[Giant polyfunctional neuron of the edible snail]

The structure of the receptive field of LPa3 neurone and its connection with the periphery were studied on semi-intact preparations of the snail Helix pomatia. It was found that: 1) The mechano-sensitive receptive field (excitatory) of the LPa3 neurone occupies nearly the whole surface of the snail's skin and internal organs. But latencies of LPa3 reactions to mechanical stimulation, the whole field may be divided into four zones: 50 to 60 ms, 100 ms, 130 to 140 ms and 200 to 250 ms. 2) Blockade of synaptic transmission with magnesium or cobalt has shown that relaying of the signal from the mantle receptors to the LPa3 neurone takes place in the peripheral nervous system. 3) Cobalt ionophoresis showed that the LPa3 neurone gives off processes to the right and left pallial nerves, the anal nerve and, occasionally, to the cutaneous nerve. During simultaneous intracellular recording from the LPa3 neurone and extracellular from the above nerves, action potentials are in every case recorded at first in the neurone body, and then, with a 20 to 30 ms delay, in the nerves. This means that the LPa3 neurone processes joining the nerves are axons. It is suggested that the sensory inputs and wide branching structures output of the LPa3 neurone axons make it an integrating polyfunctional system.