DORSO-VENTRAL EXPRESSION OF POLYSIALYLATED NEURAL CELL ADHESION MOLECULE IN THE RAT DENTATE GYRUS FOLLOWING LEARNING

Lesion studies have suggested afferent/efferent pathways distributed through the dorso-ventral axis of the hippocampus to process task-specific information for long-term memory consolidation. As evidence for neuroplastic change that accompanies memory consolidation within these distinct pathways is lacking, we investigated the transient increase in hippocampal granule cell neural cell adhesion molecule polysialylation (NCAM PSA) throughout its dorso-ventral axis following training in spatial learning and avoidance conditioning paradigms. Given the hippocampus is a C-shaped structure, the brain was sectioned in two directions. Initially, coronal sections were collected in a rostro-caudal manner and subsequently horizontal sections in a dorso-ventral manner. Thirteen levels, separated by 0.5mm intervals equally distributed over the entire dorso-ventral axis of the hippocampus, were investigated for polysialylated cell expression. The frequency distribution of polysialylated cells was found to decrease over the dorso-ventral axis of the hippocampus. Following passive avoidance training the greatest proportional increase in polysialylated granule cells was observed at 7.1mm ventral to bregma (Trained: 20.48±0.43 (mean ± sem) vs. Passive: 14.52±0.41). By contrast, water maze spatial learning resulted in an increase of polysialylated cells restricted to a dorsal region 3.3mm caudal to bregma (Trained: 36.28±2.19 vs. Passive: 28.68±1.38, p<0.05, t-test, n=5). Localisation of the neuroplastic response to spatial learning in the dorsal aspect of the hippocampus and to the ventral hippocampal aspect following avoidance conditioning supports the lesioning studies and, further, gives a cellular typography to further investigate the discrete afferent/efferent pathways serving different forms of learning