Synapsin function in GABA-ergic interneurons is required for short-term olfactory habituation

Area of Science:

• Neuroscience
• Animal Behavior
• Molecular Biology

Background:

• Olfactory habituation in Drosophila, including short-term (STH) and long-term (LTH), is linked to synaptic potentiation in the antennal lobe.
• The precise molecular mechanisms governing these habituation forms, particularly STH, remain largely unelucidated.

Purpose of the Study:

• To investigate the role of synapsin (syn) in the mechanisms underlying olfactory habituation in Drosophila.
• To identify the specific neuronal populations and molecular pathways involved in STH.

Main Methods:

• Utilized Drosophila genetic mutants (syn(97)-null) to assess behavioral deficits in olfactory habituation.
• Employed rescue experiments by expressing synapsin cDNA in specific GABAergic local interneurons (LN1).
• Performed biochemical analyses using phospho-synapsin-specific antiserum and assessed the necessity of Ca(2+) calmodulin-dependent kinase II (CaMKII) in LNs.

Main Results:

• Synapsin function was found to be essential for STH, with defects in syn(97)-null mutants rescued by expression in LN1 interneurons.
• Phosphorylation of synapsin at serine residues 6 and/or 533 is critical for its function in STH.
• CaMKII directly phosphorylates synapsin in vivo, and CaMKII function within LNs is necessary for STH.

Conclusions:

• A presynaptic mechanism involving CaMKII-mediated synapsin phosphorylation in GABAergic LNs underlies olfactory STH.
• This phosphorylation facilitates synaptic vesicle mobilization and enhances GABA release, contributing to STH.
• Signaling pathways for STH and LTH diverge upstream of synapsin function, indicating distinct molecular underpinnings for these memory forms.