Abstract
Publisher Summary This chapter reviews the Retzius cell of the leech hirudo medicinalis. The central nervous system of the leech consists of a chain of very similar ganglia along a ventral nerve cord. There is one ganglion per body segment has been observed, with several ganglia being fused together in the anterior and posterior ends of the animal. Two lateral roots run to the body wall from both sides of each ganglion. The ganglia are divided into six compartments or packets. The Retzius cells are the two largest cells on the ventral surface of the anterior packet. The Retzius cells in each ganglion are electrically coupled such that firing of one cell induces activity in the other. The major Retzius cell processes go to the body wall. They appear to control the secretion of mucus from the skin of the leech. Thereafter, electrophysiological responses of the Retzius cells to exogenous 5-HT and dopamine are inhibitory, while acetylcholine is excitatory to the Retzius cells. However, known inhibitory neurons of the leech muscle do not contain 5-HT.
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