Altered signaling by neuromodulators, such as biogenic amines or neuropeptides, underlies human brain diseases including mood disorders and Parkinson's disease, yet our understanding of exactly how neuromodulators produce proper functioning of neural circuit's remains vague. How do neuromodulators collaborate with fast-acting neurotransmitters to create patterns of activity in neural circuits that underlie complex behaviors? Our goal is to understand for the first time precisely how neuromodulators function in a model neural circuit. The egg-laying circuit of C. elegans contains just three types of neurons and one set of postsynaptic muscles. This circuit involves just one fast-acting neurotransmitter, acetylcholine, plus a set of neuromodulators: the biogenic amines serotonin and tyramine, and several neuropeptides. The circuit generates a two-state behavior that alternates between a ~2.5 minute active phase in which rhythmic egg-laying contractions occur, and a ~20 minute inactive phase. Over the past 16 years, we have developed a battery of C. elegans mutants that show increased or decreased egg laying due to defects in specific signaling molecules in the circuit. We have also developed cell-specific promoters that allow us to express any protein we want in any individual cell type of the egg-laying system. We have now developed new tools to optogenetically manipulate activity of the individual cell types and to use the genetically-encoded Ca2+ sensor GCaMP to quantitatively analyze activity of each cell type within freely-behaving animals. These new tools have brought us to a tipping point at which we are ready to delineate how each cell and each neurotransmitter in the circuit act to together produce the activity pattern of the circuit. We expect a newly meaningful understanding of neuromodulators will be revealed now that we can finally analyze their function in the context of detailed investigation of a circuit they modulate. We will generate this understanding through three aims, each focused on dissecting the function one of the three neuron types in the circuit:
Aim 1. We will determine how serotonin and the neuropeptide NLP-3, co-released from the HSN motor neuron, signal onto other cells in the circuit to initiate the active phase of egg laying.
Aim 2. W will determine how acetylcholine, released from the VC motor neurons within the active phase, acutely triggers egg-laying contractions only when serotonin and NLP-3 have activated the circuit.
Aim 3. We will determine how the uv1 neuroendocrine cells release tyramine to lengthen the inactive phase of egg laying and to space out egg-laying events during the active phase.

Public Health Relevance

This proposal aims to understand in unprecedented detail how medically-important neuromodulators, including serotonin, help generate the dynamic pattern of activity in a neural circuit. Defects in neuromodulator function appear to underlie many human brain diseases, such as mood disorders and Parkinson's disease, yet it is difficult to understand these diseases because we as yet have little understanding of how neural circuits work. By deeply studying one neural circuit in the simple model organism C. elegans that uses the same types of neuromodulators found in the human brain, we hope to spearhead a new level of understanding of neural circuit activity that will advance our understanding of neuromodulators and their roles in brain disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS086932-02
Application #
8915782
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Stewart, Randall R
Project Start
2014-09-01
Project End
2018-07-31
Budget Start
2015-08-01
Budget End
2016-07-31
Support Year
2
Fiscal Year
2015
Total Cost
Indirect Cost
Name
Yale University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
043207562
City
New Haven
State
CT
Country
United States
Zip Code
Ravi, Bhavya; Nassar, Layla M; Kopchock 3rd, Richard J et al. (2018) Ratiometric Calcium Imaging of Individual Neurons in Behaving Caenorhabditis Elegans. J Vis Exp :
Tang, Sicheng; Zhang, Yang; Dhakal, Pravat et al. (2018) Photochemical Barcodes. J Am Chem Soc 140:4485-4488
Ravi, Bhavya; Garcia, Jessica; Collins, Kevin M (2018) Homeostatic Feedback Modulates the Development of Two-State Patterned Activity in a Model Serotonin Motor Circuit in Caenorhabditis elegans. J Neurosci 38:6283-6298
Banerjee, Navonil; Bhattacharya, Raja; Gorczyca, Michael et al. (2017) Local neuropeptide signaling modulates serotonergic transmission to shape the temporal organization of C. elegans egg-laying behavior. PLoS Genet 13:e1006697
Thapaliya, Ek Raj; Zhang, Yang; Dhakal, Pravat et al. (2017) Bioimaging with Macromolecular Probes Incorporating Multiple BODIPY Fluorophores. Bioconjug Chem 28:1519-1528
Collins, Kevin M; Bode, Addys; Fernandez, Robert W et al. (2016) Activity of the C. elegans egg-laying behavior circuit is controlled by competing activation and feedback inhibition. Elife 5:
Koelle, Michael R (2016) Neurotransmitter signaling through heterotrimeric G proteins: insights from studies in C. elegans. WormBook :1-78