Differential antagonism of the stimulant effects of MK-801 and methamphetamine by ceruletide: evaluation by discrete shuttle avoidance response in mice.

A noncompetitive NMDA antagonist MK-801 (0.03-0.3 mg/kg, i.p.) increased the response rate of mice trained under the discrete shuttle avoidance situation to a degree similar to the increase by methamphetamine (0.1-1 mg/kg, i.p.). The cholecystokinin-like decapeptide ceruletide significantly reduced the response-increasing effect of MK-801 (0.1 mg/kg) at 0.001 micrograms/kg; however, only 10 micrograms/kg of ceruletide, which per se inhibited the response, attenuated that of methamphetamine (0.3 mg/kg). The coadministration of MK-801 (0.1 mg/kg) and methamphetamine (0.3 mg/kg) produced no potentiation of the effect, and almost the same effect was maintained even after the additional administration of ceruletide (0.1 microgram/kg).