Figure 1.

Learning increases IL-1β protein specifically within the hippocampus, and this increase is modulated by neonatal infection. a, Rats treated with PBS or E. coli on P4 were injected as adults with saline (SAL) or LPS, and fear conditioned 24 h later (n = 8/group). Memory was assessed 1 or 72 h after conditioning. A separate group of rats from each neonatal treatment were injected as adults with SAL or LPS, and 24 h later received Fear Conditioning, Shock only, or Context exposure only (n = 8/grp). Brains were collected 2 h later to assess IL-1β protein. b, Freezing to the context did not differ between groups at the 1 h test, although freezing was greater overall in LPS-injected rats (**p < 0.05). At the 72 h test, freezing to the context was significantly lowest in NI rats treated with LPS 24 h prior (*p < 0.001). Freezing to the tone cue (CS) in an altered environment was significantly greater than the pre-CS period, but there was no neonatal group difference (^#p < 0.001). c, IL-1β was exaggerated within the HP of NI rats following LPS (*p < 0.02). Moreover, IL-1β was detectable only in HP following SAL injection (**p < 0.001), and concentrations were highest overall in HP (^#p < 0.001). d, Neither Shock nor Context alone produced the same exaggerated response within the HP of NI plus LPS rats, and concentrations were undetectable 24 h after SAL. Error bars indicate SEM.