MK-801 PROTECTION AGAINST METHAMPHETAMINE-INDUCED STRIATAL DOPAMINE TERMINAL INJURY IS ASSOCIATED WITH ATTENUATED DOPAMINE OVERFLOW

Repeated administrations of methamphetamine (m-AMPH) produce high extracellular levels of dopamine (DA) and subsequent striatal DA terminal damage. Pharmacological blockade of N-methyl-D-aspartate (NMDA) receptors has been shown previously to prevent m-AMPH-induced striatal DA terminal injury, but the mechanism for this protection is unclear. In the present study, in vivo microdialysis was used to determine the effects of blockade of NMDA receptors with the noncompetitive antagonist MK-801 on m-AMPH-induced striatal DA overflow. Four injections of MK-801 (0.5 mg/kg, ip) alone did not significantly change extracellular striatal DA concentrations from pretreatment values. Four treatments with m-AMPH (4.0 mg/kg, sc at 2-hr intervals) increased striatal DA overflow, and the overflow was particularly extensive following the fourth injection. This m-AMPH regimen produced a 40% reduction in striatal DA tissue content 1 week later. Treatment with MK-801 15 min before each of the four m-AMPH injections or prior to only the last two m-AMPH administrations attenuated the m-AMPH-induced increase in striatal DA overflow and protected completely against striatal DA depletions. Other MK-801 treatment regimens less effectively reduced the m-AMPH-induced striatal DA efflux and were ineffective in protecting against striatal DA depletions. Linear regression analysis indicated that cumulative DA overflow was strongly predictive (r = -.68) of striatal DA tissue levels measured one week later. These findings suggest that the extensive DA overflow seen during a neurotoxic regimen of m-AMPH is a crucial component of the subsequent neurotoxicity. Blockade of NMDA receptors with MK-801 apparently prevents damage to DA neurons by attenuating this stimulant-induced DA overflow.