Orientation-disturbing magnetic treatment affects the pigeon opioid system

Keeping homing pigeons in an oscillating magnetic field of low intensity is known to increase the scattering of initial bearings and/or their deflection towards a specific direction. To determine whether these effects on orientation are the outcome of direct interference with the birds' navigational mechanism or are the side-effect of problems in another biological system, experiments were performed to test whether the same effects could be induced by non-magnetic treatments. The initial orientation of pigeons treated with the prototypic opiate antagonist naloxone (1 mg kg-1) displayed similar disturbances to those observed in magnetically treated birds. In both cases, the orientation was significantly different from that of control birds. The concentration and affinity of the brain's mu-opiate receptors were then assessed in magnetically treated birds by using [H-3]dihydromorphine as a ligand. The concentration of u-opiate receptors fell significantly in these birds, whereas the affinity of the receptors was unaffected. We conclude that it appears improbable that the navigational mechanism of pigeons is directly influenced by magnetic treatments. What these do seem to produce is a lack of compensation for the stress experienced by pigeons subjected to a test release.