Stimulation of the anterodorsal thalamic nucleus elicits an evoked potential in the dentate gyrus in the rat brain

King, Zoe (2001) Stimulation of the anterodorsal thalamic nucleus elicits an evoked potential in the dentate gyrus in the rat brain. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The hippocampus has long been theorized to play an important role in learning, memory, and spatial navigation. An input conveying vestibular information is likely to exist if the hippocampus plays a significant role in spatial navigation. Cells that respond to the spatial location of an animal have been found in the mammalian hippocampus, and their firing is influenced by vestibular cues (O’Keefe & Dostrovsky, 1971; Wiener et al. 1995), which originate in the semicircular canals and traverse the vestibular nuclei, the mammillary nuclei and the anterior thalamic nucleus (ADTN). -- In this study, monopolar stimulation of the ADTN reliability elicited an EPSP in the dentate gyrus (DG), the first structure in the trisynaptic relay network of the hippocampus. A series of experiments designed to determine the route by which an ADTN-DG signal would travel had mixed results. While a DG depth-profile and perforant path (PP)-lesion trials suggested at least part of the signal was the result of PP activation, cross- potentiation data did not yield results entirely consistent with a lateral perforant path (LPP) or medial perforforant path (MPP) route of travel. -- Norepinephrine (NE), a neuromodulator, may play a role in input attenuation and selection in the PP-DG connection. The effect of norepinephrine on the ADTN evoked potential was investigated in this study to ascertain if there is a consistent effect on this potential vestibular input, to determine its consistency with the hypothesis that such input is through the PP, and to look for evidence that NE effects are path and/or modality-specific. 500 μg/kg idazoxan had a different effect on the ADTN EPSP than a known LPP input, suggesting a different route for ADTN input; however, the idazoxan effects on the LPP input were not consistent with norepinephrine effects on the LPP. PGi stimulation, another method of enhancing NE input, yielded mixed effects on the ADTN EPSP, even when effects on the PP EPSP were consistent. -- The results suggest the ADTN EPSP may enter the DG in a mixed fashion or via a route not examined in this study. The existence of the ADTN signal in the DG is consistent with the theory that there is an ADTN input to the hippocampus that may play a role in head-direction and place-code processing.

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