Figure 1.

The medicinal leech and experimental design. A, Diagram of the central nervous system of the leech, characterized by a ventral nerve cord interspersed with 21 segmental ganglia descending from a compound cephalic ganglion. B, Schematic of the placement of neuronal somata on the ventral surface of a single ganglion. The bilateral Retzius cells are colored red and labeled R. C, Neurobiotin fill of a Retzius cell showing its soma, neurites, and axons (a faintly labeled contralateral soma is present because of electrical coupling of the two cells). D, US paradigm demonstrating the positioning of the transducer, intracellular electrode, and ganglion preparation. E, Side view of the electrode displacement paradigm demonstrating the movement of the recording electrode.