Fig. 3.
Examples of two mechanisms of short-term synaptic plasticity in the olfactory system. Left, Afferent input to the olfactory bulb can be regulated by dopaminergic feedback to D2 receptors on the olfactory receptor axons. As described in the text, dopamine levels are modulated by odor stimulation such that reduced odor stimulation reduces dopamine expression and releases olfactory nerve axon terminals from presynaptic inhibition. This could produce an activity-dependent regulation of afferent input efficacy. In the piriform cortex (right), mitral cell axon transmitter release is modulated by mGluR autoreceptors. During periods of intense input (e.g., prolonged odor stimulation), transmitter release is reduced, potentially producing cortical odor adaptation.