M4 sends two ventral branches, which run around the nerve ring on each side. These processes then cross to the other side and continue to run posteriorly in the subventral nerve cords. In the isthmus, M4 makes neuromuscular synapses on pm5. The two processes turn dorsally in the terminal bulb commissure, meet each other in gap junctions and run anteriorly in the dorsal nerve cord for some variable distance through the isthmus before ending. These also make synapses on pm5 on the dorsal side. Unlike other pharyngeal motor neurons, M4 contains darkly-staining vesicles, similar to the 65 nm dense core vesicles associated with some amphidial neurones (Albertson and Thomson, 1976)
Neurotransmitter/ Neuropeptide:
- Acetylcholine
- Glutamate - weak
- FLP-21; FMRFamide-related neuropeptide (FaRP)
(Pereira et al., 2015; Duerr et al., 2008; Rogers et al., 2003; Rand and Nonet, 1997-Appendix 2; O. Hobert pers comm.)
Innexin expression:
None, yet reported, although described to have gap junctions in adult animals (Albertson and Thomson, 1976)
Receptor expression:
- SER7b ; G-alpha(s) coupled 5-HT7-like receptor
- GLR-8; glutamate receptor subunit
(Hobson et al., 2003; Brockie et al., 2001)
Function:
-M4 is essential for feeding in wild-type worms. M4 synapses on the isthmus and the terminal bulb, and is necessary for posterior isthmus peristalsis (Avery and Thomas, 1997). Worms lacking M4 continue pumping, however, bacteria become trapped in corpus and anterior isthmus and these worms fail to grow since they can not pass the food to their intestines |
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