Description: Hermaphrodite specific motor neurons. These cells die in male embryo. The HSNs are generated in the tail of the embryo and then migrate anteriorly to positions near the middle of the animal in both sexes. Therefore, it appears that the decision for cell death in male is not made at the time that the cells are born (Sulston et al., 1983). HSNR axon travels in the right fascicle of VNC, whereas HSNL axon travels in the left side. Axon outgrowth begins during L2 and L3 and is guided by the epithelial cells of the developing vulva and processes of the ventral nerve cord (PVP and PVQ processes). Vulval precursor cells guide the emerging HSN processes ventrally. They also organize the two HSN processes to join the ventral nerve cord in two separate fascicles and induce them to defasciculate from the ventral nerve cord and branch at the vulva (Garriga et al.,1993). Synapse formation takes place in the L3 and L4 stages. For a more detailed anatomical description of HSN neurons also refer to Reproductive System-Egg-laying apparatus.
Neurotransmitter: Serotonin (Desai et al., 1988). Express VMaT, CAT-1 (Duerr et al., 1999). Express tryptophan hydroxylase, TPH-1 (Sze et al., 2000). Acetylcholine (weak and variable staining). Rand and Nonet, 1997. Express neuropeptide-like proteins NLP-3 and NLP-15 (Nathoo et al., 2001) and NLP-8 (M. Barr, pers. comm.; Nathoo et al., 2001). Express FMRFamide-like neuropeptide FLP-5 (M. Barr; K. Kim and C. Li, pers. comm.).
Function: Innervate the vulval muscles and stimulate egg laying by hermaphrodites. Laser ablation of both HSN neurons results in animals that fail to lay eggs normally and become severely bloated with eggs retained in the uterus (egl phenotype). HSN neurons are the only neurons of the egg-laying circuitry, as defined by the synaptic connectivity, that have been shown to be required for normal egg-laying (Chalfie and White, 1988). Hermaphrodites that lack the HSN motor neurons do lay eggs in response to exogenous serotonin (Trent et al, 1983).
Receptor Expression: Express MEC-6 which is part of the degenerin/epithelial Na+ channel complex (Chelur et al., 2002). Express G protein-linked acetylcholine receptor GAR-2 (Lee et al., 2000). Possibly express glutamate receptor subunit GLR-5 (Brockie et al., 2001). Suggested to express GABA-A/glycine receptor-like protein GGR-2 (Fujiwara et al., 1996).