Synaptic connections of buccal mechanosensory neurons in the opisthobranch mollusc, Navanax inermis

Mechanical stimulation of various areas of the pharyngeal wall and lips can produce EPSPs and IPSPs, as well as abruptly rising impulses, in primary sensory cells. IPSP fields are generally larger than EPSP fields and these fields are distributed without obvious order around fields from which afferent spikes are evoked. Apparentlly monosynaptic excitatory and inhibitory contacts are formed between primary sensory neurons. These synapses are blocked by high Mg²⁺ indicating chemical transmission. IPSPs are inverted by Cl^- injection. Excitatory inputs can be electrically far from the soma. Sensory cells form apparently monosynaptic excitatory or inhibitory contacts on motoneurons mediating pharyngeal expansion. Brief sensory excitation can initiate sustained firing within this neuronal population and sustained synaptic activity in moto-neurons. Interactions of sensory neurons may be important in information processing and in generating motor patterns. These neurons serve both primary sensory and interneuronal functions.