RIA is a set of two prominent interneurons with cell bodies situated in the lateral ganglia, adjacent to the neuropile of the nerve ring. Large processes enter the nerve ring directly sub-dorsally and run round the ring initially near the posterior face and enter the ventral cord. They loop round into the neuropile of the ventral ganglion and re-enter the ring on the ipsilateral side (g). They then run round the nerve ring near the anterior surface and in close association with the processes of their contralateral partners and the processes of RMD which often surround them (*d). RIA is presynaptic only on the distal regions ofits processes in the nerve ring, which have many synapses (f). It synapses onto SMD (a) and RMD (e) at numerous sites in these regions. There are also a few synapses to RIV (b). SMDand RMDL/RMDR (but not RMDD/RMDV) synapse back onto RIA reciprocally. Often reciprocal pairs are adjacent (d, e). RIA is one of the major integrating neurons in the nerve ring; it receives synaptic input from ADF (*a), SMD(d), RMDL/RMDR (e), AIZ (*a), RIH (*a), AIY (*e), AUA (*a), BAG (*a), AQR (*d), URX(*a), RIR (*a), RIB (*f), ASH (*d), AWB (*b) and RIV (*e). Characteristic structures are seen in the neuropile of the ventral ganglion, where RIA receives synapses from AIZ and AIY (c). Magnifications; (a, d, e) x 25500, (b) x 17000, (c, f) x 12750.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002