Thesis advisor: Renato Mirollo / A typical neuron receives input from more than 10,000 other neurons. These inputs each get processed differently, depending on the neuron's morphology, chemistry, etc. The neuron may fire, in turn stimulating other nerve cells. The structure of a nerve cell determines the rules that govern the system but not the neuronal response. Also, the type of input affects the firing decision. Hence, a neuron can be viewed as a dynamical system and may be studied as such. The Hodgkin-Huxley model describes neuronal dynamics but this model is very complex. Here, I will study some simpler models in an attempt to determine what makes a neuron fire. In particular, I will ask: What is the effect of "rhythmic" impulses on a neuron? / Thesis (MA) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Mathematics.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

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Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 115-124).

Thesis supervisor: Steven H. Green. Includes bibliographic references (p. 171-202).

Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on Mar. 2, 2009). Includes bibliographical references.

The effects of a soft coral derived product and its major active component, 3-carboxyl-methylpyridinium (CMP), were assessed in cultured neurones from dorsal root ganglion (DRG) and the hippocampus, and in hippocampal slices. Application of the soft coral preparation or CMP to cultured DRG neurones reduced an outward potassium current, causing attenuation of spike frequency adaptation. This evoked a switch to multiple firing in previously single firing DRG neurones.

L’activité électrique des neurones est déterminée par des interactions complexes entre leurs propriétés morphologiques et biophysiques. Les neurones dopaminergiques (DA) de la substance noire compacte (SNc) présentent une caractéristique morphologique peu commune parmi les neurones de mammifères: leur axone émerge fréquemment d’une dendrite à une distance très variable du soma. Malgré cette importante variabilité dans la localisation de l’axone, peu d’articles ont étudié un lien potentiel entre morphologie neuronale et activité électrique dans ces cellules. Dans un premier article, nous avons exploré l’importante variabilité observée dans les neurones DA en caractérisant de nombreux paramètres morphologiques et biophysiques. Nos résultats suggèrent que la géométrie de l’AIS n’affecte pas significativement la forme du potentiel d’action ni l’activité pacemaker. En revanche, l’activité électrique est influencée par la morphologie et les conductances somatodendritiques. Dans une seconde étude, nous avons caractérisé le développement morphologique des neurones DA au cours des trois premières semaines post-natales. Nous avons observé une croissance asymétrique de l’arbre dendritique: la dendrite portant l’axone semble se complexifier plus que les autres dendrites. Cette asymétrie est associée à une contribution différente de la dendrite portant l’axone et des dendrites ne portant pas l’axone à la forme du potentiel d’action. Ces résultats suggèrent que les neurones DA de la SNc sont robustes aux variations morphologiques de l’axone et que les particularités morphologiques et biophysiques de leur arbre dendritique minimisent l’influence de l’AIS sur leur activité électrique. / Neuronal output is defined by the complex interplay between the biophysical and morphological properties of neurons. Dopaminergic (DA) neurons of the substantia nigra pars compacta (SNc) are spontaneously active and generate a regular pacemaking activity. While most mammalian neurons have an axon emerging from the soma, the axon of DA neurons often arises from a dendrite at highly variable distances from the soma. Despite this large cell-to-cell variation in axon location, few studies have tried to unravel the potential link between neuronal morphology and electrical behaviour in this cell type. In a first article, we explored the high degree of cell-to-cell variability found in DA neurons by characterising several morphological and biophysical parameters. While AIS geometry did not seem to significantly affect action potential shape or pacemaking activity, we found that the electrical behaviour of DA neurons was particularly sensitive to somatodendritic morphology and conductances. In a second study, we characterised the morphological development of DA neurons during the first three post-natal weeks. We observed an asymmetric development of the dendritic tree, favouring the elongation and complexity of the axon-bearing dendrite. This asymmetry is associated with different contributions of the axon-bearing and non-axon bearing dendrites to action potential shape. Overall, the two studies suggest that DA neurons of the SNc are highly robust to cell-to-cell variations in axonal morphology. The peculiar morphological and biophysical profile of the dendritic arborization attenuates the role of the AIS in shaping electrical behaviour in this neuronal type.

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