THE MUSCARINIC ACETYLCHOLINE ANTAGONIST SCOPOLAMINE IMPAIRS SHORT-DISTANCE HOMING PIGEON NAVIGATION

The present study employed intramuscular (IM) injections of the acetyl choline (ACh) receptor antagonist scopolamine hydrobromide (0.10 mg/kg ) to investigate the possible involvement of ACh in naturally occurrin g spatial navigation in homing pigeons (Columba livia). Control pigeon s receiving injections of saline or scopolamine methylbromide, an ACh antagonist that does not cross the blood-brain barrier, were oriented in a homeward direction when released from a location 8 km from home. In contrast, pigeons injected with scopolamine hydrobromide (0.10 mg/k g, IM) were less well oriented and took more lime to return home from the same location. These results suggest that homing pigeon navigation is regulated, in part, by central cholinergic mechanisms.