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Dopamine and octopamine altered odor-driven neural and behavioral responses in opposite directions in a 2026 study of the American grasshopper, Schistocerca americana. But they did not work as mirror images: dopamine reduced activity in a subgroup of inhibitory neurons in the antennal lobe, while octopamine reduced the main neural response without changing that measured inhibition. The findings show how chemical signals can tune an insect olfactory circuit—not how humans subjectively experience smell.
Where odor signals are adjusted in the locust brain
Odor information begins at sensory neurons in the antenna and travels to the antennal lobe, the first central olfactory circuit. There, local neurons and projection neurons shape the signal. Projection neurons carry processed information onward to higher brain regions, including the mushroom body, which is involved in learning and memory.
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Neuromodulators are chemical signals that can change how neurons or circuits respond. A useful way to picture their effect is as changing a circuit’s gain: the same incoming odor signal can produce a different neural output. That analogy describes the circuit response, not a change in an insect’s conscious or human-like perception.
What the 2026 dopamine–octopamine study found
Yelyzaveta Bessonova and colleagues reported the comparison in The Journal of Neuroscience on September 14, 2026. Their experiments involved both sexes of Schistocerca americana. The study measured odor-evoked activity in the antennal lobe and an appetitive behavior: opening the palps, appendages near the mouthparts that touch or grasp food.
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| Modulator | Measured antennal-lobe effect | Measured behavioral effect | Mechanism and evidence status |
|---|---|---|---|
| Dopamine | Reduced odor-stimulated activity in a subgroup of GABAergic local neurons; principal neural responses increased for all tested odorants. | Increased appetitive palp opening across the tested odorants. | The reduction in local-neuron activity and the resulting release from inhibition were reported findings. |
| Octopamine | Reduced odor-evoked principal neural activity without altering the measured GABAergic local-neuron inhibition. | Reduced palp-opening responses across the tested odorants. | The authors describe a distinct mechanism involving intrinsic excitability. A projection-neuron explanation is a proposed interpretation, not a settled direct finding. |
The odor set was described using familiar analogies such as grass, lemon or citrus, rose, almond, and a spicy floral scent. These are labels to help readers identify the odorants presented; they do not mean locusts perceive or categorize smells as people do. The accessible study abstract and institutional accounts do not provide sample sizes or numerical effect sizes, so the magnitude of the changes cannot be stated here.
Why the two modulators are not simple opposites
Dopamine reduced one measured inhibitory influence
GABAergic local neurons contribute inhibition within the antennal-lobe network. In the study, dopamine suppressed odor-stimulated activity in one local-neuron subgroup. With that inhibitory influence reduced, principal neural responses rose for every tested odorant, alongside more palp opening. This is a circuit-level account of the measured response; it does not establish that dopamine universally makes odors stronger or more rewarding.
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Octopamine reduced output by a different route
Octopamine also reduced odor-evoked principal neural activity and palp opening, but it did not change the local-neuron inhibition measured in the experiment. The authors discuss intrinsic excitability as the distinct mechanism. The suggestion that octopamine acts through projection-neuron excitability remains an interpretation to test, rather than a demonstrated explanation of every step.
Barani Raman, a coauthor and professor of biomedical engineering at Washington University in St. Louis, summarized the difference: “What we found was that octopamine did not affect the activity of local neurons at all,” and “But dopamine, on the other hand, suppressed one subpopulation of local neurons. It released the circuit from inhibition to get that boost in the neural network output. Octopamine did not do that.”
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How serotonin and other locust findings fit the picture
Serotonin: a different site and question
A 2024 review by Zhang and Xu focuses on serotonin receptor 2 and odor input at the locust antenna—the sensory periphery, before signals reach the antennal lobe. The review notes that neuromodulation in peripheral olfactory systems is less understood than modulation within the antennal lobe. Earlier findings summarized in a Washington University report also indicate that serotonin’s behavioral effect may depend on odor identity. This is relevant context, but serotonin was not the central subject of the 2026 dopamine–octopamine comparison.
Octopamine in the mushroom body: a separate learning study
Other locust research describes octopamine modifying odor-specific, previously tagged synapses in the mushroom-body β-lobe after spike-timing-dependent plasticity. That work concerns plasticity in a higher brain area and a learning-related question. It is not a replication of, or direct explanation for, the antennal-lobe effect reported in 2026; it illustrates that a modulator’s effect depends on circuit location and experimental context.
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What this result can—and cannot—tell us
The study offers a specific lesson about insect olfaction: neuromodulators can change odor-linked output through different cellular routes, even when their effects on the measured neural and behavioral responses point in opposite directions. The evidence concerns the antennal-lobe circuit and appetitive palp opening in S. americana under the study’s conditions. It does not establish a general rule for all insects, mammals, or human smell.
Sources: PubMed-indexed study abstract; Washington University in St. Louis study report; Zhang and Xu’s 2024 review of serotonergic modulation in locust antennae; 2018 review of neuromodulation in olfactory processing; Commentary on locust olfactory coding and octopamine-related plasticity; Washington University McKelvey Engineering interview with Barani Raman.
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