Worm Breeder's Gazette 4(1): 22
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Egg-laying by C. elegans has a variety of features that make it an attractive system with which to study the development and functioning of a simple behavioral network. First, egg-laying is a quantitative behavior, making it easy to assay. Second, the egg-laying system is anatomically simple, involving only 16 muscle cells and about 20 neurons. Third, the 'wiring diagram' has been established by reconstruction from serial section electron micrographs. Fourth, the cell lineages that generate most of the egg-laying system are rigidly determined and precisely known. Fifth, genetic studies are straightforward: egg-laying is a nonessential behavior, and both egg- laying deficient mutants and revertants of such mutants can be obtained by selections. Sixth, egg-laying is influenced by environmental stimuli, such as food and touch, allowing one to examine how this behavior is modulated. Anatomical studies indicate that the vulva, 8 vulval muscles, 8 uterine muscles, 6 Class C ventral cord neurons, and 2 hermaphrodite- specific neurons appear likely to be involved in egg-laying. Elimination of these elements, either by mutation (see Newsletter Vol. 1 No. 2 for how egg-laying deficient mutants have been isolated) or by using a laser microbeam, confirms the involvement of all of them except the Class C neurons. Destruction of the Class C neurons with a laser does not inhibit egg-laying. Since the Class C neurons innervate the vulval muscles, it appears that they have a modulatory, possibly inhibitory, role in egg-laying. Many pharmacological agents have been tested for possible effects on egg-laying. A variety of nicotinic (e.g., nicotine and arecoline) but not muscarinic (e.g., methacholine and bethanachol) acetylcholine agonists stimulate egg-laying, suggesting that a nicotinic acetylcholine receptor may be involved. Serotonin (5- hydroxytryptamine) and related compounds (5-hydroxytryptophan and 5- methoxytryptamine) also stimulate egg-laying. Octopamine (p- hydroxyphenylethanolamine) appears to inhibit egg-laying. Mutants or laser-ablated animals defective in egg-laying have been tested for response to 12 drugs that stimulate egg-laying by normal hermaphrodites. Such experiments indicate whether each of these drugs acts before or after the egg-laying lesion in the animal tested. Using this approach, we hope that it will prove possible to deduce a pathway for egg-laying that is consistent with the known neuroanatomy.