Characterization of periaqueductal grey circuits for top-down motor/autonomic control and bottom-up cardiac interoception in fear and anxiety.
Clinical Neurology; Neurosurgery and Neuroradiology
Molecular and Cellular Neurology and Neuropathology
Final Report Abstract
We were able to address all 3 objectives outlined in the original proposal. First, addressing neuroarchitecture of vlPAG circuit elements, we characterized the descending glutamatergic output to the dorsal vagal complex (DVC), through which ventrolateral periaqueductal grey (vlPAG) pathways may control cardiac function. Our work now adds important detail to this output pathway in that it shows differential density of inputs within DVC subregions, i.e. glutamatergic projections predominantly targeting the dorsal vagal motor nucleus (DMNV) over the nucleus of the solitary tract (NTS). In turn, the DVC receives GABAergic inputs from the central amygdala, which is a major source of inhibition to the vlPAG. The CEA GABAergic innervation of the DVC is particularly dense within the NTS, suggesting a route through which CEA could influence ascending interoceptive information flow in the NTS. Similarly, neuroanatomical tracings allowed us to identify a subgroup of inhibitory vlPAG neurons, a cluster of glycine-producing neurons, which receive strong ascending inputs from the NTS and specifically project to forebrain regions involved in the defense reaction, such as the lateral and ventromedial hypothalamus. Second, we used cell-type specific optogenetics to better understand the functional role of vlPAG circuit elements. Our data refines the current view of vlPAG network for defensive states in that we identified a novel circuit element, the Chx10-expressing neurons as a subgroup of glutamatergic neurons. These neurons specifically evoke a freezing concomitant with bradycardia microstate, whereas glutamatergic neurons activated together trigger freezing or flight responses, together with bradycardia. Intersectional approaches, together with gain- and loss-of-function experiments and in-depth comparison of spontaneous and optically evoked responses revealed that activation of Chx10 neurons resulted in naturalistic states whereas high intensity stimulation of glutamatergic vlPAG neurons induced non-natural cardio-behavioral states. Optogenetic investigation of glycinergic vlPAG neurons suggested a role for this vlPAG circuit element in specifically modulating cardiac microstate dynamics. Third, based on detailed description and analysis of a large data set of behavioral and cardiac dynamics during threat exposure, we developed a conceptual framework for better characterization of cardio-behavioral defensive states that serves as the basis for a comprehensive understanding of complex neuronal mechanisms underlying aversive emotions such as fear and anxiety. Novel analyses allowed us to define transient microstates and their interaction with longer-lasting macrostates to explain tachycardic as well bradycardic defensive responses and associated behavioural patterns. In addition to revealing cue- and context- dependency of integrated defense states, heart rate indices precisely identify defensive state transitions as well as contextual threat levels. The application of this framework to our characterization of glycinergic vlPAG neurons will allow us to better understand their role in regulating defensive states. Our data from miniscope-assisted recordings of calcium activity during threat exposure revealed strong associations between glycinergic neuronal activity and heart rate changes, consistent with the hypothesis that this circuit element plays a role in cardiac interoception. Overall, the complexity of the interplay between cardiac and behavioral components of the defense response forced us to invest a large amount of work into standardized data acquisition and novel data analyses of cardiobehavioral defensive state dynamics. Although this took considerable effort and time, it already constituted the basis for first circuit investigations, helps ongoing studies on cardiac interoception and will guide future studies addressing the neuronal basis for integrated defensive states. With this project, we took a step back with a stringent data-driven approach, to provide a framework for characterization of multimodal, integrated defensive states, thereby reopening a pathway towards translational research across species and from normal to maladapted fear and anxiety.
Publications
- A Critical Role for Neocortical Processing of Threat Memory. Neuron. 2019 Dec 18;104(6):1180-1194.e7
Dalmay T, Abs E, Poorthuis RB, Hartung J, Pu DL, Onasch S, Lozano YR, Signoret-Genest J, Tovote P, Gjorgjieva J, Letzkus JJ
(See online at https://doi.org/10.1016/j.neuron.2019.09.025) - Central amygdala micro-circuits mediate fear extinction. Nat Commun. 2021 Jul 6;12(1):4156
Whittle N, Fadok J, MacPherson KP, Nguyen R, Botta P, Wolff SBE, Müller C, Herry C, Tovote P, Holmes A, Singewald N, Lüthi A, Ciocchi S
(See online at https://doi.org/10.1038/s41467-021-24068-x) - Circuits for State-Dependent Modulation of Locomotion. Front Hum Neurosci. 2021 Nov 10;15:745689
Pernía-Andrade AJ, Wenger N, Esposito MS, Tovote P
(See online at https://doi.org/10.3389/fnhum.2021.745689) - A Versatile Synthetic Affinity Probe Reveals Inhibitory Synapse Ultrastructure and Brain Connectivity. Angew Chem Int Ed Engl. 2022 Jul 25;61(30):e202202078
Khayenko V, Schulte C, Reis SL, Avraham O, Schietroma C, Worschech R, Nordblom NF, Kachler S, Villmann C, Heinze KG, Schlosser A, Schueler-Furman O, Tovote P, Specht CG, Maric HM
(See online at https://doi.org/10.1002/anie.202202078) - Centralized gaze as an adaptive component of defensive states in humans. Proc Biol Sci. 2022 May 25;289(1975):20220405
Merscher AS, Tovote P, Pauli P, Gamer M
(See online at https://doi.org/10.1098/rspb.2022.0405) - Integrated cardio-behavioural defensive states
Signoret-Genest J, Schukraft N, Reis SL, Segebarth D, Tovote P
(See online at https://doi.org/10.1101/2022.09.22.509009)
