# RP3:  Cell Phenotyping: Intrinsic physiology and genetic characteristics

> **NIH NIH U19** · SALK INSTITUTE FOR BIOLOGICAL STUDIES · 2023 · $696,877

## Abstract

Summary: Project 3 – Cell Phenotyping: Intrinsic Physiology and Genetic Characteristics
The identification of developmental pathways and neuronal subtype markers has made circuit studies of the
spinal cord one of the most tractable CNS systems to investigate how neural networks control behaviorally
relevant activity. Although a general framework now exists for labeling cardinal interneuron and motor neuron
populations within the ventral spinal cord using Cre-mouse lines, it is apparent that each cardinal spinal neuron
population is in fact a complex mixture of many heterogeneous cell types when viewed from the perspective of
inputs, outputs, firing properties, and molecular-genetic attributes. Despite clear evidence for this
heterogeneity, the relationship between each of these cellular properties is very fragmentary. The goal of
Project 3 is to interrelate how cell lineage (cardinal neuron identity), connectivity to motor pools, intrinsic firing
properties, and molecular genetics define cell types to provide a true definition of cell identity. This
interconnected framework of cell features is critical because it will allow modeling to predict how spinal circuitry
modulates the control of movement, and it will serve as the basis for genetic experiments that perturb neuronal
function in order to test predictions of the model.
This U19 Spinal Cord Circuit Team hypothesizes that the heterogeneity among premotor interneurons will
scale with the complexity of motor functions mediated by different motor pools. If this hypothesis is correct,
muscle groups controlling the wrist will be controlled by a more diverse population of premotor interneurons
than the subset controlling the elbow because the degrees of freedom in movement differ between these two
joints. There are two main approaches that will be employed to define interneuron heterogeneity: patch clamp
electrophysiology in order to define input/output relationships, and single cell sequencing transcriptomics
(scRNAseq) to define molecular heterogeneity. These methods will be anchored to connectivity and lineage by
recording and sequencing cells that have been Cre-tagged to mark their lineage of origin (i.e. V1, V2a, V2b,
V3) and retrograde trans-synaptically labeled with rabies to identify motor pool connectivity.
How will the characterization of cell type-specific intrinsic firing patterns and transcriptome be applied to the
broader understanding of neuroscience and limb movements in particular? First, each cardinal interneuron
group will be divided into many additional subtypes based on their unique combinatorial patterns of gene
expression. However, the goal is not to attempt to fractionate the cardinal interneuron groups into as many
subpopulations as possible, rather it is to establish a set of molecular landmarks that can be used to reliably
identify and genetically perturb subsets of interneurons with known firing patterns and connectivity. It is only
with information about cell numbers, c...

## Key facts

- **NIH application ID:** 10696198
- **Project number:** 5U19NS112959-05
- **Recipient organization:** SALK INSTITUTE FOR BIOLOGICAL STUDIES
- **Principal Investigator:** SAMUEL L. PFAFF
- **Activity code:** U19 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $696,877
- **Award type:** 5
- **Project period:** 2019-09-15 → 2026-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10696198

## Citation

> US National Institutes of Health, RePORTER application 10696198, RP3:  Cell Phenotyping: Intrinsic physiology and genetic characteristics (5U19NS112959-05). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10696198. Licensed CC0.

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