Figure 1.

The expression of extinction is associated with activation of ilPFC projections to MDH. A, Responses on the active and inactive nose pokes during extinction (left) or test (right). Rats were trained in context A, extinguished in context B, and then tested in either context A (group ABA) or context B (ABB). Group ABB showed significantly less responding on test than group ABA. B, Representative photomicrograph of an MDH CTb injection. Placements were anatomically verified with dual immunofluoresence for prodynoprhin (red) and CTb (green). Scale bar, 100 μm. C, Representative photomicrograph of immunoreactivity (IR) in ilPFC. Arrows point to neurons dual-IR for CTb (brown cell body) and c-Fos (black nuclei). Scale bar, 50 μm. D, Total counts through ilPFC of neurons CTb-IR (left), c-Fos-IR (middle), and dual-IR (right). There were no differences between groups in total CTb-IR neurons. Group ABB had higher numbers of total c-Fos-IR neurons than group ABA. Importantly, there was a significant increase in dual-IR in group ABB compared with group ABA. Data are expressed as mean (±SEM). *p < 0.05 comparing group ABB to ABA.