The structure of the nervous system of the nematodeCaenorhabditis elegans

Abstract

The structure and connectivity of the nervous system of the nematode Caenorhabditis elegans has been deduced from reconstructions of electron micrographs of serial sections. The hermaphrodite nervous system has a total complement of 302 neurons, which are arranged in an essentially invariant structure. Neurons with similar morphologies and connectivities have been grouped together into classes; there are 118 such classes. Neurons have simple morphologies with few, if any, branches. Processes from neurons run in defined positions within bundles of parallel processes, synaptic connections being made en passant. Process bundles are arranged longitudinally and circumferentially and are often adjacent to ridges of hypodermis. Neurons are generally highly locally connected, making synaptic connections with many of their neighbours. Muscle cells have arms that run out to process bundles containing motoneuron axons. Here they receive their synaptic input in defined regions along the surface of the bundles, where motoneuron axons reside. Most of the morphologically identifiable synaptic connections in a typical animal are described. These consist of about 5000 chemical synapses, 2000 neuromuscular junctions and 600 gap junctions.

High-accuracy neurite reconstruction for high-throughput neuroanatomy

“…The few published reconstructions of entire neurites from EM data were performed by highly trained and dedicated experts, and extensively proof-read by the same or other experts 3,11,[19][20] . For the C. elegans connectome a number of corrections were published recently 21 , using the original image series.…”

A Predictable Worm: Application of Caenorhabditis elegans for Mechanistic Investigation of Movement Disorders

“…The relatively small number of neurons in the worm represents a conveniently quantifiable population of cells that may be used to discern the effects of genetic and environmental factors on neuron health and function. The fate and synaptic connections of the neurons of C. elegans are well characterized [1]. Readily available references for the lineage and connectivity of each of the neurons provide a valuable resource for investigating the phenotypic effects associated with genes of interest [2].…”

Temperature sensing across species

“…Electron microscopy reconstruction analyses of the nematode nervous system have shown that the interneuron AIY is the primary postsynaptic partner of AFD. AIY in turn makes a functional synapse with the interneuron AIZ and the major integrating interneuron RIA, which also receives synaptic input from AIZ [6]. When AIY and AIZ interneurons in animals are individually ablated, these animals are also deficient in isothermal tracking.…”

“…AFD sensory nerve endings are severely defective in these mutants [14]. AFD neurons are distinguished by their elaborate microvillar finger-like structures that emanate from a single cilium [6,14]. However, these microvilli are completely lost in ttx-1 mutants, and the morphology of the cilia is grossly abnormal with its length approximately three times the norm [14], suggesting that Ttx-1 mediates the morphogenesis of AFD sensory nerve endings [13].…”