Catecholamine Synthesizing Enzymes and Their Modulation by Immobilization Stress in Knockout Mice

A bstract : The c‐fos knockout mice (c‐fos KO) and corticotropin‐releasing hormone knockout mice (CRH KO) can serve as interesting models for studying mechanisms involved in response of the organism to stress, focused mainly on the hypothalamic‐pituitary‐adrenal (HPA) axis and sympathoadrenal system (SAS). The present study focused on the investigation of changes in gene expression of catecholamine biosynthesizing enzymes tyrosine hydroxylase (TH), dopamine‐β‐hydroxylase (DBH), and phenylethanolamine N‐methyltransferase (PNMT) in adrenal medulla of c‐fos KO and CRH KO mice stressed by immobilization. Levels of TH, DBH, and PNMT mRNA were determined by reverse transcription‐polymerase chain reaction (RT‐PCR). Single immobilization for 2 h significantly increased adrenomedullary TH, DBH, and PNMT mRNA levels in both c‐fos KO and wild‐type (WT) mice compared to unstressed controls. In CRH KO mice, PNMT gene expression was not increased to the same extent after single, but especially after repeated immobilization as in WT mice, in contrast to TH and DBH mRNA levels. Thus, our data indicate that CRH deficiency can influence the PNMT mRNA level in adrenal medulla during stress, confirming the idea that the HPA axis plays the crucial role in PNMT gene regulation in mice. On the other hand, c‐Fos protein probably does not play a crucial role in TH, DBH, and PNMT gene expression in adrenal medulla under stress conditions.