Abstract
A Ca(2+)/calmodulin-dependent signaling cascade has been implicated in the regulation of dopaminergic neurotransmission after chronic administration of amphetamine and methamphetamine (METH). We found a decrease in Ca(2+)/calmodulin-dependent protein kinase II (CaM-kinase II) activity in five regions of the rat brain (parietal cortex; frontal cortex; hippocampus; striatum; and nucleus accumbens) after a single injection of METH. Pretreatment with the selective dopamine D1 receptor antagonist SCH 23390 prevented the acute METH-induced decrease in CaM-kinase II activity in the parietal cortex, striatum, nucleus accumbens, and substantia nigra/ventral tegmental area (SN/VTA). Pretreatment with the N-methyl-D-aspartate receptor antagonist MK-801 significantly restored the acute METH-induced decrease in CaM-kinase II activity in the parietal cortex, nucleus accumbens, and SN/VTA. Striatal CaM-kinase II activity was still significantly lower than that of the chronic saline-treated controls after a 1-week, but not a 4-week, abstinence from chronic administration of METH. A METH challenge after a 4-week abstinence period induced a more pronounced decrease in CaM-kinase II activity in rats chronically injected with METH than in rats chronically injected with saline. Western blot analysis revealed that the amount of CaM-kinase II protein was not altered after a single METH injection or after chronic METH injections, compared with saline-treated controls. However, amounts of phosphorylated (Thr(286)) CaM-kinase II in the parietal cortex, striatum and SN/VTA were significantly decreased at 3 h after an acute METH injection compared with saline-treated controls. These results suggest that dephosphorylation of CaM-kinase II may contribute to the decreased enzyme activities induced by acute METH administration, and that chronic treatment with METH leads to an enhanced capacity of METH to decrease CaM-kinase II activity after an extended withdrawal period.
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