Effects of restraint stress and spontaneous hypertension on neuropeptide Yneurones in the brainstem and arcuate nucleus

Neuropeptide Y (NPY) is found in autonomic neurones and participates in reg ulation of autonomic functions. To investigate the role of NPY in the stres s response in normo- and hypertensive rats, activation of brainstem and arc uate nucleus (ARC) NPY neurones and levels of NPY mRNA in the ARC were meas ured in response to restraint stress in adult spontaneously hypertensive ra ts (SHRs) and two strains of normotensive rats. Controls from each strain w ere not restrained. Sections of the brain were prepared for Fos immunohisto chemistry and NPY in-situ hybridization to identify activated NPY neurones in the nucleus of the tractus solitarii (NTS), ventrolateral medulla (VLM), and ARC. NPY mRNA levels were quantified in the ARC. In the NTS and VLM of restrained rats, approximate to 33% and 75%, respectively, of NPY neurones were activated. No differences among strains were found. In the ARC, about 36% of neurones activated by restraint contained NPY mRNA with no differen ces found among strains. In unrestrained rats, NPY mRNA levels were signifi cantly elevated in SHRs compared to the normotensive rats. Restraint led to significant decreases in mRNA levels in all strains and mRNA levels among strains were no longer different from one another. These data show that NPY likely participates as a neurotransmitter in the autonomic pathways utiliz ed during stress and originating in the NTS, VLM, and ARC. On the other han d, the decreased gene expression of NPY in the ARC in response to restraint stress argues against a role for activation of autonomic pathways or the h ypothalamo-pituitary-adrenal (HPA) axis by NPY from the ARC of stressed rat s. The elevated NPY gene expression in resting SHRs compared to normotensiv e rats is abrogated after restraint, suggesting that this gene is different ially regulated in SHRs compared to normotensive rats.