SHEETS LAB
The main objectives of The Sheets laboratory are to elucidate the functional organization of circuit pathways involved in pain modulation and to understand how these same pathways are altered by different modalities of pain. Our lab uses a multifaceted approach (pain models in mice, retrograde labeling, slice electrophysiology, laser scanning photostimulation, high resolution imaging, optogenetics, behavior) to resolve these critical unknowns. The rationale for our work is that identifying the neural mechanisms through which pain alters circuit function in defined brain pathways will produce critical knowledge regarding the affective and emotional dimensions of pain. Such an understanding can lead to novel strategies for therapeutic intervention and improvement of clinical guidelines.
Reverse engineering mPFC pain circuits
We use transgenic breeding strategies to identify specific subtypes of inhibitory interneurons in the mPFC such as somatostatin (SOM+) or parvalbumin (PVIN). This approach allows for a multi-faceted analysis (electrophysiology, circuit mapping, high-resolution imaging, optogenetics) that aims to understand how acute or chronic pain alters activity of specific inhibitory neurons in the mPFC. These methods are useful when examining the dynamics of circuits in slice, and we aim to measure pain-induced changes to local connections of these inhibitory neurons onto specific subclasses of output excitatory neurons in the mPFC involved in descending pain modulation such as those projecting to the periaqueductal gray (PAG).
Elucidating the role of mPFC dynorphin circuits in the modulation of different pain states
Dynorphin (Dyn) is the endogenous opioid peptide that binds with high affinity to kappa opioid receptors (KORs), which are associated with mediating the negative valence (i.e. aversion component) of pain. Chronic pain increases transcription of Dyn in the mPFC, and injection of Dyn derivatives into the mPFC evokes placed aversion. These findings support the notion that Dyn+ mPFC circuits play a critical role in modulating negative valence associated with pain. Unfortunately, significant gaps in knowledge remain regarding 1) how Dyn-KOR signaling regulates the activity of mPFC circuits, 2) how mPFC Dyn+ circuit dynamics are altered in response to acute and chronic pain, and 3) how mPFC Dyn+ circuit activity modulates sensory and affective behaviors associated with pain. Addressing these knowledge gaps is critical for a complete understanding of how the brain assigns negative valence to pain, which is essential for developing new strategies aimed at treating sensory pain, affective pain and pain-associated comorbidities including anxiety, depression, mood-disorders and cognitive deficits.
Lipid signaling and the central amygdala
Neurons in the central amygdala (CeA) contribute to pain modulation. However, the heterogeneity of these neurons and their contribution to the sensory-discriminative and/or emotional-affective dimensions of chronic pain are not understood, nor is their neurochemical modulation. For this project we 1) Use transgenic mouse lines, retrograde labeling, electrophysiology, optogenetics, and behavior to test the hypotheses that CeA circuits are comprised of heterogeneous populations of neurons (based on intrinsic excitability, molecular markers, and long-range connectivity) that are differentially sensitized in various models of acute and chronic pain. 2) Test the hypotheses that the bioactive lysophospholipid, sphingosine-1-phosphate (S1P) differentially alters CeA neurons based on their molecular and intrinsic identity and that reducing S1P signaling reverses the sensitization of CeA neurons altered in various models of pain. 3) Determine if modulation of S1P receptor signaling in the CeA attenuates pain behavior (collab with Taylor Lab @ UPitt). Our preliminary data using slice recordings and behavioral pharmacology provides a compelling premise for the idea that S1P contributes to the endogenous inhibition of persistent inflammatory pain and chronic neuropathic pain. Experimental support of these novel concepts will facilitate the development of novel S1P compounds for the treatment of chronic pain.
Investigating the role of cortical circuitry in both pain and alcohol disorders
Alcohol consumption and chronic pain are strongly comorbid. Relative to the general population, patients with chronic pain are twice as likely to meet the criteria of alcohol use disorder. Similarly, chronic alcohol intake can exacerbate chronic pain progression and can heighten pain during abstinence. This suggests a potential overlap in alcohol and pain circuits, which facilitates a positive feedback loop that contributes the high incidence of comorbidity. Unfortunately, how these neural circuits are regulated in comorbid conditions of chronic pain and alcoholism is poorly understood. Lack of such knowledge is a serious problem because it prohibits a broader understanding of functional neural networks that may worsen both pain experience and alcohol dependence. The long-term goal of this project is to delineate the overlapping mechanisms of alcohol addiction and pain pathology so we can improve strategies for therapeutic approaches. Our primary collaborators for this work are the Lapish Lab at IUSM and the Atwood Lab at U Minnesota.
The combination of SNI and alcohol consumption increases the intrinsic excitability of AIC→DLS neurons.
Acute alcohol has no effect on local excitatory inputs but increases local inhibitory input currents on layer 2/3 neurons in the dmPFC.