Baer, T. M. | bioRxiv Science

bioRxiv2026

Opioid- and NMDA-receptor-dependent neural plasticity mediates long-term analgesia from motor cortical stimulation

Exogenous opioids that activate -opioid receptors (MORs) in nociceptive circuits mediate transient pain relief lasting minutes to hours but have more limited utility for treating chronic pain. By comparison, electrical or magnetic stimulation of the motor cortex can induce pain relief lasting weeks, for which the underlying mechanisms have remained unclear. Here we report an unconventional role for endogenous opioidergic signaling in the rapid induction of long-lasting analgesia from motor cortical stimulation, which triggers opioid-peptide-dependent neural plasticity in the rostral ventromedial medulla (RVM), a key node in the brains descending pain control pathways. To dissect the circuit and cellular bases for these effects, we created a miniaturized, millimeter-sized device allowing focal, non-invasive transcranial magnetic stimulation (TMS) of the mouse motor cortex. In mice with chronic neuropathic pain, reflexive and affective pain behaviors diminished for 1-2 weeks after one session of TMS treatment. Chemogenetic and optogenetic manipulations showed that motor cortical layer 5 pyramidal neurons with axonal projections to the RVM mediated TMS-induced pain relief. High-density electrophysiological recordings revealed that TMS treatment shifted the balance of RVM activity between pain-ON and pain-OFF neurons to a state promoting greater suppression of pain. Genetic and neuropharmacological manipulations revealed that NMDA-receptor-dependent signaling and MOR activation by endogenous opioid peptides in the RVM jointly mediate the long-lasting analgesia induced by a transient bout of TMS. Strikingly, enkephalinase inhibition in the RVM during TMS treatment enhanced the amplitude and duration of analgesia, showing that transiently boosting endogenous opioidergic signaling during TMS increases analgesia-conferring plasticity. In accord, re-analyses of data from human subjects with chronic pain support the idea that opioid administration amplifies analgesia from motor cortical TMS. Overall, our results showcase miniaturized TMS devices as versatile tools for basic and translational neuroscience and detail a hybrid, long-range neural network and NMDA- and opioid-receptor-dependent plasticity mechanism for durable pain relief. These findings point the way to mechanistically grounded, synergistic neurostimulation and drug therapies for brain diseases and disorders that jointly target neural circuit and molecular signaling pathways.

neuroscience↗

bioRxiv2023

A BCG Skin Challenge Model for Assessing TB Vaccines

Controlled Human infection models (CHIM) are valuable tools for assessing relevant biological activity in vaccine candidates, with the potential to accelerate Tuberculosis vaccine development into the clinic. Tuberculosis infection poses significant constraints on the design of a CHIM using the causative agent Mycobacterium tuberculosis. As a safer alternative, we propose a challenge model using the attenuated vaccine agent Mycobacterium bovis BCG as a surrogate for Mycobacterium tuberculosis, and intradermal (skin) challenge as an alternative to pulmonary infection. We have developed a unique non-invasive imaging system based on fluorescent reporters to quantitatively measure bacterial load over time, thereby determining a relevant biological vaccine effect. We assessed the utility of this model to measure the effectiveness of two TB vaccines: the currently licenced BCG and a novel subunit vaccine candidate. To assess the efficacy of the skin challenge model a pharmacometric model was built describing the decline of fluorescence over time. The results show that vaccination is a statistically significant factor which reduced the fluorescence readout of both fluorophores. The higher decline in vaccinated mice correlated with bacterial burden in the lungs. This supports the fluorescence output from the skin as a reflection of vaccine induced functional pulmonary immune responses. This novel non-invasive approach allows for repeated measurements from the challenge site, providing a dynamic readout of vaccine induced responses over time. This BCG skin challenge model represents an important contribution to the ongoing development of controlled challenge models for Tuberculosis.

microbiology↗