Brain Research, 498 (1989) 145-148 145 Elsevier BRES 23720 Comparative studies on the retinal dopamine response to altered magnetic fields in rodents James Olcese I and Edward Hurlbut 2 1Department of Biology, Rhodes College, Memphis, TN 38112 (U.S.A.) and 2Departmentof Biology, Mesa College, Grand Junction, CO 81501 (U.S.A.) (Accepted 30 May 1989) Key words: Dopamine; Magnetic field; Pigmentation; Retina; Rodent Previously it was demonstrated that experimental alteration of the ambient magnetic field at night significantly reduced catecholamine levels in the retinae of Sprague-Dawley rats. As this effect appeared to depend on intact photoreceptors, it seemed of interest to examine whether the dopamine response to altered magnetic fields (MFs) differed between rod-dominant retinae and cone-dominant retinae. Furthermore, the effect of MFs on daytime dopamine content was explored. As in previous nocturnal investigations, dopamine levels in light-adapted (i.e. daytime) retinae from albino rats were significantly reduced by MFs. In the cone-dominant retina of the pigment ground squirrel, a similar MF effect was observed. However, in the rod-dominant retina of the golden hamster, dopamine levels increased significantlyfollowing daytime MF exposure. These results indicate that the retinal dopaminergic system is differentially responsive to MFs in various rodent species. Hence, the retina may play an important role in the perception of MFs by mammals. Research over the past decade has pointed to a new mode of environmental influence on the mam- malian central nervous system (CNS), namely that from electromagnetic fields. Several reviews on this subject have appeared recently L7"18. Among the structures in the CNS that respond to experimental alteration of the ambient magnetic field (MF) are the pineal gland and the retina. Electrophysiological and biochemical parameters of pineal function undergo significant changes following MF stimuli 23-25"29. These MF effects on pineal function, however, appear to require intact innervation between the eyes and brain 15 and retinal activation by dim light 22. Hence, the retina is probably antecedent to the pineal gland in the neural pathways relaying mag- netic information through the CNS. Recently, a retinal catecholamine response to altered MFs at night has been reported for the Sprague-Dawley rat 17. This response is dependent on intact photoreceptors 19. As these experiments were conducted at night and only with the albino rat, which has a rod-dominant retina, it seemed impor- tant to examine the issue of possible MF effects during other times of the day and in other rodent species. We chose to examine the effects of daytime MF stimuli on the dopamine contents of the rat, hamster and ground squirrel retina. The golden hamster (Mesocricetus auratus) is, like the rat, a nocturnal rodent with a rod-dominant retina. How- ever, unlike the rat, the hamster is fully pigmented, contributing to differences in photic sensitivity 3a° and perhaps pineal magnetosensitivity 16. Further- more, the hamster seemed appropriate for the present study because it has been shown capable of behavioral responses to magnetic stimuli 4. On the other hand, the Richardson's ground squirrel (Sper- mophilus richardsonii) is a feral, pigmented diurnal rodent with a cone-dominant retina 9. The effects of MFs on this species have never been investigated previously. Adult, male Sprague-Dawley rats (240 g average b. wt.), male golden hamsters (110 g), and wild- captured Richardson's ground squirrels (400 g) of mixed sex were used for these experiments. All Correspondence: J. Olcese. Current address: Institute for Hormone and Fertility Research, Grandweg 64, 2000 Hamburg 54, F.R.G. 0006-8993/89/$03.50 © 1989 Elsevier Science Publishers B.V. (Biomedical Division)