Glanfield, Wendy (1997) A morphological and electrophysiological study of the cephalopod posterior chromatophore lobe. PhD thesis, University of Sheffield.
Abstract
1. A unique feature of cephalopods is their skin, which contains thousands of chromatophore organs under direct neural control from the chromatophore lobes of the brain. Control of skin colour changes are described in this thesis in terms of the morphology, electrical activity, and pharmacology, of the Posterior Chromatophore Lobe (PCL) neurons, in the cephalopods Alloteuthis sub ulat a, Loligo vulgaris, Eledone cirrhosa, and Octopus vulgaris. The morphology and electrophysiology of the Lateral Basal Lobe (LBL) neurons and the influence of this lobe on PCL neurons are also investigated. 2. The chromatophore lobe neurons are inaccessible in vivo and thus a brain slice preparation was developed to allow access to the motoneurons in the PCL. This allowed a study of the morphology, electrical activity, and pharmacology of these neurons to be carried out. 3. An artificial sea water solution was developed to provide a suitable bathing medium for the brain during slicing and recording procedures. The brain slice could be maintained for up to eight hours using this medium, and stable intracellular recordings could be obtained. 4. Over 500 neurons in PCL slices, from 146 animals, were impaled with intracellular recording electrodes and of these, 115 were subsequently filled with the fluorescent dye Lucifer Yellow to reveal their morphologies. It was found that PCL neurons are regularly arranged, with the largest cell somata being on the periphery of the lobe. On the basis of differences in the morphologies and locations of these cells, they could be divided into four types, referred to in this thesis as cell type I, II, III and IV. 5. The intracellular recordings revealed four different types of spontaneous electrical activity: tonic, irregular bursting, regular bursting, and excitatory postsynaptic potentials (EPSPs). Regular bursting activity was only observed in cell type II. EPSP activity was observed in all the cell types but was most predominant in cell type III. 6. Evidence of both dye and electrical coupling between PCL neurons was obtained. The possible implications of this coupling are discussed. 7. In the light of the existing morphological data, the afferent input from the Lateral Basal Lobe (LBL) was established physiologically by electrical stimulation of the LBL tract connecting with the PCL. The effect on the PCL neurons was excitatory or inhibitory. It is proposed that one LBL cell influences many PCL motoneurons via inhibitory and excitatory synapses. Patterning on the skin could therefore be achieved by control of the frequency of activity displayed in PCL motoneurons, which is regulated by the LBL neurons. 8. Extracellular field potentials revealed the extent and nature of the activity in groups of PCL neurons in response to LBL tract stimulation. These responses were largest in the neuropil area, becoming weaker towards the periphery of the lobe. Field potential responses showed that the synaptic connections between the LBL and PCL neurons occurred at the point where the LBL tract enters the PCL neuropil. 9. Application of acetylcholine (ACh) and carbachol to tissue slices, caused tonically active PCL motoneurons to stop firing, while 5-HT caused an increase in the frequency of tonic activity and the number of EPSPs. The application of antagonist drugs of putative neurotransmitters revealed that L-glutamate, 5-HT and ACh receptors are present on the postsynaptic membrane of PCL cells. 10. These results demonstrate that the brain slice is a useful and versatile preparation for the study of the electrical properties and connections of cells in the cephalopod brain and provide the first physiological clues about how PCL neurons may be controlled as they change the colour of cephalopod skin.
Metadata
Keywords: | Zoology |
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Awarding institution: | University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Animal and Plant Sciences (Sheffield) |
Identification Number/EthosID: | uk.bl.ethos.264449 |
Depositing User: | EThOS Import Sheffield |
Date Deposited: | 12 Oct 2023 11:05 |
Last Modified: | 12 Oct 2023 11:05 |
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