Summary: Closely related dopamine-releasing neurons in the olfactory bulb behave in fundamentally different ways depending on their physical structure. One subtype releases neurotransmitters from dendrites instead of axons—an unusual mechanism that allows the cells to act locally and even self-inhibit.
Another subtype follows the classic neuronal model, using long axons to send signals across distant regions. These structural differences mean each cell type plays a distinct role in shaping how odors are processed, offering new insights into sensory coding and the diversity of neuronal communication.
Key Facts:
- Two Distinct Dopamine Neuron Subtypes: One lacks an axon and releases neurotransmitters from dendrites; the other uses axons in the traditional way.
- Functional Consequences: Anaxonic neurons act locally and self-inhibit, while axon-bearing neurons coordinate activity across distant regions of the olfactory bulb.
- Sensory Processing Impact: These differences suggest each subtype contributes uniquely to odor perception and contrast sharpening.
Source: King’s College London
Closely related subtypes of dopamine-releasing neurons may play entirely separate roles in processing sensory information, depending on their physical structure.
New research from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s College London has found that variations in the physical structure of neurons might have a striking impact in the role that they play when processing sensory information.
It identified two different sub-types of interneuron in the olfactory bulb which is where the brain first processes information about smell. One of these sub-types was found to communicate in a highly unusual manner, releasing signals from a part of the neuron that has most commonly been associated with receiving signals.
Published in eLife, the research examined the olfactory bulbs of mice brains to assess the structure of different sub types of neuron that produce and release the chemical dopamine.
It is the first study to provide anatomical and physiological evidence that distinct subtypes of dopaminergic neurons in the bulb transmit signals in fundamentally different ways based on the shape and structure of the cell.
Most neurons send their signals by releasing chemical neurotransmitters via long thin arm-like protrusions of the cell called axons. In the classic view, neurons also receive signals from other neurons via other types of branching tree-like protrusions, known as dendrites.
This distinction in role performed by these different structures forms the backbone of how neurons are believed to function. However, this new study provides evidence that these structures in the neuron might not always behave this way.
Researchers in this study found that neurons within the olfactory bulb can be separated into two distinct subtypes, distinctly characterised by how they transmit and receive signals.
One type of dopamine interneuron in the olfactory bulb did not possess an axon at all, rather it released neurotransmitter signals from its dendrites, normally the input not the output part of the cell. These cells are called ‘anaxonic neurons’.
These unusual anaxonic neurons acted locally within the olfactory bulb and were able to self-inhibit, which means that they can turn down their own activity levels.
This study was the first to show that a separate sub-type of neurons in the olfactory bulb that have axons, known as “axon-bearing dopaminergic neurons”, do not release signals from their dendrites and cannot self-inhibit.
These neurons followed the classical model of how neurons send signals to each other with the release sites contained almost wholly within the axon. These axons travel long distances across the olfactory bulb rather than influencing their own cell’s electrical activity through self-inhibition, like the anaxonic neurons.
Dr Ana Dorrego-Rivas, a post-doctoral researcher at King’s IoPPN and the study’s first author said, “Our findings support that the two dopaminergic subclasses play fundamentally different roles in the olfactory bulb.
“While the neurons without an axon act locally, shaping the processing of odour signals within specific spherical structures in the brain; axon-bearing cells act over long distances, coordinating activity between these spherical structures and potentially enhancing contrast between distinct odours.
“Despite the fact that they both release dopamine and are located in the olfactory lobe, our findings suggest that these neurons contribute to smell processing in remarkably different ways.”
Professor Matthew Grubb, Professor in Neuroscience at King’s IoPPN and the study’s senior author said, “The olfactory system is weird and wonderful, so it was a big surprise to find some cells there that behave just like ‘standard’ neurons. It’s going to be fun to try to figure out how these abnormally-normal cells contribute to the perception of smell stimuli.”
Funding: This research was funded by the Wellcome Trust, the European Research Council, and UKRI through the Biotechnology and Biological Sciences Research Council and the Medical Research Council.
Key Questions Answered:
A: Their physical design determines where and how they release neurotransmitters, which shapes their role in processing odor signals.
A: They release neurotransmitters from dendrites—typically input structures—and can tune down their own activity through self-inhibition.
A: They transmit signals over longer distances, helping coordinate activity across the olfactory bulb and refine odor discrimination.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
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
Abstract
Strikingly different neurotransmitter release strategies in dopaminergic subclasses
Neuronal function is intimately tied to axodendritic polarity. Neurotransmitter release, for example, is usually the role of the axon. There are widespread exceptions to this rule, however, including many mammalian neuronal types that can release neurotransmitter from their dendrites.
In the mouse olfactory bulb, closely related subclasses of dopaminergic interneuron differ markedly in their polarity, with one subtype lacking an axon entirely. These axon-bearing and anaxonic dopaminergic subclasses have distinct developmental profiles and sensory responses, but how their fundamental polarity differences translate to functional outputs remains entirely unknown.
Here, we provide anatomical evidence for distinct neurotransmitter release strategies among these closely related dopaminergic subtypes: anaxonic cells release from their dendrites, while axon-bearing neurons release exclusively from their intermittently myelinated axon.
These structural differences are linked to a clear functional distinction: anaxonic, but not axon-bearing dopaminergic neurons are capable of self-inhibition.
Our findings suggest that variations in polarity can produce striking distinctions in neuronal outputs, and that even closely related neuronal subclasses may play entirely separate roles in sensory information processing.
