Biology subjects

Posa, L.

Publications and source records attributed to Posa, L..

4 recordsLinked to original sources

bioRxiv2024

An opioid efficacy switch for reversible optical control of peripheral analgesia

The mu-opioid receptor (MOR) is a major target for the treatment of pain. However, opioids are prone to side effects which limit their effectiveness as analgesics and can lead to opioid use disorders or, even, lethal overdose. The systemic administration of opioid agonists makes it both very difficult to decipher their underlying circuit mechanisms of action and to limit drug action to specific receptor subpopulations to isolate therapeutic effects from adverse side effects. Here we design, synthesize, and characterize a reversibly photoswitchable morphinan agonist termed "azo-morphine-3" (AM-3) which interconverts from low to high efficacy in response to different wavelengths of light to enable optical control of MOR signaling. Cryo-EM structures of the low efficacy "trans" and high efficacy "cis" states of AM-3 bound to the MOR reveal distinct binding modes of the photoswitchable azobenzene moiety, each inducing unique structural dynamics, providing insight into the molecular basis of agonist efficacy. In mice, AM-3 drives reversible and repeatable optical control of anti-nociception with a reduced side effect profile owing to its restriction to the periphery and its ability to be locally activated at the site of pain.

pharmacology and toxicology↗

bioRxiv2024

Peripheral opioid tolerance involves skin keratinocytes and platelet-derived growth factor type B signaling

Opioid analgesic tolerance drives dose escalation which hampers the therapeutic utility of opioids by increasing centrally mediated deleterious side-effects, including respiratory depression or addiction. Peripheral opioid delivery provides a safer, effective alternative to systemic delivery by avoiding centrally mediated opioid side-effects. However, tolerance still occurs peripherally via mechanisms that remain unknown. Centrally, activation of the mu-opioid receptor (MOPr) by opioids induces release of platelet-derived growth factor-B (PDGF-B); and inhibition of PDGF receptor beta (PDGFR{beta}) prevents opioid tolerance. In the periphery, MOPr and PDGF-B are expressed in keratinocytes, and PDGFR{beta} is expressed in peripheral sensory neurons (PSNs), which are involved in tolerance. Previous studies showed that optogenetic stimulation of keratinocytes modulates PSNs via release of keratinocyte-derived factors. Thus, we hypothesized that mechanisms of peripheral opioid tolerance involve keratinocytes and PDGFR{beta} signaling. Using behavioral pharmacology, optogenetics and imaging in mice, we found that selective inhibition of peripheral PDGFR{beta} prevents peripheral morphine tolerance caused by repeated intraplantar (i.pl.) morphine injections. In addition, we show that PDGF-B is both necessary and sufficient to cause peripheral morphine tolerance. Repeated peripheral morphine injections lead to an increase in PDGF-B mRNA in MOPr-expressing keratinocytes and induce changes in the biophysical properties of keratinocytes as measured by patch-clamp electrophysiology. In parallel, we discovered that repeated optogenetic activation of keratinocytes is sufficient to induce peripheral morphine tolerance in a PDGF-B/PDGFR{beta}-dependent manner. Together, we show a novel epithelial-neuronal communication mechanism that incorporates keratinocytes and PDGF-B/PDGFR{beta} to mediate peripheral opioid tolerance, opening the door to safer, more effective pain therapeutics. Significance StatementPeripheral opioids are a safer alternative to systemic opioids. However, peripheral tolerance leads to reduction of analgesia over time, hampering clinical use of peripheral opioids. Here, we highlight a novel epithelial-neuronal communication mechanism that mediates peripheral tolerance. We discovered that intraplantar (i.pl.) morphine injections in mice cause peripheral tolerance via release of platelet-derived growth factor type B (PDGF-B) and activation of platelet-derived growth factor beta (PDGFR{beta}). We find that morphine i.pl. increases PDGF-B in mu-opioid receptor-expressing keratinocytes, which could be released to activate PDGFR{beta} in cutaneous nociceptor endings to mediate peripheral tolerance. Moreover, we show that photostimulation of keratinocytes is sufficient to cause peripheral tolerance in a PDGF-B/PDGFR{beta}-manner. Thus, keratinocytes and PDGF-B are new promising targets for peripheral opioid tolerance.

neuroscience↗

bioRxiv2023

Elevated serotonin in mouse spinal dorsal horn is pronociceptive

Serotonergic neurons in the rostral ventral medulla (RVM) contribute to bidirectional control of pain through modulation of spinal and trigeminal nociceptive networks. Deficits in this pathway are believed to contribute to pathological pain states, but whether changes in serotonergic mechanisms are pro or anti-nociceptive are debated. We used a combination of optogenetics and fiber photometry to examine these mechanisms more closely. We find that optogenetic activation of RVM serotonergic afferents in the spinal cord of naive mice produces mechanical hypersensitivity and conditioned place aversion. Neuropathic pain, produced by chronic constriction injury of the infraorbital nerve (CCI-ION), evoked a tonic increase in serotonin concentrations within the spinal trigeminal nucleus caudalis (SpVc), measured with liquid chromatography-tandem mass spectroscopy (LC-MS/MS). By contract, CCI-ION had no effect on the phasic serotonin transients in SpVc, evoked by noxious pinch, and measured with fiber photometry of a serotonin sensor. These findings suggest that serotonin release in the spinal cord is pronociceptive and that an increase is sustained serotonin signaling, rather than phasic or event driven increases, potentiate nociception in models of chronic pain. Significance StatementSerotonergic neurons of the rostral ventral medulla participate in descending pain modulation by regulating spinal and trigeminal nociceptive circuits. Whether changes in serotonergic mechanisms are pro or anti-nociceptive is debated. We show that serotonin release within the spinal trigeminal nucleus is pronociceptive and that enhanced tonic, but not phasic serotonin release may contribute to sensitization in mouse models of chronic pain. These results further clarify the role of serotonin in nociception and suggest that local inhibition of serotonin release or increase of uptake may be a viable therapeutic approach in treating chronic pain.

neuroscience↗

bioRxiv2022

Noradrenergic input from nucleus of the solitary tract regulates parabrachial activity in mice

The parabrachial complex (PB) is critically involved in aversive processes, and chronic pain is associated with amplified activity of PB neurons in rodent models of neuropathic pain. Here we demonstrate that catecholaminergic input from the caudal nucleus of the solitary tract (cNTScat)--a stress responsive region that integrates intero- and exteroceptive signals--causes amplification of PB activity and their sensory afferents. We used a virally mediated expression of a norepinephrine (NE) sensor, NE2h, fiber photometry, and extracellular recordings in anesthetized mice to show that noxious mechanical and thermal stimuli activate cNTS neurons. These stimuli also produce prolonged NE transients in PB that far outlast the noxious stimuli. Similar NE transients can be evoked by focal electrical stimulation of cNTS, a region that contains the noradrenergic A2 cell group that projects densely upon PB. In vitro, optical stimulation of cNTScat terminals depolarized PB neurons and caused a prolonged increase the frequency of excitatory synaptic activity. A dual opsin approach showed that sensory afferents from the caudal spinal trigeminal nucleus are potentiated by cNTScat terminal activation. This potentiation was coupled with a decrease in the paired pulse ratio, consistent with an cNTScat - mediated increase in the probability of release at SpVc synapses. Together, these data suggest that A2 neurons of the cNTS generate long lasting NE transients in PB which increase excitability and potentiate responses of PB neurons to sensory inputs. These reveal a mechanism through which stressors from multiple modalities may potentiate the aversiveness of nociceptive stimuli. Significance StatementIncreased excitability of the parabrachial nucleus (PB), a key integrative hub for aversive stimuli, is linked to amplified pain behaviors. We show that prolonged norepinephrine (NE) transients in PB following noxious stimulation in mice. These NE transients potentiate sensory input to PB and arise, at least in part, from catecholaminergic projections from the caudal nucleus of the solitary tract (cNTScat). We propose that activity this cNTScat to PB pathway may potentiate the aversiveness of pain.

neuroscience↗