Morphological and electrophysiological evidences of synaptic switching in vestibular nerve of land snail Helix lucorum L

It is well known that the initiation of the reflex arcs of the vertebrate vestibular system occurs in the receptors of the labyrinthine organs which transmit the sensory signals via the ribbon synapses to the vestibular nerve afferents (an interneuron). In invertebrate species, and in particular, the statocyst of pulmonate mollusks, it is thought that the receptors send their axons out of the statocyst in the vestibular connective and establish the first synapse onto cerebral ganglia neurons, thereby bypassing the interneuron in the reflex arc. Morphological and electrophysiological techniques were used in this study to identify the first synapse in the vestibular arc of the mollusk Helix is actually within the vestibular connective on its way from the statocyst to cerebral ganglia. Cerebral interneurons were found that sent their neurites to the vestibular nerve, and thus have the potential to respond to the statocyst output or send efferent input to the statocyst. •Spikes in vestibular nerve do not pass trough the whole length of the nerve.•Neurotracer do not pass trough the whole length of the vestibular nerve.•These two facts suggest location of first synapse in vestibular system in the nerve.