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Fig. 1. Projections and activity patterns of the inferior ventricular (IV) neurons.
(A) Schematic drawing of the foregut of the crab C. pagurus with the
brain and the stomatogastric nervous system (STNS) attached. The foregut
consists of four chambers with different functions: the esophagus
(swallowing), the cardiac sac (storage of food), the gastric mill (chewing of
food) and the pylorus (filtering of food). The STNS is located on the dorsal
side of the foregut, and the brain on the dorsal side of the esophagus. The
dorsal ventricular nerve (dvn) and the inferior ventricular nerve
(ivn) were recorded extracellularly. For the ivn, we used a
pair of hook electrodes to determine the direction of spike propagation.
Adapted from Katz et al. (Katz et al.,
1989). (B) Representation of the isolated STNS and the brain in
C. pagurus. The STNS consists of four ganglia, including the unpaired
stomatogastric ganglion (STG, 26 cells) and esophageal ganglion (OG,
15–16 cells) and the paired commissural ganglia (CoG, each about 500
cells). The brain and the STNS are connected via the unpaired
ivn and the paired circumesophageal commissures (coc, dashed
lines). In preparations using the isolated STNS, the coc were
transected. dgn, dorsal gastric nerve; dpon, dorsal
posterior esophageal nerve; ion, inferior esophageal nerve;
lgn, lateral gastric nerve; lvn, lateral ventricular nerve;
mvn, medial ventricular nerve; son, superior esophageal
nerve; stn, stomatogastric nerve. (C) Extracellular recordings of the
ivn (top and middle traces) and the dvn (bottom trace) in
the intact animal. Both the ivn recording closer to the brain
(ivn high; top trace) and the ivn recording closer to the
STNS (ivn low; middle trace) show the activities of neurons that
descend from and ascend to the brain. LP, lateral pyloric neuron; PD, pyloric
dilator neurons; PY, pyloric constrictor neurons. (D) Magnification of Fig.
1C, showing the spikes of two neurons that descend from the brain to the STNS.
The descending spikes first occurred on the ivn high recording (top
trace) and then on the ivn low recording (lower trace).
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