Functional Correlates of Exposure to Complex, Spatial Environments in Rat Dentate Gyrus
Green, Edward Jonathon
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Permalink
https://hdl.handle.net/2142/77676
Description
Title
Functional Correlates of Exposure to Complex, Spatial Environments in Rat Dentate Gyrus
Author(s)
Green, Edward Jonathon
Issue Date
1985
Department of Study
Neuroscience
Discipline
Neuroscience
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Language
eng
Abstract
Most theoretical accounts of learning hold that experience-related alterations in the pattern or efficacy of synaptic connections form the neural substrate for learning. Behavioral and neurophysiological studies have provided strong evidence for a hippocampal role in learning and memory, but there is little direct evidence for experience-related synaptic alterations within the hippocampus. In these experiments, synaptic transmission was evaluated in the dentate gyrus of hippocampal slices maintained in vitro after rearing rats in relatively complex (EC) or non-complex (IC) environments.
Pre- and postsynaptic extracellular field responses to activation of medial perforant path (MPP) axons were examined in hippocampal slices taken from rats reared in different environments. Slices taken from EC rats exhibited significantly greater perforant path-granule cell synaptic transmission, manifested as larger population spikes and greater slopes of EPSPs recorded at the site of synaptic activation in the dentate molecular layer and at the major current source in the dentate granule cell layer. There were no significant effects of rearing environment on the amplitude of the presynaptic fiber volley, or on granule cell excitability. Antidromic activation of dentate granule cells was not significantly affected by rearing environment, suggesting that tissue impedance was not affected by rearing environment. There were no significant differences in MPP synaptic transmission between slices taken from animals reared for 7-8 weeks in non-complex environments, or for 4 weeks in complex environments followed by 3-4 weeks in a non-complex environment. The results of these experiments suggest that: (a) experience in a relatively complex environment is associated with greater MPP synaptic transmission arising from an increased synaptic input to granule cells, (b) the greater MPP synaptic transmission associated with EC rats is largely independent of behavioral state, influences from extrahippocampal brain regions and intrahippocampal inhibitory processes, and (c) the experience - dependent synaptic alterations in dentate gyrus are transient relative to experience - dependent morphological alterations occurring in occipital cortex.
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