We have shown previously that the inactivation of the zinc finger gene
Krox-20 affects hindbrain segmentation, resulting in the elimination
of rhombomeres 3 and 5. We demonstrate here that Krox-20 homozygous mu
tant mice exhibit abnormally slow respiratory and jaw opening rhythms,
indicating that a modification of hindbrain segmentation influences t
he function of neuronal networks after birth. Central neuronal network
s that control respiratory frequency are made predominantly depressant
by the elimination of a previously undescribed rhythm-promoting syste
m. Recordings of rhythmic activity from the isolated hindbrain followi
ng progressive tissue transections indicate that the reorganization ta
kes place in the caudal pontine reticular formation. The newborn (P0)
Krox-20(-/-) mice, in which apneas are ten times longer than in wild-t
ype animals, may be a valuable model for the study of life-threatening
apneas during early infancy.