Michael R. Tadross - US grants

ABSTRACT. DART2.0: comprehensive cell type-specific behavioral neuropharmacology Neuro-active drugs have provided hope to millions. However, a major gap in identification of novel therapeutic targets can be attributed to a poor understanding of how neuropharmaceuticals work at the circuit level; in particular, how behavioral effects of drugs are mediated by individual neuron types in the brain. As a preliminary step to address this gap, we developed DART (drugs acutely restricted by tethering), the first and only method to date that enables behavioral effects of clinically relevant drugs to be deconstructed with cellular specificity. This proposal aims to substantially expand the chemical diversity of DART ligands, enabling cell type specific and bi-directional control of key ionotropic receptors, neuromodulatory receptors, reuptake transporters, and voltage-gated ion channels. In a parallel effort, the genetic components of DART will be engineered to afford subcellular drug localization and to improve ease- of-use for multiplexing with recording devices and interrogation of large brain volumes. The overarching objective is to maximize adoption by empowering the neurobiology community to address previously intractable questions of broad public-health relevance. Reagents will be characterized in vitro and in vivo, and a robust system of authentication and distribution will be implemented. The decision to prioritize ease- of-use and commitment to the free dissemination of reagents are likely to pay dividends in overall impact.

Abstract Animal behavior depends on diverse neuronal cell types whose dynamic activity is shaped by many receptors. However, because receptors are often broadly expressed, it has been difficult to manipulate a specific receptor on a defined cell type. The resulting knowledge gap has significant implications for understanding normal and aberrant behaviors. As a preliminary step to address this gap, we recently developed DART (Drugs Acutely Restricted by Tethering), a genetically encoded drug-targeting technology that offers the first opportunity to establish behavioral roles of a specific receptor on a defined cell type. This proposal aims to expand applicability of DART to diverse neurobiological preparations and promote widespread adoption of the technology. The proposal will: (1) minimize barriers to entry with a universal and easy to use whole-brain DART delivery platform; (2) maximize payoff by enabling bidirectional control of key excitatory, inhibitory, and neuromodulatory receptors; and (3) demonstrate conceptual utility of the approach as applied to a previously intractable neuro-dynamics debate of broad interest. If successful, the resulting innovations may impact the hypotheses that drive the upcoming decade of neurobiology.

Parkinson?s disease (PD) is a debilitating neurodegenerative movement disorder, characterized by loss of dopaminergic cells. Primary treatments have relied on replenishing dopamine (e.g. levodopa), however, over time these drugs lose efficacy and lead to incapacitating levodopa induced dyskinesias (LID). These shortcomings suggest that PD cannot be understood or treated by dopaminergic pathways alone. Among non- dopaminergic mechanisms, synaptic receptors are prime candidates for manipulation, however relevant experiments have thus far not yielded promising results. These interventions have suffered from a lack of cellular specificity?the striatum, robustly implicated in PD, contains distinct cell types with opposing behavioral functionality. The inability to target pharmacological agents to just one of these cell types has produced a major gap in the understanding and treatment of PD. To address this limitation, we recently developed DART (Drugs Acutely Restricted by Tethering), a genetically encoded drug-targeting technology that offers the first opportunity to establish behavioral roles of a specific receptor on a defined cell type. In this proposal we will apply cell type- specific synaptic receptor interventions in PD and LID in mouse models. This work will provide unprecedented circuit and molecular insights into PD and LID pathophysiology. In addition, it may provide a roadmap for cell type-specific restriction as a potentially general paradigm for increasing drug efficacy.

ABSTRACT: Interrogating the cholinergic basis of opioid use disorder Opioids offer unmatched clinical efficacy in the treatment of pain, and offer pronounced therapeutic potential in the treatment of anxiety, depression, and psychosis. Nevertheless opioids come with equally harmful side effects that can lead to opioid use disorder. Three major subtypes of opioid receptors have been identified, which are each expressed in numerous cells. Because traditional drugs impact all cells in a given volume, it has been difficult to map cell type-specific contributions of drug-mediated behavior. To address this gap, we developed DART (drugs acutely restricted by tethering), which works by genetically programming a subset of cells to capture and concentrate a specific drug to levels ~1000 times higher than anywhere else, thus restricting drug action to the chosen subset of cells. Here, we propose to develop, characterize, and distribute a comprehensive toolset focused on opioid neuropharmacology. As a roadmap for the widespread adoption of these reagents, we propose behavioral experiments motivated by a recent double-blind placebo-controlled trial in which a cholinergic drug demonstrated efficacy in the treatment of opioid use disorder. We will test the hypothesis that ?ORs on cholinergic interneurons mediate the harmful (addictive) effects of opioids, independent of helpful (analgesic) effects. The proposed technologies will offer the unprecedented opportunity to establish causal behavioral roles of opioid neuropharmaceuticals mediated by defined cell types. Because the technologies are rooted in therapeutically relevant neuropharmaceuticals, clinical relevance is provided without the need to sacrifice mechanistic rigor.