Noradrenergic (NA) neurons in the brain stem have been implicated in transmission of the stress and emotional inputs to the hypothalamus. However, it is not yet clear how the NA system functions in relationship with other neuronal systems. Nor is it clear how NA interacts with other neurotransmitters that are co-expressed in the NA neuron. First, rats were exposed to hypotensive hemorrhagic shock, then Fos expression was examined in the brain stem tyrosine-hydroxylase (TH)-immunoreactive neurons. The ratio of Fos-positive neurons increased not only in the A1, A2, and A6 regions following hemorrhagic shock, but also in the prolactin-releasing peptide (PrRP)-containing neurons in the A1 and A2. Thus, PrRP, together with NA, may mediate the visceral stress signals from the medulla to the hypothalamus. Second, a novel approach to examine the functions of the TH neurons is introduced. A transgenic mouse line was used that express green fluorescent protein (GFP) under the control of TH promoter. The embryonic brain of the transgenic mouse was digested with trypsin and the dispersed GFP-positive neurons were sorted by flow-cytometry (FACS). The sorted GFP-positive neurons can be used for many purposes, but preliminary results are presented focusing on the relationship between the TH-neurons and the proopiomelanocortin (POMC) neurons. Expression of melanocortin receptor mRNAs was demonstrated in the GFP-positive (TH) neurons by PCR, suggesting a functional role of POMC peptides in the regulation of TH neurons. [Jpn J Physiol 55 Suppl:S16 (2005)]