Histamine is a neuromodulator in the brain, and the hippocampus is one
of the regions of the brain that is innervated by histaminergic neuro
ns. When applied to cultured hippocampal neurons, histamine selectivel
y increased by up to tenfold the amplitude of the component of synapti
c transmission that was mediated by N-methyl-D-aspartate (NMDA) recept
ors. Spontaneous miniature synaptic currents and the current elicited
by applied NMDA also were enhanced, indicating that the histamine effe
ct was expressed primarily postsynaptically. These results suggest tha
t histamine may modulate processes involving NMDA receptors, such as t
he induction of long-term potentiation.