Cite as: Hines R, Cichon J. Research grant updates. ASRA Pain Medicine News 2025;50. https://doi.org/10.52211/asra050125.014.

2024 Graduate Student Award

Regan Hines

Examining Effects of Pain on Sphingosine-1-Phosphate and Neurons of the Central Amygdala

Signaling pathways of sphingosine-1-phosphate (S1P), a bioactive sphingolipid, have been established as a promising therapeutic target for treating multiple sclerosis, including improvement in pain symptoms with approved drugs currently being administered clinically.^1-3

My interest lies in determining the mechanisms by which S1P signaling modulates pain circuits in the central nervous system, particularly in the brain. The remaining unknowns address where and how S1P signaling regulates activity in the brain. Exogenous application of an agonist for the primary receptor of S1P, S1PR¹, broadly evokes activity in the central amygdala (CeA).^4-6 This is of interest in the pain field as the CeA is a key region in processing ascending nociceptive inputs⁷ and modulating sensory and affective dimensions of pain.⁸ The CeA consists of a heterogeneous population of neurons.⁹ One major subclass of CeA neurons expresses corticotropin-releasing hormone (CRH; CeA^CRH+ neurons) that are excited by acute neuropathic pain, while another major subclass expressing somatostatin (SST; CeA^SST+ neurons) is inhibited by acute nerve injury.¹⁰ Therefore, both subclasses of CeA neurons likely play a significant role in pain processing. Still, the mechanisms by which pain drives changes to the circuit and synaptic function of these neurons remain unclear. With the support of this grant, I have begun to investigate the hypothesis that bioactive sphingolipid S1P regulates synaptic activity onto CeA^CRH+ and CeA^SST+ neurons in a neuropathic pain model.⁶

My work on this project has primarily consisted of whole-cell patch clamp electrophysiology recordings from fluorescently labeled CeA^CRH+ and CeA^SST+ neurons in acute brain slices from mice. My current data have revealed distinct effects on the synaptic activity of CeA^CRH+ and CeA^SST+ neurons in the spared nerve injury (SNI) model of neuropathic pain, as well as the application of an S1PR¹ agonist. At postoperative day 14 , excitatory inputs onto CeA^CRH+ neurons are unaffected by SNI. Interestingly, the addition of an S1PR¹ agonist only decreases synaptic activity in CeA^CRH+ neurons from uninjured mice with the effect lost in SNI mice. At this same point in time , CeA^CRH+neurons from SNI mice have increased inhibitory synaptic input, and the application of an S1PR¹ agonist reduces inhibitory synaptic input back to levels similar to those of uninjured mice. Interestingly, neither SNI nor an S1PR¹agonist has any effect on CeASST+ neurons, although there is considerable variability among all experimental groups, suggesting that there may be different populations of CeA^SST+ neurons.¹¹ Together, my data indicate that neuropathic pain differentially affects molecularly distinct populations of CeA neurons and that S1PR₁ can modulate neurotransmission to specific CeA neuronal subtypes. Future experiments will further dissect pain-induced and S1P-induced changes in distinct synapses onto CeACRH+ and CeASST+ neurons, both in the SNI pain model and the Complete Freund's Adjuvant model of inflammatory pain.

1. Quancard J, Bollbuck B, Janser P et al. A potent and selective s1p(1) antagonist with efficacy in experimental autoimmune encephalomyelitis. Chem Biol 2012;19:1142-51. https://doi.org/10.1016/j.chembiol.2012.07.016
2. Chaudhry BZ, Cohen JA, Conway DS. Sphingosine 1-phosphate receptor modulators for the treatment of multiple sclerosis. Neurotherapeutics 2017;14:859-73. https://doi.org/10.1007/s13311-017-0565-4
3. Marciniak A, Camp SM, Garcia JGN,et al. An update on sphingosine-1-phosphate receptor 1 modulators. Bioorg Med Chem Lett 2018;28:3585-91. https://doi.org/10.1016/j.bmcl.2018.10.042
4. Waeber C, Chiu ML. In vitro autoradiographic visualization of guanosine-5'-o-(3-[35s]thio)triphosphate binding stimulated by sphingosine 1-phosphate and lysophosphatidic acid. J Neurochem 1999;73:1212-21. https://doi.org/10.1046/j.1471-4159.1999.0731212.x
5. Selley DE, Welch SP, Sim-Selley LJ. Sphingosine lysolipids in the CNS: endogenous cannabinoid antagonists or a parallel pain modulatory system? Life Sci 2013;93:187-93. https://doi.org/10.1016/j.lfs.2013.06.004
6. Sim-Selley LJ, Goforth PB, Mba MU, et al. Sphingosine-1-phosphate receptors mediate neuromodulatory functions in the CNS. J Neurochem 2009;110:1191-202. https://doi.org/10.1111/j.1471-4159.2009.06202.x
7. Carrasquillo Y, Gereau RW. Activation of the extracellular signal-regulated kinase in the amygdala modulates pain perception. J Neurosci 2007;27:1543-51. https://doi.org/10.1523/JNEUROSCI.3536-06.2007
8. Neugebauer V, Li W, Bird GC, et al. The amygdala and persistent pain. Neuroscientist 2004;10:221-34. https://doi.org/10.1177/1073858403261077
9. Dumont EC, Martina M, Samson RD,et al. Physiological properties of central amygdala neurons: Species differences. Eur J Neurosci 2002;15:545-52. https://doi.org/10.1046/j.0953-816x.2001.01879.x
10. Kiritoshi T, Yakhnitsa V, Singh S, et al. Cells and circuits for amygdala neuroplasticity in the transition to chronic pain. Cell Rep 2024;43:114669. https://doi.org/10.1016/j.celrep.2024.114669
11. Mork BE, Lamerand SR, Zhou S, et al. Sphingosine-1-phosphate receptor 1 agonist sew2871 alters membrane properties of late-firing somatostatin-expressing neurons in the central lateral amygdala. Neuropharmacology2022;203:108885. https://doi.org/10.1016/j.neuropharm.2021.108885

2024 Chronic Pain Medicine Grant

Joseph Cichon

Investigating the Therapeutic Potential of Psychedelic Medicines in Rodent Models of Chronic Pain

Chronic pain and mood disorders coexist, exacerbate one another, and share neurobiological mechanisms, but whether a single intervention could promptly treat both conditions remains unclear. In two established chronic pain models, the Cichon lab shows that a single dose of psilocybin induces a rapid and sustained rescue of both mechanical allodynia and anxio-depression-like states in adult rodents. Using local psilocin injections, the key active metabolite of psilocybin, we pinpointed the engagement of prefrontal cortical circuits as critical for the concurrent alleviation of both conditions. Two-photon calcium imaging reveals that psilocin rapidly normalizes chronic pain-associated hyperactivity in anterior cingulate cortex layer 2/3 pyramidal neurons, suggesting the effect involves local serotonergic receptor signaling. Specific pharmacologic manipulations of 5-HT2A and 5-HT1A receptor signaling suggest that psilocin's cellular and behavioral effects are mediated through a combinatorial mechanism of partial agonism within shared circuits involved in pain and mood processing, providing new insights into its therapeutic potential.