Some like it hot: decoding neurotransmission in the worm's thermotaxis circuit.

Caenorhabditis elegans neuroscientists are on track to describe the world’s first functional connectome. The work by Ohnishi et al (2011) is an excellent example of this effort. Characterizing glutamatergic transmission within the neural circuit controlling locomotion in thermal gradients, they found that two thermosensory neurons, AFD and AWC, transmitted glutamate signals of opposite polarity to downstream interneuron AIY. The inhibitory glutamatergic signal from AFD promoted cryophilic locomotion, while the excitatory glutamatergic signal from AWC promoted thermophilic locomotion. The balance between these opposing transmissions determined temperature preference. Understanding information processing in the simplest of circuits will give insights into the workings of more complex neural networks. Translating sensory input to appropriate behavioural output is the fundamental problem addressed by nervous systems. Decoding the neural activity that makes this possible is the Holy Grail of neuroscience. To this end, Ohnishi et al (2011) demonstrate the power of studying a simple circuit. Simple is a relative term when it comes to nervous systems, but C. elegans is an excellent starting point. In their 1986 publication, White et al reported the structure and connectivity of the C. elegans nervous system. Using serial section electron micrographs, they identified B5000 chemical synapses and 600 gap junctions linking the worm’s 302 brain cells. C. elegans is the only