Effects of centrally administered neuropeptide Y (NPY) and NPY13-36 on the brain monoaminergic systems of the rat.

The effects of centrally administered NPY on the brain monoamine systems were investigated in the rat. Neuropeptide Y (0.2-5.0 nmol), its C-terminal 13-36 amino acid (a.a.) fragment, NPY13-36 (0.4-10.0 nmol), or saline were injected into the right lateral cerebral ventricle of unrestrained rats. After 1 h the animals were decapitated, and the brains were taken out. Two cortical regions ('frontal' and 'parietal'), the striatum, the hypothalamus, and the brain stem were dissected out. The tissue contents of noradrenaline (NA), dopamine (DA) and serotonin (5-HT), as well as of their major metabolites, 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-indole acetic acid (5-HIAA) were measured. The most consistent finding was a dose-related increase of both DA and DOPAC levels after treatment with NPY. This effect was reproduced by NPY13-36 in cortical tissue, whereas, in the sub-cortical regions, NPY13-36 only reproduced the effects of NPY on the DOPAC levels. Less consistent effects were found on the NA systems, in which NA levels showed a tendency to increase following low, and decrease after high doses of NPY. These effects were largely reproduced by NPY13-36. In addition, NPY increased tissue levels of MHPG in frontal cortical tissue in a dose-related manner. The brain 5-HT systems were not affected.