Nitric oxide modulates rhythmic slow activity in rat hippocampal slices.

We investigated the role of nitric oxide (NO) in controlling the rate of occurrence of muscarinic rhythmic slow activity (RSA) episodes induced by carbachol in rat hippocampal slices. Typically, a series of several short intervals (< 40 s) between RSA episodes alternated with one or two longer intervals. Treatments with inhibitors of NO synthesis (NG-nitro- or NG-methyl-L-arginine) or with hemoglobin shortened and stabilized all intervals. By contrast, applications of an NO donor (sodium nitroprusside) or membrane permeant cGMP analogs (8-bromo-cGMP or dibutyryl-cGMP) during blockade of NO synthesis lengthened and destabilized the intervals. The importance of cholinergic mechanisms in learning and memory is well known and our findings suggest that NO could influence synaptic plasticity by modulating the occurrence of a muscarinic component of hippocampal RSA.