Methamphetamine (METH) is a potent psychostimulant with neurotoxic properties. Heavy use increases the activation of neuronal nitric oxide synthase (nNOS), production of peroxynitrites, microglia stimulation, and induces hyperthermia and anorectic effects. Most METH recreational users also consume cannabis. Preclinical studies have shown that natural (D9- tetrahydrocannabinol, D9-THC) and synthetic cannabinoid CB1 and CB2 receptor agonists exert neuroprotective effects on different models of cerebral damage. Here, we investigated the neuroprotective effect of D9-THC on METH-induced neurotoxicity by examining its ability to reduce astrocyte activation and nNOS overexpression in selected brain areas. Rats exposed to a METH neurotoxic regimen (4610 mg/kg, 2 hours apart) were pre- or post-treated with D9-THC (1 or 3 mg/kg) and sacrificed 3 days after the last METH administration. Semi-quantitative immunohistochemistry was performed using antibodies against nNOS and Glial Fibrillary Acidic Protein (GFAP). Results showed that, as compared to corresponding controls (i) METH-induced nNOS overexpression in the caudate-putamen (CPu) was significantly attenuated by pre- and post-treatment with both doses of D9-THC (219% and 228% for 1 mg/kg pre- and post-treated animals; 225% and 221% for 3 mg/kg pre- and post-treated animals); (ii) METH-induced GFAP-immunoreactivity (IR) was significantly reduced in the CPu by post-treatment with 1 mg/kg D9-THC1 (250%) and by pre-treatment with 3 mg/kg D9-THC (253%); (iii) METHinduced GFAP-IR was significantly decreased in the prefrontal cortex (PFC) by pre- and post-treatment with both doses of D9-THC (234% and 247% for 1 mg/kg pre- and post-treated animals; 237% and 229% for 3 mg/kg pre- and post-treated animals). The cannabinoid CB1 receptor antagonist SR141716A attenuated METH-induced nNOS overexpression in the CPu, but failed to counteract the D9-THC-mediated reduction of METH-induced GFAP-IR both in the PFC and CPu. Our results indicate that D9-THC reduces METH-induced brain damage via inhibition of nNOS expression and astrocyte activation through CB1-dependent and independent mechanisms, respectively.
