Figure 3.

ZD1839 effects on latent inhibition of tone-dependent fear-conditioning. ZD1839 (1 mg ml⁻¹; 12 μg per day) or vehicle (10% dimethyl sulfoxide) was administered to the lateral cerebroventricle of rats treated with epidermal growth factor (EGF) or a control protein as neonates. Learning ability and latent inhibition in EGF and control rats were determined with a tone-paired fear-conditioning procedure and compared between vehicle- and ZD1839-infused groups. One day before the conditioning, rats in the preexposure group had been preexposed to the same tone cue without shock (+PRE; n=10 each). Rats in the non-preexposure group were directly subjected to conditioning on day 8 (n=10 each). Mean freezing rates (%) were measured for 2 min during conditioning (a) or during tone exposure in the test paradigm (b) Data represent means±s.e.m. *P<0.05, **P<0.01, ***P<0.001, compared between preexposed and non-preexposed groups and ⁺P<0.05, compared between vehicle- and drug-treated groups (by Fisher LSD).