Biology subjects

Mercer Lindsay, N.

Publications and source records attributed to Mercer Lindsay, N..

3 recordsLinked to original sources

bioRxiv2026

Layer 5 anterior cingulate cortical neurons engage dorsolateral periaqueductal gray excitatory neurons to facilitate the affective component of pain

Pain is a conscious perceptual experience characterized by its aversive quality and consequent motivation to quench pain perception. The anterior cingulate cortex (ACC) critically contributes to the emotional dimension of pain. In both humans and rodents, ACC neural activity increases during acute and chronic pain, whereas ACC lesioning or excitability reduction decreases emotional reactivity during pain. However, the ACC is connected to many brain regions and is engaged during experiences beyond pain. Thus, it remains unclear through which circuit mechanisms the ACC shapes pain experience, and how specific those circuits are to nociception. Here, we show that excitatory input from the ACC to the dorsolateral periaqueductal gray (dlPAG) facilitates the affective-motivational dimension of pain. We first examined ACC[->]dlPAG connectivity using histology, optogenetics, and electrophysiology. We found that the axons of layer 5 ACC neurons terminate in the dlPAG and monosynaptically excite Slc17a6+ (VGLUT2-expressing) dlPAG neurons. Second, we genetically targeted ACC[->]dlPAG neurons with viral vectors to express the inhibitory DREADD hM4Di and then exposed the animals to an array of pain tests. We found that, across acute and chronic pain states, inhibition of the ACC[->]dlPAG pathway reduced affective-motivational but not reflexive pain behaviors. Third, we used fiber photometry to record neural calcium activity in the ACC in behaving mice and found that ACC[->]dlPAG neurons are engaged during a broad array of aversive experiences, rather than exclusively during pain, and exhibit task-specific activity patterns. Collectively, these results uncover the direct contribution of ACC[->]dlPAG neural activity to pain unpleasantness and the necessity of this pathway for generating aversive behavioral responses in general, rather than specifically for encoding the unpleasant quality of noxious stimuli.

neuroscience↗

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↗

bioRxiv2022

Opioid receptor architecture for the modulation of brainstem functions

Opioids produce profound and diverse effects on a range of behaviors, many driven by brainstem activity; however, the presence of opioid and opioid-like receptors at this level has been poorly studied outside of nociceptive structures and components of respiratory circuitry. While previous studies identified expression of {micro}, {delta}, {kappa}, and nociceptin opioid and opioid-like receptors in the brainstem, patterns have not been fully delineated, and neither has receptor coexpression nor the behavioral implications of their expression in most structures. We aimed to elucidate expression patterns for all four receptors across somatosensory-motor, auditory, and respiratory brainstem circuits; identify recurring themes to provide insight into the mechanisms by which exogenous opioids affect broader brainstem circuits; and characterize the function of endogenous opioids in subcortical processing and behavior modulation. Using a fluorescent reporter mouse line for each receptor, we created a comprehensive atlas of brainstem receptor distribution and identified novel expression patterns in modality-specific circuits. Each receptor showed unique expression patterns across the brainstem with minimal correlation between receptors. Orofacial somatosensory-motor circuits expressed all four receptors, though generally in distinct regions, suggesting differential opiate modulation of afferent and efferent trigeminal signaling. Within the auditory circuits, receptors segregated along the vertical and horizontal processing pathways with minimal colocalization. Finally, the respiratory circuit strongly expressed the {micro} opioid receptor in multiple crucial structures with minimal presence of the other three receptors. We further assessed the functional significance of these expression patterns, using the respiratory circuitry as an example, by characterizing respiratory responses to selective opioid agonists, finding that each agonist caused unique alterations in breathing pattern and/or breath shape. Together, these results establish a comprehensive atlas of opioid and opioid-like receptor expression throughout the brainstem, laying the essential groundwork for further evaluation of opioid neuromodulation across the broad spectrum of behaviors.

neuroscience↗