Neurobiological consequences of acute footshock stress: effects on tyrosine hydroxylase phosphorylation and activation in the rat brain and adrenal medulla

Stress activates selected neuronal systems in the brain and this leads to activation of a range of effector systems. Our aim was to investigate some of the relationships between these systems under basal conditions and over a 40-min period in response to footshock stress. Specifically, we investigated catecholaminergic neurons in the locus coeruleus (LC), ventral tegmental area and medial prefrontal cortex (mPFC) in the brain, by measuring tyrosine hydroxylase (TH) protein, TH phosphorylation and TH activation. We also measured the effector responses by measuring plasma adrenocorticotrophic hormone, corticosterone, glucose and body temperature as well as activation of adrenal medulla protein kinases, TH protein, TH phosphorylation and TH activation. The LC, ventral tegmental area and adrenal medulla all had higher basal levels of Ser19 phosphorylation and lower basal levels of Ser31 phosphorylation than the mPFC, presumably because of their cell body versus nerve terminal location, while the adrenal medulla had the highest basal levels of Ser40 phosphorylation. Ser31 phosphorylation was increased in the LC at 20 and 40min and in the mPFC at 40min; TH activity was increased at 40min in both tissues. There were significant increases in body temperature between 10 and 40min, as well as increases in plasma adrenocorticotropic hormone at 20min and corticosterone and glucose at 20 and 40min. The adrenal medulla extracellular signal-regulated kinase 2 was increased between 10 and 40min and Ser31 phosphorylation was increased at 20min and 40min. Protein kinase A and Ser40 phosphorylation were increased only at 40min. TH activity was increased between 20 and 40min. TH protein and Ser19 phosphorylation levels were not altered in any of the brain regions or adrenal medulla over the first 40min. These findings indicate that acute footshock stress leads to activation of TH in the LC, pre-synaptic terminals in the mPFC and adrenal medullary chromaffin cells, as well as changes in activity of the hypothalamic-pituitary-adrenal axis.