Figure 1.
Fear-potentiated startle values in light alone, shock alone, paired CS-US and unpaired CS-US groups.
Rats in the paired group received 7 light-shock pairings, whereas the unpaired rats received 7 lights and 7 shocks in a pseudorandom manner. Light alone (n = 8); shock alone (n = 8). * p<0.05, paired (n = 12) vs. unpaired (n = 8).
Figure 2.
A schematic diagram showing BP alterations induced by light (CS) and footshock (US) during the training session of fear-potentiated startle.
The light-on period is marked as the shaded region. PA: averaged BP in 3 s before light on; PCS: averaged BP in 3 s after light on; ST0: averaged resting sympathetic tone in 177 s before the initial PA; STUS: averaged post-US sympathetic tone in 177 s starting at 3 s after a footshock.
Figure 3.
PCS/PA and STUS/ST0 in the learning session.
PCS/PA represents the CS-induced BP response, while STUS/ST0 represents the US-induced sympathetic tone response. Both parameters show learning trial-dependent changes under paired CS-US conditions, but not under unpaired CS-US conditions (A–D). Additionally, the trial-averaged values of these two parameters negatively correlate with each other under paired CS-US conditions, but not under unpaired CS-US conditions (E, F). Results were analyzed by Pearson's correlation analysis for individual group.
Figure 4.
Coupling between PCS/PA and STUS/ST0 in individual trials of the learning session.
Data points represent the values of individual trials in the learning session. There were 7 data sets for each animal when PCS/PA and STUS/ST0 values were derived from the same trial, i.e., a CS followed by an US of the same trial (A). There were 6 data sets for each animal when PCS/PA and STUS/ST0 values were derived from two consecutive trials, i.e., an US followed by a CS from the next trial (B). Both parameters correlated with each other either in the same trial or in two consecutive trials.
Figure 5.
The CS-evoked BP alterations after the completion of a training session with 7 paired CS-US trials.
Under our standard protocol, an animal in the training cabinet remained quiescent after finishing the training session (A). As a comparison, if a similarly trained animal encountered an extra CS (B), it showed high values of PCS/PA (3-s average) and STCS/ST0 (180-s average).
Figure 6.
PCS/PA and STUS/ST0 in the learning session forecasted the performance of fear-potentiated startle.
The trial-averaged values of both parameters in training sessions under paired CS-US conditions effectively established the fear-potentiated startle (A, C), but those under unpaired CS-US conditions were unable to do so (B, D).
Figure 7.
Correlation between potentiated startle and PCS/PA (testing) values.
PCS/PA (testing) values were obtained by measuring the 3-s averaged BP values before and after the light (CS) during the testing session (averaged 10 times of the CS-evoked response for each rat, n = 12).
Figure 8.
Pharmacological interventions showing two pathways involved in the fear-potentiated startle.
The blockers were locally injected into BLA, CeA, MeA or VMH 30 min before the training session to block local neuron activity during fear learning. *p<0.05, blocker-treated vs. vehicle; # p<0.05, other brain areas vs. BLA under blocker-treated conditions. GR: GR 82334 (a SP receptor antagonist), TTX: tetrodotoxin, V: vehicle.
Figure 9.
Pharmacological interventions to locally block one or both of the fear learning pathways and the consequences on the fear-potentiated startle.
The blockers were locally injected into BLA, CeA, MeA or VMH to block local neuron activity before training session. Results were analyzed by Pearson's correlation analysis for individual group. Panels with line marks indicate significant correlation between the ordinate and the abscissa. Results from measuring PCS/PA values in the training session indicated that the MeA/VMH-mediated fear learning pathway, but not the CeA-mediated pathway, was BP-related (A–L). However, local blockages in CeA, MeA, or VMH all retained partial fear learning and memory (M–P).