The Input-Output Relationship of AIY Interneurons in Caenorhabditis elegans in Noisy Environment

Determining how neurotransmitter input causes various neuronal activities is crucial to understanding neuronal information processing. In Caenorhabditis elegans, AIY interneurons receive several sources of sensory information as glutamate inputs and regulate behavior by integrating these inputs. However, the relationship between glutamate input and the Ca²⁺ response in AIY under environmental noise, in other words, without explicit stimulation, remains unknown. Here, we show that glutamate-input fluctuations evoke a sporadic Ca²⁺ response in AIY without stimulation. To ensure that Ca²⁺ response can be considered AIY output, we show that the membrane-potential depolarization precedes Ca²⁺ responses in AIY. We used an odor as model stimulation to modulate the sensory inputs. Simultaneous imaging of glutamate input and Ca²⁺ response, together with glutamate transmission mutants, showed that glutamate-input fluctuations evoke sporadic Ca²⁺ responses. We identified the input-output relationships under environmental noise in vivo, and our results address the relationship between sensory-input fluctuations and behavioral variability.