Threshold effects of N-methyl D-aspartate (NMDA) and 2-amino 5-phosphono valeric acid (2APV) on the spontaneous activity of neocortical single neurones in the urethane anaesthetised rat.

Spontaneous activity of single neurones in neocortex was sampled using pairs of microelectrodes in rats anaesthetised with urethane. In confirmation of previous studies, many cells recorded from middle layers characteristically fired in bursts, the onset times of which were synchronous both unilaterally and bilaterally. Iontophoresis of 2APV onto such cells either caused an abolition of bursts or a reduction in spikes per burst. In the latter case action potentials which occurred later in the burst were preferentially abolished. Iontophoresis of NMDA onto the same cells caused a prolongation of bursts with minimal effect on intraburst interspike interval. In interactive trials with the two drugs the effect of NMDA could be abolished by 2APV, and NMDA counteracted the effect of 2APV. It is concluded that spontaneous burst generation in neocortex during urethane anaesthesia is generated through a cortical NMDA/2APV-sensitive receptor mechanism.