tokens: Haloperidol - induced catalepsy was challenged with prior intracollicular microinjections of glutamate NMDA receptor antagonists , MK - 801 ( 15 or 30 mmol / 0 . 5 microl ) and AP7 ( 10 or 20 nmol / 0 . 5 microl ) , or of the NMDA receptor agonist N - methyl - d - aspartate ( NMDA , 20 or 30 nmol / 0 . 5 microl ) .