The action of acetylcholine, dopamine and 5-hydroxytryptamine on the spontaneous activity of the cells of Retzius of the leech, Hirudo medicinalis.

Neuropharmacological and neurophysiological studies have been undertaken on both the longitudinal muscle and on the segmental ganglionic neurones of the leech, Hirudo medicinalis. The longitudinal muscle of the leech was developed by Minz (1932) from the initial observations of Fuehner (1918) as an assay procedure for acetylcholine. More recently this same preparation has been used as an assay tissue for 5-hydroxytryptamine (Poloni, 1955), and has subsequently been reinvestigated by Schain (1961). Acetylcholine causes the muscle to contract whereas 5-hydroxytryptamine has a relaxing action and reduces the amplitude of contractions produced by acetylcholine. Electrophysiological recordings from the neurones of the leech ventral nerve cord were first performed by Hagiwara & Morita (1962) and by Eckert (1963). Studies concerning the role of the glial cells in this preparation were made by Kuffler & Potter (1964) and Nicholls & Kuffler (1964). Penn & Loewenstein (1966) have studied the role of calcium in maintaining electrical connections between the nerve cells of Retzius. The actions of acetylcholine and 5-hydroxytryptamine on ganglionic transmission in the leech have been studied by Kostowski (1965) using extracellular recording methods. Kostowski suggests that acetylcholine enhances transmission in the leech cord, while 5-hydroxytryptamine may act as an inhibitory agent. The present study was undertaken to investigate the action of possible chemical transmitter agents on the bioelectrical activity of the cells of Retzius (Retzius, 1891). A preliminary report of this investigation has been communicated to the Physiological Society (Kerkut, Sedden & Walker, 1967a).