Expression of messenger RNA (mRNA) for brain dopamine receptors and enkephalin before and after wheel running in rats selectively bred for high-and low- aerobic capacity
Monroe, Derek Christopher
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We examined whether female rats selectively bred for high intrinsic aerobic capacity (High Capacity Runners, HCR) and low intrinsic aerobic capacity (Low Capacity Runners, LCR) differentially express mRNA in the dopaminergic and opiodergic pathways of the basal ganglia and that 3 weeks of access to activity wheels alters expression in those pathways. Consistent with predicted outcomes, enkephalin (ENK) was expressed at lower levels in the nucleus accumbens septi (NAS) and olfactory tubercle (OT) in HCR females compared to LCR females. D1 receptor mRNA expression in the dorsal striatum and NAS was decreased in rats with running wheel access compared to those that were sedentary for 3 weeks. Contrary to predictions, tyrosine hydroxylase (TH) and D2 mRNA expressions were not significantly different between HCR and LCR strains and were not affected by wheel running. The results suggest that female rats selectively bred for intrinsically high aerobic capacity demonstrate a high level of voluntary physical activity that is associated with high dopaminergic tone, consistent with low ENK mRNA expression in the basal ganglia. Increased voluntary wheel running results in downregulation of D1 transcription in the ventral striatum regardless of intrinsic running capacity.