Electron-Microscopic Immunocytochemistry of Neuropeptide Y Immunoreactive Innervation of Vasopressin Neurons in the Paraventricular Nucleus of the Rat Hypothalamus

Abstract

The neuropeptide Y (NPY) immunoreactive synaptic input to neurons containing neurophysin II (NPII) the carrier protein of vasopressin (VP) was observed in the paraventricular nucleus (PVN) of the rat hypothalamus by double-labeling immunocytochemistry combining the preembedding peroxidase-antiperoxidase (PAP) method with the postembedding immunogold staining method at the electron-microscopic level. NPY-like immunoreactivities were detected by the PAP method in the dense granular vesicles (70–100 nm in diameter) in the immunoreactive presynaptic axon terminals. NPY-like immunoreactive large neurosecretory granules labeled with gold particles were found in the neurons receiving synaptic input of the NPY-like immunoreactive terminals. This suggests that NPY may be a neuro-transmitter or neuro modulator and that NPY neurons may through synaptic contacts regulate the secretion of VP neurons.