Worm Breeder's Gazette 15(1): 44 (October 1, 1997)

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.

Serotonin and acetylcholine act in parallel to induce egg laying.

David Weinshenker, James H. Thomas

Department of Genetics, University of Washington, Seattle, WA 98195

We have been investigating the role of ACh (acetylcholine) in egg
laying.  5-HT (serotonin) is a strong inducer of egg laying in both the
wild type and in animals that lack HSN neurons (Trent et al., Genetics
104, pp.619-647, 1983), suggesting that it acts directly on the
egg-laying muscles.  Levamisole, a nicotinic ACh agonist, is also a
strong inducer of egg laying in the wild type, but on its own fails to
induce egg laying in animals that lack HSN neurons (Weinshenker et al.,
J Neurosci 15(10), pp. 6975-6985, 1995).  Based on this evidence, it
has been proposed that ACh acts upstream of the HSNs.  However, we
showed that mutants defective in ACh transmission, such as cha-1 and
unc-17, do not lay eggs in response to high levels of 5-HT (Weinshenker
et al., ibid.).  Based on this experiment, we proposed a model in which
5-HT and ACh act in parallel on the egg-laying muscles to induce egg
laying.  To further address this model, we tested whether levamisole
could potentiate 5-HT-induced egg laying in egl-1 mutants, which lack
HSN neurons.  We found that levamisole significantly increased the
number of eggs laid by 5-HT-treated egl-1(n487) animals in a well assay
(Figure 1).  Other combinations of drug dosages showed similar though
less robust results.  This demonstrates that levamisole does not
require HSN neurons to enhance egg-laying.  The egg-laying muscles are
innervated by two classes of neurons:  the HSNs, which contain both
5-HT and Ach vesicle transporters (VMAT and VAChT, respectively), and
the VCs, all of which contain VAChT and a subset (VC4 and VC5) which
contain VAChT and VMAT (Duerr et al., 1997 IWM abstract).  The
localization of both transmitter systems in neurons that innervate the
egg-laying muscles, in conjunction with our pharmacological data,
support the model that 5-HT and ACh act in parallel to induce egg

[The original article contains a figure.]

Figure 1.  Pharmacology of egl-1(n487) egg-laying.  Each data point
represents 48 animals.  Error bars represent SEM. * indicates a P value
calculated by the Mann-Whitney nonparametric test of <0.0001 comparing
5-HT 5 mg/ml and 5-HT 5 mg/ml + levamisole 10 ug/ml.