Description: Pharyngeal interneuron. I5 has a very large cell body which is located on the ventral side of the terminal bulb. Two short branches come out of the cell body and split into anterior and posterior projections. At the level of the terminal bulb commissure, the anterior processes end on the cell bodies of M2 motor neurons and are linked to them by desmosomes. Posteriorly, the processes run between pm6 and pm7 and reach a subdorsal position adjacent to the subdorsal marginal cells. Each branch then travels anteriorly to the terminal bulb commissure where they fuse across the dorsal side. Ventrally, these also become attached to the cell bodies of M2 motor neurons by desmosomes. At the level of the subventral nerve cords each branch turns anteriorly and travels to the nerve ring. They make a single closed loop within the nerve ring. A short anterior projection is also seen in the dorsal side of the nerve cord (Albertson and Thomson, 1976).
Neurotransmitter: Serotonin, based on serotonin immunoreactivity (Sawin et al., 2000). Possibly glutamate (Lee et al., 1999).
Function: M3 and I5 are suggested to facilitate bacterial trapping by regulating the relative duration of muscle relaxation in different regions of the pharynx (Avery, 1993). Pharyngeal relaxation becomes quicker when I5 is ablated. When both I5 and M3 are ablated there is a delay in relaxation that is indistinguishable from that caused by ablation of M3 alone, suggesting I5 slows down relaxation by inhibiting M3 (Avery and Thomas, 1997)
Receptor Expression: