[
Worm Breeder's Gazette,
1984]
The anatomy of the nervous system of the large parasitic nematode Ascaris des is similar in many respects to the nervous system of C. elegans. An adult Ascaris can be as large as 30 cm and weigh 10 grams while a typical C. elegans may be 1 mm long and weigh a few micrograms. Yet, both worms have about the same number of neurons. In addition, the nerve cells are arranged in the same basic pattern throughout the animals and many of the neurons have similar shapes in the two worms. It has been known for some time, for example, that motorneurons in the two animals have identical shapes and make similar synaptic connections. On the other hand, homologies between interneurons in the two species have been less clear. In order to compare different classes of neurons more fully, we have examined the anatomy of the retrovesicular ganglion (RVG) of Ascaris, which contains both interneurons and motorneurons. We find that each RVG cell in Ascaris appears to have a homolog in the RVG of C. elegans. The homologies are based on the unpublished reconstructions of head neurons by John White. [see Figure 1]
[
Worm Breeder's Gazette,
1977]
The motor nervous system of Ascaris consists of five sets of segmented neurons each containing eleven cells that make synapses onto muscle, together with six ventral interneurons that make synapses onto some of the motorneurons. The neurons can be divided into seven classes (see figure) that appear to be structurally identical to the seven classes in C. elegans, with the following equivalences . [See Figure 1] The dorsal n.m.j. cell types C, D and E receive interneuron input, but the A cell receives synapses only from ventral motorneurons. The ventral F and G cells receive input from interneurons; the B cells receive synapses only from dorsal motorneurons. All these output cells make synapses with muscle only in one nerve cord. Each segment has one copy of cell types A, D and E, and two copies of types B, C, F and G. Anatomical similarities (relative positions in nerve cords; details of the patterns of neuromuscular connectivity) are used to assign functional equivalences in the dorsal and ventral cords. [See Figure 2] The function of types of A, B, C, D and E neurons has been determined physiologically (see Walrond and Kass). The motorneuron synapses onto the inhibitory neurons provide pathways for reciprocal inhibition, between both cords, that is generated peripherally rather than centrally. [See Figure 3]