Figure 3.

Impairment of retrieval by xamoterol is prevented by a β₂ but not a β₁ antagonist. (A) Co-injection of xamoterol (Xam, 6 mg/kg) with the β₂ antagonist ICI 118,551 (ICI) blocked xamoterol-induced impairment of contextual fear, with 1 mg/kg ICI completely preventing disruption of retrieval. ICI (1 mg/kg) alone had no effect on retrieval. There were 5 mice per group except at 0.3 mg/kg ICI (6). F_(5,25) = 9.4 and P < 0.0001 for the main effect of treatment. (B) ICI does not enhance low levels of contextual fear in the absence of xamoterol (P = 0.9). There were 5 and 4 mice for vehicle and xamoterol. Animals were trained with lower shock intensity (0.35 mA) to approximate xamoterol-impaired freezing. (C) Xamoterol (6 mg/kg) reduced retention latencies for inhibitory avoidance relative to vehicle. Co-administration of xamoterol with ICI (1 mg/kg) prevented xamoterol-induced disruption of avoidance, while co-injection of xamoterol with the β₁ antagonist betaxolol (Bet, 1 mg/kg) failed to prevent disruption of retrieval. Neither Bet nor ICI altered avoidance when administered alone. There were 24, 22, 12, 15, 7, and 6 mice per group from left to right. F_(5,80) = 5.14 and P = 0.0004 for the main effect of treatment. (* = P < 0.05, ^∧ = P < 0.01, and # = P < 0.001 for post-hoc comparisons.)