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Evidence for dual mechanisms involved in methamphetamine-induced increases in striatal preprotachykinin mRNA
1Laboratory of Molecular Neurobiology, Sinai Research Institute, Detroit, Michigan 48235.
Abstract:
The mechanism(s) whereby the indirect dopamine agonist methamphetamine causes a 2-3-fold increase in rat striatal preprotachykinin (PPT) mRNA was investigated. It was determined that the increase in PPT mRNA levels following a single injection of 5 mg of methamphetamine/kg of body weight was initiated in the cell nucleus, ruling out cytoplasmic PPT mRNA stabilization as a primary mechanism for this increase. It was established with T1 nuclease/RNA protection protocols that methamphetamine injection increased mature PPT message approximately 3-fold over a 2-h period, and this increase was sustained for at least 4 h after drug treatment. Striatal content of the PPT gene primary transcript (containing transcribed introns) was decreased by 50% within 20 min and remained suppressed for at least 4 h post-methamphetamine. Nuclear transcription assays indicated a 2-3-fold increase in the rate of gene transcription that lasted 60-90 min after methamphetamine treatment; by 2 h the transcription rate had returned to control levels. Taken together, these changes and their time courses suggest the indirect dopamine agonist alters striatal PPT gene expression at two levels: 1) a transient increase in the rate of PPT gene transcription and 2) a more sustained increase in the rate at which PPT hnRNA is processed to mature PPT mRNA. It is unclear whether these two changes are linked or are independent modes of action by methamphetamine.
Insights
Methamphetamine increases striatal preprotachykinin (PPT) mRNA by boosting gene transcription and enhancing RNA processing. This dopamine agonist
Area of Science:
- Neuroscience
- Molecular Biology
- Pharmacology
Background:
- Methamphetamine is an indirect dopamine agonist with known effects on gene expression.
- Preprotachykinin (PPT) mRNA levels in the striatum are modulated by various stimuli.
Purpose of the Study:
- To investigate the molecular mechanisms by which methamphetamine increases striatal PPT mRNA levels in rats.
- To determine whether the increase in PPT mRNA is due to altered gene transcription or mRNA stabilization.
Main Methods:
- Rats were administered methamphetamine (5 mg/kg) and striatal tissue was analyzed.
- T1 nuclease/RNA protection assays were used to quantify mature PPT mRNA and primary transcripts.
- Nuclear transcription assays measured the rate of PPT gene transcription.
Main Results:
- Methamphetamine increased mature PPT mRNA levels 3-fold, sustained for at least 4 hours.
- The primary transcript of the PPT gene decreased by 50% within 20 minutes.
- Gene transcription rate transiently increased 2-3 fold for 60-90 minutes post-treatment.
Conclusions:
- Methamphetamine alters striatal PPT gene expression at both the transcriptional and post-transcriptional levels.
- The drug transiently increases PPT gene transcription and more persistently enhances hnRNA processing to mature mRNA.
- The interplay between these two mechanisms requires further investigation.