Activity of Tyrosine Hydroxylase and C-Fos Protein in the Retrorubral Field in Rats with Differential Novelty-Induced LocomotionAuthor(s): Grazyna Jerzemowska, Karolina Plucinska, Kacper Ptaszek, Aleksandra Piwka, Jolanta Orzel-Gryglewska
Individual differences in the intensity of rodent locomotor response to a novel environment (exploratory reaction) are useful as a model for studying individual vulnerability to stress and drug addiction. The present study attempted to determine if elevated dopaminergic system activation occurred in the retrorubral field (RRF) (A8 dopaminergic group) in male Wistar rats with high (HR) versus low (LR) novelty-induced locomotor activity. Additionally, we measured for correlations between the number of cells containing the enzyme tyrosine hydroxylase (TH+), differences in the morphology of these cells (immunohistochemistry and immunofluorescent) and the locomotor activity in these rats (HR and LR rats). Finally, density of c-Fos expressing cells was assessed to measure activation of the remaining neurons in both behavioral groups. The total number of TH+ cells in the whole RRF area correlated with locomotor activity response level and HR/LR differences in TH+ cell distribution varied across the anterio-posterior axis by region. All of the morphometric factors analyzed in TH+ cells differed significantly between HR rats and LR rats, while we observed no HR/LR differences in density of c-Fos+ cells. Together the results suggest that a behavioral indicator of increased susceptibility to stress or propensity to develop drug addictions, variable rodent activity in a novel environment, varies with TH+ cell population characteristics in the differentiated central dopaminergic system. This consideration may be useful when interpreting results in animal models that engage the dopaminergic system, such as rat models of drug addiction.