Striatal enkephalinergic differences in rats selectively bred for intrinsic running capacity

Area of Science:

• Neuroscience
• Behavioral Genetics
• Animal Behavior

Background:

• Locomotory behavior motivation is linked to dopaminergic transmission.
• Rats selectively bred for high- (HCR) and low-capacity (LCR) running differ in wheel-running behavior.
• The role of enkephalinergic activity in voluntary wheel running is not understood.

Purpose of the Study:

• To investigate the association between voluntary wheel running and enkephalinergic activity in the ventral striatum.
• To determine if genetic differences in running capacity correlate with enkephalin (ENK) mRNA expression in specific brain regions.

Main Methods:

• Forty male and forty female rats (20 HCR and 20 LCR each) were exposed to activity wheels or sedentary conditions for 3 weeks.
• Brains were extracted, and in situ hybridization histochemistry was used to analyze enkephalin (ENK) mRNA expression in the ventral striatum.
• Specific brain regions analyzed included the nucleus accumbens and olfactory tubercle.

Main Results:

• HCR rats exhibited significantly lower ENK mRNA expression compared to LCR rats in the nucleus accumbens (females only) and olfactory tubercle (males and females).
• No significant effect of 3 weeks of wheel running on ENK mRNA expression was observed in any group.
• These findings indicate a genetic basis for differences in ENK expression related to running capacity.

Conclusions:

• Genetic line differences in ENK expression within the olfactory tubercle and nucleus accumbens contribute to divergent wheel-running behaviors.
• Lower striatal ENK levels in HCR rats align with enhanced dopaminergic tone, potentially explaining their increased motivation for wheel running.
• These findings provide insights into the neurobiological mechanisms underlying motivated locomotion and exercise behavior.