Fig. 5.

Effects of presession treatments with (+)-MK-801 or memantine on self-administration of d-methamphetamine, heroin, remifentanil substitution for heroin, or ketamine. Ordinates: responses per second; abscissae: drug dose (mg/kg/injection or μg/kg/injection), log scale. Each point represents the mean ± S.E.M. of response rates on the active lever in six subjects. A dose of 0 mg/kg of each test compound indicates saline vehicle injections. (A, C, E, G) Effects of (+)-MK-801 on self-administration of ketamine, d-methamphetamine, heroin, or remifentanil, respectively. (B, D, F, H) Effects of memantine on self-administration of ketamine, d-methamphetamine, heroin, or remifentanil, respectively.