Understanding Circuits

Although considerable information about neuronal circuits has been generated from experiments where retrograde transsynaptic tracing has been performed using Rabies Virus, there is no comparable technique for transsynaptic tracing in the anterograde direction. The purpose of this grant is to optimize and validate a method for mediating anterograde transsynaptic tracing from genetically or physiologically determined cells. This method is monosynaptic, only marks cells that are postsynaptic to the starter cells and has negligible toxicity.

Project Summary Brain-wide correlation of single-cell firing properties to patterns of gene expression Every neuron expresses thousands of proteins which, through their interactions with each other and with other small molecules, imbue the neuron with its functional properties. The primary function of each neuron is to receive synaptic inputs, to produce electrical spikes, and to release neurotransmitters to its downstream neighbors. Neurons show widely varying patterns of gene expression, and also show widely varying patterns of electrical spiking.

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.

PROJECT SUMMARY The mammalian brain is arguably the most complex biological structure. Investigating cellular functions and mapping neural connections in the brain are critical tasks to better understand the brain in health and disease. This is particularly challenging in vivo due to the inherent limitations in experimental latitude and simultaneous access to multiple brain regions within the same animal. These shortcomings hinder multimodal interrogation of multi-synaptic circuits and mesoscale connectomics.

PROJECT SUMMARY The use of current and emerging genetically encoded tools could greatly benefit from advanced methods for gene delivery to the desired cell population. When used in conjunction with transgenic animals to restrict expression to cell populations of interest, adeno-associated viruses (AAVs) can provide well-tolerated and targeted transgene expression that enables long-term behavioral, in vivo imaging, and physiological experiments. Lacking from the current suite of vector tools is a way to achieve cell- or circuit-specificity with AAVs without the use of transgenic animals.

PROJECT SUMMARY The brain is the most complex organ in the body, consisting of hundreds of molecularly, physiologically, and anatomically distinct cells. Recently, methods have been developed that can cost-effectively measure mRNA abundance in tens of thousands of single cells, and this has led to a revolution in the identification and classification of new types of cells in the brain. But these methods only measure one aspect of gene regulation – mRNA levels.

 DESCRIPTION (provided by applicant): It is a longstanding goal in neuroscience to reveal how specific cell types contribute to different neural circuits that underlie cognition, behavior, and disease pathology. Although cell types can be grouped into descriptive categories (excitatory, inhibitory, peptidergic etc.), we know there is a great combinatorial diversity of cels that differ in ion channel and receptor expression levels and fulfill discrete roles within neural circuits.

 DESCRIPTION (provided by applicant): The BRAIN Initiative seeks to understand the spatial, temporal and chemical nature of the brain.

 DESCRIPTION (provided by applicant): Fundamental to understanding brain function is the ability to relate the spatio-temporal firing patterns of specific neurons to their functional connectivity and determine the strength and experience-dependent regulation of those connections.

 DESCRIPTION (provided by applicant): The proteins in synapses are the fundamental regulators of synaptic plasticity, which ultimately controls the neural circuits that underlie behavior. A major advance in our understanding of how synaptic connectivity is linked to animal behavior comes from transcranial two-photon imaging of dendritic spines in living animals. However, despite the advances made by two-photon microscopy, most experiments have been observational.