From injury to full repair: nerve regeneration and functional recovery in the common octopus, Octopus vulgaris

Abstract

Spontaneous nerve regeneration in cephalopod molluscs occurs in a relative short time after injury, achieving functional recovery of the lost capacities. In particular, transection of the pallial nerve in the common octopus (Octopus vulgaris) determines loss and subsequent restoring of two functions fundamental for survival, i.e., breathing and skin patterning, the latter involved in communication between animals and concealing. The phenomena occurring after lesion have been investigated in a series of previous studies, but a complete analysis of the changes occurring at the level of the axons and the effects on animals’ appearance during the whole regenerative process is still missing. Our goal is to determine the course of events following injury, from impairment to full recovery. Through imaging of the traced damaged nerves we were able to characterize the pathways followed by fibres during regeneration and end-target re-innervation, while electrophysiology and behavioural observations highlighted regaining of functional reconnections between central brain and periphery, using the contralateral nerve in the same animal as internal control. The final architecture of a fully regenerated pallial nerve does not exactly mirror the original structure, however, functionality returns to match the phenotype of an intact octopus with no observable impact on the behaviour of the animal. Our findings provide new important scenario for the study of regeneration in cephalopods and highlight octopus pallial nerve as a valuable ‘model’ among invertebrates.