THE NMDA-RECEPTOR ANTAGONIST MK-801 IMPAIRS NAVIGATIONAL LEARNING IN HOMING PIGEONS

The present study employed the N-methyl-o-aspartate (NMDA) receptor an tagonist MK-801 to investigate the possible importance of NMDA recepto r activation for naturally occurring spatial learning in birds by expl oiting the navigational ability of homing pigeons (Columba livia). Con trol pigeons released from two unfamiliar release sites displayed vani shing bearings that were poorly oriented. However, when released a sec ond time from the same sites they displayed improved homeward orientat ion. The control birds apparently learned something about the spatial relationships of stimuli at the release sites on the first releases an d used that information to orient better when released a second time f rom the same locations. Experimental pigeons given the NMDA receptor a ntagonist MK-801 (0.10 mg/g) initially behaved as controls, orienting poorly when released for the first time from the two sites. In contras t to controls, the experimental birds failed to show significant impro vement in orientation when released again from the same sites without MK-801. A second experiment revealed no state-dependent learning. Resu lts of a position/color discrimination task showed that the impairment s observed did not generalize to associative learning in an operant ch amber, and together with field observations were not a result of senso ry or motor drug effects. The data indicate that blocking NMDA recepto rs can disrupt navigational learning in homing pigeons. As such, the r esults are consistent with the hypothesis that NMDA receptor activatio n plays an important role in spatial learning in birds. (C) 1994 Acade mic Press, Inc