Role of neuropeptide Y in the regulation of tyrosine hydroxylase messenger ribonucleic acid levels in the male rat arcuate nucleus as evaluated by in situ hybridization.

Neuroanatomical data have clearly demonstrated the existence of synaptic contacts between neuropeptide Y (NPY) endings and tuberoinfundibular dopaminergic (TIDA) neurons in the rat arcuate nucleus. In order to determine the influence of NPY in the biosynthesis of dopamine, we have studied the effects of NPY and some NPY analogs on tyrosine hydroxylase (TH) gene expression in TIDA neurons in the male rat. The following peptides: NPY, PYY, [Leu31, Pro34]-NPY (a Y1 receptor agonist) and NPY13-36 (a Y2 receptor agonist) were injected into the left lateral ventricle of adult male rats. All the animals were perfused with 4% paraformaldehyde 4 h after injection. Cryostat sections through the arcuate nucleus were processed for quantitative in situ hybridization. The intracerebroventricular injection of NPY, PYY and [Leu31, Pro34]-NPY induced an increased of 43, 33 and 42%, respectively, in the number of grains overlying TH neurons. On the other hand, the Y2 receptor agonist NPY13-36 did not influence mRNA levels. These data then strongly suggest that NPY positively regulates the genetic expression of TH in rat TIDA neurons via the Y1 NPY receptor subtype.