Effects of chronic stress on contextual fear conditioning and the hippocampal expression of the neural cell adhesion molecule, its polysialylation, and L1

Chronic stress has been shown to induce time-dependent neurodegeneration in the hippocampus, ranging from a reversible damage to a permanent neuronal loss. This damage has been proposed to impair cognitive function in hippoca mpus-dependent learning tasks. In this study, we have used a 21-day restrai nt stress procedure in rats, previously reported to induce reversible atrop hy of apical dendrites of CA3 pyramidal cells, to assess whether it may inf luence subsequent performance in the contextual fear conditioning task unde r experimental conditions involving high stress levels (1 mA shock intensit y as the unconditioned stimulus). In addition, we were interested in the st udy of the possible cellular and molecular mechanisms involved in the rever sible phase of neural damage. Cell adhesion molecules of the immunoglobulin superfamily, such as the neural cell adhesion molecule and LI, are cell-su rface macromolecules that, through their recognition and adhesion propertie s, regulate cell-cell interactions and have been reported to play a key rol e in cognitive functioning. A second aim of this study was to evaluate whet her chronic stress would modulate the expression of the neural cell adhesio n molecule, its polysialylation, and L1 in the hippocampus. The results sho wed that chronic stress facilitated subsequent contextual fear conditioning . They also showed that chronically stressed rats displayed reduced hippoca mpal neural cell adhesion molecule, but increased polysialylated expression as well as a trend towards exhibiting increased L1 expression. In summary, these results support the view that a 21-day chronic stress reg imen predisposes individuals to develop enhanced contextual fear conditioni ng responses. They also indicate that cell adhesion molecules might play a role in the structural remodelling that occurs in the hippocampus as a cons equence of chronic stress exposure. (C) 2001 IBRO. Published by Elsevier Sc ience Ltd. All rights reserved.