Figure 2.

Increases in mPFC Erk phosphorylation correlate with the association of stimuli separated by time. A, Representative Western blots for dually phosphorylated Erk (p44/42) and total Erk in samples taken from the prelimbic/infralimbic cortices. B, Graph displays the mean ± SEM phospho-Erk immunoreactivity of prefrontal samples taken immediately after each condition, normalized by using the total Erk immunoreactivity of the same blots. C, Photomicrographs of immunohistochemistry for dually phosphorylated Erk in the prelimbic/infralimbic cortices in naive, CS-alone, US-alone, delay conditioning, unpaired, and immediately and 1 and 4 hr after trace fear conditioning. The figure shows an increase in Erk-positive cells specifically after trace conditioning. Scale bar, 200 μm. The asterisk indicates a significant difference as compared with control.