| Description |
Although it is well known that METH damages the dopamine (DA) system, the mechanisms underlying such toxicity have not been elucidated. Previous work indicates that animals with partial DA loss from prior exposure to METH are resistant to further decreases in DA when reexposed to METH 30 days later. This experimental paradigm results in four treatment groups based on postnatal day (PND)60:PND90 treatment (Saline:Saline, METH:Saline, Saline:METH, METH:METH) and allows for examination of factors associated with METH toxicity in animals matched for METH exposure, but differentiated with respect to acute METH neurotoxicity. We used this paradigm to examine factors implicated in METH-induced neurotoxicity. First, we investigated the possible contribution of nitric oxide (NO) by examining nitric oxide synthase (NOS) expression, activity, and protein nitration. We found that acute METH administration increased NO production; however, METH did not change expression of endothelial NOS or result in induction of inducible NOS. The number of cells positive for neuronal (nNOS) mRNA or the amount of nNOS mRNA per cell also did not change. However, NOS activity was increased acutely after METH exposure, suggesting that increased NO production after METH exposure arises from NOS activity and most likely, nNOS. Furthermore, animals resistant to METH-induced DA depletions show equivalent degrees of NO production, suggesting that NO alone is not sufficient to induce METH-induced neurotoxicity. Using the same paradigm, we then examined glial reactivity using glialfibrillary acidic protein (GFAP; astrocytes) and CD11b (Microglia), as well as markers of proliferation (BrdU and Ki67) immunohistochemistry. Animals experiencing acute toxicity (Saline:METH) showed activated microglia and astocytes, whereas those resistant to toxicity (METH:METH) did not show activated microglia. Furthermore, animals experiencing acute toxicity (Saline:METH) also showed increased proliferation compared to all other groups and a large proportion of proliferating cells were microglia with a smaller proportion being astrocytes. Interestingly, GFAP expression remained elevated in animals exposed to METH at PND60 (METH:Saline), and was not further elevated in resistant animals (METH:METH). These data suggest that astrocytes remain reactive up to 30 days post-METH exposure and that astrocyte reactivity does not reflect acute METH-induced neurotoxicity whereas microglial reactivity parallels acute METHinduced neurotoxicity. |
