Projection of the Grüneberg ganglion to the mouse olfactory bulb.

In mammals, sensory neurons from the main olfactory and vomeronasal systems project their axons to the olfactory bulbs in the brain. We here report that a cluster of neurons, distinct from these two systems, located at the very tip of the mouse nose and called the Grüneberg ganglion expresses the mature olfactory-sensory neuron-specific marker olfactory marker protein (OMP), but is unlikely to express known odorant or pheromone receptors. The ganglion is present at birth and maintained during adult life. Tracing experiments indicate that these neurons target ipsilaterally to a specific set of glomeruli located on the caudal part of the olfactory bulb, and that this connection is necessary for the survival of the ganglion. The glomerular targets are structures previously proposed to be associated with suckling behaviour. These observations strongly suggest that this peculiar olfactory neuronal population plays a sensory role, possibly linked to chemoperception.