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.