The proposed research brings cutting-edge genetic tools to bear on understanding the neural circuitry under- lying aggression and motivated behavior. Our recent progress reveals that these behaviors in mice are regu- lated by two molecularly distinct, small subsets of brain serotonergic (5-HT) neurons: one subset, ~3,000 neurons, uniquely defined among 5-HT neurons by expression of the D1 dopamine (DA) receptor (Drd1a gene), and the other, ~1,000 neurons, by the D2 DA receptor (Drd2 gene). These results combined with the enabling genetic tools, like a powerfully sharpened wedge, can now be used to """"""""break open"""""""" and access the circuitry, cellular properties, and molecular pathways underlying these consequential behaviors. Here we propose applying this """"""""wedge"""""""" in the form of four aims to answer: What cellular and molecular properties are unique to these behavior-critical 5-HT neurons? As suggested by receptor expression, are these 5-HT neu- rons responsive to DA - a neurochemical commonly associated with the reward system of the brain? Through what forebrain circuitry do these subtypes modulate aggression and motivation? Do these parame- ters change across the life span, perhaps bearing on human age-related propensity for impulsivity, aggres- sion, and substance abuse? In Aim 1, we will identify functional properties of the Drd1a and Drd2 5-HT neu- ron subtypes by transcriptional profiling (RNA-seq) and electrophysiological recording. This work is enabled through novel genetic tools for neuron subtype-specific marking, suitable for neuron subtype sorting and mo- lecular profiling, and for whole-cell recording. These same genetic tools not only offer access to the soma of a 5-HT neuron subtype, but also to axons and terminals, thus allowing precise identification of target brain re- gions under neuron-subtype control - the goal of Aim 2. Functional postsynaptic connections will also be ex- plored, with our intersectional genetic marking tools conferring unprecedented resolution to classic tract- tracing techniques as well as to cutting-edge viral approaches that involve trans-synaptic tracers. Thus, Aim 2 will define, label, and allow for molecular characterization of """"""""aggression-relevant"""""""" postsynaptic neurons downstream in these circuits.
In Aim 3, we will explore more deeply the behavioral facets modulated by these two 5-HT neuron subtypes and if their contributions vary across life span. Similar subtype-specific silencing methods will be employed as in the foundational aggression studies, but now additional social behaviors and neurological functions will be queried.
In Aim 4, we will use pharmacogenetics (DREADDs) to transiently si- lence each Drd 5-HT neuron subtype during """"""""childhood,"""""""" asking if lasting changes occur that predispose to hyperaggression and altered social motivation in adulthood, as predicted by human studies that associate genetic predisposition via the 5-HT system, childhood stress, and adult pathological aggression. Our ap- proaches are technically and conceptually innovative, and are foundational for discovering new, potentially behavior-selective, age-suitable therapeutics. Results compel a redefinition of 5-HT system organization.

Public Health Relevance

The proposed research aims to identify brain cells, circuits, and molecular pathways that predispose individuals to pathological aggression and social dysfunction, including motivated behaviors relevant to substance abuse and affective disorders. This work will provide cutting-edge technologies and novel targets for the development of behavior- and age-specific therapeutics for these serious disorders of extensive societal consequence.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
1R01DA034022-01A1
Application #
8628623
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Wu, Da-Yu
Project Start
2014-04-15
Project End
2019-03-31
Budget Start
2014-04-15
Budget End
2015-03-31
Support Year
1
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Harvard Medical School
Department
Genetics
Type
Schools of Medicine
DUNS #
City
Boston
State
MA
Country
United States
Zip Code
02115
Weinhard, Laetitia; Neniskyte, Urte; Vadisiute, Auguste et al. (2018) Sexual dimorphism of microglia and synapses during mouse postnatal development. Dev Neurobiol 78:618-626
Abraira, Victoria E; Kuehn, Emily D; Chirila, Anda M et al. (2017) The Cellular and Synaptic Architecture of the Mechanosensory Dorsal Horn. Cell 168:295-310.e19
Niederkofler, Vera; Asher, Tedi E; Okaty, Benjamin W et al. (2016) Identification of Serotonergic Neuronal Modules that Affect Aggressive Behavior. Cell Rep 17:1934-1949
Teissier, Anne; Chemiakine, Alexei; Inbar, Benjamin et al. (2015) Activity of Raphé Serotonergic Neurons Controls Emotional Behaviors. Cell Rep 13:1965-76
Niederkofler, Vera; Asher, Tedi E; Dymecki, Susan M (2015) Functional Interplay between Dopaminergic and Serotonergic Neuronal Systems during Development and Adulthood. ACS Chem Neurosci 6:1055-1070
Okaty, Benjamin W; Freret, Morgan E; Rood, Benjamin D et al. (2015) Multi-Scale Molecular Deconstruction of the Serotonin Neuron System. Neuron 88:774-91
Jensen, Patricia; Dymecki, Susan M (2014) Essentials of recombinase-based genetic fate mapping in mice. Methods Mol Biol 1092:437-54