Decrease of N-methyl-D-aspartate responses by noradrenaline in the rat motorcortex in vivo.

The influence of noradrenaline (NA) on cortical field potential changes (CFPs) induced by the glutamate subreceptor agonist N-methyl-D-aspartate (NMDA) was tested in the motorcortex of anesthetized and artificially ventilated rats. Substances were applied through a 3-barrelled micropipette by pressure ejection in different motorcortical laminae. NMDA elicited negative and NA no or small positive CFPs. Applications of NA before (up to 60 s) or overlapping the ejection of NMDA decreased the amplitude of the negative CFP induced by the excitatory amino acid. The alpha 1-adrenoceptoragonist phenylephrine mimicked the NA effect, whereas the alpha 2-adrenoceptoragonist clonidine had differential actions with decreasing and increasing NMDA elicited CFP. The beta-agonist isoproterenol was without effect. It is suggested that the diminution of NMDA effects by NA may be mediated by an intracellular pathway mechanism.