Neuropeptide Y produces anxiolytic effects in spontaneously hypertensive rats

The sedative and anxiolytic effects of intracerebroventricular administration of neuropeptide Y (NPY) were studied in spontaneously hypertensive rats (SHR) and in normotensive Wistar-Kyoto (WKy) rats using the two-compartment exploratory test, and in the open-field test after habituation. In the two-compartment tests, NPY produced anxiolytic effects by increasing the exploratory activity in SHR at a dose (0.25 nmol) lower than the minimal effective dose in WKy rats (1.25 nmol). In SHR, anxiolytic effects were observed for the whole NPY dose range (0.25-5.0 nmol), whereas in normotensive WKy rats the highest dose (5.0 nmol) failed to increase exploratory activity. The open-field test showed reduced locomotor activity and rearings in WKy rats when injected with 5.0 nmol NPY. These effects were not observed in SHR. The absence of sedative effects and the higher sensitivity to the anxiolytic effects of NPY in SHR are suggestive of a genetically determined difference in central NPY systems involved in behavioral adaptation that may be relevant for the development of hypertension.