The Input-Output Organization Of a Pair of Giant Neurones in the Mollusc, Anisodoris Nobilis (MACFARLAND)

1. Each of the two gastro-oesophageal ganglia of the nudibranch mollusc, Anisodoris nobilis , contains one giant neurone ( G cell) whose axon is directed toward the oesophagus in the gastro-oesophageal nerve. 2. In the absence of stimulation the G cells are normally silent. However, they receive inhibitory and excitatory synaptic inputs from more central ganglia and a predominantly excitatory input from the periphery. The inputs from the central ganglia are bilaterally distributed to both G cells, whereas the inputs from the periphery are limited to the ipsilateral G cell. 3. Intracellular stimulation shows that there is no interaction between the G cells, nor between the G cell and other cells in the same or contralateral gastro-oesophageal ganglia. 4. The axon of the G cell makes synaptic contact with a series of peripheral cells ( P cells). In most P cells the post-synaptic potential elicited by intracellular stimulation of the G cell is constant in amplitude and latency and probably results from a unitary monosynaptic contact. Intracellular stimulation shows that the P cells are not connected to the G cell. 5. The P cells are inter-connected by low-resistance electrotonic junctions which allow slow potentials of either polarity to spread between cells. These junctions exist between distant as well as adjacent peripheral neurones. 6. Our results show that the G cell functions as a command interneurone for an aggregate of electrically interconnected peripheral neurones.