Voluntary running distance is negatively correlated with striatal dopamine release in untrained rats

This study examined the relationship between voluntary running distance and glutamate- and K+-stimulated dopamine release in the striatum (nucleus accumbens and caudate-putamen) of male Long-Evans rats. Twenty-one rats were housed individually in cages with attached running-wheels for 1 week. There was a 19-fold variability between rats in voluntary running distances over this period (range = 2.3-44.6 km). The average distance completed during the week was 16 +/- 2.8 km. There was a strong positive correlation between the running distances completed during the first 24 h (day 1) and the last 24 h. Certain rats were therefore inclined to run from the start. The average daily running distance (2.4 +/- 0.4 km per day) was negatively correlated with the weight of the rat (r = -0.82). Glutamate-stimulated release of dopamine was not a significant predictor of voluntary running distance. However, the average daily running distance was negatively correlated with K+-stimulated dopamine release in the nucleus accumbens core and caudate-putamen but not the nucleus accumbens shell. The present findings suggest that decreased depolarization-induced release of striatal dopamine may be a predictor of hyperactivity. The results show, in a normal population of Long-Evans rats, that there are, at the end of the continuum, rats that display some of the neurochemical and behavioral characteristics of a rat model for attention-deficit hyperactivity disorder.