CATECHOLAMINERGIC INNERVATION OF OXYTOCIN NEURONS IN THE PARAVENTRICULAR NUCLEUS OF THE RAT HYPOTHALAMUS AS REVEALED BY DOUBLE-LABELING IMMUNOELECTRON MICROSCOPY

The catecholaminergic innervation of neurons that contain oxytocin in the paraventricular nucleus (PVN) of the rat hypothalamus was examined by a combination of methods in the same tissue sections at the electr on-microscopic level as follows: (1) Rats were treated with 5-hydroxyd opamine (5-OHDA) with peroxidase-antiperoxidase (PAP) staining of sect ions for oxytocin prior to embedding. (2) Preembedding immunoperoxidas e staining with avidin-biotin complexes was used to demonstrate tyrosi ne hydroxylase (TH) activity, with postembedding staining with immunoc olloidal gold for visualization of oxytocin. (3) Prior to embedding, a double-staining technique was used that was based on consecutive stai ning with silver-gold-intensified PAP complex and 3,3'-diaminobenzidin e. We used an antiserum against oxytocin and an antiserum against dopa mine-beta-hydroxylase (DBH) for localization of antigens. We found tha t TH- and DBH-like immunoreactive terminals were distributed throughou t the rat hypothalamus and were abundant in all parts of the PVN. Ultr astructural observations revealed 5-OHDA-labeled, TH- or DBH-like immu noreactive axon terminals that contained granular vesicles (70-80 nm i n diameter) and small clear synaptic vesicles (30-50 nm in diameter). The terminals appeared at times to be making synapses with cell bodies and with the processes of oxytocin-containing neurosecretory neurons in the PVN. These findings provide morphological evidence for a direct synaptic influence of catecholaminergic elements on the secretory act ivity of oxytocin-containing neurosecretory neurons in the rat hypotha lamic PVN.