ABSTRACT
The distribution of neurotensin (NT) and neuropeptide Y (NPY) in the rat hypothalamic arcuate nucleus has been studied ultrastructurally by means of double labeling preembedding immunoelectron microscopic PAP technique. First, the NPY immunoreaction was demonstrated by chromogen DAB, and second, the NT immunoreaction was demonstrated by ammonium molybdate-TMB method. After being stabilized by DAB-cobalt chloride, the vibratome sections were processed for electron microscopic study. The results showed that in the arcuate nucleus the NPY immunoreactive products appeared as high electron-dense granular or flocculent materials deposited diffusely in the organelles and matrix of perikaryon, around the dendritic microtubules and axonic small clear vesicles. Whereas the NT immunoreactive products were dense needle- or mass-like deposits distributed dispersively in the perikaryon, dendrites and axon terminals. They can easily be distinguished although being intermingled together. The NPY-containing dendrites and axons formed synaptic connections with immuno-negative axon terminals, NT-containing somata and dendrites formed also synaptic conections with negative axon terminals. In addition, NPY-positive axon terminals formed symmetrical axodendritic synapses with NT-positive dendrites. The present results provided another new ultrastructural evidence for the peptidergic synaptic regulation of NT neurons in hypothalamus.