Catecholamine distribution and relationship to magnocellular neurons in the paraventricular nucleus of the rat

The distribution of catecholamine synthesizing enzymes within the paraventricular nucleus of the rat hypothalamus is elucidated immunocytochemically by use of antibodies to tyrosine hydroxylase, dopamine beta-hydroxylase, and phenylethanolamine-N-methyltransferase. Tyrosine hydroxylase-immunostained cell bodies are localized in the periventricular stratum and adjacent parvocellular regions, but rarely in magnocellular subnuclei of the paraventricular nucleus. Tyrosine hydroxylase-immunostained fibers are present in greatest density in the periventricular zone, and moderate density in the parvocellular and magnocellular subnuclei. Dopamine beta-hydroxylase-immunostained fibers are remarkably dense in the posterior magnocellular division of the paraventricular nucleus, especially in the dorso-lateral portion where vasopressin-containing cells predominate. Noradrenergic fiber input to these magnocellular neurons is likely since phenylethanolamine-N-methyltransferase-immunostained fibers are sparse in magnocellular subnuclei of the paraventricular nucleus. Dual immunocytochemical staining of thick and thin tissue sections demonstrates with clarity an anatomical association of dopamine beta-hydroxylase-immunostained fibers and magnocellular neurons. Dopamine beta-hydroxylase-immunostained and phenylethanolamine-N-methyltransferase-immunostained fibers are dense in the medial parvocellular component of the paraventricular nucleus; distinct features of both antisera are presented.