The RIP interneurons mediate the only direct interconnections between the pharyngeal and
the central nervous systems. They have two laterally situated cell bodies immediately anterior
to the nerve ring. A dorsally directed process emanates from each cell body and runs round
the anterior surface of the ring neuropile to the contralateral side. These processes then turn
and run anteriorly, in the lateral labial process bundles, finally entering the pharynx near its
anterior extremity (d). The processes from RIP end soon after entering the pharynx with a
gap junction to the I1 interneurons of the pharyngeal nervous system (Albertson & Thomson
1976). A dorsal and a ventrally directed process leave each cell body, run round the anterior
surface of the ring and then enter the ring neuropile sub-dorsally and sub-ventrally. Here, the
processes fan out into dendrites, which intercept NMJs from URA (*a) and IL1 (*e). The
central part of each process carries on running posteriorly in the centre of the bundle of
processes from the labial sensory neurons (b) and eventually peters out. No obvious chemical
synapses are made by RIP, although what appear to be presynaptic specializations with no
synaptic vesicles are present adjacent to OLQ neurons on the dorsal side of the ring (+ and
a). The main synaptic inputs are from IL1 (*e), URA (*a), IL2 (*a), RIH (*c) and PVR (*c). There are gap junctions to RMED (c) ventrally.
Magnifications: (a-d) x 25500.
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