Summary: Two closely related types of dopamine-releasing neurons in the olfactory bulb behave very differently because of their physical shape. One subtype lacks an axon and releases neurotransmitters from its dendrites—a rare arrangement that confines signaling to the local region and allows the cell to inhibit its own activity. The other subtype uses conventional axonal release to communicate across longer distances. These structural differences point to distinct roles in odor processing and sharpen our understanding of sensory coding and neuronal diversity.
Researchers at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN), King’s College London, examined dopaminergic interneurons in the mouse olfactory bulb and discovered clear anatomical and functional divisions between two subclasses. The study, published in eLife, shows that differences in neuronal polarity—whether a cell has an axon or not—translate directly into different neurotransmitter release strategies and distinct contributions to smell processing.
Traditionally, neurons transmit signals via axons and receive input through dendrites. That axon–dendrite polarity underpins most models of neuronal communication. Yet many exceptions exist, and this new work demonstrates a striking example: within the olfactory bulb, dopaminergic interneurons fall into two anatomically and functionally distinct groups.
One group—referred to as anaxonic dopaminergic neurons—lacks an identifiable axon and instead releases neurotransmitter from dendrites. Releasing from dendrites is uncommon for output signaling and produces highly localized effects. These anaxonic neurons operate within confined spherical structures in the olfactory bulb and can self-inhibit, regulating their own excitability and adjusting local circuit activity in a compact domain.
The contrasting group, called axon-bearing dopaminergic neurons, follows the classic neuronal model. Their neurotransmitter release sites are almost entirely localized to intermittently myelinated axons that extend across larger regions of the olfactory bulb. Because they do not release from dendrites and cannot self-inhibit, axon-bearing neurons coordinate activity between distant local circuits and likely enhance contrast between different odor representations by linking separate processing units.
This anatomical dichotomy has clear functional consequences. Anaxonic cells shape odor processing locally and provide fine-tuned inhibition within a limited radius, while axon-bearing cells integrate and broadcast signals over longer distances to synchronize and differentiate activity across the olfactory bulb. Despite both cell types releasing dopamine and residing in the same brain area, their outputs and roles in sensory computation are markedly different.
Dr Ana Dorrego-Rivas, the study’s first author and a postdoctoral researcher at King’s IoPPN, commented that the findings support a model in which the two dopaminergic subclasses serve fundamentally different purposes in odor coding. Anaxonic neurons appear specialized for local modulation and gain control, whereas axon-bearing neurons are poised to coordinate information between separate glomerular modules and potentially sharpen odor discrimination.
Professor Matthew Grubb, senior author of the study, noted that the olfactory system contains surprising cellular diversity, and discovering neurons that conform to the “standard” axon-bearing model alongside unusual anaxonic cells reveals how varied strategies of neurotransmitter release can coexist to support complex sensory processing.
Funding: The research was supported by the Wellcome Trust, the European Research Council, and UK Research and Innovation through the Biotechnology and Biological Sciences Research Council and the Medical Research Council.
Key Questions Answered:
A: A neuron’s polarity determines where it releases neurotransmitter and how it influences other cells. These structural differences define whether a cell acts locally or coordinates activity across distant regions, shaping odor signal processing.
A: Anaxonic neurons release neurotransmitter from dendrites—the typical input structures—and can self-inhibit, allowing them to regulate their own activity and exert precise, local effects within the olfactory bulb.
A: Axon-bearing neurons transmit signals over longer distances, linking different processing modules in the olfactory bulb and helping to refine odor discrimination by coordinating activity across compartments.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full by the editorial team.
- Additional context was added by staff to clarify the findings.
About this dopamine and olfaction research news
Author: Patrick O’Brien
Source: King’s College London
Contact: Patrick O’Brien – King’s College London
Image: The image is credited to Neuroscience News
Original Research: Open access. “Strikingly different neurotransmitter release strategies in dopaminergic subclasses” by Ana Dorrego-Rivas et al., eLife. DOI: 10.7554/eLife.105271.2
Abstract
Strikingly different neurotransmitter release strategies in dopaminergic subclasses
Neuronal function is tightly linked to axodendritic polarity: axons typically carry output while dendrites receive input. Yet many neurons can release neurotransmitter from dendrites, and in the mouse olfactory bulb closely related dopaminergic interneuron subclasses differ sharply in polarity—one subtype lacks an axon. These axon-bearing and anaxonic subclasses show distinct development and sensory responses, but how polarity differences influence output remained unclear.
Here, anatomical and physiological evidence indicates distinct release strategies: anaxonic cells release from dendrites, while axon-bearing neurons release exclusively from intermittently myelinated axons. Functionally, only anaxonic dopaminergic neurons are capable of self-inhibition. These findings demonstrate that polarity variation can produce major differences in neuronal outputs, and that closely related neuronal subclasses can play separate roles in sensory information processing.