Figure 6. Lateral/ventrolateral periaqueductal gray-cholecystokinin-expressing (l/vlPAG-CCK) activation robustly enhances avoidance from a live predator without altering freezing.

(A) Schematic of live predator exposure assay. Mice are placed in a long rectangular chamber (70 × 25 × 30 cm) containing an awake rat restrained with a harness to one end. The chamber does not contain a barrier and mice can move freely. The area containing the rat is considered a ‘threat zone,’ and the area furthest from the rat is considered a ‘safe zone.’ (B) Exposure to a live rat increased freezing and threat distance while reducing time in threat zone compared to exposure to a toy rat (n = 10, paired t-tests; freezing, ***p=0.0065; threat distance, ****p<0.0001; time in threat zone, ****p<0.0001). (C) EYFP or ChR2-eYFP was expressed in l/vlPAG-CCK cells and a fiber-optic cannula was implanted over the l/vlPAG. (D) Timeline of live predator assay. Blue light was delivered in alternating 2 min epochs during toy rat exposure and live rat exposure. (E) Example locomotion maps during laser-off (left) and laser-on (right) epochs of an eYFP mouse (top) and ChR2-eYFP mouse (bottom). (F–K) Optogenetic stimulation of l/vlPAG-CCK cells reduced time in threat zone (F; eYFP, n = 10; ChR2, n = 9; unpaired t-test, **p=0.0014), increased threat distance (G, unpaired t-test, **p=0.0048), and reduced stretch-attend postures (I, unpaired t-test, **p=0.0012). Number of approaches to the rat trended toward significance (H, #p=0.066). Freezing (J) and distance traveled (K) were not significantly affected. Errorbars: mean ± SEM.

Figure 6—figure supplement 1. Optogenetic activation of lateral/ventrolateral periaqueductal gray-cholecystokinin-expressing (l/vlPAG-CCK) neurons during toy rat exposure.

(A) Example locomotion maps during laser-off (left) and laser-on (right) epochs of an l/vlPAG-CCK-eYFP mouse (top) and an l/vlPAG-CCK-ChR2 mouse (bottom). Stimulation induced robust traversal of all four corners of the enclosure (bottom-right). (B–G) Optogenetic stimulation of l/vlPAG-CCK cells reduced time spent in threat zone (B, eYFP, n = 10, ChR2, n = 9; unpaired t-test, *p=0.0104), increased threat distance (C, eYFP, n = 10, ChR2, n = 9; unpaired t-test, **p=0.0032), increased number of approaches to the toy rat (D, eYFP, n = 10, ChR2, n = 9; unpaired t-test, **p=0.0011), reduced stretch bouts (E, eYFP, n = 10, ChR2, n = 9; unpaired t-test, *p=0.0107), and increased distance traveled (G, eYFP, n = 10, ChR2, n = 9; unpaired t-test, ***p=0.0002). Stimulation did not alter freezing (F). Errorbars: mean ± SEM.