Figure 3.

Intact acquisition and extinction of hippocampus-dependent trace eyeblink conditioning in CB₁ knock-out mice. A, Top, CR% in wild-type (open circles; n = 8) and CB₁ knock-out (KO) (filled circles; n = 7) mice were analyzed daily during the trace conditioning paradigm. The trace conditioning experiment consisted of an acquisition phase (10 d) and an extinction phase (4 d). In both acquisition and extinction phases, no difference was observed between wild-type and CB₁ knock-out mice. The temporal relationship between CS and US is depicted at the top. sp, Spontaneous eyeblink response. A, Bottom, CR% with every 10 trial block of the daily extinction session (day 11–14). CB₁ knock-out mice exhibited normal extinction. B, The averaged EMG amplitude of eyeblink response for wild-type (gray trace) and CB₁ knock-out (black trace) mice on day 10 (top) and day 14 (bottom), indicating no significant difference in EMG amplitude and the temporal pattern during both acquisition and extinction phases. Experiments were performed with CB₁ knock-out mice and their wild-type littermates at 11–19 weeks of age.