An olfactory sensory map develops in the absence of normal projection neurons or GABAergic interneurons

Olfactory sensory neurons expressing a given odorant receptor project to tw o topographically fixed glomeruli in the olfactory bulb. We have examined t he contribution of different cell types in the olfactory bulb to the establ ishment of this topographic map. Mice with a homozygous deficiency in Tbr-1 lack most projection neurons, whereas mice with a homozygous deficiency in Dlx-1 and Dlx-2 lack most GABAergic interneurons. Mice bearing a P2-IRES-t au-lacZ allele and deficient in either Tbr-1 or Dlx-1/Dlx-2 reveal the conv ergence of axons to one medial and one lateral site at positions analogous to those observed in wild-type mice. These observations suggest that the es tablishment of a topographic map is not dependent upon cues provided by, or synapse formation with, the major neuronal cell types in the olfactory bul b.