EXISTENCE OF NITRIC-OXIDE SYNTHASE IN RAT HIPPOCAMPAL PYRAMIDAL CELLS

It has been proposed that nitric oxide (NO) serves as a key retrograde messenger during long-term potentiation at hippocampal synapses, link ing induction of long-term potentiation in postsynaptic CA1 pyramidal cells to expression of long-term potentiation in presynaptic nerve ter minals. However, nitric oxide synthase (NOS), the proposed NO-generati ng enzyme, has not yet been detected in the appropriate postsynaptic c ells. We here demonstrate specific NOS immunoreac tivity in the CA1 re gion of hippocampal sections by using an antibody specific for NOS typ e I and relatively gentle methods of fixation. NOS immunoreactivity wa s found in dendrites and cell bodies of CA1 pyramidal neurons. Culture d hippocampal pyramidal cells also displayed specific immunostaining. Control experiments showed no staining with preimmune serum or immune serum that was blocked with purified NOS. These results demonstrate th at CA1 pyramidal cells contain NOS, as required were NO involved in re trograde signaling during hippocampal synaptic plasticity.