HISTAMINE INCREASES THE BURSTING ACTIVITY OF PYRAMIDAL CELLS IN THE CA3 REGION OF MOUSE HIPPOCAMPUS

An excitatory action of histamine was investigated by intracellular re cording in the CA3 region of hippocampal slices. Bath application of h istamine or impromidine, a H2 receptor agonist, had the following effe cts: (1) a depolarisation in 60% and no changes in membrane potential in 40% of the CA3 pyramids; (2) single cell firing and burst activity were evoked or more than doubled when spontaneously present; (3) the b ursts were prolonged and often followed by afterdischarges instead of the normal afterhyperpolarisations (AHPs); (4) synaptic stimulation ev oked large bursts instead of excitatory synaptic potentials (EPSPs) an d primary burst responses became prolonged. CA3 bursts may play a deci sive role in memory trace formation, their facilitation and potentiati on is in keeping with a positive role of the histaminergic system in a ttention and learning. (C) 1998 Elsevier Science Ireland Ltd.