A developmentally regulated switch in neuronal responsiveness to NCAM and N-cadherin in the rat hippocampus.

Monolayers of control 3T3 fibroblasts and 3T3 cells expressing transfected NCAM or N-cadherin have been used as a culture substratum for rat hippocampal neurons. Both NCAM and N-cadherin are expressed in the hippocampus through embryonic day 17 (E17) to postnatal day 4 (PND4); however, whereas E17 neurons responded to transfected NCAM by extending considerably longer neurites, PND4 neurons responded very poorly. The converse was true for responsiveness to N-cadherin. These data demonstrate a switch in neuronal responsiveness to NCAM and N-cadherin in the developing hippocampus. NCAM-dependent neurite outgrowth from E17 neurons was largely dependent on the presence of alpha 2-8-linked polysialic acid (PSA) on neuronal NCAM. NCAM-dependent neurite outgrowth could be fully inhibited by pertussis toxin or a combination of L- and N-type calcium channel antagonists thus providing direct evidence concerning the nature of the second messenger pathway activated in primary neurons by cell adhesion molecules (CAMs).