Through millions of years of trained evolution, all living organisms adapt their behavior in response to infection, however, the mechanisms behind this are less understood. Now, a study led by researchers at Aix-Marseille Université shows neurons modulate egg production in response to bacterial infection in fruit flies. The team states their findings represent a case of ‘behavioral immunity’ in response to bacterial infection where fruit flies use nerve signaling pathways to reduce the impact of infection on their offspring and their environment. The opensource study is published in the journal eLife.
Previous studies show in addition to developing strategies to reduce infection, animals also engage in behaviors lowering the impact of the infection. Earlier studies from the group showed that following bacterial infection in fruit flies, there was a temporary reduction in their egg-laying activity. This caused the lab to concentrate on peptidoglycan, a component of the bacterial cell wall known to activate the NF-kB pathway, which controls the immune response in the fruit fly. The lab found an injection of purified peptidoglycan into the flies also affects egg-laying, suggesting the same bacterial component regulates both immune and behavioral responses to bacterial infections. The current study investigates exactly how egg-laying in fruit flies is altered based on the premise peptidoglycan also activates the NF-kB pathway to control egg-laying.
The current study shows flies with infections had three times as many mature eggs in the ovary as uninfected flies. Results show as egg-laying resumes after 24 hours, the infection temporarily blocks the release of the eggs into the oviduct. Data findings show peptidoglycan is sensed by neurons which ensure normal egg-laying resumes once the threat of infection has passed.
Results show the neuron that produces octopamine, a key neurotransmitter involved in ovulation, are the ones responsible for sensing peptidoglycan to regulate egg-laying. Data findings show peptidoglycan dependent NF−κB pathway activation in octopaminergic neurons triggers the decrease of egg-laying post-infection.
The team surmises their findings show bacterial infection regulates ovulation by affecting the octopaminergic signaling pathway in neurons, via activation of the NF-kB pathway. For the future, the researchers state they plan to test whether this neuronal response to peptidoglycan following infection also occurs in the neurons of higher organisms.
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