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CELL TYPE LINEAGE LOCATION NEUROTRANSMITTER ASSOCIATED GLIA

M4

Pharyngeal motor neuron

MS.paaaaaa

Pharynx anterior
bulb

Possibly Ach (Duerr J. et al, 1994).

Express the FMRFamide-related neuropeptide (FaRP), FLP-21 (Rogers C. et al, 2003).

None
DESCRIPTION

The cell body of M4 is located dorsally at the level of the nerve ring. 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 D. J. and Thomson J. N., 1976).

Functions: 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 L, and Thomas J. H., 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.

Receptor expression: Expresses G-alpha(s) coupled 5-HT7-like receptor, SER7b (Hobson R. J. et al., 2003). Suggested to express G-protein coupled muscarinic acetylcholine receptor ACM-2 (F47D12.2). acm-2 mutants display an increased pharyngeal pumping rate and an increased sensitivity to nicotine (Steger K and Avery L., 2001). Expresses glutamate receptor subunit GLR-8 (Brockie P.J. et al 2001).

See EM sections of M4 neuron in Handbook-Alimentary System/Pharyngeal Neurons .