Modulatory actions of light on the behavioural responses to magnetic fields by land snails probably occur at the magnetic field detection stage

Abstract

The attenuation of opioid peptide-mediated antinociception or analgaesia is a well-established e¡ect of extremely low frequency (ELF) magnetic ¢elds. Results of prior studies indicated a modulatory role for light such that when the ELF exposures were carried out in the absence of light, the inhibitory e¡ect on analgaesia was reduced. Here, we investigated whether this modulatory e¡ect of light occurs at either the magnetic ¢eld detection stage or is associated with a post-detection mechanism. We compared the e¡ects of the presence and absence of light on the attenuation of opioid-induced analgaesia in the land snail, Cepaea nemoralis, by (i) an ELF magnetic ¢eld (15 min, 60 Hz, 141 mT peak), and (ii) the prototypic opiate antagonist, naloxone. Determinations were performed during the subjective`day' and`night' in the presence (1.9 W m À2 and 1.0 mW m À2 , respectively) and absence of light (less than 10 À6 W m À2 ). The inhibitory e¡ects of the ELF magnetic ¢elds and naloxone on opioid-induced analgaesia were similar in the presence of light; whereas in the absence of light the inhibitory e¡ects of the ELF magnetic ¢elds as a percentage of sham were markedly reduced, while those of naloxone were una¡ected. This indicates that the modulatory e¡ects of light on the actions of the ELF magnetic ¢elds probably a¡ect the detection mechanism prior to its coupling to the opioid system.

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

“…We have experimentally validated predictions of this theory suggesting that magnetic field effects in the land snail might not depend on magnetite or induced electric currents (Prato et al 1996b). Furthermore, we have accumulated indirect evidence that the light effect probably occurs at the magnetic field detection stage (Prato et al 1998) and the predictions of Lednev's theory are also light dependent (Prato et al 1996a(Prato et al , 1997(Prato et al , 2000. We have proposed that Lednev's theory could be modified to include the need for photon excitation (Prato et al 1996a).…”

“…(Prato et al 1998). Unfortunately to date, the light intensity and wavelength for this effect have not been investigated except for the evidence that exposure to red light does not modulate the magnetic field sense in these experiments (Betancur et al 1994;Prato et al 1998). By contrast, the work on magnetic field shielding suggests that repeated daily shielding of the ambient magnetic field during the day cycle can induce analgesia.…”

“…Furthermore, it has been shown that this effect is dependent on simultaneous exposure to light (Prato et al 1996a), and that this is likely to occur at or near the magnetic field detection stage as it is not due to a direct effect of light on opioid-induced analgesia The same experiment was run except that the duration was 10 days and 14 mice per light condition were used (experiment 1b). (Prato et al 1998). Unfortunately to date, the light intensity and wavelength for this effect have not been investigated except for the evidence that exposure to red light does not modulate the magnetic field sense in these experiments (Betancur et al 1994;Prato et al 1998).…”

“…In our previous publications regarding the modulation effects of light on magnetic field effects (Prato et al 1996a(Prato et al , 1997(Prato et al , 1998Kavaliers et al 1998;Kavaliers & Prato 1999), we have repeatedly pointed out that there are light-dependent and -independent effects. We have suggested that the mechanisms may be similar to the one proposed by Lednev (1996), which has some similarities to the free radical mechanism but, as formulated, does not require optical pumping.…”

“…Rather than an electronic level being excited by a photon as in the current radical pair mechanism espoused for animal orientation, in Lednev's theory it is proposed that a metal ion such as calcium in a proteingenerated potential well be excited by a photon. We have previously shown that a potential candidate for this protein well is the calcium well within the calmodulin-dependent nitric oxide synthase (Kavaliers et al 1998;Kavaliers & Prato 1999). This 'mouse in a box' protocol may provide new opportunities to collect new data towards the development of a theory of magnetic field detection that explains both the animal orientation and non-orientation data.…”