Somatotopic organization of mechanosensory afferents in the stellate ganglion of the squid, Euprymna.

Cephalopod molluscs are growing in popularity and use as comparative models of complex brains and behaviors. Although the gross anatomy of their central and peripheral nervous systems have been well characterized for decades, there is still very limited information about the diversity of cell types in each ganglion or lobe, their arrangement or their network properties. Unlike more standard neuroscience models, there are limited tools available for cephalopods and few validated techniques for imaging neural activity. Here, live calcium imaging in a reduced preparation of the stellate ganglion and mantle tissue reveals mechanosensory afferents and interneurons, which are arranged somatotopically in the ganglion. Retrograde labeling from stellate nerves confirms that neurons sending axonal projections to distinct dermatomes are organized in roughly oblong clusters along the dorsal side of the ganglion. This is the first demonstration of afferent somatotopy in cephalopods, and the first direct visualization of mechanoreceptive and mechano-nociceptive neurons that fire in response to localized, firm touch on the body surface. The methods and findings in this study open multiple new lines of enquiry related to sensory processing in the cephalopod nervous system.