Immediate-early gene response to methamphetamine, haloperidol, and quinolinic acid is not impaired in Huntington's disease transgenic mice

Striatal neurons in symptomatic Huntington's disease (HD) transgenic mice are resistant to a variety of toxic insults, including quinolinic acid (QA), kainic acid and 3-nitropropionic acid. The basis for this resistance is currently unknown. To investigate the possibility that the immediate-early gene (IEG) response is defective in symptomatic HD mice leading to a lack of response to these compounds, we examined the expression of c-Fos and Krox 24 after administration of the indirect dopamine agonist methamphetamine, the dopamine D₂ receptor antagonist haloperidol and the neurotoxin QA in 5- and 10-week-old R6/2 transgenic HD and wild-type mice. Unlike wild-type and pre-symptomatic R6/2 transgenic HD mice, 10-week-old symptomatic HD mice were resistant to methamphetamine-induced gliosis and QA lesion. There was, however, no difference in the number or distribution of c-Fos-immunoreactive nuclei 2 hr after single injections of methamphetamine or haloperidol among 5- and 10-week-old wild-type mice and 5- and 10-week-old R6/2 HD mice. Similarly, despite their resistance to QA-induced lesioning and lower basal levels of krox-24 mRNA, the symptomatic R6/2 mice had equivalent increases in the amount of c-fos and krox-24 mRNA compared to wild-type and pre-symptomatic R6/2 HD mice as determined by in situ hybridization and densitometry 2 hr after QA administration. These data demonstrate that the c-Fos and Krox 24 IEG response to dopamine agonists, dopamine antagonists and neurotoxic insult is functional in symptomatic R6/2 HD mice. Resistance to toxic insult in R6/2 mice may be conferred by interactions of mutant huntingtin with proteins or transcriptional processes further along the toxic cascade.