Characteristics of central endocrine neurons and their catecholaminergic afferent innervation patterns during the aging process were examined in the Fischer 344 rat using a combined histofluorescence-immunocytochemical approach. Staining of peptidergic target neurons remained strong and largely unchanged with age for neurophysin, LHRH and somatostatin-containing perikarya. A sharp decline was seen in the noradrenergic innervation patterns of the supraoptic nucleus; as much as a 50% drop in varicosity-perikaryal juxtapositions occured with age. This terminal field decline was paralleled by similar changes in LHRH and somatostatin staining of fibers in the median eminence. An hypothesis that target neuron peptide may be essential for the maintenance of catecholaminergic afferent fibers was tested in the vasopressin-deficient Brattleboro rat wherein catecholamine fiber density appeared reduced in the vasopressin deficient portions of the supraoptic nucleus.