Activity of brain stem groups of catecholaminergic cells in tumor-bearing rats: response to immobilization stress

The aim of the present study was to investigate the activity of tyrosine hydroxylase (TH) immunopositive neurons, measured by Fos protein expression, in the hindbrain noradrenergic (NA) cell groups in animals exposed to visceral tumor growth for 28 days induced by intraperitoneal implantation of fibrosarcoma cells. We were also interested in determining whether brain stem NA neurons of tumor-bearing and intact animals exhibit similarities in their response to a strong heterotypic stimulus-immobilization (IMO) stress. We found increased Fos expression in NA cells of the nucleus tractus solitarii (A2 cell group) and of the A1 cell group of tumor-bearing rats. However, Fos expression in other brain stem NA cell groups, including A5, locus ceruleus, and A7, were similar to control rats. The effect of 60 min of IMO was evident in both groups, but there were no differences between Fos expression in brain stem NA cell groups in control and tumor-bearing rats. This indicates that the sensitivity of NA cells in tumor-bearing animals was not altered by the IMO-induced stress challenge. However, whether the increased Fos expression in NA cells in tumor-bearing animals is a consequence of a specific visceral response activated by cancer development or just a nonspecific event accompanying the cancer progression requires further study.