Role of sympathetic nerves during recovery from submersion in ducklings

1. 1. Chronic administration of a sympatholytic neurotoxin (6-hydroxydopamine hydrobromide, 50mg kg^-1 on alternate days for 15-29 days post-hatch) significantly enhanced the pressor responses of ducklings to exogenous norepinephrine. 2. 2. 6-Hydroxydopamine treated ducklings did not differ from vehicle-injected controls in their responsiveness to exogenous acetylcholine or their resting cardiac frequency, arterial pressure, ischiatic arterial flow and vascular resistance. 3. 3. During apneic submersion, the increase in ischiatic vascular resistance was retarded, arterial pressure decreased and cardiac frequency elevated in the 6-hydroxydopamine treated ducklings compared to controls. 4. 4. When ventilation resumed upon emersion however, ischiatic vascular resistance fell rapidly to pre-submersion levels in controls but remained elevated in 6-hydroxydopamine treated ducklings. 5. 5. Thus 6-hydroxydopamine treatment depressed ischiatic arterial flow and elevated arterial pressure during the recovery period. 6. 6. Post-asphyxic cardiac frequency was correspondingly lower in treated than in control ducklings. 7. 7. The data indicate that the rapid vasodilation associated with recovery from involuntary apneic submersion in ducklings is significantly impaired in the absence of an intact neuronal mechanism of catecholamine reuptake.