| Survival is a common everyday task throughout the animal kingdom, while the mechanisms by which survival is accomplished are a common focus of scientific research. One survival strategy that has been intriguing scientists for centuries is body patterning behavior in unshelled cephalopod molluscs---octopus, squid, and cuttlefish.; Used for protective camouflage as well as for inter- and intraspecific communication, cephalopod body patterns are produced primarily by chromatophore organs within the animals' skin. As a result of the direct neural innervation of the radial muscles surrounding these pigment-containing organs, cephalopods are able to alter their body coloration in less than a second, faster than any other member of the animal kingdom. A multitude of studies has been conducted concerning the morphology, physiology, and pharmacology of chromatophores in this unique system; however, little attention has been given to the motoneurons that control chromatophores. Therefore, this dissertation focuses on chromatophore motoneurons in the European cuttlefish Sepia officinalis, specifically those motoneurons controlling chromatophores of the animal's fin.; In the experiments presented here, the location as well as the peripheral and central organization of the fin chromatophore motoneurons was investigated. Through mapping and extracellular stimulation of the fin nerve, areas of the Sepia fin innervated by individual nerve branches were identified; further, a topographic pattern of axonal innervation of fin chromatophores was demonstrated. Subsequent retrograde labeling of fin nerve branches revealed the primary location of fin chromatophore motoneurons to be the posterior subesophageal mass (PSEM) of the brain. Analyses of three-dimensional reconstructions of this brain region suggested a possible topographic arrangement of fin chromatophore motoneuron somata. Taken together, these results expand our current knowledge of cephalopod body patterning control at the motoneuron level, opening doors for further exploration aimed at better understanding the mechanisms of this amazing survival behavior.; This dissertation includes my previously published co-authored materials. |
