Periodic Reporting for period 1 - DescendPain (Descending control of pain)
Période du rapport: 2023-01-01 au 2025-06-30
Pain is a large societal and health problem. Although often thought of as an invariant representation of active nociceptors, pain varies a lot under the influence of different mental states, with near complete analgesia in, for example, acute stress situations. Such modulation of pain is thought to occur through a descending pathway originating in the brain and to be executed by Rostral Ventromedial Medulla (RVM) neurons that project to the spinal cord. Deciphering the complexity of the cell types involved and how they contribute to the descending control of pain has been challenging, but recent advances in single-cell omics, computational biology and advanced genetic technologies now open for unbiased system-wide insights.
DescendPain will uncover the power of the brain to control pain. We will classify RVM neuron types by single-cell RNA-sequencing and use scRNAseq-based stimulus-to-cell-type mapping to identify neuronal ensembles (or “modules”) conferring analgesia and hyperalgesia during morphine, naloxone, stress, sleep deprivation and exercise. Using activity-based mouse genetics, we will reveal the full complexity of the combinations of neurons engaged and unravel their role in pain modulation, thus identifying for the first time the cellular basis for how cognitive and emotional states modulate pain. We will also use novel intersectional strategies—combining virus-based technologies and scRNAseq with new technologies for dual capturing of active neurons—to determine how the descending RVM controls the transmission of pain in the ascending pathway of the spinal cord. Finally, we will identify the memory substrate underlying chronic pain, providing evidence for the existence of RVM neuron ensembles of chronic pain and revealing underlying cellular and molecular mechanisms.
DescendPain will uncover the power of the brain to control pain. We will classify RVM neuron types by single-cell RNA-sequencing and use scRNAseq-based stimulus-to-cell-type mapping to identify neuronal ensembles (or “modules”) conferring analgesia and hyperalgesia during morphine, naloxone, stress, sleep deprivation and exercise. Using activity-based mouse genetics, we will reveal the full complexity of the combinations of neurons engaged and unravel their role in pain modulation, thus identifying for the first time the cellular basis for how cognitive and emotional states modulate pain. We will also use novel intersectional strategies—combining virus-based technologies and scRNAseq with new technologies for dual capturing of active neurons—to determine how the descending RVM controls the transmission of pain in the ascending pathway of the spinal cord. Finally, we will identify the memory substrate underlying chronic pain, providing evidence for the existence of RVM neuron ensembles of chronic pain and revealing underlying cellular and molecular mechanisms.
Opioids have been used for medicinal and recreational purposes for millennia. They constitute a broad group of pain-relieving medicines, which includes morphine, that remain effective treatments for managing pain today. Opioids attach to opioid receptors in brain cells, not only blocking pain messages but also boosting feelings of pleasure. As a result, the use of opioids for pain relief has led to growing dependence, abuse, overdose, and death. Insight into the cells and neural pathways that provide pain relief is needed to explain how morphine can have such a powerful analgesic effect as well as how they differ from neurons and pathways eliciting feelings of euphoria, well-being, and addiction. Despite decades of research, the exact neural circuit that is responsible for pain relief has remained blurred. We found that the RVM consists of multiple molecular types of γ-aminobutyric acid–mediated (GABAergic) neurons as well as a few types of glutamatergic and serotonergic neurons. Among these, morphine activated a select set of neurons, which together formed a “morphine ensemble.” Synthetic activation of the genetically captured morphine ensemble produced mechanical pain relief, mimicking the effects of morphine, and its inactivation completely abolished the effects of morphine on pain. Among the neurons in the ensemble, glutamatergic neurons projecting to the spinal cord called RVMBDNF neurons (BDNF, brain-derived neurotrophic factor) were essential. Within the spinal cord, RVMBDNF neurons were connected to GABAergic inhibitory neurons expressing the neuropeptide galanin (SCGal neurons). Inhibition of SCGal neurons completely prevented pain inhibition after administration of morphine or synthetic activation of the RVMBDNF neurons. Notably, the neurotrophic factor BDNF produced within the RVMBDNF neurons was necessary for morphine to have any effect on the sensitivity to painful stimuli. Conversely, increasing BDNF expression in the RVMBDNF neurons markedly potentiated morphine’s effects, with efficacy at doses where morphine alone was insufficient.
We discovered that neural activity alone in the RVM induces the key features of morphine-induced mechanical pain relief, and when this activity is inhibited, morphine has little effect. Pain relief is mediated by glutamatergic RVMBDNF neurons projecting to inhibitory SCGal neurons, which attenuate incoming pain signalling in the spinal cord on the way to the brain. Within this circuit, BDNF is an essential component modulating neurotransmission. Finding the molecular identity of neurons that regulate morphine-induced antinociception advances the search for alternative therapeutic strategies to provide pain relief across various pain conditions.