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Rats with complete excitotoxic hippocampal lesions or selective damage to the dorsal or ventral hippocampus were compared with controls on measures of contextually conditioned freezing in a signaled shock procedure and on a spatial water-maze task. Complete and ventral lesions produced equivalent, significant anterograde deficits in conditioned freezing relative to both dorsal lesions and controls. Complete hippocampal lesions impaired water-maze performance; in contrast, ventral lesions improved performance relative to the dorsal group, which was itself unexpectedly unimpaired relative to controls. Thus, the partial lesion effects seen in the 2 tasks never resembled each other. Anterograde impairments in contextual freezing and spatial learning do not share a common underlying neural basis; complete and ventral lesions may induce anterograde contextual freezing impairments by enhancing locomotor activity under conditions of mild stress.

Type

Journal article

Journal

Behav Neurosci

Publication Date

12/1999

Volume

113

Pages

1189 - 1203

Keywords

Analysis of Variance, Animals, Conditioning, Classical, Excitatory Amino Acid Antagonists, Fear, Hippocampus, Immobilization, Male, Maze Learning, Microinjections, N-Methylaspartate, Orientation, Rats, Rats, Inbred Strains, Time Factors