Synaptic regulation of intrinsic dynamics in ell pyramidal cells
Date
2008
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Abstract
A near ubiquitous feature of neuronal architecture is an extensive dendritic tree, an anatomical specialization that allows large numbers of synaptic inputs from presynaptic cells to influence the firing of a postsynaptic neuron. However, the dendrite is also able to directly influence somatic firing dynamics. Because of the electrotonic coupling between somatic and dendritic compartments, somatic events can charge dendritic membrane or trigger active dendritic spikes, promoting current flow which reflects back to the soma. This thesis is focused on dendrosomatic feedback, its regulation by inhibition, and the resulting effects on sensory processing in pyramidal cells of the electrosensory lobe (ELL) of the weakly electric fish Apteronotus leptorhynchus. I show that feedback arising from dendritic spike backpropagation has a multiplicative effect on the response gain of pyramidal cells. Morever, gain can be regulated in a divisive manner by dendritic inhibition from GABAA receptor activation which decreases the amplitude of the dendritic spike. In contrast, GAB An receptor activation alters the timing of the dendritic feedback to cause a qualitative change in firing dynamics and a paradoxical increase in burst output. Thus, distinct subtypes of synaptic inhibition can have different nonlinear effects on the firing of the cell. I further model a direct feedback pathway known to recruit GABA8 inhibition of pyramidal cells, whereas regulation of burst dynamics modulates frequency tuning and spike patterning, even when embedded in a dynamic network. FinaJly, I examine the intrinsic properties of pyramidal cell spike and burst discharge in relation to frequency tuning across three sensory maps of the ELL with known behavioural contribution . These interactions are important in determining how this animal and central neural circuit encodes electric signals that are used to detect prey, examine its environment, and for social interactions. Since these interactions are often distinguishable by their frequency content, frequency tuning is of distinct ethological relevance in this system. I show that spike bursts that arise through dendritic feedback are correlated with low frequency tuning across the maps, and thus may contribute to specialized detection of prey-like events.
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Bibliography: p. 228-239
Some pages are in colour.
Some pages are in colour.
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Mehaffey, W. H. (2008). Synaptic regulation of intrinsic dynamics in ell pyramidal cells (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/2082