From an ATPL manual I have:
MNPS ORGANISED TRACK SYSTEM
The MNPS area that is the volume of airspace between FL285 and FL420 extending between 27ºN and the North Pole, bounded in the east by the eastern boundaries of control areas Santa Maria OCA, Shanwick OCA and Reykjavik and in the west by the western boundary of Reykjavik CTA, the western boundaries of Gander OCA and New York OCA excluding the area west of 60ºW and south of 38º30'N.