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CELL TYPE LINEAGE LOCATION NEUROTRANSMITTER ASSOCIATED GLIA

MCL

MCR

Pharyngeal neuron

(Motor neuron, putative sensory )

AB.alpaaappp

AB.arapaappp

Pharynx anterior
bulb

Ach (Niacaris T, and Avery L., 2003, Raizen D. M. et al, 1995).

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

None
DESCRIPTION

MC's are a pair of cholinergic excitatory (motor) neurons. Anteriorly, they have free subcuticular (putative proprioceptive) endings between pm3 and pm4. Posteriorly, each cell sends a process which enters the nerve ring from the subventral nerve cord and makes a loop around the nerve ring. On the dorsal side these processes send a branch to the outside edge of the pharynx under the marginal cell 2 (mc2) of the opposite side. Once they reach the opposite ventral side, each process continues to run posteriorly under the ventral marginal cell, terminating at the very anterior of the isthmus. Their most prominent connections are gap junctions to M2 and they synapse strongly on the mc2 (Albertson D. J. and Thomson J. N., 1976). MC's also synapse onto pm4 (L. Avery pers. comm.)

Functions: MC's control the frequency of pharyngeal pumping (Avery L, and Thomas J. H., 1997). They initiate pharyngeal muscle action potentials, and hence, function as pacemakers of pumping. Release of Ach from MC neurons stimulates the muscle via a postsynaptic nicotinic ACh receptor encoded by eat-2 (Niacaris T, and Avery L., 2003, McKay J. P. et al, 2004). In eat-2 mutants MC is decoupled from pharyngeal muscle and the pharynx is unable to pump rapidly in the presence of food. Modulators of pharyngeal pumping such as exogenous serotonin mostly act through MC neurons.

Receptor expression: Express glutamate receptor subunit GLR-8 (Brockie P.J. et al 2001).