DEVELOPMENT OF NEUROPEPTIDE-Y AND TYROSINE-HYDROXYLASE IMMUNOREACTIVEINNERVATION IN POSTNATAL RAT-HEART

Neuropeptide Y (NPY), immunoreactive (IR), and tyrosine hydroxylase (T H)-IR nerve fibers were scarce at birth in rat heart, but increased ra pidly during the first 2 postnatal weeks, reaching approximately adult levels by the third week. The sequence of development was: interatria l septum and atrial wall, free ventricular wall starting from the epic ardium, and finally the atrial appendages and interventricular septum. In ventricles and atrial appendages both fiber types developed simila rly. In interatrial septum and atrial walls more NPY-IR than TH-IR fib ers were evident, and NPY-IR, but not TH-IR, neurons were detected in intrinsic ganglia. Double-label immunohistochemistry provided further evidence that NPY is located in ventricular and atrial noradrenergic n erves, but is also located in nonnoradrenergic nerves in atria.