In a groundbreaking exploration of neural circuit plasticity, researchers have unveiled a sophisticated reconfiguration within the olfactory system of fruit flies, challenging long-standing notions about fixed neuronal wiring and synaptic specificity. Utilizing advanced optogenetic imaging techniques, this study elegantly demonstrates that altering the molecular identity of olfactory receptor neurons (ORNs) facilitates a functional and anatomical rewiring with projection neurons (PNs) previously thought to be unconnected, illuminating new avenues for understanding sensory processing complexity.
At the core of the investigation lies the DA1-ORN to VA1v-PN pathway, a discrete olfactory circuit segment traditionally understood to maintain exclusive synaptic partnerships. The team harnessed the genetic LexA/LexAop system to express the calcium indicator GCaMP7b specifically in VA1v projection neurons, enabling real-time visualization of intracellular calcium fluctuations—used here as a faithful proxy for neuronal activity. Concurrent expression of the red fluorescent protein tdTomato in DA1-ORNs provided a robust anatomical marker to verify the rewiring at high resolution.
The sophistication of their approach was exemplified by two-photon excitation microscopy, which allowed precise measurement of calcium dynamics within the dendritic compartments of VA1v-PNs in living tethered flies. This methodology, combined with carefully controlled odor stimulation protocols, provided an unparalleled window into the functional consequences of synaptic reorganization induced by cell-surface molecular code manipulation.
Olfactory stimulation was delivered using two pheromones with well-characterized receptor affinities: 11-cis-vaccenyl acetate (cVA), which specifically activates DA1-ORNs, and palmitoleic acid (PA), known to activate VA1v-ORNs. In wild-type flies, GCaMP7b fluorescence intensities in VA1v-PNs increased in response to PA, aligning with established neuronal selectivity, while exposure to cVA led to a suppression of activity, indicative of lateral inhibitory mechanisms mediated by local interneurons within the antennal lobe circuitry.
Remarkably, in flies engineered to exhibit the DA1-ORN to VA1v-PN rewiring, VA1v-PNs displayed robust activation not only to PA but also to cVA. This functional gain of cVA responsiveness underscores the formation of excitatory synaptic connections between DA1-ORN axons and VA1v-PN dendrites, a phenomenon actively quantified by increases in calcium signal intensity. These findings imply that the engineered rewiring confers cross-activation, fundamentally altering the odor coding landscape within the antennal lobe.
The inhibitory response traditionally observed in VA1v-PNs to cVA in wild-type flies results from lateral inhibition orchestrated by various local interneurons, which sculpt the olfactory processing network’s dynamic range and sensitivity. Intriguingly, examination of the responses to odours outside the typical activation profiles of DA1 or VA1v ORNs revealed largely conserved inhibitory patterns in both wild-type and rewired flies. This persistence suggests that while the direct ORN-PN connectivity was modified, the broader interneuronal inhibitory network remained intact.
From a mechanistic standpoint, the work leverages the conserved cholinergic neurotransmitter system that mediates excitatory ORN-PN synapses across different olfactory pathways. By altering the cell-surface combinatorial molecular codes that guide axonal targeting and synaptic specificity, the study provides compelling evidence that molecular identity cues are instrumental in defining, yet also flexible within, the neural wiring blueprint.
Beyond technical prowess, the study addresses longstanding questions about the plasticity of hardwired sensory circuits in adult animals. While developmental plasticity in olfactory networks is well-documented, the capacity to rewire existing synaptic connections via molecular manipulation offers profound insights into circuit adaptability, potentially informing strategies for neuroregenerative therapies and artificial sensory system design.
This research also underscores the nuanced balance between anatomical rewiring and functional circuit output. The coexistence of newly formed excitatory connections alongside preserved inhibitory interactions implies a modular approach to circuit remodeling without wholesale disruption of network homeostasis. Whether such rewiring affects olfactory behavior or perception remains an enthralling avenue for future investigations.
Using state-of-the-art, genetically encoded calcium sensors and fluorescent markers allowed for simultaneous anatomical and functional verification of rewired synapses within intact neural tissue, reinforcing the importance of multimodal imaging in neuroscience research. The combination of targeted genetic tools and two-photon microscopy constitutes a powerful platform for dissecting intricate circuit modifications in vivo.
Moreover, these findings challenge the dogma that olfactory receptor neuron projections to defined glomeruli are immutable, implicating that combinatorial expression patterns on the cell surface can effectively redirect axonal targeting and reshape odor representation maps. This capability opens possibilities for reprogramming sensory circuits to alter perception or behavior in a precise, circuit-specific manner.
While the study is focused on Drosophila melanogaster, the broader implications resonate across taxa, given the evolutionary conservation of many molecular guidance mechanisms and neurotransmitter systems. Such cross-species relevance elevates the significance of this research for the wider neuroscience community, inspiring approaches to modulate neural connectivity in diverse contexts.
In sum, the meticulous work of Lyu et al. unveils a new dimension of neural circuit flexibility by demonstrating that peripheral olfactory neurons can be coerced into forming ectopic, functional synapses with projection neurons typically outside their domain. This paradigm-shifting discovery redefines our understanding of neural specificity and plasticity within sensory systems and holds vast potential for unraveling the principles of brain wiring and reconfiguration.
Subject of Research: Neural circuit plasticity and olfactory system rewiring in Drosophila melanogaster
Article Title: Rewiring an olfactory circuit by altering cell-surface combinatorial code
Article References:
Lyu, C., Li, Z., Xu, C. et al. Rewiring an olfactory circuit by altering cell-surface combinatorial code. Nature (2025). https://doi.org/10.1038/s41586-025-09769-3
Image Credits: AI Generated
