FIGURE 8: Changes in glutamate release and intrinsic membrane properties shift synaptic processing in the NTS.

Model diagram summarizing the observed changes in synaptic function across time of day. A-B) During the light phase high spontaneous glutamate release drives elevated postsynaptic action potential firing, while increased postsynaptic membrane conductance diminishes afferent driven throughput. Together this produces a high tone / low responsive synaptic state. In contrast, during the night spontaneous glutamate release is low resulting in decreased basal action potential firing. However, decreased postsynaptic membrane conductance facilitates a high fidelity of synaptic throughput and potentiated post-stimulation bursts. Thus, at night, the synapse has low basal tone and is highly responsive to incoming vagal afferent signals. C) Schematic drawing proposing the relationship between each oscillating component within ST afferents and NTS neurons. The axon terminal represents vagal afferents from the solitary tract. Increased glutamate release and membrane conductance enhance firing at rest during the day; while, reduced glutamate release during the night combined with increased membrane resistance enhances afferent evoked AP firing. The symbol ‘g’ represents a change in conductance/membrane resistance.