title: Topographical disorientation after ischemic mini infarct in the dorsal hippocampus: whispers in silence.
abstract: Silent focal ischemic mini infarcts in the brain are thought to cause no clinically overt symptoms. Some populations of hippocampal cells are particularly sensitive to ischemic events, however, rendering hippocampal functions especially vulnerable to ischemia-induced deficits. The present study investigated whether an otherwise silent ischemic mini infarct in the hippocampus (HPC) can produce impairments in spatial performance in rats. Spatial performance was assessed in the ziggurat task (ZT) using a 10-trial spatial learning protocol for 4 days prior to undergoing hippocampal ischemic lesion or sham surgery. Hippocampal silent ischemia was induced by infusion of endothelin-1 (ET-1), a potent vasoconstrictor, into either the dorsal or the ventral hippocampus (dHPC and vHPC). When tested postoperatively in the ZT using a standard testing protocol for 8 days, rats with hippocampal lesions exhibited no spatial deficit. Although spatial learning and memory in the ZT were not affected by the ET-1-induced silent ischemia, rats with dHPC stroke showed more returns when navigating the ZT as opposed to the vHPC rats. Comparison of region-specific HPC lesions in the present study indicated that dorsal hippocampal function is critically required for topographic orientation in a complex environment. Topographic disorientation as reflected by enhanced return behaviors may represent one of the earliest predictors of cognitive decline after silent ischemic insult that may be potentially traced with sensitive clinical examination in humans.
authors.affiliation: Department of Neuroscience, Canadian Centre for Behavioural Neuroscience (CCBN), University of Lethbridge Lethbridge, AB, Canada ; Faculty of Nursing and Midwifery, Golestan University of Medical Sciences Gorgan, Iran.
authors.forename: Jamshid
authors.initials: J
authors.lastname: Faraji
authors.affiliation: Department of Anatomy, Biology and Molecular Research Center, Babol University of Medical Sciences Babol, Iran.
authors.forename: Nabiollah
authors.initials: N
authors.lastname: Soltanpour
authors.affiliation: Department of Behavioural Studies, Avicenna Institute of Neuroscience Yazd, Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Moeeini
authors.affiliation: Department of Behavioural Studies, Avicenna Institute of Neuroscience Yazd, Iran.
authors.forename: Shabnam
authors.initials: S
authors.lastname: Roudaki
authors.affiliation: Department of Neuroscience, Canadian Centre for Behavioural Neuroscience (CCBN), University of Lethbridge Lethbridge, AB, Canada.
authors.forename: Nasrin
authors.initials: N
authors.lastname: Soltanpour
authors.affiliation: Faculty of Nursing and Midwifery, Golestan University of Medical Sciences Gorgan, Iran.
authors.forename: Ali-Akbar
authors.initials: AA
authors.lastname: Abdollahi
authors.affiliation: Department of Neuroscience, Canadian Centre for Behavioural Neuroscience (CCBN), University of Lethbridge Lethbridge, AB, Canada.
authors.forename: Gerlinde A S
authors.initials: GA
authors.lastname: Metz
keywords: early cognitive decline; endotelin-1; hippocampus; return behavior; silent stroke; spatial navigation; topographical disorientation; ziggurat task