Electrophysiology and anatomy of the large neuron pairs in the subesophageal ganglion of the leech

Abstract

1. 1. The functional and structural characteristics of the large neuron pairs located within each of the four subganglia which comprise the subesophageal ganglion of the horse leech, Haemopis marmorata (Say), were investigated by intracellular recording and iontophoretic injection of the fluorescent dye, Procion Yellow. 2. 2. The large paired neurons of the three posterior subganglia are very similar to Retzius cell pairs in segmental ganglia: they are coupled by a bidirectional electrotonic junction and send their axons into their ipsilateral roots. 3. 3. The pair of large neurons in the anterior subganglion have decussating axons which enter their contralateral neuropiles, but lack both electrotonic interconnections and peripheral axons. 4. 4. The four large neuron pairs are probably serial homologues to Retzius cells and the anterior pair appears to have lost the peripheral function of Retzius cells—the control of mucus release by the skin.