A reduction in hippocampal GABAA receptor α5 subunits disrupts the memory for location of objects in mice


F. Crestani, Institute of Pharmacology & Toxicology, Winterthurerstrasse 190, 8057 Zurich, Switzerland. E-mail: crestani@pharma.uzh.ch


The memory for location of objects, which binds information about objects to discrete positions or spatial contexts of occurrence, is a form of episodic memory particularly sensitive to hippocampal damage. Its early decline is symptomatic for elderly dementia. Substances that selectively reduce α5-GABAA receptor function are currently developed as potential cognition enhancers for Alzheimer's syndrome and other dementia, consistent with genetic studies implicating these receptors that are highly expressed in hippocampus in learning performance. Here we explored the consequences of reduced GABAAα5-subunit contents, as occurring in α5(H105R) knock-in mice, on the memory for location of objects. This required the behavioral characterization of α5(H105R) and wild-type animals in various tasks examining learning and memory retrieval strategies for objects, locations, contexts and their combinations. In mutants, decreased amounts of α5-subunits and retained long-term potentiation in hippocampus were confirmed. They exhibited hyperactivity with conserved circadian rhythm in familiar actimeters, and normal exploration and emotional reactivity in novel places, allocentric spatial guidance, and motor pattern learning acquisition, inhibition and flexibility in T- and eight-arm mazes. Processing of object, position and context memories and object-guided response learning were spared. Genotype difference in object-in-place memory retrieval and in encoding and response learning strategies for object–location combinations manifested as a bias favoring object-based recognition and guidance strategies over spatial processing of objects in the mutants. These findings identify in α5(H105R) mice a behavioral–cognitive phenotype affecting basal locomotion and the memory for location of objects indicative of hippocampal dysfunction resulting from moderately decreased α5-subunit contents.