Figure 3.

Acquisition of trace fear conditioning in rats without functional RE did not require DH NMDA receptor activation. The upper and middle panels showed the immobility levels of the RE-intact animals (upper panels) and the RE inactivation animals (middle panels) during the BL and each of the 10 tones (CS) during the conditioning and test sessions, and the lower panels summarized the overall immobility level across the BL and tones for respective groups. For RE-intact animals, DH NMDA receptor blockade resulted in a slower increase in immobility level during acquisition and a lower freezing response to the tone during early retrieval (upper panels). For RE inactivation animals, these animals displayed a rapid increase in immobility level during acquisition and a high level of fear expression during test session regardless of DH NMDA receptor blockade during conditioning (middle panels). Moreover, RE_MUS groups exhibited an overall higher immobility level compared to the RE_VEH groups during both the conditioning and the test sessions. BL, baseline; CS, conditioned stimulus; DH, dorsal hippocampus; RE, nucleus reuniens. ^*, P < .05. a, P < .05 between RE_VEH-NoCOND_SAL and RE_MUS-NoCOND_SAL groups.