Fig. 7: Head-fixed fear conditioning increases NAergic multipeak signals in 1st conditioning.

a, b Sample traces of NAergic fibers’ Ca²⁺ activity in 1st conditioning (a) and 5th conditioning (b). Filled red circles indicate MP signals. c, d Duration of multipeak signals were analyzed between before FS (0–60 s) and immediately after FS (60–70 s). Significant increase of duration was observed in the 1st conditioning, but disappeared in the 5th conditioning (n = 5 sessions, 5 mice). e–g Quantifications of NAergic multipeak signals: mean duration (e) (n = 5 mice for all analyses), frequency (f), and total time (g). h–l Total times of MP signals in 1–5th conditionings are shown. Post-FS1 has significantly longer total time only during 1st conditioning. 1st (h), 2nd (i), 3rd (j), 4th (k), and 5th conditioning (l). m Comparison of each conditioning session between 1st and 5th conditioning. Increased total time of post-FS, particularly post-FS1, in 1st conditioning disappear in 5th conditioning. n–p mimicking NAergic fiber activation during the head-fixed fear conditioning show that dense PS (o, p total time = 42%, corresponding to post-FS1 phase) significantly increases the extracellular NA concentration than sparse PS (n, p total time = 20%, correspond to control phase; n = 6 sessions, 4 mice). Analysis was performed from individual MP signals in c and d and average of individual sessions for other graphs. Bar graphs: mean + SEM. Box plots: box range, 25–50–75% quatile; square, mean; whiskers, max–min. Student’s t-test with Welch’s correction: c, d, p; one-way ANOVA with Turkey’s test: f–h; paired t-test: m; *p < 0.05, **p < 0.01.