Emotional stress evoked by immobilization of the rat induces c-fos mRNA or other immediate early genes. This response is mediated by activation of alpha- and beta-adrenoceptors, through mechanisms that have not yet been elucidated. Here we show that immobilization stress activates p44/p42 Mitogen-Activated Protein kinase (p44/p42 MAP kinase, Erk1/Erk2). Pretreatment with the beta1-blocker, metoprolol, did not inhibit the activation of stress-induced MAP kinase, while blockage of the alpha1-adrenoceptor by pretreatment with alpha1-blocker, prazosin or the alpha/beta-blocker, amosulalol, attenuated the activation. Application of the alpha1-agonist, phenylephrine, but not the beta-agonist, isoproterenol, to the perfused rat heart elicited MAP activation. Thus, emotional stress activates the alpha1-adrenoceptor-mediated MAP kinase pathway, whereas the pathway of the response mediated by the beta-adrenoceptor remains unknown.