# CRCNS: The diffusional complexity of the brain's extracellular space

> **NIH NIH R01** · UNIVERSITY OF TEXAS SAN ANTONIO · 2024 · $213,979

## Abstract

This proposal brings together two laboratories with complementary experimental and computational 
expertise to determine the complexity of the extracellular space (ECS) in the brain at nanoscopic 
resolution in live tissue and its effects on neuronal function. The Spanish laboratory has spearheaded the 
development of super-resolution shadow imaging (SUSHI). The US team will use computer models to 
study the consequences of using competing hypotheses of how the ECS complexity affects the diffusion 
of neurotransmitters, which they will test experimentally. Neuronal structural complexity can cause a 
breakdown of classical diffusion, resulting in anomalous diffusion. A molecule can experience anomalous 
and normal diffusion at different temporal scales. Depending on which diffusional process dominates will 
affect the spread and relative concentration of ECS diffusing signals, such as neurotransmitters. SUSHI 
experiments will measure the structure of the ECS in live hippocampal organotypic and acute slices 
focusing on perisynaptic excitatory and inhibitory areas of CA1 pyramidal neurons. The values of the ECS 
volume fraction and the pore-size of the interstitial fluid (ISF) will be determined as a function of age, 
which is known to affect the ECS structure. SUSHI will be used to measure diffusional properties of the 
ECS at nanoscopic resolution over microscopic regions. These measurements will determine whether 
diffusion is anomalous or normal and over which periods of time. Monte Carlo and differential equation 
models and theory will examine the anatomical properties that cause anomalous or normal diffusion. The 
models will be extended to predict the effects of ECS structure on biochemical signaling at different 
spatio-temporal scales. The team will test the hypothesis that modifying the ECS volume directly affects 
the relative strength of neurotransmitter signals. Experiments will use a combination of electrophysiology 
with pharmacological and optogenetic manipulations to determine the effects of changes in ECS volume 
on the relative strength of excitatory and inhibitory (tonic and phasic) synapses. The experimental 
manipulations will mimic pathological conditions such as epilepsy and gliosis. The experiments will be the 
basis to build biophysical detailed models of pyramidal hippocampal cells to determine how the excitability 
of these cell changes as a function of ECS structure.

## Key facts

- **NIH application ID:** 10908313
- **Project number:** 5R01NS130759-03
- **Recipient organization:** UNIVERSITY OF TEXAS SAN ANTONIO
- **Principal Investigator:** Fidel Santamaria
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $213,979
- **Award type:** 5
- **Project period:** 2022-09-01 → 2026-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10908313

## Citation

> US National Institutes of Health, RePORTER application 10908313, CRCNS: The diffusional complexity of the brain's extracellular space (5R01NS130759-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10908313. Licensed CC0.

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