Figure 7.

Behavioral effects of bilateral intra-mPFC DA D₁ receptor activation on the expression (recall) of suprathreshold associative fear-conditioning memory. A, Rats receiving intra-mPFC saline displayed normal expression (recall) of suprathreshold (0.8 mA footshock) fear conditioning when administered saline immediately before testing. In contrast, administration of a D₁ agonist (SKF 38393; 100–1000 ng/0.5 μl) immediately before testing completely blocked the expression (recall) of previously acquired emotional learning, with rats displaying no significant difference in freezing behavior in response to CS+ relative to CS− presentations. Similarly, bilateral intra-mPFC administration of the full D₁ receptor agonist SKF 81297 (1–100 ng/0.5 μl) produced a dose-dependent attenuation of emotional memory recall at the highest dose of 100 ng, but not at subthreshold doses (1–10 ng/0.5 μl). B, Similar effects were observed in conditioned suppression of exploratory behavior scores after CS+ versus CS− presentations, with intra-mPFC D₁ receptor activation blocking conditioned suppression of exploratory behavior after pretesting microinfusions of SKF 38393 (100–1000 ng/0.5 μl), relative to saline controls. Bilateral intra-mPFC administration of another D₁ receptor agonist, SKF 81297 (1–100 ng/0.5 μl), also produced a dose-dependent attenuation of emotional memory recall reflected in conditioned suppression of exploratory behavior, at the highest dose of 100 ng but not at subthreshold doses of 1–10 ng/0.5 μl.