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Title:Structural and functional heterogeneity of cells in the rat hippocampus
Author(s):Naseri Kouzehgarani, Ghazal
Director of Research:Gillette, Martha
Doctoral Committee Chair(s):Gillette, Martha
Doctoral Committee Member(s):Llano, Daniel; Popescu, Gabriel; Sweedler, Jonathan
Department / Program:Neuroscience Program
Degree Granting Institution:University of Illinois at Urbana-Champaign
Dentate Gyrus
Circadian Rhythms, Astrocytes
Membrane Excitability
Gap-Junction Coupling
Abstract:Memory is encoded in the structure and function of the hippocampus. The laminar structure and organization of information flow are well established. The dentate gyrus (DG) is the initial layer that receives and parses incoming signals. The signal is then transmitted to the CA3 and subsequently the CA1 layer. CA1 pyramidal neurons are the primary hippocampal projection neurons that provide a significant output pathway from the hippocampus. DG granule neurons are the primary signal receivers from the major input pathway through the Perforant Path (PP) from the entorhinal cortex (EC). These neurons send their dendrites into the molecular layer of the dentate gyrus (ML/DG), where populations of astrocytes reside. This clear topographic segregation positions astrocytes of the molecular layer to strongly influence signals coming into the DG. Additionally, time-of-day significantly influences hippocampal neuronal excitability and functions in both CA1 and DG, including long-term potentiation, memory acquisition, and recall of learned tasks (Chaudhury et al., 2005). However, mechanisms underlying these diurnal changes are still an open question. Preliminary evidence from Gillette lab revealed for the first time that hippocampal astrocytes in the ML/DG region in brain slices undergo significant changes in structural and morphological complexity over the day-night cycle (Irving et al., 2015). However, this observation brings up the questions of what effects could these morphological changes exert on astrocyte connectivity and, in turn, on their physiological functions, specifically with regards to the time of the day. We proposed a set of experiments to understand the diurnal dynamics in the structure and function of hippocampal neurons and glial cells. We found that 1) the excitability of CA1 pyramidal neurons exhibits a rhythm in resting membrane potential which is coupled to its near-24-h intrinsic redox oscillation, 2) the membrane potential of DG granule neurons displays oscillation over the day-night cycle that is anti-phase to that of the CA1 pyramidal neurons, 3) the peak time of neuronal excitability in the DG coincides with the peak time of seizure incidence in this layer, 4) ML/DG astrocytes are structurally dynamic and their connectivity through gap-junction coupling increases significantly from day to nighttime, 5) ML/DG astrocytes display larger cell body volumes during the day than the nighttime, with no significant diurnal difference in the dry mass, 6) the oligodendrocyte precursor cells, also known as NG-glia, undergo diurnal cell division where they divide in the early day and reside as isolated cells during the nighttime, 7) astrocyte coverage of active synapses is higher at night, the active phase of the nocturnal animal. Thus, we have characterized electrophysiological properties of both neurons and glial cells of hippocampal CA1 and DG layers and the degree of network connectivity over the day-night cycle at both cell and circuit levels. Understanding the dynamics of neurons and astrocytes will enable a greater comprehension of hippocampal network function.
Issue Date:2020-01-21
Rights Information:Copyright 2020 Ghazal Naseri Kouzehgarani
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05

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