The Mind of 
	a Worm


In this section, all the detailed connectivity data for each of the neuron classes are presented. The neuron classes are arranged in alphabetical order; the data for each class are fairly self-contained. Some classes have been grouped together because they share many common features; PLM is listed with ALM, PLN with ALN, PVM with A V M and PQR with AQR. The data that are presented were derived primarily from three reconstructed animals; the N2T series, the N2U series and the JSE series. Together these series covered the whole of the animal except for a region in the posterior body (figure A 1). This region was covered by a partial reconstruction of a male (N2Y series). Data from this animal provided information on the neurons of the posterior lateral ganglia and the motoneurons of the posterior ventral cord. The neuropile of the nerve ring and anterior ventral cord was also reconstructed from an L4 larva (JSH series, figure A 1). These data were mainly used as a check on the N2U reconstructions, which covered this region and are not shown, except in the case of RMF, where there was a significant difference between the two series.

Neuron topographies are shown in semidiagrammatic form for simplicity in presentation. Processes of neurons in C. elegans have few, if any, branches and tend to run in parallel process bundles. It is therefore possible to give a reasonably accurate impression of their three- dimensional structure by means ofsuch diagrams. Neurons that inhabit the regions of the nerve ring and anterior ventral cord are plotted out in diagrams on templates of the form shown in figure A 2. Similarly, neurons that have processes in the posterior ventral cord are plotted out in diagrams on templates of the form shown in figure A 3. Additional diagrams show the disposition of the cell bodies and processes of the class members within the animal, as seen from a lateral viewpoint. The nerve ring or anterior ventral cord diagrams are drawn as if from a dorsal viewpoint of an animal in which the nerve ring has been flattened so as to lie in the same plane as the ventral cord. The diagrams of neurons in posterior regions are again drawn from a dorsal viewpoint, but in this case an imaginary cut has been made along the dorsal mid-line and the animal opened out flat so that the ventral mid-line runs along the centre of the diagrams (figure A 3).

Processes that run in the regions covered by these types of diagram have been drawn out with all their synaptic connections listed. Synaptic connections mediated by chemical synapses are depicted by arrows. The direction in which the arrow points relative to the process indicates whether the process is presynaptic or postsynaptic for that particular contact. Synaptic contacts in which the process is one of several that are postsynaptic to a single presynaptic element are marked with an asterisk. All possible postsynaptic partners of contacts in which the process is presynaptic are shown. Gap junctions only appear between two elements and are marked with a T; no directionality is implied.

Certain synaptic connections have additional labels. These labels refer to a set of electron micrographs, which illustrate these connections. Many illustrations were taken from the JSH series because of the better quality of the pictures that were obtained from this series. Although the diagrams refer to connections seen in the other series, it was nevertheless possible to use these illustrations, because in most cases synaptic connections equivalent to those indicated in the diagrams could be found in the JSH series. References to illustrations of synaptic contacts are made by an index letter. These refer to the set of illustrations that is associated with the neuron class currently under discussion. If the index letter is preceded by an asterisk then the index letter refers to the set of illustrations associated with the class being referenced.

The two diagram formats described above do not cover the central body region, particularly the region of the ventral cord in which there are many synaptic contacts. Data from this region are presented in two ways: either as a table of synaptic contacts, in the case of interneurons which have processes that enter the region, or as individual diagrams, for motoneurons that are totally contained within the region. The motoneurons of the ventral cord have up to thirteen members in each of the classes, compared with a maximum of four members for all the other neuron classes in the animal. Only one 'typical' member of each of the ventral cord motoneuron classes is plotted, together with any atypical members that there may be in the class.

FIGURE A 1. The regions covered by the five separate reconstructions. The N2T, N2U and JSE series were adult hermaphrodites, the JSH series was an L4 larva and the N2Y series was an adult male.

FIGURE A 2. Diagram of the projection and template used for the plots of processes that run in the nerve ring and ventral cord. The nerve ring has been flattened out to lie in the same plane as the ventral cord, so that the posterior face of the nerve ring and the dorsal face of the ventral cord are directed out of the page. The shaded region indicates the extent of the neuropile in these regions. The isthmus of the pharynx passes through the hole in the middle of the nerve ring. The disposition of the major process tracts thatjoin this region of neuropile are shown.

FIGURE A 3. Diagram of the projection and template that is used for the plots of processes in the tail region. This is a dorsal view of the projection obtained by making an imaginary cut along the dorsal mid-line and then opening and flattening the animal. The outlines indicate the dispositions of the process tracts and ganglia. The rectum passes through the hole in the middle.

Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002