Chronic NMDA receptor blockade in early postnatal period, but not in adulthood, impairs methamphetamine-induced conditioned place preference in rats

•Rats with chronic NMDA receptor blockade were tested in conditioned place preference in adulthood.•Early postnatal NMDA receptor blockade impaired conditioned place preference induced by methamphetamine.•The same treatment in adulthood did not produce impairment.•Abnormal development by NMDA receptor blockade may cause classical conditioning deficit.

Early postnatal glutamatergic N-methyl-d-aspartate (NMDA) receptor blockade in animals is known to produce various behavioral deficits in adulthood. In the present study rats postnatally (day 7–20) treated chronically with MK-801, an NMDA receptor antagonist, were tested later in adulthood in methamphetamine (MAP)-induced conditioned place preference (CPP) using a unbiased procedure in a three-compartment apparatus. Rats with the same chronic treatment in adulthood were also tested. CPP test consisted of a baseline test before conditioning, place conditioning, and a preference test after conditioning. Rats postnatally treated with MK-801 did not show any evidence of preference for MAP-paired compartment compared with that for unpaired one in the preference test that was shown in rats postnatally treated with saline. On the other hand, rats treated with MK-801 in adulthood were not affected by the treatment and showed significant CPP as was shown in saline-treated control animals. Results suggest the possibility that chronic early postnatal, but not adulthood, NMDA receptor blockade induces persistent deficit of subsequent appetitive classical conditioning.