title: Immunostaining reveals accumulation of serotonin and coexistence with tyrosine hydroxylase in hypothalamic neurons of acutely stalk-sectioned baboons.
abstract: The distribution of serotonin (5-HT) and tyrosine hydroxylase (TH) was examined in the hypothalamus of juvenile baboons, 24 h after infundibular stalk section. Simultaneous immunostaining for 5-HT with peroxidase-antiperoxidase (PAP) and TH with 15 nm colloidal gold (IGS) was performed on Vibratome sections from 3 operated and 1 control female. Light microscopy revealed fine 5-HT immunopositive (5-HT+) fibers, presumably axons, in the suprachiasmatic nuclei and ventromedial hypothalamus (VMH) after stalk section. In addition, focal accumulations of swollen and heavily stained 5-HT+ fibers occurred on the side of the surgical approach. Enlarged fibers were densest in the medial preoptic area, lateral and VMH areas, and the median eminence. TH immunoreactivity (TH+) in VMH cell bodies and axons was only slightly increased over that in controls. Electron microscopy of areas of 5-HT+ and TH+ overlap (medial VMH and adjacent periventricular zone) showed that 5-HT+ profiles were mostly unmyelinated axons and irregular varicosities. A few myelinated 5-HT+ axons were also observed. TH+ perikarya, dendrites, axons and terminals showed gold labeling characteristic for this enzyme. However, colocalization of 5-HT (PAP) and TH (IGS) was present in a number of fiber varicosities in experimental animals only. Both single- and double-labeled profiles occurred in individual thin sections, thus arguing against antibody cross-reactivity. These results indicate that: hypothalamic 5-HT+ fibers project to the median eminence in primates; 5-HT fibers become more obvious after stalk section due to accumulation of transmitter; focal 5-HT+ immunoreactivity in the hypothalamus can increase dramatically after distant and mild surgical trauma, and coexistence of 5-HT and TH in single neurons can appear after acute stalk section and/or trauma in experimental animals. These findings might represent uptake of exogenous 5-HT or amplified expression of endogenous neurotransmitter, suggesting that plasticity of transmitter phenotype might follow acute surgical and/or endocrine intervention in mature primate brain. Neuroendocrine studies employing the stalk-sectioned primate might thus be radically affected.
mesh_terms: D000818:Animals; D001369:Axons / Q000032:analysis; D005260:Female; D006046:Gold; D006651:Histocytochemistry; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D007124:Immunoenzyme Techniques; D008853:Microscopy; D008854:Microscopy, Electron; D009434:Neural Pathways / Q000502:physiology; D010215:Papio; D010902:Pituitary Gland / Q000502:physiology; D012701:Serotonin / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D012701:Serotonin; D006046:Gold; D014446:Tyrosine 3-Monooxygenase