A self-regulating feed-forward circuit controlling C. elegans egg-laying behavior.
BACKGROUND
Egg laying in Caenorhabditis elegans has been well studied at the genetic and behavioral levels. However, the neural basis of egg-laying behavior is still not well understood; in particular, the roles of specific neurons and the functional nature of the synaptic connections in the egg-laying circuit remain uncharacterized.


RESULTS
We have used in vivo neuroimaging and laser surgery to address these questions in intact, behaving animals. We have found that the HSN neurons play a central role in driving egg-laying behavior through direct excitation of the vulval muscles and VC motor neurons. The VC neurons play a dual role in the egg-laying circuit, exciting the vulval muscles while feedback-inhibiting the HSNs. Interestingly, the HSNs are active in the absence of synaptic input, suggesting that egg laying may be controlled through modulation of autonomous HSN activity. Indeed, body touch appears to inhibit egg laying, in part by interfering with HSN calcium oscillations.


CONCLUSIONS
The egg-laying motor circuit comprises a simple three-component system combining feed-forward excitation and feedback inhibition. This microcircuit motif is common in the C. elegans nervous system, as well as in the mammalian cortex; thus, understanding its functional properties in C. elegans may provide insight into its computational role in more complex brains.
Zhang
Mi
M
San Diego State University and University of California, San Diego Joint Doctoral Program, La Jolla, CA 92093, USA.
Chung
Samuel H
SH
Fang-Yen
Chris
C
Craig
Caroline
C
Kerr
Rex A
RA
Suzuki
Hiroshi
H
Samuel
Aravinthan D T
AD
Mazur
Eric
E
Schafer
William R
WR
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D017173:Caenorhabditis elegans / Q000502:physiology*; D006706:Homeostasis; D009046:Motor Neurons / Q000502:physiology*; D009479:Neuropeptides / Q000378:metabolism; D009994:Osmolar Concentration; D052287:Oviparity / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism; D013569:Synapses / Q000378:metabolism; D013997:Time Factors; D014110:Touch
D009479:Neuropeptides; D012701:Serotonin; D000109:Acetylcholine