Serotonin Modulates Odor-Evoked Neural and Behavioral Responses in Locusts

Core Concepts

Serotonin can increase or decrease innate appetitive behavioral responses to odorants in an odor-specific manner, while uniformly amplifying odor-evoked neural responses in the antennal lobe.

Abstract

The study examined how serotonin modulates odor-evoked neural and behavioral responses in locusts. The key findings are: Serotonin modulates innate appetitive behavioral responses (palp-opening responses, PORs) in an odor-specific manner. Serotonin increased PORs to some odorants (hexanol, benzaldehyde) but decreased PORs to others (linalool). In the antennal lobe, serotonin uniformly increased the strength of odor-evoked neural responses across projection neurons, without altering the temporal features or the combinatorial response profiles. This suggests serotonin enhances the sensitivity to odorants. The uniform neural response amplification appeared to be at odds with the observed stimulus-specific behavioral modulation. A simple linear model with neural ensembles segregated based on behavioral relevance was able to explain the serotonin-mediated flexible mapping between neural and behavioral responses. Serotonin was also found to modulate hunger-state dependent appetitive behavioral responses, with serotonin application recovering the reduced PORs in fed locusts. In summary, the study provides insights into how a specific neuromodulator (serotonin) alters neural circuits to produce flexible, odor-specific changes in behavioral outcomes.

Stats

Serotonin increased the probability of palp-opening responses (PORs) to hexanol and benzaldehyde odorants across a wide range of concentrations. Serotonin decreased the probability of PORs to the linalool odorant. Serotonin did not significantly alter the PORs to the ammonium odorant.

Quotes

"Serotonin can increase or decrease innate appetitive behavioral responses to odorants in an odor-specific manner." "In the antennal lobe, serotonin uniformly increased the strength of odor-evoked neural responses across projection neurons, without altering the temporal features or the combinatorial response profiles." "A simple linear model with neural ensembles segregated based on behavioral relevance was able to explain the serotonin-mediated flexible mapping between neural and behavioral responses."

Key Insights Distilled From

Serotonergic amplification of odor-evoked neural responses maps onto flexible behavioral outcomes

by Bessonova,Y.... at www.biorxiv.org 08-12-2023

https://www.biorxiv.org/content/10.1101/2023.08.08.552516v2

Deeper Inquiries

How do the serotonergic modulation of neural responses and behavioral outcomes vary across different insect species or even within the same species under different ecological or physiological conditions

The serotonergic modulation of neural responses and behavioral outcomes can vary significantly across different insect species or even within the same species under different ecological or physiological conditions. Insects exhibit a wide range of behaviors, and serotonin plays a crucial role in modulating these behaviors. For example, in fruit flies, serotonin has been linked to aggression, mating, and feeding behaviors. In locusts, serotonin is associated with triggering phenotypical plasticity and modulating appetitive responses. The specific effects of serotonin on neural responses and behavioral outcomes can vary based on the ecological context, such as hunger state or social interactions. Additionally, different insect species may have unique neural circuitry and receptor profiles that interact with serotonin, leading to species-specific responses.

What are the potential mechanisms by which serotonin can selectively enhance or suppress behavioral responses to specific odorants while uniformly amplifying neural responses

The potential mechanisms by which serotonin can selectively enhance or suppress behavioral responses to specific odorants while uniformly amplifying neural responses involve complex interactions within the olfactory system. Serotonin can modulate the excitability of individual projection neurons in the antennal lobe, leading to changes in odor-evoked responses. One potential mechanism is the segregation of neural ensembles based on behavioral relevance. By assigning positive or negative weights to different subsets of neurons based on their response to specific odorants, serotonin can amplify or suppress the overall behavioral response. This segregation allows for odor-specific changes in behavior while maintaining overall neural response amplification. Additionally, serotonin may interact with other neuromodulatory systems or feedback mechanisms to fine-tune the balance between excitatory and inhibitory signals in the olfactory circuitry.

Could the principles of segregated neural ensembles encoding behavioral relevance be a general strategy employed by other neuromodulatory systems to flexibly map sensory inputs to behavioral outputs

The principles of segregated neural ensembles encoding behavioral relevance could be a general strategy employed by other neuromodulatory systems to flexibly map sensory inputs to behavioral outputs. Neuromodulators such as dopamine, acetylcholine, and octopamine have also been implicated in modulating sensory processing and behavioral responses in various organisms. These neuromodulatory systems may utilize similar mechanisms of segregating neural ensembles based on behavioral relevance to achieve flexible mapping between sensory inputs and behavioral outputs. By selectively modulating the activity of specific neural ensembles, neuromodulators can influence the salience of sensory cues and drive context-dependent behavioral responses. Further research into the interactions between different neuromodulatory systems and their effects on neural circuitry will provide more insights into the generalizability of these principles across different species and behavioral contexts.