73: Distinct vlPAG Neuronal Populations Orchestrate Integrated Nociceptive and Cardiac Responses

Topic: Basic Science
Subtopic: Non-specific to any diagnosis (including studies in healthy animals), Assessment and Measurement of Pain/Nociception, Neurocircuit modulation (could include opto, DREADDs), Behavioral studies

Background and Aims: Painful experience evokes coordinates behavioral, and autonomic responses, yet how these components are integrated at the cellular level remains poorly understood. The ventrolateral periaqueductal gray (vlPAG) is a central hub for response integration during defensive states, but whether distinct neuronal populations within the vlPAG differentially encode nociception and cardiac output is unclear. Previous work showed that activation of glutamatergic vlPAG neurons suppresses thermal nociception, increasing withdrawal latency in the tail immersion test (Tovote, 2016). Here, we further dissect the contribution of genetically defined vlPAG neurons to pain-related cardio-behavioral responses.

Methods: 1. Optogenetic activation of vGluT2⁺, Chx10⁺, Gad2⁺, and GlyT2⁺ vlPAG neurons;
2. Nociception testing: tail immersion assay (vGluT2⁺, Chx10⁺, Gad2⁺) and electric foot shock (GlyT2⁺);
3. Electrocardiogram;
4. Behavioral assessment: open field test and elevated plus maze;
5. Fluorescent fiber photometry of GlyT2⁺ neurons;
6. Anterograde and retrograde anatomical tracing of GlyT2⁺ neurons;
7. Chemogenetic activation and inhibition of GlyT2⁺ neurons.

Results: We demonstrate that a specific glutamatergic Chx10⁺ subpopulation evokes robust autonomic and behavioral responses, inducing bradycardia and immobility without altering thermal pain thresholds. Activation of GABAergic vlPAG neurons also fails to modulate thermal nociception. Yet, an inhibitory glycinergic GlyT2⁺ vlPAG population appears tuned to pain-associated autonomic regulation. Anatomical tracing indicates that GlyT2⁺ vlPAG neurons receive inputs from medullary viscerosensory and autonomic centers and project to forebrain and midbrain, positioning them to convey autonomic information to higher-order circuits. Optogenetic activation induces strong bradycardia without affecting locomotion. In vivo recordings show increased GlyT2⁺ neuron activity during painful events correlates with cardiac dynamics.

Conclusions: Together, our findings suggest both, functional specificity of distinct vlPAG cellular populations in mediating nociceptive and cardiac responses, as well as the existence of neuron populations serving as integrated state controllers.

References: Midbrain circuits for defensive behavior. Tovote P*#, Esposito* MS, Botta P, Chaudun F, Fadok JP, Markovic M, Wolff SBE, Ramakrishnan C, Fenno, L., Deisseroth K, Herry C, Arber S, Lüthi A#. Nature 534(7606): 206-212, 2016.

Presenting Author: Mia Wenyan Wu
Submitting Author: Mia Wenyan Wu

Senior Author: Philip Tovote

IASP 2026 Global Year theme of Neuropathic Pain: No

• Mia Wenyan Wu - Institute of Clinical Neurobiology, University Hospital Wuerzburg, Wuerzburg, Germany
• Sara L. Reis: PhD - Institute of Clinical Neurobiology, University Hospital Wuerzburg, Wuerzburg, Germany
• Fabio Felisati - Institute of Clinical Neurobiology, University Hospital Wuerzburg, Wuerzburg, Germany
• Nina Schukraft: PhD - Institute of Clinical Neurobiology, University Hospital Wuerzburg, Wuerzburg, Germany
• Jérémy Signoret-Genest: PhD - Institute of Clinical Neurobiology, University Hospital Wuerzburg, Wuerzburg, Germany; Center for Mental Health; University Hospital Wuerzburg, Wuerzburg, Germany
• Philip Tovote: PhD - Institute of Clinical Neurobiology, University Hospital Wuerzburg, Wuerzburg, Germany