Behavioural sensitization to cocaine is dissociated from changes in striatal NMDA receptor levels

Changes in glutamate transmission and alterations in glutamate receptor expression produced by the repeated administration of psychomotor stimulant drugs are considered an important neuroadaptation underlying the development and expression of behavioural and neurochemical sensitization to stimulant drugs. Two parallel experiments investigated the effects of repeated cocaine administration (five, once daily injections of 15 mg/kg, i.p.; 2 weeks withdrawal) on the expression of behavioural sensitization in response to a cocaine challenge (20 mg/kg, i.p.) and the changes in NMDA receptor binding in pooled tissue from the nucleus accumbens and the striatum. Compared with acute cocaine controls (n = 11), animals administered cocaine repeatedly displayed a sensitized stereotypic response to the cocaine challenge injection (n = 8). Despite this, no differences in either NMDA receptor density or affinity were observed between rats administered repeatedly with cocaine or saline, as indexed by [3H]MK-801 binding. The present findings call to question the rationale for NMDA receptor-based pharmacotherapies for the treatment of the enduring symptomatology of stimulant addiction.