ABSTRACT
To assess whether calmodulin (CaM) gene expression could have a role in behavioral sensitization induced by repeated, intermittent amphetamine, CaM protein and mRNA of the three separate CaM genes were measured in several different brain areas from rats repeatedly administered saline or amphetamine. Rats were injected twice weekly for five weeks, followed by one week of withdrawal. CaM protein and mRNA were measured in dorsal striatum, limbic forebrain, prefrontal cortex, ventral mesencephalon and piriform cortex. There were increases of CaM protein content and decreases of CaM I mRNA in the dorsal striatum and prefrontal cortex. CaM II mRNA was also decreased in the dorsal striatum. A decrease of CaM protein and an increase of CaM I mRNA were found in the ventral mesencephalon. There was no change of CaM protein in the limbic forebrain, although a decrease of CaM I mRNA was detected. CaM protein and mRNA were not altered in the piriform cortex. Our findings demonstrate that both CaM content and mRNA are altered after an amphetamine regimen leading to sensitization. The fact that the changes in CaM content and mRNA are in dopaminergic brain areas associated with sensitization suggests that CaM could contribute to neurochemical events underlying behavioral sensitization to amphetamine.
Subject(s)
Amphetamine/pharmacology , Brain/drug effects , Calmodulin/analysis , Calmodulin/genetics , RNA, Messenger/biosynthesis , RNA, Messenger/drug effects , Alternative Splicing , Amphetamine/administration & dosage , Animals , Blotting, Northern , Brain Chemistry , Corpus Striatum/chemistry , Drug Administration Schedule , Female , Injections, Intraperitoneal , Mesencephalon/chemistry , Prefrontal Cortex/chemistry , RNA, Messenger/analysis , Rats , Rats, Sprague-Dawley , Time FactorsABSTRACT
Repeated, intermittent treatment with amphetamine leads to a behavioral sensitization characterized in rats by an increase in locomotor activity and a more rapid onset of stereotyped behaviors. Induction of amphetamine sensitization is blocked by dopamine and N-methyl-D-aspartate (NMDA) antagonists. We have reported an increase in the content of the Ca2(+)-binding protein, calmodulin, in striatum and limbic forebrains from rats given repeated, intermittent amphetamine. To determine whether the increase was related to development of amphetamine sensitization, we examined whether the increase in calmodulin would be blocked by the dopamine antagonist, haloperidol, or the NMDA antagonist, MK-801. Rats were given amphetamine or saline twice weekly for 5 weeks. Thirty min prior to the amphetamine, rats were pretreated with 0.25 mg/kg haloperidol s.c., 0.1 mg/kg MK-801 i.p. or saline. Twice weekly amphetamine treatment increased calmodulin in the cytosol fraction of striatum and limbic forebrain and the increase was blocked by pretreatment with either haloperidol or MK-801. Neither antagonist alone affected cytosolic calmodulin. Haloperidol pretreatment, but not amphetamine or MK-801, increased calmodulin in striatal but not limbic forebrain membranes. Calmodulin-binding proteins were examined by biotinylated calmodulin blotting to determine if repeated, intermittent amphetamine altered the content of calmodulin-binding proteins in striatal cytosol or membranes. A band of 73 kDa was increased in striatal membranes. Immunoblotting with antisera to caldesmon, a cytoskeletal calmodulin-binding protein of 77 kDa, demonstrated increases in immunoreactivity in striatal membranes and cytosol. These data suggest that dopaminergic and glutamatergic components are required for the increases in striatal and limbic forebrain calmodulin and that the rise in calmodulin is related to the development of amphetamine sensitization. In addition, the content of select calmodulin-binding proteins can be coordinately regulated with increases in calmodulin.
