Long-term depression at olfactory nerve synapses.

The synapses formed by the olfactory nerve (ON) convey sensory information to olfactory glomeruli, the first stage of central odor processing. Morphological and behavioral studies suggest that glomerular odor processing is plastic in neonate rodents. However, long-term synaptic plasticity, a cellular correlate of functional and structural plasticity, has not yet been demonstrated in this system. Here, we report that ON-->mitral cell (MC) synapses of 5- to 8-d-old mice express long-term depression (LTD) after brief low-frequency ON stimulation. Pharmacological techniques and imaging of presynaptic calcium signals demonstrate that ON-MC LTD is expressed presynaptically and requires the activation of metabotropic glutamate receptors but does not require fast synaptic transmission. LTD at the ON--> MC synapse is potentially relevant for the establishment, maintenance, and experience-dependent refinement of odor maps in the olfactory bulb.