Inputs and outputs of giant neurons B1 and B2 in the buccal ganglia of Helix pomatia: an electrophysiological and morphological study.

The identified giant neurons B1 and B2 in the buccal ganglia of Helix pomatia were studied with electrophysiological and morphological techniques in order to establish a baseline for the study of neuronal communication in a relatively simple nervous system. Different synaptic inputs to neurons B1 and B2 were found to come from neurons of the buccal ganglia and to come via buccal nerves. In the epithelium of the pharynx, fibers of bipolar peripheral neurons could be stained, the central fibers of which probably contribute to the synaptic inputs of neurons B1 and B2. The dendrites of neurons B1 and B2 are mainly situated in anterior and lateral parts of the neuropil of the buccal ganglia, respectively. The axon of neuron B1 was traced to the esophagus/stomach. Intracellular stimulation of the neuron induces both a contraction of the longitudinally oriented fibers and an increase in the amplitude of spontaneously occurring peristaltic contractions of the esophagus. The axons of neuron B2 run to both salivary glands. Thin axon collaterals showing multiple swellings follow the bases of the epithelial cells of the salivary gland. The functioning of neurons B1 and B2, which are homologous to giant neurons in the buccal ganglia of other molluscs, is discussed.