How does the nervous sytem change during development to enable mature behavior? We use the development of chemotaxis behavior as model to study maturation and have shown that L3 larvae respond worse than adults in attractive diacetyl chemotaxis assays. However, L3 larvae are not generally bad at chemotaxis, since they respond similarly to adults in repulsive nonanone chemotaxis assays. To begin to identify neural mechanisms underlying maturation, we mapped both the adult and larval sensory circuits required for attractive diacetyl chemotaxis. Based on behavioral analysis of sensory neuron mutants, we found that the adult sensory circuit contains more neurons than the L3 circuit, suggesting that changing circuit composition may play a crucial role in behavioral maturation.
To further characterize differences between the adult and L3 cellular circuits we examined the activity of individual sensory neurons from each circuit. While a microfluidic device for recording neuronal activity from adult worms is published, none had existed for L3 worms. In collaboration with N. Chronis and D. Bazopoulou we developed a novel microfluidic device that traps L3 animals and enables ready imaging of individual neurons. We previously reported that in both adult and L3 worms AWA sensory neurons respond to the addition of diacetyl. Interestingly, our current results show that L3 AWA responses are less reliable than adult responses at a lower diacetyl concentration. We also find, in support of our behavioral results, that different sets of sensory neurons encode diacetyl in adult and L3 animals. Moreover, the functional adult circuit is larger than the L3 one. Collectively, our results show that for adult and L3 worms different cellular circuits are required for attractive chemotaxis behavior, different sensory neurons encode diacetyl, and odors are encoded by cells which are dispensable for behavior. We will present these findings and our results analyzing differences in molecular pathways between L3 and adults.
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