Type: Motor neuron
Connectivity:
- In MoW: HSN
- In WormWiring: HSNL_h, HSNR_h
- In Nemanode: HSN
In Wormbase: HSN, HSNL, HSNR
Lineage: AB plapppappa, AB prapppappa
Location: Midbody, close to vulva

Description: Hermaphrodite specific motor neurons, which 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/ Neuropeptide:
- Serotonin
- Acetylcholine - after late L4
- NLP-3; neuropeptide-like protein
- NLP-8; neuropeptide-like protein
- NLP-15; neuropeptide-like protein
- FLP-5; FMRFamide-like neuropeptide
(Pereira et al., 2015; Loer and Rand, 2022; Duerr et al., 2008; Nathoo et al., 2001; Sze et al., 2000; Desai et al., 1988; Duerr et al., 1999; Rand and Nonet, 1997; M. Barr; K. Kim and C. Li, pers. comm.)
Innexin expression:
- INX-1a
- INX-1b
- INX-2
- INX-3
- INX-7
- INX-10a
- UNC-7
- UNC-9
(Altun et al., 2009; Bhattacharya et al., 2019)
Receptor expression:
- ACR-14; nicotinic AChR non-alpha subunit
- MEC-6; part of the degenerin/epithelial Na⁺channel complex - interacts physically with the MEC-4 degenerin ion channel
- GAR-2; G protein-linked (muscarinic) acetylcholine receptor
- Possibly GLR-5; kainate-type ionotropic glutamate receptor subunit
- Possibly GGR-2; GABA-A/glycine receptor-like protein
(Fox et al., 2005; Chelur et al., 2002; Brockie et al., 2001; Lee et al., 2000; Fujiwara et al., 1996)
Function:
- Egg-laying: Laser ablation of HSN neurons and mutants lacking HSN reduced egg-laying while optogenetic activation of HSN stimulates egg-laying (Trent et al., 1983; Emtage et al., 2012)
- Locomotion: HSN modulates locomotion speed occurring in association with egg-laying behavior (Hardaker et al., 2001; Huang et al., 2023)
Reporters:
- At CGC: SK4013 zdIs13 [tph-1p::GFP]IV
- Other: