Histamine slows the onset of desensitization of rat cortical NMDA receptors.

The effects of histamine on N-methyl-d-aspartate (NMDA) receptor-mediated ion current in cultured rat cortical neurones have been investigated by superfusion of voltage-clamped (-80 mV) cells with 100 mM NMDA and with various concentrations of histamine. In a subpopulation of the neurones tested (30/53), histamine (10-100 mM) enhanced the peak amplitude, and slowed down the onset of desensitization of the NMDA-induced ion currents, both in a concentration-dependent manner. No effects of histamine on the kinetics of recovery from desensitization were detected. In other neurones (21/53), histamine had no effect on the NMDA-induced currents and in two of the neurones tested histamine potentiated NMDA-induced currents without a detectable effect on desensitization kinetics. The results indicate that in a subpopulation of rat cortical neurones histamine potentiates NMDA-induced ion currents by slowing the kinetics of onset of desensitization.