The cardio-regulator nerves of the hermit crabs: anatomical and electrophysiological identification of their distribution inside the heart

Abstract

1. The cardiac ganglion and the routes of the cardio-regulator nerves inside the heart were investigated anatomically and electrophysiologically in the hermit crabs (Aniculus aniculus andDardanus crassimanus). It was proved that the dorsal cardiac nerve containing three regulator axons on each side, one inhibitor and two accelerators, pierced the heart wall and connected with the cardiac ganglion. 2. The cardiac ganglion consisted of five large neurons and four small neurons. Configuration of the cardiac ganglion was analogous to the crab (Cancer orPortunus) cardiac ganglion in having a pair of circular trunks. However, arrangement of the large cells and the small cells was analogous to the lobster (Homarus, Panulirus orPalinurus) cardiac ganglion in alignment of the ganglionic cells. 3. The two acceleratory nerves had almost identical innervating routes. The route of the inhibitory nerve was significantly different from the routes of the acceleratory nerves inside the heart. 4. The inhibitory axon had the route only along the main trunk of the cardiac ganglion. IPSPs were recorded from large ganglionic cell bodies, one-toone to inhibitory impulses. 5. The acceleratory axons were carried not only in the main trunk but also in the circular trunk. There were acceleratory branches extending toward the periphery away from both the trunks. 6. EPSPs were recorded from large cell bodies in a one-to-one relationship to acceleratory stimuli. This provided direct evidence for ordinary synapses of the accelerator on the large ganglionic cells.