Summary: Researchers have introduced DELTA, a powerful imaging approach that maps synaptic changes across the entire brain during learning. By labeling synaptic proteins before and after behavioral training, scientists can now visualize where and how neural connections are remodeled over time.
Using DELTA, the team tracked changes in the synaptic protein GluA2 and identified brain regions engaged by new learning, while also observing widespread protein turnover in animals exposed to enriched environments. This method narrows the gap between observable behavior and the cellular processes that support learning and memory.
Key Facts:
- Whole-brain mapping: DELTA reveals the locations of synaptic protein turnover associated with learning.
- Learning-specific changes: Alterations in GluA2 pinpoint brain areas recruited by a learned task.
- Flexible application: DELTA detects both localized and widespread synaptic changes, including effects of environmental enrichment.
Source: HHMI
Janelia researchers have created a new approach to map how individual neuronal connections change across the whole brain during learning, offering a clearer link between behavior and synaptic-level mechanisms.
Neurons communicate across synapses—tiny junctions that transmit quick electrical or chemical signals. Synaptic plasticity, the process by which synapses strengthen or weaken in response to experience, is central to learning and memory. Yet pinpointing where these synaptic changes occur throughout the brain during learning has been difficult.
Led by the Spruston and Lavis laboratories and building on work from former Janelia group leader Karel Svoboda, the researchers developed DELTA to visualize synaptic protein turnover with single-synapse resolution across the entire brain. The method leverages bright Janelia Fluor (JF) dyes and genetically engineered HaloTag mice to mark specific synaptic proteins before and after behavioral change.
DELTA operates by labeling a synaptic protein of interest with one fluorescent dye, allowing the animal to continue behaving or undergo further training, and then labeling the same protein again with a second dye. Proteins that were present at the first time point but have been degraded or replaced by the second label appear different from stable proteins that retain the original label. Whole-brain imaging then reveals where significant protein turnover has occurred.
To test the approach, the team studied mice trained on an associative task in which two visual cues were linked to a water reward. After initial labeling, one cohort continued receiving water randomly at both cues, while the other cohort experienced a change in task rules so that only one cue predicted the reward. Following several days of behavior, the researchers applied the second label and imaged the brains to compare protein turnover between the groups.
The results showed that learning the altered task produced changes in the synaptic glutamate receptor subunit GluA2 in distinct brain regions, highlighting localized sites of synaptic plasticity tied to the new behavior. In a separate comparison, animals housed in enriched environments—provided with toys and social companions—exhibited more widespread GluA2 turnover throughout the brain, indicating that complex sensory and social experiences drive broader synaptic remodeling.
Because DELTA reveals where synaptic proteins are changing, it equips researchers with a focused set of brain regions to examine in greater detail. From that starting point, scientists can perform targeted experiments to uncover the molecular pathways and circuit dynamics that produce learning-related synaptic changes.
“A major obstacle in identifying the molecules responsible for learning-related changes is not knowing where those changes occur,” says Boaz Mohar, a research scientist in the Spruston Lab and lead author on the work. “DELTA gives us a brain-wide view so we can concentrate on the most relevant locations and then dive down to subcellular mechanisms.”
The team is refining DELTA to add temporal resolution, aiming to determine when during the learning period proteins are turned over. The project exemplifies interdisciplinary collaboration: chemists, imaging specialists, behavioral scientists, and geneticists at Janelia contributed expertise, and outside collaborators helped validate the method.
Janelia is supporting dissemination of DELTA through programs that enable visiting researchers to apply the method in their own laboratories. “This project required doing something new and combining many areas of expertise,” says Nelson Spruston. “It underscores how collaborative science can open up entirely new views of brain function.”
About this brain mapping and synaptic plasticity research news
Author: Nanci Bompey
Source: HHMI
Contact: Nanci Bompey – HHMI
Image: The image is credited to Neuroscience News
Original Research: Open access. “DELTA: a method for brain-wide measurement of synaptic protein turnover reveals localized plasticity during learning” by Boaz Mohar et al. Nature Neuroscience
Abstract
DELTA: a method for brain-wide measurement of synaptic protein turnover reveals localized plasticity during learning
Experience-dependent synaptic plasticity reshapes neuronal connections and is believed to underlie learning and memory. Yet the exact locations and spatial distribution of learning-related plasticity across the brain remain poorly understood.
Here we present DELTA, a technique that maps synaptic protein turnover throughout the brain with single-synapse precision, using Janelia Fluor dyes together with HaloTag knock-in mice. During associative learning, turnover of the AMPA receptor subunit GluA2—used as a marker of synaptic remodeling—increased in several regions, most prominently in hippocampal area CA1. In contrast, environmental enrichment led to broader, brain-wide increases in synaptic protein turnover.
In CA1, GluA2 stability varied by input source, showing greater turnover in layers receiving input from CA3 than in layers targeted by entorhinal cortex. DELTA enables exploration of the molecular and circuit-level bases of learning and other forms of plasticity at scales ranging from individual synapses to the whole brain.