Figure 10.

Schematic summary of hippocampal terminations in the upper and deep layers of A25 and relationship to postsynaptic D1 receptors. Hippocampal terminations were comparable in the upper and deep layers of A25 in size and proportion on each type of postsynaptic target. More hippocampal axon boutons formed synapses on spines with D1 receptors (light gray) in the deep layers than in the upper layers, consistent with the distribution of D1 receptors in A25. The background color indicates the effect of dopamine on the pyramidal neuron. Left, Proposed circuit engagement for novelty, uncertainty, and rewards that can elevate dopamine level within the normal range in healthy individuals and enhance information transfer from hippocampus to A25 to modulate goal-directed action via downstream structures. Right, Proposed circuit activation during abnormal states, including uncontrollable stress that excessively increases dopamine level, accompanied by overactivity in A25 and likely demotivating and anhedonic effects that disable goal-directed action, as seen in major depression.