Worm Breeder's Gazette 14(4): 75 (October 1, 1996)

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.

Acetylcholine is an Important Neurotransmitter for the Regulation of Egg-laying

David Ramirez, William Schafer

Department of Biology, University of California, San Diego La Jolla, CA 92093-0116

Previously our lab observed that cha-1 mutants, which are defective in
choline acetyltransferase, an enzyme required for the synthesis of
acetylcholine (Ach), are both Egl-c and serotonin hypersensitive. This
suggests that Ach plays an inhibitory role in egg-laying. This is a
surprising result since the cholinergic agonist, levamisole, stimulates
egg-laying. Further evidence of acetylcholine's regulatory role is that
the ace-2; ace-1  double mutant is egg-laying defective (Egl-d). The
ace-2; ace-1 double mutant, is defective in two of three Acetylcholine
esterases and thus has very low levels of Ach esterase activity.
Additionally we have obtained pharmacological evidence for this proposed
down-regulatory mechanism. Application of mecamylamine, a general
cholinergic antagonist, stimulates egg-laying.

Interestingly, carbachol, a general cholinergic agonist also stimulates
egg-laying but requires the HSN's while mecamylamine can also stimulate
egg-laying in egl-1  mutants. This leads us to the belief that Ach could
have a stimulatory role that requires the HSN's and also have an
inhibitory role that is parallel to the HSN's.

We have tested mutants known to affect Ach receptor function for serotonin
hypersensitivity ( unc-29, unc-38, unc-63, unc-74, lev-1, lev-9, and
lev-10). All of the mutants conferred hypersensitivity to serotonin except
lev-1  and lev-9  gene mutations. These results suggest that Ach is
working through nicotinic cholinergic receptors, though we haven't
excluded the possibility that Ach may also be working via muscarinic
cholinergic receptors.

Furthermore, we have attempted to identify the location of Ach release
(i.e. from the VA's, VB's, or VC's). Using an unc-17 (e813) allele, shown
by Jim Rand to be a promoter mutation which blocks Ach synthesis in the
VA's and VB's but not in the VC's, we have found that these mutants are
Egl-c and serotonin hypersensitivity. This result is interesting since the
VC's, rather than the VA's and VB's, seemed to be more likely to function
as regulators of the vulval muscle because of their location and synaptic

We are now taking further steps to attempt to identify the location of the
cholinergic receptors (i.e. on nervous vs. muscle tissue or both). We are
beginning mosaic analysis to answer this question. In addition we are
carrying out a screen to identify genes that rescue the Egl phenotype of
the ace-2; ace-1 double mutant.