Final Report Summary - YTANIZAWA (Dissecting dynamic monoaminergic nervous system in c. elegans with genetically-encoded neuron activator protein channelrhodopsin-2)
The nervous system of the nematode c. elegans, a tiny worm which is around 1 mm long, consists of 302 neurons which were described by electron microscopic observation along with all the synaptic connections. The latter description included approximately 7 000 chemical and 700 electrical synapses.
Despite the simplicity of their nervous system, worms can sense and respond to various sensory stimuli including taste, odour, temperature, ultraviolet (UV) light and mechanical stimuli. Ease of genetic manipulation and its transparent body rendered it possible to control and monitor activity of specific neurons in vivo with genetically encoded tools. Finally, a huge repository of mutants allowed us to examine the roles of genes in the nervous system. These characteristics were anticipated to make c. elegans a satisfactory model to study multisensory processing in its simplest form at multiple levels, ranging from gene to behaviour.
Using c. elegans as a model we studied how sensory stimuli in different modalities interacted with each other in the nervous system. We utilised two stimuli as sensory inputs, namely actual mechanical stimuli to body and artificial activation of nociceptive neurons with light-gated ion channel channelrhodopsin-2, allowing for precise control of stimulus strength and location. The analysis of behavioural, i.e. withdrawal, response to these inputs had so far indicated no sign of additive effect when the two inputs were presented simultaneously. However, when interval was given between the two stimuli, significant enhancement of response to the second stimulus with enhanced motor activity was observed. This result indicated the existence of an 'arousal' change in the worm nervous system, which was also important for understanding indirect interaction among different modalities. By screening available mutants we also found that neuropeptide signalling played a role in arousal modulation.
By the time of the project completion, we were trying to measure the activity of neurons in behaving worms using genetically-encoded activity sensors, in order to understand where and how this change occurred at cellular level. In addition, activity monitoring could possibly identify multisensory integration effect at cellular level even though this was not previously behaviourally identified. We also planned to use stimuli in other modalities to discover novel interactions amongst them in multisensory integration and arousal modulation.
Despite the simplicity of their nervous system, worms can sense and respond to various sensory stimuli including taste, odour, temperature, ultraviolet (UV) light and mechanical stimuli. Ease of genetic manipulation and its transparent body rendered it possible to control and monitor activity of specific neurons in vivo with genetically encoded tools. Finally, a huge repository of mutants allowed us to examine the roles of genes in the nervous system. These characteristics were anticipated to make c. elegans a satisfactory model to study multisensory processing in its simplest form at multiple levels, ranging from gene to behaviour.
Using c. elegans as a model we studied how sensory stimuli in different modalities interacted with each other in the nervous system. We utilised two stimuli as sensory inputs, namely actual mechanical stimuli to body and artificial activation of nociceptive neurons with light-gated ion channel channelrhodopsin-2, allowing for precise control of stimulus strength and location. The analysis of behavioural, i.e. withdrawal, response to these inputs had so far indicated no sign of additive effect when the two inputs were presented simultaneously. However, when interval was given between the two stimuli, significant enhancement of response to the second stimulus with enhanced motor activity was observed. This result indicated the existence of an 'arousal' change in the worm nervous system, which was also important for understanding indirect interaction among different modalities. By screening available mutants we also found that neuropeptide signalling played a role in arousal modulation.
By the time of the project completion, we were trying to measure the activity of neurons in behaving worms using genetically-encoded activity sensors, in order to understand where and how this change occurred at cellular level. In addition, activity monitoring could possibly identify multisensory integration effect at cellular level even though this was not previously behaviourally identified. We also planned to use stimuli in other modalities to discover novel interactions amongst them in multisensory integration and arousal modulation.