Tuchina, O.P., Zhukov, V.V. and Meyer-Rochow, V.B. 2012. Central and peripheral neuronal pathways revealed by backfilling with neurobiotin in the optic, tentacular and small labial nerves of Lymnaea stagnalis. —Acta Zoologica (Stockholm) 93: 28–47.
The TOLm complex in Lymnaea stagnalis contains nerves n. tentacularis, n. opticus and n. labialis minor. Ligatures close to where the complex enters the central nervous system (CNS) did not prevent penetration of retrograde-transported neurobiotin into fibres of an adjacent nerve. Axonal bifurcation within the common nerve trunk or tight junctions may be involved, providing a basis for peripheral axon reflexes. Peripheral terminations of n. tentacularis, n. labialis minor and n. opticus revealed numerous cell bodies in the tentacular epithelium, some in the tentacle and lip region, and some in the retina. These cell bodies’ central projections were mapped by neurobiotin and verified by dissections of the cerebro-cerebral commissure and cerebro-pleural connective. Afferent fibres of the nerves form dense sensory neuropils in the ipsilateral cerebral ganglia. Direct connections between n. tentacularis and some visceral as well as parietal nerves were demonstrated by backfillings through n. pallialis dexter internus et externus, n. pallialis sinister and n. intestinalis. Labelling of n. tentacularis revealed neuronal bodies in every ganglion and stained fibres in most of the peripheral nerves. Fewer neurons were identified through n. labialis minor and n. opticus. We discuss our results in relation to different behavioural forms like defence and feeding reactions in L. stagnalis.