Functional properties of interganglionic motor neurons in the stomatogastric nervous system of the rock lobster

Abstract

1. In the decapod crustacea the stomatogastric nervous system, which involves the oesophageal (OG) and the stomatogastric (STGG) ganglia, commands the movements of the four successive parts of the foregut: oesophagus, cardiac sac, gastric mill and pylorus. The limited number of neurons (42) contained in the two ganglia are organized in several small networks producing various motor activities that are entirely centrally patterned. 2. In the rock lobster,Palinurus vulgaris, the motricity of the cardiac sac is ensured by three motor neurons. Two of them, CD1 and CD2, innervate all the extrinsic dilator muscles (7 paired muscles). 3. The CD1 cell body is located in theOG, and one of its axon branches reaches theSTGG. The CD2 cell body has been identified in theSTGG and its axon is connected to theOG region by the Stomatogastric nerve (stgn). 4. For the CD2, two sites of spike initiation (one in theOG and the other in theSTGG) produce two different activities (bursting and tonic discharges) and induce spikes travelling in opposite directions (orthodromic and antidromic) in itsstgn axon branch. In the CD2 cell body the intracellular potentials correlated in time to orthodromic and antidromic spikes have different waveforms. 5. The possibility of CD2 excitation from two functionally different ganglia suggests that this motor neuron a. might be involved in various motor programs, b. could be considered as a “two-way coordinating system” 6. The physiological properties of CD1 and CD2 are discussed in comparison with data on the stomatogastric nervous system of other rock lobster species.