Brain noradrenergic responses to footshock after chronic activity-wheel running

Effects of physical activity on brain noradrenergic response to footshock w ere examined. Male Fischer 344 rats were randomly assigned to shoebox cages with (AW) or without (SED) 24-hr access to an activity wheel for 4-5 weeks . Extracellular levels of norepinephrine (NE) and 3,4-dihydroxyphenyl-aceti c acid (DOPAC) in the brain frontal cortex were measured in 20-min samples of microdialysate taken during a 2-hr baseline, 40 min of scrambled footsho ck, and a 1-hr recovery. Levels of messenger RNA (mRNA) for tyrosine hydrox ylase (TH), c-fos, and prepro-galanin in the locus coeruleus were measured by in situ hybridization histochemistry with autoradiographic analysis. NE levels were the same for SED and AW rats at baseline but were elevated in S ED compared with AW during and after footshock. Levels of mRNA for TH and c -fos were elevated after footshock but did not differ between SED and AW. O ur findings suggest that wheel running blunts NE release in the brain front al cortex in response to footshock but does not influence expression of the gene that encodes TH in the locus coeruleus.