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 40 min and in the mPFC at 40 min; TH activity was increased at 40 min in both tissues. There were significant increases in body temperature between 10 and 40 min, as well as increases in plasma adrenocorticotropic hormone at 20 min and corticosterone and glucose at 20 and 40 min. The adrenal medulla extracellular signal-regulated kinase 2 was increased between 10 and 40 min and Ser31 phosphorylation was increased at 20 min and 40 min. Protein kinase A and Ser40 phosphorylation were increased only at 40 min. TH activity was increased between 20 and 40 min. TH protein and Ser19 phosphorylation levels were not altered in any of the brain regions or adrenal medulla over the first 40 min. 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.

The expression of c-Fos defines brain regions activated by the stressors hypotension and glucoprivation however, whether this identifies all brain sites involved is unknown. Furthermore, the neurochemicals that delineate these regions, or are utilized in them when responding to these stressors remain undefined. Conscious rats were subjected to hypotension, glucoprivation or vehicle for 30, 60 or 120 min and changes in the phosphorylation of serine residues 19, 31 and 40 in the biosynthetic enzyme, tyrosine hydroxylase (TH), the activity of TH and/or, the expression of c-Fos were determined, in up to ten brain regions simultaneously that contain catecholaminergic cell bodies and/or terminals: A1, A2, caudal C1, rostral C1, A6, A8/9, A10, nucleus accumbens, dorsal striatum and medial prefrontal cortex. Glucoprivation evoked phosphorylation changes in A1, caudal C1, rostral C1 and nucleus accumbens whereas hypotension evoked changes A1, caudal C1, rostral C1, A6, A8/9, A10 and medial prefrontal cortex 30 min post stimulus whereas few changes were evident at 60 min. Although increases in pSer19, indicative of depolarization, were seen in sites where c-Fos was evoked, phosphorylation changes were a sensitive measure of activation in A8/9 and A10 regions that did not express c-Fos and in the prefrontal cortex that contains only catecholaminergic terminals. Specific patterns of serine residue phosphorylation were detected, dependent upon the stimulus and brain region, suggesting activation of distinct signaling cascades. Hypotension evoked a reduction in phosphorylation in A1 suggestive of reduced kinase activity. TH activity was increased, indicating synthesis of TH, in regions where pSer31 alone was increased (prefrontal cortex) or in conjunction with pSer40 (caudal C1). Thus, changes in phosphorylation of serine residues in TH provide a highly sensitive measure of activity, cellular signaling and catecholamine utilization in catecholaminergic brain regions, in the short term, in response to hypotension and glucoprivation.

Impairments in cognitive and locomotor functions usually occur with advanced age, as do changes in brain volume. This study was conducted to assess changes in brain volume, cognitive and locomotor functions, and oxidative stress levels in middle- to late-aged rats. Forty-four male Sprague-Dawley rats were divided into four groups: 14, 18, 23, and 27months of age. H magnetic resonance imaging (MRI) was performed using a 7.0-Tesla MR scanner system. The volumes of the lateral ventricles, medial prefrontal cortex (mPFC), hippocampus, striatum, cerebellum, and whole brain were measured. Open field, object recognition, and Morris water maze tests were conducted to assess cognitive and locomotor functions. Blood was taken for measurements of malondialdehyde (MDA), protein carbonyl content, and antioxidant enzyme activity. The lateral ventricle volumes were larger, whereas the mPFC, hippocampus, and striatum volumes were smaller in 27-month-old rats than in 14-month-old rats. In behavioral tasks, the 27-month-old rats showed less exploratory activity and poorer spatial learning and memory than did the 14-month-old rats. Biochemical measurements likewise showed increased MDA and lower glutathione peroxidase (GPx) activity in the 27-month-old rats. In conclusion, age-related increases in oxidative stress, impairment in cognitive and locomotor functions, and changes in brain volume were observed, with the most marked impairments observed in later age.