dPAG optical stimulation and amygdala recordings.
(A) Virus injection in dPAG and tetrode array implantation targeting BLA. Light stimulation during single-unit recordings in freely-moving rats. (B) Stimulation testing sessions: in pre- and post-stim trials, rats freely procured pellets; in stim trials, optical stimulation prevented procurement of pellets. (C,D) During dPAG stimulation, animals showed increased outbound foraging time (C; Χ2 = 117.8, P < 0.0001, Friedman test; Ps < 0.0001, Dunn’s test) and decreased success rate (D; Χ2 = 154.0, P < 0.0001, Friedman test; Ps < 0.0001, Dunn’s test). ****P < 0.0001 compared to pre-robot and post-robot sessions. ####P < 0.0001 compared pre-robot session. (E) Subset of BLA units (10.0%) responsive to optical stimulation (Stim cells; left), and a representative (center) and all stimulation-responsive (nonStim cells; right) raster plots with PETHs. (F) Subset of animals underwent additional robot trials following the post-stim session. (G) Increased outbound foraging time during robot session compared to post-stimulation session (t(15) = 6.655, P < 0.0001; paired t-test). ****P < 0.0001. (H) Twenty-two BLA units were dPAG stimulation-responsive. (I) Representative raster plots of dPAG stimulation-responsive and -nonresponsive units. (J) Proportions of robot vs. non-robot cells differed between stimulation-responsive and -nonresponsive units (Χ2 = 11.134, P < 0.001; Chi-squared test). ***P < 0.001. (K) PETHs of stim and non-stim cells during stimulation and robot sessions. (L) Relationship between maximal firing rates during first 500 ms subsequent to robot activation and maximal firing rates during first 500 ms after stimulation onset (r(85) = 0.405, P < 0.001; Pearson correlation). (M) Population CCs with significant synchrony during robot session were higher than other sessions. Dotted vertical lines indicate 0-100 ms window for testing significance. Grey, blue, and dark yellow ***P < 0.001 compared to pre-stimulation, stimulation, and post-stimulation sessions, respectively. (N) Among synchronized BLA cell pairs, those including dPAG stimulation-responsive cell(s) (stim pairs; 61.5%) showed increased correlated firings (area under the curve, AUC, during 0-100 ms window) during the robot session compared to other sessions. In contrast, synchronized BLA cell pairs that consisted of stimulation non-responsive cells only showed no AUC differences across sessions. Grey *, blue **, and dark yellow **P < 0.05 compared to pre-stimulation, P < 0.01 compared to stimulation, and P < 0.001 compared to post-stimulation sessions, respectively. (O) Comparing CCs during testing windows (0-50 ms and 50-100 ms) between stim and non-stim pairs, stim pairs exhibited higher correlated firing than non-stim pairs during the 0-50 ms block (t(21.99) = 2.342, P = 0.0286; t-test), while displaying decreased correlated firings in the second block (50-100 ms; U = 42, P = 0.045; Mann-Whitney U test). *P < 0.05 compared to the non-stim pairs.