Overview

   Research in the Banghart Lab aims to understand how neuromodulatory signaling contributes to physiological processes such as pain modulation, associative learning, and behavioral reinforcement. Major focus areas include the role of endogenous opioid neuropeptide and biogenic amine neurotransmitters in top-down pain modulation, as well as the molecular mechanisms that regulate neuropeptide secretion from neurons. Our approach is multi-faceted and interdisciplinary. To understand neuromodulation at the circuit level, we rely on contemporary "circuit hacking" methods such as chemogenetic and optogenetic manipulations, as well as in vivo imaging of Ca2+ and neuromodulator signaling in awake, behaving mice. To uncover the underlying cellular, synaptic, and molecular mechanisms, we rely on electrophysiological and fluorescence imaging experiments in brain slices. Uniquely, our in vivo and ex vivo studies are complemented, and sometimes driven entirely, by the in-house development of photopharmacological tools for manipulating neuromodulatory signaling with high spatiotemporal precision. 

Current projects

Neuromodulatory control of pain perception

Pain perception is highly malleable. Our detection and interpretation of pain are not only shaped by analgesic drugs (e.g. opiates), but also by internal state and prior experience (e.g. stress-induced analgesia and placebo analgesia). Neuromodulators such as endogenous opioid neuropeptides and biogenic amines, including serotonin and noradrenaline, are involved in both pharmacological and cognitive pain modulation. Despite the clinical importance, our understanding of the neural circuit mechanisms by which these and other neuromodulators are recruited by drugs and top-down processes, and of how they act in target circuits to shape pain perception are incomplete. 

We aim to uncover the neural pathways by which opiate drugs and cognitive processes related to expectation and learned association engage pain modulatory systems to regulate nociception and pain processing. We are particularly interested in understanding 1) neural circuit mechanisms by which top-down pain modulatory pathways engage the descending pain modulatory system, and 2) how endogenous opioid peptide and biogenic amine signaling is orchestrated within these descending circuits. To address these issues, we employ a combination of anatomical and histological methods, behavioral pharmacology, chemogenetic and optogenetic manipulations in vivo, as well as brain slice electrophysiology. These studies are driven in part by the availability of light-activated opioid drugs developed in our lab. To help address the current epidemic of opioid-related deaths in America, a long-term goal of this work is to develop non-addictive analgesics. We are grateful to the Rita Allen Foundation for supporting this research. 

Molecular mechanisms of neuropeptide release

Neuropeptidergic signaling contributes to numerous fundamental physiological processes ranging from pain modulation to sleep, feeding, and reproduction. Recent large-scale single-cell RNAseq studies indicate that nearly every neuron in the brain is likely to release one or more neuropeptides, in addition to a fast neurotransmitter such as glutamate or GABA (Smith SJ et. al., eLife, 2019). In contrast to fast synaptic transmission, relatively little is known about the neural activity patterns and biochemical signals that govern the release of neuropeptides from dense-core vesicles. In general, dense-core vesicle exocytosis follows "high frequency activity," but the precise activity patterns, the underlying molecular pathways, the subcellular sites of neuropeptide release, and the regulation of these features by biochemical signaling within neurons are all poorly understood. 

We aim to understand the cellular and molecular pathways that regulate neuropeptide release from mammalian central neurons. Our efforts are currently focused on the the release of dynorphin and substance P from striatonigral neurons and enkephalin from striatopallidal neurons. To detect neuropeptide secretion, we rely on slice electrophysiology and both ex vivo and in vivo imaging. Our imaging experiments are largely driven by the development of genetically-encoded optical neuropeptide sensors by our collaborator Lin Tian at UC Davis. Our studies into the fundamental mechanisms of dense-core vesicle secretion are generously supported by the NIGMS.

​The lessons learned in striatum, which  contains many peptide-releasing neurons, are guiding our studies into peptide release in other pain modulatory circuits.

Neuropeptide photopharmacology

The ability to control brain function with light (i.e. optogenetics) has revolutionized neuroscience, in part by providing a well-defined, time-locked stimulus to which physiological responses can be quantitatively associated. While traditional pharmacological probes can provide critical information about the role of specific neurochemical pathways in biological processes, the inability to precisely control the location and timing of drug and peptide action has limited our understanding of how their actions in specific brain regions impact neural activity and behavior. Because neuropeptides activate GPCRs, which are prone to desensitization, the ability to study responses within seconds-to-minutes of receptor activation is particularly critical.

Using synthetic chemistry, we are developing photopharmacological tools that allow endogenous neuropeptide receptors to be activated or inhibited with light. We have published extensively on "caged" opioid neuropeptides and their implementation in ex vivo brain slice preparations to study opioid receptor signaling pathways. We are currently extending this approach to additional neuropeptide targets through a BRAIN Initiative funded effort, with an emphasis on novel peptide caging strategies. We have also developed caged small molecule opioid drugs that can be administered systemically in rodents and photoreleased in vivo through optical fibers implanted in the brain. We are currently extending this approach to other neuroactive small molecules. 

Our studies with caged opioid peptides and drugs demonstrate how photopharmacological reagents provide a robust stimulus-response relationship that can serve as the foundation of quantitative studies into not only receptor signaling mechanisms, but also neural circuit mechanisms that underlie neural and behavioral responses to drug action. We hope to translate these efforts in the context of non-addictive analgesics.