Integrative Molecular and Ultrastructural Characterization of the Intramuscular Nerve Cords of the Octopus Arm
Meaghan Klos, Mox Engelman, John Benedict
Department of Biology
Faculty Supervisor: Robyn Crook
Cephalopod arms possess a complex, interconnected system of nerve tracts and ganglia comprised of diverse complements of neurons and other cells. Parallel to the main axial tract run four intramuscular nerve cords (INC) that span the length of each arm and link together distant arms. While anatomical studies have begun elucidating INC structure and function, little is known about the specific cell types within the INC. In this study we characterized ultrastructural features and molecular identity of cell types in both the oral and aboral cords. Using complementary datasets of serial blockface electron microscopy and multiplex HCR in fixed tissue, we identified glutamatergic and peptidergic neurons, and multiple types of morphologically distinct cells. We also show that the oblique connectives, hypothesized to integrate with INCs, remain physically separate despite close contact. This study provides new information about the structure of the intramuscular nerve cord of Octopus bocki, and insight as to what functions these characterized neurons might provide. Overall we show that the INCs are more complex than reported, lending novel understanding into integrative control of sensing and movement in semi-autonomous octopus arms.