Dorsal premammillary projection to periaqueductal gray controls escape vigor from innate and conditioned threats

Abstract

Escape from threats has paramount importance for survival. However, it is unknown if a single circuit controls escape vigor from innate and conditioned threats. Cholecystokinin (cck)-expressing cells in the hypothalamic dorsal premammillary nucleus (PMd) are necessary for initiating escape from innate threats via a projection to the dorsolateral periaqueductal gray (dlPAG). We now show that in mice PMd-cck cells are activated during escape, but not other defensive behaviors. PMd-cck ensemble activity can also predict future escape. Furthermore, PMd inhibition decreases escape speed from both innate and conditioned threats. Inhibition of the PMd-cck projection to the dlPAG also decreased escape speed. Intriguingly, PMd-cck and dlPAG activity in mice showed higher mutual information during exposure to innate and conditioned threats. In parallel, human fMRI data show that a posterior hypothalamic-to-dlPAG pathway increased activity during exposure to aversive images, indicating that a similar pathway may possibly have a related role in humans. Our data identify the PMd-dlPAG circuit as a central node, controlling escape vigor elicited by both innate and conditioned threats.

Hippocampal-hypothalamic circuit controls context-dependent innate defensive responses

“…Fear of predators is an aversive emotional state that elicits defensive behaviors such as freezing and escape flight ( Wang et al, 2021a ; Gottfried et al, 2004 ; Clinchy et al, 2013 ). Therefore, we probed the emotional valence of AHN activation in a close loop real-time place avoidance assay (RTPA) ( Figure 2a and b ).…”

“…Interestingly, the same study identified the PMD, not the AHN, as the most responsive hypothalamic region to predatory context despite the relative scarcity of hippocampal innervation in the PMD. Furthermore, a recent study by Wang et al, 2021a found that the PMD activation evokes an organized escape in which mice quickly assess environment’s layout and find efficient flight path, whereas the activation of other hypothalamic nuclei, including the AHN and VMHdm/c, only induced stereotyped panic-related escape responses such as running and jumping ( Wang et al, 2021b ). We found that a direct AHN activation evokes panic-related running and jumping in an empty open field arena with no shelter.…”

“…Innate defensive behaviors are generated by the medial hypothalamic defensive system ( Canteras, 2002 ), consisting of the anterior hypothalamic nucleus (AHN) ( Fuchs et al, 1985 ; Lamontagne et al, 2016 ), the dorsomedial and central region of the ventromedial hypothalamus (VMHdm/c) Fuchs et al, 1985 ; Wang et al, 2015 ; Silva et al, 2016b ; Pérez-Gómez et al, 2015 and the dorsal premammillary nucleus (PMD) ( Canteras, 2002 ; Canteras, 2008 ; Wang et al, 2021a ; Wang et al, 2021b ). These three distinct nuclei are densely interconnected and become highly active upon predator exposure ( Dielenberg et al, 2001 ; Blanchard et al, 2005 ; Martinez et al, 2008 ; Mendes-Gomes et al, 2020 ) to control motor outputs at the level of periaqueductal gray (PAG) ( Evans et al, 2018 ; Wang et al, 2015 ; Canteras and Goto, 1999 ; Tovote et al, 2016 ).…”

Sparse genetically defined neurons refine the canonical role of periaqueductal gray columnar organization

“…Quantification showed that CCK-GFP cells comprise approximately 5% of l/vlPAG neurons and are more prevalent in the l/vlPAG than dlPAG ( Figure 1C ; n = 4, t (3) = 8.743, p=0.0032). CCK cells in several brain regions such as cortex, hippocampus, and amygdala are reported to be inhibitory ( Kepecs and Fishell, 2014 ; Mascagni and McDonald, 2003 ; Nguyen et al, 2020 ; Whissell et al, 2015 ), though glutamatergic CCK+ cells have also been reported in other regions ( Wang et al, 2021a ). To determine if these cells are glutamatergic, we immunostained against the glutamatergic marker vGlut2 in PAG slices containing GFP-expressing CCK+ cells ( Figure 1D ).…”

“…To address this question, we optogenetically activated l/vlPAG-CCK cells while introducing mice to live predator exposure ( Figure 6A ). In this assay, mice are placed in an elongated rectangular arena that contains an awake rat restrained to one end by a harness ( Reis et al, 2021a ; Wang et al, 2021a ; Wang et al, 2021b ). Rats are natural predators of mice, and mice exhibit robust defensive reactions during exposure to a live rat but not a similarly shaped toy rat such as increased freezing, increased distance from the live rat, and reduced time in the zone containing the live rat ( Figure 6B ; n = 10; freezing: t(9) = 3.519, p=0.0065; threat distance: t(9) = 13.09, p<0.0001; threat zone: t(9) = 7.604, p<0.0001; Wang et al, 2021b ).…”