a RPM in rodents [Thalau et al, 2006], although there is evidence that rodents have a magnetic compass [Muheim et al, 2006].…”

“…As the initial exposures to the shielded environment were in the dark but during the mid-light phase of the diurnal cycle, we reintroduced white light into the shielded environment and the analgesic effect was eliminated [Koziak et al, 2006]. This effect of light is dependent on both wavelength and intensity [Prato et al, 2009]. We have shown that the effect is not due to electric field shielding [Prato et al, 2005] and likely not due to shielding of the ambient static component of the magnetic field [Choleris et al, 2002].…”

Low-frequency pulsed electromagnetic field exposure can alter neuroprocessing in humans

“…The initial biophysical detection mechanism of magnetoreception remains controversial, but three candidate general mechanisms exist: (i) detection by magnetic dipoles within cells and tissue; (ii) detection of an induced current; and (iii) detection via the different chemical reaction rates when the electron spins of free radicals are affected by a magnetic field. Evidence to date suggests that the effect on animal orientation is mediated by tissue dipoles and/or the free radical mechanism ( Johnsen & Lohmann 2008), while the evidence for anti-nociceptive effects may depend on several mechanisms (Thomas et al 1997;Prato et al 2000Prato et al , 2009Del Seppia et al 2007). …”

Exposure to inhomogeneous static magnetic field beneficially affects allergic inflammation in a murine model

“…The applied light sources emit light with several wavelength peaks between 403 and 710 nm. The calculated integral light intensity maximum corresponds to 3.9 Â 10 16 photons s 21 m 22 , which is below the intensity threshold for altering behavioural responses in mice in SMF-shielded environments [15]. The illumination conditions inside the cage were basically independent of the location of the mouse within the cage.…”