BASAL AND APICAL SYNAPSES OF CA1 PYRAMIDAL CELLS EMPLOY DIFFERENT LTPINDUCTION MECHANISMS

Nitric oxide (NO) production has been widely reported to be required f or the induction of long-term potentiation (LTP) in hippocampal CAI ce lls, Of the two constitutive isoforms of NO synthase, the endothelial form (eNOS) has been implicated in the induction of LTP in these cells . The distribution of eNOS within CA1 cells is not uniform, however, b eing present in the cell bodies and apical dendrites but absent from t he basal dendrites, Using extracellular and intracellular recording te chniques, we demonstrate that LTP induction in stratum radiatum synaps es (onto apical dendrites) is dependent on NO production, being attenu ated by pretreatment with a NOS inhibitor, LTP induced in stratum orie ns synapses (onto basal dendrites) is, however, resistant to NOS inhib itors. Both forms of LTP require the activation of N-methyl-D-aspartat e (NMDA) receptors because induction of LTP in both stratum radiatum a nd stratum oriens is blocked by AP5. Thus, it appears that synapses on to apical and basal dendrites of CA1 cells use different cellular mech anisms of LTP induction.