Co-localization of tyrosine hydroxylase (TH)- and serotonin (5-HT)-immunoreactive innervation in the rat pituitary gland.

Adult male Sprague-Dawley rats were examined for possible co-localization of tyrosine hydroxylase (TH) and serotonin (5-HT) within innervation of the pituitary neurointermediate lobe. Use of sheep antiserum to TH and a secondary antibody coupled to fluorescein isothiocyanate (FITC), followed by rabbit anti-5-HT, then rhodamine-coupled second antibody, produced co-existent staining in some, but not all fibers of both the neural and intermediate lobes, using paraffin embedded tissues. Application of a combination of the two primary antibodies followed by sequential application of secondary antibody also resulted in co-localized antigens in selected fibers. Multiple 'classic' neurotransmitters within the same nerve terminals may modulate selected areas of endocrine tissue to control hormone release.