Cortically evoked excitatory synaptic transmission in the cat red nucleus is antagonised by D-AP5 but not by D-AP7

Extracellular recordings were made from magnocellular red nucleus neurons (mRN) in alpha-chloralose (50 mg/kg, iv.) anaesthetised cats. Iontophoretically applied N-methyl-D-aspartate (NMDA) excited the neuronal firing which was antagonised by 4 selective NMDA receptor antagonists: 2-amino-5-phosphonopentanoate (AP5), 2-amino-7-phosphonoheptanoate (AP7), RS-4-(phosphonomethyl) piperazine-2-carboxylic acid (PMPC) and R-4-(3-phosphonopropyl) piperazine-2-carboxylic acid (CPP), whereas AMPA responses were uneffected. Monosynaptic excitatory responses were produced by stimulation of the sensorimotor cortex. These responses were reduced and often abolished by AP5 and PMPC but not by AP7 or CPP. It is postulated that two NMDA receptor subtypes exist on mRN neurones.