1. Howard Hughes Medical Institute, Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA
2. The Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
3. Present address: The National Institute of Neurological Disorders and Stroke, National Institutes of Health, 36 Convent Drive, Bethesda, Maryland 20892-4150, USA.

Correspondence to: Leonardo Belluscio^1,2Peter Mombaerts³ Correspondence and requests for materials should be addressed to L.B. (e-mail: Email: belluscl@ninds.nih.gov).

Abstract

The mammalian olfactory system detects and discriminates thousands of odorants using many different receptors expressed by sensory neurons in the nasal epithelium¹. Axonal projections from these neurons to the main olfactory bulbs form reproducible patterns of glomeruli in two widely separated regions of each bulb, creating two mirror-symmetric maps of odorant receptor projections². To investigate whether odorant receptors organize neural circuitry in the olfactory bulb, we have examined a genetically modified mouse line, rI7 M71, in which a functionally characterized receptor, rI7^{3, 4}, has been substituted into the M71 receptor locus⁵. Here we show that despite their ectopic location the resulting glomeruli are responsive to known ligands of the rI7 receptor, attract postsynaptic innervation by mitral/tufted cell dendrites, and endow these cells with responses that are characteristic of the rI7 receptor. External tufted cells receiving input from rI7 M71 glomeruli form precise intrabulbar projections that link medial and lateral rI7 M71 glomeruli anatomically, thus providing a substrate for coordinating isofunctional glomeruli. We conclude that odorant receptor identity in epithelial neurons determines not only glomerular convergence and function, but also functional circuitry in the olfactory bulb.